Steve6443 wrote:
my new steed. 120 knots true at 2000 feet whilst burning 17 litres per hour, means around 7.6litres per 100/km
That’s fantastic. What’s your new steed?
Steve6443 wrote:
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….
I tend to think in A2B category and on my typical race tracks flight miles are about 20 to 30 percent less than car miles, but strongly dependent on destination. Last year I was commuting to a place where car miles were more than double the flight miles – remote East Germany with the advantage office in walking distance of a small airfield.
Steve6443 wrote:
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….
That sounds really impressive, heard quite some stories of the 912iS already, but had no chance to try out one. Which bird did you get?
I think that one of the more efficient and fast aircraft, if not the most, nowadays is the Risen of Porto Aviation Group. Attached a screenshot of the EFIS of a friend of mine with his Risen 912iS doing 158KTAS burning 14Lt/h (3,7gal/h) resulting in 20,9km/L (49,2 mi/gal). The combination of a very sleek and efficient airframe with the electronic fuel injected engine is simply outstanding, still maintaining under 32kt of stall speed and side by side seats. Soon I will have the 915iS version with shorter wings and higher typical speeds, it will be a rocket but a bit less efficient.
Predator wrote:
158KTAS burning 14Lt/h (3,7gal/h)
That is a really impressive number!
Oh, wait, I notice 50fpm descent in the VSI, that may be worth 5 KTAS ;!
andy_flyer wrote:
Do you know of planes (2-4 seater SEP) that are especially fuel efficient ?
The Europa is really good at economy cruise – you’re still doing around 120kt, but with about the fuel per nm (no wind) better than most cars. But if you’ve ever been in a Europa, you know the trade off is for a pretty tight cabin.
I can confirm that (fuel economy and tight cabin :-)
andy_flyer wrote:
Do you know of planes (2-4 seater SEP) that are especially fuel efficient ?
gazaile2. 3.5 l / 100km @ 120 knots.
LH10 iirc was supposed to be very fuel efficient, but i don’t know if they actually sold any before they went the military route. Also can’t find actual numbers.
Canards should be very fuel efficient, but I don’t know if they can beat a gazaile2. Maybe with an engine thats more modern than a lycosaurus. They do fly a lot faster though.
Predator wrote:
Risen 912iS
Didn’t know that one, but i’d assume most of those modern fast sleek 2-seaters – also vl3 and shark – should be rather fuel efficient when flying slow.
Airframe design and the associated need for power is mostly what drives economy. As many have mentioned many times before unless you’re comparing turbo with non-turbo the particular choice of engine design or manufacturer has limited impact on fuel economy in cruise flight. It doesn’t seem to sink in.
Having said that and moving on to more substantial issues, unlike with cars the comparative fuel economy of a given aircraft design depends a great deal on how you use the plane. It seems to me that if the intent is only long distance flying, and if airspace design is reasonable, you fly up high where many high horsepower designs go and do well in terms of mpg, with the additional benefit of being also able to burn more fuel when needed, to have good load carrying and good takeoff climb capability.
On the other hand if your intent is to utilize the plane for local low altitude flying AND cross country flights, you need a low powered engine to be economical – high powered engines don’t like to run at low power to save fuel when at low altitude, even if the speed and airframe performance would be OK if they did. That choice of a low powered engine tends to sacrifice utility because you can only do so much at low altitude with a limited amount of power and fuel burn.
Turbonormalizing attempts to get the best of both worlds and it helps, at the expense of considerable complexity. And there’s no substitute for high rated horsepower when you need to climb fast after takeoff while carrying weight.
Different aircraft designs mix these factors in different ways, making designs that are economical and/or useful in different applications. Planes are not cars, where a single number or maybe two (highway and city fuel economy) is almost enough to compare any of them – highway speed and carrying capacity is generally equal and climb/altitude is not a factor.
When buying a plane, I think that many people subconsciously weigh these factors in their head, and select a design for their own particular version of economical use. Naturally enough, they then assume everybody else’s use of an aircraft is similar to their own 
Most of our airplanes can do quite nice MPG figures. I did some calcs a few years back following another debate here and some numbers I came across are quite neat for an airplane in comparison to cars: (MPG meaning SM per USG)
The best MPG I found in my list was the Mooney 201, which will do 18 MPG or 13.1 l/100km and the C model is following close behind with 17.5 MPG and 13.5 l/100km. Most of the others are somewhere between 14 and 15 MPG with corresponding values of 15 l/100km.
This however is absolutely raw consumption. It does not take into account something VERY important: Airplanes usually fly a very much shorter route than a car would. I did some calcs out of ZRH once and found that the average is around 25% shorter ground distance with the airplane than by car with extreme examples going up to 30% and others down to 15%.
So looking at it that way, the MPG figures change to values between 23 MPG tops and 18 MPG average, corresponding to 10 and 11 liters per 100 km.
And that is not really optimized for max efficiency but simple 65% cruise out of the POH. I am sure with some optimizing one can operate one’s airplane a lot more efficiently yet.
6 NM per Liter is very impressive. I wonder what plane that is.
If you’re just looking for big mpg numbers, for that purpose a lot of people like to point to Klaus Savier’s Long-Eze: a little under 40 mpg at 252 mph. (in statute miles and USG). That’s 9 NM per liter at 220 knots.
He also claims a climb rate of 2500 fpm.
