The most effective way to use your fuel?

[tofri]

It happens many times that I run out of gas on the way back to base.
Especially when the roll ends 50m before the runway.
Certainly my fault, but had someone evaluated some data about the best way to save fuel.

When I drive a car the whole time with kick down and smoking wheels, I get only half the distance driving like a pensioner in a rush hour.  

Had anyone noticed something like that?
How should I put the throttle to get the greatest distance for my rare fuel?

I do not speak of the GV with their atomic power plant for eternal cruising  

[wells]

You need to find the speed that requires the least amount of power to maintain.  It's probably around 200 mph for most fighters.

[flakbait]

Here's what I do:

1) Figure out the manifold pressure levels for desired cruise. I use either actual aircraft charts or just throttle back to about 60%. HTC has some charts up for a few planes, but only about half of them are actually done. Zeno's has some engine info or power charts for quiet a few planes here.

2) Drain any external tanks first. And don't forget to punch them off before you start a fight!

3) Leave fuel tank selection on automatic, unless you actually want to manage the various tanks. If you chose the latter and drive any Fw, drain off the AUX and AFT tanks first. That AFT tank is the last tank the automatic gizmo drains off, making the tail nose heavy.


Going to just patrol around a few sectors? Ok, keep your power back to 75-80% and leave it there. For patrols always take drop tanks and 75% fuel, climb out on full power since you're draining the drop tanks. Once you hit the altitude you want, throttle back as above and start the patrol. What I do is patrol at full power until my tanks are half-empty, then turn back and reduce power to 60%. Granted it takes a while to get home, but you get home with a little gas to spare.

-----------------------
Flakbait [Delta6]
Delta Six's Flight School
Put the P-61B in Aces High
"With all due respect Chaplian, I don't think God wants to hear from me right now.
I'm gonna go out there and remove one of His creations from this universe.
And when I get back I'm gonna drink a bottle of Scotch like it was Chiggy von
Richthofen's blood and celebrate his death."
Col. McQueen, Space: Above and Beyond
   

[This message has been edited by flakbait (edited 03-29-2001).]

[funked]

And don't play with the RPM.  I did some structured tests a while back, comparing real world RPM/MP settings to AH and there is a fuel economy penalty for RPM decrease in AH, a penalty that did not exist in real life.  So use only the throttle to slow your plane down.

200 mph, as Wells says, is a pretty good estimate.  I have also had very good results engaging the auto-trim for best climb speed, and modulating throttle to hold level flight.  You will be very slow and a sitting duck, but you can fly forever on a little gas this way.

[This message has been edited by funked (edited 03-29-2001).]

[Ripsnort]

It must be per plane, Funked, because my tests with the F4U showed a significant reduction in fuel while reducing RPM with MP, best fuel economy in the F4U-1D is 23 rpm and 40 MP.

[Jigster]

between 25 and 35 MP is generally the best cruise setting for all planes...the F4U will fly about a sector and a half on an eighth of a tank at that setting, most others get close to that.

The only exception is the P-38...fuel economy is much better if you cut one engine and reduce throttle slightly on the reamaining one.

[funked]

Rip, we've discussed this before, and you're getting the reduction because you are reducing the speed of the aircraft.  If you measure miles/gallon at 2300 rpm and 40", then set RPM to maximum and use the throttle to fly at the same speed as the 2300/40 setting, you will see better miles/gallon.

[This message has been edited by funked (edited 03-29-2001).]

[funked]

I tested it, and I'm right, of course.    

F4U-1D, 1 DT, 25% Internal Fuel.
No wind, 7,000 feet altitude, fuelburnratemult set to 5.0.

Procedure:  Take off with DT, climb to 7,000 feet, set desired MP and RPM.  Allow airspeed to stabilize and record it.  Switch to internal fuel and start stopwatch simultaneously.  When engine stops, stop the watch and record the time.

RPM MP TAS Time
2300 40 295 3:35
2700 33 295 4:05
(Red TAS mark was just barely touching the 300 mark in both cases.  MP in second case was just under 33 but I rounded up.)

Lesson Learned:  Don't fiddle with the RPM if you are looking to save fuel.  It's all about airspeed.

[This message has been edited by funked (edited 03-29-2001).]

[Ripsnort]

Yes, my test was reducing speed, I wasn't try to maintain speed,was using fuel conservation, and tests were done at 20k.

Funked, try this:

2300 33 (to hell with speed, who cares when trying to save fuel)

[This message has been edited by Ripsnort (edited 03-29-2001).]

[Tac]

Jigster:

Best fuel economy on the P-38 is 40 Manifold once your plane reaches 300mph.

for BEST results, climb to 25k+ with external tanks, reach 400mph and cut man to 1/3rd. I can fly the whole map and halfway back with that setting (halfway gliding that is..but glide from 30k in p-38 is like having fuel anyway   ).

To fly on one engine? Never tried it, but when I've had an engine shot out and had to manage fuel to get home I've had to burn more fuel and fighting loss of airspeed every time I did course corrections because of the dead engine.

[funked]

 

to hell with speed, who cares when trying to save fuel

Actually speed is critical.  The lowest fuel consumption rate (gal/hr) will occur near the minimum drag speed.  Flying at this best endurance speed will give you the maximum time aloft.  But we are looking for maximum range here, so maximum time aloft is not important.

What is important is maximum distance flown (range) for a given amount of fuel.  The lowest fuel consumption per mile flown is what we are looking for.  This means best range will occur at the speed which maximizes the ratio of the true airspeed (mi/hr) and the fuel consumption rate (gal/hr).  Those of you scoring at home my notice that this ratio has units of mi/gal, aka mpg.

For the type of aircraft we are talking about, the best range speed is a bit higher than the best endurance speed.  Speeds below the best range speed may give a lower fuel consumption rate but since the airspeed is also lower, the ratio of mi/hr to gal/hr does not improve.

The key is to fly at the best range speed with the powerplant at the most efficient setting for that airspeed.  Here is where we break with reality:  In AH, reducing RPM while holding MP constant reduces powerplant efficiency.  Thrust goes down but fuel consumption rate (gal/hr) does not change much if at all.  Maximum efficiencies occur at maximum RPM in AH.

Look at the data I presented.  That is a direct measurement of efficiency.  Both aircraft were in the same configuration and airspeed, meaning they had the same drag and the same propulsive power.  But the one with reduced RPM used fuel at a higher rate.

I'll try 2300 RPM and 33" at that altitude, but I know what will happen.  Speed will drop, and the time will increase.  Since the speeds in my first test were a bit high for best range, I think the mi/gal may improve as well.  But I also guarantee that a 2700 RPM setting that gives the same speed as 2300/33 will give better mi/gal.

If you want to get home with minimum fuel, don't play with the RPM.  You may get better range than with wide open throttle, but it's not the best range.  It's like a guy who starts eating nothing but milkshakes and cheeseburgers 10 times a day but also starts running 20 miles every day.  He might lose some weight, but was it the diet or the exercise that did it?  

[This message has been edited by funked (edited 03-29-2001).]

[Naudet]

Hey tofri, noch en Oecher, cool, vielleicht sollten wir mal gemeinsam den AH Himmel unsichermachen.

And to ur fuel prob, i dunno what planes u fly, but if u fly i.e. a BF 109 flying at full throttle will make u a glider many times, also do not forget a DT with the 109er. In a FW it depends on ur mission, if u fly a defences for a airfield 1 grid away, dont use a DT, burn fuel while getting alt so u r not to heavy when entering combat, but on long patrols never forget ur DT.
I think only the the US and JP fighters can stay in the air for a long time without DT.
But in them, choose a DT, put only 50% fuel in the tanks so ur not to heavy in an engagment.

[Graywolf]

 

Originally posted by funked:


If you want to get home with minimum fuel, don't play with the RPM

Not always true.

If you're wanting to lose altitude and save fuel at the same time, as I often do when returning home (there aren't many airfields at 20,00' on the current maps) then a very low throttle setting couple with low RPM is the best. If you leave the RPM high you get too much drag from the airspeed 'pushing' the propellor around rather than the engine doing it.




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Graywolfe <tim@flibble.org>

[juzz]

There is an easier way in that case - get above the airfield, spin down to 2k or so and then land...

[funked]

Hmm Graywolf you are probably right.  I have noticed a definite decrease in drag when setting RPM to minimum in a glide.  But remember that the AH fuel consumption is proportional to MP, so there is going to be a tradeoff.