Best lift/drag speed question
Hi everyone,
Been having a little argument over what is the best lift/drag ratio speed in a C152.
Just quickily to re-cap, best L/D speed is usually at an angle of attack of 4 degrees, correct? Cessna manual gives the best glide speed at 60kts, which we can assume is at 4 degrees, for the best lift/drag ratio(max glide range).
Problem is I'm told that 60 kts is also the best lift/drag ratio speed for level flight. This I can't understand.
Firstly in a glide, the path travelled of the AC is downwards, so the relative airflow is opposite(coming from below as well as in front). Where in straight and level the relative airflow is from directly ahead. This would affect the way the wing produces lift.
Any also just thinking about it logically, aircraft are designed to crusie at around 4 degrees angle of attack, so one would think the best L/D ratio speed would be around 95 to 100kts? Think about the nose attitue you would have flying straight and level at 60kts, surely the angle of attack must be higher than 4 degrees.
Cheers,
Stefan