NAVWEPS OD-BOT-BO  APPLICATION OF AERODYNAMICS  TO SPECIFIC PROBLEMS OF FLYI ’ NG  to judge and control the point of touchdown.  The LSO, mirror landing system, and various  approach lighting systems will aid the pilot  in achieving the desired approach flight path.  deficiency. It is most desirable that the power-  plant be capable of effecting rapid changes in  thrust to allow precise control of the airplane  during approach.  The type of approach path is an important  factor since it affects the requirement of the  flare, the touchdown rate of descent, and-to  some extent-the ability to control the point  of touchdown.  Approach path A of figure  6.4 depicts the steep, low power approach.  Such a flight path generally involves a low  power setting near idle conditions and a high  rate of descent. Precise control of the air-  plane is difficult and an excess  airspeed usually  results from an approach path similar to A.  Waveoff may be difficult because of the re-  quired engine acceleration and the high rate  of descent. In addition, the steep approach  path with high rate of descent requires con-  siderable flare to reduce the rate of descent at  touchdown.  This extreme flare requirement  will  be di,fficult to execute with consistency  and will  generally result in great variation  in the speed, rate of descent, and point of  touchdown.  THE LANDING  FLARE AND TOUCH-  DOWN.  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 de-  sirable because of the possibility of certain  critical dynamic landing loads or because of  the necessity for a certain standard of tech-  nique when aerodynamic flare characteristics  are critical.  The landing speed should be the  lowest practical speed above the stall or mini-  mum 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 LID,  and relatively high lift curve slope, the airplane  usually will have good landing flare charac-  teristics. If the airplane characteristics are  high wing loading, low L/D, and relatively low  lift curve slope, the airplane may not possess  desirable flare characteristics  and landing tech-  nique may require a minimum of flare to  touchdown. These extremes  are illustrated by  the lift curves of figure 6.4.  Approach path C of figure 6.4 typifies the  long, shallow approach with too small an  inclination of the flight path.. Such a flight  path requires a relatively high power setting  and a deficiency of airspeed is a usual conse-  quence. This extreme of an approach path  is not desirable because it is difficult to control  the point of touchdown and the low speed  may allow the airplane to settle prematurely  short of the intended landing touchdown.  In preparation for the landing, several  factors  must be accounted for because of their effect  on landing distance, landing loads, and arrest-  ing loads. These factors are:  (1) Landing gross weight must be con-  sidered 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  Some approach path between the extremes  of A and C must be selected, e.g., flight path  B.  The desirable approach path must not  incur excessive speed and rate of descent or  require excessive  flaring prior to touchdown.  Also, some moderate power setting must be  required which will  allow accurate control  of the flight path and provide suitable waveoff  characteristics.  The approach flight  path  cannot be too shallow for excessive power  setting may be required and it may be difficult  362 