Fuel burn on AR-1

JEFF TIPTON · May 17, 2016

Based on the engines I have run on the dynamometer I would expect the pounds of fuel per horsepower hour to go up as manifold pressure goes down at the same RPM.

Vance I am perhaps perplexed. I would expect if the vacuum pressure is increasing you would have a higher fuel burn.

With manifold pressure, I am used to seeing a low number like 15 at idle power settings and at fuel throttle numbers like 27 or 28; roughly atmospheric pressure. This assumes no turbocharger or supercharger, etc.

Abid · May 17, 2016

MilesW said:
What??????

What, what

.
Its simple you cannot calculate percentage power or power being used unless you have manifold pressure and OAT measurements.
Rotax 912ULS defines 75% power at 5000 RPM when the manifold is 27.2 "Hg. If you don't have the manifold reading you are not at 75% power regardless of if you are at 5000 RPM. Its very simple.

Vance · May 17, 2016

JEFF TIPTON said:
Vance I am perhaps perplexed. I would expect if the vacuum pressure is increasing you would have a higher fuel burn.

With manifold pressure, I am used to seeing a low number like 15 at idle power settings and at fuel throttle numbers like 27 or 28; roughly atmospheric pressure. This assumes no turbocharger or supercharger, etc.

Pounds of fuel per horsepower hour is a measure of how much fuel it takes to make one horsepower for an hour.

At idle and engine is making less power so even though it is less efficient it is using less fuel.

In my opinion an engine is most efficient with maximum cylinder filling (highest Brake Mean Efficiency Pressure). This is often near peak torque with wide open throttle.

There are many things that can alter this.

Abid · May 17, 2016

Vance said:
One of the things that can be measured on a dynamometer is pounds of fuel per horsepower hour.

It is measured at different rpms because the efficiency of an engine may vary at a specific rpm.

Put simply; make more power and you burn more fuel regardless of the RPM.

The Cavalon consistently burned slightly over four gallons per hour flying at 75kts because of how much power we were using, not how many rpms we the engine was turning.

The manifold pressure and engine rpm can give a rough idea of how much power the engine is producing and how much fuel it should use if properly tuned.

My guess is they were using around 55 horsepower to burn 4.1 gallons per hour at 75kts.

Actually we did the calculations again and there was indeed a mistake in calculation and the fuel burn comes out to be 4.57 gallons per hour not 4.15 gallons per hour I had calculated before. Just a correction point.

For example on one of the legs they burned (and filled) exactly 8 gallons and the time for the leg was 1.75 hours, give or take a couple of minutes.

Abid · May 17, 2016

kmtck said:
Fara and Vance, for a two up gyro at gross 1250 lbs, 55HP for 75 knot is pretty good.

Based on power and drag relation:
85knots ~97mph @75% (75HP)
75 knots ~86 mph
So, 75HP*(86/97)^3 ~ 52HP.

Based on fuel burn ratio:
4.1gph*75HP/ 5.5gph(@75HP)~ 56HP

52 & 56 are pretty close.
Can a linear fuel burn be assumed for the 912 ULS to produce ~41 HP @3gph fuel burn?

I ask because the drag & power equation give ~80mph at 41HP and I do not think that only 41HP can get you to 80mph at 1250lb gross.

Anyone can shine some more light on this?

First 75% power on R 912ULS burns 5.25 GPH not 5.5
Second, AR1 like a couple of other gyroplanes starts to unload the rotor a tiny bit at around 68 knots and above because the landing gear fairings produce lift.

You can see R912uls data here
http://www.flyrotax.com/files/Bilder/Produkte Rotax/Datasheets/Produktdatenblatt_912_100hp_RZ.pdf

As you see 5000 RPM is giving about peak torque

CGameProgrammer · May 17, 2016

fara said:
Actually we did the calculations again and there was indeed a mistake in calculation and the fuel burn comes out to be 4.57 gallons per hour not 4.15 gallons per hour I had calculated before. Just a correction point.

For example on one of the legs they burned (and filled) exactly 8 gallons and the time for the leg was 1.75 hours, give or take a couple of minutes.

That works out to 19 mpg which is reasonable given it's the 912 two-up. The 914 might be slightly more efficient.

Fuel burn on AR-1

JEFF TIPTON

Senior Member

Abid

AR-1 gyro manufacturer

Vance

Gyroplane CFI

Abid

AR-1 gyro manufacturer

Abid

AR-1 gyro manufacturer

CGameProgrammer

Member

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