Page 198 - Understanding Flight

CH07_Anderson 7/25/01 9:00 AM Page 185

Airplane Performance 185

Absolute ceiling

Min. level
flight speed

Altitude Max. climb rate

Max. climb angle

Speed
Fig.7.8. The minimum flight speed and climb speeds meet at the
absolute ceiling.

As the airplane climbs, its rate of climb decreases. The The world altitude record for an
military defines the combat ceiling as the altitude where the airplane was set on August 22,
best rate of climb drops to 500 ft/min (150 m/min). For some 1963, at 354,200 ft (107,960 m)
small general-aviation airplanes that is not much above the by an X-15.
runway at sea level. The service ceiling of an airplane is
defined by the FAA as the altitude at which the airplane’s best rate of
climb drops to 100 ft/min (30 m/min). This is a useful measure of the
performance of an airplane. If one flies out of a high airport such as
the 10,000-ft (3000-m) airport at Leadville, Colorado, an airplane with
a 20,000-ft (6000-m) service ceiling is certainly much more desirable
than one with a service ceiling of only 14,000 ft (4200 m). The latter
airplane will take much more runway to take off and will climb much
more slowly.
Let us look at two high-altitude aircraft that have taken two different
approaches for the same mission. The first is the U-2 high-altitude
reconnaissance airplane, shown in Figure 3.5. The airplane is an
updated 1950s design with a service ceiling over 70,000 ft (21,000 m).
This airplane has a high aspect ratio wing to increase lift efficiency by
minimizing drag and maximizing L/D. Its engines are not powerful