# How to calculate best glide speed at a 30 degree bank?

The Best Glide speed is the indicated airspeed that guarantees the maximum glide distance during an engine out scenario. However, the landing straight ahead option after an engine failure may not be the best option especially if there is nothing but houses in front of you after an engine failure. Sometimes turning back towards the field may be the best option.

The Best Glide speed is actually tied to a best Lift/Drag ratio for a specific angle of attack. When in a banked turn, the pilot must increase the angle of attack to avoid a spiral dive. So this implies that the best glide speed would increase during a banked turn in order to maintain the best L/D angle of attack. My question is how would one calculate the Best Glide speed for an aircraft in a 30 degree bank based off the POH listed Best Glide at Gross Weight (I do realize best glide varies with weight).

• This doesn't quite add up. (A) You say "When in a banked turn, the pilot must increase the angle of attack to avoid a spiral dive." When gliding, why must the pilot increase the AoA? Let's say you want to fly at the AoA for Min Sink Rate. Isn't this the same AoA in wings-level flight as in a banked turn? Same for stall AoA? Same for best L/D AoA? The concept of increasing AoA when banked pertains more to flying with a motor and trying to maintain a constant altitude. (ctd) – quiet flyer Mar 18 at 19:21
• I think your presumptions are incorrect. When turning in an engine out glide you still want to maintain best glide speed, which will correlate to best L/D AOA. However, in order to do so you will need to lower the nose, which will increase sink rate. – Michael Hall Mar 18 at 19:21
• (ctd) Then you say (B) "So this implies that the best glide speed would increase during a banked turn in order to maintain the best L/D angle of attack." --yes, it must increase according to the square root of the change in wing loading . So (B) is true. But (B) doesn't follow logically from (A), because (A) is incorrect. – quiet flyer Mar 18 at 19:23
• I think you can still fix this w/o invalidating the single answer posted so far, because the answer only addresses (B), not (A). – quiet flyer Mar 18 at 19:25
• Another huge complication is that a 180 degree reversal arguably has nothing to do with best L/D at all. You are in no sense trying to maximize forward distance covered. You want to minimize time spent in the reversal and you also want to minimize the sink rate during the reversal. I seem to recall I've seen analyses suggesting a 45-degree banked turn is the way to go, letting the airspeed bleed off (or even pulling the stick aft to help the airspeed bleed off) to near min sink for that bank angle -- but certainly not lower!-- I'd have to look some more to relocate those analyses-- – quiet flyer Mar 18 at 19:31

The load factor at 30 degrees bank is $$n=\frac{1}{\cos{\theta}} \approx 1.2$$
The best glide speed is thus the best glide speed for a weight that is 1.2 times your actual weight. This will be proportional to the square root of the load factor. $$V_{opt,\theta}= \sqrt{\frac{1}{\cos{\theta}}} V_{opt,0^\circ}$$