aero engines

powerplant accessories
air injection starters
inertia starter
electrical starters
combustion starter

air injection starter

In limited use at the present time, the air injection starter has been developed as a light-weight and efficient starting means for aircraft engines rated up to 250 horsepower. Operated from self generated air pressure, this type of starter was particularly suitable for application on engines of small output where an electrical installation was not possible and manual hand-cranking undesirable and inadequate.

The Air injection starter equipment consisted of a small and compact engine-driven air compressor, a timed rotating distributing valve, integral with the compressor, a tubular air storage tank, an automatic pressure. regulating valve, pressure release starting valve, and an instrument panel mounted pressure gauge and primer. However, as the majority of light powered airplanes at the present time are equipped with engines designed to accommodate a generator of low output, the direct cranking electric type of starter is replacing the majority of air injection starter installations due to its light weight, simplified installation, and freedom from service troubles. Due to the extensive plumbing required, and the corresponding possibility of air leakage in the system, the air injection type of starter is only recommended for installations where battery and generator are not available. Although primarily confined to use on engines rated up to 250 horsepower, a starter employing this principle of operation is widely used on foreign aircraft for starting aircraft engines of all capacities.


The principle of operation of the air injection starter is as follows: The engine is cranked from an initial air pressure of approximately 450 pounds per square inch, which is contained in a storage tank. Release of the compressed air is controlled from the pilot's compartment and is transmitted by a distributor valve to the cylinders in the proper cyclic order, thus rotating the engine. A portion of the compressed air, in passing through the distributing valve, forces liquid fuel into the cylinders on the compression stroke. This carburettor priming charge is followed by a greater volume of air which rotates the engine and assures instant firing. The air pressure dissipated in starting is replenished by the compressor shortly after the engine has been started. As the maximum operating pressure of 450 pounds per square inch is reached, the pressure regulating valve, which is an integral part of the storage tank, automatically stops further charging of the storage tank, thus the compressor, driven direct from the main aircraft engine, is temporarily relieved of pumping against pressure and rotates freely under no load until further dissipation of the air pressure by- starting occurs. Due to the variations which are encountered in different installation, no definite performance data can be given, however, under normal conditions, approximately 20 to 30 starts can be obtained from one fully charged tank of air without replenishment in the meantime.

Later Developments

Of more recent application in this country is the hand or combination hand and electric inertia starters, which have been designed primarily for use by the military services and are suitable for installation on engines rated up to 2,000 horsepower. The starters are particularly suited for installations where dependability and provisions for emergency hand-cranking are required. The basic design of all inertia starters consists of the storage of energy in a small flywheel by accelerating it to a high speed either manually or electrically. The energy thus stored is expended in rotating the engine crankshaft. Transmittal of the kinetic energy of the rotating flywheel to the engine is accomplished through reduction gearing, a multiple disc clutch, an engaging mechanism, and driving jaw.