Technology Notebook Contents

Ground Loads

The ground load tests consist of landings, straight taxi over 1-COS shaped bumps, and braking and non_breaking straight and turning taxi maneuvers. In addition, loads during minimum radius and towing operations must be evaluated. Ground loads are developed primarily for the wing, pylon, fuselage, and landing gear. No detailed analysis is normally planned for the horizontal or vertical stabilizer since it is generally not anticipated that these structural components will experience any critical ground loads. The components, however, should be monitored during testing to verify that no critical load condition exists.

Air Zeros

Prior to each series of ground maneuvers, zero load for the landing gear is established from a record of a landing approach. Zero load for the gear is taken just prior to touchdown with the gear extended. Zero load points for the wing, fuselage, etc. can be obtained from either structural and fuel inertia data and a ground zero record, or from basic and additional airload data, structural and fuel inertia data and an air zero record.

Landing Loads

Time history data are developed for the wing, pylon, fuselage, and landing gear loads during landing impact and roll-out. The selection of a peak load from the time history data is based upon the combination of component loads along the x, y, and z axis which produces the highest percentage load level with respect to design load envelopes. This philosophy is illustrated in Figure 1 by the example of main landing gear loads during landing impact and roll-out.

As can be seen from this example, several "peaks" occur during the landing. Peak spin-up and spring-back drag loads occur at points (A) and (B) respectively while peak vertical occurs at point (C). At point (D) a peak vertical load due to spoiler deployment and reverse thrust application occur. Similarly, brake application produces another load as illustrated by point (E). The peak loads determined from the time history data are potted on design load envelopes such as the vertical/drag load envelope shown in Figure 2 .

Obviously point (A) produces the highest impact drag load level while point (E) produced the highest vertical load level during roll-out. Thus, illustrated in Figure 3, following the above concept of all other structures (wing, pylon, etc. ) are continuously monitored to insure there is no excessive and/or unexpected load buildup.

Takeoff Loads

Takeoff loads are generally low but still need to be evaluated. Generally problems may develop by tire sidewall over heating during long taxis to the takeoff position.

Taxi Loads

Peak vertical, side and drag loads for the nose gear are plotted versus ground speed for constant steering angles prior to brake application as illustrated in Figure 4 .

Turning Loads

Analysis of these data will indicate whether or not a nose gear load problem exists during normal operational braking taxi turns. If such a problem does exist, a ground maneuvering envelope can be constructed. This envelope is a plot of ground speed/steering angle combinations for which limit load conditions on ;the nose gear wil occur and is illustrated in Figure 5 .

Braking Loads

A note here, is that the maximum side load on the nose gear is usually just prior to stop in the maximum yawing inertia configuration, i.e., maximum wing fuel.

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