Post by volkerboehme on Aug 10, 2008 9:14:04 GMT -5
Tom and I have been studying this reported problem in depth since the first post, but not until post 12 in this thread was it clear from the information provided that the issue being reported is failure to unstick after rotation at Vr rather than inadequate acceleration and excessive distance to achieve Vr. In fact Tom and I had managed to focus on that issue before post 12, but mostly by luck.
When making prospective bug reports please be as precise as possible about the problem encountered and also report altitude, weight, and weather being used (not the details of the weather, just if user weather, or no weather, or real weather). These things matter and can save a lot of time during bug hunting. Indeed if the report has inadequate detail it is very likely that I will not have time to work through all the possibilities, because most such prospective bug reports turn out to relate to pilot error.
Let me provide an insight to the world of the Flight Dynamics developer. As with the recent flight dynamics revisions to the CV34 and CV24 I am willing to go bug hunting if enough information is available and I am willing to patch the FD if a bug is found. In this case there is a bug in the DC7C rotation code and it will be fixed shortly. There is however no other bug discernable that might explain difficulty to climb after unstick so I will go through the techniques and phases for DC7C climb, one by one, in detail later in this post.
There are a dozen variables in any set of FD that can be enhanced at random to enhance any aspect of aircraft performance, but my goal is to replicate aircraft performance, not to enhance it, so that users can understand what was good, and what was nasty, about a particular propliner.
The DC7C has a serious rotation problem in real life. At high weights it is very difficult to rotate to unstick at Vr without a tail scrape. Note the tail scrape protector depicted in the MDL. My FD for the DC7C are intended to portray that unpleasant characteristic, not just when used with the on screen handling notes, but also when used by those who have access to manuals and certification documents. I try to incorporate as many of the real problems that characterised operation of the real aircraft as I can.
Page 7 of the certification schedule mandates use of no more than FLAP 1 for take off at weights exceeding 141,750lbs. This is because the DC7C cannot accelerate to Vx after departing with FLAP 2 above that weight at max gross before the TOGA limit expires.
Given the nature of the routes flown by DC7Cs in the classic era I concluded that most DC7C departures exceeded that weight and DC7CF departures more so. Of course any airline could load full fuel and offload seven passengers or 3000lbs of cargo and use FLAP 2. Was FLAP 2 the norm? Well that depends on the average route (stage length) for a given airline, but I have always been reluctant to load less fuel by default than was available in real life since nothing annoys users of FD more than running out of fuel just before a destination they could have reached in real life.
So my decision to make max gross the default weight was driven by my wish to allow users to have max fuel by default and a wish to portray the real payload that could be lifted, which was 44 pax with FLAP 1 rather than just 37 pax with FLAP 2. We know the configuration mandated for a max gross departure. It is not a guess.
So having decided to make max gross with full tanks the default in the aircraft.cfg the handling notes must match. My code was then intended to make this very difficult, but actually makes it impossible at Vr. Unstick is correctly, but excessively delayed in the FS9 FD. It is always my intention to portray how marginal these aircraft were in performance, and what it was really like to cope with that small margin for error.
No public documentation provides the CL data for intermediate stages of flap. I have to estimate it. The lift encoded for FLAP 1 is currently too low. That is the source of the excessively delayed unstick. I don't believe there is any other problem not induced by pilot error.
During development back in 2003 I did consider misrepresenting the maximum weight as the FLAP 2 limit and making that the default weight, but using FLAP 2 impedes acceleration so much between Vr and Vx that users will find a FLAP 2 departure at 141,750 more difficult to keep under control after unstick than a FLAP 1 departure at 143,000. Feel free to try this out. Both techniques are real, but require different departure weights.
Using FLAP 2 reduces both available VSI and available climb gradient compared to FLAP 1. The lift to drag ratio is worse not better. The goal of the take off phase is acceleration to the Vx value and airframe configuration associated with stage 1 climb power, before the TOGA time limit expires. Best climb gradient is *not* in FLAP 2, but FLAP 2 sure helped what was obviously a difficult rotation without tail strike in real life. After using FLAP 2 to unstick with lower AoA rotation the real crew had squandered rate of climb and climb gradient. We know exactly how much was squandered. They were mandated to dump 7 pax or 3000 lbs of cargo in the DC7CF to make up for the post unstick performance squandered to make rotation easier.
The 'problem' in the FD is entirely real. I just made it too difficult and the delay to unstick too great.
After a crew departed with FLAP 2 to aid the rotation they had to climb at even lower VSI to accelerate to the point where they could transition to FLAP 1 as soon as safe to do so. Perhaps at 137 KIAS. The time after throttle up at which Vx for climb 1 configuration is achieved does not vary. 7 pax or 300lbs of cargo must be dumped so that it does not.
Some of the FD available from Calclassic.com are for aircraft that could not rotate without FLAP 2 at max gross. With FLAP 1 they were bound to suffer a tail strike. FLAP 2 was mandated and max gross was restricted by the FAA accordingly. The handling notes will reflect that nasty reality. However the DC7C could (just) rotate safely at Vr = 122 at max gross with FLAP 1, but airlines could depart below gross with FLAP 2 to make rotation without tail strike easier and sooner. Easier rotation with sub optimal FLAP for subsequent climb increased workload and the need for skill after unstick and squandered payload.
There is always a negative consequence for using FLAP 2 to aid rotation.
The goal remains to make the DC7C FD nasty enough to make acceleration to Vx impossible with FLAP 2 at max gross, but with enhanced possibility of unsticking soon after Vr with perfectly judged rotation to + 8 pitch with FLAP 1 at max gross. Revised FD that deliver both realities will be uploaded as soon as Tom and I have agreed on the best way to alter the FD to achieve that purpose. There are alternative solutions to consider.
So there is currently a rotation to unstick bug in the FS9 DC7C flight dynamics, but even when it has been carefully patched this will remain an aircraft that all bar experienced FS9 users will find difficult to master. These big four engine prop liners are right at the top of the flight simulation learning curve. Since I expect that many users will still struggle (at least at high weights or in adverse weather) after the fix I will now attempt to provide what I hope are the most useful tips for learning to master the big four prop airliners.
In FS9 I always advise users to apply auto mixture unless they have real world experience of leaning aero engines. The real DC7C had auto mixture. The exact take off distance required depends on weight and weather and how the cowl flaps are set in relation to the 'MID' range specified in the handling notes. This will depend on whether outside air is above or below 59F/15C. The more you open the cowl flaps to drag air across the engines for cooling the slower the acceleration achieved and the longer the take off roll to Vr.
Real world DC7C target performance at max gross / nil wind / ISA / sea level calls for the aircraft to be 10 metres above the runway 6400 feet after brake release. Few airline pilots would actually have achieved this at every attempt. The updated FS9 FD will deliver that possibility to within the usual error % present in any MSFS flight dynamics which must also deliver many other cases. At 25C and at 2000 feet QNH that distance becomes 6900 feet. Any FS9 flight dynamics are likely to be a little 'long' for one case and a little 'short' for another.
Some users may have unrealistic expectations that the take off distance for a DC7C should be less.
At max gross with only FLAP 1 deployed at around 125 KIAS a DC7C needs a very substantial angle of attack to fly at all. The rotation (at 122 KIAS at max gross) must be very positive, but not excessive. Once the wing's angle of attack (AoA) is enough for flight the aircraft will unstick and climb away of its own accord, but not if the aircraft is rotated to a tail scrape at 9 degrees pitch, or to less than 8 degrees. Unless rotation is degree perfect at +8 the aircraft will unstick late. This is realistic, but the delay in the current FD is excessive. Rotating to the correct angle requires practice, practice, practice. We must learn where the horizon intersects the VC at + 8 pitch so that we have the appropriate pitch reference. When departing in fog the artificial horizon must be used instead.
In DC7C terms 122 KIAS is not a lot of airflow. The elevators are not fully effective and a large aft yoke movement is necessary to achieve a large angle of elevator deflection to achieve + 8 pitch quickly. We don't need to be nearly as aggressive when flaring for the landing from a similar IAS because we have full flap deployed and developing much more lift.
Once we unstick with very positive rotation the problem is then not lack of climb performance but preventing excessive climb rates. Rate of climb must quickly be restrained to almost nothing until the drag reaches 160 KIAS.
****************************
Take Off:
APPLY BRAKES
MIXTURE - AUTO in realism screen
COWL FLAPS - MID
TRIM 30% full range NOSE UP
FLAP - STAGE 1
CALL for TOGA POWER (3400hp)
PROPS FULLY FINE
Slowly apply FULL THROTTLE
BRAKES - OFF
ROTATE at 122 KIAS (143,000lbs)
Establish positive rate of climb
GEAR UP
ACCELERATE 160 KIAS @ <= 500 VSI
CLIMB 300 feet QFE (agl)
CALL for METO Power
**********************************
Note that we should hold the aircraft below 300 AGL until 160 KIAS is achieved. Climb rate should be very low. This post unstick phase is all about using the only briefly available TOGA power to accelerate the aircraft to the 'right side' of the drag curve as fast as possible. It is not about climbing.
Once we have achieved 160 KIAS about 300 feet above the runway elevation we stop thrashing the engines to death and reduce to METO power.
**********************************
METO Power: (Climb stage 1)
COWL FLAPS - MID
51 inches MAP
2650 RPM
160 KIAS
Climb 2000 feet QFE (agl)
FLAP - UP
ACCELERATE 190 KIAS @ 500 VSI
CALL for climb power
***********************************
We have just shifted up from first gear to second. All propliners have manual shift gear boxes. One gear shift lever for each airscrew. In an aeroplane we call the gear shift levers rpm levers. In a car with manual shift we need to select first gear for pulling away from the kerb. The engine must be revved hard even at very low speed to get things rolling.
Once we are rolling and have developed enough speed we must select second gear. Staying in first gear would be wrong and shifting straight up to third would be wrong. In first the rpm would be too high and in third too low. When we are about to climb a hill in a car we must make the gear ratio (rpm) match both the steepness of the hill and the speed we approach the bottom of the hill. Aeroplanes are no different. We have to shift up (reduce rpm) manually in a piston propliner, as we accelerate, whether or not we are going up hill.
In the DC7C first gear = 2900 rpm is great for pulling away from a standing start and getting things rolling, but now we have reached 160 KIAS and we intend to steepen the gradient of the climb to 500 VSI. We must shift up to second gear (2650rpm). We cannot accelerate a car with a manual shift gear box to economical cruising speed in first gear and it doesn't work in aeroplanes either.
The principle reason that users of the DC7C fail to climb the hill after take off without stalling is that they try to climb a steep hill at 500 VSI before building up speed to 160 KIAS and also try to do it in the wrong gear. We have to both build up speed and select the correct gear (rpm) before tackling a hill climb. In an aeroplane we choose when and at what speed to tackle a climb. Much of the Propliner Tutorial is about how and when to even try.
Once the DC7C is in the correct gear ratio (2650rpm when throttle = 51 inches of MAP) it will accelerate to 190 KIAS even whilst climbing a hill. If we try to tackle a hill that steep with the speed below 160 at the bottom of the hill, or in the wrong gear for that gradient at that entry speed, it just won't make it up the hill.
We are now accelerating up hill in second gear (2650rpm at 51 inches). When we get the speed up to 190 second gear is too low even though we have no intention of changing the climb rate from 500 VSI. We shift up to third by selecting 43 inches and 2500rpm.
**********************************
Climb Power: (Climb stage 2)
MIXTURE - AUTO
COWL FLAPS - MID
43 inches MAP
2500 RPM
500 VSI
SPEED WILL DECAY - MINIMUM 172 KIAS
IF UNABLE to maintain =>172 KIAS
REQUEST LEVEL OFF & STEP CLIMB from ATC
ACCELERATE > 190 KIAS
WHEN CLEARED BY ATC CLIMB 500 VSI
IN 2000 foot steps - Repeat as necessary
Plan 950 PPH
***********************************
Each time our increased speed allows us to shift up we reduce the load on the engine (reduce its rpm) and extend its useful life (time between overhauls). Once we are at a really decent speed we can get into gears that allow as to continue acceleration (up hill), with less and less power, burning less and less fuel, so we choose to do just that. High gears (low rpm) are more efficient, but they are incompatible with climbing hills at low speed. We can only shift up as speed increases, but we must shift up (reduce rpm) at the right time and make sure we choose the correct climb rate for the current speed and gear selected.
The handling notes explain how steep a climb we can handle, what speed we have to be when we arrive at the bottom, what power we need to supply with the throttles, and what gear we need to select using the rpm levers.
After the take off phase is over international law requires us to climb at not less than 500 VSI. If our virtual airline or military employer wants us to climb faster they supply handling notes that explain the throttle and rpm values required for the higher target VSI or they specify constant IAS with varying VSI. A DC7C normally climbs at the legal minimum rate of 500 VSI from the end of obstacle avoidance / noise abatement to the cruise phase. More about those phases later.
Of course when we are ready to cruise (reach operational ceiling) we shift up again from third to fourth.
***********************************
Econ Cruise at max weight (about 1700hp):
COWL FLAPS - CLOSED
2300 RPM
735 PPH
****************************
In a DC7C we don't move the throttles we just shift up (reduce to 2300 rpm). When we are running light we still don't move the throttles but we take the opportunity to shift up to fifth (overdrive = 2100rpm).
****************************
Econ Cruise at light weight (about 1600hp):
COWL FLAPS - CLOSED
2100 RPM
680 PPH
****************************
Just don't try climbing steep hills from a low speed at the bottom in overdrive. When we hit the built up area and the traffic near our destination we need to slow down and shift down again (to higher rpm).
****************************
Approach and Landing:
MIXTURE - MANUAL RICH
COWL FLAPS - MID
2300 RPM
***************************
If we need to go around we must select full throttle and first gear because we will be about to climb a steep hill from very low speed,
***************************
Baulked Landing:
CALL for EMERGENCY POWER
PROPS FULL FINE
FULL THROTTLE
***************************
Maybe this is all more apparent to Europeans who nearly always drive cars with manual shift, but I suspect that failure to climb the DC7C without much difficulty is the result of not fully understanding the above even though it was always promulgated in the handling notes.
Although not strictly relevant at this point note that the flight planning fuel flow values in the DC7C handling notes are per engine which is anomalous compared to my other handling notes which promulgate the total for all engines.
Finally Part 4 of the Propliner Tutorial explains how to make the departure phase more realistic and uses the Sebago departure from KIZG as the worked example. That worked example in the tutorial talks about the DC7B rather than the DC7C so I have abridged it here with specific relevance to the DC7C.
Climb Stage 1 is for obstacle clearance. The obstacle can be a mountain, a mast, a gunnery range, another airfield's holding pattern, a nature reserve, or just noise abatement at a sensitive site such as a hospital. The departure procedures for the runway will not usually tell us why we must proceed to a given fix after take off and cross that fix at a minimum altitude, but we must.
When we receive, (issue to ourselves), the realistic ATC clearance, 'cross Sebago 3500 or above' we must bear in mind that Sebago is a fixed distance from KIZG. Climb rate is unimportant. We must instead target a good climb gradient. We achieve a better climb gradient (per mile) by restricting IAS even if we climb at the same rate (per minute).
Remember this is just an example. A DC7C would need to be very light and have a favourable headwind to depart KIZG at all.
The DC7C handling notes cannot cover the details of all real departure procedures everywhere. We have to adapt them to each specific case during flight planning. In this case we will not terminate stage 1 climb until we have complied with the realistic local clearance 'cross Sebago (at an ALTITUDE of) 3500 QNH or above'. We will substitute this specific local restriction for the generic handling note noise abatement restriction which is climb 2000 feet QFE (agl).
**********************************
METO Power: (Climb stage 1)
COWL FLAPS - MID
51 inches MAP
2650 RPM
160 KIAS
Climb 2000 feet QFE (agl) <<<<<<<<<<
FLAP - UP
ACCELERATE 190 KIAS @ 500 VSI
CALL for climb power
***********************************
Departing KIZG in a DC7C we will climb in METO power towards Sebago with FLAP 1 extended at 160 KIAS until passing 3500 QNH. The generic requirements of the handling notes must be translated into the specific requirements of the departure phase from each particular runway. We will not begin acceleration to 190 KIAS until we have achieved the cross above restriction of the departure clearance and we will not exit METO power until we have achieved our final stage 1 climb operating target of 190 KIAS, which we only attempt after clearing all obstacles.
Or to put it the other way round. We must retain FLAP 1, and climb at only 160 KIAS (Vx), using exactly METO power = 51/2650, achieving much more than 500 VSI, until we are clear of all obstacles, but once we are clear of all obstacles we will retract the flap and accelerate to 190 KIAS (Vy) at only 500 VSI. Only when we have achieved 190 KIAS at 500 VSI can we proceed to climb stage 2.
During each departure we decide when we are clear of all obstacles, ideally using the real airfield departure procedure downloaded from the web site of the real federal authority, else we must decide what altitude is adequate by other means and on passing the altitude we decided upon in our flight plan begin acceleration from Vx (best climb gradient) to Vy (normal climb).
If that is not making much sense or you are thinking of obstacles as things the size of trees and buildings near the runway try departing Los Angeles eastbound and turn direct for New York in good visibility. Those mountains are the obstacles to be avoided during this departure. Handling notes are not a check list. They explain the targets to be achieved and the captaincy decisions to be made. If we do not download the real procedures with the real departure route and the real cross above restrictions we must determine by visual reference to the surface when it is safe to exit stage 1 climb airframe configuration, IAS, MAP and rpm criteria and begin stage 2 climb. Just like cruising level the correct solution varies day by day, even on the same route, towards the same obstacles, at the same weight, because it varies with the weather, especially headwind vector.
The handling notes for the DC7C have always reflected the fact that it has a poor post take off climb gradient at Vy = 190 KIAS and that unlike most propliners it has to target a lower IAS = Vx = 160 in a higher lift configuration (FLAP 1) for an extended period after take off. What the DC7C must do as a norm, any other propliner may need to do during some particular departures. Part 4 of the Propliner Tutorial goes on to provide worked examples for the Convair 340.
The phase by phase on screen handling notes tell us the targets which we must achieve one at a time, in exactly the sequence specified, before we can move to the next phase of the flight. Doing things in a different sequence is not an option. Moving on without achieving all the targets is not an option. The exception is transition from climb to cruise.
In general when we cannot sustain 500 VSI at constant Vy using the correct throttle and rpm setting for the correct and current climb phase we have reached operational ceiling and must transition to cruise. For aircraft like the DC6B or DC7C which climb at 500 (constant) VSI after obstacle avoidance / noise abatement the climb phase exit criterion is decay of IAS at constant VSI instead. As I have explained in another thread that would normally be triggered by decay through 160 KIAS in a DC6B, but as the handling notes repeated above explain by decay through 172 KIAS in a DC7C. We may also need to exit climb for cruise if max specified engine temperatures are reached during climb.
Big complex aeroplanes are designed to be flown by the numbers. The input numbers such as Trim %, FLAP stage, MAP and rpm and the output targets such as IAS and VSI. Hit all the numbers in the correct sequence and they handle nicely. Miss them, or even achieve them in the wrong order, and they may handle like pigs.
FSAviator 12/06
When making prospective bug reports please be as precise as possible about the problem encountered and also report altitude, weight, and weather being used (not the details of the weather, just if user weather, or no weather, or real weather). These things matter and can save a lot of time during bug hunting. Indeed if the report has inadequate detail it is very likely that I will not have time to work through all the possibilities, because most such prospective bug reports turn out to relate to pilot error.
Let me provide an insight to the world of the Flight Dynamics developer. As with the recent flight dynamics revisions to the CV34 and CV24 I am willing to go bug hunting if enough information is available and I am willing to patch the FD if a bug is found. In this case there is a bug in the DC7C rotation code and it will be fixed shortly. There is however no other bug discernable that might explain difficulty to climb after unstick so I will go through the techniques and phases for DC7C climb, one by one, in detail later in this post.
There are a dozen variables in any set of FD that can be enhanced at random to enhance any aspect of aircraft performance, but my goal is to replicate aircraft performance, not to enhance it, so that users can understand what was good, and what was nasty, about a particular propliner.
The DC7C has a serious rotation problem in real life. At high weights it is very difficult to rotate to unstick at Vr without a tail scrape. Note the tail scrape protector depicted in the MDL. My FD for the DC7C are intended to portray that unpleasant characteristic, not just when used with the on screen handling notes, but also when used by those who have access to manuals and certification documents. I try to incorporate as many of the real problems that characterised operation of the real aircraft as I can.
Page 7 of the certification schedule mandates use of no more than FLAP 1 for take off at weights exceeding 141,750lbs. This is because the DC7C cannot accelerate to Vx after departing with FLAP 2 above that weight at max gross before the TOGA limit expires.
Given the nature of the routes flown by DC7Cs in the classic era I concluded that most DC7C departures exceeded that weight and DC7CF departures more so. Of course any airline could load full fuel and offload seven passengers or 3000lbs of cargo and use FLAP 2. Was FLAP 2 the norm? Well that depends on the average route (stage length) for a given airline, but I have always been reluctant to load less fuel by default than was available in real life since nothing annoys users of FD more than running out of fuel just before a destination they could have reached in real life.
So my decision to make max gross the default weight was driven by my wish to allow users to have max fuel by default and a wish to portray the real payload that could be lifted, which was 44 pax with FLAP 1 rather than just 37 pax with FLAP 2. We know the configuration mandated for a max gross departure. It is not a guess.
So having decided to make max gross with full tanks the default in the aircraft.cfg the handling notes must match. My code was then intended to make this very difficult, but actually makes it impossible at Vr. Unstick is correctly, but excessively delayed in the FS9 FD. It is always my intention to portray how marginal these aircraft were in performance, and what it was really like to cope with that small margin for error.
No public documentation provides the CL data for intermediate stages of flap. I have to estimate it. The lift encoded for FLAP 1 is currently too low. That is the source of the excessively delayed unstick. I don't believe there is any other problem not induced by pilot error.
During development back in 2003 I did consider misrepresenting the maximum weight as the FLAP 2 limit and making that the default weight, but using FLAP 2 impedes acceleration so much between Vr and Vx that users will find a FLAP 2 departure at 141,750 more difficult to keep under control after unstick than a FLAP 1 departure at 143,000. Feel free to try this out. Both techniques are real, but require different departure weights.
Using FLAP 2 reduces both available VSI and available climb gradient compared to FLAP 1. The lift to drag ratio is worse not better. The goal of the take off phase is acceleration to the Vx value and airframe configuration associated with stage 1 climb power, before the TOGA time limit expires. Best climb gradient is *not* in FLAP 2, but FLAP 2 sure helped what was obviously a difficult rotation without tail strike in real life. After using FLAP 2 to unstick with lower AoA rotation the real crew had squandered rate of climb and climb gradient. We know exactly how much was squandered. They were mandated to dump 7 pax or 3000 lbs of cargo in the DC7CF to make up for the post unstick performance squandered to make rotation easier.
The 'problem' in the FD is entirely real. I just made it too difficult and the delay to unstick too great.
After a crew departed with FLAP 2 to aid the rotation they had to climb at even lower VSI to accelerate to the point where they could transition to FLAP 1 as soon as safe to do so. Perhaps at 137 KIAS. The time after throttle up at which Vx for climb 1 configuration is achieved does not vary. 7 pax or 300lbs of cargo must be dumped so that it does not.
Some of the FD available from Calclassic.com are for aircraft that could not rotate without FLAP 2 at max gross. With FLAP 1 they were bound to suffer a tail strike. FLAP 2 was mandated and max gross was restricted by the FAA accordingly. The handling notes will reflect that nasty reality. However the DC7C could (just) rotate safely at Vr = 122 at max gross with FLAP 1, but airlines could depart below gross with FLAP 2 to make rotation without tail strike easier and sooner. Easier rotation with sub optimal FLAP for subsequent climb increased workload and the need for skill after unstick and squandered payload.
There is always a negative consequence for using FLAP 2 to aid rotation.
The goal remains to make the DC7C FD nasty enough to make acceleration to Vx impossible with FLAP 2 at max gross, but with enhanced possibility of unsticking soon after Vr with perfectly judged rotation to + 8 pitch with FLAP 1 at max gross. Revised FD that deliver both realities will be uploaded as soon as Tom and I have agreed on the best way to alter the FD to achieve that purpose. There are alternative solutions to consider.
So there is currently a rotation to unstick bug in the FS9 DC7C flight dynamics, but even when it has been carefully patched this will remain an aircraft that all bar experienced FS9 users will find difficult to master. These big four engine prop liners are right at the top of the flight simulation learning curve. Since I expect that many users will still struggle (at least at high weights or in adverse weather) after the fix I will now attempt to provide what I hope are the most useful tips for learning to master the big four prop airliners.
In FS9 I always advise users to apply auto mixture unless they have real world experience of leaning aero engines. The real DC7C had auto mixture. The exact take off distance required depends on weight and weather and how the cowl flaps are set in relation to the 'MID' range specified in the handling notes. This will depend on whether outside air is above or below 59F/15C. The more you open the cowl flaps to drag air across the engines for cooling the slower the acceleration achieved and the longer the take off roll to Vr.
Real world DC7C target performance at max gross / nil wind / ISA / sea level calls for the aircraft to be 10 metres above the runway 6400 feet after brake release. Few airline pilots would actually have achieved this at every attempt. The updated FS9 FD will deliver that possibility to within the usual error % present in any MSFS flight dynamics which must also deliver many other cases. At 25C and at 2000 feet QNH that distance becomes 6900 feet. Any FS9 flight dynamics are likely to be a little 'long' for one case and a little 'short' for another.
Some users may have unrealistic expectations that the take off distance for a DC7C should be less.
At max gross with only FLAP 1 deployed at around 125 KIAS a DC7C needs a very substantial angle of attack to fly at all. The rotation (at 122 KIAS at max gross) must be very positive, but not excessive. Once the wing's angle of attack (AoA) is enough for flight the aircraft will unstick and climb away of its own accord, but not if the aircraft is rotated to a tail scrape at 9 degrees pitch, or to less than 8 degrees. Unless rotation is degree perfect at +8 the aircraft will unstick late. This is realistic, but the delay in the current FD is excessive. Rotating to the correct angle requires practice, practice, practice. We must learn where the horizon intersects the VC at + 8 pitch so that we have the appropriate pitch reference. When departing in fog the artificial horizon must be used instead.
In DC7C terms 122 KIAS is not a lot of airflow. The elevators are not fully effective and a large aft yoke movement is necessary to achieve a large angle of elevator deflection to achieve + 8 pitch quickly. We don't need to be nearly as aggressive when flaring for the landing from a similar IAS because we have full flap deployed and developing much more lift.
Once we unstick with very positive rotation the problem is then not lack of climb performance but preventing excessive climb rates. Rate of climb must quickly be restrained to almost nothing until the drag reaches 160 KIAS.
****************************
Take Off:
APPLY BRAKES
MIXTURE - AUTO in realism screen
COWL FLAPS - MID
TRIM 30% full range NOSE UP
FLAP - STAGE 1
CALL for TOGA POWER (3400hp)
PROPS FULLY FINE
Slowly apply FULL THROTTLE
BRAKES - OFF
ROTATE at 122 KIAS (143,000lbs)
Establish positive rate of climb
GEAR UP
ACCELERATE 160 KIAS @ <= 500 VSI
CLIMB 300 feet QFE (agl)
CALL for METO Power
**********************************
Note that we should hold the aircraft below 300 AGL until 160 KIAS is achieved. Climb rate should be very low. This post unstick phase is all about using the only briefly available TOGA power to accelerate the aircraft to the 'right side' of the drag curve as fast as possible. It is not about climbing.
Once we have achieved 160 KIAS about 300 feet above the runway elevation we stop thrashing the engines to death and reduce to METO power.
**********************************
METO Power: (Climb stage 1)
COWL FLAPS - MID
51 inches MAP
2650 RPM
160 KIAS
Climb 2000 feet QFE (agl)
FLAP - UP
ACCELERATE 190 KIAS @ 500 VSI
CALL for climb power
***********************************
We have just shifted up from first gear to second. All propliners have manual shift gear boxes. One gear shift lever for each airscrew. In an aeroplane we call the gear shift levers rpm levers. In a car with manual shift we need to select first gear for pulling away from the kerb. The engine must be revved hard even at very low speed to get things rolling.
Once we are rolling and have developed enough speed we must select second gear. Staying in first gear would be wrong and shifting straight up to third would be wrong. In first the rpm would be too high and in third too low. When we are about to climb a hill in a car we must make the gear ratio (rpm) match both the steepness of the hill and the speed we approach the bottom of the hill. Aeroplanes are no different. We have to shift up (reduce rpm) manually in a piston propliner, as we accelerate, whether or not we are going up hill.
In the DC7C first gear = 2900 rpm is great for pulling away from a standing start and getting things rolling, but now we have reached 160 KIAS and we intend to steepen the gradient of the climb to 500 VSI. We must shift up to second gear (2650rpm). We cannot accelerate a car with a manual shift gear box to economical cruising speed in first gear and it doesn't work in aeroplanes either.
The principle reason that users of the DC7C fail to climb the hill after take off without stalling is that they try to climb a steep hill at 500 VSI before building up speed to 160 KIAS and also try to do it in the wrong gear. We have to both build up speed and select the correct gear (rpm) before tackling a hill climb. In an aeroplane we choose when and at what speed to tackle a climb. Much of the Propliner Tutorial is about how and when to even try.
Once the DC7C is in the correct gear ratio (2650rpm when throttle = 51 inches of MAP) it will accelerate to 190 KIAS even whilst climbing a hill. If we try to tackle a hill that steep with the speed below 160 at the bottom of the hill, or in the wrong gear for that gradient at that entry speed, it just won't make it up the hill.
We are now accelerating up hill in second gear (2650rpm at 51 inches). When we get the speed up to 190 second gear is too low even though we have no intention of changing the climb rate from 500 VSI. We shift up to third by selecting 43 inches and 2500rpm.
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Climb Power: (Climb stage 2)
MIXTURE - AUTO
COWL FLAPS - MID
43 inches MAP
2500 RPM
500 VSI
SPEED WILL DECAY - MINIMUM 172 KIAS
IF UNABLE to maintain =>172 KIAS
REQUEST LEVEL OFF & STEP CLIMB from ATC
ACCELERATE > 190 KIAS
WHEN CLEARED BY ATC CLIMB 500 VSI
IN 2000 foot steps - Repeat as necessary
Plan 950 PPH
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Each time our increased speed allows us to shift up we reduce the load on the engine (reduce its rpm) and extend its useful life (time between overhauls). Once we are at a really decent speed we can get into gears that allow as to continue acceleration (up hill), with less and less power, burning less and less fuel, so we choose to do just that. High gears (low rpm) are more efficient, but they are incompatible with climbing hills at low speed. We can only shift up as speed increases, but we must shift up (reduce rpm) at the right time and make sure we choose the correct climb rate for the current speed and gear selected.
The handling notes explain how steep a climb we can handle, what speed we have to be when we arrive at the bottom, what power we need to supply with the throttles, and what gear we need to select using the rpm levers.
After the take off phase is over international law requires us to climb at not less than 500 VSI. If our virtual airline or military employer wants us to climb faster they supply handling notes that explain the throttle and rpm values required for the higher target VSI or they specify constant IAS with varying VSI. A DC7C normally climbs at the legal minimum rate of 500 VSI from the end of obstacle avoidance / noise abatement to the cruise phase. More about those phases later.
Of course when we are ready to cruise (reach operational ceiling) we shift up again from third to fourth.
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Econ Cruise at max weight (about 1700hp):
COWL FLAPS - CLOSED
2300 RPM
735 PPH
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In a DC7C we don't move the throttles we just shift up (reduce to 2300 rpm). When we are running light we still don't move the throttles but we take the opportunity to shift up to fifth (overdrive = 2100rpm).
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Econ Cruise at light weight (about 1600hp):
COWL FLAPS - CLOSED
2100 RPM
680 PPH
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Just don't try climbing steep hills from a low speed at the bottom in overdrive. When we hit the built up area and the traffic near our destination we need to slow down and shift down again (to higher rpm).
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Approach and Landing:
MIXTURE - MANUAL RICH
COWL FLAPS - MID
2300 RPM
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If we need to go around we must select full throttle and first gear because we will be about to climb a steep hill from very low speed,
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Baulked Landing:
CALL for EMERGENCY POWER
PROPS FULL FINE
FULL THROTTLE
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Maybe this is all more apparent to Europeans who nearly always drive cars with manual shift, but I suspect that failure to climb the DC7C without much difficulty is the result of not fully understanding the above even though it was always promulgated in the handling notes.
Although not strictly relevant at this point note that the flight planning fuel flow values in the DC7C handling notes are per engine which is anomalous compared to my other handling notes which promulgate the total for all engines.
Finally Part 4 of the Propliner Tutorial explains how to make the departure phase more realistic and uses the Sebago departure from KIZG as the worked example. That worked example in the tutorial talks about the DC7B rather than the DC7C so I have abridged it here with specific relevance to the DC7C.
Climb Stage 1 is for obstacle clearance. The obstacle can be a mountain, a mast, a gunnery range, another airfield's holding pattern, a nature reserve, or just noise abatement at a sensitive site such as a hospital. The departure procedures for the runway will not usually tell us why we must proceed to a given fix after take off and cross that fix at a minimum altitude, but we must.
When we receive, (issue to ourselves), the realistic ATC clearance, 'cross Sebago 3500 or above' we must bear in mind that Sebago is a fixed distance from KIZG. Climb rate is unimportant. We must instead target a good climb gradient. We achieve a better climb gradient (per mile) by restricting IAS even if we climb at the same rate (per minute).
Remember this is just an example. A DC7C would need to be very light and have a favourable headwind to depart KIZG at all.
The DC7C handling notes cannot cover the details of all real departure procedures everywhere. We have to adapt them to each specific case during flight planning. In this case we will not terminate stage 1 climb until we have complied with the realistic local clearance 'cross Sebago (at an ALTITUDE of) 3500 QNH or above'. We will substitute this specific local restriction for the generic handling note noise abatement restriction which is climb 2000 feet QFE (agl).
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METO Power: (Climb stage 1)
COWL FLAPS - MID
51 inches MAP
2650 RPM
160 KIAS
Climb 2000 feet QFE (agl) <<<<<<<<<<
FLAP - UP
ACCELERATE 190 KIAS @ 500 VSI
CALL for climb power
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Departing KIZG in a DC7C we will climb in METO power towards Sebago with FLAP 1 extended at 160 KIAS until passing 3500 QNH. The generic requirements of the handling notes must be translated into the specific requirements of the departure phase from each particular runway. We will not begin acceleration to 190 KIAS until we have achieved the cross above restriction of the departure clearance and we will not exit METO power until we have achieved our final stage 1 climb operating target of 190 KIAS, which we only attempt after clearing all obstacles.
Or to put it the other way round. We must retain FLAP 1, and climb at only 160 KIAS (Vx), using exactly METO power = 51/2650, achieving much more than 500 VSI, until we are clear of all obstacles, but once we are clear of all obstacles we will retract the flap and accelerate to 190 KIAS (Vy) at only 500 VSI. Only when we have achieved 190 KIAS at 500 VSI can we proceed to climb stage 2.
During each departure we decide when we are clear of all obstacles, ideally using the real airfield departure procedure downloaded from the web site of the real federal authority, else we must decide what altitude is adequate by other means and on passing the altitude we decided upon in our flight plan begin acceleration from Vx (best climb gradient) to Vy (normal climb).
If that is not making much sense or you are thinking of obstacles as things the size of trees and buildings near the runway try departing Los Angeles eastbound and turn direct for New York in good visibility. Those mountains are the obstacles to be avoided during this departure. Handling notes are not a check list. They explain the targets to be achieved and the captaincy decisions to be made. If we do not download the real procedures with the real departure route and the real cross above restrictions we must determine by visual reference to the surface when it is safe to exit stage 1 climb airframe configuration, IAS, MAP and rpm criteria and begin stage 2 climb. Just like cruising level the correct solution varies day by day, even on the same route, towards the same obstacles, at the same weight, because it varies with the weather, especially headwind vector.
The handling notes for the DC7C have always reflected the fact that it has a poor post take off climb gradient at Vy = 190 KIAS and that unlike most propliners it has to target a lower IAS = Vx = 160 in a higher lift configuration (FLAP 1) for an extended period after take off. What the DC7C must do as a norm, any other propliner may need to do during some particular departures. Part 4 of the Propliner Tutorial goes on to provide worked examples for the Convair 340.
The phase by phase on screen handling notes tell us the targets which we must achieve one at a time, in exactly the sequence specified, before we can move to the next phase of the flight. Doing things in a different sequence is not an option. Moving on without achieving all the targets is not an option. The exception is transition from climb to cruise.
In general when we cannot sustain 500 VSI at constant Vy using the correct throttle and rpm setting for the correct and current climb phase we have reached operational ceiling and must transition to cruise. For aircraft like the DC6B or DC7C which climb at 500 (constant) VSI after obstacle avoidance / noise abatement the climb phase exit criterion is decay of IAS at constant VSI instead. As I have explained in another thread that would normally be triggered by decay through 160 KIAS in a DC6B, but as the handling notes repeated above explain by decay through 172 KIAS in a DC7C. We may also need to exit climb for cruise if max specified engine temperatures are reached during climb.
Big complex aeroplanes are designed to be flown by the numbers. The input numbers such as Trim %, FLAP stage, MAP and rpm and the output targets such as IAS and VSI. Hit all the numbers in the correct sequence and they handle nicely. Miss them, or even achieve them in the wrong order, and they may handle like pigs.
FSAviator 12/06