Exactly! Your question is very valid.
The question should be phrased "What effect does "high altitude have" on the efficiency of a UA propeller?
high density altitude seems to be an oxymoron. At high altitude the air is less dense.
"Aircraft pilots know this.... Lower air density penalizes pilots in three ways: The lifting force on an airplane’s wings or helicopter’s rotor decreases, the power produced by the engine decreases, and the thrust of a propeller, rotor or jet engine decreases. These performance losses more than offset the reduced drag on the aircraft in less dense air. "
We don't have worry about combustion engine power loss, only propeller lift force loss.
Good point.
I guess the only thing comes to mind is that the Mavic will compensate, but the battery life will be shorter.
Not quite that simple, because at high altitude you must of course calculate density altitude in order to be safe when taking off, but geberally, only in an aircraft you are sitting in. However, when compensating you must also take into account the ambient air temp, because this affect density altitude. The hotter the air at that high altitude, the greater the density altitude, or in other words, the thinner the air, so the longer the runway needs to be in order to take off and the less performance you will have in that aircraft as you carefully climb out.
I used to fly out of a dirt strip in Granby Colorado of 1,800 ft in length and our runway altitude was 8,200ft with a barbwire fence at the end and beyond that a slight rising hill. There was only one way out because of a mountain side close to the other end of the runway. In winter it was no problem to get off and be well clear of everything on take off and climb out. But in summer we were not so lucky. Most days we were fine from sunrise but as the morning temps rose, it was only until about 9:20am before it was not safely possible to take off and clear the fence or the rising hills past the end of the runway. And even earlier to shut down take offs if you had a passenger on board, because of the added wait, combined with the drop in performance of engine/prop and lift efficiency of your lifting surfaces (wings or rotor blades).
Cold summer days were still fine to fly past 9:20am but warm or hot summer days meant that there was no more flying until later in the evening after a certain time passed in the morning (between 8:30 to 9:30am most days), because you could not get off the ground in time to clear the fence at the end, or could not clear the rising ground after the end of the runway if you did manage to clear that fence, and don't even think about making a turn just after take off.
Several pilots have taken off from high altitude runways in summer with full flaps and been flying at a shallow climb angle, more or less still in ground effect, then dumped theor flaps to clean up the aircraft, thinking they were improving their performance, only to find their aircraft dropped to the ground once they dumped the flaps, and of course crashed. After flying at our runway altitude, we used to think of Denver as sea level!
As has been stated, this is very important to know for real pilots sitting in aircraft, but of little use to a drone pilot, for anything other than lowered battery life and slower climb performance.
