should be equal to the gross weight of the glider. The following additional assumptions should be made:

For wheel type landing gears, the minimum vertical limit load factor should be 4.0. The resultant ground reaction should pass through the center of the axle and should be obtained by combining the vertical component with a rearward acting horizontal component equal to one-quarter of the vertical component.

• For skid type landing gears, the minimum vertical limit load factor should be 5.0. The resultant ground reaction should pass through the center of the skid's contact area, and should be obtained by combining the vertical component with a rearward acting horizontal component equal to one-half of the vertical component.

Compliance Suggestion

DETERMINATION OF LOADING

The loading for this condition is illustrated in fig. 1-XVII. As it is difficult to accurately define "level altitude," any approximately level altitude with the tail well off the ground will be considered satisfactory. If in the level landing condition the resultant load does not pass through the center of gravity, it will generally be acceptable to apply a balancing couple composed of an upward force acting near the nose of the fuselage and an equal downward force acting at the same distance to the rear of the center of gravity. These arbitrary forces can be considered as approximately representing angular inertia forces and may be divided between the nearest panel points, if desired. These forces are illustrated in fig. 1-XVII (a).

Level landing with side load.-As a separate condition, a limit side load equal to 0.167 times the limit vertical component should be assumed to act at the center of the contact area of the tire or skid, together with the loads specified under "level landing." The side load should be assumed to act in either direction normal to the plane of symmetry.

Compliance Suggestion

DETERMINATION OF LOADING

The loading for this condition is shown in fig. 1-XVIII. An acceptable method of balancing externally applied rolling moments about the longitudinal axis resulting from the side load is also shown in fig. 1-XVIII (a). Forces resisting angular acceleration are assumed to be applied by the wing. The arbitrary location shown is based on the fact that the effectiveness of any item is proportional to its distance from the center of gravity. Balancing loads may be assumed to be vertical, although they actually act normal to a radius line through the center of gravity of the glider.

Nose-down landing. For this landing condition, the following assumptions should be made:

• For wheel type landing gears, the glider should be assumed to make contact on the nose skid or wheel and the main wheel or wheels. The minimum limit resultant inertia force should act at the center of gravity of the glider, should be equal to 4.0 times the weight, and should act forward and downward at an angle of 14 degrees with the vertical. The direction of ground reactions at the contact points should be opposite to the resultant inertia force.

. For skid type landing gears, the glider should be assumed to be nosed down 15 degrees. The minimum limit, vertical component of the ground reaction should be equal to 5.0 times the weight. The resultant ground reaction should pass through the most forward point suitable for the application of oblique loads, and should be obtained by combining the vertical component with a horizontal component equal to one-half of the vertical component.

NOTE.-These conditions are illustrated in figure 1-XIX.

Head-on landing.—The forward portion of the fuselage should be capable of resisting an ultimate load of 6.0 times the gross weight of the glider acting aft through the foremost point(s) suitable for the application of such a load. Partial failure of the structure under

these conditions is tenable provided that the specified ultimate load can be resisted without endangering the occupants, assuming safety belts to be fastened. (Also Chap. 3, p. 115.) (Note the 6.0 factor above is ultimate and not a limit load factor.)

Wing-tip landing. Suitable provisions should be made to provide adequate structure to resist possible severe ground reactions at the wing tips.

Compliance Suggestion

LOADING CONDITIONS

It may be assumed that a limit load of 150 pounds acts aft at the point of contact of one wing tip, or wing skid, and the ground in a direction parallel to the longitudinal axis. The unbalanced turning moment may be assumed to be resisted by: • The methods shown in fig. 1-XX, or The angular inertia of the glider.

LAUNCHING AND TOWING LOADS

The towing and launching fittings (and/or mechanisms) and that portion of the structure ahead of the main wing fittings should be checked as recommended below. Holding fittings and the structures