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Comment by goodcanadian | Hacker News Reader

. . . average power setting of around 35%

That actually sounds about right. You only need full power for take-off.

EDIT: Thanks for the corrections.

Like the others, I’m also a pilot and confirm that we cruise in the 65-75% of rated power range in piston ops. Turboprops do have a larger power reserve / larger spread between rated and cruise power, but it’s nowhere near 25% in cruise.

How much would that change if you had a possibly lighter engine, and an empty hull (all extra weight disposed off)?

It’s only on max range flights that I throttle back as my airplane gets lighter. On typical flights, I instead take the 3-4% speed increase as the fuel burns off.

Lightness is a hugely important feature in airplanes. I’m not sure that current battery tech is poised to deliver on lighter aircraft for a given mission range. An additional drag (pun intended) for electrics is that landing weight is the same as takeoff weight except for skydiving ops.

As a pilot, I fly full power at takeoff, of course. In my usual piston plane, I fly at 75% power until it cannot maintain that power (due to normal aspiration and no boost from, eg, a turbocharger), and then "flat out" beyond that.

I do not think I have ever flown at 35% power except in the short time between final and touchdown.

At the risk of sticking my foot in it even further . . .

I fly at 75% power until it cannot maintain that power

Does that not mean that you are actually flying at well under 75% of the rated power even if it is the maximum power available at that altitude?

Yes, though normally aspirated pistons typically stay under 8500 MSL and very rarely exceed 12500 MSL. IIRC, you can make 75% power unboosted through around 7000’ MSL. I’d guess at least 90% of normally aspirated flight is under 7000’. It certainly was for me, even though my previous airplane could climb higher, it was slower up there, so I rarely flew it over 10K unless there was a screaming tailwind up high or terrible turbulence down low.

If I looked over all my engine monitor downloads for power settings under 35% while airborne, I bet the average would be under 1 minute per flight and it would be between 200’ and landing.

It happens to fly low power, but only in rare occasions. I do that when I cross the mountains and I reduce the power while loosing altitude from ~ 10k to 200 ft at landing. The longest I flew with the engine turned off was ~ 30 miles, that was in a motorglider with the propeller feathered. These cases are so rare, but still exists.

That is ridiculous - you wouldn't carry the weight around for that power level for such a short flight segment need. If you are averaging 35% power you have WAY to big an engine in your plane!!

Electric motors are very cheap and light for a given power output, especially for forced air cooling, so oversizing them doesn't impact the cost or weight too much.

They might use that fact to oversize them giving better redundancy (eg. one can fail during takeoff and it not be an issue).

In aviation where every kilogram matters and where you can put more batteries instead of an over-sized engine, that logic does not work. There is zero redundancy from oversizing the engine.

I think they meant that you can have engine-out during takeoff in a twin-prop, as long as you can steer against the prop's torque. It also gives you much steeper climbs, which is highly beneficial, particularly in some mountainous regions.

> particularly in some mountainous regions.

Yep. I lived in Truckee for awhile, and the local airport there is notorious for pilots making "unexpected landings" into the mountainside right after takeoff because they didn't climb fast enough.

not even close.

Piston planes cruise at about 75% rated power (engine manufacturers do not suggest running engines beyond that for extended periods of time). Jets closer to 90

Jets typically can’t make 90% power in cruise and are often flying at 50% or lower fuel flows than takeoff. (You might be setting almost 100% N1 speed as your power setting, but that’s not the same as setting 100% actual power in a jet in high-altitude cruise.)

Fuel flow is a good proxy for power. From the Citation II flight manual: max cruise thrust settings (104% N1 over 25K feet) have a peak fuel flow of 1716 lb/hr at 15K feet vs 1083 lb/hr at 35K vs 721 lb/hr at 43K ft. Sea-level takeoff fuel flows are not given in the manual, but are around 2000 lb/hr, so typical low 30s cruise flight is 55-65% power.

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