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?

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?

Cheers, I Will compile the direct quotes tonight.

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.

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?

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 ;)

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 :rolleyes:

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.

You are making the right conclusions. The basics of operating an controllable pitch propeller are given above.

There is another quote in that book, I copy & paste the part from bugtracker where we discussed increasing RPM of the DB 601A : http://www.il2bugtracker.com/issues/211

Quote from 'Spitfire on my tail' by U. Steinhilper, a Bf 109 pilot who has been shot down on 27.10.1940 - before the above document has been issued:

'We had to stay alert if we were to survive that day. Things had started to go wrong as we reached our operational height for the mission. When we flew at that height, the engine only just gave enough pull and we constatnly changed propeller pitch and RPM to improve performance. With a flat pitch we could increase the rpm of the engine and get more pressure from the supercharger. Then, by changing the piitch to a coarser setting, we could make up some speed. (... he then describes some issues with the prop pitch gears, probably from the moisture freezsing up at the altitude)... I decided to set the pitch at its flattest, this way I would be able to run the motor at high revs and gain the benefit from the supercharger. It would mean that the motor would have to be runing well above the maximum recommended RPM, but this had happened before in combat, without total dosaster.' (page 25 of the above book, describing how he got in trouble and got shot down / baled out on that very day)

It's not just about maniaining the optimap pitch and engine RPM...

.....except miss out all of the bits where he whines about Galland/Radios and mistreatment of his parents. Shouldn't take long to re-read then...... ;)

Hah! Yeah there is only about 5% flying and combat in the book..

A question, and waaay OT - just how often did German pilots yell "Achtung Spitfire!!!" and did they ever yell "Spitfire!!" - I have long taken this to be an urban myth peddled by old British comics (a few years ago I flipped through an olde collection of Victor and Commando comics - every time a German pilot got bounced he yelled "ACHTUNG, SCHPITFUERER!!" or a variation thereof, then "AAARGH!!" as their 109 or 190 was torn apart...)

Did German pilots and aircrew actually use the British "Spitfire", or were they more likely to use the German equivalent Hitzkopf or Feuerkopf?. Just a question and pardon my ignorance.

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.

How am i getting the feeling about those quotes that they "kick the clutch" to acquire better rpm powerband?

Like with those insane 80s turbocharged cars they used clutch slip to keep engine at better rpm (in the narrow maxpower area). Even without charger it would give technically short boost --> In car you kick the clutch for so long that you can rise RPM to best rpm usually the power from engine and momentun in driveshafts makes your car "burn rubber," or go "slowly sideways"

Technically would it be the same thing with prop pitch? "feather" prop to add rpm and then kick in the more coarser? pitch to force that engine power and momentum to movement for that narrow timeline.
I really don't think that pitch would change fast enough for that have any kind off use.

As for milling pitch up down in narrow area there might be some advantages if doing this at point where engine starts to lose RPM.

Well working or not i'll might test this for my own amusement.

You would not feather the prop to add rpm. Feathering is where you coarsen the blade pitch to the point the chord is parallel to the relative wind.

A feathered propeller produces no thrust at all and minimal drag. It would be very poor practice to run the engine with a feathered propeller and the engine is shut down when the propeller is feathered.

It is done to keep the shut down engine propeller from windmilling and causing loss of control.

http://www.youtube.com/watch?v=E7x8iAjFtzI

You are right about the Bf-109 pilots doing the aerial equivilent of "popping the clutch". That is exactly what they are doing so to speak. It is an advantage of a controllable pitch propeller. It is something that would take experience to do. The pilot must understand the principles of propeller operation regarding pitch and the relationship of manifold pressure and rpm.

I'd like to think that they did, and as the RAF Flyboy gritted his teeth and fired rounds into the terrified Hun he would've yelled things like "Not so fast Fritz!" and "Your number is up Herr Leutnant!" :D

Sorry about that, I really do did'nt know the exact terms in english. So term would be quite opposite what i meant.
Still you did understand what i meant. Great!

I knew exactly what you meant! You expressed it well.

:grin:

I understand how it works, no need for bold writing mate. My point was that it's not all about setting your engine for certain (optimal) rpm and keeping it that way - but especially at the altitudes, you would need to work with it constantly to get more speed. This is all relevant to the thread title which is about supercharger and rpm in 109s.

To mainatin speed / performance. Not rpm... it's all explained in detail in the above quote...

Geez robo,

Quit being dense on this, I have explained how it works. What I am saying is what the pilots are doing.

Your point is wrong.

Right...by maintain rpm!!!!!

If you lived close by, I would take you and show you how it all works. My plane has a very accurate Engine Monitoring System.

Manifold pressure, rpm, and mixture are all interelated to produce a given performance.

Steinhilper explains how he's constantly changing pitch and rpm to improve speed performance. It would be interesting to know if the perceived increase in speed was placebo or not, but that doesn't change the method.

Thank you, I appreciate how you're trying prove you're right at all times, especially when you happen to be wrong. :grin:

Again - 'to maintain rpm' in my book means keeping it constant. That is possible and desirable for optimal performance of a 109 (even in CloD), but it is clearly not the case with the practice described in Steinhilper's quote, he was actually changing (changing is the word here) rpm up and down to maintain his speed = he would be slower without doing that = he would be in more danger with all those Spitfires around. I thought that quote would be interesting for virtual pilots in here and it is on topic with this thread (especially for supercharger part), but you obviously assumed that I don't know how things work because it is soo complicated. I am so glad to have you on this forums so thank you again for your kind offer.

Are you talking about prop rpm, or engine rpm?
Steinhilper makes it clear that engine RPM is changing with this technique.
I'm unclear about whether or not prop RPM fluctuates also.

Prop and engine are linked at a fixed gear ratio and if engine rpm changes, prop rpm changes as well. For the DB 601 on the 109E the ratio was 1:1.55, so if the engine is at 2400 rpm, the prop is at 1550 rpm.

Ok..

Ok..

Ok..

So we have

JtD pointing out that a change in engine RPM will result in an change in prop RPM

And we have a conflict between what Crumpp and Steinhilper are saying, i.e.

Steinhilper saying change the RPM
Crumpp saying maintain the RPM

Thus the only thing left is to decide who do you want to belive

Crumpp or Steinhilper

If this is the case (I don't know) the prop and engine RPM should be linked, so an increase in one results in an increase in the other.... in which case Crumpp's description appears to be contradictory.

Can we all specify exactly when we are referring to prop rpm, when we a re referring to engine rpm, and when we are referring to both?
That would sure help me understand.

the problem is the lack of information from the devs, whats working best in game.

surely the only RPM that can be refered to is prop RPM, I don't think there is an engine RPM gauge in most of these aircraft, engines can run happily at a range of RPM's but a prop must run within a certain range for efficiency, typically between 2,600 to 3,000, therefore it is more important to know what the prop is doing, certainly this is the case with modern aircraft...engine RPM is practically irrelevent and only fixed pitch non reduction geared aircraft you can assume engine and prop RPM are the same.

jtd is correct that prop and engine RPM are fixed in a ratio but a prop turning at 1500 RPM is not producing much thrust, so it would be more like prop RPM at 2400 and engine is at 3720 with that 1:1.55 ratio, I know were talking 1930/40 tech here but I'm pretty sure the typical aero engine of those days could cope with RPM's that high.

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

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.

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

Steinhilper and Crumpp are saying the exact same thing.

Partial quote, sorry. But what you're saying is not correct. The rpm gauges you see in the aircraft are engine rpm, I'm not aware of any aircraft showing prop rpm (unless the gear is missing and the ratio is 1:1). Also the rpm limits as listed in manuals give engine rpm limits. In case of the DB 601, the 2400 rpm is the 5 minute engine limit - and the prop will be at 1550.

I'm not so convinced, the gauges normally just say RPM and dont apparently distinguish whether it's engine or prop, like I said a prop turning at 1500 rpm is not going to be very useful, I can believe the actual RPM gauge is being driven by the engine itself but I would think the actual calibration on the gauge is for propellor rpm, easy enough to do considering the ratio is fixed so no need for special gears, the manuals may state the engine limits but it may just be that the figures stated are on the basis of prop rpm taking into account the known ratio.

You can skip all the plane manuals and go directly to engine data, if you find plane manuals confusing. Engine limits are engine limits, they don't change.

Are you Crumpp in alias?....you seem to have much the same charm, no need to get patronising.

I don't find aircraft manuals confusing thank you, I just find the idea of a prop turning at 1500 rpm being efficient less than believeable.

What is referred to as propeller rpm is actually measuring engine rpm but you use the propeller governor to control it in a constant speed propeller. In a direct drive, meaning the propeller is bolted right to the crankshaft, fixed pitch propeller the engine control is just the throttle which sets the rpm.

In a variable pitch propeller, the throttle controls manifold pressure and the propeller controls are used to set the engine rpm. What is confusing people is at the limits of the propeller blade movement, it will change rpm. So if you pull the power to idle from cruise, your rpm will change too. You are not controlling rpm with manifold pressure though, it is just an effect because they are dependant upon each other.

The rpm and manifold pressure settings found in the Operating Notes correspond to a specific point of maximum efficiency. This point is based on the speed of the aircraft.

First of all, what is a propeller?

It is just a wing that moves in a circle. Like any wing, it has limited range of angle of attack from zero lift to maximum lift coefficient. It is also subject to critical mach effects like any wing.

All propellers reach peak efficiency for a give pitch angle at a specific velocity. Just like the wings on the airplane have a point of highest lift to drag ratio, a propeller is no different.

That is why fixed pitch propellers come in "cruise" and "climb" propellers.

A variable pitch gives the pilot the advantage of being able to use a wide range of peak efficiencies by adjusting the pitch angle of the blades and the speed at which the propeller rotates. It allows us to adjust the angle of attack and dynamic pressure our rotating wing requires to keep it at the point it can transfer the most thrust force to the air.

The "popping the clutch" analogy was very good for what the German pilots were doing. The engine has a finite amount of power and thrust it can generate. The point of maximum thrust production is defined by a velocity and the most efficient engine setting. We cannot produce extra power from nothing and just changing blade angle is NOT going to change that point of maximum efficiency or necessarily get us there quicker.

Popping the clutch in your car does not increase the cars power or speed it can attain. Done correctly, you gain an increase in acceleration to the maximum point of efficiency. Done poorly, you loose traction and it takes longer to reach the point of maximum efficiency.

Bongodriver, he is just right. Can you accept that?

:rolleyes:

I find that very insulting. I'm not calling you names just because you don't want to "believe" a simple technical fact.For your consideration: 1500 rpm with a 3.1m diameter prop is 240m/s prop tip speed. Combined with 430km/h cruise you're at 270m/s. If you now consider going supersonic (300ish m/s at altitude) is a bad thing, you might find the figure much more believable. Hope that helps, even if my charm is still lacking.

as soon as I'm shown data that says a prop turning at 1500 rpm is going to be efficient.....yes I would happily accept it, it's all I'm asking for and not a tirade of sarcasm.....so you can stick your little blue face up your rectum.

I was eqally insulted by your sarcasm, I don't recall putting my query in any form that called your intelligence in to question.

bongo, what is the prop tip speed of a 3.1m prop at 2400rpm and 1500rpm?

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

http://www.epi-eng.com/propeller_tec..._propeller.htm

You should probably spend more time reading such things as the Pilot's Handbook of Aeronautical Knowledge instead of lurking on gaming sites if you are professional pilot who does not know this kind of basic stuff.

Just saying, it would be safer for you and your passengers.

I wasn't being sarcastic, the plane manuals did not appear to clarify the things for you. With the benefit of hindsight the if clause wasn't necessary, but not meant as an offence in the first place.

:rolleyes:

But is not in conflict and agrees with what is related in the anecdotes.

If you understood how an adjustable pitch propeller works in conjunction with the engine, you would see that.

It is useless to discuss it with you. Have a nice life, Tagert.

Ok, sorry for jumping on you, actually likening you to Crumpp was probably the most insulting thing for which I am most regretfull, I have to admit my mistake was not thinking 10 foot diameter props.....goes to show how your own experience can get you stuck in a rut sometimes, I fly a Stearman with a 7 foot and a bit prop and 1500 rpm is practically idling, the R-670 engine has no reduction drive.

I dont need some walt without a pilots license telling me what I should concentrate on thank you.

:rolleyes:

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

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

:rolleyes:

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

:rolleyes:

Not really Tagert.

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

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?

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.

Baloney, read what I wrote.

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.

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

Exactly....

As the speed increases, they will have to coarsen pitch to maintain rpm.

So you're saying (again!) that they were constantly changing the rpm to maintain rpm? :grin: :o:rolleyes:

On a 109, if you touched the rpm lever either way (up or down), the rpm changed. Simple as that.

You didn't have to 'reaquire' rpm in level flight after you accelerated (e.g. by overreving the engine for a short while). It was where you set it and it didn't go anywhere unless you touched it again. The comparsion with the CSP is not entirely right as the propeller blades won't adjust themselves. You adjust them by moving that Drehzahl lever. So after you accelerate, you need to coarsen up the propeller pitch, that much is correct, but your rpm will drop and stay where they are after you let the lever go. You start slowing down again after a while because of the low rpm / supercharger action (you can go all the way down to coarse for good speed in game) at which point you go to finer pitch again (fiddling with the rpm that is, not mainaining it) to accelerate a bit and get a bit of a boost from the supercharger again. Rinse and repeat.

Maintaining rpm = I am flying at 6km altitude and I don't touch the rpm lever.

It's interesting to see how you're trying to twist everything to prove that you've been actually right. I don't mind you doing that, it's actually quite funny.

So like with car going up hill with 5th gear you can not sustain you speed it is declining down and you change to 4th gear you could use that gear to sustain efficient speed or you can accerate but you can not sustain the accelerated speed because of the strain to the engine and cooling. So you change back to 5th gear where your speed starts to decline but the straing is not as big at the point where drag and inertia start to slow you enormously (as with propeller driving engine) you change back to 4th gear. (manual or auto transmission technically the same --> except auto forces to change to bigger gear)

--> Same with automatic variable transmission would be like with autoprop in bf109 you are pushing at the theorethical best efficient gear ratio for your throttle setting but with variable transmission you cannot get that small boost when you need it of rpm.

the problem is, that i think in game overreving the engine does nothing in regards of speed, but only affects the temperatures..

Yes, yes. but i really think that Crumpp has a point in this thing.

as with car and transmission example where you did'nt have the perfect gear ratio. Its hard to have perfect pitch with Bf109

As with manual prop pitch when you change the angle of attack to most efficient at that point, plane speed will change because of this and angle is not efficient anymore. Meaning you need to suffle pitch to opposite way to get more efficient pitch and again because of this change plane speed changes and the angle is not the best anymore. You would think that after while suffling pitch forward and backwards you would hit the sweet spot, but because pitch controller changes engine RPM also that means that engine power output changes as you change you pitch, technically you got more boost from the engine before you coarsened the pitch but if you had'nt coarsened the pitch, you would have started to lose efficiency because you have too much RPM. This could make them jiggle the proppitch and as with the rookie pilot that was falling behind he just could not keep the engine at the sweet area and was falling over from there.

---> BTW you can hear pitch change of the planes when you change pitch. I noticed it with Hurricane 2 pitch version in game.

Edit: My head starts to hurt thinking this prop pitch thing.

Have you tried this at high altitude? Below full throttle altitude, there's little use in increasing rpm above the normal limit, but at high altitude, it should make a difference. And maybe once at high rpm, change back to the pitch you were originally using and see what speed you're getting to. If it's faster than your original speed, Steinhilpers technique is working in game.

(No time to check on my own.)

You noticed that too?

Talk about trying to have your cake and eat it too! Or put another way, he is just not able to admit he made a mistake! ;)

Simple fact is the 109 pilot accounts clearly show that they were not trying to 'maintain' the RPMs..

They purposely changed the pitch (flatten) to allow the RPM to increase (rev up), even exceed the recommended RPM limit..

Which in turn allowed the supercharger to rev up!

Than the pilot would change the pitch back (course) to convert the excess RPM into a boost in speed and/or climb as the RPM decreased..

This process was not done once, but done over and over, back to back..

Which is what the 109 pilot noted accounted for that 'wa-wa' sound.

The analogy of the manual transmission clutch fits well here!

Back when I raced dirt bikes we called it 'clutch revving'..

In this analogy, the clutch pressure plate is the prop.. and the flywheel is the air, and the clutch lever is the prop pitch adjustment.. As in pulling in or releasing the clutch lever is analogous to adjusting the prop pitch from flat to course..

The way it worked was you would pull in the clutch to let the engine 'rev up'.. Than release the clutch to convert that revved up energy into a boost in speed or torque..

Here too we did this more than once, not all the time mind you, but when ever you needed a little boost..

Notably, this process also produced a 'wa-wa' sound..

Crumpp as others have stated, Steinhilper is clearly not complaining that rookies fell behind because of their inability to manually duplicate a CSP (i.e. continuously changing their variable prop pitch for a constant optimal rpm).

From his account he believed that he could only get optimal performance from pulsing the rpm, i.e duplicating a CSP with the rpm control being moved back and forth. This seems a little odd, and we must consider that it wasn't actually true. Perhaps if the rookie pilot managed to manually control his rpm at an optimum value like a CSP, he could have overtaken Steinhilper busily pulsing his rpms back and forth.

It is hard to state a good technical reason why the pulsing would have helped. Steinhilper believed that the thrust from the rpm boost could only occur if rpm was dropped again, implying that the extra rpm was high enough to not increase thrust. Perhaps 109 pilots decided it was OK to exceed rpm limits if they only did pulses above the limit, they achieved some extra thrust and speed this way but mistook the reason. Or perhaps a quirk of 109 engine/supercharger/prop design did allow a small performance increment doing this over maintaining rpm at a constant optimal value.

Your explanation of CSP function are correct but not relevant to what Steinhilper described.

Yes but mind you this only applies at very high altitudes. Fiddling with the rpm, as he describes it, was because of the supercharger design and function, not because of trying to mimic the CSP. Apparently this practice made a difference in average speed up there.

The chap falling behind on the other hand, that was while they were climbing below fth. He was simple a rookie pilot fresh from the training and due to the lack of experience he could not use the manual rpm lever at all and was struggling to keep up. After he got an order to turn back to France he got the navigation wrong, too, and was heading straight to the UK. At this point Steinhilper left the formation and herded him back to the correct heading.

The two 'rpm quotes' are totally unrelated.

See explanation above - pulsating the rpm is only applicable at high altitudes way above the FTH.

He got shot at and baled out because he was using his older 109 that was not in use for a while, there was some condensed water in the propellel hub and that water froze up in the altitude so he could not change the prop pitch and overreved his engine quite badly.

Good technical reason was the supercharger function at that alt and rpm, just as you said below.

Yes they decided so, because it obviously worked, they knew why it was working that way, even Steinhilper explains that in the book. Overreving the engine at altitudes above FTH was actually approved and recommended by LW authorities shortly after the BoB. There is no doubt the pilots knew what they were doing, at least in my opinion... Again this does not apply for flying below the FTH.

yes we have tried it as a squad with different rpms at above 5000meters.
the outcome was, that there is no difference in speed(at least not that anyone could recognize a difference), although the ata rises with higher rpm that high.the only difference was, that those with higher rpm overheated their engines much quicker.

Thanks robo, that clarifies the story considerably. As I don't have the book I was going on what text was available in this thread and online. It makes sense that the two situations (below FTH and above FTH) are different.

Increasing rpm and supercharger output at high alt will give access to higher boost, in fact the FTH will increase for any particular boost level. But it still seems odd to me that a useful strategy would be to attempt a cycle of rpm pulsing in between maximal power and thrust settings (with the conversion inefficiencies inherent in this). Once you give yourself permission for higher rpm (and boost/power) at height, then it seems more likely that an intermediate constant rpm than the extremes of your pulsing would deliver better performance.

I'm never sure whether doubting a historical pilot assertion is really appropriate from behind a computer in 2012, and Steinhilper could well be right that there was real edge doing the pulsing. However there are many examples of pilots using procedures that the engineers would have frowned upon to give a perceived edge. The edge may have been good for morale but vanishingly small or even a placebo.

My favorite example is the RAF bomber pilots who always turned on their IFF sets over Germany, in the belief that it confused radar operated searchlights. The brass encouraged it in the belief that it improved morale, the scientist RV Jones thought this was totally unacceptable as the IFF sets generated radiations that Germans could exploit for detection sooner or later.

There is another possible explanation as to why pilots were doing this:

http://i91.photobucket.com/albums/k3...e/R-28002a.jpg
http://i91.photobucket.com/albums/k3...e/R-28001a.jpg

http://www.amazon.com/2800-Pratt-Whi.../dp/0768002729

If the hydraulic coupling of the supercharger was generating too much heat then the pilots had to take steps to cool the supercharger down

Pstyle's first post the hydraulically coupled supercharger was being "rested" and cooled.

I am being a nit picker here (and thread drifter) Camber :)

"My favorite example is the RAF bomber pilots who always turned on their IFF sets over Germany, in the belief that it confused radar operated searchlights. The brass encouraged it in the belief that it improved morale, the scientist RV Jones thought this was totally unacceptable as the IFF sets generated radiations that Germans could exploit for detection sooner or later."

I think you are referring to "Monica" an active Tail warning radar. The Hun were quick to exploit it and home passively on it using devices like Flensburg. Using the basis of the radar equation they were capable of homing on it from twice the range it was capable of actually detecting them. This info was withheld from the crews (to their detriment) based on the good morale that Monica was a good defensive system.

Drift away Ivan! You had me worried for a second there... :)

"Most Secret War" by RV Jones, p 275

"Bombers were frequently being caught in German searchlights, and the idea had grown up that the searchlight control could be upset if a bomber switched on its IFF radar recognition set, and so the bomber could then escape. The proffered explanation was that the searchlights were directed by radar which was somehow jammed by British IFF"

So I remembered a bit wrong, the IFF was only (pointlessly) switched on when a searchlight found the bomber or was nearby. Jones worried that the Germans would find a way to interrogate the IFF set to the bomber's detriment.

The Monica system problem sounds a bit similar, although Monica was an initially useful countermeasure which became a disadvantage, rather than being a placebo countermeasure from the beginning.

Thanks for posting your findings.

At high altitudes, the airplane is essentially in slow flight for most of the envelope. That makes cooling harder and overboost conditions will heat the motor up faster.

If they wanted to use a limited overboost condition, they would be constantly changing rpm between maximum continious and higher limited overboost to cool the motor.

Not the same thing as maintaining constant rpm at the overboost condition to realize the speed gain. In otherwords, when you set the engine to say, 1.35ata @ 2400U/min, you will adjust pitch to maintain a constant 2400U/min rpm to achieve best performance.



You must change pitch, rpm, or airspeed. If you increase rpm and airspeed, you must coarsen the pitch to keep rpm steady and airspeed increasing.....

That is how it works.

Same as a CSP. Reduce pitch to increase rpm and then coarsen the pitch as the speed increases to take advantage of the new rpm setting.

Same as it ever was and what I have repeated for several pages....

RPM stays constant....

They overloaded the super by increasing rpm at high altitude, the engine will have a cooling problem in a short time period.

A complete sidetrack as to how they are using the propeller and rpm to gain speed.

See?

See what?

Look at the Operating Notes for any aircraft.

If I am in cruise flight and want to achieve maximum level speed, then I must change the settings from cruise manifold pressure and rpm to a higher limited overboost manifold pressure and rpm.

Performance occurs at the specific manifold pressure and rpm setting.

You must maintain that rpm setting at a constant rate.

In a selectable pitch propeller, this is done manually by coarseing the pitch to maintain a constant rpm.

Is that hard to understand or something? It must be as we have multiple pages on this simple concept.

so RPM doesnt stay constant if pilots increase RPM at higher alts for more speed?

Of course it does. Best thing of keeping something unchanged is to change it, obviously.

I am trying hard to figure out why is this happening - reading this:

...I reckon Crumpp is not aware of the fact that by coarseing the pitch in the 109 the rpm drops accordingly.

Crumpp wake up!

Not if you are using it right.

Rpm will drop as the speed increases and the propeller begins to drive the engine. Coarsen pitch as the rpm begins to drop to maintain it.

I really start to believe we are losing something in translations or then I am only one. (Honestly I needed to take dictionary on my hand)

You must maintain that rpm setting at a constant rate.
- You must pursue that (efficient) rpm setting at a continuous rate (by manual pitch)

Its like Bouy rocking after a wave.
Wave hits Buoy -> it must maintain its stability at a constant rate

I really believe that most of us are speaking of the same thing but everybody have their eyes fixed on one single point of this issue

Not really, Only thing that makes it hard to read is Crumpp's atempt at trying to redefine the word 'maintain'.. Clinton would be proud! ;)

Interesting how this only now becomes a measure to cool the hydraulic supercharger, according to our resident aviation expert; still it is correct that the hydraulic coupling of the DB supercharger led to problems with overheating that the pilots needed to control by constantly altering rpm - not maintaining it.

Wrong; the pilots were needing to adjust rpm and pitch constantly to periodically rest the supercharger - any gain in speed was a by-product, not a tactic.

eh?

rpm will increase as speed increases not drop, until you adjust pitch, at least my 109 does anyway lol

OOPs, yes it should increase and you coarsen the pitch to keep rpm constant.



Correct.

They are changing rpm to an overboost condition, adjusting pitch to maintain the overboost rpm setting, and then reducing it let things cool down.

When they reduce rpm, they also adjust the pitch to maintain the new rpm setting as the aircrafts speed changes.

:rolleyes:

Maybe it is time for your stability and control documents.

You know, the ones with the picture of the Spitfire and the general comments that have nothing to do with the Spitfire?

Perhaps this might help

http://i91.photobucket.com/albums/k3...e/maintain.jpg

is different to

http://i91.photobucket.com/albums/k3...e-page-002.jpg

but, rather than keeping things

http://i91.photobucket.com/albums/k3...t-page-002.jpg

Crumpp likes to change context and words to maintain whatever argument he thinks he has.

Bingo! ;)

Nope, it's incorrect. Hydraulic couplings generate more heat to the oil during slip (friction generating heat), but it doesn't mean the oil was overheating, because

a) the fact that increased oil cooling requirements could be and were compensated by increasing oil cooling capacity (note the rather sizeable oil radiator on the 109)

b) the fact that at and above FTH the hydraulic coupling has minimum slip (in the order of about 3%) and therefore, the heat load is only marginally different from a fixed ratio mechanically geared supercharger. If there's no extra friction, there is no extra heat, simple as that.

This is evident from DB heat charts, i.e. the DB 605A lubricant heat transfer was 65 000 kcal/hour at sea level, when the hyd. supercharger was operating at maximum slip, but only 43 000 kcal, or roughly 2/3s at FTH, where the hyd. supercharger was operating at minimum slip.

Bull on all accounts.. the supercharger itself does not "overheat", its just a piece of magnesium alloy and does not operate at extreme temperatures, neither does it have any sort of forced cooling.

Secondly, increasing revs by about 200 rpm _was_ a sanctioned tactic that increased the supercharger capacity and altitude output of the engine, as noted in the November 1940 LWHQ notice that has been already posted, and led to some noteworthy speed increase above rated altitude, as noted by the 109F manual. And if the speed increases, the pitch angle does need to be changed of course, just as at any rpm and at any altitude, when the speed increases.

All they did was manipulating the pitch to let rpm increase, and then - by when the rpm has increased - manipulating pitch to compensate for increase airspeed AND maintain increased rpm.

Exactly.

I have been saying this for how many pages now??

:rolleyes:

This community is toxic.

No. You were saying that they were changing the pitch to keep it constant. That is something completely different.

The rpm won't stay up when you coarsen up, it will drop when you touch the rpm lever again. That's all I am saying.

Go back and read what I wrote. You did not understand it and keep misinterpreting something.


Second thought, don't...

Just keep believing you have the concept and are correct. Welcome to the ignore list.

So how exactly do you change the rpm to keep it constant again? :grin:

About the supercharger...

At "normal flying alttitude" I really don't believe that pulsing engine rpm to add small boost to supercharger rpm would be efficient. As it takes its RPM directly from engine RPM there would be no (turbo)lag and it would not transfer the "kick" when coarsening the pitch.
Centrifugal Supercharger (as in DB601) gives more boost the higher the rpm is and because the rpm relevant of the Engine RPM, the extra boost is lost when engine RPM is dropped.

Still if there is some changes on superchargers own pitch on level flight this is incorrect but I would believe that Chargers pitch changes only by alltidute Untill it hits its top performance pitch. --> After this point the extra oxygen was given by water-Methanol injection? because german belived that extra stage or added turpo would be heavier for added high alt performance than MV-50

Cruising at Dauerleistungen 1.15ata @ 2200U/min our pilot wants to increase speed.

So he puts the propeller to fine pitch until the rpm gauge reads 2400/U min and then increases manifold pressure until the manifold pressure gauge reads 1.3ata.

The airplane acelerates and he coarsens the pitch to maintain 2400/U min.

Pretty simple stuff.....

So we have gone from Steinhilper talking about maintaining max climb rate by adjusting prop RPM (which makes a pulsating resonance indicating frequent changes of RPM) to 'cruising' at 2200 RPM and simply changing to 2400 RPM to maintain and Crumpp hasn't changed the story how?

Our pilot flies at 7km, he's struggling with performance up there, way above the FTH, his manifold pressure will not read 1.3 ata in the first place.

We're not talking about Dauerleisting below FTH. Down there the fiddling with rpm doesn't help much. You don't want to keep the engine at 2400/U, you want to coarsen down afterwards (your rpm drops down again), keep that speed and repeat that whole process again. That is the difference between 'change' and 'maintain'. Sorry I can't explain that any better or simpler. Just read what Steinhilper is saying and doing.

Only one way..

He has to redefine the meaning of 'maintain'


Clinton would be proud! ;)

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

Also that there would be a corresponding oscillation in engine sound. Steinhilper footnotes this.