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eddiemac0
01-03-2005, 11:11 AM
Hey everyone,

I'm teaching myself complex engine management, and was wondering where I could find the different propeller characteristics, optimal RPM settings, and so on and so forth, for each aircraft; all in the interest of learning prop pitch.

Thanks.

eddiemac0
01-03-2005, 11:11 AM
Hey everyone,

I'm teaching myself complex engine management, and was wondering where I could find the different propeller characteristics, optimal RPM settings, and so on and so forth, for each aircraft; all in the interest of learning prop pitch.

Thanks.

Bikewer
01-03-2005, 06:07 PM
Much of this info was in the PDF file in the game folder, dunno about the newer aircraft.

For me, I just sort of seat-of-the-pants the thing. Find the tach for your particular aircraft. Most all will have a redline indicated. When you get to altitude, decrease the prop pitch till you get to an RPM figure that's in the optimal zone.

mroseland
01-03-2005, 06:48 PM

http://people.ee.ethz.ch/~chapman/il2guide/cemguide/intro.htm

flyinmick
01-03-2005, 08:12 PM
One thing that is inaccurate in this sim is the relationship between Manifold pressure and RPM. The pressure as measured in the engine intake manifold is static air pressure measured at the inside. If the engine is not running then the MP guage should show local atmospheric pressure. This does not happen in some of the maps on IL2. Atmospheric pressure drops 1" per thousand feet of altitude. Standard pressure at sea level is 29.92". Therefore, an aircraft sitting at an airfield 2000' above sea level should indicate 28" or so while at rest.
Start the engine, and you will see a drop in MP. Some of the energy in the atmosphere (experienced as pressure) in the manifold is now being directed along the manifold toward the engine. This moving air has increased DYNAMIC pressure and, in consequence, reduced static pressure since the energy in the air is the same, just being distributed differently. Open the throttle (which is choking or thottling the air supply to the engine) and more air is admitted into the manifold. MP will increase as the throttle is opened even more until MP will almost, though never quite, equal atmospheric pressure. As the aircraft climbs, MP will be reduced 1" per thousand.
Let's do a "run up" and check the prop. Advance the engine to 1700 RPM. You'll probably see about 21"MP or so at sea level. Pull the prop lever all the way back. You are looking for a reduction in RPM and an INCREASE in MP. The air in the manifold has slowed down, reducing it's dynamic and increasing it's static pressures.
In IL2, this effect is reversed and needs to be fixed!! Advance the prop again to High RPM and Low pitch and you should see the origional RPM/MP settings. Now time for a Magneto and a power check. Open the throttle and set MP to local atmospheric pressure. You did note that before you cranked, didn't you? On a P&W R2800 and all the other radials that I'm familiar with, you should get 2100 RPM. This means that all the cylinders are firing. If they weren't, the engine would not generate sufficient power to turn the prop that fast. radials are very smooth, even when they drop a jug, so this is the only way to really tell. Check the mags, one at a time, looking for a drop in RPM of no more than 125 RPM. Look at each actual engine when you do this and make sure there is no vibration. Reduce power and look at the ground under each engine to make sure that an oil cooler or line has not burst; the oil is at it's coolest and thickest and it's pressure highest during run up.
A constant speed prop governer works by balancing the drag of the rotating blades against the torque created by the engine. When the prop blade creates thrust, it is actually creating lift. The creation of lift creates induced drag in turn. As you advance the throttle, the engine increases it's RPM and so increases the airspeed of the prop blade. At some point, the RPM reaches the maximum permissable for the installation and, at sea level, this will happen well below Max MP, especially if supercharged. At this point the prop governer meters engine oil, under pressure, into the prop hub and forces the blades out of fine pitch. As MP, and therefore engine torque, increases the blades increase their pitch or angle of attack thus generating more lift or thrust.
In cruise, MP is reduced followed by RPM and a cruise power setting is set. 30" and 1800RPM is reasonable for an R2800. Mixture is reduced untill it begins to affect MP and then is increased slightly. There should be an Auto Rich and Auto Lean setting but it's not in IL2. Let's say you start do a loop. As you pitch up, airspeed decreases and the angle of attack of each prop blade is increased. The prop begins to slow, the governer senses this, allows oil to port from the prop hub back to the engine oil tank, pitch is reduced, angle of attack (and therefore drag) is reduced and RPM maintained. On the downhill side, the opposite occurs; AOA decrease for the prop blades reducing drag and tending to increase RPM. The governer pumps oil into the dome forcing the blades into a coarse pitch restoring AOA and drag and maintaining RPM. At some very high airspeed, of course, the prop blades will be on the coarse pitch stops and it will no longer govern, resuting in an overspeed if power is not reduced.
At no time should the prop be allowed to drive the engine. For reasons of lubrication, MP in inches should ALWAYS equal or exceed RPM in hundreds e.g. 30" & 1800 or 30/18. This does not apply at low airspeeds such as for landing. At high airspeeds, operating "under square" will trash an engine inside of a minute.
Hope all this helps.

Crash_Moses
01-03-2005, 09:06 PM
I did a small amount of research on this myself and have found, in practice, that a one to one ratio between throttle settings and prop pitch works pretty well (i.e. 70% throttle and 70% prop pitch.)

I realize, of course, that this is not 100% accurate and that many variables are involved (altitude, supercharger level, manifold pressure, fuel mixture, etc.) However, it works pretty well in the middle of furball.

The main reason to use it is to keep your engine from overheating either in battle or while nursing a damaged plane back to base (more of the latter probably).

I like to cruise with both values somewhere between 75% and 80%. You don't really gain that much speed by setting everything to 100% and it's nice to have a little headroom when you need rapid acceleration which is really what you get when you max your engine out.

Also, prop pitch comes in handy when you have a tailgater and you can't outrun him. Dropping your prop pitch and throttle to 0% will slow you down a lot faster than throttle alone. Just remember that it take a couple of seconds for your RPMs to come back up so you'd better be ready to shoot when your little buddy zips past you.

oldschool1992
01-03-2005, 09:08 PM
so what should the prop pitch be set at on the P51 flying at say 5K for max level flight speed with 110% power

oldschool1992
01-04-2005, 06:04 AM
bump, anyone out there????

Fliger747
01-04-2005, 06:29 AM
Despite the long and informative post above by 'flynmick' most people still misundestand how the props work and what the function of pitch control is. You are not, at normal power settings, directly setting a prop pitch! What you are doing is setting a RPM, a rotational speed. The prop automatically changes angle with changes in throttle setting to absorb he power transmitted to maintain a constant engine RPM.

Some believe that you slow down by moving the prop pitch to 'zero', which should be called minimum. That is actually moving in the direction of feather (not available on fighters) and results in less drag if the prop is driving the engine, as it would be if you cut the throttle!

MAXIMUM power and aircraft speed is obtained when you are running the thing at maximum RPM and manifold pressure (100% pitch/full throttle). The real engines weren't too tollerant of this for any period of time.

For range and engine life considerations moderate engine RPM and MP(throttle) were the norm for all flight regiems except takeoff and direct combat situations.

eddiemac0
01-04-2005, 07:41 AM
Well, ok, I think I understand the basic principles, but I still need some numbers; I can wreck a bf-109 with the slightest ease, just pop off the screw and run the throttle and pitch up. I can't seem to do it in a P-38J, F6F-5, A6M2-21, or A6M5 (so I'll get specific). I can over heat the engines at WEP, but that's about it. The American planes seems operate at any throttle at 100% pitch, and I can't read the gagues on the Zero. I want RPM numbers for economy cruise, cruise, and combat speeds. I would also like to know whether these planes have automatic RPM governance (aero-screws and the like), supercharger automation? I spent a good deal of time yesterday trying to destroy engines, and for the most part couldn't.
Thanks.

Jason Bourne
01-04-2005, 08:27 AM
well, AFAIK, the only plane were it is disastrous to set your own prop pitch is with the 109. For me though, i never really mess with the prop pitch except for the previosly mentioned instance of zeroing pitch to drop you speed instantly.

rurik
01-04-2005, 08:44 AM
This is my take on how it works in the game, (RL pilots can correct me here):
You want to maintain the best RPM setting for what you are doing and this is directly correlated to the air speed and the prop pitch.

As an example; I find that the best cruise setting for a Bf-109F is around 2200rpm and the best power setting is around 2600rpm. As you increase speed for a given prop pitch setting your rpm will rise, when it gets above your target rpm adjust the prop pitch down to maintain the desired setting. You will do the opposite when you reduce speed.

You will have to find out for yourself what works best on what aircraft, (use the QMB and experiment) unless you can find optimal rpm data on the aircraft you want to fly.

I hope that makes sense.

joeap
01-04-2005, 09:46 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by rurik:
This is my take on how it works in the game, (RL pilots can correct me here):
You want to maintain the best RPM setting for what you are doing and this is directly correlated to the air speed and the prop pitch.

As an example; I find that the best cruise setting for a Bf-109F is around 2200rpm and the best power setting is around 2600rpm. As you increase speed for a given prop pitch setting your rpm will rise, when it gets above your target rpm adjust the prop pitch down to maintain the desired setting. You will do the opposite when you reduce speed.

You will have to find out for yourself what works best on what aircraft, (use the QMB and experiment) unless you can find optimal rpm data on the aircraft you want to fly.

I hope that makes sense. <HR></BLOCKQUOTE>
Yup that's how I do it.

geetarman
01-04-2005, 10:57 AM
I believe the Zeno's Warbirds website has some engine performance charts for the main US fighters. There you will find all you need about proper RPM and MP for different flight regimes.

Very loosely, I find on US planes that prop pitch controls RPMs and throttle controls MP. You can run a P-51 up to 3000rpm (basically 100% prop pitch) and MP at 55"-60" almost all day with the rads open.

Was it like that in RL? I doubt it! I used to fiddle with it all on the Mustang. However, OL most guys don't and if you want to survive, you've got to push the plane. I run it at 100% all the time and never drop the MP below 45".

Darkbluesky
01-04-2005, 12:55 PM
Do you know another CEM guide on inet? I know the Vulgar one and the Eastern Skies.

Tx! I'm interested in radiator settings, supercharger.