Engines Ch. 4 Propellors & Turbos

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Props mounted by?

A shaft attached to a crankshaft or gearbox.

BHP

Brake HP supplied by engine to the prop

THP

Thrust HP created by prop from Brake hp.

Never 100% bhp as at least 13% power lost

Propeller slip

How much the prop should push the plane (geometric pitch) vs how much it actually does (effective pitch)

Prop shape

A twisted aerofoil of irregular platform. Needs to create the same amount of lift across the entire blade

Blade back

Chambered lift side, facing out. The top if it was a wing

Blade face

The side the pilot sees in the flight deck

Blade angle (pitch)

Angle from chord of prop to the linear rotation.

Fine = low angle to oncoming air (looks flatish)

Coarse = biting the air more, (close to feathered)

Centripetal force

Provided by hub, circular force inward

Aerodynamic Thrusting Force

tip of prop wants to bend back when it spins, prop strength required to counteract

prop thrust

tips want to move forward

prop torque

incoming air pushes against prop blades

constant speed prop

adjustable pitch for different phases of flight

feathered prop

prop turns fully sideways to reduce drag, requires special force to undo

governors

controls constant speed props, regulates pitch for speed, pressurized with oil

engine failures

prop continues to spin to prevent restart

Supercharger

increases pressure, attached to accessory case, centrifugal compressor after carburetor takes power from engine, works if engine is.

Turbochargers

more common, exhaust gases turn turbine, turbine turns compressor, compresses incoming air. up to 12 sec lag, gate or valve to release extra pressure preventing over boosting