Yak 1 propeller control system

Keith, it might be worth looking at air temperature parameters if altitude isn’t there.. .though that surprised me.

Nothing that one can vary, the standard temperature & pressure lapse rate is built in as far as I can see. So it will need someone with a lot more knowledge & capability to try a fix. Not having P3D, I can’t tell if that is any better. ( Throws in towel!) 🙁
Keith

Hi Graham – I stand corrected on the more common prop on a Spit V. Yes, that was the reason to use Hydromatics.. though it would, I think, require a mod. The Hydros as standard would cycle to ‘feathered’ at extreme coarse, while fine limits were roughly the same as bracket CS types. I reckon it needed the blades moved round a few stops from ‘factory’ settings to get a finer ‘max fine’. They wouldn’t fully feather any more, but then that functionality on a single-engined aircraft won’t make much difference, compared to on a multi-engine (where it could get you home), which they were designed for.

Visual differences.. there might be none at all. The DH/Rotol difference was largely down to the difference in lateral position of the blades (the Rotol blades were further forward), while between bracket and hydro there was none. The spinner front section would attach slightly differently, so the spinner would have a different drawing number, there might have been tiny differences in profile but as shape (lateral position of blades aside) was largely dictated by an aerodynamic matching with the cowl behind, not much.

Keith, it might be worth looking at air temperature parameters if altitude isn’t there.. .though that surprised me.

Regarding the experimentation with pitch and its effects on rpm – once again, that is not the action of a constant speed prop you are describing – the fact there even was a pitch control in the cockpit makes it peculiar, and the fact that operation of it had an effect on rpm also says that rpm was not being regulated.
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The object of my experiment was to hope that ones airspeed increased & then the rpm & hence prop pitch would match, as long as the prop was not on the stops of course.
Oh well, will probably never know.

Back to your WW, I think it might be possible to program M$FS to replicate the compressibility effect, but maybe not at the altitude which is where you want it, as I cannot see any altitude parameter except for engine turbo (not supercharger) critical altitude, hence back to square one.
Keith

Precisely the point of the carrier take-off. However, the DH prop wasn’t exactly non-standard on the Mk.Vb and Vc. Many Mk.Vb were built with the DH prop. A point of interest arising is distinguishing between the DH bracket CS and the DH Hydromatic externally? If at all. They appeared to have shared the same problem of freezing up and failing at altitude.

Perhaps more importantly the Hydromatic range was also greater than that of the (by then) more standard Rotol unit.

Yes 🙂

Slight digression coming up, perhaps. In the books on the Malta supply ferries, reference is made to the adoption of the Hydromatic propeller system on the Spitfire Mk.Vc because its greater pitch range greatly benefited take-offs from a carrier. However, this was not until mid-1942. So was this additional to the pitch change introduced with the change to CS in July 1940?

Yes, with a manually-controlled 2-position variable-pitch prop that’s absolutely the case. It was only a way to get around the increasing disparity in appropriate pitch between take-off and max flight speeds, it was never going to be a way of optimising engine speed in all conditions of flight. That’s why constant-speed units were developed, initially either ‘working’ that balance point in the case of the Spit conversion, or designed from scratch as a complete system, like the Hydromatic.

The DH conversion is feasible because it’s a very narrow rpm range that things are being kept in. It seems counter-intuitive, but it works when you work through all the forces.

Regarding the experimentation with pitch and its effects on rpm – once again, that is not the action of a constant speed prop you are describing – the fact there even was a pitch control in the cockpit makes it peculiar, and the fact that operation of it had an effect on rpm also says that rpm was not being regulated.

As an addendum, the range of the Spit prop was also increased by 5 degrees via a mod at the same time as the CSU’s were fitted. Actual complete underspeeding was thus avoided. This was overlooked on the Whirlwind. Another story. Actual overspeeding was not really an issue. The main reason was compressibility massively increased load, in the region just slightly faster than normal tip speeds in the 30’s and 40’s. It became an issue later when blades got thinner.

Keith, have you got to the bottom of what was happening with the Proctor?

In real life or in M$ Flight Sim?

I’ve no way of checking real life until I can ask Tango Charlie, when he gets one of his airborne!
I did once persuade my father to coarsen pitch in one air race, but he went from full fine to fully coarse, which was more than I wanted to experiment, as the RPM dropped from 2400 down to 1700, & thats not good on the engine, I think 1900 is the minimum recommended, so he went back to fully fine very quickly, so did not see any other result!

As for M$ Flight Sim, I’ve not found a way into the inbuilt programming.

Your explanation at the top of your message is what I would expect, re: manual intermediate setting of a two position prop. But fiddling with the throttle in fine & coarse still needs to be used to avoid over or even underspeeding as far as I can see.
So I think stalemate at the moment, unless I can stir up some of the few grey cells remaining & get a flash of inspiration!
Keith

How a controller works depends in part on how the prop works. So for example the DH original VP was indeed two-position, fine or coarse. Coarse was attained by letting the counterweights under centrifugal force pull the blade around (sometimes, on larger props, assisted by a spring), fine relied on a mechanical push from oil pressure in a cylinder. It was difficult but possible to balance it such that the two forces were equal and the blade sat somewhere in the middle, and if you then increased the revs the centrifugal force increased and the blades moved in the coarse direction, reduce the revs and it went finer again. One story, put about by Hamilton Standard, was that it was a pilot doing this who had a light-bulb moment and the constant speed prop was born. Doubtful. Other VP’s were designed to be constantly variable, but the pilot workload was heavy if indeed he attempted to use it as such, and always maintain a constant RPM though manual variations in pitch! It was only really feasible with a CSU/governor. The same 2-position DH VP prop on the Spit I became constant speed with the addition of such a thing, while maintaining the counterweight system.

Keith, have you got to the bottom of what was happening with the Proctor?

It may be worth going to `avweb.com`,Pelican`s perch,#16,Propellers`,which should clarify some points…#15 is also worth a read…

Thanks Sycamore, interesting and with simple language. Have read & bookmarked #16, now need to read #15. Would still like to find how the controller for a VP airscrew works, as only info so far seems to say that it’s a 3 way valve, so no intermediate capability.
Keith

Yes, it is. Ultimately I am looking for someone who ‘gets’ all of this (and that article, Sycamore, covers some of it nicely) as well as an understanding of compressible flow (more fun) to model the props on a Westland Whirlwind. In a very small way a wrong might be righted.

If we are talking Flight Sim prop action, then its a case of how the creator of the model addresses the prop efficiency, prop Power coefficient & engine power curves in the models .air file, and the prop angle limits & the rpm at which the constant speed cuts in, in the aircraft.cfg.
How accurate they are is any ones guess, unless the designer has the appropriate original design data. I must admit that in my models I try to get rpm, power output & airspeed as close as I can get at say take off, cruise & flat out, anything in between is a pure guess. I don’t have the mathematical knowledge to calculate these curves even if I had the necessary data!
How the M$ software calculates all of that is also unknown to me.
As noted above, the Proctor using the DH counterweight prop in real life should be started & stopped in coarse pitch, but that is not programmed in Flight Sim!
My model will start controlling at 1400 rpm, & one can move the pitch control that will change the blade angle (as seen using Herve Sors AFSD program), this will also affect power output & thrust when static. In flight likewise & flat out fine pitch will give max IAS & if one changes the prop lever towards coarse, the rpm drops, HP & IAS also, but I think that’s because its following the curves for ‘J’ vs efficiency as well as the curves for HP & Propeller power coefficient vs Blade angle & ‘J’ – the advance ratio.
There is a complex .xml programme that has been developed by a genius that can apparently replicate a VP prop, but is very complex & IIRC does not use a 3 position valve, i.e. resulting in the two position device.
Back to square one I fear! Very interesting discussion though.
Keith

It may be worth going to `avweb.com`,Pelican`s perch,#16,Propellers`,which should clarify some points…#15 is also worth a read…

The history of engineering around props gets one that way 😉 Of no interest until you start thinking about it, then very quickly fascinating when you do.

What you might have there is the blades ‘hitting the stops’. If they are genuinely at full fine already, and at high revs, decreasing throttle would make the revs drop as the blades can’t go any finer to compensate. I know that the Yak prop had a very narrow pitch range for an aircraft of its performance.

Is it possible to get it into a condition where revs are lower and the lever is still at the extreme end? Try low altitude cruise. You might find a speed range where the CSU still has authority- ie not physically against the stops at ‘fully fine’. Alternatively, it might be some kind of override..

Or it may just have been modelled without as great a degree of detailed reference to reality as we are attempting here!

Certainly the aim of fully fine IRL as described earlier by someone who had RTFM was to lock the revs at 2,700 via some kind of internal governor override, not to create a variable-speed throttle override.

The plot thickens indeed. As an aside, the most intelligent discussions of the physics and mechanisms of flight are coming from the gaming community. Unfortunately, so are some of the stupidest! Glad to be having the former.

The plot thickens.

Assuming that it is right and that the developers have their facts right…. At full fine, the rpm will drop/ increase directly with throttle movement. Take the blades out of fully fine and the control unit kicks in and does what you would expect.

I guess that gives some weight to what is said about VVS pilots ‘leaving the propeller at fully fine’.

I know it is just a game, but the theory and principles behind it all have interested me big time.

Nice. Do you get a variation in manifold pressure with throttle?

I reckon the original had the additional function of being able to set an absolute 2,700rpm – which is subtly different from contemporary UK/US controllers, which didn’t allow a specific speed to be selected via the controller alone – instead the pilot could only watch the gauge while moving the lever. But it still wasn’t really a pitch control, it just shifted the CSU datum, for most of its range.

There seems to be a lot of doubt out there about the operation of the R-7 ‘constant speed’ unit. If the modelling is correct, it doesn’t behave as it would if it were the Hamilton /DH type – http://forum.il2sturmovik.com/topic/12407-yak1-engine-rpm/ – I love the very Russian-sounding pragmatic answer ‘You are thinking too much, just keep it at 2,700’

I think that it really was a controllable pitch prop system that engaged a simple, non-controllable rpm governor that kept things at 2,700 when pushed fully forward – so not like ‘western’ types.

This would explain a lot. This is from an interview with Vladimir Alexeevich Tikhomirov, published here: http://mig3.sovietwarplanes.com/pilots/tikhomirov/tikhomirov2.htm

“Did you use propeller pitch control?”

“Rarely. Most commonly we would push pitch control all the way forward, and then only used throttle”.

Gem of a Yak training film here: https://www.youtube.com/watch?v=T_iGXO1cmM4

Funnily enough, it is the Yak in that game I am trying to find out about. :).

I have looked into it in the game. Set an RPM and action the throttle through its range, the prop RPM stays at were you set it. It even lags with the time it takes for the oil to move through the system.

Understood the prop was mechanically different. It was more the mode of operation – to be exact, how any constant speed unit regardless of prop design (including Hydromatic and Rotol) is allowing revs to increase with throttle (which is exactly what it is there to prevent), unless it was over-ridden somehow, as it could be (as an example I discovered) on the Spit IX

The ability to put the blades in coarse while stationary again suggests manual pitch control. You’ll note the absence of a pitch lever in CSU equipped aircraft (the Yak appears to have a hybrid system, above). You could achieve the same thing by reducing RPM in flight on a constant speed prop control, but that is not what you are describing here.

On the WW you could lock the blades fully coarse via the prop speed control by taking it to the min RPM setting stops. Thinking about it, was it that one was doing in the Proctor? As I say I know nothing about Proctors, and you have flown one.. it’s just something niggles!

Dev One, I reckon the Proctor had the Spit Mk.IX system as in my previous post above, where pulling the prop lever fully back caused a ‘throttle over-ride’. That would explain a lot.

Not sure at all about that, as far as I’ve been able to ascertain, the Spit had a Hydromatic type prop, whereas the Proctor had a ‘Bracket’ or counterweight type, so the CSU I think would be different. Certainly the Proctor Pilot’s Notes tell you on shut down to place prop lever in coarse & blip the throttle to get the prop into coarse pitch. Thats the other thing, when starting a Gipsy Six II always start it in Coarse pitch. I need to revisit the ‘latching’ of the prop statement I think. The only interconnection on the Proctor is the mixture control with the throttle, so on closing the throttle it automatically goes into rich mixture.