Originally Posted by
hans brinker
A levels in highschool, studied physics. Show me your PhD
No paper show to you, though I do have a PhD in physics......
Maybe consider the following situation. We all know, that to physically "destroy an airplane" against a solid surface, we need to start with a sufficient amount of Potential + Kinetic energy (so, either height or speed, or a combination of that).
Assume, have an airplane (stall speed 35Kts) 1 mm above the runway, have a headwind of 40 Kts (Alaska, can happen) and an airspeed V of 40 Kts. Engine powered to keep that airspeed. Your ground speed will be zero. Your potential energy (relative to the runway) is very small and can be ignored.
Do the thought-experiment to snap turnoff the headwind as well as the engine. Of course, the airplane will immediately settle, with minimal mechanical movement, since it was not moving compared to the runway, even, the wheels will not start turning.
Will the airplane bleed off a Kinetic energy of 0 (IE effectively nothing happens) ?
Or will it bleed off a Kinetic energy of 0.5 * m * V(airspeed) ^2 and effectively destroy the airplane ? Given common sense tells us, the airplane will not be destroyed, the presumed amount of Kinetic energy has to go "somewhere". When not knowing where Energy goes, it is usually turned into heat. So, will the airplane (or the ground, or the -now no longer moving- air) heat up ?
The reverse of this experiment: Airplane on the runway. Have a headwind of 40 Kts, use the engine to keep the airplane steady on (!) the runway, wheels not moving. Your airspeed will show 40 Kts. To avoid, the airplane climbs above the runway, hold the elevator down, to stay on the ground. What is the Kinetic energy of the airplane ?
Do the same, by holding the brakes (instead of the engine). What airspeed will be shown ? What is the Kinetic energy of the airplane ?
Now, return to the first experiment. The airplane not 1 mm above the runway, though on the ground, with non-compressed struts. What is the Kinetic energy of the airplane ?
The same, though now with struts compressed. What is the Kinetic energy of the airplane ?
Next step. No headwind. No ground speed. With increasing headwind, the airspeed will go live, with the airplane stationary using brakes. What will be the Kinetic energy of the airplane ? What will happen when we snap-turn-off the headwind ? Assuming the airspeed will be the measure for the Kinetic energy, where will the Kinetic energy go, when the headwind turns off ?
Gives me the feeling to argue with "The Truth"........