# How does aircraft weight affect the glide performance? [duplicate]

Since the L/D ratio remains unaffected by the aircraft weight, will there be any effect to the gliding range?

• – Federico May 24 '16 at 6:59

## 1 Answer

The gliding slope, which equals $D/L$, does not change with weight. Hence, starting from a given height $h$, the longest gliding distance will be $d = h \cdot max(L/D) = h \cdot max(C_L/C_D)$, i.e., independent of weight.

However, the gliding speed, and, consequently, the gliding time, do change with weight, and significantly. If $C_{L,max}$ is the lift coefficient when $C_L/C_D$ is maximal, the gliding speed at best slope, $\bar{V}$, is obtained from $W = (1/2) \cdot rho \cdot \bar{V}^2 \cdot S_{ref} \cdot C_{L,max}$.

• You might add that the gliding speed can then still affect distance: gliding against the wind you'll get further if you go fast (that is, are heavy) and gliding with the wind you get further if you go slow (that is, are light). – Jan Hudec May 24 '16 at 9:18
• You are right, Federico. My experience with sport flying (engine out exercises) tells me, however, that maximizing glide distance is not a good strategy (unless you are at 10,000 feet attempting to reach a not-to-far marked airfield.) In a low-altitude engine out situation, one should concentrate on the essentials, certainly not on how to adjust the glide slope to the wind. And the most essential thing is to select a relatively near open space to land on, near enough so that you can see its features and judge that it wo'nt kill you. – DEL May 24 '16 at 19:21