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Fuel efficiency in cruise

MedEwok wrote:

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

having been overtaken by a roller blader while cycling yesterday, I beg to differ…

Biggin Hill

Not at a grass strip you won’t be ;-)

tmo
EPKP - Kraków, Poland

The DA-42 that crossed the Atlantic averaged less than 6gal/hr in total! But I think he was flying at 35% power and had the benefit of a good tailwind. He had 76gal LR tanks and an onboard ferry tank with another 26gal, but I don’t think he ever used the ferry reserve. Think he landed having burned 72gal, so had another 45min of reserves on the standard tanks! I mean, if you ignore maintenance, engine reserves and capital, this guy crossed the Atlantic for $200 in fuel cost! Try finding an airline ticket for that.

With tailwind, best MPG is obtained at a speed below the still-air optimum (so you get the most benefit of the tailwind) and the opposite with a headwind.

What was the DA42’s route? The Atlantic direct (UK to US) is about 2500nm.

Administrator
Shoreham EGKA, United Kingdom

Cirrus SR20 G1 operated ROP (full rich but engine has altitude compensating fuel metering)
Average for a 3 hour trip at FL070
45 lph 147kts TAS

Pilot-H wrote:

Cirrus SR20 G1 operated ROP (full rich but engine has altitude compensating fuel metering)
Average for a 3 hour trip at FL070
45 lph 147kts TAS

Unless I’ve been in a hurry, I’ve never felt the need to fly at ROP – we typically flew our SR20 G1 FL070 with TAS around 135knots with average 35.5lph LOP, that meant 16 minutes more flight time for the same distance but 106 litres fuel instead of 135litres….. The benefits of the SR20’s single level is no messing with manifold pressure / rpm settings – all we did was just to turn the MFD onto engine page and then perform a big mixture pull back to 9.4GPH whilst leaving the throttle wide open….. the first engine went 2500 hours before we decided to go for an overhaul due to oil burn but even then, the reports came back that the engine would have been good to go for at least five or six hundred more hours, had we just elected to have some cylinder work done…

EDL*, Germany

A very comfortable cruise setting I use often in the DA62 is 85% power between FL100 and FL120, Jet A is relatively cheap compared to Avgas so I choose to fly at higher power settings.

On a recent trip at FL115 @ 182kts:

8.2 gallons / hr / engine (16.4 gallons total / hr) = 62 lts / hour
Fuel consumption = 0.34 ltrs / nm

EGTR

PA46-350P: 0.41l/nm at FL190. That’s babbying the engine (29", 2400RPM, ROP 20.7usg/h, 367 highest CHT, TIT well below 1600, oil temp around 170 degrees). I don’t run LOP in the cruise, only in the descent, but that would give about 0.35l/nm, I reckon (loosing 10 kias, FF c. 15.5usg/h, 340 highest CHT, TIT at 1600).

This is quite an improvement for me compared to last year, where I was running above 22usg/h. Three factors:

  1. a deep clean of the injectors providing such better fuel flow on take off and climb, leaving everything nice and cool;
  2. thanks to FlyingFish and the TxI EIS instruments giving me a view on the intercooler efficiency, I’ve massively improved it (I now see 50% in the cruise, vs 43% before).
  3. I was limiting myself to 360 degrees TIT, but I now feel very much comfortable around 375 degrees).
EGTF, LFTF

How did you clean the injectors?

Normally this issue (common on TB20/21 too) is addressed by adjusting the fuel servo to run at the very top end of its tolerance band (25 GPH on the TB20). For injectors to affect this they would need to be seriously bunged-up, which some claim is possible and others claim is impossible because avgas is a powerful solvent

Administrator
Shoreham EGKA, United Kingdom
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