Does it take more power to fly downwind?
Of course not! Your wing doesn’t care which way the air is moving. Or does it?
You can verify that wind makes no difference by going up high on a windy day and doing a level 360. It’s the same power required all the way around. Hold the power steady and watch your altimeter. The physics, aerodynamics and experiment all show this to be true.
But there is one little exception where the downwind demon is real, albeit in a minor, rare way.
The gist is that, with a wind gradient very close to the ground, the wing may be flying in different airflow than the motor 15 feet below.
Chapter 19: Risk & Safety covers risks associated with various aspects of the “Downwind Demon”
The discovery of this was kind of funny.
At a fly-in Nick Scholtes quietly pulled me aside and said “Jeff, now we both know that there is no difference in flying upwind or downwind but I just got back and swear that it took me more power to fly downwind than upwind.” He went on to explain how he did several runs to verify it and only noticed it down low, at maybe five feet high. So I went out to see if I could duplicate his observation and, sure enough, I did—needing several hundred more RPM to go downwind as upwind. That’s what got me trying to figure out what was going on and a few days later put it all together. Read the PDF to see what was happening.