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XyZspineZyX
08-27-2003, 08:00 PM
ok im postin this again since my last post for some reason didn't seem to make it to the forum i wonder why (this sucks to say the least)...

well it's all about prop pitch and the naive way it's modelled... suppose you're diving at 700kph it's clear your engine is working in the user zone... for all the non-engineers out there, that means your engine is actually acting as an air brake... now, drop your pitch, what you should get is your engine running in the red zone and your plane should slow down... it's like driving your car down a steep slope suppose your going at say 50kph and then kick your first gear in (in our analogy, this is like lowering your prop pitch), your engine should start crying and your car speed would be dramatically cut... forgive my rough example but the analogy should be clear enough for everybody to make something out of what I mean with the prop pitch thing...
any idea?
regards

XyZspineZyX
08-27-2003, 08:00 PM
ok im postin this again since my last post for some reason didn't seem to make it to the forum i wonder why (this sucks to say the least)...

well it's all about prop pitch and the naive way it's modelled... suppose you're diving at 700kph it's clear your engine is working in the user zone... for all the non-engineers out there, that means your engine is actually acting as an air brake... now, drop your pitch, what you should get is your engine running in the red zone and your plane should slow down... it's like driving your car down a steep slope suppose your going at say 50kph and then kick your first gear in (in our analogy, this is like lowering your prop pitch), your engine should start crying and your car speed would be dramatically cut... forgive my rough example but the analogy should be clear enough for everybody to make something out of what I mean with the prop pitch thing...
any idea?
regards

XyZspineZyX
08-27-2003, 08:05 PM
You're right Garbazz. I also think the present system is backwards; 100% pitch in the game is actually 0% pitch. Agree?

XyZspineZyX
08-27-2003, 08:09 PM
yes! in fact before posting il-2 i had to fire up il2 and check that thing out and make sure I was "in keep" with oleg's weird misconception about prop pitch and percentage http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

XyZspineZyX
08-27-2003, 08:19 PM
I think maybe the terminology is incorrect, should be coarse or fine. From what I can make out 100% in the game is fine which gives max rpm at low air speed. Prop angle changes to maintain same angle of attack (which is varied by power setting) at various airspeeds, the faster you go the coarser the angle. Or maybe I'm just confused cause I still havn't worked it out in the game.

XyZspineZyX
08-27-2003, 08:41 PM
garbazzz wrote:
- ok im postin this again since my last post for some
- reason didn't seem to make it to the forum i wonder
- why (this sucks to say the least)...
-
- well it's all about prop pitch and the naive way
- it's modelled... suppose you're diving at 700kph
- it's clear your engine is working in the user
- zone... for all the non-engineers out there, that
- means your engine is actually acting as an air
- brake... now, drop your pitch, what you should get
- is your engine running in the red zone and your
- plane should slow down... it's like driving your car
- down a steep slope suppose your going at say 50kph
- and then kick your first gear in (in our analogy,
- this is like lowering your prop pitch), your engine
- should start crying and your car speed would be
- dramatically cut... forgive my rough example but the
- analogy should be clear enough for everybody to make
- something out of what I mean with the prop pitch
- thing...
- any idea?
- regards

The analogy between car gears and prop pitch only goes so far. And I'm not sure what you mean by "drop your pitch". Let's start clean here. If you're diving at 700kph and your pitch is increased to full "fine" (100% in the game) then your engine is gonna over-rev. The engine is now being over-spun by the prop. If you coarsen the pitch before going into the dive by a good amount you keep the engine from over-revving. And it will act somewhat as a break to slow the acceleration of the plane in the dive. But the plane is still gonna pick up speed. This is what happens in the sim. How the percentage figures are assigned to pitch isn't really important as long as you know that 100% is full fine and anything lower is coarsening the pitch. Not terribly naive IMHO.

XyZspineZyX
08-27-2003, 09:16 PM
I agree. The analogy whith a car is corret but
the propeller doesn't act a brake during the dive.
The weight of the plane win and put the engine in
overrun.

saluti
Klotsche

XyZspineZyX
08-27-2003, 09:25 PM
LilHorse wrote:
- If you coarsen the pitch
- before going into the dive by a good amount you keep
- the engine from over-revving. And it will act
- somewhat as a break to slow the acceleration of the
- plane in the dive. But the plane is still gonna pick
- up speed. This is what happens in the sim. How the
- percentage figures are assigned to pitch isn't
- really important as long as you know that 100% is
- full fine and anything lower is coarsening the
- pitch. Not terribly naive IMHO.

I think you are missing a few details here... let's forget about the dive and suppose for some reason your plane is flying level at a fair high speed, say 700kph... this way we won't have potential enery getting in the way because of the plane being in a dive, suppose you've just come out of a dive... now, it's clear your engine is being overspun by the overflow, and the loss of kinetic energy (ie your plane slowing down) is partly due to the prop acting as an airbrake... if you increase your pitch (that is, you lower that silly x%) a higher momentum is applied to your prop, hance making it accelerate and taking it to a faster regime... that means your engine is absorbing more energy in the time unit than before from the kinetic energy pool, and over time that would cause the plane to slow down FASTER at the expense of your engine being taken deeply into the red zone... the car-and-slope analogy i brought up before is totally legitimate

XyZspineZyX
08-27-2003, 10:19 PM
garbazzz wrote:

- I think you are missing a few details here... let's
- forget about the dive and suppose for some reason
- your plane is flying level at a fair high speed, say
- 700kph... this way we won't have potential enery
- getting in the way because of the plane being in a
- dive, suppose you've just come out of a dive... now,
- it's clear your engine is being overspun by the
- overflow, and the loss of kinetic energy (ie your
- plane slowing down) is partly due to the prop acting
- as an airbrake... if you increase your pitch (that
- is, you lower that silly x%) a higher momentum is
- applied to your prop, hance making it accelerate and
- taking it to a faster regime... that means your
- engine is absorbing more energy in the time unit
- than before from the kinetic energy pool, and over
- time that would cause the plane to slow down FASTER
- at the expense of your engine being taken deeply
- into the red zone... the car-and-slope analogy i
- brought up before is totally legitimate

Okay, let me see if I'm following you. You've just come out of a dive and let's say your engine is over-revving. If you pull out and fly straight and level and yes your prop will act as an airbrake and slow you down. Now it has been my experience that if you lower that silly x% (coarsen the pitch) your engine should not over-rev. And how fast you slow down can be due much in part to the optimal pitch of your prop for a given amount of forward motion. A more coarse pitch (that is, somewhere below 100%) may allow you to DEcelerate SLOWER than if it were at 100% pitch or at a pitch lower than the "optimal" pitch you have it set to for your given forward speed.

XyZspineZyX
08-27-2003, 11:01 PM
garbazz...you need to clarify whether you are talking about VVS planes or LW planes. The prop pitch controls are different types of mechanisms.

http://home.cogeco.ca/~jkinley/rcafpost.jpg

XyZspineZyX
08-28-2003, 12:00 AM
pik_as wrote:
- You're right Garbazz. I also think the present
- system is backwards; 100% pitch in the game is
- actually 0% pitch. Agree?
-
-
Oleg stated that this is in fact the case, not long after FB was released. IIRC it stems fom someone in the dev team getting confused with the programming/spec. It was supposed to be fixed in the patch....... er Oleg????



<CENTER>


<IMG SRC="http://www.apqa16.dsl.pipex.com/sig5.jpg"


The world is your lobster, Terence.

XyZspineZyX
08-28-2003, 09:47 AM
Fillmore replied to my other post and what he pointed out makes perfect sense, it was me who was mistaken and fooled by that odd percentage indicator working backwards, hence, let's clarify this once for all:

0%, COARSE pitch: HIGHEST gear
100%, LIGHT pitch: LOWEST gear

Thanks Fillmore! /i/smilies/16x16_smiley-happy.gif /i/smilies/16x16_smiley-happy.gif

michapma
08-28-2003, 09:58 AM
Hi guys,

garbazzz, you are close but there is something you are overlooking. Since you haven't specified I am going to assume you are referring to Russian or American aircraft, most of which have constant-speed propellers. If you are talking about German aircraft there are more options, including variable-pitch aircraft such as the Emils. As has been noted, the different mechanisms have to be considered differently.

So, assuming the constant-speed prop, which work much like many modern aircraft prop systems, you do not directly control propeller pitch. Instead, you control the setting of a governer, and it is basically an rpm control. You set the desired rpm by adjusting the lever, and the governer uses a system&mdash;usually of flyweights, springs and oil pressure&mdash;to alter the prop pitch in order to get that rpm. The prop is only reasonably efficient within a certain range, so there are mechanical stops. (There are exceptions to this on modern aircraft, which are irrelevant for us, and on bombers, which can feather their props if an engine stops, to prevent it from catching too much air.) When the prop hits its coarsest (highest angle) or finest (lowest angle) settings, the governor can do no more to regulate engine rpm.

The thing is that with a constant-speed prop you have no direct control over prop pitch, although some aircraft could switch over to manual control for emergency procedures (the P-40 is an example in real life). In FB, when you set 0% with a constant-speed prop you set the governor to min rpm, and full rpm (redline) when you hit 100%. Try it, I happen to know that for the I-16 if you are cruising at "100% prop pitch," which actually means "100% of redline," then your rpm gauge will go off the scale, which is (silly or not) where the max rpm setting is. If you reduce to 70%, the governor coarsens the prop pitch, loading the engine and rpm drops to closer to 1800rpm.

Now what happens in your scenario, that is, the 700kph or so dive, is that the prop governor already has the blades set to their coarsest pitch! You are right that the airstream windmills the prop and tends to overrev the engine. If you dive with full throttle your engine will overrev, and it doesn't matter if you use 0% or 100%, because of the windmilling and overrevving the prop gov has the pitch at its coarse mechanical stop trying to get that rpm back down to at least redline.

That's why in a dive the only way to keep your engine from overrevving is to throttle back and not build up such ridiculously high speeds. By the way, the only way to use the prop to brake even harder by setting it to full prop pitch is if you have a system that allows you manual prop control, such as in the 109s.

I'm not saying that the prop systems are modeled 100% accurately. They're not. The engines don't detonate, for example. You can have full manifold pressure and set min rpms and no detonation occurs. You can overrev your engine and in my experience nothing occurs. Engine damage seems to come in the form of overly high manifold pressure and poor cooling, as well as structural damage from shells and shrapnel.

The whole 0&ndash;100% "prop pitch" labeling is very unfortunate. In constant-speed props and some of the automatic German designs, it should say 100% rpm or something similar. In variable-pitch systems such as 109s in manual mode, the 100% prop pitch is okay.

I'm writing this stuff up in a CEM guide, I hope to have it done in the next few weeks.

Hope that helps,
Mike

<table width="100%" border="0" cellspacing="0" cellpadding="10"><tr valign="middle" bgcolor="#3e463b"><td height="40" colspan="3" align="center">The ongoing IL-2 User's Guide project (http://people.ee.ethz.ch/~chapman/il2guide/)</a></td></tr><tr bgcolor="#515e2f"><td width="40%">FB engine management:
Manifold Pressure sucks (http://www.avweb.com/news/columns/182081-1.html)
Those Marvelous Props (http://www.avweb.com/news/columns/182082-1.html)
Mixture Magic (http://www.avweb.com/news/columns/182084-1.html)
Putting It All Together (http://www.avweb.com/news/columns/182085-1.html)
Those Fire-Breathing Turbos (Part 1 of 6) (http://www.avweb.com/news/columns/182102-1.html)</td><td align="center">

‚ =69.GIAP=Chap‚

69.GIAP (http://www.baseclass.modulweb.dk/giap/)</p></td><td width="40%" align="right" valign="top">Hardware:
Flight Simulation Performance Analyzed (http://www.simhq.com/_air/air_062a.html)
Building a home-made throttle quadrant step by step (http://forums.ubi.com/messages/message_view-topic.asp?name=us_il2sturmovik_gd&id=zkavv)
Sound Can Be Hazardous for Games (http://www6.tomshardware.com/game/20030405/index.html)</td></tr></table>

XyZspineZyX
08-28-2003, 01:27 PM
So:if I understand this correctly;

On planes in which we directly control the prop pitch.
ie manual control of prop pitch, US and USSR planes.
When the plane is moving forward:

100% prop pitch= prop blade is almost flat to the air flow, i.e. if the aircraft is moving forward and the propeller is stationary it is offering the most resistance to forward speed of the plane. but I think here is the confusion. if the engine is running, turning the prop, there is actually less air resistance(low pitch), in the direction of rotation, to the turning prop, as it is biting less air with each rotation, which allows the engine to reach maximum rpm ie hp, which increases the rpm of the propeller, giving maximum forward speed, even though it is biting less air with each rotation, there are many more rotations per unit of time.


0% prop pitch, prop blade is parallel to direction of plane forward travel, and this is when, if aircraft is moving and propeller is not turning it is considered 'feathered'. But if the engine tries to turn it, it meets with a lot of resistance to rotational speed, which, because of the load,lowers the rpm thus hp of engine.

confusion is coming into play in the wording
in this game, in my opinion

100%=LOWest pitch setting
(but this IS the lowest pitch of the blade as it meets the air in it's DIRECTION OF ROTATION, not the direction of flight, the wing of a plane can be said to have a low pitch, called AOA, when moving forward in level flight)

0%=HIGHest pitch setting
(opposite of the above)

an unfortunate combination of words and numbers....

and now you know why it was so hard for the Wright brothers to figure it out.

Note of interest, if you had enormous HP you could turn a prop at 1% pitch and really haul a$$.

I hope you'll understand me, but as the C of FMOC said:

If you understand what I just said, then perhaps I misspoke

Message Edited on 08/28/0312:57PM by RxMan

michapma
08-28-2003, 01:46 PM
RxMan,

I probably didn't make it clear enough in my long post. There is no manual control of the prop pitch in constant-speed prop systems. This includes every Russian and American plane I can think of in FB. You are always controlling rpm with these planes, and not prop pitch.

Therefore, think of it this way:
0% - minimum rpm
100% - maximum rpm (redline)

Cheers,
Mike

<table width="100%" border="0" cellspacing="0" cellpadding="10"><tr valign="middle" bgcolor="#3e463b"><td height="40" colspan="3" align="center">The ongoing IL-2 User's Guide project (http://people.ee.ethz.ch/~chapman/il2guide/)</a></td></tr><tr bgcolor="#515e2f"><td width="40%">FB engine management:
Manifold Pressure sucks (http://www.avweb.com/news/columns/182081-1.html)
Those Marvelous Props (http://www.avweb.com/news/columns/182082-1.html)
Mixture Magic (http://www.avweb.com/news/columns/182084-1.html)
Putting It All Together (http://www.avweb.com/news/columns/182085-1.html)
Those Fire-Breathing Turbos (Part 1 of 6) (http://www.avweb.com/news/columns/182102-1.html)</td><td align="center">

‚ =69.GIAP=Chap‚

69.GIAP (http://www.baseclass.modulweb.dk/giap/)</p></td><td width="40%" align="right" valign="top">Hardware:
Flight Simulation Performance Analyzed (http://www.simhq.com/_air/air_062a.html)
Building a home-made throttle quadrant step by step (http://forums.ubi.com/messages/message_view-topic.asp?name=us_il2sturmovik_gd&id=zkavv)
Sound Can Be Hazardous for Games (http://www6.tomshardware.com/game/20030405/index.html)</td></tr></table>

XyZspineZyX
08-28-2003, 02:03 PM
But I think the point being,
when you move that lever the prop pitch changes,
no matter how many steps it goes through to get there.

michapma
08-28-2003, 02:53 PM
RxMan, I read your post more closely. You said many things right but a few things wrong. I agree with your main point, which I take to be that the numbering system is unfortunate. /i/smilies/16x16_robot-happy.gif My point is that in most aircraft you need not think of prop pitch, but rather rpm.


Please allow me to see if I can clear up some things I think might still be unclear. I hope it helps more than it hurts. /i/smilies/16x16_robot-wink.gif I am only going to discuss constant-speed props.

To begin with, let's look at which angle prop pitch measures. I made this little diagram for my guide:

http://people.ee.ethz.ch/~chapman/il2guide/images/fmbguide/proppitch.gif


Prop pitch measures the angle between the plane of blade rotation and the angle of propeller chord, chord meaning the line drawn from the leading edge to the trailing edge. Actually the propeller changes pitch along its length, so this is just a representative chord for the entire blade length.

The mechanical stops are not set at 0‚? and 90‚?! As an example I'll use the Curtiss prop used on the P-40 since I have a handbook here. The prop can be adjusted by the governor through a 30‚? arc, between 24.5‚? (fine pitch) and 54.5‚? (coarse pitch). If you could control the prop manually (you could in the real thing) minimum prop pitch would be 24.5‚?, and maximum prop pitch would be 54.5‚?. The reason that the stops do not swing through 90‚? is because it is out of the useful range of the prop, meaning that the prop efficiency would be terrible and the forces at angles much farther during engine operation might even cause enough stress to start breaking things.

Think of the 0 and 100% any way it helps you, but just be sure that you know that lower prop pitch (smaller blade angle) means less load on the engine and thus higer rpm.

Here is how it works in FB:

Variable-pitch prop (such as 109 in manual mode)
0% - coarsest prop pitch, low rpms
100% - finest prop pitch, high rpms

Constant-speed props and everything else
0% - low rpms
100% - high rpms

In constant-speed props, if the rpm dips below the given rpm setting the governor will try to increase the prop pitch to bring the rpm back up to the desired setting. If rpm is too high, the guv tries to coarsen the prop pitch to reduce rpms to the desired setting. I say try because the stops might be reached.


You wanted to explain some things with airflow. You are right, the propeller has two components of movement: forward (with aircraft airspeed) and rotation. Thus the relative wind (the airflow that the propeller sees) depends both on rpm and aircraft airspeed. That's why in the diagram the Vpropeller is not coming in exactly opposed to the Vaircraft. But you can see that if the prop pitch is increased (counter-clockwise in the diagram), the angle of attack will increase, and that increases the drag, loading the engine and decreasing rpm. Decreasing prop pitch has the opposite effect.

Feathering is a special feature of engines that might be shut off in flight, especially on multi-engined aircraft. You only have to bother with it in bombers in FB. Feathering allows the prop to go beyond the normal coarsest mechanical stop, to a setting close to 90‚?.

My understanding, and I could be wrong here, is that rpm is the dominant factor in the production of thrust. effte posted yesterday that airplane engines are designed to develop max torque at the redline, which makes good sense. Since power is directly proportional to rpm and torque, you get max power at max rpm and max torque, which occurs at redline. That usually coincides with a fine prop pitch, at least in level flight.

I think from your explanations you had most of this right, I just felt like writing an essay. /i/smilies/16x16_robot-very-happy.gif

Regards,
Mike

<table width="100%" border="0" cellspacing="0" cellpadding="10"><tr valign="middle" bgcolor="#3e463b"><td height="40" colspan="3" align="center">The ongoing IL-2 User's Guide project (http://people.ee.ethz.ch/~chapman/il2guide/)</a></td></tr><tr bgcolor="#515e2f"><td width="40%">FB engine management:
Manifold Pressure sucks (http://www.avweb.com/news/columns/182081-1.html)
Those Marvelous Props (http://www.avweb.com/news/columns/182082-1.html)
Mixture Magic (http://www.avweb.com/news/columns/182084-1.html)
Putting It All Together (http://www.avweb.com/news/columns/182085-1.html)
Those Fire-Breathing Turbos (Part 1 of 6) (http://www.avweb.com/news/columns/182102-1.html)</td><td align="center">

‚ =69.GIAP=Chap‚

69.GIAP (http://www.baseclass.modulweb.dk/giap/)</p></td><td width="40%" align="right" valign="top">Hardware:
Flight Simulation Performance Analyzed (http://www.simhq.com/_air/air_062a.html)
Building a home-made throttle quadrant step by step (http://forums.ubi.com/messages/message_view-topic.asp?name=us_il2sturmovik_gd&id=zkavv)
Sound Can Be Hazardous for Games (http://www6.tomshardware.com/game/20030405/index.html)</td></tr></table>

XyZspineZyX
08-28-2003, 04:41 PM
Thanks gentlemen for taking out the time to answer my question and help me get a better understanding of this prop matter, in particular I'd like to thank Michapma for his very clear explanation, thanks cap'!

michapma
08-29-2003, 09:07 AM
I'll bump this one because it seems that it was hard for garbazzz to find, and he started the thread over.

I also want to add that a knowledgeable someone advised me to leave the car analogy alone in order to stick to a factual discussion. That analogy never made thorough sense to me, and ever since I read the article in my sig (Those Marvelous Props) I have realized that it's nowhere near as useful as a simple look at the constant-speed prop system. In the past I've tried to work with it when people bring it up in order to encourage them to think about it, but I think the advice is good to just avoid it. It only confuses.

Cheers,
Mike

<table width="100%" border="0" cellspacing="0" cellpadding="10"><tr valign="middle" bgcolor="#3e463b"><td height="40" colspan="3" align="center">The ongoing IL-2 User's Guide project (http://people.ee.ethz.ch/~chapman/il2guide/)</a></td></tr><tr bgcolor="#515e2f"><td width="40%">FB engine management:
Manifold Pressure sucks (http://www.avweb.com/news/columns/182081-1.html)
Those Marvelous Props (http://www.avweb.com/news/columns/182082-1.html)
Mixture Magic (http://www.avweb.com/news/columns/182084-1.html)
Putting It All Together (http://www.avweb.com/news/columns/182085-1.html)
Those Fire-Breathing Turbos (Part 1 of 6) (http://www.avweb.com/news/columns/182102-1.html)</td><td align="center">

‚ =69.GIAP=Chap‚

69.GIAP (http://www.baseclass.modulweb.dk/giap/)</p></td><td width="40%" align="right" valign="top">Hardware:
Flight Simulation Performance Analyzed (http://www.simhq.com/_air/air_062a.html)
Building a home-made throttle quadrant step by step (http://forums.ubi.com/messages/message_view-topic.asp?name=us_il2sturmovik_gd&id=zkavv)
Sound Can Be Hazardous for Games (http://www6.tomshardware.com/game/20030405/index.html)</td></tr></table>