Caleb Elliott
Enthusiast
As we were flying from headwind to tailwinds near the storms, everytime we turned into the inflow (making a headwind relative to the aircraft) I would reduce power slightly to maintain a constant indicated airspeed and TAS while noting a reduced groundspeed. Everytime we turned to fly with the wind, I would increase power just a bit, as the indicated and TAS would decrease by about 10-15kts and the groundspeed would increase by roughly the amount of wind aloft. Although the increase can be seen the closer to the ground you are, I spent most of my time monitoring instruments and less time looking out the window than I would have liked. Relative to the airfoil/aircraft, the wind changes do cause performance changes. An increase in headwind will yield a slower ground speed, increased TAS and increased indicated airspeed, and vice versa. When the change happens faster, say in a microburst, this is noted as windshear or LLWS and can be fatal if not prepared for the performance changes.
Any time that we turned the aircraft into the wind or away from the wind, although the indicated and TAS would fluctuate 10-15kts, the biggest and most noticeable factor that the aircraft was experience increases or decreases in wind related performance was our altitude. When we would turn to a tailwind, the aircraft (in order to maintain its trimmed airspeed) would start to descend as a result of the loss of headwind component. Anytime turning into a headwind, the aircraft wanted to climb.
The same was also noted when transitioning boundaries. On our way to KFSD we crossed the cold front into the warm sector. The cooler, descending air that was a tailwind for most our trip there was lifting the warm air up and over the cold. We transitioned with moderate turbulence, large ascending altitude deviations, and and huge increase of indicated and TAS. This was also similar near KOMA later that day as we transitioned several outflow boundaries near the tornado warned cell west of Omaha. During one of the outflow transitions, our headwind sheared to a tailwind, which resulted in a decreased TAS(true airspeed is the speed of the aircraft moving through the air and is directly responsible for aircraft performance). The decreased TAS was enough to allow the aircraft to start a 1200fpm descent. I increased power, pointed the nose down to increase my TAS and recovered. Point is, you dont fly an airplane based on groundspeed for anything other than descent rates, fuel burns, ETA's, etc. Aircraft performance is based on TAS, which is again, what the aircraft "feels".
If you reduce power to maintain a constant groundspeed it is very possible you could stall the aircraft, due to lack of TAS, and still have a 75kt groundspeed. On the other hand, and this we did to lengthen our time videoing storms, is to reduce power with an increased head wind and maintain a relatively slow, if not stationary position over the ground. At one point, near the La Crosse, KS supercell, we slowed the aircraft down to 10kts above its Vref landing speed (70-75kts w/ flaps at 10-20degrees) and were maintaining around 25kts across the ground.
Caleb Elliott
Commercial Pilot (SEL, MEL, IFR)
Flight Instructor (CFI, CFI-I, MEI-I)
Ground Instructor (Advnaced and Instrument)
