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Chapter-3 Climbs and Descents-V20_Sport Pilot Handbook 8/30/2021 5:48 PM Page 20

3-20 Rod Machado’s How to Fly an Airplane Handbook

The Airplane’s
Drag Curve And
Its Relationship
To Actual Glide
Performance

At airspeeds below L/D Max, the Maximum glide distance in calm
glide performance decreases air is achieved at L/D Max

At airspeeds above L/D Max, the
glide performance decreases
Fig. 25
The lowest spot on the total drag curve re-
sults in a specific airspeed known as the best The Remos GX Has A
L/D speed. This is pronounced best L over D Glide Ratio of 10 to 1
speed, which gives you the best lift over drag
ratio). It is also often referred to as L/D max.
This speed yields the airplane’s maximum
power-off glide range, which is why it’s often
referred to as the best glide speed (Figure 25).
Should your engine stop working (most often
because the pilot forgot to put fuel in the
tanks), you are now the pilot of a glider and At the best L/D speed, the Remos will glide
Fig. 26A
should be looking for a landing spot. Here is 10 feet forward for every foot of altitude lost.
where you’ll immediately establish the proper
gliding attitude to obtain the best glide air- High Performance
speed. Gliders Can Have
Glide Ratios Of
For example, the Remos GX (Figure 26A) 60 to 1
has a lift-to-drag ratio of approximately 10 to 1
(or 10:1) at its best L/D speed of 56 knots indi-
cated airspeed. At this speed the airplane ex-
periences minimum total drag (it’s now flying © Jon Lewis
at the bottom of its total drag curve) and
moves ten feet forward for every foot it de-
scends (in calm winds, of course). On the other At the best L/D speed, some gliders will glide
hand, high performance gliders (Figure 26B) Fig. 26B 60 feet forward for every foot of altitude lost.
can have glide ratios in the range of 60 to 1.