Originally Posted by
hans brinker
So you think that in cruise, with a steady wind from the left and no power changes, if you turn left your airspeed will increase, and if you turn right it will decrease?
If your aircraft has a finite inertial mass, and there is a rate of change, then, yes.
Now, you can go on line to a web page like this one:
https://www.planeandpilotmag.com/article/downwind-turn/
and amongst the pretty pictures you will note a statement that is made that is the logical limit of the problem, and yet, the wrong conclusion is made from the limit case.
If indeed you turned 180 degrees from a 50 kt headwind to a 50 kt tailwind and you started at, say 50kts, you would indeed have a problem, you have just had a 100kt instantaneous shear occur, so how does the aircraft, which includes tin, plastic, protoplasm and gas, e.g., has mass, how does that go from the zero ground speed to 100kt ground speed in zero time? That would be an acceleration required of....:
(50m/sec)/0.5= 100m/sec,
which is a shade over 10g horizontal. In the same case, the C-172 or Piper Cub can accelerate at.... around 0.15g longitudinally. A lear gets about 0.2g with TFEs, a B773W gets about 0.18g... An F-18 gets just around 1.0g, an F-16 light gets about... 1.1g down in the weeds. roughly.
For most flight training, the ground reference case is not done pulling 2g in a steep turn, and with a 50kt wind, but if it did, you would still be looking at a modest shear rate... at 100kts CAS, you would take 9.8 seconds to do the 180, and meet a shear of 100 kts, so that is about 10kts/sec, which is going to need an inertial acceleration of 0.5g. That would actually exceed most aircraft out there. take the normal ground reference cases at a 25-degree bank, and that equates to rate 2, or just on 35 seconds for the same 180 turn, and that gives just on 3 kts shear per second, a relatively trivial amount, which you would see as a need for a bit of thrust change, as in... 0.15g longitudinal, well within a Lycoming or Conti's capability. And that is with a 50 kt wind... Most training is done in winds around 15-20kts for the same case, and the effect is perpetuating the position that planes. have no inertial effects. (15kts... 0.05g, etc... barely enough to set off an entry interface for the space shuttle).
Why this is a factor mainly at high altitude or with rapid wind shear is where there is a considerable rate of change, limited excess thrust, and high inertia. It is observable with 200kt jetstreams, or high vertical shear rates when climbing and descending at high rates of VS. It also is
why losing a 30kt headwind on an approach will result in an instantaneous loss of airspeed, and a delay as the GS increases....
If you need more background, you can PM me, and I will forward some reading for you.