109 prop pitch (rpm) and the supercharger

[pstyle]

Here is an illustration of what I understand Steinhilper to be talking about;
http://s18.postimage.org/4wlow6b2v/s..._technique.jpg

[ACE-OF-ACES]

Originally Posted by pstyle

My understanding from the text is that rpm would oscillate with this technique.

oscillate, change, vary, etc..

A rose by any other name!

In summary, the word 'maintain' is not a rose! It is more of a turnip in Crumpps analogy!

[Crumpp]

My understanding from the text is that rpm would oscillate with this technique.

The rpm will vary and in a manual selectable pitch propeller, the pilot has to adjust the pitch to maintain rpm.

[kohmelo]

Hmmm... Just wondered about one thing with this prop pitch thingy...

How about early Hurricane and Spits with 2-stage pitch?

Should'nt they have the same "clutch pop" benefit as some of us are speculating about Bf109?

As You are flying at top speed with fine pitch and you kick in the coarse pitch for a short time should it make a little jump in Spit/Hurri before the speed starts to decline?

[JtD]

Related - at lower altitudes, Merlin engines developed at least as much power at 2850 rpm as they did at 3000 rpm (depending on source). Below full throttle altitude, climb was to be done at 2850 rpm, while at high altitude, above full throttle altitude, these rpm were to be increased to 3000 rpm. Just like with any other engine, it increased boost and engine power. However, the handbook said to always fly at these 3000, not change pitch back and forth. No idea if pilots ever tried that.

With the two stage pitch, it would probably be too hard to get the timing right to make it an efficient, practical option, though maybe pilots on occasion had to employ a similar scheme - with high rpm being too high to sustain and low rpm being too low for sufficient power output.

[ATAG_Snapper]

Not modelled in Cliffs of Dover, but apparently the BoB Spit pilots discovered that with the 2-speed props they could manipulate the pitch control lever in the center of its travel and get a variable pitch response, which they used to great effect in optimizing performance.

This is not to be confused with a Constant Speed Propellor, which to a great extent could maintain a desired speed (rpm) by automatically adjusting the pitch in response to throttle (boost) settings or aircraft maneuvring. The 2-speed prop, even at intermediate pilot-manipulated settings, would change rpms at different throttle settings and different changes in plane maneuvring, and thus bear careful watching (and listening).

This little trick pre-empted the need or desire to abruptly shift from Full Coarse to Full Fine (and vice versa).

[Robo.]

Originally Posted by Crumpp

The rpm will vary and in a manual selectable pitch propeller, the pilot has to adjust the pitch to maintain rpm.

Well of course, this is how it usually works. BUT in this specific scenario (109E way above FTH) the pilots decided to change the rpm almost constantly up and down to get better performance, where their engines and supercharges struggled a bit. So they were adjusting the pitch almost constantly to mainatin speed. So you accelerate a bit by overreving the engine, but you won't be able to keep the speed just by 'adjusting the pitch to mainain rpm' (which is normally enough, say below FTH and this is where you are wrong or failing to understand what the big deal here is), they had to adjust it soon enough the opposite direction (=up) to overrev a bit and accelerate. As you see the trick is based on repeating the process constantly, hence changing the rpm constantly, not maintaining it. Just maintaining the rpm it would make them fly slower up there. The mechanism was based on the supercharger rpm.

So you say maintain rpm, Steinhilper says keep working on it constantly. I don't think you're saying the same thing. What you're saying is pretty obvious and this procedure is only mentioned because it is interesting and on topic of prop pitch (rpm) and supercharger at specific condition = high altitude.

[Crumpp]

Steinhilper says keep working on it constantly

Only issue is that is not what the man says.....

Ulrich Steinhilper, in his auto-biography (chapter 16) , talks about managing the prop-pitch on the early (E3 and E4 variant) 109s during the Battle of Britain. He states that, in order to achieve max climb rate and airspeed (particularly at higher altitudes) one had to constantly increase and decrease the propeller pitch. Increasing the pitch would engage the supercharger, which would be run for a short period (i.e. a second or less?) to force more air into the cylinders, then the pitch would be dropped back down again to disengage the supercharger and convert the power gained into airspeed, and allowing the engine/ supercharger to rest.

He does not say a thing about changing rpm. He says to constantly manage the pitch.

That is what you have to do in order to maintain rpm!!!

The pitch must be constantly adjusted to maintain rpm as the speed increases!

[Crumpp]

Crumpp says:

The rpm will vary and in a manual selectable pitch propeller, the pilot has to adjust the pitch to maintain rpm.

[Robo.]

Originally Posted by Crumpp

Only issue is that is not what the man says.....



He does not say a thing about changing rpm. He says to constantly manage the pitch.

That is what you have to do in order to maintain rpm!!!

The pitch must be constantly adjusted to maintain rpm as the speed increases!

If you type it in bold it doesn't make it right. I am not saying you're wrong here (you're not saying anything new here re angine management), you're just completely missing the whole point of this conversation (that is non standard pitch management at high altitudes as described by a LW pilot who has actually been there).

What you're trying to do here is instead of contributing to an interesting topic or even discussing it, you're doing everything possible to prove that you, Crumpp, were right even if you used wrong semantics and therefore said something completely different to actual WWII 109 pilot.

If you're saying that Stainhilper was actually maintaining the rpm even though he was working with the prop pitch lever to get more rpm (here is the catch!) to get a boost from his supercharger above FTH, then you're obviously right and he was maintaining his rpm by rising his rpm for short periods of time.