What effect does high density altitude have on the efficiency of a UA propeller?
Why →
At high density altitude, air is less dense. A propeller blade moving through thin air encounters fewer air molecules per rotation, generating less thrust for a given RPM. To maintain the same thrust, the motor must spin faster, drawing more current and reducing battery endurance.The trap →
"Less resistance" sounds like it would improve efficiency, but propellers need air molecules to push against to generate thrust. Less density means less thrust per rotation, not better performance.SOURCE → PHAK Chapter 11, FAA UAG Sample Question 38CHECKED APR 21ACS III.B.K2MED