NAVWEPS OO-ROT-80  APPLICATION OF AERODYNAMICS  TO SPECIFIC PROBLEMS OF FLYING  and greater power changes required to hold  position.  Another important form of direct inter-  ference  is common when the two airplanes are  in a trail position and stepped down. As shown  in figure 6.10, the single airplane in flight de-  velops upwash ahead of the wing and down-  wash behind and any restriction accorded the  flow can alter the distribution and magnitude of  the upwash and downwash.  When the trailing  airplane is in close proximity aft and below the  leading airplane a mutual interference takes  place betweetrthe two airplanes. The leading  airplane above will experience  an effect which  would be somewhat similar to encountermg  ground effect, i.e., a reduction in induced drag,  a reduction in downwash at the tail, and a  change in pitching moment nose down.  The  trailing airplane below will experience  an effect  which is generally the opposite of the airplane  above. In other words, the airplane below  will experience  an increase in induced drag, an  increase  in downwash at the tail, and a change  in pitching moment nose up.  Thus, when  the airplanes are in close proximity, a definite  collision possibility exists because of the trim  change experienced by each airplane.  The  magnitude of the trim change is greatest  when the airplanes are operating at high lift  coefficients, e.g., low speed flight, and when  the airplanes are in close proximity.  A common collision problem is the case of  an airplane with  a malfunctioning landing  gear. If another”airpIane is called to inspect  the malfunctioning landing gear, great care  must be taken to maintain adequate separation  and preserve orientation.  Many instances  such as this have resulted in a collision when  the pilo: of the trailing airplane became dis-  oriented and did not maintain adequate sepa-  ration.  During inflight  refueling, essentially the  same problems of interference exist.  AS the  receiver approaches the tanker from behind  and below, the receiver will  encounter the  downwash from the tanker and require a  slight, gradual increase in power and pitch  attitude to continue approach to the receiving  position.  While. ‘ the  .receiver may not be  visible to the pilot  ‘ of  the tanker, he will  anticipate the receiver coming into position  by the slight reduttion in power required and  nose down changein pitching moment. Ade-  quate clearance and, proper position must be  maintained by the pilot of the receiver for a  collision possibility is enhanced by the rela-  tive positions of the airplanes. A hazardous  condition exists if the pilot of the receiver  has excessive  speed and runs under the tanker  in close proximity.*  ‘ The  trim change expe-  rienced by both airphines may be large and  unexpected and it may be difficult to avoid a  collision.  In formation flying, this sort of interference  must be appreciated and anticipated. In cross-  ing under another airplane, care must be  taken to anticipate the trim  change and  adequate clearance must be maintained, other-  wise a collision may result.  The pilot of the  leading aircraft will know of the presence  of  the trailing  airplane by the trim change  experienced. Obviously, some anticipation is  necessary  and adequate separation is necessary  to prevent a disturbing magnitude of the  trim change. In a close diamond formation  the leader will be able to “feel”  the presence  of the slot man even though the airplane is  not within view.  Obviously, the slot man  will  have a difficult job during formation  maneuvers  because  of the unstable trim changes  In addition to the forms of interference  previously mentioned, there exists the possi-  bility of strong interference between airplanes  in supersonic flight.  In this case, the shock  waves from one airplane may strongly affect  the pressure  distribution and rolling, yawing,  and pitching moments of an adjacent air-  Pl  ane.  It is difficult to express general rela-  tionships of the effect except that magnitude  of the effects will be greatest when in close  proximity at low altitude and high 4. General-  ly, the trailing airplane will  be most affected. 