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).
During a turn the load factor increases. This increases the apparent weight. Thus, during a turn, the best glide speed is selected according to the weight times the load factor.
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.
$$V_{opt,\theta}= \sqrt{\frac{1}{\cos{\theta}}} V_{opt,0^\circ}$$