Post by volkerboehme on Aug 10, 2008 9:09:32 GMT -5
Greetings Tom,
> A nice guy from Brazil has convinced Greg Pepper to help him finish a very
> nice model of a C-46 Commando. I am wondering if you have anything
> already prepared for it, by chance.
Yes and no, but I am happy to produce them for Greg anyway.
I have all the aerodynamic code. I have generic R-2800 code. I know the maxima for any relevant R-2800-?? and can insert them easily, but I have no information relating to the norms for most R-2800-?? of WW2 vintage.
The next problem is that the FAA hated the C-46 and all the varieties of R-2800 fitted and consequently made the airline certification so restrictive that few were retained in the U.S. where the rules more or less had to be obeyed. The FD and handling notes that would apply to any air force are very different to the FD that would apply to any airline, anywhere, anytime. The British / European certification appears to have been even more restrictive.
The ones used by the airlines had the same aerodynamics but different weights and different power maxima to those supplied to air forces, during WW2, or after disposal. The norms may or may not have been the same. Logically they would be despite the different maxima.
Whether or not the FD are realistic the user will need handling notes matched to the FD content. Obviously I can deliver FD that have all the MAPs and all the rpms in there somewhere. I can mix and match them at random to deliver more or less correct power output and promulgate the guesses within handling notes, but the guesses for MAP and rpm may be quite wrong even though the resulting power and thrust would be 'realistic'.
If you let me know which variant of the C-46 e.g. A or D the FD are to represent then I should be able to deliver FD and handling notes matching post war FAA airline certification produced on the above basis by Sunday evening; depending on whether I need to do any further work on the C-4 etc in that timeframe.
I request that you do the usual proof reading and alpha testing to the usual standards to ensure that the aircraft can be operated to the handling notes even though they may not be 'realistic'. Fixing stuff that crops up may have to spread beyond Christmas depending on the nature of the problem.
There is a pretty good C-46 panel bitmap which just about supports 6141, (and therefore the cheek windows needed to taxi with reference to a taxiway edge), already available, produced by Paulo Alfonso Pizzato. It might need some different gauges to work correctly in FS9, but your parts box should have all of them anyway.
Is this new MDL going to have a VC? Is there going to be another panel?
Getting the tail up is just! a case of writing realistic FD and then remembering that taildraggers use nose down trim for take off (to get the tail up). Getting aircraft to behave properly is often a lot more to do with the (lack of) realistic handling instructions than lack of realism in the FD, but if you ever need to design such FD you will find starting from my B247 FD and handling notes a lot easier than fixing the mistakes, and understanding all the complication, in the default DC-3 files.
You always have to start with the handling notes and then impose them on MSFS, even if you just invented (large parts of) the handling notes. I hope to invent only small parts relating to certain norms. The easiest data to impose on the real Newtonian equations within MSFS is the real input data as it all multiplies together nicely to create predictable output that needs little tweaking. The less I know about the inputs the longer it takes to create realistic output or even docile output by time consuming iterative experimentation. The fewer unknown inputs I have to iterate concurrently the better. In some ways realistic FD are easier to create than unrealistic ones because unrealistic ones tend to have unfortunate conjunctions in which equations turn negative at the wrong time with unpredictable results whose cause is difficult to fathom.
Regards, FSAviator
Greetings Tom,
I can always use Mike Stone's MDL and a pre existing panel with some new gauges for testing.
The new MDL looks nice. The fact that it is a C-46A from later post noted.
I believe most of the C-46s in use in the U.S. were really owned by the USAF and just painted in airline livery just like the B314As were owned by the USN but had PAA titles. Like the B314As they could then be flown on government contracts by civilian aircrew to military safety criteria rather than FAA criteria. This will have been true of some SA airlines too.
I can get round this fairly easily. I will set the maximum weights to military but only load it by default to FAA limits then put notes on how to achieve military overload in the aircraft.cfg just as for the C-54s. The gap is bigger for the C-46 I think. Still researching but I suppose the cargo carriers who had USAF C-46s could also tender for civilian contracts but then had to operate to FAA rules.
<I assume that he would prefer handling notes that would match the more recent SA operations>
I will make the handling notes relate to FAA rules and thus the default loads. I know what the FAA criteria were, I just don't know why exactly, presumably lousy engine out handling and performance.
I see someone just did a paint of the default C-46 as the C-55 Commando (CW-20) used by BOAC. It had R-2600 engines like the B314A so I might try cutting and pasting the dynamic bits together to replicate that as well, but not yet.
Regards,
FSAviator
Greetings Tom,
The aircraft.cfg contains some MDL data for Mike Stone's MDL which should be replaced in due course. Retained gear limits in contact points etc. All the rest of the code is mine.
Engines have no high blower as the FAA required removal. I will research the military data if I can, but I am not certain that I will find everything required to annotate the aircraft.cfg to allow conversion. V0.90 is therefore FAA compliant only. Only slight testing so various things may need to change. No testing of ground handling or take off data done yet.
I won't have time to do anything else today so I will try to respond to any new mail tomorrow. No more updates to anything until Tuesday evening GMT.
Regards, FSAviator
Greetings Tom,
<<Thanks for the C-46 FDE. Works great for the most part. The things I've noticed so far:>>
<<1. In the handling notes you mention max landing wt as 44000 lbs, which is also max TO wt. Is this correct?>>
Yes. The FAA forced the MTOW down to MLW so that it could land immediately if it had an engine failure after take off. In general they required the ability to dump fuel before they would allow MTOW > MLW but that also depended on how well the aircraft to be certificated could survive losing one engine at max gross. No problem with four engines. You just burn off fuel in a hold.
<<2. At 43,500 lbs it runs out of up trim on final approach (on AP) at about 87 kts .>>
That is an FD error I will fix that.
<<At flaps 1 it is also somewhat nose up at 110 kts, the speed given for flaps 2. >>
That is a handling note error.
The flaps are weak by post war standards. FLAP 1 limit is 131 matching the gear and the flap 2 limit is 117. I guess the crew added flap 1 and flap 2 as soon as they could, but bear in mind that 43,500 is an emergency return landing. This may well relate to (1) above.
I will change the handling notes to say 116 which should be easier to attain on a 3 degree slope at 20/2000.
The FLAP 3 limit is also 117 so they probably went to FLAP 3 earlier at high approach weights.
The USAF operated the A to at least 56,000lbs during WW2. I don't think the aircraft had any real chance of surviving an engine failure after take off at that weight, nor can I find any clear max gross information concerning US airline operation on Logair contracts etc.
I may have underestimated the drag. If not it seems that econ power was less than I have put in the handling notes. I think it may be cruising too fast and have too much range. Still researching.
The AoA in the cruise won't change enough to matter so the V0.9 FD can be used for any panel development after FLAP 2 goes to 116 as normal extension. I think the view must have been compromised on the ground or at low IAS else I do not understand why they developed the C-46E. Evidently it did not solve the problem whatever it was.
Regards, FSAviator
Greetings Tom,
Firstly I think the 'high' cruising speeds are just the interpolated consequence of the much lower weights when flown under FARs. I may revise this view if you come up with real low blower data later.
> Also, .....(MDL author).... has it set to steer using the yoke (a la a tricycle gear
> plane); I assume his preference. When I change the current contact points
> steering angle to 180 to simulate a real taildragger, it acts very badly,
> and I'm not able to steer it (unlike the default DC-3). As long as we
> keep it steerable no real problem, but I thought I'd mention it.
The C-46 has retractable tailwheel with connected hydraulics. This makes it more likely that it had steering with an unlock to castor facility, but I don't know what it actually had.
Castoring v not castoring is not really a nosewheel versus tailwheel thing. It's a cost thing.
If you believe that it had a castoring only tailwheel then you will need to add lock/unlock to the contact points, an unlock lever to the panel and probably a differential braking factor to the braking section.
> Finally, I can only get the tail up on the C-46 above 65 kts. By the time
> I've got it up all the way I'm almost ready to rotate.
With trim neutral the tail up IAS is a function of current weight and mainwheel distance ahead of CoG. I did not have time to do any take off testing which is why the handling notes say,
TRIM = NEUTRAL (MAY CHANGE)
Tailwheel aircraft (with flaps) begin the take off with whatever (nose down) trim is required to get the tail up at whatever IAS the captain desires. I don't know the real tail up IAS for a C-46 but @ 44,000 Vr = 85 so 65 is late but not very late. I have never seen a C-46 take off in real life. I have only seen one land.
From here on I won't have time to do much bug fixing on the C-46 until January so if it the handling notes need to change before then you will have to work on them. Not a lack of interest/willingness just a lack of time.
<Here is a message from Greg. Note that the current 0,0,0 datum is not at the CG. I told him to move it to simplify the FDE editing (since I assume you assumed it to be there in your FDE). >
Yes I did,
reference_datum_position = 0.000, 0.000, 0.000
empty_weight_CG_position = 0.000, 0.000, 0.000
<Editing the eyepoint, contact points and lights shouldn't be too bad.>
That is fine by me of course, but for future reference if the payloads and fuel loads in combination are simpler to edit ('in the opposite direction') then that is a valid alternative.
Obviously if you did your take off test with the planned release data the mainwheel to CoG offset will have been false, but tail up = 65 is quite likely to be true for the ones I sent with trim only neutral. Obviously I don't know if Mike Stone's mainwheel to CoG offset is correct anyway.
<<Also note that Greg's C-46 manual CD is on it's way, so hopefully you'll have some hard data soon. Once he gets the panel bitmap finished I'll send you a copy if you think you need it.>>
The stuff I would 'need' from the manual is the usual power relationships. What MAP and rpm create what power and data to inform what we should publish as climb, max cruise and econ cruise power and how to impose it. There is a problem however. The manuals will probably be for the military spec not the demilitarised aircraft and may also lack data for -51 engine which was the norm in the A. For the FAA spec I would only need low blower data.
Concerning panel bitmaps the eyepoint from which the panel bitmaps of a taildragger are 'designed' can only be chosen after the contact points are final and must be chosen to deliver the ability to taxi using the VIEW_DIR that projects the correct scenery in the windscreen for both the tail down and tail up cases. In the tail down case it must at the very least include the ability to see the vanishing point of the runway with the tail down, just before throttle up, so that pilot flying can line up carefully, (and lock the tailwheel), before throttle up. This needs to work with SIZE_Y = 6144. The cheek windows are likely to require very high SIZE_Y anyway.
The contact points can perhaps be adjusted from their current values for oleo compression to lower the nose a little, but all the rest of the compromise must be in the carefully designed crop of the cockpit photo. If it is cropped (or drawn freehand) to allow the runway vanishing point to be visible at Y = 6144 with the final oleo compression (at low weights) it will work, else it won't.
The amount I can compress the oleos to help Greg won't be much and will anyway depend on the relevant MDL animation code. The dynamics will override the MDL and the tyres will start moving down into the runway if the oleos need a lot of compression and that much compression is not already 'animated'.
I can also move the mainwheels dynamically without any change to the MDL, but that will make rotation more difficult and obviously will affect the 'sit' in external views. Ideally if the current oleo compression and 'sit' at 44K look 'right' Greg should make all the compromise. I think it will be tough to get much more than the runway vanishing point into view. I don't think the real view was wonderful with the tail down, but it was 'adequate'.
The 0.91 air file has greater trim authority as requested, but no other changes even though some will be needed. Keep bug reports coming if you wish but I don't expect to have time to do much with them until January. Feel free to play with oleo compression and mainwheel offset in the contact points during panel development, but test dynamic rotation and static sit after changes.
Regards, FSAviator
Greetings Tom,
I have located the problem in the C-46 code. Where I intended to code the max elevator trim as 15 degrees I actually have 5. I have now tripled the value in the air file to compensate. I have also recalculated Vref for 44000lbs more carefully and it should be 83 KIAS. I have also tweaked a few things relating to stability and damping, but there are a few low IAS handling issues remaining that I will have to address when I have more time. I have altered a few other values in the _ref including Vx climb in METO and a second version is enclosed. Most of the reference speeds in the cfg are wrong but I will alter those later. The original cfg stands for now.
Please experiment with take off trim values versus the new trim authority as well as verifying the ability to trim for <= 83 with full flap and adequate power.
If you are still short of trim just increase the value in the cfg slowly from 5.
Regards, FSAviator
Greetings Tom,
> This version solves all trim problems for me.
Good.
> However, trying to land
> softly at 83 kts over the boundary at 43,500 lbs is something I am unable
> to do. The plane tends to "dump" itself onto the runway. There is no
> "float" like all the other aircraft you've done. Of course this is the
> first taildragger, so I don't know what it should be like. Landing at 90
> kts or at 40,000 lbs is OK.
>
You are probably running out of elevator authority which is a different issue to elevator trim authority.
During the limited amount of time I have had for flight testing the C-46 FD I have become aware that there are a range of very low IAS handling issues. At some point I need time to study and resolve these with an integrated rather than piecemeal solution, but I will struggle to fit in a sufficiently long and intense testing/rewriting session before early January.
None of the changes to the interaction between stability, damping, inertia or control authority variables that will eventually emerge will have any implications for anyone making any other files for this project. The problems are internal to the FD.
If it can all be done in a two hour session I may get it done before Christmas. It is one of those things where I have no idea how many iterations of the four conflicting variable types I will have to go through to find a good 'fit' that solves all potential low IAS problems.
Regards, FSAviator
Greetings Tom,
I might have time to work on the C-46 low speed handling tomorrow.
>New zip file available if you want it.
Yes, send it please so that I have it if I need to refer to anything in it.
>Note he has configuration data available if you need it (don't think so?).
No I won't need those data. I don't believe that much can be calculated from them anyway. I think force feedback devices might use some of it though. Not sure.
<Considering I spent Thursday, Friday and Saturday in bed sicker then a dog, I did get a lot done on the C-46.>
Sorry to hear Greg has been ill.
<Note his problem with the RPM; I'm not seeing this. Suggested he start with default flight. >
The rpm problem sounds as though he was using an airscrew rpm gauge. He (the panel) needs engine rpm gauges. He will not have been using the correct rpm for climb as he could not set it. The climb rate in climb power was only just over 500 VSI at FAA gross anyway. If they had ATC restrictions to make or mountains to cross they stayed in METO. See _ref.
Greg may be missing a couple of inches of TOGA MAP for some reason anyway. It should give 52 at SL in ISA.
Regards, FSAviator
Greetings Tom,
Greg's gauges are displaying airscrew rpm. The only remaining question is why. I didn't think there was a way to toggle engine rpm gauges to show airscrew rpm. Gregg can test what they are displaying using AFSD which runs outside FS9 and will show both rpm regardless of how he has installed or configured stuff inside FS9. Some of Greg's aircraft have used aircrew rpm gauges in the past. Maybe he still has old versions in his gauges folder or in the folder he is using for testing. Ask him to test this using the default DC-3 engine rpm gauges.
I have done the further testing on the C-46 low speed handling and re-examined all outstanding reported issues.
At 35/2400 it accelerates well beyond 130 KIAS at 500 VSI in ISA at max FAA gross so I still think that is a good value for climb power. 2 x METO (3200hp) represents huge surplus available power in any weather.
I have enough elevator authority to stall the aircraft from any IAS in any flap and gear state. Flying straight and level at any IAS > stall is just a question of supplying the power required. Consequently propensity to float on landing is just a matter of back pressure and power applied. It can be made to float forever if not stalled.
Note that the AP should not have trim authority to stall the aircraft from Vref. You do have the elevator authority to achieve any IAS you like including Vs or Vs0 plus 1 or minus several (from level flight).
Around MLW Vref is 83 KIAS and zero pitch is at about that speed whilst descending down a 3 degree glidepath with full flap. VSI will be about minus 500 as you hit Vref. The flare begins from nose level and has the intention to reduce sink by about 400 VSI to place the wheels on the runway at about minus 100 VSI a few knots slower and a few seconds later.
The stalling angle is much greater than the tail down angle. The flare should never be enough to cause a tailstrike so the flare terminates well above stall speed and well below stall angle. A C-46 should always be 'wheeled on' and never three pointed. I can control negative VSI with elevator quite easily below Vref (83) and well above Vs0 which is about 62. I have no difficulty flaring to minus 100 VSI or whatever touchdown sink rate I choose if I carry enough power and do not allow speed to drop more than a few knots during the flare.
I think you may be removing too much power too soon if the 'arrival' seems sudden. If in doubt leave all the power that was required to descend at minus 3 degrees and minus 500 VSI in place until the main wheels are wheeled on at not much less than 80 KIAS. It won't bounce from minus 100 VSI because the power supplied could only sustain minus 500.
After this further testing I think the low speed handling in pitch was OK after the last revision. It is mostly yaw at low IAS that I have been working on during the further testing.
The problem that I cannot resolve is the single engine performance. I see no evidence that the single engine ceiling is above sea level at 44,000lbs in the real aircraft. 1600hp = 40% power is not enough to sustain flight. I don't know how the FAA managed to certificate it at that weight. I know no one else would.
The FAA imposed at least 26 mandatory modifications before they would certificate it at all, one of which was removal of the C-46A elevators and replacement with those from a C-46F. As far as I can tell Britain would not certificate anything other than a full F.
If it cannot fly on one engine then rudder authority following engine failure is a non issue. As far as I can tell the C-46F was the first variant that could fly on one engine at 44K, but I not certain that it could either. I only know it had a second rudder trim tab because none of the earlier versions could be trimmed in yaw at low IAS.
I have emulated this design failure but it may not be precise. If I assume that it is impossible to fly the C-46A on one engine at 44K then my original estimates of the yaw and roll data stand. Consequently there are no new FD after the further testing. The pitch handling is real or a bit better, the yaw handling probably about real and the roll handling can only be a guess anyway. It is coded to be 'adequate'.
The existing FD assume that the same air file will be used with any military livery but that the high speed blower will be put back in the cfg. Apart from default payload those would be the only two changes for a mil v civil C-46A as far as FD go. METO in the air file and _ref is therefore set to be delivered at the high blower MAP and rpm settings. METO power is the same in either blower it is only the mix and match of MAP and rpm that differ. They cannot differ in FS9 without a WEP gauge which I do not recommend for this aircraft anyway.
The mil _ref would reflect mil weights and the engine data from Greg's manual assuming it is for the R-2800-51. I have seen no evidence that the -51 had a MIL rating but maybe the manual that Greg has now will shed light on any MIL rating and the max weight for sustained flight on one engine.
I have examined the C-46 2D bitmap but not the MDL. Whether the 2D bitmap works is just a question of whether Greg can integrate VIEW_FORWARD_DIR and SIZE_Y for that bitmap and the VC (see enclosed detailed reply to Glen on same subject). I have not had time to test the aircraft.cfg revisions from Greg, but do not expect a problem, and I assume that you have tested anyway by now.
I will be 'around' over Christmas, but do not intend to do any 'FS development' between now and about the 28th at the earliest and maybe more like the 2nd.
Merry Christmas etc.,
FSAviator
Greetings Tom,
May not have time to reply to all mail today, but making a start. Glad to hear you are feeling a bit better.
<< Flaps get added at either handling note speeds or altitudes AGL, whichever comes last. I would assume that this adjusts automatically for weight and winds - seems to work for me, but remember I'm a fair weather flyer.>>
Target pitch at the reference altitude (typically 50 QFE for propliners) is a constant (assuming identical flap angle for each landing). Flaring angular rotation is a constant. It is Vref that must change [proportional to SQR(W)] to permit this. At higher weight you have to have higher IAS to generate the same lift at the same AoA (pitch). If you watch jetliners of a given type you will see that they always fly the slope at the same pitch wherever they are from and whatever the landing weight (if they do it right). They reduce to variable Vref = constant pitch sooner so they do not have to spool the engines up or down near the ground to change IAS (if they do it right).
Thanks for the links. I did see a TWA C-46 at Heathrow once. I believe they used it to ferry engines to aircraft that could not otherwise be repaired in situ.
N registered aircraft can be used anywhere by an American operator of course, but a British airline could not own or dry lease one, even for use in the U.S. They could wet lease, but I doubt they ever did. BOAC seem to have had a poor opinion of the CW-20 and the RAF seem to have taken no further interest as a result. I think the Swedish aircraft in the photo is a C-46D. I am still researching slowly in odd minutes. I know Italy certificated the C-46F. SAM had one that flew their Rome - Milan - Paris cargo service in the early sixties. I think they may have been the only other European operator. Transair had three in the late 1950s and I think they retired the last about the time that photo was taken.
The existing FD assume that the same air file will be used with any military livery>>
<<Understood. I assume the critical altitude value for a plane like the CV-240 would work OK.
Not really. I will provide a value. I am waiting to see if Greg's manual is military and if it quotes a climb MAP and rpm in high blower. The CV24 was more powerful all round despite being restricted to a lower weight.
Regards, FSAviator
Greetings Tom,
I found time to work through the key aerodynamic issues arising from the new data. This post relates solely to aerodynamics not engine dynamics. It is mostly a matter of deciding which way you and Greg want to jump on two key issues which are just design time choices for the handling notes. It will give you something to get your teeth into whilst I work through the engine data.
The wing on the C-46 is NACA 23017 at the tip blending to NACA 4410.5 at the root. When I wrote the FD I could estimate CLmax to better than 3% and I knew CLmax(aug) for the blend and the flaps used. I could calculate Vs0 in KCAS to better than 1 knot and estimate Vs to within SQR(3%) which is also pretty much within one knot KCAS.
We have not discussed it for some time but any ASI has read errors arising from pitot tube placement and variable AoA. In real life these are non linear. In FS9 they are absent or linear. What the ASI indicates in real life are just KIAS with potentially huge errors. When these are corrected the values become KCAS. The data in an ops manual are KIAS. KIAS are what the pilot actually sees and reacts to, however false.
The numbers in the FD have to be KCAS. The real dynamics. If the user is to see uncorrected KIAS instead the pitot error has to be encoded in the aircraft.cfg. The real C182 has a pitot error of minus 24 knots at Vs0. Its aircraft.cfg includes;
[airspeed_indicators]
airspeed_indicator.0 = 1.3, -24.0
The gauge error must be coded only after the real dynamics are written and tested using KCAS.
In all previous propliners we have ignored pitot error. Most appear to have little error in real life. Since we now know that Vs0 is 67 MIAS = 58.3 KIAS and the KCAS value is 78 KIAS we now know that the real C-46A has a pitot error of 19.7 knots at Vs0, much less than the real C182, but nevertheless significant.
This can be added to the aircraft.cfg if you wish.
[airspeed_indicators]
airspeed_indicator.0 = 1.3, -19.7
If you add it the handling note values all have to alter by the diminishing encoded linear error. The code above causes it to diminish to zero error at Vref = 1.3 * Vs0. I have no idea what the real slope is and it will not be linear, but 1.3 or greater seems likely. It may be more but not less. More to the point some users will demand that the ultra low values in the handling notes be explained if they are uncorrected KIAS not KCAS.
I leave it up to you whether the handling notes are in KCAS like the other propliners or in uncorrected KIAS after encoding the gauge error in the aircraft.cfg.
>
Everything that follows relates to the (uncorrected) MIAS in the real manual and assumes that the slope will be 1.3 or greater in FS9 with KIAS in use; or that KCAS will be used.
> Manual: USAAF C-46A March 1945
>
> Takeoff:
> Tail wheel will come up around 60 mph.
That would be a question of trimming more nose down than currently stated in the handling notes, else reviewing the mainwheel placement versus CoG. I will leave Greg to decide which or in what combination. The real take off distance will have depended on it being achieved since the induced drag is much greater when tail down. Less important in FS9 but still relevant.
> Flaps up slowly
Strange command. The USAAF manual obviously assumes at least two stages of flap and seems to imply full flap for take off. The current FD and handling notes are for a take off with only one stage (see bottom).
Do you agree the notes imply that the C-46A employs full flap for take off?
The speeds to be employed and promulgated in the handling notes obviously depend on the answer to this regardless of whether they are KCAS or KIAS.
> Turning Final:
> Flaps down,
Do you agree the manual calls for all three stages at once?
> Over Fence:
> 100 mph
> Pull power off slowly during flare
In theory you could increase Vref from 83 KCAS to 87 KIAS/KCAS = 100 MIAS, but itis illogical to rotate slower than Vref when you are at equal weight or heavier than at Vref.
>Take off at 85-95 mph.
What is dangerous when light is more dangerous when (equally) heavy. The two values are inconsistent.
You can put whatever values you like in the handling notes for Vr and Vref. It just varies the difficulty the user will experience taking off and landing. How realistic do you want the difficulty to be?
Put the error correction above into the cfg and test fly with the real ASI error in place and decide how difficult you find the take off and landing using the uncorrected values in the USAAF manual if you use full flap for take off.
If you think they 'work' with full flap then that procedure can go in the handling notes, but it still makes no sense to placard Vref > Vr at the same weight. The late go around case is never worse than the max gross take off case.
However we can now see that the USAAF claim Vmc = 105mph.
>Critical single engine speed: 105 mph
I doubt this really means gear down and full flap. I don't believe the C-46A could fly at all on one engine in that configuration at 44K but if you give it credence then the FAA would have required the aircraft to be held on the runway until Vmc so Vr becomes 105mph = 91 KIAS or KCAS regardless of weight.
In which case only one stage of flap would have been used for take off in airline use since more flap gives more drag and a longer distance to 91 knots. I think that would be easier for most users to cope with but the take off distance will be longer than they read about in books if the USAAF used full flap for take off and rotated sooner with more lift and drag.
None of the above relates to time or distance to reach any Vr. That may be wrong in the current FD anyway and I will correct it once the above handling note issues have been resolved. Use a very long runway for testing
So far I haven't seen anything that would cause me to alter anything else in the FD, but the release handling notes may differ substantially depending on how many stages of flap for take off and the KIAS v KCAS decisions.
I will take a look at the other (mostly engine) data later in the week and flag up similar problems as they arise.
Regards,
Greetings Tom,
The requirement to raise flaps slowly after take off is not compatible with use of no flap or even minimal flap. There is no way to vary the rate at which each stage retracts in the real aircraft, so retracting slowly requires multiple flap stages. I have done some testing and I conclude that since the flaps only travel to 35 degrees they probably did use full flap for high weight take offs.
To avoid complications between military and civilian operation, particularly since many of the US based airline operated aircraft were owned by the USAF, I will rewrite the handling notes to call for full flap take offs and no flap inbound until slow and on short final. This may not reflect operation at low weights but most users will only fly at default weights anyway.
AFSD claims that the current FD have minus 2.8 knots of pitot error but I think it is only true in FS8. I will leave the aerodynamics in the FD as they are. I may increase either the elevator or the elevator trim authority a little further, but only if this seems necessary to enable full flap departure.
The revised handling notes will say KIAS but will really be KCAS as per previous aircraft.
The Christmas break caused me to rather lose track of where I was up to with the C-46A. I had not determined the KCAS stalling speeds as I thought. In the existing FD the stall is at 66.4 KCAS and I intend to say 67 in the aircraft.cfg. The real pitot error therefore appears to be only about minus 9 knots at Vs0 reducing to zero at around Vref. I will raise Vref to 87 KCAS to match the USAAF manual. I will re-examine the climb speeds and may alter them to match the manual if I conclude that ASI error really has reduced to zero before Vx in the real aircraft.
I will move Vr to 87 to match the revised Vref and I will then fake the thrust below Vr so that the TOD using full flap and Vr=87 is about what it was in real life using whatever technique was used in real life. Distance will be correct but time will be wrong.
I won't send a revised _ref until power issues are also resolved. I will study those later today. If I need decisions from you I will probably post this evening else I will make necessary revisions as time permits and send revised files when ready which may not be before Sunday evening. Depends what problems arise.
Regards, FSAviator
Greetings Tom,
The power data in the ops manual had no conflicts and pretty much fell into place requiring only minor revisions to the handling notes for operations under FARS. Military operation at overload weights using MIL power not yet considered.
Consequently V0.94 C-46A FD air file has only detailed changes to the power curve, CHT, oil temp and engine pressures reflecting new power data from the ops manual. They are all linear in FS9 and so only match at one intermediate point. Only slight testing performed on the revised Ts and Ps. If you think they matter test further and add whatever CHT limits you think make sense to the _ref.
The following sections need to be pasted over the existing ones in the aircraft.cfg.
description=V0.94 C-46A FD
[Reference Speeds]
flaps_up_stall_speed = 78
full_flaps_stall_speed = 67
cruise_speed = 178
max_indicated_speed = 209
They are all KCAS except cruise which is KTAS
If your cfg does not have the gear limits at the end of the contact points set to 131,131 please paste that into place for each wheel.
At some point you may need to re-arrange the fuel tank names to match the contents gauges. The V0.94 FD as they stand now should drive any other default power related gauges except prop rpm which must be avoided.
If you think torque and p-factor are too high add the following to the aircraft.cfg and adjust to taste.
[flight_tuning]
p_factor_on_yaw = 0.3
torque_on_roll = 0.3
V0.94 handling notes enclosed have full flap take off procedure, additions for long range cruise and holding plus minor changes to required inputs in most stages of flight.
Retain the old _ref and decide which departure procedures you prefer. If you prefer the old ones then the old take off and METO sections will need to be pasted over the new ones.
The revised handling notes match the real ops manual about as closely as I can (with KCAS in use), but the flap handling as described in the data you sent remains unclear. These procedures should 'work'.
Regards, FSAviator
Greetings Tom,
I realise you are out of town, but I needed to get this done today rather than the middle of next week when I will be busy.
> I have re-read the manual, and am now convinced that "normal" takeoffs did not use
> flaps of any kind. This manual (as typical of AAF manuals) is *very* detailed in it's
> description of flight procedures, and the takeoff procedure never mentions flaps at all
> (extension and retraction). The gear is completely covered, so this cannot be a simple
> omission.
I have rewritten the handling notes to match.
Now that Vr=91 (actually Vmc) and Vref =87 I have been able to reduce the elevator trim authority and the procedures are easier to fly. If you think the aircraft now balloons too much on flap selection during the approach I will re-examine this again.
I have added driver code for aileron and rudder trim. Rudder trim is potentially inadequate as in the real A series. Rudder authority is also reduced but remains more than adequate and probably more than real.
Now that we are sure what the take off configuration will be at 44K (no flap) I have rewritten the thrust curves so that the TOD (somewhat) matches the real TOD. This has to be a compromise if the aircraft is to be able to fly on one engine at all. I decided to allow this although I am not convinced that the real one could at 44K. It is now possible to make an emergency return following engine failure after departing a coastal airfield or a Pacific atoll at 44K up to fairly high temperatures. The take off is somewhat shorter (thrust probably higher) than it should be to allow this.
No other changes in V0.95
The real manual calls for 2400rpm after engine failure. In FS9 it will be necessary to use 2300. I have added this requirement to the V0.95 handling notes.
I have also gone back to calling for FLAP 1 below 130 KIAS during the approach or in the circuit since real life AoA is excessive at MLW without it. Since the real manual calls for late extension of the gear and the handling notes still concur the aircraft.cfg must alter as follows to prevent the gear horn sounding.
[gear_warning_system]
gear_warning_available=1
pct_throttle_limit=0.1
flap_limit_power=12
flap_limit_idle=11
Regards, FSAviator
Greetings Tom,
Sorry to hear that Greg has run into further problems with the project MDL. I guess there was a good reason that the original developer had problems and gave up. The MDL you sent me always crashed FS9:
Whilst I am a great fan of VCs I don't see them as necessary for IFR simulation in propliners. If MDL + VC development has ceased then the goal must be to create a superior 2D cockpit operating environment to that created by Capt. Paulo Alfonso Pizzato and available from Avsim within C-46.zip.
I enclose the panel.cfg I have been using during the latter part of testing. You and Greg may, or may not, have all the gauges but the purpose of the enclosure is to demonstrate the situation awareness available, ahead and to the side, in the air and on the ground, at 8192 x 6144 (true perspective) with the pre existing panel bitmap. Use of the contact points I supplied (Mike Stone's with minor mods) assumed for ground testing.
The only gauges that really need to change identity (but not even location) are the ASI, the fuel pressure gauge and the elevator trim indicator. I am sure you have suitable gauge names to substitute in the panel.cfg. The AP could easily be changed. I just like the ERK AP for testing. I will install the default Sperry for my own use, but most users will prefer one of yours. You can add to, and improve upon, on the existing content as you see fit.
A suitable CV twin sound set is readily available from your website.
In v0.95 I overdid the reduction in elevator trim authority. I have partially increased it again. The handling notes now call for neutral trim during the take off, but are otherwise unchanged. It takes a good haul on the yoke at Vr to unstick but the climb out is stable whilst retracting the gear and retrimming for Vx or Vy according to departure clearance obtained. The aircraft.cfg as updated stands. The other V0.96 components are attached.
Regards, FSAviator
Greetings Tom,
<<2. The plane seems very sensitive to altitude. While it has the normal TO MAP of 50" at SL, at 3800 ft it only has a MAP of 44". The DC-6B doesn't lose any MAP at 3600 ft. I know that the C-46 only has a single stage blower, but I didn't think it would make that kind of difference at such low altitudes. My critical altitude is set to 0, which seems very low...>>
It has always been set at zero. This value prevents development of METO, climb and max cruise power above the altitudes at which they were actually available. It reduces the maximum altitude for TOGA to sea level which is not quite true, but this matters little since the take of distance is still somewhat optimistic in the 096 FD. Whatever the altitude it will get airborne as quickly as in real life with full throttle applied. The MAP will read a little lower during take off than in real life but the thrust is correct on average between brake release and Vr. The take off procedure is full throttle at any altitude not a specific MAP so the reduced MAP is of no consequence.
The R-2800-51 had to be throttled back to 41.5 = METO by 300 feet AGL anyway and during most departures would be throttled back to 35 inches = Climb MAP at 1000 AGL or less. See C46_ref.txt. More than 41.5 inches is only available for two minutes from throttle up without risk of engine fire. This applies whether or not the high speed blower is present.
<<3. It takes 30" of MAP to start moving on the runway at SL. I've noticed this slowly climb with the recent FDE (the DC-4 doesn't move until 25" MAP, while the older DC-6B FDE starts moving at 20" MAP). This is causing problems for me on dirt strips in Alaska - I cannot move at 80% fuel from a stop at FT. They don't use any smoothing, so might have more rolling resistance?>>
Yes I have been reducing low speed thrust to increase the take off run to make it more realistic.
Surface friction is a bgl variable. The aliased texture has no relevance but if the relevant bgl author knew what he was doing and coded dirt then it will offer more friction than tarmac or concrete. Each surface type has a fixed value whereas concrete could be smooth or rough in real life and dirt can be rock hard or mud. The take off should be longer from a dirt strip but obviously you should be able to move on dirt.
Is the relevant runway bgl MS default, freeware. or payware as I would like to test using the same bgl.
Ability to overcome friction depends on thrust (f=ma), not power so this is not a MAP issue but I may need to do more work on the airscrew thrust curves. I am very surprised that it won't move at all using 2700 rpm and wonder if the bgl actually has the code for gravel rather than dirt.
At 44K in a C-46A you will need a tarmac runway of about 4400 feet at sea level in nil wind and even more at altitude. Longer from dirt and a whole lot longer from gravel, if the wheels don't just dig a hole in the gravel. A C-46A needs about as much runway at 44K as a C-54A needs at 70K. They were designed to use the same strategic runways at very different weights. A C-46A at 44K needs 2.2 times the length of runway needed by a DC-3 at max gross. The C-46A is a strategic transport aircraft not a tactical transport aircraft. The C-46A is a great fat lump of an aeroplane. If the environment was dirt or gravel and not grass or similar vegetation to bind the surface C-46s, C-54s and other WW2 strategic transports (or bombers) generally required rolls of steel matting to be laid over the unbound surface in order to operate at high weights.
The problem you are having may be realistic. It depends on what surface the bgl author coded and what invariant value MS assigned to it. I would need to test using the bgl that demonstrates the problem.
4. The neutral trim makes me haul back quite a bit. I like 20% up trim much better, and I can still get the tail up OK on TO.
If you can get the tail up soon enough that the take off run from tarmac at sea level in nil wind does not exceed about 4400 feet then using nose up trim is acceptable. The more nose up trim you use the longer the take off, but the less force needed to rotate. Make sure the trim chosen promotes acceleration to 110 KIAS below 300 feet AGL after rotation. See C-46_ref.txt.
Regards, FSAviator
Greetings Tom,
I ran a couple of tests on the surface type problem using MS default bgls. I ran the gravel test at Seldovia (PASO) and had no great difficulty getting the aircraft to move away from rest on MS default gravel although the runway is obviously too short for a C-46A.
I used Port Alsworth (TPO) for the MS default dirt strip test with the same result although the dirt strip was so narrow that the C-46 mainwheels were on the snow either side of the dirt texture. I don't know if the bgl matches the aliased textures that accurately. Is this an AFCAD issue?
So I think I conclude that the reported test involved a third party scenery bgl (or perhaps AF2***.bgl ??) that contained non compliant runway surface type friction code.
I am quite willing to test with the relevant scenery bgl and any related AF2 if they can be isolated and supplied or identified, but for the moment I conclude that the V096 FD are compatible with MS default dirt and gravel runways.
However it may be that Greg has made apparently appropriate changes to the contact points or scrape points and is using different values to those in the cfg I supplied. He needs to check this and if they differ that might be the source of the problem especially if e.g. the scrape points are in contact with the surface by mistake. Unlikely but worth checking since it is the most obvious possible source of surface friction discrepancy if all bgls are MS default.
Can you replicate the problem at PASO and TPO using my (probably Mike Stone's) contact points if Greg's are different? I assume you have not installed third party scenery or AFCADS for those airfields? If you have then use somewhere else where you are sure you are using MS default runway surface code.
Regards, FSAviator
I have now grasped that you are operating from an unknown default generic surface type of unknown friction. Without access to 'totally flat mesh' we cannot test what is encoded as its co-efficient of friction. If you are going to start publicly supporting bush flying there are new things to consider that are not in place. I will say more about that below, but in V097 I have addressed the more important issue of dirt and gravel runway friction.
I know a significant number of C-46s were based in Alaska but as far as I can tell the airfields they were able to use at high weights in nil wind were no smaller and no less suitable than the current situation at Bettles (PABT) which is probably unchanged from the C-46 era in Alaska.
If you are going to use aircraft from sloping bush terrain you need to park downhill, take off downhill, and if you ever need to take off uphill due to a significant headwind you need to hit the runway rolling with a take off clearance from the holding point, whatever the aircraft.
Airscrews are very inefficient at low advance ratios. They suffer the equivalent of very bad wheelspin when high power is applied from standstill. A C-46 can sustain about a 1 in 24 uphill gradient in flight when the advance ratio is around 80%, but it would not cope with 1:24 uphill slopes on the ground, especially from rest, especially on dirt or gravel, when the advance ratio is near zero.
I think the 'wheelspin' problems you are encountering are realistic, but I have revised various things as below. If users are going to fly from gravel and dirt it becomes even more important to get the tail up early. You will need to change the contact points to facilitate that.
IF
reference_datum_position = 0, 0, 0
empty_weight_CG_position = 0, 0, 0
THEN the V097 data should become;
[contact_points]
point.0 = 1, -39, 0.0 , -3.5, 1200, 0, 1.1, 45, 0.500, 0.500, 1.000, 10, 10, 0, 131,131 point.1 = 1, 1.25, -11.7, -8.4, 1600, 1, 1.4, 0 , 0.500, 2.500, 0.850, 10, 10, 2, 131,131 point.2 = 1, 1.25, 11.7 , -8.4, 1600, 2, 1.4, 0 , 0.500, 2.500, 0.850, 10, 10, 3, 131,131
Which should be the same as moving the mainwheels back 1.25 feet and extending the tailwheel downward by 0.2 feet (restoring static pitch) from wherever you have them now. Dynamically of course, not in the MDL.
Even so the only way to overcome your uphill slope plus static inertia problem is to significantly increase static thrust to a value that I think is probably unrealistic. Better still always park aeroplanes downhill on slopes and have the ground crew chock them.
V096 has sea level static thrust at 2 x 1800lbs. V097 attached has 2 x 2050lbs static thrust which I regard as optimistic for the R-2800-51.
During scenery design the surface slope is just pitch minus tail down angle which you should test with a nosewheel aircraft of zero static pitch for convenience. You have to test for the static case (use AFSD) else you will be measuring dynamic oleo compression.
F=ma and in an aeroplane we say T = MG and G = T/M
From rest at max FAA gross V096 gave 2 * 1800 / 44000 G acceleration = 0.082 G (static case).
Increasing static thrust to 2050 obviously gives you 0.095G (static case to overcome the inertia).
That is the situation for frictionless ice. Much of the available thrust is negated by drag (mostly from the surface friction at low velocity). If the drag is that of gravel then the residual G available to counter a slope is tiny.
The useful thrust is only T * COS(taildown angle) and the useful G is only G * COS(surface upslope).
V097 incorporating the contact point changes above and the revised static thrust produces a take off run less than 3800 feet at max gross on flat tarmac which I think is somewhat optimistic. However if the surface type is swapped to MS default gravel the TOR increases to just under 5000 feet based on the MS default friction co-efficients of the two runway surfaces when both are flat. Whether that hard coded difference is a realistic penalty for gravel just depends on a strip by strip basis. I am sure it is right for some pair somewhere!
Within MSFS in most cases any slope will be the lesser problem.
If the FD are for public release then they will be used almost entirely from flat polygon airfields. The C-46 is a strategic transport for use from big runways regardless.
Using no flap at default Bettles PABT (alt 643 feet) a flat runway consisting of 5200 feet of default gravel is just sufficient at 44K with nil wind. PABT represents the kind of gravel runway that a C-46A could actually cope with at high weights in real life. In real life it would depart downhill unless there was a significant tailwind and the crew would refuse line up and hold clearances. They would await a rolling take off clearance from the holding point and would have achieved ten knots at the point where many FS consumers will start from zero.
No one is going to be able to calculate how much runway they need versus weight, surface type, altitude and headwind vector in FS9. They just need to understand that the C-46 is a strategic asset not a tactical asset. It's not remotely a bush plane even though it operated from strategic gravel runways like the one at PABT.
Everyone will need to remember that default autogen trees are 2.5 times overscale and reduce autogen density as necessary to remove them from the flight path. Reducing the autogen texture size does not reduce the dynamic collision risk with the hard coded autogen scrape points, but it is worth substituting realistic size tree textures for bush flying anyway.
Using V097 with the contact point changes described above a departure from default PABT is scary but possible at max gross even QFU 19 into the rising ground and that is about how it should be. I believe I have default PABT BGLs (since they have the default file names and locations) but enhanced mesh for Alaska outside the flat airfield.
I understand the technique for making sloping runways, but of course the mesh is not accurate and they end up with excessive slopes. I expect most of them deliver wholly unrealistic take off distances regardless of encoded surface friction. I see no future in faking FD to match a particular mesh at a particular location or mesh in general. Users will just have to be aware that the C-46 is not by any means a bush plane and use it accordingly. What I have done in V097 is ensure that the C-46A is compatible with MS default gravel runways and will crash only when it should. If anyone decides to take off uphill they should reasonably expect to crash unless they have a significant headwind (15% Vr).
I think that the V097 FD with the contact point change above demonstrate the perils of gravel runways (sloping or otherwise) for the C-46A quite nicely, but at the expense of somewhat exaggerated performance from typical blacktop runways. The default values for friction should not be adjusted within sim1.dll as that screws up all AI aircraft FDE.
I think you may believe that 5200 feet of gravel near sea level in nil wind should be no problem in a C-46A at 44K, but in reality it should. It's a great fat pig of an aeroplane, but once you achieve 35/2300 having reduced the rpm and power to bring the advance ratio over 0.8 at > 120 KTAS the airscrews will each pump out around 2500lbs of thrust for the climb in V096 or V097 and rising ground is no problem.
This is really just a question of having the appropriate expectation concerning the barely adequate performance envelope of the C-46A even when used as a strategic transport from strategic airfields.
For your own personal use you may wish to bear in mind that unless you have a significant tailwind (15% Vref) you would normally land net uphill on sloping runways especially in temperatures below 32F.
As a separate case when landing on dirt or gravel in a low wing aeroplane you should assume that you cannot use any flap in a taildragger and only FLAP 1 in a nosewheel aircraft. They will be punctured by the gravel spat up by the wheels if further extended.
Bush planes cannot have low wings because that inhibits use of flap.
[Reference Speeds]
flaps_up_stall_speed = 78
C-46A Vref becomes 78 * 1.3 = 101 KIAS for gravel runways like PABT. If you wheel it on inside the touchdown zone it will stop from 101 well before the end, (because its a hell of a job to get it up to Vr=91 by the end using around 4000hp to help), but short strips with unconsolidated surfaces are not compatible with low wing aircraft. Sharp lumps of ice penetrate thin aluminium quite easily too.
There have been a few low wing aircraft with especially thick lower flap skins, but if you are going bush flying you should penalise yourself for using a low wing aeroplane. Bush flying is a whole new can of worms and the C-46 is not a good aeroplane for anyone to begin with because it is simply not a bush plane by any means.
Note that I did not test the C-54 (or any other FD on your web page) from gravel as I did not see it as relevant.
Regards, FSAviator
Greetings Tom,
I regard the encoded surface friction values in MSFS as almost entirely random. The more third party scenery people use the more random it becomes since the displayed textures and the types get mismatched. I assume all flight planners can read encoded type? I remain unclear whether AF2 files can also vary runway surface type and not just aliased texture?
I make the take off distance about real for level dry tarmac and if there is false data in a particular bgl then I don't regard it as my problem. Until we had this conversation I never considered it important that the static value be realistic or greater so long as the mean thrust between static and Vr was correct and the value at Vr was correct for further acceleration. Static thrust is difficult to estimate without a lot of airscrew data which never seems to be available.
The DC-4 as released has 4 x 1925lbs static versus a mass of c 73K. 4 x 1925 = 7700 / 73000 = 1.05 G static.
However the contact point geometry and oleo damping are important. They vary the net dynamic friction as well as the useful thrust vector. It occurs to me that the main oleo damping may be too soft on the C-46. I suspect it is still 'Mike Stone's' so maybe the number should be varied for copyright reasons anyway? I think the stiffer the gear the lower the MSFS net friction since the force used to create the 'oleo bounce' is subtracted from the thrust. Energy is conserved (wasted).
The thrust value at Vr has to promote acceleration to Vx < 500 VSI so it has to be 'real'. The need to keep the mean value real constrains the maximum value of static thrust, but I guess in MSFS it should be as unrealistically high as it can be without precluding a realistic mean value. I could produce curves with acceleration falling in the middle of the take off run, but that is not what happens and it would feel odd.
The take off performance of the real standard C-46 is so bad that I believe it must have poor static thrust. I have allowed the screws to go to 15 degrees but the Curtiss screws only went to 17 in real life so maybe that is the reason. It could be fitted with Hamilton screws that went all the way to 10 and I assume they had better traction from static, however the c4400 feet to clear a 10 metre screen is with the Hamilton low pitch screws.
Does V097 solve the local problem?
The problem with dirt strips is that there is usually no regular inspection or sweeping of the surface. Anywhere that the surface freezes and thaws the surface breaks up. Anywhere it gets rained on regularly (or hard) it breaks up. Either way the erosion leaves loose stones which get thrown up. Sweeping erosion debris off dirt runways gradually leaves you with a trench. I guess if it stays warm and dry erosion is not much of a problem and ultimately if a mine makes enough money it's worth damaging old aircraft anyway. Taildraggers suffer worst.
Flatten issue understood.
C-46 useful load is around 13K cf perhaps 28K for a C-54 from the same runway, but of course if they are short hauling the C-54 cannot land greater than 63.5K and its useful load falls to around 20K. In the classic era the resale price of a C-54 was about 2.5 times higher than for a C-46 with the same hours, reflecting its much greater utility even when short hauling.
Regards, FSAviator
Greetings Tom,
<<
> A nice guy from Brazil has convinced Greg Pepper to help him finish a very
> nice model of a C-46 Commando. I am wondering if you have anything
> already prepared for it, by chance.
Yes and no, but I am happy to produce them for Greg anyway.
I have all the aerodynamic code. I have generic R-2800 code. I know the maxima for any relevant R-2800-?? and can insert them easily, but I have no information relating to the norms for most R-2800-?? of WW2 vintage.
The next problem is that the FAA hated the C-46 and all the varieties of R-2800 fitted and consequently made the airline certification so restrictive that few were retained in the U.S. where the rules more or less had to be obeyed. The FD and handling notes that would apply to any air force are very different to the FD that would apply to any airline, anywhere, anytime. The British / European certification appears to have been even more restrictive.
The ones used by the airlines had the same aerodynamics but different weights and different power maxima to those supplied to air forces, during WW2, or after disposal. The norms may or may not have been the same. Logically they would be despite the different maxima.
Whether or not the FD are realistic the user will need handling notes matched to the FD content. Obviously I can deliver FD that have all the MAPs and all the rpms in there somewhere. I can mix and match them at random to deliver more or less correct power output and promulgate the guesses within handling notes, but the guesses for MAP and rpm may be quite wrong even though the resulting power and thrust would be 'realistic'.
If you let me know which variant of the C-46 e.g. A or D the FD are to represent then I should be able to deliver FD and handling notes matching post war FAA airline certification produced on the above basis by Sunday evening; depending on whether I need to do any further work on the C-4 etc in that timeframe.
I request that you do the usual proof reading and alpha testing to the usual standards to ensure that the aircraft can be operated to the handling notes even though they may not be 'realistic'. Fixing stuff that crops up may have to spread beyond Christmas depending on the nature of the problem.
There is a pretty good C-46 panel bitmap which just about supports 6141, (and therefore the cheek windows needed to taxi with reference to a taxiway edge), already available, produced by Paulo Alfonso Pizzato. It might need some different gauges to work correctly in FS9, but your parts box should have all of them anyway.
Is this new MDL going to have a VC? Is there going to be another panel?
Getting the tail up is just! a case of writing realistic FD and then remembering that taildraggers use nose down trim for take off (to get the tail up). Getting aircraft to behave properly is often a lot more to do with the (lack of) realistic handling instructions than lack of realism in the FD, but if you ever need to design such FD you will find starting from my B247 FD and handling notes a lot easier than fixing the mistakes, and understanding all the complication, in the default DC-3 files.
You always have to start with the handling notes and then impose them on MSFS, even if you just invented (large parts of) the handling notes. I hope to invent only small parts relating to certain norms. The easiest data to impose on the real Newtonian equations within MSFS is the real input data as it all multiplies together nicely to create predictable output that needs little tweaking. The less I know about the inputs the longer it takes to create realistic output or even docile output by time consuming iterative experimentation. The fewer unknown inputs I have to iterate concurrently the better. In some ways realistic FD are easier to create than unrealistic ones because unrealistic ones tend to have unfortunate conjunctions in which equations turn negative at the wrong time with unpredictable results whose cause is difficult to fathom.
Regards, FSAviator
Greetings Tom,
I can always use Mike Stone's MDL and a pre existing panel with some new gauges for testing.
The new MDL looks nice. The fact that it is a C-46A from later post noted.
I believe most of the C-46s in use in the U.S. were really owned by the USAF and just painted in airline livery just like the B314As were owned by the USN but had PAA titles. Like the B314As they could then be flown on government contracts by civilian aircrew to military safety criteria rather than FAA criteria. This will have been true of some SA airlines too.
I can get round this fairly easily. I will set the maximum weights to military but only load it by default to FAA limits then put notes on how to achieve military overload in the aircraft.cfg just as for the C-54s. The gap is bigger for the C-46 I think. Still researching but I suppose the cargo carriers who had USAF C-46s could also tender for civilian contracts but then had to operate to FAA rules.
<I assume that he would prefer handling notes that would match the more recent SA operations>
I will make the handling notes relate to FAA rules and thus the default loads. I know what the FAA criteria were, I just don't know why exactly, presumably lousy engine out handling and performance.
I see someone just did a paint of the default C-46 as the C-55 Commando (CW-20) used by BOAC. It had R-2600 engines like the B314A so I might try cutting and pasting the dynamic bits together to replicate that as well, but not yet.
Regards,
FSAviator
Greetings Tom,
The aircraft.cfg contains some MDL data for Mike Stone's MDL which should be replaced in due course. Retained gear limits in contact points etc. All the rest of the code is mine.
Engines have no high blower as the FAA required removal. I will research the military data if I can, but I am not certain that I will find everything required to annotate the aircraft.cfg to allow conversion. V0.90 is therefore FAA compliant only. Only slight testing so various things may need to change. No testing of ground handling or take off data done yet.
I won't have time to do anything else today so I will try to respond to any new mail tomorrow. No more updates to anything until Tuesday evening GMT.
Regards, FSAviator
Greetings Tom,
<<Thanks for the C-46 FDE. Works great for the most part. The things I've noticed so far:>>
<<1. In the handling notes you mention max landing wt as 44000 lbs, which is also max TO wt. Is this correct?>>
Yes. The FAA forced the MTOW down to MLW so that it could land immediately if it had an engine failure after take off. In general they required the ability to dump fuel before they would allow MTOW > MLW but that also depended on how well the aircraft to be certificated could survive losing one engine at max gross. No problem with four engines. You just burn off fuel in a hold.
<<2. At 43,500 lbs it runs out of up trim on final approach (on AP) at about 87 kts .>>
That is an FD error I will fix that.
<<At flaps 1 it is also somewhat nose up at 110 kts, the speed given for flaps 2. >>
That is a handling note error.
The flaps are weak by post war standards. FLAP 1 limit is 131 matching the gear and the flap 2 limit is 117. I guess the crew added flap 1 and flap 2 as soon as they could, but bear in mind that 43,500 is an emergency return landing. This may well relate to (1) above.
I will change the handling notes to say 116 which should be easier to attain on a 3 degree slope at 20/2000.
The FLAP 3 limit is also 117 so they probably went to FLAP 3 earlier at high approach weights.
The USAF operated the A to at least 56,000lbs during WW2. I don't think the aircraft had any real chance of surviving an engine failure after take off at that weight, nor can I find any clear max gross information concerning US airline operation on Logair contracts etc.
I may have underestimated the drag. If not it seems that econ power was less than I have put in the handling notes. I think it may be cruising too fast and have too much range. Still researching.
The AoA in the cruise won't change enough to matter so the V0.9 FD can be used for any panel development after FLAP 2 goes to 116 as normal extension. I think the view must have been compromised on the ground or at low IAS else I do not understand why they developed the C-46E. Evidently it did not solve the problem whatever it was.
Regards, FSAviator
Greetings Tom,
Firstly I think the 'high' cruising speeds are just the interpolated consequence of the much lower weights when flown under FARs. I may revise this view if you come up with real low blower data later.
> Also, .....(MDL author).... has it set to steer using the yoke (a la a tricycle gear
> plane); I assume his preference. When I change the current contact points
> steering angle to 180 to simulate a real taildragger, it acts very badly,
> and I'm not able to steer it (unlike the default DC-3). As long as we
> keep it steerable no real problem, but I thought I'd mention it.
The C-46 has retractable tailwheel with connected hydraulics. This makes it more likely that it had steering with an unlock to castor facility, but I don't know what it actually had.
Castoring v not castoring is not really a nosewheel versus tailwheel thing. It's a cost thing.
If you believe that it had a castoring only tailwheel then you will need to add lock/unlock to the contact points, an unlock lever to the panel and probably a differential braking factor to the braking section.
> Finally, I can only get the tail up on the C-46 above 65 kts. By the time
> I've got it up all the way I'm almost ready to rotate.
With trim neutral the tail up IAS is a function of current weight and mainwheel distance ahead of CoG. I did not have time to do any take off testing which is why the handling notes say,
TRIM = NEUTRAL (MAY CHANGE)
Tailwheel aircraft (with flaps) begin the take off with whatever (nose down) trim is required to get the tail up at whatever IAS the captain desires. I don't know the real tail up IAS for a C-46 but @ 44,000 Vr = 85 so 65 is late but not very late. I have never seen a C-46 take off in real life. I have only seen one land.
From here on I won't have time to do much bug fixing on the C-46 until January so if it the handling notes need to change before then you will have to work on them. Not a lack of interest/willingness just a lack of time.
<Here is a message from Greg. Note that the current 0,0,0 datum is not at the CG. I told him to move it to simplify the FDE editing (since I assume you assumed it to be there in your FDE). >
Yes I did,
reference_datum_position = 0.000, 0.000, 0.000
empty_weight_CG_position = 0.000, 0.000, 0.000
<Editing the eyepoint, contact points and lights shouldn't be too bad.>
That is fine by me of course, but for future reference if the payloads and fuel loads in combination are simpler to edit ('in the opposite direction') then that is a valid alternative.
Obviously if you did your take off test with the planned release data the mainwheel to CoG offset will have been false, but tail up = 65 is quite likely to be true for the ones I sent with trim only neutral. Obviously I don't know if Mike Stone's mainwheel to CoG offset is correct anyway.
<<Also note that Greg's C-46 manual CD is on it's way, so hopefully you'll have some hard data soon. Once he gets the panel bitmap finished I'll send you a copy if you think you need it.>>
The stuff I would 'need' from the manual is the usual power relationships. What MAP and rpm create what power and data to inform what we should publish as climb, max cruise and econ cruise power and how to impose it. There is a problem however. The manuals will probably be for the military spec not the demilitarised aircraft and may also lack data for -51 engine which was the norm in the A. For the FAA spec I would only need low blower data.
Concerning panel bitmaps the eyepoint from which the panel bitmaps of a taildragger are 'designed' can only be chosen after the contact points are final and must be chosen to deliver the ability to taxi using the VIEW_DIR that projects the correct scenery in the windscreen for both the tail down and tail up cases. In the tail down case it must at the very least include the ability to see the vanishing point of the runway with the tail down, just before throttle up, so that pilot flying can line up carefully, (and lock the tailwheel), before throttle up. This needs to work with SIZE_Y = 6144. The cheek windows are likely to require very high SIZE_Y anyway.
The contact points can perhaps be adjusted from their current values for oleo compression to lower the nose a little, but all the rest of the compromise must be in the carefully designed crop of the cockpit photo. If it is cropped (or drawn freehand) to allow the runway vanishing point to be visible at Y = 6144 with the final oleo compression (at low weights) it will work, else it won't.
The amount I can compress the oleos to help Greg won't be much and will anyway depend on the relevant MDL animation code. The dynamics will override the MDL and the tyres will start moving down into the runway if the oleos need a lot of compression and that much compression is not already 'animated'.
I can also move the mainwheels dynamically without any change to the MDL, but that will make rotation more difficult and obviously will affect the 'sit' in external views. Ideally if the current oleo compression and 'sit' at 44K look 'right' Greg should make all the compromise. I think it will be tough to get much more than the runway vanishing point into view. I don't think the real view was wonderful with the tail down, but it was 'adequate'.
The 0.91 air file has greater trim authority as requested, but no other changes even though some will be needed. Keep bug reports coming if you wish but I don't expect to have time to do much with them until January. Feel free to play with oleo compression and mainwheel offset in the contact points during panel development, but test dynamic rotation and static sit after changes.
Regards, FSAviator
Greetings Tom,
I have located the problem in the C-46 code. Where I intended to code the max elevator trim as 15 degrees I actually have 5. I have now tripled the value in the air file to compensate. I have also recalculated Vref for 44000lbs more carefully and it should be 83 KIAS. I have also tweaked a few things relating to stability and damping, but there are a few low IAS handling issues remaining that I will have to address when I have more time. I have altered a few other values in the _ref including Vx climb in METO and a second version is enclosed. Most of the reference speeds in the cfg are wrong but I will alter those later. The original cfg stands for now.
Please experiment with take off trim values versus the new trim authority as well as verifying the ability to trim for <= 83 with full flap and adequate power.
If you are still short of trim just increase the value in the cfg slowly from 5.
Regards, FSAviator
Greetings Tom,
> This version solves all trim problems for me.
Good.
> However, trying to land
> softly at 83 kts over the boundary at 43,500 lbs is something I am unable
> to do. The plane tends to "dump" itself onto the runway. There is no
> "float" like all the other aircraft you've done. Of course this is the
> first taildragger, so I don't know what it should be like. Landing at 90
> kts or at 40,000 lbs is OK.
>
You are probably running out of elevator authority which is a different issue to elevator trim authority.
During the limited amount of time I have had for flight testing the C-46 FD I have become aware that there are a range of very low IAS handling issues. At some point I need time to study and resolve these with an integrated rather than piecemeal solution, but I will struggle to fit in a sufficiently long and intense testing/rewriting session before early January.
None of the changes to the interaction between stability, damping, inertia or control authority variables that will eventually emerge will have any implications for anyone making any other files for this project. The problems are internal to the FD.
If it can all be done in a two hour session I may get it done before Christmas. It is one of those things where I have no idea how many iterations of the four conflicting variable types I will have to go through to find a good 'fit' that solves all potential low IAS problems.
Regards, FSAviator
Greetings Tom,
I might have time to work on the C-46 low speed handling tomorrow.
>New zip file available if you want it.
Yes, send it please so that I have it if I need to refer to anything in it.
>Note he has configuration data available if you need it (don't think so?).
No I won't need those data. I don't believe that much can be calculated from them anyway. I think force feedback devices might use some of it though. Not sure.
<Considering I spent Thursday, Friday and Saturday in bed sicker then a dog, I did get a lot done on the C-46.>
Sorry to hear Greg has been ill.
<Note his problem with the RPM; I'm not seeing this. Suggested he start with default flight. >
The rpm problem sounds as though he was using an airscrew rpm gauge. He (the panel) needs engine rpm gauges. He will not have been using the correct rpm for climb as he could not set it. The climb rate in climb power was only just over 500 VSI at FAA gross anyway. If they had ATC restrictions to make or mountains to cross they stayed in METO. See _ref.
Greg may be missing a couple of inches of TOGA MAP for some reason anyway. It should give 52 at SL in ISA.
Regards, FSAviator
Greetings Tom,
Greg's gauges are displaying airscrew rpm. The only remaining question is why. I didn't think there was a way to toggle engine rpm gauges to show airscrew rpm. Gregg can test what they are displaying using AFSD which runs outside FS9 and will show both rpm regardless of how he has installed or configured stuff inside FS9. Some of Greg's aircraft have used aircrew rpm gauges in the past. Maybe he still has old versions in his gauges folder or in the folder he is using for testing. Ask him to test this using the default DC-3 engine rpm gauges.
I have done the further testing on the C-46 low speed handling and re-examined all outstanding reported issues.
At 35/2400 it accelerates well beyond 130 KIAS at 500 VSI in ISA at max FAA gross so I still think that is a good value for climb power. 2 x METO (3200hp) represents huge surplus available power in any weather.
I have enough elevator authority to stall the aircraft from any IAS in any flap and gear state. Flying straight and level at any IAS > stall is just a question of supplying the power required. Consequently propensity to float on landing is just a matter of back pressure and power applied. It can be made to float forever if not stalled.
Note that the AP should not have trim authority to stall the aircraft from Vref. You do have the elevator authority to achieve any IAS you like including Vs or Vs0 plus 1 or minus several (from level flight).
Around MLW Vref is 83 KIAS and zero pitch is at about that speed whilst descending down a 3 degree glidepath with full flap. VSI will be about minus 500 as you hit Vref. The flare begins from nose level and has the intention to reduce sink by about 400 VSI to place the wheels on the runway at about minus 100 VSI a few knots slower and a few seconds later.
The stalling angle is much greater than the tail down angle. The flare should never be enough to cause a tailstrike so the flare terminates well above stall speed and well below stall angle. A C-46 should always be 'wheeled on' and never three pointed. I can control negative VSI with elevator quite easily below Vref (83) and well above Vs0 which is about 62. I have no difficulty flaring to minus 100 VSI or whatever touchdown sink rate I choose if I carry enough power and do not allow speed to drop more than a few knots during the flare.
I think you may be removing too much power too soon if the 'arrival' seems sudden. If in doubt leave all the power that was required to descend at minus 3 degrees and minus 500 VSI in place until the main wheels are wheeled on at not much less than 80 KIAS. It won't bounce from minus 100 VSI because the power supplied could only sustain minus 500.
After this further testing I think the low speed handling in pitch was OK after the last revision. It is mostly yaw at low IAS that I have been working on during the further testing.
The problem that I cannot resolve is the single engine performance. I see no evidence that the single engine ceiling is above sea level at 44,000lbs in the real aircraft. 1600hp = 40% power is not enough to sustain flight. I don't know how the FAA managed to certificate it at that weight. I know no one else would.
The FAA imposed at least 26 mandatory modifications before they would certificate it at all, one of which was removal of the C-46A elevators and replacement with those from a C-46F. As far as I can tell Britain would not certificate anything other than a full F.
If it cannot fly on one engine then rudder authority following engine failure is a non issue. As far as I can tell the C-46F was the first variant that could fly on one engine at 44K, but I not certain that it could either. I only know it had a second rudder trim tab because none of the earlier versions could be trimmed in yaw at low IAS.
I have emulated this design failure but it may not be precise. If I assume that it is impossible to fly the C-46A on one engine at 44K then my original estimates of the yaw and roll data stand. Consequently there are no new FD after the further testing. The pitch handling is real or a bit better, the yaw handling probably about real and the roll handling can only be a guess anyway. It is coded to be 'adequate'.
The existing FD assume that the same air file will be used with any military livery but that the high speed blower will be put back in the cfg. Apart from default payload those would be the only two changes for a mil v civil C-46A as far as FD go. METO in the air file and _ref is therefore set to be delivered at the high blower MAP and rpm settings. METO power is the same in either blower it is only the mix and match of MAP and rpm that differ. They cannot differ in FS9 without a WEP gauge which I do not recommend for this aircraft anyway.
The mil _ref would reflect mil weights and the engine data from Greg's manual assuming it is for the R-2800-51. I have seen no evidence that the -51 had a MIL rating but maybe the manual that Greg has now will shed light on any MIL rating and the max weight for sustained flight on one engine.
I have examined the C-46 2D bitmap but not the MDL. Whether the 2D bitmap works is just a question of whether Greg can integrate VIEW_FORWARD_DIR and SIZE_Y for that bitmap and the VC (see enclosed detailed reply to Glen on same subject). I have not had time to test the aircraft.cfg revisions from Greg, but do not expect a problem, and I assume that you have tested anyway by now.
I will be 'around' over Christmas, but do not intend to do any 'FS development' between now and about the 28th at the earliest and maybe more like the 2nd.
Merry Christmas etc.,
FSAviator
Greetings Tom,
May not have time to reply to all mail today, but making a start. Glad to hear you are feeling a bit better.
<< Flaps get added at either handling note speeds or altitudes AGL, whichever comes last. I would assume that this adjusts automatically for weight and winds - seems to work for me, but remember I'm a fair weather flyer.>>
Target pitch at the reference altitude (typically 50 QFE for propliners) is a constant (assuming identical flap angle for each landing). Flaring angular rotation is a constant. It is Vref that must change [proportional to SQR(W)] to permit this. At higher weight you have to have higher IAS to generate the same lift at the same AoA (pitch). If you watch jetliners of a given type you will see that they always fly the slope at the same pitch wherever they are from and whatever the landing weight (if they do it right). They reduce to variable Vref = constant pitch sooner so they do not have to spool the engines up or down near the ground to change IAS (if they do it right).
Thanks for the links. I did see a TWA C-46 at Heathrow once. I believe they used it to ferry engines to aircraft that could not otherwise be repaired in situ.
N registered aircraft can be used anywhere by an American operator of course, but a British airline could not own or dry lease one, even for use in the U.S. They could wet lease, but I doubt they ever did. BOAC seem to have had a poor opinion of the CW-20 and the RAF seem to have taken no further interest as a result. I think the Swedish aircraft in the photo is a C-46D. I am still researching slowly in odd minutes. I know Italy certificated the C-46F. SAM had one that flew their Rome - Milan - Paris cargo service in the early sixties. I think they may have been the only other European operator. Transair had three in the late 1950s and I think they retired the last about the time that photo was taken.
The existing FD assume that the same air file will be used with any military livery>>
<<Understood. I assume the critical altitude value for a plane like the CV-240 would work OK.
Not really. I will provide a value. I am waiting to see if Greg's manual is military and if it quotes a climb MAP and rpm in high blower. The CV24 was more powerful all round despite being restricted to a lower weight.
Regards, FSAviator
Greetings Tom,
I found time to work through the key aerodynamic issues arising from the new data. This post relates solely to aerodynamics not engine dynamics. It is mostly a matter of deciding which way you and Greg want to jump on two key issues which are just design time choices for the handling notes. It will give you something to get your teeth into whilst I work through the engine data.
The wing on the C-46 is NACA 23017 at the tip blending to NACA 4410.5 at the root. When I wrote the FD I could estimate CLmax to better than 3% and I knew CLmax(aug) for the blend and the flaps used. I could calculate Vs0 in KCAS to better than 1 knot and estimate Vs to within SQR(3%) which is also pretty much within one knot KCAS.
We have not discussed it for some time but any ASI has read errors arising from pitot tube placement and variable AoA. In real life these are non linear. In FS9 they are absent or linear. What the ASI indicates in real life are just KIAS with potentially huge errors. When these are corrected the values become KCAS. The data in an ops manual are KIAS. KIAS are what the pilot actually sees and reacts to, however false.
The numbers in the FD have to be KCAS. The real dynamics. If the user is to see uncorrected KIAS instead the pitot error has to be encoded in the aircraft.cfg. The real C182 has a pitot error of minus 24 knots at Vs0. Its aircraft.cfg includes;
[airspeed_indicators]
airspeed_indicator.0 = 1.3, -24.0
The gauge error must be coded only after the real dynamics are written and tested using KCAS.
In all previous propliners we have ignored pitot error. Most appear to have little error in real life. Since we now know that Vs0 is 67 MIAS = 58.3 KIAS and the KCAS value is 78 KIAS we now know that the real C-46A has a pitot error of 19.7 knots at Vs0, much less than the real C182, but nevertheless significant.
This can be added to the aircraft.cfg if you wish.
[airspeed_indicators]
airspeed_indicator.0 = 1.3, -19.7
If you add it the handling note values all have to alter by the diminishing encoded linear error. The code above causes it to diminish to zero error at Vref = 1.3 * Vs0. I have no idea what the real slope is and it will not be linear, but 1.3 or greater seems likely. It may be more but not less. More to the point some users will demand that the ultra low values in the handling notes be explained if they are uncorrected KIAS not KCAS.
I leave it up to you whether the handling notes are in KCAS like the other propliners or in uncorrected KIAS after encoding the gauge error in the aircraft.cfg.
>
Everything that follows relates to the (uncorrected) MIAS in the real manual and assumes that the slope will be 1.3 or greater in FS9 with KIAS in use; or that KCAS will be used.
> Manual: USAAF C-46A March 1945
>
> Takeoff:
> Tail wheel will come up around 60 mph.
That would be a question of trimming more nose down than currently stated in the handling notes, else reviewing the mainwheel placement versus CoG. I will leave Greg to decide which or in what combination. The real take off distance will have depended on it being achieved since the induced drag is much greater when tail down. Less important in FS9 but still relevant.
> Flaps up slowly
Strange command. The USAAF manual obviously assumes at least two stages of flap and seems to imply full flap for take off. The current FD and handling notes are for a take off with only one stage (see bottom).
Do you agree the notes imply that the C-46A employs full flap for take off?
The speeds to be employed and promulgated in the handling notes obviously depend on the answer to this regardless of whether they are KCAS or KIAS.
> Turning Final:
> Flaps down,
Do you agree the manual calls for all three stages at once?
> Over Fence:
> 100 mph
> Pull power off slowly during flare
In theory you could increase Vref from 83 KCAS to 87 KIAS/KCAS = 100 MIAS, but itis illogical to rotate slower than Vref when you are at equal weight or heavier than at Vref.
>Take off at 85-95 mph.
What is dangerous when light is more dangerous when (equally) heavy. The two values are inconsistent.
You can put whatever values you like in the handling notes for Vr and Vref. It just varies the difficulty the user will experience taking off and landing. How realistic do you want the difficulty to be?
Put the error correction above into the cfg and test fly with the real ASI error in place and decide how difficult you find the take off and landing using the uncorrected values in the USAAF manual if you use full flap for take off.
If you think they 'work' with full flap then that procedure can go in the handling notes, but it still makes no sense to placard Vref > Vr at the same weight. The late go around case is never worse than the max gross take off case.
However we can now see that the USAAF claim Vmc = 105mph.
>Critical single engine speed: 105 mph
I doubt this really means gear down and full flap. I don't believe the C-46A could fly at all on one engine in that configuration at 44K but if you give it credence then the FAA would have required the aircraft to be held on the runway until Vmc so Vr becomes 105mph = 91 KIAS or KCAS regardless of weight.
In which case only one stage of flap would have been used for take off in airline use since more flap gives more drag and a longer distance to 91 knots. I think that would be easier for most users to cope with but the take off distance will be longer than they read about in books if the USAAF used full flap for take off and rotated sooner with more lift and drag.
None of the above relates to time or distance to reach any Vr. That may be wrong in the current FD anyway and I will correct it once the above handling note issues have been resolved. Use a very long runway for testing
So far I haven't seen anything that would cause me to alter anything else in the FD, but the release handling notes may differ substantially depending on how many stages of flap for take off and the KIAS v KCAS decisions.
I will take a look at the other (mostly engine) data later in the week and flag up similar problems as they arise.
Regards,
Greetings Tom,
The requirement to raise flaps slowly after take off is not compatible with use of no flap or even minimal flap. There is no way to vary the rate at which each stage retracts in the real aircraft, so retracting slowly requires multiple flap stages. I have done some testing and I conclude that since the flaps only travel to 35 degrees they probably did use full flap for high weight take offs.
To avoid complications between military and civilian operation, particularly since many of the US based airline operated aircraft were owned by the USAF, I will rewrite the handling notes to call for full flap take offs and no flap inbound until slow and on short final. This may not reflect operation at low weights but most users will only fly at default weights anyway.
AFSD claims that the current FD have minus 2.8 knots of pitot error but I think it is only true in FS8. I will leave the aerodynamics in the FD as they are. I may increase either the elevator or the elevator trim authority a little further, but only if this seems necessary to enable full flap departure.
The revised handling notes will say KIAS but will really be KCAS as per previous aircraft.
The Christmas break caused me to rather lose track of where I was up to with the C-46A. I had not determined the KCAS stalling speeds as I thought. In the existing FD the stall is at 66.4 KCAS and I intend to say 67 in the aircraft.cfg. The real pitot error therefore appears to be only about minus 9 knots at Vs0 reducing to zero at around Vref. I will raise Vref to 87 KCAS to match the USAAF manual. I will re-examine the climb speeds and may alter them to match the manual if I conclude that ASI error really has reduced to zero before Vx in the real aircraft.
I will move Vr to 87 to match the revised Vref and I will then fake the thrust below Vr so that the TOD using full flap and Vr=87 is about what it was in real life using whatever technique was used in real life. Distance will be correct but time will be wrong.
I won't send a revised _ref until power issues are also resolved. I will study those later today. If I need decisions from you I will probably post this evening else I will make necessary revisions as time permits and send revised files when ready which may not be before Sunday evening. Depends what problems arise.
Regards, FSAviator
Greetings Tom,
The power data in the ops manual had no conflicts and pretty much fell into place requiring only minor revisions to the handling notes for operations under FARS. Military operation at overload weights using MIL power not yet considered.
Consequently V0.94 C-46A FD air file has only detailed changes to the power curve, CHT, oil temp and engine pressures reflecting new power data from the ops manual. They are all linear in FS9 and so only match at one intermediate point. Only slight testing performed on the revised Ts and Ps. If you think they matter test further and add whatever CHT limits you think make sense to the _ref.
The following sections need to be pasted over the existing ones in the aircraft.cfg.
description=V0.94 C-46A FD
[Reference Speeds]
flaps_up_stall_speed = 78
full_flaps_stall_speed = 67
cruise_speed = 178
max_indicated_speed = 209
They are all KCAS except cruise which is KTAS
If your cfg does not have the gear limits at the end of the contact points set to 131,131 please paste that into place for each wheel.
At some point you may need to re-arrange the fuel tank names to match the contents gauges. The V0.94 FD as they stand now should drive any other default power related gauges except prop rpm which must be avoided.
If you think torque and p-factor are too high add the following to the aircraft.cfg and adjust to taste.
[flight_tuning]
p_factor_on_yaw = 0.3
torque_on_roll = 0.3
V0.94 handling notes enclosed have full flap take off procedure, additions for long range cruise and holding plus minor changes to required inputs in most stages of flight.
Retain the old _ref and decide which departure procedures you prefer. If you prefer the old ones then the old take off and METO sections will need to be pasted over the new ones.
The revised handling notes match the real ops manual about as closely as I can (with KCAS in use), but the flap handling as described in the data you sent remains unclear. These procedures should 'work'.
Regards, FSAviator
Greetings Tom,
I realise you are out of town, but I needed to get this done today rather than the middle of next week when I will be busy.
> I have re-read the manual, and am now convinced that "normal" takeoffs did not use
> flaps of any kind. This manual (as typical of AAF manuals) is *very* detailed in it's
> description of flight procedures, and the takeoff procedure never mentions flaps at all
> (extension and retraction). The gear is completely covered, so this cannot be a simple
> omission.
I have rewritten the handling notes to match.
Now that Vr=91 (actually Vmc) and Vref =87 I have been able to reduce the elevator trim authority and the procedures are easier to fly. If you think the aircraft now balloons too much on flap selection during the approach I will re-examine this again.
I have added driver code for aileron and rudder trim. Rudder trim is potentially inadequate as in the real A series. Rudder authority is also reduced but remains more than adequate and probably more than real.
Now that we are sure what the take off configuration will be at 44K (no flap) I have rewritten the thrust curves so that the TOD (somewhat) matches the real TOD. This has to be a compromise if the aircraft is to be able to fly on one engine at all. I decided to allow this although I am not convinced that the real one could at 44K. It is now possible to make an emergency return following engine failure after departing a coastal airfield or a Pacific atoll at 44K up to fairly high temperatures. The take off is somewhat shorter (thrust probably higher) than it should be to allow this.
No other changes in V0.95
The real manual calls for 2400rpm after engine failure. In FS9 it will be necessary to use 2300. I have added this requirement to the V0.95 handling notes.
I have also gone back to calling for FLAP 1 below 130 KIAS during the approach or in the circuit since real life AoA is excessive at MLW without it. Since the real manual calls for late extension of the gear and the handling notes still concur the aircraft.cfg must alter as follows to prevent the gear horn sounding.
[gear_warning_system]
gear_warning_available=1
pct_throttle_limit=0.1
flap_limit_power=12
flap_limit_idle=11
Regards, FSAviator
Greetings Tom,
Sorry to hear that Greg has run into further problems with the project MDL. I guess there was a good reason that the original developer had problems and gave up. The MDL you sent me always crashed FS9:
Whilst I am a great fan of VCs I don't see them as necessary for IFR simulation in propliners. If MDL + VC development has ceased then the goal must be to create a superior 2D cockpit operating environment to that created by Capt. Paulo Alfonso Pizzato and available from Avsim within C-46.zip.
I enclose the panel.cfg I have been using during the latter part of testing. You and Greg may, or may not, have all the gauges but the purpose of the enclosure is to demonstrate the situation awareness available, ahead and to the side, in the air and on the ground, at 8192 x 6144 (true perspective) with the pre existing panel bitmap. Use of the contact points I supplied (Mike Stone's with minor mods) assumed for ground testing.
The only gauges that really need to change identity (but not even location) are the ASI, the fuel pressure gauge and the elevator trim indicator. I am sure you have suitable gauge names to substitute in the panel.cfg. The AP could easily be changed. I just like the ERK AP for testing. I will install the default Sperry for my own use, but most users will prefer one of yours. You can add to, and improve upon, on the existing content as you see fit.
A suitable CV twin sound set is readily available from your website.
In v0.95 I overdid the reduction in elevator trim authority. I have partially increased it again. The handling notes now call for neutral trim during the take off, but are otherwise unchanged. It takes a good haul on the yoke at Vr to unstick but the climb out is stable whilst retracting the gear and retrimming for Vx or Vy according to departure clearance obtained. The aircraft.cfg as updated stands. The other V0.96 components are attached.
Regards, FSAviator
Greetings Tom,
<<2. The plane seems very sensitive to altitude. While it has the normal TO MAP of 50" at SL, at 3800 ft it only has a MAP of 44". The DC-6B doesn't lose any MAP at 3600 ft. I know that the C-46 only has a single stage blower, but I didn't think it would make that kind of difference at such low altitudes. My critical altitude is set to 0, which seems very low...>>
It has always been set at zero. This value prevents development of METO, climb and max cruise power above the altitudes at which they were actually available. It reduces the maximum altitude for TOGA to sea level which is not quite true, but this matters little since the take of distance is still somewhat optimistic in the 096 FD. Whatever the altitude it will get airborne as quickly as in real life with full throttle applied. The MAP will read a little lower during take off than in real life but the thrust is correct on average between brake release and Vr. The take off procedure is full throttle at any altitude not a specific MAP so the reduced MAP is of no consequence.
The R-2800-51 had to be throttled back to 41.5 = METO by 300 feet AGL anyway and during most departures would be throttled back to 35 inches = Climb MAP at 1000 AGL or less. See C46_ref.txt. More than 41.5 inches is only available for two minutes from throttle up without risk of engine fire. This applies whether or not the high speed blower is present.
<<3. It takes 30" of MAP to start moving on the runway at SL. I've noticed this slowly climb with the recent FDE (the DC-4 doesn't move until 25" MAP, while the older DC-6B FDE starts moving at 20" MAP). This is causing problems for me on dirt strips in Alaska - I cannot move at 80% fuel from a stop at FT. They don't use any smoothing, so might have more rolling resistance?>>
Yes I have been reducing low speed thrust to increase the take off run to make it more realistic.
Surface friction is a bgl variable. The aliased texture has no relevance but if the relevant bgl author knew what he was doing and coded dirt then it will offer more friction than tarmac or concrete. Each surface type has a fixed value whereas concrete could be smooth or rough in real life and dirt can be rock hard or mud. The take off should be longer from a dirt strip but obviously you should be able to move on dirt.
Is the relevant runway bgl MS default, freeware. or payware as I would like to test using the same bgl.
Ability to overcome friction depends on thrust (f=ma), not power so this is not a MAP issue but I may need to do more work on the airscrew thrust curves. I am very surprised that it won't move at all using 2700 rpm and wonder if the bgl actually has the code for gravel rather than dirt.
At 44K in a C-46A you will need a tarmac runway of about 4400 feet at sea level in nil wind and even more at altitude. Longer from dirt and a whole lot longer from gravel, if the wheels don't just dig a hole in the gravel. A C-46A needs about as much runway at 44K as a C-54A needs at 70K. They were designed to use the same strategic runways at very different weights. A C-46A at 44K needs 2.2 times the length of runway needed by a DC-3 at max gross. The C-46A is a strategic transport aircraft not a tactical transport aircraft. The C-46A is a great fat lump of an aeroplane. If the environment was dirt or gravel and not grass or similar vegetation to bind the surface C-46s, C-54s and other WW2 strategic transports (or bombers) generally required rolls of steel matting to be laid over the unbound surface in order to operate at high weights.
The problem you are having may be realistic. It depends on what surface the bgl author coded and what invariant value MS assigned to it. I would need to test using the bgl that demonstrates the problem.
4. The neutral trim makes me haul back quite a bit. I like 20% up trim much better, and I can still get the tail up OK on TO.
If you can get the tail up soon enough that the take off run from tarmac at sea level in nil wind does not exceed about 4400 feet then using nose up trim is acceptable. The more nose up trim you use the longer the take off, but the less force needed to rotate. Make sure the trim chosen promotes acceleration to 110 KIAS below 300 feet AGL after rotation. See C-46_ref.txt.
Regards, FSAviator
Greetings Tom,
I ran a couple of tests on the surface type problem using MS default bgls. I ran the gravel test at Seldovia (PASO) and had no great difficulty getting the aircraft to move away from rest on MS default gravel although the runway is obviously too short for a C-46A.
I used Port Alsworth (TPO) for the MS default dirt strip test with the same result although the dirt strip was so narrow that the C-46 mainwheels were on the snow either side of the dirt texture. I don't know if the bgl matches the aliased textures that accurately. Is this an AFCAD issue?
So I think I conclude that the reported test involved a third party scenery bgl (or perhaps AF2***.bgl ??) that contained non compliant runway surface type friction code.
I am quite willing to test with the relevant scenery bgl and any related AF2 if they can be isolated and supplied or identified, but for the moment I conclude that the V096 FD are compatible with MS default dirt and gravel runways.
However it may be that Greg has made apparently appropriate changes to the contact points or scrape points and is using different values to those in the cfg I supplied. He needs to check this and if they differ that might be the source of the problem especially if e.g. the scrape points are in contact with the surface by mistake. Unlikely but worth checking since it is the most obvious possible source of surface friction discrepancy if all bgls are MS default.
Can you replicate the problem at PASO and TPO using my (probably Mike Stone's) contact points if Greg's are different? I assume you have not installed third party scenery or AFCADS for those airfields? If you have then use somewhere else where you are sure you are using MS default runway surface code.
Regards, FSAviator
I have now grasped that you are operating from an unknown default generic surface type of unknown friction. Without access to 'totally flat mesh' we cannot test what is encoded as its co-efficient of friction. If you are going to start publicly supporting bush flying there are new things to consider that are not in place. I will say more about that below, but in V097 I have addressed the more important issue of dirt and gravel runway friction.
I know a significant number of C-46s were based in Alaska but as far as I can tell the airfields they were able to use at high weights in nil wind were no smaller and no less suitable than the current situation at Bettles (PABT) which is probably unchanged from the C-46 era in Alaska.
If you are going to use aircraft from sloping bush terrain you need to park downhill, take off downhill, and if you ever need to take off uphill due to a significant headwind you need to hit the runway rolling with a take off clearance from the holding point, whatever the aircraft.
Airscrews are very inefficient at low advance ratios. They suffer the equivalent of very bad wheelspin when high power is applied from standstill. A C-46 can sustain about a 1 in 24 uphill gradient in flight when the advance ratio is around 80%, but it would not cope with 1:24 uphill slopes on the ground, especially from rest, especially on dirt or gravel, when the advance ratio is near zero.
I think the 'wheelspin' problems you are encountering are realistic, but I have revised various things as below. If users are going to fly from gravel and dirt it becomes even more important to get the tail up early. You will need to change the contact points to facilitate that.
IF
reference_datum_position = 0, 0, 0
empty_weight_CG_position = 0, 0, 0
THEN the V097 data should become;
[contact_points]
point.0 = 1, -39, 0.0 , -3.5, 1200, 0, 1.1, 45, 0.500, 0.500, 1.000, 10, 10, 0, 131,131 point.1 = 1, 1.25, -11.7, -8.4, 1600, 1, 1.4, 0 , 0.500, 2.500, 0.850, 10, 10, 2, 131,131 point.2 = 1, 1.25, 11.7 , -8.4, 1600, 2, 1.4, 0 , 0.500, 2.500, 0.850, 10, 10, 3, 131,131
Which should be the same as moving the mainwheels back 1.25 feet and extending the tailwheel downward by 0.2 feet (restoring static pitch) from wherever you have them now. Dynamically of course, not in the MDL.
Even so the only way to overcome your uphill slope plus static inertia problem is to significantly increase static thrust to a value that I think is probably unrealistic. Better still always park aeroplanes downhill on slopes and have the ground crew chock them.
V096 has sea level static thrust at 2 x 1800lbs. V097 attached has 2 x 2050lbs static thrust which I regard as optimistic for the R-2800-51.
During scenery design the surface slope is just pitch minus tail down angle which you should test with a nosewheel aircraft of zero static pitch for convenience. You have to test for the static case (use AFSD) else you will be measuring dynamic oleo compression.
F=ma and in an aeroplane we say T = MG and G = T/M
From rest at max FAA gross V096 gave 2 * 1800 / 44000 G acceleration = 0.082 G (static case).
Increasing static thrust to 2050 obviously gives you 0.095G (static case to overcome the inertia).
That is the situation for frictionless ice. Much of the available thrust is negated by drag (mostly from the surface friction at low velocity). If the drag is that of gravel then the residual G available to counter a slope is tiny.
The useful thrust is only T * COS(taildown angle) and the useful G is only G * COS(surface upslope).
V097 incorporating the contact point changes above and the revised static thrust produces a take off run less than 3800 feet at max gross on flat tarmac which I think is somewhat optimistic. However if the surface type is swapped to MS default gravel the TOR increases to just under 5000 feet based on the MS default friction co-efficients of the two runway surfaces when both are flat. Whether that hard coded difference is a realistic penalty for gravel just depends on a strip by strip basis. I am sure it is right for some pair somewhere!
Within MSFS in most cases any slope will be the lesser problem.
If the FD are for public release then they will be used almost entirely from flat polygon airfields. The C-46 is a strategic transport for use from big runways regardless.
Using no flap at default Bettles PABT (alt 643 feet) a flat runway consisting of 5200 feet of default gravel is just sufficient at 44K with nil wind. PABT represents the kind of gravel runway that a C-46A could actually cope with at high weights in real life. In real life it would depart downhill unless there was a significant tailwind and the crew would refuse line up and hold clearances. They would await a rolling take off clearance from the holding point and would have achieved ten knots at the point where many FS consumers will start from zero.
No one is going to be able to calculate how much runway they need versus weight, surface type, altitude and headwind vector in FS9. They just need to understand that the C-46 is a strategic asset not a tactical asset. It's not remotely a bush plane even though it operated from strategic gravel runways like the one at PABT.
Everyone will need to remember that default autogen trees are 2.5 times overscale and reduce autogen density as necessary to remove them from the flight path. Reducing the autogen texture size does not reduce the dynamic collision risk with the hard coded autogen scrape points, but it is worth substituting realistic size tree textures for bush flying anyway.
Using V097 with the contact point changes described above a departure from default PABT is scary but possible at max gross even QFU 19 into the rising ground and that is about how it should be. I believe I have default PABT BGLs (since they have the default file names and locations) but enhanced mesh for Alaska outside the flat airfield.
I understand the technique for making sloping runways, but of course the mesh is not accurate and they end up with excessive slopes. I expect most of them deliver wholly unrealistic take off distances regardless of encoded surface friction. I see no future in faking FD to match a particular mesh at a particular location or mesh in general. Users will just have to be aware that the C-46 is not by any means a bush plane and use it accordingly. What I have done in V097 is ensure that the C-46A is compatible with MS default gravel runways and will crash only when it should. If anyone decides to take off uphill they should reasonably expect to crash unless they have a significant headwind (15% Vr).
I think that the V097 FD with the contact point change above demonstrate the perils of gravel runways (sloping or otherwise) for the C-46A quite nicely, but at the expense of somewhat exaggerated performance from typical blacktop runways. The default values for friction should not be adjusted within sim1.dll as that screws up all AI aircraft FDE.
I think you may believe that 5200 feet of gravel near sea level in nil wind should be no problem in a C-46A at 44K, but in reality it should. It's a great fat pig of an aeroplane, but once you achieve 35/2300 having reduced the rpm and power to bring the advance ratio over 0.8 at > 120 KTAS the airscrews will each pump out around 2500lbs of thrust for the climb in V096 or V097 and rising ground is no problem.
This is really just a question of having the appropriate expectation concerning the barely adequate performance envelope of the C-46A even when used as a strategic transport from strategic airfields.
For your own personal use you may wish to bear in mind that unless you have a significant tailwind (15% Vref) you would normally land net uphill on sloping runways especially in temperatures below 32F.
As a separate case when landing on dirt or gravel in a low wing aeroplane you should assume that you cannot use any flap in a taildragger and only FLAP 1 in a nosewheel aircraft. They will be punctured by the gravel spat up by the wheels if further extended.
Bush planes cannot have low wings because that inhibits use of flap.
[Reference Speeds]
flaps_up_stall_speed = 78
C-46A Vref becomes 78 * 1.3 = 101 KIAS for gravel runways like PABT. If you wheel it on inside the touchdown zone it will stop from 101 well before the end, (because its a hell of a job to get it up to Vr=91 by the end using around 4000hp to help), but short strips with unconsolidated surfaces are not compatible with low wing aircraft. Sharp lumps of ice penetrate thin aluminium quite easily too.
There have been a few low wing aircraft with especially thick lower flap skins, but if you are going bush flying you should penalise yourself for using a low wing aeroplane. Bush flying is a whole new can of worms and the C-46 is not a good aeroplane for anyone to begin with because it is simply not a bush plane by any means.
Note that I did not test the C-54 (or any other FD on your web page) from gravel as I did not see it as relevant.
Regards, FSAviator
Greetings Tom,
I regard the encoded surface friction values in MSFS as almost entirely random. The more third party scenery people use the more random it becomes since the displayed textures and the types get mismatched. I assume all flight planners can read encoded type? I remain unclear whether AF2 files can also vary runway surface type and not just aliased texture?
I make the take off distance about real for level dry tarmac and if there is false data in a particular bgl then I don't regard it as my problem. Until we had this conversation I never considered it important that the static value be realistic or greater so long as the mean thrust between static and Vr was correct and the value at Vr was correct for further acceleration. Static thrust is difficult to estimate without a lot of airscrew data which never seems to be available.
The DC-4 as released has 4 x 1925lbs static versus a mass of c 73K. 4 x 1925 = 7700 / 73000 = 1.05 G static.
However the contact point geometry and oleo damping are important. They vary the net dynamic friction as well as the useful thrust vector. It occurs to me that the main oleo damping may be too soft on the C-46. I suspect it is still 'Mike Stone's' so maybe the number should be varied for copyright reasons anyway? I think the stiffer the gear the lower the MSFS net friction since the force used to create the 'oleo bounce' is subtracted from the thrust. Energy is conserved (wasted).
The thrust value at Vr has to promote acceleration to Vx < 500 VSI so it has to be 'real'. The need to keep the mean value real constrains the maximum value of static thrust, but I guess in MSFS it should be as unrealistically high as it can be without precluding a realistic mean value. I could produce curves with acceleration falling in the middle of the take off run, but that is not what happens and it would feel odd.
The take off performance of the real standard C-46 is so bad that I believe it must have poor static thrust. I have allowed the screws to go to 15 degrees but the Curtiss screws only went to 17 in real life so maybe that is the reason. It could be fitted with Hamilton screws that went all the way to 10 and I assume they had better traction from static, however the c4400 feet to clear a 10 metre screen is with the Hamilton low pitch screws.
Does V097 solve the local problem?
The problem with dirt strips is that there is usually no regular inspection or sweeping of the surface. Anywhere that the surface freezes and thaws the surface breaks up. Anywhere it gets rained on regularly (or hard) it breaks up. Either way the erosion leaves loose stones which get thrown up. Sweeping erosion debris off dirt runways gradually leaves you with a trench. I guess if it stays warm and dry erosion is not much of a problem and ultimately if a mine makes enough money it's worth damaging old aircraft anyway. Taildraggers suffer worst.
Flatten issue understood.
C-46 useful load is around 13K cf perhaps 28K for a C-54 from the same runway, but of course if they are short hauling the C-54 cannot land greater than 63.5K and its useful load falls to around 20K. In the classic era the resale price of a C-54 was about 2.5 times higher than for a C-46 with the same hours, reflecting its much greater utility even when short hauling.
Regards, FSAviator
Greetings Tom,
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