This type of starter consists basically of an electric motor, a gear reduction and an automatic engaging and disengaging mechanism, which operates through an adjustable torque overload release. The engine is cranked directly by the starter and there is no preliminary storage of energy as with the inertia type of starter. Therefore, it can be assumed that for a specific engine under extreme low temperature conditions, with resultant high cranking torque, the current consumption will be somewhat higher than would be the case with an electric inertia starter on the same engine under similar conditions, because of the direct connection between the starter motor and the engine during the cranking period. The direct cranking electric starter is intended for use on large commercial transports and privately owned airplanes, which are normally stored in hangars and are not subject to cold weather starting. The use of external batteries in the form of a dolly are recommended for cranking engines of large aircraft transports equipped with direct cranking electric starters in order to save the airplane batteries.

The direct cranking electric starters are normally furnished less hand crank mechanism with the exception of large capacity units which are supplied with a hand crank mechanism if required. The starters are designed for operation from a 12 or 24 volt battery source. Upon the application of current to the motor terminals, the torque of the motor is transmitted through a gear reduction unit to the adjustable torque overload release, which in turn actuates a splined screw shaft which moves the starter jaw axially outward into engagement with the engine cranking member before the starter jaw begins to rotate. Thus, complete engagement is effected before cranking commences. The torque overload release in the form of a multiple disc clutch is adjusted to a predetermined value so as to deliver sufficient, yet not excessive cranking torque to the engine. In case of engine back-fire, the clutch slips, preventing damage to the engine and starter. With this type of starter, engine cranking is continuous but at a lower speed than that obtained with the inertia type of starter. The current draw of the direct cranking electric starter varies directly with engine size and torque characteristics. It will therefore be considerably higher than that required for the operation of the inertia type starters.

The direct cranking electric starter with integrally mounted hydraulic feathering pump has been developed to replace the standard type of direct cranking electric starter and separately mounted electric motor driven hydraulic feathering pump for installations utilizing the Hamilton Standard Hydromatic Propeller. Primarily designed and developed for use in conjunction with Hamilton Standard Hydromatic Propellers, the starter pump unit incorporates all of the features of the conventional direct cranking electric starter, with the exception that the hand crank mechanism fitted to starters of this type has been removed and a hydraulic pump mounted in its place. With this type of starter, a reversible motor is utilized in order to permit driving of the hydraulic feathering pump when the starter is not in operation. The starter pump unit, in addition to providing a saving in weight due to the elimination of an additional electric motor and excess line tubing, provides a compact and light weight installation integral with the power plant and available for operation as required. The design of the starter pump unit is such that when used in conjunction with two solenoid starting relays, battery booster coil and a suitable control switch, remote control of both starter and feathering pump is provided. As with the conventional type of direct cranking electric starter, jaw engagement is automatic upon closing of the motor circuit. An overrunning clutch, interposed between the starter and pump provides starter operation without rotation of the hydraulic pump. The hydraulic pump, which may be of either the internal or external gear type, provides a dependable and efficient source of hydraulic pressure for the feathering and unfeathering of Hamilton Standard Hydromatic Propellers.

Among the most outstanding recent developments in aircraft engine starting equipment has been the combination direct cranking electric and inertia starter, which incorporates all the features of the hand or combination hand and electric inertia starters and in addition, provides, by means of a heavy duty integral accelerating motor, continuous cranking of the aircraft engine after dissipation of the flywheel kinetic energy. Thus the energy stored in the starter flywheel at the initial engagement of the starter and engine jaws is used to overcome the heavier breakaway torque after which the lighter load of continuous cranking is assumed by the electrical system. The result is notably less drain on the source of electrical energy with greater convenience and starting ease. Although only available at the present time for use in conjunction with engines, rated at approximately from 1500 to 1800 horsepower, this starter can be readily modified.

The design of the starter is such, that when used in conjunction with a separately mounted solenoid starting relay, battery booster coil and three position starter control switch, remote control of motor acceleration and starter jaw engagement is provided. The starter may be operated as a direct cranking electric starter or as a combination, direct cranking electric and inertia starter, by means of the control switch, as required. For cold weather starting, operation of the unit as a combination direct cranking electric and inertia starter is recommended, whereas for warm weather starting or where immediate continuous cranking is desired, the unit may be operated as a direct cranking electric starter. For emergency operation when the source of electrical energy is not sufficient to permit proper electrical operation as a combination direct cranking electric and inertia starter, the unit may be operated as an electric inertia starter, in which case manual engagement of starter and engine jaws is required. In addition, the unit may be operated as a hand inertia starter for emergency operation, in which case it is also necessary to manually engage the starter and engine jaws. A universal hand crank mechanism is provided on these starters with provisions for either clock or counter clock rotation hand cranking. With this type of hand crank mechanism the position for hand crank take off may be readily adjusted to facilitate starter installation, available for 12 or 24 volt operation.