Strange headwind phenomenon
Another naive question!
Flying circuits with 11 - 15kn of wind reasonably aligned with the runway (runway 07, wind around 050) I found that I had to significantly increase the power to achieve the desired airspeed on finals. I would normally expect to trickle along at 70kn IAS with around 1,700rpm as I descend on finals, this time I was using > 2,000rpm. It felt reasonable at the time as I was battling a headwind, but in retrospect I find it hard to understand. Of course I expect the groundspeed to fall in proportion to the headwind, but why is the IAS apparently declining for the same power setting? I can't work this out. I guess my sink rate has to also reduce as my groundspeed falls, because I am flying slower with respect to the glide-slope. So I guess I am maintaining more power to descend more slowly? Can that explain the whole of what seemed to be a big effect? Or was power required to counter increased drag from the modest amount of crabbing I must have been doing?
(It was great fun coping with the occasional blasts and swirls, and the headwind made for some sweet, short landings)