NAVWEPS OD-8OT-80 
APPLICATION OF AERODYNAMICS 
TO SPECIFIC PROBLEMS OF FLYfNG 
an increase in lift coeflicient and reduction in 
thrust required. Hence, a “floating” sensa- 
tion may be experienced. Because of the re- 
duced drag and power-off deceleration in 
ground effect, any excess speed at the point of 
flare may incur a considerable “float” distance. 
As the airplane nears the point of touchdown 
on the approach, ground effect will be most 
realized at altitudes less than the wing span. 
An exact appreciation of the ground effect may 
be obtained during a PcZd approach with the 
mirror landing system furnishing an exact 
reference of the flight path. During the final 
phases of the field approach as the airplane 
nears the ground plane, a reduced power 
setting is necessary or the reduced thrust re- 
quired would allow the airplane to climb 
above the desired glide path. During ship- 
board operations, ground effect will be delayed 
until the airplane passes the edge of the deck 
and the reduction in power setting that is 
common to field operations should not be 
encountered. Thus, a habit pattern should 
not be formed during field landings which 
would prove dangerous during carrier oper- 
ations. 
An additional factor to consider is the aero- 
dynamic drag of the airplane during the land- 
ing roll. Because of the reduced induced drag 
when in ground effect, aerodynamic braking 
will be of greatest significance only when 
partial stalling of the wing can be accom- 
plished. The reduced drag when in ground 
effect accounts for the fact that the brakes 
are the most effective source of deceleration 
for the majority of airplane configurations. 
During the takeoff pharc of flight ground 
effect produces some important relationships. 
Of course, the airplane leaving ground effect 
encounters just the reverse of the airplane 
entering ground effect, i.e., the airplane leaving 
ground effect will (1) require an increase in 
angle of attack to maintain the same lift 
coefficient, (2) experience an increase in in- 
duced drag and thrust required, (3) experience a 
decrease in stability and a nose-up change in 
moment, and (4) usually a reduction in static 
source pressure and increase in indicated air- 
speed. These general effects should point out 
the possible danger in attempting takeoff 
prior to achieving the recommended takeoff 
speed. Due to the reduced drag in ground 
effect the airplane may seem capable of takeoff 
below the recommended speed. However, as 
the airplane rises out of ground effect with a 
deficiency of speed, the greater induced drag 
may produce marginal initial climb perform- 
ance. In the extreme conditions such as high 
gross weight, high density altitude, and high 
temperature, a deficiency of airspeed at takeoff 
may permit the airplane to become airborne 
but be incapable of flying’out of ground effect. 
In this case, the airplane may become airborne 
initially with a deficiency of speed, but later 
settle back to the runway. It is imperative 
that no attempt be made to force the airplane 
to become airborne with a deficiency of speed; 
the recommended takeoff speed is necessary to 
provide adequate initial climb performance. 
In fact, ground effect can be used to advantage 
if no obstacles exist by using the reduced drag 
to improve initial acceleration. 
The results of the airplane leaving ground 
effect can be most easily realized during the 
deck launch of a heavily loaded airplane. As 
the airplane moves forward and passes over the 
edge of the deck, whatever ground effect exists 
will be lost immediately. Thus, proper rota- 
tion of the airplane will be necessary to main- 
tain the same lift coefficient and the increase 
in induced drag must be expected. 
The rotor of the helicopter experiences a 
similar restraint of induced flow when in prox- 
imity to the ground plane. Since the induced 
rotor power required will predominate at low 
flight speeds, ground effect will produce a con-