THE LANDING FLARE AND TOUCH­DOWN

. The specific techniques of landing flare and touchdown will vary considerably between various types of airplanes. In fact, for certain types of airplanes, a flare from a properly executed approach may not be de­sirable because of the possibility of certain critical dynamic landing loads or because of the necessity for a certain standard of tech­nique when aerodynamic flare characteristics are critical. The landing speed should be the lowest practical speed above the stall or mini­mum control speed to reduce landing distances and arresting loads. Generally, the landing speed will be from 5 to 25 percent above the stall speed depending on the airplane type and the particular operation.

The technique required for the landing will be determined in great part by the aerodynamic characteristics of the airplane. If the airplane characteristics are low wing loading, high L/D, and relatively high lift curve slope, the airplane usually will have good landing flare charac­teristics. If the airplane characteristics are high wing loading, low LID, and relatively low lift curve slope, the airplane may not possess desirable flare characteristics and landing tech­nique may require a minimum of flare to touchdown. These extremes are illustrated by the lift curves of figure 6.4.

In preparation for the landing, several factors must be accounted for because of their effect on landing distance, landing loads, and arrest­ing loads. These factors are:

(1) Landing gross weight must be con­sidered because of its effect on landing speed and landing loads. Since the landing is accomplished at a specific angle of attack or margin above the stall speed, gross weight will define the landing speed. In addition, the gross weight is an important factor in determining the landing distance and energy dissipating requirements of the brakes. There will be a maximum design landing weight specified for each airplane and this limitation must be respected because of critical landing loads, arresting loads, or brake requirements. Of course, any air­plane will have a limiting touchdown rate of descent specified with the maximum land­ing weight and the principal landing load limitations will be defined by the combina­tion. of gross weight and rate of descent at touchdown.

(2) The surface winds must be considered because of the large effect of a headwind or tailwind on the landing distance. In the case of the crosswind, the component of wind along the runway will be the effective headwind or tailwind velocity. Also, the crosswind component across the runway will define certain requirements of lateral control power. The airplane which exhibits large dihedral effect at high lift coefficients is quite sensitive to crosswind and a limiting crosswind component will be defined for the configuration.

(3) Pressure altitude and temperature will affect the landing distance because of the effect on the true airspeed for landing. Thus, pressure altitude and temperature must be considered to define the density altitude.

(4) The runway condition must be con­sidered for its effect on lauding distances. Runway slope of ordinary values will ordi­narily favor selection of a runway for a favorable headwind at landing. The surface condition of the runway will determine braking effectiveness and ice or water on the runway may produce a considerable increase in the minimum landing distance.

Thus, preparation for the landing must in­clude determination of the landing distance of the airplane and comparison with the runway length available. Use of the angle of attack indicator and the mirror landing system will assist the pilot in effecting touchdown at the desired location with the proper airspeed. Of course, the landing is not completed until the airplane is slowed to turn off the runway. Control of the airplane must be maintained after the touchdown and proper technique must be used to decelerate the airplane.

TYPICAL ERRORS. There are many un­desirable consequences when basic principles and specific procedures are not followed during the approach and landing. Some of the typical errors involved in landing accidents are out­lined in the following discussion.

The steep, low power approach leads to an excessive rate of descent and the possibility of a hard landing. This is particularly the case for the modern, low aspect ratio, swept wing airplane configuration which incurs very large induced drag at low speeds and does not have very conventional flare characteristics. For this type of airplane in a steep, low power approach, an increased angle of attack without a change of power setting may not cause a reduction of rate of descent and may even in­crease the rate of descent at touchdown. For this reason, a moderate stabilized approach is necessary and the principal changes in rate of descent must be controlled by changes in power setting and principal changes in airspeed must be controlled by changes in angle of attack.

’An excessive angle of attack during the ap­proach and landing implies that the airplane is being operated at too low an airspeed. Of course, excessive angle of attack may cause the airplane to stall or spin and the low altitude may preclude recovery. Also, the low aspect ratio configuration at an excessively low air­speed will incur very high induced drag and will necessitate a high power setting or other­wise incur an excessive rate of descent. An additional problem is created by an excessive angle of attack for the airplane which exhibits a large dihedral effect at high lift coefficients. In this case, the airplane would be more sensi­tive to crosswinds and adequate lateral control may not be available to effect a safe landing at a critical value of crosswind.

Excess airspeed at landing is just as undesira­ble as a deficiency of airspeed. An excessive airspeed at landing will produce an undesirable increase in landing distance and the energy to be dissipated by the brakes for the field landing or excessive arresting loads for the shipboard landing. In addition, the excess airspeed is a corollary of too low an angle of attack and the airplane may contact the deck or runway nose wheel first and cause damage to the nose wheel or begin a porpoising of the airplane. During a flare to landing, any excess speed will be difficult to dissipate due to the reduction of drag due to ground effect. Thus, if the air­plane is held off with excess airspeed the air­plane will “float” with the consequence of a barrier engagement, barricade engagement, bolter, or considerable runway distance used before touchdown.

A fundamental requirement for a good land­ing is a well planned and executed approach. The possibility of errors during the landing process is minimized when the airplane is brought to the point of touchdown with the proper glide path and airspeed. With the proper approach, there is no need for drastic changes in the flight path, angle of attack, or power setting to accomplish touchdown at the intended point on the deck or runway. Late corrections to line up with the deck or diving for the deck are common errors which eventu­ally result in landing accidents. Accurate control of airspeed and glide path are ab­solutely necessary and the LSO, angle of attack indicator, and the mirror landing system pro­vide great assistance in accurate control of the airplane.