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Lucius_Esox
02-01-2004, 01:46 PM
Hello all,
I love the P40 but am unsure what is the most realistic setting for prop pitch, manual or auto? Flying manual prop pitch is rewarding but with the setup on the P40 it is very different to say the Bf series, i.e. it can do almost anything (apart from a power dive) without having to change from 100% on auto. Is this because in real life the pilot didn't have to do it? Sorry am not a techno head on these things.

Thx in advance. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Lucius_Esox
02-01-2004, 01:46 PM
Hello all,
I love the P40 but am unsure what is the most realistic setting for prop pitch, manual or auto? Flying manual prop pitch is rewarding but with the setup on the P40 it is very different to say the Bf series, i.e. it can do almost anything (apart from a power dive) without having to change from 100% on auto. Is this because in real life the pilot didn't have to do it? Sorry am not a techno head on these things.

Thx in advance. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

xTHRUDx
02-01-2004, 04:52 PM
keep the RPM's at 30 or below

aerick2
02-01-2004, 05:34 PM
I'm still getting myself used to manual prop pitch. Is 3000 RPM a good number to shoot for in most aircraft?

Lucius_Esox
02-01-2004, 06:14 PM
aerick,
Not really, no. It's about finding the "sweet" spot. This, from my experience, can only be done by experiment. Aiming to hit a constant 3000rpm in some planes will result in a knackered engine pdq. My original question was pretty dumb really I suppose I was just wondering about the prop pitch range via a vis the 109 series. In the G2 for instance I seem to use a lot more of the range (sometimes 45% or lower in dive) compared to the P40 where most of it's power seems to work between about a 100% to 75%? I'm just curious!

Raider_356th
02-01-2004, 06:54 PM
i run about 90% in all american planes. it allows the prop to bite the air more and i get more speed out of the bird, i was flyin the P-40 the other night, also noticed that she really needs alot of down trim too...

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ZG77_Lignite
02-01-2004, 07:10 PM
Some mis-information in this thread, imho.

The P-40 series and the Bf-109 series use completely different engine governing (RPM) control systems.

The Bf-109 is a variable pitch prop (manual mode) with a RPm governor retrofitted to control RPM (auto mode).

The P40 is a Constant Speed prop and is not affected by by auto/manual modes (this is in reference to Complex Engine Managment ON). The pilot (you) adjust the engine RPM to your preference, and the prop automatically adjusts itself to maintain that RPM. Historically (and arguably in FB), constant speed props develope the most horsepower when prop lever is full forward, also known as climb/combat power (and read incorrectly as '100% pitch' in FB).

There is an excellent and indepth article about all of these aircraft created by a gentleman named Michapma, my apologies as I've already lost the URL, but do a search for his name and you'll find it.

Maple_Tiger
02-01-2004, 08:36 PM
Most alied plane's did not have Manuel prop pitch.

Did you not notice there is no option for manuel prop pitch when your in the P-40, P-47, P-51, P-39 ,La5, La7 and yaks?

ElfunkoI
02-01-2004, 10:09 PM
Lower prop pitch results in less RPM. Means less faster. You won't "Bite". You "bite" air with higher RPM. You "increase drag of propeller" with lower RPM. Don't have basics of flight book here with me, its in car, but I've always not enjoyed this urban legend.

Lucius_Esox
02-02-2004, 03:26 PM
Thx 4 the help people that has cleared it up in my mind now. I did notice the lack of option for manual prop control but when moving the pitch up and down with a corrosponding rise/drop in revs I assumed this was manual control. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

DaBallz
02-02-2004, 04:13 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by ElfunkoI:
Lower prop pitch results in less RPM. Means less faster. You won't "Bite". You "bite" air with higher RPM. You "increase drag of propeller" with lower RPM. Don't have basics of flight book here with me, its in car, but I've always not enjoyed this urban legend.<HR></BLOCKQUOTE>

In real life the faster you turn the engine without over revving
the more power you make. It's that simple.
Now for the problems.....
If you turn your engine real fast it reduces the
life of the engine, increases fuel consumption
and there is really a "bite factor".

It goes like this, at high angles of attack
and low speed the prop will stall, yes just
like stalling the plane.
The RPM will surge and can overspeed. That's a good way
to burn a piston, throw a rod or more importantly
loose all thrust, stall and crash.
Playing with prop pitch when the situation
arizes can prevent it or delay it.

Also high engine/prop speeds will set up supersonic
shock waves long before the plane gets near
the speed of sound. At very high speeds
reducing the engine speed will make you
able to dive faster.
All P-51 race planes have the reduction gears
changed to allow higher engine speeds with
LOWER prop speeds to allow higher speeds, more bite
so to speak.

There is a point where the speed of a prop plane
has hit the wall, it's around 500mph.
The reason is that no matter how much power
you have the prop is at the limit of it's ability
to make thrust and any coarser pitch simply
won't provide thrust no matter how much
power you have.
Turning it faster and the tips go supersonic
and you get a huge drag increase. also along
with the drag increase you get nasty shock waves
that will likely pound your plane to junk in a few seconds.

So the absolute speed limit in level flight
for a prop plane is around 540mph. In a racing
P-51 you will need around 4,000hp to do it.

Da...

michapma
02-03-2004, 04:11 AM
Lignite is almost spot-on. The governing systems adjust prop pitch automatically, which in turn directly affects engine rpm. You're not directly controlling prop pitch, unless you switch to manual in the 109. The P-40s and 109s definitely do use different control systems. The P-40 and practically every Russian, UK and US plane uses a constant-speed propeller system. The 109s use an "aeromechanical screw" system, and can also be switched to manual pitch control. The 109s are totally "hands-off" unless you switch to manual control, which then requires a LOT of attention and skill. The constant-speed prop systems used in most Allied aircraft are practically hands-free, you just adjust to a lower rpm setting for those times when you don't need full power. Power settings are made by adjusting both throttle and rpm with these CSP systems.

You can read a lot more about it at the guide mentioned, which starts on this page:

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


The P-40 E and M models are supplied with American-made Allison engines. Here is a page from the P-40 pilot's notes, specifying power settings (manifold pressure for throttle, rpm for prop governor) for various flight conditions. The Russian-modified field model uses a Russian engine (the same found in the LaGG, going by memory), so these settings do not apply for it!
http://people.ee.ethz.ch/~chapman/flightsims/images/p-40/poh_page45.jpg


Just to provide a comparison, and to emphasize that the settings depend on the engine, here are the P-40 settings for types with the Rolls-Royce engine. The P-40 F and L types (not in FB) were equipped with Packard Rolls-Royce engines, although some were retro-fitted.
http://people.ee.ethz.ch/~chapman/flightsims/images/p-40/poh_page46.jpg



In general, the tachometers are marked with a red line (sometimes a thick white mark). It is safe to run the engine up to the red line, which corresponds to maximum safe rpm. If the engine goes above this, it is overspeeding, and the engine is not designed to absorb the stresses associated with that. Although running the engine at red-line is safe and provides the most power (aircraft engines are generally designed to deliver max power at red-line), it will also keep your engine very hot and consume fuel at a high rate.

c!

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Targ
02-03-2004, 04:35 AM
Simple way to think of it is that the throttle controls the manifold pressure and the prop governer controls the rpm.
adjust the manifold pressure and the prop governer will adjust the pilot valve to maintain the set rpm.
However I am not certain that IL2 works this way.

Tully__
02-03-2004, 04:44 AM
Some real world information on various modes of propellor control at Pelican's Perch (http://www.avweb.com/news/columns/182082-1.html) on avweb

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ElfunkoI
02-03-2004, 07:14 AM
So in a 109 I can increase maximum dive rate, or increase my acceleration to critical speed in a dive, by lowering the prop pitch? Sounds like its worth a test. God knows we need every edge we can get.

michapma
02-03-2004, 07:58 AM
All of what DaBallz wrote is not necessarily applicable in FB. For one thing, much of it may not even be coded. Test it for yourself, but I wouldn't expect too much difference. The biggest factor in a dive is overspeeding the engine: with increasing airspeed the windmilling effect on the prop will cause it to unload the engine, often resulting in overspeeding the engine, which is destructive. I have recently tested a constant speed prop and found out that lowering the engine rpm control (labeled "prop pitch" in the HUD) actually reduced rpm significantly in a dive at the point where the throttle was at idle and could no longer reduce engine rpm. This should not be so, since it doesn't correspond to the real situation. In real aircraft it's important to realize that in a dive at high airspeeds the only way to prevent engine overspeeding is to reduce throttle or reduce the steepness of the dive. Reducing the selected rpm setting won't help, because the governor will have already driven the prop to its coarsest pitch. Note that I'm talking about constant-speed props here, although the aeromechanical props have a similar issue. I will have to test it further and possibly revise my advice in the CEM guide to make it relative to FB instead of the real world. It's unfortunate that this doesn't correspond to real-life behavior.

In the real life issues DaBallz addressed, the prop speed is a question of propeller efficiency. At very high airspeeds and rotational speeds (both contribute to the relative wind the prop sees) propellers become inefficient, as DaBallz wrote and as you can read in the article Tully quoted (it's an excellent one and given as a reference in my guide). Engines by comparison work more efficiently at higher speeds. Thus there is most often a gearbox that reduces the prop rpm from the engine rpm. That means that when your tachometer reads 2600 rpm the prop is very probably rotating more slowly, even though its speed is directly proportional to the engine speed: the increases and decreases are proportional. Some aircraft though are equipped with the ability to change this gear ratio between engine crankshaft and the prop, for example reducing the ratio so that at high airspeeds you can keep the engine rpm high while keeping the rpm of the prop low. This is made necessary because of the windmilling effect at such high speeds as in the Mustang trying to fly at maximum prop speeds, but also for aircraft with large propeller diameters, such as those described in Deakin's article that Tully linked to. As far as I know, it is beneficial to reduce the prop rotational speed at very high airspeeds (approaching 500mph aircraft airspeed) in an effort to reduce the relative wind speed. However, our discussion is a bit simplified and it gets hard to think about, because prop pitch (i.e., true prop pitch, the actual blade angle), rotational prop speed and forward airspeed of the aircraft all contribute to angle of attack. I won't offer any advice along these lines, as I am not familiar with the actual practice or theory of flying at the edge of possible performance. I think it's sufficient to say that this is not really a factor in FB.

When DaBallz writes "At very high speeds reducing the engine speed will make you able to dive faster" this must be properly understood to be, as he says, at very high speeds. If you dive at very high speed and don't keep the engine rpms down it will fry the engine, so reducing engine rpms to within the allowed red-line limit will allow you to dive at a higher speed. This is not to say that reducing rpms will help you dive faster, on the contrary! ("Lowering prop pitch" is only a relevant thing to say when using manual prop pitch control in an aircraft that has that possibility, notably some 109s and 190s. Read this section (http://people.ee.ethz.ch/~chapman/il2guide/cemguide/controllingrpm.htm) of my guide if that confuses you.) Keeping the engine at its max allowed rpm in the dive will provide you with max acceleration, getting you to a high speed faster. In a 109, that means keeping max rpms during the acceleration phase (whether you do it with manual control or the automatic system) will get you to high speed fastest. Keep in mind that controlling rpm in a dive also involves adjusting the throttle. As airspeed increases and windmilling causes your prop and engine to want to overspeed, you will have to reduce throttle to keep the engine speed withing limits. In FB, it appears you can further reduce engine speed in a dive by reducing the "prop pitch" (this is a most unfortunate term, since in most aircraft you are controlling the rpm setting and not the actual prop pitch, except as mentioned when in manual mode in some 109s and 190s). As said, this is only in FB and possibly only for some aircraft; it doesn't apply in real life.

I think I've written all this correctly, please correct me if you see any mistakes. I'd better get it right if I'm going to offer a CEM guide to the whole community. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

Cheers,
Mike

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michapma
02-04-2004, 02:22 AM
Bump

Did this help?

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DaBallz
02-04-2004, 04:17 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by michapma:
Bump

Did this help?

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_http://people.ee.ethz.ch/~chapman/il2guide/_ | http://www.forgottenskies.com/&lt;HR&gt;&lt;/BLOCKQUOTE&gt; (http://www.forgottenskies.com/<HR></BLOCKQUOTE>)

Reducing the engine/propeller speed in high speed
flight will delay the onset of shock waves as the propeller
exceeds the speed of sound (long before the plane does).

Yes, max RPM "over the top" will get you there more
quickly, but then cut your rpm (by changing pitch and throttle).

The primary function of the change in pitch is
the prevention of engine over speeding.

But it will also reduce drag at very high speeds.
As soon as those prop tips go supersonic the drag goes
through the roof and potentially damaging shock waves
will result.

i seriously doubt the effects mentioned in the previous posts
are modeled in to FB.

Da...