109 prop pitch (rpm) and the supercharger

[ACE-OF-ACES]

Originally Posted by Osprey

Jeez, stop being so dense. Obviously Crumpp, Steinhilper is just a pilot of the era, he knew nothing about aerodynamic engineering. Duh.......

You Jest..

But this is a good example IMHO of where 'anecdotal evidence' is useful!

Here we have a WWII pilot telling us how they actually used the equipment..

Which may/can be different from how the engineers intended them to use it..

Again, not enough info to say anything wrt validating a flight model

But from the WWII accounts, we know they did 'something' that seemed to improve the performance..

How much.. We don't know for sure

But as for 'how' they did it

I would be more incline to take this WWII combat pilot's accounts over some civilian pilot's interpretation of the account some 70 years after the fact

[Crumpp]

If that is true..

If you understood the mechanics of how adjustable pitch propellers work, you would know it is true.

[ACE-OF-ACES]

Originally Posted by Crumpp

If you understood the mechanics of how adjustable pitch propellers work, you would know it is true.

Ah, but the point your missing here is..

If that is true..

Why get so upset and say I was attacking you?

Brings to mind the old saying..

thou dost protest too much

[Crumpp]

upset

Not really Tagert.

[Robo.]

Originally Posted by Crumpp

Steinhilper and Crumpp are saying the exact same thing.

Nope. You were saying something completely different and you were wrong. But no worries, that happens to everyone.

[ACE-OF-ACES]

Originally Posted by Robo.

Nope. You were saying something completely different and you were wrong. But no worries, that happens to everyone.

I would have to agree with this assement

[kohmelo]

Have anyone thinked about the tehcnology differense what we are having here?

What I'm meaning with this is that in 1940s they where just learning what happens near sonic speeds.
oh look we are losing power because prop is going too fast, maybe we should build bigger one may that gives as more power at the same rpm oh noes its start to lose power at lower rpm than the last one!

Also they did not have many other things what they now about aviation today. I really doubt that they could have calculated every thing in 100% accuracy (how many died because near sonic speed jammed lightnings controls?)

Even the engines where little bit different. For example we have synthetic oils what they did not have back at the days.
--------------------------

I had one more point about the pitch twingling thing in my mind when i remembered all those 2-stroke engines is busted years back.

I burned hole in couple of piston because i drove too "fast" for the engine to cool down. After second engine, I learned when i was driving straight long road and having accelerated to the max i needed to relax the throttle for a couple of moment and accelerate again. This acceleration deceleration cycle gave much better average speed than what speed would have been with the highest possible rpm for not overheating the engine.
What if they did the same with bf109?

Little bit Overrev/overboost which give spike in the temperature and little cool down to minimize the damage? ---> Or maybe they just they had boost and revs to add but cooling could not handle it all and they used that power reserve in short periods not giving enought time for sudden engine failure or over heating?

To move between .88 and .92 mach usually takes a change of about 110 to 120 RPM.

If plane would go 400km/h at sea level with prop hitting .88 mach in 2400 rpm would it give even 5km/h hour if pushing rpm to 2500rpm? if the rise would be linear it would be 16km/h

What if they suffling the pitch near this area giving more revs untill engine would start to noise up at .93 mach (believing it would be near braking point) lowering it to near .88 mach then pushing it up untill the noise would go up etc. They just did not know it that day what they where doing.

Aw man... Sorry about huge 'what if' post... And sorry if you just lost 5 minutes of your life with it... Amateur speaking.

[Crumpp]

You were saying something completely different and you were wrong

Baloney, read what I wrote.

[Crumpp]

What he is talking about is doing the same a CSP does automatically, a controllable pitch propeller has to be done manually.

Fine Pitch to maximize rpm and coarsen the pitch to maintain rpm as speed increases.

If you don't lower the pitch, the propeller will begin to drive the engine and you will lose performance.

A given manifold pressure and rpm as listed in the POH will deliver the maximum performance for the condition flight listed. The pilot must maintain that rpm by controlling the pitch.

I have my pitch control set on a slider for the Bf-109 and adjust it constantly to maintain the desired rpm.

The basics of operating an controllable pitch propeller are given above.

It is all about maintaining optimum pitch and rpm.

As you coarsen the pitch to reacquire the rpm, you will notice an increase in performance.

In the quoted cases, they are setting the engine to a limited over boost and coarsening the pitch to maintain rpm.

That is how it works.

The experienced pilots you are quoting are coarsening pitch before rpm drops. If you know the approximate performance for a given setting, then coarsening the pitch at rpm will cause an increase in performance within limits.
It will also cause a subsequent manifold pressure drop and the performance will suffer as a result if outside of a narrow range.

[Kurfürst]

Regarding the gain of airspeed at altitude by overevving the engine and "boosting" the supercharger this way, the F-1/F-2 Kennblatt gives some hint. Blatt 6 says that by increasing RPM to 2800 over the normal maximum of 2600 yields 10 to 15 kph increase in speed at the rated altitude.

http://kurfurst.org/Performance_test...1F2_DB601N.PDF