Fuel Burn bug

[Dawger]

In the 190D9 (I havent tried in any other aircraft) the fuel flow does not increase with RPM in a dive when diving with propeller RPM set below maximum.

High speed dive causes RPM to increase above selected RPM with no corresponding increase in fuel flow.

[kvuo75]

why should it?

[Dawger]

why should it?

For a given throttle setting the fuel flow (measured in gallons per hour) increases with RPM (revolutions per minute)

Every revolution of the engine sucks in X amount of fuel. If you produce more revolutions per minute you increase the number of gallons you burn in an hour.

Easy math Example: At full throttle and 1 revolution per minute you burn 60 gallons per hour (one gallon per revolution)

If you double the revolutions to 2 per minute and the throttle remains the same you will now burn 120 gallons per hour. The turning engine sucks in the fuel. It doesn't really matter what is making it turn.

[Jayhawk]

For a given throttle setting the fuel flow (measured in gallons per hour) increases with RPM (revolutions per minute)

Every revolution of the engine sucks in X amount of fuel. If you produce more revolutions per minute you increase the number of gallons you burn in an hour.

Easy math Example: At full throttle and 1 revolution per minute you burn 60 gallons per hour (one gallon per revolution)

If you double the revolutions to 2 per minute and the throttle remains the same you will now burn 120 gallons per hour. The turning engine sucks in the fuel. It doesn't really matter what is making it turn.

I'm not a mechanic, but this doesn't sound right at all.  Wouldn't engine RPM and prop RPM be separated by a gear system?

[Ghastly]

I'm not entirely sure that's always true, Dawger.  

If you are rolling down hill in an automobile with throttle closed, but engage the clutch which brings up the engine rpm while slowing the car, I don't believe that you draw in any more fuel than if you had simply let the engine idle and braked instead.  

On the other hand, if I had a nickel for every time I've been wrong they'd have to round every price to the nearest dime.

<S>

[kvuo75]

as far as I know, fuel is metered to how much air is going in the engine..

with throttle closed, you have low manifold pressure = less air = less fuel.. has nothing to do with RPM.

if it were sucking more fuel, it would be making more power.. if it were making more power,  it would turn faster (your example dawger), and suck more fuel, and make more power, etc. etc... you are forgetting the effect of the throttle, I think.

but now I've got myself confused now that I reread the original post. you may be right.. but then I wonder would increased rpm against a closed throttle decrease MP even more. 

[WWhiskey]

For a given throttle setting the fuel flow (measured in gallons per hour) increases with RPM (revolutions per minute)

Every revolution of the engine sucks in X amount of fuel. If you produce more revolutions per minute you increase the number of gallons you burn in an hour.

Easy math Example: At full throttle and 1 revolution per minute you burn 60 gallons per hour (one gallon per revolution)

If you double the revolutions to 2 per minute and the throttle remains the same you will now burn 120 gallons per hour. The turning engine sucks in the fuel. It doesn't really matter what is making it turn.

NO! 

[RSLQK186]

IIRC most planes adjust prop pitch and the RPM gauge is a representation of what adjustment you have. I agree that acceleration in a dive should increase the RPMs of the prop, but is the gearing between the engine and prop direct or indirect. I would think it has an inertial clutch and would not force the engine to increase. But if it is not, than the engine would counter the increase of airflow somewhat and the difference would be minuscule<<<just a guess on my part.
Any Aircraft Engineers in here?

[kvuo75]

IIRC most planes adjust prop pitch and the RPM gauge is a representation of what adjustment you have. I agree that acceleration in a dive should increase the RPMs of the prop, but is the gearing between the engine and prop direct or indirect. I would think it has an inertial clutch and would not force the engine to increase. But if it is not, than the engine would counter the increase of airflow somewhat and the difference would be minuscule<<<just a guess on my part.
Any Aircraft Engineers in here?

the props in the planes here are constant speed props.. the prop adjusts pitch automatically to maintain the selected RPM..  there is no clutch.  at the extremes of prop pitch, there is no more pitch available, so the prop/engine will turn at a RPM not selected. i.e. in a crazy dive, it cant go coarse enough to stay below the selected rpm (not sure this is possible in game), or at idle on the ground, cant go fine enough/engine doesn't make enough power to turn it to its selected rpm

the issue is whether at closed throttle, changing RPM should change the fuel flow.. this I am not sure of. 

[kvuo75]

ok i been thinkin about this all afternoon now .. I think dawger was correct all along. (sorry dawger)

even with the throttle at idle (dont know why i was stuck on this).. the faster the rpm, the more air going thru the engine = more fuel..

[WWhiskey]

ok i been thinkin about this all afternoon now .. I think dawger was correct all along. (sorry dawger)

even with the throttle at idle (dont know why i was stuck on this).. the faster the rpm, the more air going thru the engine = more fuel..

Mixture control?

[Dawger]

I'm not a mechanic, but this doesn't sound right at all.  Wouldn't engine RPM and prop RPM be separated by a gear system?

Only in a geared engine. Most aircraft engines that drive propellers are direct drive. The prop RPM and engine RPM are the same. But even in a geared engine the engine has turn faster if you make the prop go faster by diving faster than the propeller governor can handle.

An engine turning draws in fuel. The amount of fuel for each revolution is metered by carburetor or a fuel injection system. The intake stroke of each piston draws in the fuel air mixture. That amount of fuel times the number of cylinders is remarkably unchanging. The ratio of fuel to air is fairly constant. The ideal stoichiometric ratio is 14.7.

What that means is that there is 14.7 times as much air as fuel by MASS. It changes a little for various circumstances but not an incredible amount. A little richer for high power situations to lower the combustion temperature and the risk of detonation and leaner during periods of low demand for fuel economy.

But for most purposes the amount of fuel sucked into a given engine for ONE revolution does not change very much.

What we change is the number of times per minute the engine turns by giving the engine more air. More air means the engine can accelerate to a new RPM level with its attendant increase in fuel consumption over time.

The car example rolling down a hill is analogous to the aircraft. In a car you can separate the engine from the drive train using the clutch. The engine runs at idle RPM, burning X amount of gas per hour. When you engage the clutch then the engine must turn at the RPM of the drive wheels. The throttle is still set to deliver the fuel for idle. Fuel use for each RPM doesn't change but the number of RPM increases so fuel use has to increase when viewed over time.

[Dawger]

Mixture control?

The original bug report is that the fuel flow does not change when engine RPM increases for a given throttle setting. Increasing RPM is done by diving the aircraft.

In game, we do not control mixture so we will just say that it does not change.

So the conditions for the bug report are as follows:

Throttle - FULL POWER
Mixture -  FULL RICH
Propeller-2000 RPM

In level flight with these conditions set the fuel flow is 106 gallons per hour. Diving the aircraft without changing any of the above settings, the propeller RPM increases to 3000 plus RPM with no increase in fuel flow measure in gallons per hour.

[WWhiskey]

nevermind

[Chalenge]

We had just discussed the rpm thing in another thread. The rpm gauge is reading engine rpm so if you are seeing a spike in rpm in a dive (and Im not sure why you are) then it is the engine that is rising in rpm.  I dont think any of the planes in AH have direct prop/engine drives so the prop will always be at some ratio to engine rpm. kvou had it right about the constant speed props adjusting load to maintain a given engine rpm through a prop governor system (as explained by Hitech).

So I suppose your bug-report/question is a valid one although I think the question should also be why the props dont overrun or wreck when driven so hard in a dive.