HORIZONTAL TAIL SURFACES

Balancing. The limit load acting on the horizontal tail surfaces should not be less than the maximum balancing load obtained from the loading conditions specified. The load should be distributed in accordance with fig. 1-XI. The balancing loads apply only to the horizontal tail surfaces as the ailerons and the vertical tail surfaces are used only to a small extent for balancing purposes.

The chord distribution shown in fig. 1-XI is intended to simulate a relatively high angle of attack condition for the stabilizer in which very high unit loadings can be obtained near the leading edge.

Loads should also be determined for the most critical center of gravity position of the glider.

Figure 1-XI. "Balancing” and “damping” tail load distribution.

Maneuvering. (Horizontal surfaces).-The minimum average limit pressure specified in table 1-I should be applied in either direction and distributed in accordance with fig. 1-XII.

Compliance Suggestion

DETERMINATION OF MANEUVER LOAD

The recommendations above are intended to place the determination of such loads on a speed versus force-coefficient basis, to specify values which agree substantially with current practice, and to provide for the effects of increasing glider speeds. The method is designed for application to conventional gliders and, in determining the maneuver loads, the type of service for which the glider is to be used should be considered.

• The values of the average unit loading specified represents loadings which can be attained by deflecting the control surfaces. Higher values may be desirable in certain cases, depending on the purpose of the glider.

The chord distribution shown in fig. 1-XII represents approximately the type of loading obtained with the movable surface deflected. For tail surfaces, this type of loading is critical for the movable surface and for the rear portion of the fixed surface.

Damping (Horizontal stabilizer).—The total limit load acting on the fixed surface (stabilizer) in the maneuvering condition should be applied in accordance with load distribution of fig. 1-XI acting in either direction. The load acting on the movable surface in the maneuvering condition may be neglected in determining the damping loads.

Compliance Suggestion

DISTRIBUTION OF DAMPING LOAD

When a control surface is deflected suddenly the full maneuvering load tends to build up immediately, after which the glider begins to acquire an angular velocity. This angular motion causes the direction of the relative airstream over the fixed surface to change, which causes the air load on this surface to build up in a direction such as to oppose the angular rotation of the glider. This load is concentrated near the leading edge of the fixed surface and is commonly referred to as the damping load. This is considered as a supplementary condition based on the initial maneuvering condition. The damping load is closely related in magnitude to the initial maneuvering load which produces it so that it is convenient to use the latter loading condition to determine the damping load on the fixed surface. To avoid the necessity for a separate analysis for damping loads, the distribution is made the same as for the balancing loads. In the case of the horizontal surfaces, the damping load therefore acts as a minimum limit for the design of the fixed surface and need not be investigated when the balancing load is critical.

Loading for slab tail designs.-The maneuvering horizontal tail loadings shown in fig. 1-XII are applicable to all movable tail surface configurations including the slab tail design. For the balancing tail load distribution the load should be distributed in accordance with fig. 1-XII(1).

Figure 1-XII(1). Balancing load distribution, Slab Tail.

For the slab tail maneuvering and gust loading condition, the chordwise tail load distribution should be applied as shown in fig. 1-XII(2).

• In calculating the loads for slab tail designs, the effect of tabs, if used, should be accounted for. In addition to the above flight load distributions, an investigation should be made of the ground gust condition imposed on the slab tail. This results in a high trailing