109 prop pitch (rpm) and the supercharger

[Crumpp]

Steinhilper saying change the RPM
Crumpp saying maintain the RPM

Completely out of context. Silliness like this adds nothing to the discussion and simply an attack.


You change rpm to achieve a given performance. For example, best climb rate is acieved at a specific rpm and manifold pressure.

Steinhilper is changing rpm and manifold pressure in this case to an overboost or combat power rating.

Because his propeller is not constant speed, he must coarsen the pitch to maintain that rpm.

Basic propeller operation....

Only difference is a Constant Speed propeller coarsen's the pitch automatically perfectly timed to the airload.

The German pilots had to do it manually.

•When increasing power, increase the r.p.m. first, and then the manifold pressure.
• When decreasing power, decrease the manifold pressure first, and then decrease the r.p.m.

http://www.pilotoutlook.com/airplane...ller_operation

Steinhilper and Crumpp are saying the exact same thing.

[ACE-OF-ACES]

Originally Posted by Crumpp

Completely out of context. Silliness like this adds nothing to the discussion and simply an attack.

Attack?

Not at all.. I am simply pionting out that what you said about how to fly a Bf109 is in conflict with what Steinhilper said about how to fly a Bf109

At which point it is up to the reader to choose who they want to belive

Thats all

[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