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When gliding what are the effects of a crosswind on my glide path angle?

If I have head-wind, the minimum flight path angle (usually called gamma) will be lower than the one without crosswind and with an attitude with a larger lift coefficient Cl than lift coefficient of max efficiency with no wind?

On the other hand, if I have tailwind gamma will be greater and the Cl will be lower than Cl of max efficiency. Briefly if I have tailwind without engine I can glide much longer, is it right?

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  • $\begingroup$ You seem to have two questions unrelated questions - your first sentence and your last. They are both valid, but would probably be better being separated into two posts so they can be addressed individually. $\endgroup$ – FreeMan Jul 10 '15 at 15:15
  • $\begingroup$ your use of 'crosswind' and 'headwind' and 'tailwind' makes it hard to understand what you're asking $\endgroup$ – rbp Jul 10 '15 at 15:45
  • $\begingroup$ I changed horizontal wind to crosswind, so I may have misunderstood the original intent and messed things up. Feel free to undo that if necessary. $\endgroup$ – FreeMan Jul 10 '15 at 16:19
  • $\begingroup$ @FreeMan horizontal means that it simply has no vertical component. crosswind is more restrictive: the main wind direction must not be parallel to the direction of travel. Given the original intentions (the example is for headwind) I would have left the original formulation. $\endgroup$ – Federico Jul 10 '15 at 17:32
  • $\begingroup$ That makes sense, @Federico - my changes were based on the fact that OP specified head wind, tail wind, and horizontal wind, so I assumed he meant cross wind. Again, anyone is free to revert/reedit without hurting my feelings. $\endgroup$ – FreeMan Jul 10 '15 at 17:56
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Wind affects your flight path angle by affecting how far you travel while you're descending.
With no thrust from the engine an airplane is falling out of the sky at a roughly constant rate of descent. The wind direction affects the groundspeed, and thus the distance covered between when the engine failed & when the aircraft hits the ground.

This is more directly observable from outside the airplane.
Consider these 4 scenarios on a post-it note: The airplane has lost its engine, and the pilot is flying at best-glide airspeed while holding a constant magnetic heading (making no wind corrections):

Post-It Note

No Wind
The aircraft descends along the no-wind glide path (about 45 degrees in my drawing), and travels in a straight line over the ground (the "ground track") while doing so.

Headwind
The aircraft descends along a steeper glide path (about 60 degrees in my drawing), because while it's still descending at the same rate the headwind is slowing its progress over the ground. Since it's a direct headwind (right on the nose) the ground track is still straight.

Tailwind
The aircraft descends along a shallower glide path (about 30 degrees in my drawing), because while it's still descending at the same rate it has a tailwind, which is making it move faster over the ground. Since it's a direct tailwind the ground track is still straight here too.

Crosswind
The aircraft descends along the no-wind glide path (because it has neither a headwind nor a tailwind), but the crosswind pushes the ground track (in this case into the inconveniently-placed tree).


Your endurance (time aloft) will be similarly unaffected: If you've set the aircraft up at its optimum glide angle-of-attack (best glide airspeed) the descent rate is pretty much the same regardless of whether you have a headwind, tailwind, or crosswind. You will fall the same distance in the same amount of time, it's just a matter of how far you travel while you're falling (which determines where you land).
You can test this for yourself in an airplane by doing engine-out drills: Line up with a headwind, pull the throttle out, and pitch for the aircraft's best glide speed. Note your vertical speed (rate of descent), and then repeat the test in the opposite direction (tailwind) or at 90 degrees to your original course (direct crosswind): The vertical speed will be effectively the same.

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In general, wind does not affect the aerodynamics, it mostly affects where you land. So, for example, if you have a tail wind your glide time will be the same, but you will travel farther than if you had a head wind.

As far as the "minimum flight path angle", the angle of maximum drag, that is largely irrelevant to actual flight because you never (intentionally) fly at that angle. When gliding, you usually aim at the best glide speed which will take you the farthest, or occasionally at minimum sink rate rate if you want to maximize your time of flight and distance is not a factor.

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  • $\begingroup$ Why is the minimum flight path angle the angle of maximum drag ? So you're saying that that maximum range is obtained with max velocity ? And forgive me, what is the skin rate ? $\endgroup$ – Davide Jul 11 '15 at 7:55
  • $\begingroup$ @Davide I assumed you were aeronautical engineering student since minimum flight path angle is a technical term that I have never seen used except in highly technical aeronautics. In any case if you refer to an aeronautics textbook it will explain the term, which is complicated. The maximum range is attained with the best lift-to-drag ratio. The sink rate is the distance of vertical descent per unit time. $\endgroup$ – Tyler Durden Jul 11 '15 at 14:40

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