Menu Sign In Contact FAQ
Banner
Welcome to our forums

How to get the best MPG with a plane?

While some Lyco/Conti GA aircraft publish 45% cruise/range/endurance charts, many stop at 55%, as in effect this is probably a fair Vopt at MAUW and ensures the engine is reasonably happy.

In general most block planning is around 65% for these 1950’s designed GA types.

While flying higher improves TAS it doesn’t necessarily improve range. Most charts are a bow shape with an optimal altitude for no wind at a specified power setting. Wide open throttle may help improve SFC in some engines, while in others a slightly closed throttle works better

Oxford (EGTK), United Kingdom

I think at roughly 8000 feet, the engine runs at 65% WOT (NA engine). It’s therefore more a question of how much surplus HP you have in comparison to what is required to move the aircraft.

An underpowered aircraft may not be able to climb efficiently at 65% power. An “overpowered” aircraft will fly “too fast” at 65%, and therefore be more economical at higher alt than 8000 feet.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Think I’ve linked to this before, but this guy is capable of almost 100mpg in his Long-Eze. He flew from California to Florida on 26gallons of fuel. Means he could cross the Atlantic from NY to London on probably 50-60gal of fuel. That’s cheaper than taking the train across

Hypermiling aircraft

Graham wrote:

What is Vopt cruise, as a practical definition?

It’s out of this article, quoted earlier here.

http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm

LSZH(work) LSZF (GA base), Switzerland

AdamFrisch wrote:

Think I’ve linked to this before, but this guy is capable of almost 100mpg in his Long-Eze. He flew from California to Florida on 26gallons of fuel. Means he could cross the Atlantic from NY to London on probably 50-60gal of fuel. That’s cheaper than taking the train across

The Long-Eze and similar are efficient and fast aircraft. But they are also useless for anything except 2-3 km runways. A standard Lancair with a O-235 is also very efficient (and very useless unless you have a large, hard runway).

A stock Pipistrel Alphatrainer has a cruise speed of 108 knots (200 km/h) IAS at 13.6 L/h, 5300 RPM. That’s 0.067 L/km or 35 MPG. For long endurance, you can throttle back at 4000 RPM, and still get 80 kts IAS (150 km/h). Then you burn about 5 L/h, which is 0.033 L/km. That is 71 MPG. It can fly like that easily at 10k and get 96 knots TAS (178 km/h). This is 0.028 L/km or 84 MPG. This aircraft takes off from grass strips in less than 150 m. From experience, the engine will get too cold when flying like that, you would have to install variable cooler intakes or thermostats.

The elephant is the circulation
ENVA ENOP ENMO, Norway

I’m assuming the reference to 2-3 km runways was sarcasm, or a mistake in stating meters versus feet, but obviously it’s true that Rutan’s canard planes were not designed for use in off airport conditions. If I recall correctly Klaus Sevier and his Vari-Eze are based at Santa Paula airport, which has a 2665 ft or about 820 meter runway. That’s enough for the type.

For initial pilot checkout for no experience in the type, Rutan recommended 3500 ft runway length in the Vari-Eve manual which is here. That would provide substantial margin for an unfamiliar pilot.

Last Edited by Silvaire at 29 Nov 16:27

LeSving wrote:

A standard Lancair with a O-235 is also very efficient (and very useless unless you have a large, hard runway).

What use is a Pipistrel Trainer where I cannot put two people with 2 big luggage suitcases?

This thread is however how to get the max mpg from an aircraft that you already have/fly.

Last Edited by Raven at 29 Nov 22:27
Poland

So to summarize:

Best Range speed is Best Glide speed.
It is however quite slow so we may use a so called Carson speed which is about 31%higher than Best Glide, and we lose only small amount of MPG.
The altitude does not change our MPG in a piston plane. It changes the TAS but at higher altitude – we have to fly higher power setting to get the same MPG than at low altitude, which may be good if we pay for fuel AND for time.
If we go for a trip which we want to celebrate and not finish to early – go at low altitude
Best endurance should be flown at low altitude – it is about 31% lower than Best Glide, but technically very low and maybe too close to stall.
Don’t forget to fly lean of peak, or at least at peak EGT, as MPG greatly increases if we stop wasting excess of fuel which is not burnt in cylinders.
Hard for carborated engines (may require a bit of carb heat), easier on injected – especially with Gami injectors.
You cannot harm the engine with any mixture setting when below 65% and actually the CHTs will be lower at lean of peak than rich of peak (unless very rich), and we don’t contaminate the engine so much with carbon deposits.

Poland

Raven wrote:

The altitude does not change our MPG in a piston plane. It changes the TAS but at higher altitude – we have to fly higher power setting to get the same MPG than at low altitude, which may be good if we pay for fuel AND for time.

I don’t see that anyone said that? At the same power setting – and thus fuel flow – TAS will increase with altitude and thus MPG will also increase. There is no need to increase the power setting. To some extent this is offset by the climb, but I don’t think you can make any general statements of that effect.

OTOH, winds tends to totally dominate what altitude gives best MPG – at least for light aircraft.

Last Edited by Airborne_Again at 29 Nov 23:18
ESKC (Uppsala/Sundbro), Sweden
Sign in to add your message

Back to Top