Figure 7-11.  Fixed-pitch propeller.  Figure 7-12.  Test club.  Ground-Adjustable Propeller Controllable-Pitch Propeller Test Club Propeller 7-7 A test club is used to test and break in reciprocating engines.  [Figure 7-12]  They are made to provide the correct amount  of load on the engine during the test break-in period. The  multi-blade design also provides extra cooling air flow  during testing. is used on airplanes of low power, speed, range, or altitude.  Many single-engine aircraft use fixed-pitch propellers and  the advantages to these are less expense and their simple  operation. This type of propeller does not require any control  inputs from the pilot in flight. This type of propeller is not to be confused with a constant- speed propeller. With the controllable-pitch type, the blade  angle can be changed in flight, but the pilot must change  the propeller blade angle directly. The blade angle will not  change again until the pilot changes it. The use of a governor  is the next step in the evolution of propeller development,  making way for constant-speed propellers with governor  systems. An example of a two-position propeller is a  Hamilton Standard counterweight two-position propeller.  These types of propeller are not in wide use today. The controllable-pitch propeller permits a change of blade  pitch, or angle, while the propeller is rotating. This allows  the propeller to assume a blade angle that gives the best  performance for particular flight conditions. The number  of pitch positions may be limited, as with a two-position  controllable propeller, or the pitch may be adjusted to any  angle between the minimum and maximum pitch settings of  a given propeller. The use of controllable-pitch propellers  also makes it possible to attain the desired engine rpm for a  particular flight condition.  The ground-adjustable propeller operates as a fixed-pitch  propeller. The pitch, or blade angle, can be changed only  when the propeller is not turning. This is done by loosening  the clamping mechanism that holds the blades in place. After  the clamping mechanism has been tightened, the pitch of the  blades cannot be changed in flight to meet variable flight  requirements. The ground-adjustable propeller is not often  used on present-day airplanes.