# Flight path angle

## Main Question or Discussion Point

Hello,

What is flight path angle and how does it affect an airplane? What is the difference between flight path angle (glide angle or climb angle) and angle of attack? When the flight path angle is changed during flight, does the angle of attack also changed? I found that lift is always rely on angle of attack only but from aircraft performance discussion I have seen lift also changed with the variation of flight path angle (L = W cos*gamma). Could you explain what does that mean? I reaaly confused with these two angles.

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Thanks. At least, I have known the relationship between angle of attack and pitch angle. How's about angle of attack and flight path angle. In the equations of motion especially in flight performance, flight path angle directly affect the performance calculation.

Flight path angle is a factor in performance because the aircraft is either gaining or losing potential energy (for an angle other than zero). It is similar to cycling up or down a hill. In still air the climb rate is determined by how much engine power is available over and above simply keeping the aircraft in level flight.

There is not a fixed relationship between AOA and flight path. I have been in strong thermals with the nose pushed over at a low angle of attack and a high airspeed, still gaining altitude. The positive flight path angle in a case like that is mostly due to the moving airmass rather than engine power.

Conversely there is a maneuver call slow flight in which the AOA is nearly max at low airspeed in level flight.

Hope this helps.