Controllable Props

[Tom/CalClassic]

Hi,

While not directly related to any propliners hosted here (except the M-130 and B-247, AFAIK), I have been working on a panel gauge that simulates a controllable pitch prop. This is a system where the prop lever directly controls prop pitch, not RPM as in a constant speed prop (used by most later propliners).

My technique is to read the prop_beta (prop pitch) variable from FS, and model a 2D prop lever that commands a prop pitch between the beta min and beta max values (found in the aircraft.cfg file). Then I adjust the engine RPM lever variable (adjusting the RPM, and thus the prop pitch) until the commanded prop pitch has been reached. Sort of adjusting the "wrong" variable to get the "right" answer. But since FS doesn't support controllable props directly, you have to do something.

It's currently just a "test gauge" and would require a lot of work (and time) to become anything releasable. The current limitations are that the prop pitch takes a little while to come to the commanded pitch, it sometimes "hunts" a bit, and you must leave your hardware RPM lever at full fine at all times. Also, any VC RPM levers would need to be animated with the new prop pitch lever variable by the plane's author (i.e. a new version of the plane produced).

It would also require someone to create special flight dynamics for the plane. I have discussed this with FSAviator, but he has no plans to do so at the moment.

So this is just a "heads up" that such a thing may be possible in the future.

Take care,

[volkerboehme]

Hi,

thanks for the head-up and it sounds like a neat idea. However, I believe that 2-pitch-props are modelled already in the default DH Comet racer. I'm not quite sure how it is controled, though.

As far as the Martin M-130 (or the Short Empire flying boat) is concerned, FsAviator suggested to continue using constant speed models to better model the take-off run, because water drag is modelled unnaturally high in FS.

Best regards,
Volker

[Tom/CalClassic]

Hi,

I agree about the M-130 - the C/S props do indeed tend to offset the FS9 water drag problem.

The Comet used a variable pitch prop, not a controllable one. FSAviator pointed out the difference to me:

"Variable pitch allows the screw to go full course for cruise, but as in real life the crew cannot get it out of full course for the approach, which made v/p screw technology dangerous and short lived. It was the real situation in the (FS9 default) 1934 D.H.88 Comet where cruise performance in the England - Australia race was much more important than safety."

In a controllable pitch prop the crew *could* control the pitch of the prop at all times.

Thanks,

[sunny9850]

Do you have any other examples of airplanes where that technology was used

Stefan

[Tom/CalClassic]

Many Russian piston propliners, Ju-52/3m, Cessna Bobcat (AT-17D), certain models of the Spitfire, and some other RAF aircraft. That's about all I know...

[sunny9850]

Sold....If Julchen had it then it would definitely be appreciated.
I always guessed that's what the non-moving levers in all the FS versions are for.
Won't be able to make the levers move of course without access to the mdl but I am sure the rest can be figured out.

Thanks in advance.

Stefan

[jesse]

The BT-13 Basic Trainer built by Consolidated Vultee used a Pratt and Whitney 450 hp engine. Unlike the Advanced Trainer, the AT-6, it did not have a constant speed prop. The prop on the Vultee Vibrator was a two position prop. You would take off with the prop control lever in the full forward position and once you had attained your recommended airspeed for cruise, you would pull the prop control lever full back and it remained there for the duration of the flight until preparing to land at which time you would then shove the control full forward. I never did learn the reason for using that type of control. It did have one useful purpose and that was to wake up the line crew. Fly down the runway and repeatedly move the prop control lever fore and aft several times. The clattering noise made by the change in pitch would wake the dead.

Jesse

[Tom/CalClassic]

Hi Jesse,

Yes, that was a simple version of the controllable prop. Better than the Comet's variable prop because you could put it back into fine pitch for landing.

[capflyer]

Feb 1, 2011 17:41:52 GMT -5 Tom/CalClassic said:

Many Russian piston propliners, Ju-52/3m, Cessna Bobcat (AT-17D), certain models of the Spitfire, and some other RAF aircraft. That's about all I know...

As far as I'm aware, no Spitfire had a Controllable Pitch prop. There were the fixed pitch, 2-pitch that was called a variable pitch, and the constant speed. While the VP prop on the Spit could be controlled somewhat, it wasn't a full control like other aircraft equipped with CP props. You could only "feather" it between 60% and 100% so it either had "Full Coarse", "Full Fine", or anywhere between 60% of "Full Fine" and "Full Fine".

[volkerboehme]

Hi Tom,

I stand corrected. The DH-88 prop control system is actually simulated quite correctly.

Here's the line from the aircraft.cfg:
fixed_pitch_beta_auto_cruise= 35,130 //For AutoCruise, angle and airspeed at which to switch from default pitch

Seems like at some point, the prop automatically switches to 'AutoCruise', even though I have not identified the trigger. I did not manage to go back into low pitch once it switched, like it should be. Seems like MS got it right. Oh, how could I assume otherwise?

For those who aren't familiar with the DH-88 system, the prop was placed into low pitch before take-off and the pneumatic control system was charged (with a bicycle pump). Takeoff was at low pitch, high (but not constant) rpm. As airspeed would increase, air pressure on a disk in the front of the prop hub would increase and eventuall exert enough force to move a trigger that would allow the compressed air in the prop control system to escape. The prop would then switch into high pitch. In flight, the prop could not be returned into low pitch / high rpm. This would make go-arounds interesting, even though they were supposed to happen at considerably lower weight, anyway. I don't think there was a fuel dump system, either, though. But the aircraft was a thorough-bred racer designed to be flown by most experienced record-breaking pilots, not the average airline pilot, let alone someone with lower qualifications. And only 2 out of 3 actually made it.

The Ju-52 had various engine/prop combinations installed, no surprise for the world's second most numerous transport aircraft. But I believe that the prop of the most numerous versions (Lufthansa, Luftwaffe) could have his pitch only changed by mechanics on the ground before flight, in effect making it a fixed pitch plane. The original Junkers company documents certainly state so (H. Efurth: Die legendäre Ju 52, p. 90), mentioning different engines and props as an option.
However, the aircraft currently owned by Lufthansa, D-AQUI has had both two- and three-blade props installed since its return to Germany and both prop types seem to have some kind of pitch control, probably constant speed props.

I have the impression that 'controllable pitch' was available in a quite a number of european aircraft during the mid-thirties until about 1940. But it is sometimes hard to find out, because many secondary literature either does not list the type of airscrew in the first place or might not be reliable about it. I believe that the Hamilton-Standard constant speed prop governor swept the US aircraft market just as the Douglas Commercial series swept it.

Outside of the USA, local manufacturers might not have had access to this technolgy for financial or political reasons and would have to make do with whatever was available to them.

De Havilland offered its own type of c/s at the late '30s. I am not quite sure about other european airliners; I'll have a look whether I find out what kind of system was installed in Pegasus-powered DC-2s. I am not quite sure about the Airspeed Ensign - this would fit the picture of an advanced mid-thirties aircraft that would benefit from some kind of pitch control but would not neccesarily have c/s props.

RAF aircraft after about 1940 seem all to have either c/s or no pitch control at all. I vaguely recall Begian Hawker Hurricanes had fixed-pitch engines while early RAF versions had a two-speed c/p prop, but I have no source for that. Westland Lysanders had c/p props, but some used for agent insertion into areas occupied by the enemy were fitted wit c/s props, giving them about 15% more range on the same engine.

But to get back to the original post, Tom, this is certainly a good idea, particularly as it hasn't been done elsewhere, as I first assumed. It might be a good way add more realism to a number of 30's aircraft.

Best regards,
Volker

Edit:
LOT's DC-2's fitted with Pegasus VI engines, had Hamilton standard props, like the American versions.
V.

[ashaman]

Feb 2, 2011 8:28:07 GMT -5 volkerboehme said:

I have the impression that 'controllable pitch' was available in a quite a number of european aircraft during the mid-thirties until about 1940. But it is sometimes hard to find out, because many secondary literature either does not list the type of airscrew in the first place or might not be reliable about it. I believe that the Hamilton-Standard constant speed prop governor swept the US aircraft market just as the Douglas Commercial series swept it.

I can certainly reassure you, almost all the pre-war Italian planes had Controllable Pitch props. Maybe some of the more advanced, like our own four engined bomber Piaggio P108 MIGHT have had Constant Speed props (haven't been able to find any sure news on it), but all the others (that includes all the trimotors and the odd four engined Savoia Marchetti) did not.

[Tom/CalClassic]

Hi,

The terminology I am using is:

Variable Pitch Prop - not controlled by the crew (i.e. DH Comet)
Controllable Pitch Prop - controllable by the crew in some way

Others have used wildly varying names for all kinds of props.

Thus I am calling the Spitfire system a "controllable prop", even though the choice of pitch was limited. The variable pitch prop is currently available as default in FS9, any controllable pitch prop is not. With some changes to the gauge code such systems as found in the Spitfire and the BT-13 could be simulated.

Hope this helps,

[volkerboehme]

Hi,

I have the impression that a not-crew-controlled variable pitch system like the DH-88's Ratier system was the exception. Probably better this way. Apart from not being able to switch back to low pitch, it was apparently also impossible to have both engines switch at the same time. I'm not quite sure how much and how sudden the yaw moment was, but in a fully loaded race aircraft, it certainly added to the thrill.

Ashaman, according to Jarrett's 'Biplane to Monplane', the S.M. 75 had constant speed props. The S.M. 74, the Bloch 220, the Ju-160 and the early He-11 airliner, on the other hand, had controllable-pitch propellers. Unfortunately, the book contains no dedicated section for engine and prop developement. It is well written and excellently referenced and I trust it enough not to miss the difference between a constant-speed or other types of prop pitch variation (as a generic term).

Considering the amount of research that already went into the S.M. 73's FDE, I wonder whether it would be interesting to upgrade the FDE to true c/p props.

By the way, it always amazes me that there seems to be so much difference between c/s and c/p props that nobody used c/p any more after about 5 years, but over all the decades, cars use some kind of c/p-like reduction control (with both manual and automatic gear, it just isn't that apparent in auto). The difference is probably that the physical connection beween engine and road surface via drivetrain and wheels makes a c/s-like solution much more difficult to engineer, while the difference between a c/s and a c/p prop hub probably doesn't make that much difference once the technology is mastered.

Best regards,
Volker

[Tom/CalClassic]

Once you have the pitch change mechanism perfected, all you need to go from c/p to c/s is a governor and related systems. So I assume that's why the move was relatively swift. Feathering and reversing came later, often (as I think on a Hamilton Standard Hydromatic prop) they used "addon" equipment (i.e. a feathering pump, etc.). There was a little overlap (I think a few c/p props could feather), but not much (AFAIK).

[volkerboehme]

Hi,

just an update: The Lockheed L-10 Electra had two-stage controllable pitch props by Hamilton Standard.

Best regards,
Volker