View Full Version : Prop pitch control: fine VS coarse

02-08-2005, 09:10 AM
Been re-reading Pierre Clostermans The Big Show again. Also been reading Winged Combat by Arthur Bishop. Both flew Spitfires of one kind or another so I've got some good points of comparison. Closterman was an ace, Bishop was a more average combat pilot (three or four kills I think - representative of the vast majority) but he made it through alive so kudos to that.

Anyways, they make numerous mentions to switching between fine and coarse pitch for landings and flight. Anyone who's more knowledgeable on this subject?

I'd like to know what the difference is, how it works, and how it relates to the pitch control system in FB/AEP/PF.

02-08-2005, 09:27 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>I'd like to know what the difference is, how it works, and how it relates to the pitch control system in FB/AEP/PF. <HR></BLOCKQUOTE>

Hmmm... it's a bit like a gearbox in a car, only different http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif Well, not that different actually, but there's more to it. Read this to learn more: http://www.airwarfare.com/Sims/FB/fb_cem.htm

02-08-2005, 10:00 AM
I've read that (before too) and become more confused than I was before.

They say that at 100% the prop bites the least. That makes no sense...100% is where the default is on CPS aircraft and thats where I find you get maximum power. At 50% you can be at 110% throttle and you just aren't seemingly doing anything...

02-08-2005, 10:06 AM
This is probably a reference to very early Spits, that used a 'two speed' prop (as opposed to Constant Speed Prop). The propellor could be set either 'course' or 'fine' (high speed, cruise/high power, climb). This was a significant advancement over the fixed props of the era (try the P.11c or Tb3 for fixed props in FB) but was inferior to the 'infinitely' variable pitch of the early Bf109's (and obviously inferior to the constant speed units of later aircraft).

Though we don't have this system available in FB, you can get the idea if you fly a Bf109e in 'manual' mode, but only use two settings, such as 35% and 95%; the former is course and the latter is fine.

02-08-2005, 11:05 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>100% is where the default is on CPS aircraft and thats where I find you get maximum power. <HR></BLOCKQUOTE>

Yeah, you do. It's because that's where you get the minimum amount of propeller air resistance (i.e. least amount of friction), which in turn translates to maximum effective engine power output and propeller RPM. And this, in turn, usually gives you your maximum air speed as well.

You could, however, in a lossless medium, get even _more_ usable power when using coarse prop pitch with full throttle. But in RL you can't - or not as much as you'd like to anyway - because the engine can't overcome the added air friction introduced by coarsening the blade angle (that's because the prop's now "biting" more air and therefore "choking" the engine more too, with excess energy going into losses like heat etc.). Thus, your max. usable power - and airspeed - is at full throttle & full fine prop(s).

The situation changes, however, when you reach your cruising speed. Your airplane has forward inertia, which enables you to back off your throttle AND coarsen your blade angle at the same time, and still maintain your speed with these reduced power & prop settings. But bear in mind that you still can't just coarsen the prop and leave your throttle high to get more airspeed, because the coarse angle itself limits your usable power output, with all excess power wasted in form of friction, heat, etc. as I mentioned previously.

But what happens if you leave the prop pitch at, say, full fine and just back off the throttle? Well, you shouldn't, because you might then introduce the engine to something called "backloading". The term describes a situation where the _prop_ drives the engine instead of the other (the usual) way around. This happens easier than you might think in some circumstances (due to the airstream rushing past the airplane), and it reverses the forces in the engine and gearbox, possibly starving the engine of lubrication among other bad things! I'm not sure if this is a problem with inline powerplants, but radial engine drivers should be aware of this phenomenon.

Phew http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif Well, this is how I've understood the thing (which means badly). But since I'm only me, please correct me if I'm wrong, i.e. I'm talking all s*ite here... http://forums.ubi.com/images/smilies/35.gif

(EDIT: tried to clarify a couple of points & added a bit as well)

02-08-2005, 05:00 PM
Now I'm catching on....ok thats starting to make some sense to me http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Lignite: Both of these fellows were flying Spitfire LF IX's...and Arthur Bishop only flew the LF IX (or IXB as he called it http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif). I should double check on it however.

So on landings and takeoffs, should I use a coarser pitch? Would that be the thing to do?

02-08-2005, 05:15 PM
Its easier (in game) just to think of prop pitch as a 2nd throttle. 100% = most power 0% = no power.

02-08-2005, 05:22 PM
Just keep in mind what planes have a CSP and which ones have actual manual control. On the 109, which has the latter, I'm sure you know that you really need to lower it down from its default setting or else you will fry the engine, because you are actually controlling the prop's angle. However, 100% PP in CSP planes makes it so you're running at max RPM's...as your speed increases the PP decreases on its own, so you always hold maximum RPM's without overreving the engine. Lower settings are better for keeping the engine cool and crusing at better efficiency because it will keep it on a single RPM setting. Sorry IceFire if you already knew that, I know you're an experienced pilot here but I thought maybe that would help you out just in case.

As far as landing goes, I'm not sure. For some reason I'm thinking finer pitch, because a) I think I remember that from somewhere and b) even after 109's had auto PP, they would use manual during take off and landing, esp. during landing. I'm assuming this is so they could keep higher RPM's while running at a lower power setting....I could be totally off tho.


02-08-2005, 08:19 PM
In this sim, since prop pitch is not modelled very well, I just leave my pitch full fine all the time for maximun power. If it were done better, at higher altitudes you'd get better results from coarser pitches, but it don't work like that in this sim.

02-08-2005, 09:10 PM
Okay, now I'm confused ...

When I take off, do I want closer to 0% or 100%? After that, at cruising altitude ... closer to 0% or 100%? And in combat?

02-08-2005, 09:45 PM
Skycat, its OK to be confused, especially when mis-information is given (as above).

We really should petition Oleg to improve/change the wording used in the blue text. It REALLY screws people up (apparently).

In aircraft with Constant Speed Props, it IS NOT POSSIBLE to directly control the blade angles of the prop (also known as 'prop pitch'). In a CSP aircraft, you are directly controlling the engine RPM governor (the constant speed unit in the prop), which automatically adjusts the prop pitch by itself, depending upon the speed of the aircraft. Thus the blue text on the screen does not actually mean 'prop pitch', it is refering to percent of engine RPM

Skycat, to answer your question specifically, well, it can't easily be answered for all of the aircraft in the sim, please be more specific as to which type of aircraft you fly (in order to identify the prop control system).

Icefire, I'm not an expert on Spitfires, so I could easily be wrong, also, it could be that the pilots (Closterman, Bishop) are refering to the prop lever possibly incorrectly as 'prop pitch', much as people on the boards do. They probably are if flying SpitIX's, which I believe is a constant speed prop (thus it is not possible to 'coarsen' or 'fine' the blade angles directly, only adjust the RPM, and the CSP unit adjusts the blade angles accordingly)

Regardless, one normally wants to have fast horsepower available when landing, so a 'fine' prop pitch is required (remember, for a constant speed prop you don't choose a 'fine' pitch, you choose a high RPM setting).

Probably the best game description of 'Prop Pitch' (horrible term): http://people.ee.ethz.ch/~chapman/il2guide/cemguide/controllingrpm.htm

An excellent description of real-world Constant Speed Props (applies quite well to FB/PF): http://www.avweb.com/news/columns/182082-1.html

02-09-2005, 01:17 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>In aircraft with Constant Speed Props, it IS NOT POSSIBLE to directly control the blade angles of the prop (also known as 'prop pitch'). <HR></BLOCKQUOTE>

That's true, and the question _was_ about CSP-equipped planes, not variable-angle propeller systems in general. My mistake.

But let's still remember that the CSP RPM _too_ is maintained by varying the blade angle, albeit automatically, and a low throttle & high RPM setting is thus to be avoided in these aircraft as well - as is high throttle & low RPM - UNLESS manufacturer's data suggests otherwise.

Now THIS was my point actually http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

02-09-2005, 04:28 AM
Hi Ice fire

When landing try dropping prop pitch to 25% down to 10% it makes you lose speed very rapidly and you can land in the 1st third off the runway. Just started using it offline very recently before sometimes i used to overshoot becasue even at 0% throttle with the flaps down the Fw 190 still hung in the air reluctant to land chop the prop settings however and you can shed the speed very quickly.

02-09-2005, 05:35 AM
Real life SOP was/is to take-off and and land with prop in finest pitch setting(100%) so as to have the most power available for take-off or the potential go-around.

02-09-2005, 06:23 AM
When tha a/c is stationary and the props are in fine, the angle of attack of the airflow against the blade angle is at it's most efficient.
However when the a/c moves forward, due to the path the blade now makes through the air, the relative angle of attack of the airflow also moves forward, resulting in a lower angle of attack and therefore less drag against the prop., and so it tends to speed up.
Consequently, the faster the a/c moves through the air the more you need to coarsen the pitch.
Coarsen it too much and temps are likely to rise due to the drag of the prop.
If you tried to take off in coarse pitch, it would be like trying to drive away in 5th gear! Blade angle would initially be way too great and the a'c would take forever to accelerate, thats if you have'nt sent the temps through the roof due to the engine having to work hard against drag of the props and the lack of airflow cooling from your low speed !!

02-09-2005, 08:54 AM
Good points there, Messrs. wireman1 & The.Tyke...

02-09-2005, 09:18 AM
All the explainations of prop pitch and how it works in this thread are just fine but as a RL pilot, I don't find that coarsening the pitch in this sim has much effect on how the planes flies through the air. It does reduce the RPM as it should but that's about all. You get the best speed at all altitudes with full fine pitch in this game, which is not correct. At high altitudes in RL, if you have full fine pitch you just beat the thin, thin air to death ( because you need to take out a bigger bite in thin air ) and coarsening the pitch is much more efficient.
Not so in the game.

02-09-2005, 09:54 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Not so in the game <HR></BLOCKQUOTE>

Not entirely accurate. On several AC types(in game) you can add KPHs to your airspeed,at altitude, by dropping prop pitch down from fine.

Requires using CEM and higher realism settings. Must also take into consideration booster settings,throttle settings, and fuel mixture settings.

Doesn't accurately mirror real life dynamics but then again you're living in the IL2 world while playing, not the real one.

02-09-2005, 10:37 AM
the only time i use prop pitch is to manage formation flying, diving from high altitudes, and/or landing.

02-09-2005, 01:36 PM
I usually fly a Mustang. I use prop pitch to set the RPM's to where they should be according to the performance charts on the plane.

It's usually about 2500 rpm (75% prop pitch) for climb.

02-09-2005, 08:27 PM
I'll use prop pitch to lower RPMs to conserve fuel when running low and trying to get back to base.

Also, having buttons on my stick mapped to 0% and 100% Prop Pitch plus a quick drop to zero throttle helps in making an over-anxious bogey overshoot you, usually providing an easy six shot as he goes by and you wind prop pitch and throttle back up. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif