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Fuel efficiency in cruise

No, not what you might think. Following achimha's apparent surprise at the Meridian's fuel burn, I thought the following is an interesting exercise.

Type: Fuel burn at normal cruise: Burn/nm at cruise TAS:

I'll start.

P46T 276PPH/152lph 0.563 l/nm

EGTK Oxford

PA30 75PPH/47.5lph 0.31 l/nm

TB20 FL100 150kt TAS @ 10.3 GPH = 0.26 litres per nm.

But I can see where this is leading. The fuel in a TBM700, flying outside the UK (i.e. tax free private flight) costs about the same per nm as a TB20

And that was the case in 2002, too, because I remember working it out.

Administrator
Shoreham EGKA, United Kingdom

TR182 0.29l/nm (ISA FL160 65% BHP 155KTAS, my standard setting)

TR182 0.31l/nm (ISA FL200 75% BHP 175KTAS, going fast)

At FL100, I'd be at around 0.31l/nm for Peter's 150KTAS so you can see that the TB20 has a more efficient airframe (but also much smaller cabin). Going higher, I benefit from less drag and turbonormalization so the airplane gets more efficient the higher it flies. Best efficiency is at FL200.

Don't forget that one liter of Jet A-1 contains considerably more energy than one liter of Avgas so your SFC isn't just 50% worse than ours

Mooney M20C

Average [email protected] kt = 0.24 liters per NM.

FL140= 31 lph @139 kt = 0.22 liters per NM.

<FL50= 37 lph @ 142kt = 0.26 liters per NM.

LSZH, Switzerland

Citation V Encore FL 250 (short range) ca. 418KTAS 1720lb/h 2,31 l/NM -> but carries 9 passengers (0,26l/NM/passenger)

Citation V Encore FL 410 (long range) ca. 350KTAS 832lb/h 1,33 l/NM (0,15 l/NM/passenger)

Piper Pa44 Seminole FL80 (IR/ME training) ca. 140KTAS 100l/h 0,71l/NM (0,24 l/NM/passenger)

Interesting to see that the Jet consumes exactly the same fuel per passenger as the multi engine trainer while going three times as fast.

And the most amazing one in that respect that I ever flew (even if a little bit scary, loud, uncomfortable and maybe not really pretty to look at): Swearingen SA227 Metro 23: FL250, ca. 280KTAS, 450lb/h 0,9l/NM (0,05l/NM/passenger)

EDDS - Stuttgart

Cessna 210 (non-turbo) FL130 42l/h 0,28NM

EDAZ

Very interesting so far, keep them coming.

whatnext I think we are looking without passengers although as a bizjet operator that matters to you. Most GA is never flown full seats - I suspect yours aren't either.

Achimha, who cares about SFC? It is an academic number :)

And Peter, you could be right! Even without the travel outside UK.

EGTK Oxford

Most GA is never flown full seats - I suspect yours aren't either.

My experience over the years: The smaller the aircraft, the more seats are occupied. When I was flying Senecas, Cessna 340 and 421 and suchlikes, 90 percent of the time we would fly with all seats occupied. It was always kind of funny when we were parked beside some large bizjet (e.g. a Challenger) and 6 people + luggage + 2 pilots were dumped at our C421 while at the same time a large limo would drive to the Challenger and release one passenger with his little dog.

Now sometimes it's the opposite: We carry one passenger (only one is rather rare, the average must be around 5 I guess) and the Malibu next to us has 5 + pilot on board ...

EDDS - Stuttgart

I recall a recent release from Farnborough mentioning that their average passenger load is something like 2.6. I am sure they would have preferred that to not be publicised too much, given the UK attitude to business jets and anything involving wealth...

However passenger/load carrying ability has to come into the equation, otherwise a single seater would always come top, for a mostly-meaningless mission carrying one person and a toothbrush.

A typical 4-seater is a 3-seater plus some luggage.

Administrator
Shoreham EGKA, United Kingdom
138 Posts
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