Just want to start with, I'm not a pilot, just an average joe with an engineering background so I welcome any criticisms and explaining you feel like (theres no hard feelings on the internet right). I've been reading a lot about downwind turn myth stuff and just wanted to put out how i see it and see if ive got it right. Also want to pre-empt; im not including drag forces and other stuff thats relevant for real world applications here, this is just about clearing up the concepts that have been thrown around.
- I dont agree with the author of the OP link,
- there is no change in the magnitude ground speed of the aircraft when you turn into/out of wind (assuming no motor, no drag, no friction, ignoring increase in speed due to gravity or conversion of gravitational potential energy into KE); I think the big problem is that people forget about a direction change does not equal change in magnitude.
- upon changing headwind/tailwind you will change your "true airspeed" (as far as i know true airspeed is defined as velocity of airmass relative to the aircraft).
- DS relies on wind shear gradient,
- all DS flight patterns revolve around climbing in headwind and descending in tailwind
Ok so here im sort of guessing;
DS takes advantage of
- flying into headwind which assists in generating lift due to higher true airspeed flowing over the wings (assume you turn before you stall)
- flying into tailwind does impart a little kinetic energy to the aircraft (might be one of these or a combination or maybe something else)
- lower true airspeed results in less drag forces so you get higher efficiency in converting potential gravitational energy into KE
- I assume that as the heading of the aircraft changes (during the turn) some portion of the headwind is being used as a propulsive force and not a lift gaining force (AoA and
pitch/yaw will make this relative but you get the idea).
Its the relatively high frequency of loops over short 'straight legs' which allows to DS work in the real world as 'straight' legs dont net you any increase in energy while drag will still occur. Said another way is; its the turns which could theoretically(?) add energy coupled with the wind gradient which allows for more efficient energy conversion between height and momentum which DS operates on. Side note; unless there is negative true airspeed (from trailing edge to leading edge) there can be no propulsive force exerted by the wind and lets just ignore this scenario.
By all means let me know if I've used jargon incorrectly, forgot something or theres a flaw in my logic. I'm just here to learn from people more knowledge and experience than me.
Cheers guys