RPM and manifold pressure questions

[The Stalker]

Excuse my poor knowledge but I'm currently in the process of learning my way in CEM. I switched CEM on after almost 6 months of playing the game (Il-2 1946 4.09m) and learning to fly from scratch.

I did pretty well actually, from not being able to destroy a friendly bomber to having up to 5 dogfight wins per mission, so I felt ready for the next level.

The thing is, I'm having trouble understanding prop pitch, rpm and manifold pressure things. For example, I'm flying a He-111H6 bomber. I noticed that RPMs stay on combat setting (2600) from 60% to 110% throttle. That had me confused, because I figured that lowering the throttle should have an impact on rpm-s, but only the manifold pressure fell. And where does the prop pitch come into play here, since I learned that it is used to keep the engine in the powerband, but it's in the powerband by itself most of the time.
Can someone elaborate a bit, especially the purpose of prop pitch?

Also, how do I make my bomber squad wingmen drop their bombs at the same time as me when I'm doing level bombings? If I order an attack ground, they seem to just drop their bombs without aiming properly.

Thanks.

[JG53Frankyboy]

i wrote this long time ago in another forum, propably it helps

for all piston engined planes except:
Ki-27
J8A
I-16 Typ 5&6
Fokker XXI
TB-3s
Fw190 in auto mode
Ta152H in auto mode
Spitfire IX and VIII in auto mode
Bf109, Bf110,Do335,Ta152C in manual and auto mode:
the prop pitch in game is controlling the engine revolutions - so 100% pitch here means you allow the egnine to run at max rpm if enough throttle/power is available.
in combat you shoud fly always with 100%.
to lower your pitch is actually only necesarry if you want realy fly slow (that your comrades or the AI can close formation or you want safe fuel) , than you have to reduce the pitch like the throttle. same % rate or pitch 10% more than the throttle % is a good solution.

also using full throttle and useing only 90-95% pitch can reduce the overheat chance - usefull in some planes like the Tempest or the Corsair and Hellcat. that doesnt harm your speed/climb much, if at all !

very few planes in game are overrev in a power dive (full power, 100% pitch) - IIRC that are the Cr.42, G.50, Mc.200, Fw190A/F in manual mode, Fw190D/Ta152H in manual mode, the Brewsters(not sure about that , may have changed in a patch)


Fw190 in auto mode
Spitfire IX and VIII in auto mode
Bf109, Bf110,Do335,Ta152C in auto mode:
have a one lever system, if you control the throttle, the pitch is automaticly also controled


Bf109, Bf110,Do335,Ta152C in manual mode:
thats totaly different, here you control the propeller blade angle direclty ! no automatic will keep the rpm in a "good" condition. it brings you no benefit to use this manual settings anymore (there was a time ). so, dont bother it

the
Ki-27
J8A
TB-3s
I-16 Typ 5&6
Fokker XXI:
have fixed propellers, so nothing to control there

[The Stalker]

Ok thanks.

So what about those level bombings?

[K_Freddie]

Manifold pressure (MP) is essentially the amount of usefull power being produced by an engine. This pressure decreases with altitude (less oxygen), and increases with a turbo-charger.

Say at a certain altitude you have X MP at Y RPM.
As you go higher the RPM at MP both drop, but can be compensated for

1) by increasing the throttle (and fuel consumption) - this will keep your speed.
2) reducing Prop Pitch (PP) - but this will slow you down (less bite from the blades).

After a certain altitude, even with a turb/super-charger there will only be enough oxygen in the engine to burn so much fuel. Anything extra is wasted and you see a 'waste-fuel' trail behind you. You must reduce your fuel mixture (FM)% above this height.

Now this has the effect reducing MP (RPM), and PP changes have little positive effect.

Going to a lower altitude has the opposite effects as above.
Essentially at every altitude level, there is an optimum, MP, RPM, PP, and FM setting, for fuel efficiency, speed, etc...

Prop pitch adjusts the amount of thrust from the blades, but has the effect of loading the engine. The engine must then have the power (MP) to handle the load or the RPMs will drop (and MP), and compensated for by throttle or reduced PP. You tweak your fuel mixture to max your MP.

[rakinroll]

Originally Posted by JG53Frankyboy

in combat you shoud fly always with 100%.
to lower your pitch is actually only necesarry if you want realy fly slow (that your comrades or the AI can close formation or you want safe fuel) , than you have to reduce the pitch like the throttle. same % rate or pitch 10% more than the throttle % is a good solution.

I do not agree totally; in German planes, especially in FW190, 2500-2700 rpm and lower PP% makes your plane faster and cooler. And also in combat and turns, lover PP produces higher power and maneuver ability. In Bf109, during dive and climb, manuel PP makes the plane faster and manoeuvrable.

[The Stalker]

One more question if someone would be so kind:

Does a Hurricane IIb (constant speed propeller), for example, spend less fuel at 2700 RPM (prop pitch 75), than at 3000 RPM (prop pitch 100) if at both cases the throttle is set to 100%?

Thanks

[Blackdog_kt]

I don't know how it's done in the sim, but i guess that it should in reality. Less propeller RPM means less engine RPM as well (since they are connected to each other), which effectively means less combustion cycles per minute.

I had a lengthy post about these things recently. It's encouraging to see people want to learn the complex settings, but that post was a wall of text and i can't retype everything without forgetting something. I repeatedly proof-read that post and now that i look at it it's obvious i still made some typos/mistakes due to its length. I'll see if i can dig it up for you and give you a link.

Edit: Got it! Take a look here, there's also useful input by other forum members, some with attached pdf documents as well: http://forum.1cpublishing.eu/showthread.php?t=17139

[The Stalker]

Great thanks, I've read your post!

Would some care to explain the purpose and difference of best and economy cruise settings. I think I know what they are but not entirely.

[SEE]

Originally Posted by rakinroll

I do not agree totally; in German planes, especially in FW190, 2500-2700 rpm and lower PP% makes your plane faster and cooler. And also in combat and turns, lover PP produces higher power and maneuver ability. In Bf109, during dive and climb, manuel PP makes the plane faster and manoeuvrable.

I noted in Geoffrey Wellums Biography (First Light) that he adjusted his PP to have the Spit at around 2650 RPM for combat because it handled better (for him).

[Blackdog_kt]

Originally Posted by The Stalker

Great thanks, I've read your post!

Would some care to explain the purpose and difference of best and economy cruise settings. I think I know what they are but not entirely.

Ok, first of all the engine runs best at certain proportions of fuel-to-air mixture. The less fuel-more air mixture setting is obviously best for fuel economy without losing power, or at least not a lot of it. Remember, just as you can choke the engine with too much fuel, you can over-lean it too and have it lose power due to not enough fuel. The economy setting is the sweet spot where you get the highest amount of power for the least amount of fuel expense. The drawback to this is that since richer mixture has the effect of cooling the engine, lower fuel content means slightly higher temperatures.

With that in mind, this is used for cruise mostly. When using higher power settings, during climbs or combat for example, the cooling difference shows and you will either overheat or have to use radiators and cowl flaps to keep the temperatures within limits. This means that even if you don't overheat, the added drag from the open cowl flaps defeats the purpose and you end up being worse off in the net result of things.

This is when you use the richer mixture setting. In that sense, this setting is the sweet spot where you get the maximum amout of fuel in the mixture for cooling without chocking the engine and losing power. I'm not entirely sure it provides added power for the same manifold pressure and RPM, but it definitely enables you to run higher MP/RPM with less heat build-up. That obviously comes at the cost of fuel economy.

Hope it helps.

By the way, i'm no authority on these things so any corrections are welcome. What i know comes mostly from flying FSX on a friend's PC, going through some of the flight school/interactive lessons in that sim and flying some 3rd party payware add-on aircraft that are done with a higher degree of realism than the stock ones provided by M$. I'm not a real world pilot so i guess there's a world of info i'm missing here, but for simulator purposes and through whatever testing i have been able to undertake it seems to work as described.