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FM/DM threads Everything about FM/DM in CoD

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  #1  
Old 09-11-2012, 12:02 PM
pstyle pstyle is offline
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Default 109 prop pitch (rpm) and the supercharger

I think Klem had mentioned this last year someplace on the forums.. but I’m reviving the issue after having just finished reading “spitfire on my tail” - http://www.amazon.co.uk/gp/product/1...ls_o05_s00_i00

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.

Steinhilper suggests that this prop-management was responsible for the pulsating sound of the German aircraft engines as reported on the ground. The fact that he has conflated the two (rightly or wrongly) suggests to me that this propeller management was continuous, and the changes between the flatter and coarser settings occurred over a few seconds (at most).

Steinhilper indicates that this was one of the most important skills for a 109 pilot to master, so it must have had a significant performance impact.

Is this effect modelled in the game? Does this constant prop management to engage and disengage the supercharger, allowing for best continued speed?

My experience is that the prop control is modelled to move quite slowly in the 109 in the game. But perhaps the range over which this manipulation needs to occur is quite narrow, just either side of the supercharger threshold?

Last edited by pstyle; 09-11-2012 at 12:07 PM.
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Old 09-11-2012, 01:09 PM
Kurfürst Kurfürst is offline
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Its quite normal - manipulating the propeller pitch will increase/decrease engine RPM, and the engine RPM is in turn what defines the supercharger RPM. The faster the supercharger runs, of course, the more air it delivers to the engine, and it can mean that you can get a bit of extra power above the rated altitude of the engine, as it can maintain boost to higher altitudes.

Below rated altitude, it should not matter or even decrease engine power somewhat, since the engine is throttled (it wont get more than normal boost)

IIRC the DB 601 had something like an 1:10 gear ratio between the engine and the supercharger, meaning that the supercharger revolved at around 24 000 rpm if the engine was revving at 2400.) In November 1940 for example the LW even issued a circular that sanctioned this - apparently already existent - practice. See: http://kurfurst.org/Engine/Boostclea..._increase.html

Can you post this part from Steinhilper perhaps?
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  #3  
Old 09-11-2012, 01:14 PM
pstyle pstyle is offline
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Cheers, I Will compile the direct quotes tonight.
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Old 09-11-2012, 01:29 PM
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Osprey Osprey is offline
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I'll be interested to re-read that part pstyle. I remember him talking about that, I think it was in reference to new pilots who couldn't do it and just fell away behind the formations. I seem to remember him mentioning that one chap was told to turn back and land because he fell away so far.
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Old 09-11-2012, 02:06 PM
pstyle pstyle is offline
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Quote:
Originally Posted by Osprey View Post
I'll be interested to re-read that part pstyle. I remember him talking about that, I think it was in reference to new pilots who couldn't do it and just fell away behind the formations. I seem to remember him mentioning that one chap was told to turn back and land because he fell away so far.
Yes. You're right.
He does go into more detail about the technique in more than one place, not just with reference to that particular flight.
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Old 09-11-2012, 04:36 PM
pstyle pstyle is offline
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Hi guys, as promised the direct quotes:

Of special importance was teachign them how to change the pitch of their propeller to get maximum pull from the engine at high altitude.
A flat pitch would allow the enginer to rev up to its maximum so that the super-charger would deliver the maximum vlume o air to the cylinders and
produce optimum power; chnaging to coarser pitch would have that enginer power converted into more pull and consequently speed our rate of climb.
It was vital they mastered this technique if they were to keep uo in a battl climb or at high altitude.


AND

... we began our climb almost immediately afdtetr take-off and he was constatly using the radio to ask us to slow down so that he could keep up.
It was obvious that he wasn't manipulating the pitch control with the skill of the more seasoned pilots to produce the same power as our mahcines...
Eventually, about half way accross the channel and at 4000m (13,000ft) Kühle told him to leave the fomration and retun home.


What I take from this:
1. The prop-pitch manipulation had direct impact on air-speed.
2. This technique was used BOTH at high altitude AND at low altitude in the climb, and had an effect in both cases.

I understand that this is not modelled in the game. Is that correct?
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Old 09-11-2012, 04:57 PM
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David198502 David198502 is offline
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Quote:
Originally Posted by Osprey View Post
I'll be interested to re-read that part pstyle. I remember him talking about that, I think it was in reference to new pilots who couldn't do it and just fell away behind the formations. I seem to remember him mentioning that one chap was told to turn back and land because he fell away so far.
exactly what i remember....i think im going to read it again in the near future...
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Old 09-11-2012, 05:08 PM
pstyle pstyle is offline
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Quote:
Originally Posted by David198502 View Post
exactly what i remember....i think im going to read it again in the near future...
see my direct quotes in the comment above yours David, that particular incident is described
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Old 09-11-2012, 07:23 PM
TomcatViP TomcatViP is offline
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Quote:
Originally Posted by pstyle View Post
Hi guys, as promised the direct quotes:

Of special importance was teachign them how to change the pitch of their propeller to get maximum pull from the engine at high altitude.
A flat pitch would allow the enginer to rev up to its maximum so that the super-charger would deliver the maximum vlume o air to the cylinders and
produce optimum power; chnaging to coarser pitch would have that enginer power converted into more pull and consequently speed our rate of climb.
It was vital they mastered this technique if they were to keep uo in a battl climb or at high altitude.


AND

... we began our climb almost immediately afdtetr take-off and he was constatly using the radio to ask us to slow down so that he could keep up.
It was obvious that he wasn't manipulating the pitch control with the skill of the more seasoned pilots to produce the same power as our mahcines...
Eventually, about half way accross the channel and at 4000m (13,000ft) Kühle told him to leave the fomration and retun home.


What I take from this:
1. The prop-pitch manipulation had direct impact on air-speed.
2. This technique was used BOTH at high altitude AND at low altitude in the climb, and had an effect in both cases.

I understand that this is not modelled in the game. Is that correct?
It's in the game. I rember giving on this forum the same advice to rev up the the SC.

So COD is "quite accurate" again
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Old 09-12-2012, 01:50 AM
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Crumpp Crumpp is offline
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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.

Quote:
What I take from this:
1. The prop-pitch manipulation had direct impact on air-speed.
2. This technique was used BOTH at high altitude AND at low altitude in the climb, and had an effect in both cases.
You are making the right conclusions. The basics of operating an controllable pitch propeller are given above.
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