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Contributions to the Development of a Power Spectral Gust Design Procedure for Civil Aircraft

This report presents a dyrumic gust analysis Of the Boeing 720B 
airplane and outlines two proceduree for esseeging gust design strength 
for future clvil transports. This vork vag under subcontract 
for the Lockheed—California Cæpany In support Of their study contract 
vith the Federal Aviation Agency (FAA) to develop a pover spectral gust 
design procedure for civil aircraft. 
The procedures outlined are based on two approaches. The first is the 
design envelope approach, the second Is the flight profile approa h. In 
the design envelope approach, certain flight conditions are established 
by euccessive analyses to determine the most critical flight condition 
for a given portion or of the airplane for either vertical or 
lateral gust loads. The one-factor level flight load added to the rms 
load a constant will ,lvst equal the limit design strength 
Of the cæponent. This constant, represents an effective gust 
Intensity which would Just stress the structure to its limit design 
strength. 
object Of the flight profile approach is to determine the expected 
number of flight hourg that the airplane could be operated before the 
limit design Of any of Its måor components vould be exceeded. 
flight profile approach requires a description Of airplane operation 
in terms of flight profiles that best typify the airplane usage. A sep- 
arate spectral analysis Is conducted for each of the profile condi- 
tiong. In addition, a description of the atmosphere applicable to the 
altitude is determined. Prom this information, the expected 
number Of hours required to exceed the strength is computed. 
mie 720B airplane vas studied for both concepts, first, by using the 
bending moment on the ving, fuselage, and vertical tail as indicieg of 
their strengths. This procedure vag used to locate critical flight con- 
ditions, critical portions of the structure, to obtain preliminary 
values of "d by the design envelope approach, and expected hoers to 
fly to exceed limit design strength by the flight profile approach.