If the starter turns the turbine engine up to a self-sustaining  speed, the engine start process will be successful. There are  only a few types or methods used to turn the engine. Almost  all reciprocating engines use a form of electric motor geared  to the engine. Modern turbine engines use electric motors,  starter/generators (electric motor and a generator in the  same housing), and air turbine starters. Air turbine starters  are driven by compressed air through a turbine wheel that  is mechanically connected through reduction gears to one  of the engine’s compressors, generally the highest pressure  compressor. There are three general types of inertia starters: hand, electric,  and combination hand and electric. The operation of all types  of inertia starters depends on the kinetic energy stored in a  rapidly rotating flywheel for cranking ability. Kinetic energy  is energy possessed by a body by virtue of its state of motion,  which may be movement along a line or spinning action. In the inertia starter, energy is stored slowly during an  energizing process by a manual hand crank or electrically  with a small motor. The flywheel and movable gears of  a combination hand electric inertia starter are shown in  Figure 5-1 . The electrical circuit for an electric inertia  starter is shown in  Figure 5-2 . During the energizing of the  starter, all movable parts within it, including the flywheel,  are set in motion. After the starter has been fully energized,  it is engaged to the crankshaft of the engine by a cable  pulled manually or by a meshing solenoid that is energized  electrically. When the starter is engaged, or meshed, flywheel  energy is transferred to the engine through sets of reduction  gears and a torque overload release clutch.  [Figure 5-3] In the early stages of aircraft development, relatively low  powered reciprocating engines were started by pulling the  propeller through a part of a revolution by hand. Difficulty  was often experienced in cold weather starting when  lubricating oil temperatures were near the congealing point.  In addition, the magneto systems delivered a weak starting  spark at the very low cranking speeds. This was often  compensated for by providing a hot spark using such ignition  system devices as the booster coil, induction vibrator, or  impulse coupling. The most widely used starting system on all types of  reciprocating engines utilizes the direct cranking electric  starter. This type of starter provides instant and continual  cranking when energized. The direct cranking electric starter  consists basically of an electric motor, reduction gears, and  an automatic engaging and disengaging mechanism that is  operated through an adjustable torque overload release clutch.  A typical circuit for a direct cranking electric starter is shown  in  Figure 5-4 . The engine is cranked directly when the starter  solenoid is closed. As shown in  Figure 5-4 , the main cables  leading from the starter to the battery are heavy duty to carry  the high current flow, which may be in a range from as high  as 350 amperes to 100 amperes (amps), depending on the  starting torque required. The use of solenoids and heavy Some small, low-powered aircraft which use hand cranking  of the propeller, or propping, for starting are still being  operated. For general instructions on starting this type of  aircraft, refer to the Aviation Maintenance Technician— General Handbook, Chapter 11, Safety, Ground Operations,  and Servicing. Throughout the development of the aircraft  reciprocating engine from the earliest use of starting systems  to the present, a number of different starter systems have  been used. Most reciprocating engine starters are the direct  cranking electric type. A few older model aircraft are still  equipped with inertia starters. Thus, only a brief description  of these starting systems is included in this section. Direct Cranking Electric Starter Reciprocating Engine Starting Systems Inertia Starters Figure 5-1.  Combination hand and electric inertia starter. 5-2 Hand crank adapter Hard steel insert Centrifugal clutch Flywheel Torque overload release clutch Starter driving jaw