AffiSHlP AERQ.DYN AMI CS  TM 1-320  31-33  ing may be very uncomfortable because of the short and snappy period,  but there is never any danger of its reaching an excessive value.  b.  The static stability of an airship  wit~  regard  to  both roll and  pitch may be increased by lowering the car, but this gives equilibrium  only at the sacrifice of ease of control and efficiency, since lowering the  thrust line increases the thrust moment and lowering the car increases  length of suspensions and hence parasite resistance.  32. Summary.-a. Airship stability may be  summarized as  follows :  (1) Airships are very stable about their lateral axis.  In this nr  gard the designer has no trouble whatsoever.  (2) Airships must be designed carefully to give longitudinal sta› bility.  This problem is however of more interest  to  the designer than  to the pilot.  (3) Airships are statically unstable in yaw, necessitating the closest  attention on the part of the direction pilot to counteract circling by  means of the rudder.  b.  No concrete problems have been given in this section as the appli› cation of fundamentals covered therein  will be shown in section V.  33. General types.-a. Control of airships may be subdivided  into two classes, directional and altitude.  On nearly all airplanas  these two types of control are so interrelated as to necessitate their  both being performed by one pilot. In airships this is not the case,  and on all but the smallest airships two pilots are utilized, one for  direction, one for altitude.  .  b.  For efficient performance the two pilots should be familiar with  each other’s style of flying and constantly alert to render each other  assistance.  For instance,  to  obtain the proper additional superheat  to effect a landing (see TM 1- 325), the altitude pilot may desire a  longer approach than usual.  The direction pilot should so arrange  the course as to meet needs of the situation. Instances of the value of  coordination are too numerous to mention, but fortunately capable  pilots have little difficulty in achieving desired results.  47  Paragraph  General types---------------------------------------------------------- 33  Directional - ----------••••-------- ------- --- •- --- - - - ----------- - --...----- - - 34  AJtitude--------------------------------------------------------------- 35  Reverse---------------------------------------------------------------- 36  Application of dynamic contr ol to operation of  airshiPS-------------------- 37  SECTION  v  CONTROL 