BeermatBest in class probably. But there are some enduring myths. That wing, for example. Used with the aim of delaying separation and thus reducing the effects of compressibility, it proved comprehensively less capable at high transonic speeds than the Spitfire wing. For the theory to have worked the wing would have needed to be glassy-smooth. It showed you could put the thickest part further aft and the thing would still fly, but gained the P-51 nothing.
Hype is perhaps undeserved by definition? Not criticising, not my place to – I haven’t designed any high-performance piston engined fighters. But sometimes hype gets in the way of fact. The P-51 proved the right design at the right time – no argument there!
P-38 – most accounts give equal credit to both, I guess my comment was prompted by the claim that Johnson could ‘see air’. Now there is an example of unqualified myth-making. If he could see air he wouldn’t have let the P-38 out of the hangar door until it looked the way NACA remodelled it two years later.
BeermatNice. 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.
BeermatUnderstood 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!
BeermatVega ECM has touched on the current reason we will not be designing and building whole aircraft for the foreseeable future. As soon as a company shows a steady profit and gets close to being of a size necessary to undertake such a project it is floated. Shareholders that end up owning the company care less about aeroplanes than short term profit. If there is one thing designing and building a new aeroplane will not bring you, it’s short term profit.
BeermatThere 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
BeermatHI wl745
I am still looking for disused Hamilton Standard 3 blade propeller components. If they have anything like that at all I am in the market – couid you ask about that too, please? There’s quite a few owed Singhas in it..
Happy to share a container.
Beermat🙂 And I should qualify something I said ref your original post regarding indications on instruments:
http://www.flyingmag.com/technique/tip-week/constant-speed-prop-basics
“..If we now decide we want to climb to 8,000 feet, we start by rotating the blue prop knob, increasing the rpm to 2,400 and then moving the throttle forward to increase mp to 23 inches”.
For a given rpm, more throttle means higher pressures.
Beermat..and to illustrate my earlier point – Whirlwind, 2x DH props with CSU’s. No pitch control in the cockpit. The more central levers are the prop speed control (with handy dynatape writing to make this clear). On the right are the throttles (please ignore the numbered x’s, that’s for a different conversation!)
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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.
BeermatTurns out we all live and learn – especially me – I mentioned as a hypothesis ‘a more sophisticated system that takes throttle into account’.. check out the Spit Mk9 Pilot’s notes: http://zenoswarbirdvideos.com/Images/spit/SPIT9MANUAL.pdf
Under ‘propeller control’:
(i) On early aircraft the speed control lever (35) on the inboard side of the throttle quadrant varies the governed r.p.m, from 3,000 down to 1,800.
(ii) On later aircraft the propeller speed control is interconnected with the throttle control. The inter-connection is effected by a lever, similar to the normal speed control lever, which is known as the override lever. When this is pulled back to the stop in the quadrant (the AUTOMATIC position) the r.p.m, are controlled by the positioning of the throttle lever.
BeermatThe props are the potentially the same. At risk of getting repetitive, there’s no such thing as a constant speed prop, it’s what’s controlling it that counts. A pitch control controls the pitch, and the prop is called controllable pitch. This might be manual, ie the pitch control is attached to a pilot, or It might be ‘constant speed’, where it is attached to a CSU. Now, a pilot controlling the CSU will observe pitch change. What the angle the CSU ends up driving the pitch to to attain the desired rpm depends upon several factors that make up the load on the prop so the pilot is not directly controlling pitch, the CSU is.
Moving the control one way will result, all else being equal, in the blades going finer. This direction is called ‘fine’. The same with coarse. But it’s not really a pitch control, it’s an rpm control.
I am wondering whether ‘fully fine’ locks the CSU the way ‘fully coarse’ does? You are describing how a manual variable pitch works. If you are able to adjust engine revs using the throttle then in that circumstance you do not have a CSU doing its job (as it says on the tin) of maintaining a constant rpm. Unless there’s a more sophisticated version that takes throttle into account?
There is more to this. Open the throttle and you will get more power. This is correctly geared automatically by the CSU, such that the prop absorbs that power by being in coarser pitch. The rpm would be thus regulated to stay the same, near the optimum for the engine if you don’t touch the prop control, but you’ll be delivering the extra thrust through your coarsened blades. This is the can of worms I mentioned earlier.. It makes your brain melt the first time (or it did mine, anyway). But it’s the whole point of a CSU.
BeermatAlso NV – did the 105 engine really turn at 4,000 rpm? Or do you in fact mean engine revs and not prop revs when you talk of 2700 rpm? The Hurricane pilots notes certainly refer to engine revs!
BeermatThe Russian system does differ from the UK one, then. The control in fully back position on dh CS systems locks the CSU into keeping the blades fully coarse – essentially making a fixed pitch prop. Anywhere else is as I described whereby the CSU maintains a (manually selectable) rpm regardless of other conditions by varying blade angle.
NV, the bit I don’t get from your description of the Russian system is the purpose of full forward giving 2,700 rpm. Is that not achievable using the control anyway, in the same way the pilot would select any fixed rpm?
Graham, throttle would have an influence on rpm in a fixed pitch system. A constant speed system would negate throttle inputs in term of rpm (but cruciually not negate them in terms of thrust – and that’s another can of worms) by increasing or decreasing the load on the blades so that rpm remained constant. The pilots control over rpm would thus be via the constant speed control (which is not a pitch control) and not via throttle either.
BeermatGreat info Graham, and KL.
So the control was a regulator of CSU datum, used to vary revs, and not really a direct pitch control, just like the US and UK constant speed systems.
Thanks. I wonder whether the OP will reappear? This does sound like his answer.
BeermatYes!
The prop control might not actually be graduated with engine speeds, it was much more an ‘increase/decrease kind of thing, at least with DH CSUs. And full back would lock it such that the blades stayed at max coarse. Anywhere else rpm would be maintained at whatever was showing on the rpm gauge (or not 😉 ) at the time of setting, through automatic variation of pitch, until the control was moved again. However, this was still not a pitch control.
BeermatNow that is interesting. What you describe in take off and climb procedure is the manual operation of a variable pitch prop, as one would if one did not have a CSU. If the proctor had a CSU then there would be a conflict, in that if one changed the pitch for a given throttle setting as you describe one would alter the rpm. A CSU wouldn’t like that and would want to bring the rpm back to the set value. I am not doubting, instead learning. I am interested in what the mechanism was in a Proctor, and how it resolved this.
I know it was possible to lock the DH CS system into full coarse pitch for an economical cruise.
Edit.. I don’t know much about the Proctor, but is it possible that your father’s had a constantly variable pitch control as opposed to a constant speed unit?
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