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View Full Version : Prop Pitch, Again, sorry.



medialab
01-28-2009, 05:08 PM
Hi. I know there have been other posts about this but I havent found a simple, non-debated, explanation of how prop pitch works or an understanding of how it affects aircraft performance.

This may be wrong, but this is the way I understand it at the moment:

100% pitch (in game) gives the most thrust at low altitude and low speed. so for takeoff, you would use 100%throttle/100%pitch. But as airspeed increases, this pitch angle actually adds to aerodynamic drag so even if you are max'd on throttle and pitch(100%) you could go faster by changing prop angle (pitch<100%)? is this somewhat correct?

Also why do RPMs decrease as you lower prop pitch (<100%)? Aren't you in effect making the prop "bite" less, reducing the workload for a given throttle setting (less engine drag) which would make RPMs increase?

Also, a feathered prop IS definitely different than a 0% pitch prop, right? A feathered prop turns the blades neaerly parallel to airflow to reduce drag significantly and a 0% pitch prop is nearly 90degrees rotated from that so that there is very little thrust product. is this correct?
I may be oversimplifying things and may just be flat out wrong.

Sorry, I am kind of slow with this, I am just trying to get a simple understanding of how this works. Thanks.

medialab
01-28-2009, 05:08 PM
Hi. I know there have been other posts about this but I havent found a simple, non-debated, explanation of how prop pitch works or an understanding of how it affects aircraft performance.

This may be wrong, but this is the way I understand it at the moment:

100% pitch (in game) gives the most thrust at low altitude and low speed. so for takeoff, you would use 100%throttle/100%pitch. But as airspeed increases, this pitch angle actually adds to aerodynamic drag so even if you are max'd on throttle and pitch(100%) you could go faster by changing prop angle (pitch&lt;100%)? is this somewhat correct?

Also why do RPMs decrease as you lower prop pitch (&lt;100%)? Aren't you in effect making the prop "bite" less, reducing the workload for a given throttle setting (less engine drag) which would make RPMs increase?

Also, a feathered prop IS definitely different than a 0% pitch prop, right? A feathered prop turns the blades neaerly parallel to airflow to reduce drag significantly and a 0% pitch prop is nearly 90degrees rotated from that so that there is very little thrust product. is this correct?
I may be oversimplifying things and may just be flat out wrong.

Sorry, I am kind of slow with this, I am just trying to get a simple understanding of how this works. Thanks.

M_Gunz
01-28-2009, 05:18 PM
Prop pitch is not the same between all planes nor even between manual and automatic on those that have it,
so it's very easy to get a mixed-up picture if you think of it as one thing.

Good luck trying to get everyone to give you the same story. especially from those who only know full power operation.
That's another factor in the confusion. What you should do is try some things out where people said "do this and see".

julian265
01-28-2009, 06:44 PM
All aircraft with variable pitch in IL2 have a prop pitch governor (109 and 190 work differently).

The "pitch" setting does NOT directly control blade pitch.

The "pitch" setting (lever) tells the governor what RPM you want the engine to spin at, and the governor then continuously alters blade angle (real pitch) so that the desired RPM is achieved. (which is why RPM lowers as you decrease the "pitch" setting)

The tempest for example - 100% pitch (no boost) will give you 3150 RPM, and 0% will give you around 1700 - which is not feathered.

Lowering the "pitch" setting will increase angle, making it HARDER for the engine to turn.

Lowering engine RPM REDUCES engine output power in most cases. It also brings the engine to a more efficient operating speed.

In every case I've tested, the highest level speed is obtained with full power and pitch. Some claim that you should reduce pitch when diving above max level speed, but I have not tested it, and not noticed a difference when flying. I plan on doing some side by side testing online.

na85
01-28-2009, 06:51 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by medialab:
Hi. I know there have been other posts about this but I havent found a simple, non-debated, explanation of how prop pitch works or an understanding of how it affects aircraft performance.

This may be wrong, but this is the way I understand it at the moment:

100% pitch (in game) gives the most thrust at low altitude and low speed. so for takeoff, you would use 100%throttle/100%pitch. But as airspeed increases, this pitch angle actually adds to aerodynamic drag so even if you are max'd on throttle and pitch(100%) you could go faster by changing prop angle (pitch&lt;100%)? is this somewhat correct?

Also why do RPMs decrease as you lower prop pitch (&lt;100%)? Aren't you in effect making the prop "bite" less, reducing the workload for a given throttle setting (less engine drag) which would make RPMs increase?

Also, a feathered prop IS definitely different than a 0% pitch prop, right? A feathered prop turns the blades neaerly parallel to airflow to reduce drag significantly and a 0% pitch prop is nearly 90degrees rotated from that so that there is very little thrust product. is this correct?
I may be oversimplifying things and may just be flat out wrong.

Sorry, I am kind of slow with this, I am just trying to get a simple understanding of how this works. Thanks. </div></BLOCKQUOTE>

I've never seen a straightforward answer to this either.

But basically IIRC, in every plane except the 109, when you decrease pitch you are telling the engine governor to run the engine at a lower RPM. So, the governor adjusts the angle of attack of the blades to take a larger bite out of the air which loads up the engine, causing it to run slower.

Whether or not you get better speed when doing this is dependent on a lot of things.

Chevy350
01-28-2009, 07:23 PM
so does anyone know if lowering pitch in a dive or at really high altitude actually works? and what should i lower it to?

WTE_Galway
01-28-2009, 08:20 PM
Be careful reading explanations as a lot of people seem to assume the auto pitch in game works the same as the CSU fitted to modern planes (like you might get in FSX for example). This is not the case.

M_Gunz
01-28-2009, 08:43 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chevy350:
so does anyone know if lowering pitch in a dive or at really high altitude actually works? and what should i lower it to? </div></BLOCKQUOTE>

Take your favorite CSP equipped plane up to FTH, get it going as fast level as possible, roll over and pull till you're going
straight down. See what alt you start losing parts. Try it again except crank the RPMs back to 50% and see if you start losing
parts higher or lower. If you make tracks then you can be more sure. If you run UDPSpeed or UDPGraph then you can tell better.

Don't take anyone's word for it. That never works around here, someone else always knows different. Do it and see.

Buzzsaw-
01-28-2009, 08:44 PM
Salute

For Constant velocity props: (most western allied aircraft)

If Prop pitch works correctly in the game, then reducing pitch setting below 100% should give you more speed, or reduce overall drag allow you to retain speed better when your aircraft is currently exceeding its maximum level speed.

Ie. if the aircraft's maximum level speed at 5000 meters is 500 kph, and you are travelling at 600 kph, reducing prop pitch should theoretically allow you to retain the higher than max speed for a longer period.

This is because when at 100% pitch and over your max level, you are generating more drag with the prop than you are gaining in thrust.

Diving: Again, theoretically, if you are diving, keep prop pitch to 100% till you reach the max. level for the altitude, then reduce pitch. This should allow you to continue to accelerate at a faster rate in the dive, and allow you to retain the dive speed for longer.

Otherwise, in any situation where your current speed is less than the max for your alt, you will have better acceleration and power at 100% pitch.

German aircraft have different pitch control systems, and the game has allowed players to take advantage of the incorrect modelling of their systems.

The 190 can attain higher speeds, and climb better when prop pitch is varied manually, and throttle left at a constant. This is the opposite of the historical aircraft, which with its Kommandogerat control system, was best left in auto.

The 109 used to also have this advantage, but with the fragility of the 109 engine, it is generally not worth using manual pitch, unless you are prepared to take the risk of permanent damage as a result of a slight error.

TS_Sancho
01-28-2009, 09:54 PM
There is a lot of game specific info concerning prop pitch in this thread (I would like to see more posts like the thread I'm linking, its fantastic) http://forums.ubi.com/eve/foru...283/m/5641027835/p/1 (http://forums.ubi.com/eve/forums/a/tpc/f/23110283/m/5641027835/p/1)

K_Freddie
01-28-2009, 11:23 PM
I don't thinK this is modelled but here's the idea.
Most piston engines have a safe operation power band (RPM), where engine power and efficiency peak.
You can operate in this power band by various means.
- For fuel efficiency, you reduce throttle to say 50%, and increase prop pitch from say again, 50% upwards until the engine reaches the right rpm.
This is used cruising - the boring part of an escort mission.
- For Combat 'efficiency' (bugger the fuel economy) - max the throttle, and try keep the rpm in the band.
This is where the automatic pitch controls, CVP systems come in.

Also on some aircraft there is a manual turbo booster, which you have to set at different altitudes. All this does is increase the air volume forced into the engine, so that you can get the same engine power output that you get at ground level. The measurement is referenced to 1 atmosphere (ATA).
This is only operated above certain altitudes where the air is thinner/less dense. If you operate it at ground level you will increase the ATA 'pressure' above the engine's rated ATA, and it will pop.

http://forums.ubi.com/groupee_common/emoticons/icon_cool.gif

vassilisukharev
01-29-2009, 10:56 AM
This article cleared my prop pitch confusion:

http://mission4today.com/index...base&op=show&kid=249 (http://mission4today.com/index.php?name=knowledge_base&op=show&kid=249)

na85
01-29-2009, 11:45 PM
This is a great quote from vassilisukharev's link for anyone who wants clarification.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">
Prop pitch set at 95% and 2,800 rpm's is going to move the aircraft faster through the air than 100% and the same 2,800 rpm's. </div></BLOCKQUOTE>

M_Gunz
01-30-2009, 05:57 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by na85:
This is a great quote from vassilisukharev's link for anyone who wants clarification.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">
Prop pitch set at 95% and 2,800 rpm's is going to move the aircraft faster through the air than 100% and the same 2,800 rpm's. </div></BLOCKQUOTE> </div></BLOCKQUOTE>

Do you see the catch there? It won't *stay* at 2800 at 95%, he is doing a key-dance exploit to get that. Would it
work IRL? Do blades change pitch instantly IRL and then slow down? Would this be done in a real 109 pushing beyond
combat setting load then w@nking the prop control?