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Fuel efficiency in cruise

On Mooney (poh numbers are 5kts-10kts higher),
55%: 145TAS at 6GPH
65%: 155TAS at 8GPH
75%: 165TAS at 10GPH

Given avgas price, something to think about on Speed vs MPG, is 10kts worth 2GPH?

For DA40ng, given (UK) price of JetA, I wonder if it make sense to fly it at 40% power and not 92%? althought I was told flying it at 70% power lead to the lowest maintenance cost…

Last Edited by Ibra at 11 Jul 17:30
Paris/Essex, France/UK, United Kingdom

Ibra wrote:

I was told flying it at 70% power lead to the lowest maintenance cost

What engine maintenance costs would this describe for an engine with a fixed interval between total replacement, with no engine overhaul supported by the manufacturer or other parts suppliers? Accessory replacement as a function of increased RPM? Turbocharger replacements?

Ibra wrote:

The M20J at 8000ft does 145TAS at 6GPH, that is 0.15L/nm but I fly it WOT/2500rpm at 165TAS at 10GPH (the POH is is 175TAS)

Acrually flying it LOP at 125IAS all the way climb/cruise/descent does the job for fuel efficiency

More like 7.5-8 GPH for 145k KTAS? Mine is a few knots slower than the book. Fully loaded it should do 164 kts on 10.1 GPH but I would sit in the high 150s. Let’s see if an overhaul and new engine mounts can catch me up. It was sagging a little.

EIMH, Ireland

Also curious about the question @silvaire raised.
As it is TBR, flying faster should be cheaper.
X number of flights at max speed vs X+ number of flights at slower speed.

always learning
LO__, Austria

Maule MX-7-180: about 34 l/hr @ 100 kt TAS (with extended MLG and 31” Alaskan Bushwheels and baby bushwheel); so about 0.34 l/nm.

Fuel consumption is about 5% more at MTOW, 5% less at “play” weight.

4 seats, of which 3 usable by adults with luggage and full main tanks, due to aft CG limit with glider hook, etc. – so about 0.12 l/pax.nm.

As with automobiles, there’s a fuel consumption penalty for true “off-road” capability. Still, it was more than 1 hour faster than CAT door to door from/to Glenswinton to/from Nurnberg. Longer trips would require a fuel stop.

Last Edited by Jacko at 11 Jul 22:54
Glenswinton, SW Scotland, United Kingdom

X number of flights at max speed vs X+ number of flights at slower speed.

Hmh not sure I made sense there.
It should be more distance covered in the same hours.

always learning
LO__, Austria

Gazelle SA341. 160 l/hour jet-a1. 117kts cruise=1.36 l/nm.
But it saves the drive to the airport :-)

EGKL, United Kingdom

carlmeek wrote:

But it saves the drive to the airport :-)

On short distances the MPG is an irrelevant measure otherwise dragsters don’t exist

Paris/Essex, France/UK, United Kingdom

carlmeek wrote:


But it saves the drive to the airport :-)

It is a silly question, but at what distance does a helicopter beat a bicycle in travel time?

Assuming a proper full preflight inspection, startup sequence, takeoff, landing and of course proper shutdown upon arrival, I do think the bicycle will be faster for a few km (because you just grab it and go).

Of course economically, a bicycle beats each and every other mode of transport for short distances…

Low-hours pilot
EDVM Hildesheim, Germany

I’d rather beat or thrash my way into the air anyway possible before electing to get on a bike.
;-) ;-)

United Kingdom
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