speed may encounter a variety of stability, con- 
trol, or buffet problems associated with tran- 
sonic flight. Since the equivalent airspeed for 
a given Mach number decreases with altitude, 
the magnitude of compressibility effects at 
high altitude may be negligible for the tran- 
sonic airplane. In this sense, the airplane may 
not be able to fly at high enough dynamic 
pressures within a certain range of Mach num- 
bers to create any significant stability or 
control problem. 
The transonic airplane which is buffet lim- 
ited requires due consideration of the effect of 
load factor on the onset of buffet,. Since 
critical Mach number decreases with lift coef- 
ficient, the limit Mach number will decrease 
with load factor. If the airplane is subject to 
prolonged or repeated buffet for which it was 
not designed, structural fatigue will be the 
certain result. 
The limit airspeed for each type aircraft is 
set sufficiently high that full intended appli- 
cation of the aircraft should be possible. Each 
of the factors mentioned about the effect of 
excess airspeed should provide due respect for 
the limit airspeed. 
LANDING AND GROUND LOADS 
The most critical loads on the landing gear 
occur at high gross weight and high rate of 
descent at touchdown. Since the landing 
gear has requirements of static strength and 
fatigue strength similar to any other com- 
ponent, overstress must be avoided to prevent 
failure and derive the anticipated service life 
from rhe components. 
The most significant function of the landing 
gear is to absorb the vertical energy of the air- 
craft at touchdown. An aircraft at a given 
weight and rate of descent at touchdown has 
a certain kinetic energy which must be dis- 
sipated in the shock absorbers of the landing 
gear. If the energy were not absorbed at 
touchdown, the aircraft would bounce along 
similar to an automobile with faulty shock 
absorbers. As the strut deflects on touchdown, 
NAVWEPS 00-801-80 
OPERATING STRENGTH LIMITATIONS 
oil is forced through an orifice at high velocity 
and the energy of the aircraft is absorbed. To 
have an efficient strut the orifice size must be 
controlled with a tapered pin to absorb the 
energy with the most uniform force on the strut. 
The vertical landing loads resulting at touch- 
down can be simplified to an extent by assum- 
ing the action of the strut to produce a uni- 
formly accelerated motion of the aircraft. TV 
landing load factor for touchdown at a consta 
rate of descent can be expressed by the follow- 
ing equation: 
n= F/W 
n = (ROD)’ 
w 
where 
a=landing load factor-the ratio of 
the load in the strut, F, to the 
weight, W 
ROD=rate of descent, ft. per sec. 
g= acceleration due to gravity 
= 32 ft. per sec.’ 
S= effective stroke of the strut, ft. 
As an example, assume that an aircraft touches 
down at a constant rate of descent of 18 ft. per 
sec. and the effective stroke of the strut is 18 
inches (I.5 ft.). The landing load factor for 
the condition would be 3.37; the average force 
would be 3.37 times the weight of the aircraft. 
(NOTE: there is no specific correlation between 
the landing load factor and the indication of 
a cockpit mounted flight accelerometer. The 
response of the instrument, its mounting, and 
the onset of landing loads usually prevent 
direct correlation.) 
This simplified equation points out two im- 
portant facts. The effective stroke of the strut 
should be large to minimize the loads since a 
greater distance of travel reduces the force 
necessary to do the work of arresting the ver- 
tical descent of the aircraft. This should 
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