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### AuthorTopic: Fuel mixture and prop angle question  (Read 521 times)

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#### btasm

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##### Fuel mixture and prop angle question
« on: January 21, 2019, 07:29:27 AM »

I think I've read all the posts as to fuel mixture and prop pitch, but it's all well beyond me technically.

Could someone please provide a simple - very simple - explanation as the when to increase/decrease the fuel mixture and to increase/decrease prop pitch in game. And what does "prop. pitch auto" do?

Thanks so much.

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#### Koi

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##### Re: Fuel mixture and prop angle question
« Reply #1 on: January 21, 2019, 10:09:03 AM »

Fire needs the correct balance of fuel to air to burn efficiency. Add  to much fuel and the fire is smothered a will produce nothing but a lot of smoke and eventually go out.
Before your time  automobiles had a thing call a choke which allowed a driver to adjust the amount of air to fuel mixture Today they all  have automatic chokes.
More fuel was needed on start up as the engine was cold and would not vaporize easily so one closed the choke reducing the amount of air to fuel making the engine run rich. A visible sign was black smoke out the exhaust.
When the engine had warmed up this allowed the fuel to be heated and vaporized faster so one opened the choke to in increase air flow and reduce the fuel richness lessening the black smoke. In aircraft it was much the same but with the added problem of height where the air is thin.  Thin  air  needs a bit more fuel than sea level air. Clue to reduce mixture is black smoke[too much fuel to air].
Prop angel adjust the pitch[angle]that  the prop blade is set at when cut through the air. It is much like gears on a car.  Thin slices on start, thick then traveling. "Auto"  simply means it is automatically done through a mechanical means so you, the human, don't need to worry about it .
Setting the game so complex engine management is off will also remove having to worry about it all.
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#### SpongeBob

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##### Re: Fuel mixture and prop angle question
« Reply #2 on: January 21, 2019, 10:23:38 AM »

Hi btasm.
I do not use fuel mixture (never learned how it works), but I've made extensive use of prop pitch and it is quite satisfactory.

It is said that prop pitch resembles to car gears (in case you've ever driven a car with manual gearshift). However, you do not use the prop pitch exactly as you would do with gears in a car.

100% prop pitch is equivalent to the first gear: it is the most powerful set and leads to higher RPMs. Prop pitch progressively lower than 100% would be equivalent to the second, third, fourth... gears. Lowering the prop pitch makes that the engine works more efficiently since it decreases the propeller air resistance, also decreases the RPMs, and what is more important, decreases the engine temperature.

When you need full power (as in take-offs and landings), prop pitch must be kept at 100%. When you start a car, you use the first gear and quickly you must turn to second and third gears to avoid reaching too high RPMs. However, you don't need to lower prop pitch so quickly in planes. RPMs are automatically kept in a safe range even at full throttle. I don't know if it is true in real life, but in IL-2 you can keep prop pitch at 100% all the time withouth experiencing serious trouble.

So, when should you change prop pitch? Basically it is good to lower the prop pitch when you are cruising at a constant elevation. If you are climbing, you will probably need all the power your plane can develop (100% prop pitch). Once reached your final elevation, you can lower prop pitch and throttle (I usually set both them to 70%, 60% or 50%).
You will observe two good things. (1) Even with lower throttle, you will fly slightly faster because the propeller offers less resistance to air.
(2) RPMs will decrease (you can see it looking at the RPM gauge), so the engine will cool down and you won't have to worry about engine overheating for a while.
However, when I have to engage a combat, I quickly increase prop pitch to 100%, to keep full power during turns and climbings.

In brief:
- Use prop pitch at 100% whenever you are not flying in a safe, straight course.
- Set prop pitch between 50%-70% when cruising and flying in formation, to keep your engine cold. You can make light adjustments of the throttle and prop pitch until getting the same speed as your formation mates. For example, if you are flying too slow, you can lower prop pitch to get some extra speed; or you can increase prop pitch to 100% to lower speed quickly as you do with the engine brake in cars.
- In combat, if you need to make a long dive to escape from your enemy, you can decrease prop pitch up to 0% (and close radiators if they are opened) to reduce the air resistance and get a faster dive. Once you are close to the ground, you need to set prop pitch to 100% again to keep on flying.

Concerning "prop. pitch auto", I think it has to do with German planes (such as Messerschmitts), which I rarely use, so I cannot help you there.
I hope you find it useful. All that I've said has been personally tested in IL2, and it seems to work. Probably it doesn't apply to real flight, because it seems that engine behaviour is not exactly modelled in the game, so you can find different or even contradictory statements anywhere on the web.
I recommend you to try and test in different conditions until you find your style of flying. It is very pleasant to learn a new "trick" that permits you to escape from your enemies in hard times.
I also recommend you to use some hardware with two levers for throttle and prop pitch for better control and higher immersion.
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#### btasm

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##### Re: Fuel mixture and prop angle question
« Reply #3 on: January 21, 2019, 11:00:07 AM »

Koi,, SpongeBob:

Thanks for the quick replies. I am starting to get my head around this, but just to make sure:

Koi: When I employ "increase mixture", I presume I am adding more fuel (not air) to the mixture, correct? If so, at higher altitudes, where the air is thin, wouldn't I want more air to compensate for that and, therefore, reduce the percentage of fuel, i.e. "decrease mixture"?

SpongeBob: Is it generally correct to state, in terms of prop pitch, use 100 percent for takeoffs, landings and dogfights, but cruise at 50-70 percent?

Thanks again.

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#### SpongeBob

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##### Re: Fuel mixture and prop angle question
« Reply #4 on: January 21, 2019, 02:36:31 PM »

Hi btasm,
as I told you, what I do is a consequence of testing on game. I don't know if this is the right thing in a real plane. I've been reading here and there and as you said, there is not a rightforward explanation about how to use the pitch propeller, so I chose to have fun and perform my own tests.

As a thumb rule, while cruising I use to decrease throttle and pitch propeller at the same rate. While flying in formation, I've found that most of the time I can keep keep up with my flying mates (AI) with a combination of throttle and pitch propeller both set at 50-60%. Fiddling with these controls, I can adapt my speed to keep on formation. Sometimes the plane gets so fast that I have to decrease throttle at 30% (pitch at 50%) or so to stay with my mates.

This works well with Hurricanes, Spitfires and Corsairs, which are the planes I've used more lately. But if anyone has other experiences to share, it would be very interesting to know about them.

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#### macgiver

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##### Re: Fuel mixture and prop angle question
« Reply #5 on: January 21, 2019, 04:25:03 PM »

From my experience (I mainly fly the british and soviet aircrafts): mixture changes are necessary only to decrease the amount of gasoline in soviet airplanes (mainly yaks) from certain heights (you recognize it when airplane loses power and begins to smoke black, for example Yak-1B at 3200 m). Normally information about this is in the "Aircraft Guide" (Il-2 1946) and most of the "Read Me" of official patches.
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#### Koi

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##### Re: Fuel mixture and prop angle question
« Reply #6 on: January 21, 2019, 07:12:31 PM »

Yes, you are correct, Check for the tell tale black smoke. When you see that it mean too much fuel, and thin, decrease, the mix. I never play with it much as I tend to be  down low doing ground attack stuff. We used to fly some B-29 missions and really that was the only time we needed to adjust for altitude as they can get up really high.
As for prop pitch.
The German planes like the 109's have Auto settings for prop pitch. One has to be really careful when playing with the Prop pich settings as  it can easily cause one to burn out  engines if it is set to high. The Revs get too high and it just eat out the bearings, You might hear it start to runaway, if so  hit in 70% real quick, If you start hearing a grumble squeak sound too slow to late you are walking from then on not flying. Watch your speed and rpm if they start to drop increase the pitch.  On take off much like SpongeBob, I set mine to 100% and cruise at 70% to 75%. or I set it to Auto. but yes it is best to experiment to get the feel for it.
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#### greybeard

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##### Re: Fuel mixture and prop angle question
« Reply #7 on: January 22, 2019, 03:25:27 AM »

Could someone please provide a simple - very simple - explanation...

There's no simple explanation. Both prop pitch and mixture are complex matters which require study and practice to be understood. To further confuse player, in game there are differences in respect of reality, so, even being competent, you'll find yourself wrong-foot by game simplifications and oddities.

You must play and learn the various kind of aircraft: fixed pitch airscrew, variable pitch, auto. As well as mixture management to tune it to height or to save fuel. Keep also in mind that relevant code has changed throughout versions: later versions, for instance, bound overheating also to engine RPM.
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#### Dimlee

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##### Re: Fuel mixture and prop angle question
« Reply #8 on: January 24, 2019, 12:13:41 PM »

You must play and learn the various kind of aircraft: fixed pitch airscrew, variable pitch, auto. As well as mixture management to tune it to height or to save fuel. Keep also in mind that relevant code has changed throughout versions: later versions, for instance, bound overheating also to engine RPM.

I fully support this advise. Fly your favourite a/c and learn them.
I usually do not bother with pitch once "auto" is available by default. I pay more attention to it on (for example) Pe-2 and Ki-45 as otherwise I can miss overheat message. I pay utmost and thorough attention to pitch settings along with revolution indicator on SB-2. Forget to do it for a minute and engines overrev and overheat and lose power... you are sitting duck to delight of AAA.
Mixture management is somewhat easier. Reduce by 10% per 1000m-1500m from 3000m up and you should be fine. This is rough "formula" which one might tune for better performance.
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#### cbradbury

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##### Re: Fuel mixture and prop angle question
« Reply #9 on: January 24, 2019, 01:59:48 PM »

I set my mixture from watching RPM. Always start with full mixture (usually 120%). After takeoff reduce it, watching your RPM. When the revs drop (generally 60% mixture or less) go back up one setting and the mixture should be correct.
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#### larschance

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##### Re: Fuel mixture and prop angle question
« Reply #10 on: January 25, 2019, 08:52:02 AM »

While flying the Fiat G50 I take off at 100pc throttle 140mph and climb after my unit at 100pc, settling to 80pc at cruise altitude. The overheat message tends to come up fairly quickly and too often meaning I have to adjust throttle to about 50pc ending up lower and slower than the unit. If you ignore the overheat warning you can fly for a few minutes before black smoke appears and the engine threatens to catch fire. If you drop the nose too quickly the engine cuts out like the Hurricane and early Spitfires although I am not sure the Fiat radial engine suffered the same fuel exhaustion as the Merlins in real life. As for being bounced I have learned that by hitting the rudder either way can throw off the enemy aim unless he is an ace, giving you time to escape.
Incidentally, years ago I talked to an ex 109 pilot who told me they used to fly 100pc throttle throughout a sortie if local. The DB engine was sturdy enough to cope with that.
I have not tried any variations on pitch only throttle.
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#### greybeard

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##### Re: Fuel mixture and prop angle question
« Reply #11 on: January 25, 2019, 11:50:09 AM »

The overheat message tends to come up fairly quickly and too often meaning I have to adjust throttle to about 50pc ending up lower and slower than the unit.
Did you try opening cowl flaps?

Quote
If you drop the nose too quickly the engine cuts out like the Hurricane and early Spitfires although I am not sure the Fiat radial engine suffered the same fuel exhaustion as the Merlins in real life.
From G.50 Pilot's Manual (literally translated from Italian):
"With the G.50bis, it is possible to perform all the various forms of acrobatic flight, but strictly excluding inverted flight. The reason is to be found in the carburetor of the engine that does not allow reversed operation and presents, in this case, the danger of fire."
I think this also means cut-out under negative G condition.

Speaking of mixture, I believe following diagram may be useful:

which shows power vs efficiency (η) with mixture ratio as parameter. As you can notice, there are two different ratios to save fuel and get full power, as well as upper and lower flammability limits, beyond which engine stops.
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