The best angle of glide is one that allows the airplane to travel the greatest distance over the ground with the least loss of altitude. This is the airplane's maximum L/D (lift over drag) and is usually expressed as a ratio. For example, an airplane having an L/D or glide ratio of 10:1 will travel 10 feet forward for every foot it descends.
For a particular airplane the manufacturer recommends an airspeed and configuration that will provide the maximum glide distance. This speed (best glide speed), usually found in the Airplane Flight Manual or Pilot's Operating Manual, is of primary importance because if the engine should fail in flight the pilot's chief concern may be whether or not the airplane can glide far enough to reach a suitable landing area.
The objective of this maneuver, then, is to establish a glide that will allow the airplane to travel forward the greatest possible distance from a given altitude.
To establish the glide, the landing gear and flaps should first be retracted to eliminate unwanted drag. The throttle should be reduced to idle, the propeller placed in full high pitch (low RPM) position, and the airplane then eased into a glide until the proper airspeed is established. If the airplane's nose is lowered excessively, the airplane will go into too steep a glide, and naturally will cover very little horizontal distance. On the other hand if the nose is raised too high and too much airspeed is lost, the airplane will settle and descend at a steeper angle than if the nose were somewhat lower.
When practicing the power off descents, the engine should
be cleared periodically, as is done in the steep spiral maneuver, to prevent
excessive cooling and fouling, and of course the descent should be terminated
at a safe altitude. Care must be exercised when advancing the throttle
to avoid overstressing the engine.