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Fuel economy

Recently I was going over the POH of a couple of aircraft and started calculating NM/liter values and was impressed that some 2 seaters achieve 6 or more nautical miles per liter. That is actually better than most cars (actually I’m not sure there are any cars that use 8 liters / 100 km while doing 180 km/h).

Do you know of planes (2-4 seater SEP) that are especially fuel efficient ? I’m expecting some homebuilts to achieve impressive values, at the expense of comfort and speed.

For those of you who rent or are in club, how much do you pull the power back for cruise, or do you just use “full rental power” since most rentals are wet, so it would cost more to pull the power back to an economy cruise ?

Something that surprised me when calculating NM/liter values was that I got slightly better values down low at the same power setting (usually 55%), because fuel burn increases with altitude faster than TAS does. That seems counterintuitive. Did I get my maths wrong, or is there an logical explanation for this ?

Last Edited by andy_flyer at 16 Feb 06:26
LSZF,LSZK, Switzerland

andy_flyer wrote:

Something that surprised me when calculating NM/liter values was that I got slightly better values down low at the same power setting (usually 55%), because fuel burn increases with altitude more than TAS. That seems counterintuitive. Did I get my maths wrong, or is there an logical explanation for this ?

Rotax? With a carbureted Rotax engine that is to be expected due to the type of carbs used.

EDQH, Germany

andy_flyer wrote:

For those of you who rent or are in club, how much do you pull the power back for cruise, or do you just use “full rental power” since most rentals are wet, so it would cost more to pull the power back to an economy cruise ?

I use 65%, which is also the policy of my club. Fuel consumption figures indicate that people keep to that. (But they could be better at leaning…)

ESKC (Uppsala/Sundbro), Sweden

Our beloved RF5 did about 180 km/h while burning around 14l MOGAS an hour. And you can fly in a straight line with it most of a time, unlike driving on roads which always adds overhead.

And this plane was build in 1971!

Germany

Do you know of planes (2-4 seater SEP) that are especially fuel efficient ? I’m expecting some homebuilts to achieve impressive values, at the expense of comfort and speed.

I have flown DA40NG, SR20, M20J they all show nice MPG numbers with decent 120KTAS-130KTAS…

DA40NG used to cost 17£/h in UK to fly when JetA was at 0.7£/L in flights that are exempt from fuel duty

These are certified 4 seats travel machines in the sweet “200hp” spot: they not 300hp-600h-machines that fly cross continents with 100LPH in all weather and they are not 65hp homebuilt that stay in circuit with 10LPH anytime wind is > VRB005

In M20J, I can get 5NM-6NM per L by leaning at 50%-55%, even more by flying 40% but 90kias speed becomes ridiculously low for my taste: the preferred economy profile is usually around 115kias-120kias on 6GPH, at 6kft-8kft that is near 130KTAS-135KTAS on 22LPH

Last Edited by Ibra at 16 Feb 08:23
Paris/Essex, France/UK, United Kingdom

With all the climate terrorists around, it is often forgotten that aircraft are indeed most efficient for fuel per speed and distance. Simple reason, mobility is Physics and aircraft had to be energy optimised from the beginning to even lift off. Look at the typical take off weight and compared it to cars – advantage aircraft. If you want to go with the least fuel consumption at 125 miles per hour on distances, take the aircraft – that simple.

Yes, there are two kind of aircraft, more efficient and even more efficient aircraft, but all that starts to matter when talking travel cruise, go somewhere. GA shifted rather something from travel to round the block Sunday coffee leisure flights, so arguments are different now. Focus discussion on trying to optimise costs for coffee rounds, by the least fuel consumption, will not do the topic good, imho. We might end in the same blame corner as the VSTOL approach will by adding the worst of cars to flying.

Last Edited by MichaLSA at 16 Feb 08:50
Germany

MichaLSA wrote:

With all the climate terrorists around,

Can we keep a civilised tone, please.

it is often forgotten that aircraft are indeed most efficient for fuel per speed and distance. Simple reason, mobility is Physics and aircraft had to be energy optimised from the beginning to even lift off. Look at the typical take off weight and compared it to cars – advantage aircraft. If you want to go with the least fuel consumption at 125 miles per hour on distances, take the aircraft – that simple.

Well, maybe. For the given speed, yes. OTOH the alternative if you want to travel with that speed is not cars but trains, and then the trains win.

Last Edited by Airborne_Again at 16 Feb 09:09
ESKC (Uppsala/Sundbro), Sweden

Airborne_Again wrote:

Well, maybe. For the given speed, yes. OTOH the alternative if you want to travel with that speed is not cars but trains, and then the trains win.

Only if you find 100 people on the same track at the same time and with a vast consumption of space for tracks and infrastructure.

Germany

Concerning an SR20, with our G1, we always planned on 39 litres per hour when cruising at 135 TAS (LOP) – meant around 15.6litres per 100km, so not particularly impressive. A big turbo diesel such as a BMW 530d or Audi A7 3.0 TDI could do 250km/h slurping around 11 to 12 litres per 100km, if the motorway was clear….

However I’m regularly impressed with the performance and fuel economy of my new steed. 120 knots true at 2000 feet whilst burning 17 litres per hour, means around 7.6litres per 100/km or 7NM/Litre. Just love that 912iS motor….

EDL*, Germany

Well, coming from an airline background I tend to view it on per-ASK basis (per available seat-kilometre) rather than per km or nm. While the distinction is not too relevant on cars, it seems to be on airplanes since 2-seaters vs 4 or 6-seaters are on different leagues on a per-km basis…

Also, I tend to travel with friends or family although not necessarily filling all the seats, so perhaps should be on a per-POB-km basis!

Is it less meaningful than on a per-km basis?

Last Edited by Antonio at 16 Feb 14:02
Antonio
LESB, Spain
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