Reversible Propellers for Piston Engines

Reversible propellers are preferred for a decreased landing distance of land planes or for a better maneuverability of seaplanes.

This information contains the description of the new, simple and reliable (patented) MT system for reversible hydraulic constant speed propellers with an infinite number of blades, having no mechanical linkage between the rotable propeller and the fixed control unit, unlike existing systems.

The dual piston propeller is a conventional hydraulic MT-Constant Speed Propeller with the known blade retention system and a modified hydraulic pitch change mechanism.
A dual piston system with an integrated centrifugal piston lock is added. In the normal pressure mode (constant speed) above approximately 1700 RPM, the inner and outer pistons are locked together. In high pressure mode (reverse) the outer piston stops at the low pitch stop rods and the inner piston moves the blades further into the mechanical full reverse stop. Low pitch and high pitch / feathering stops are adjustable in the field. The reverse stop is adjusted by the manufacturer.
For seaplanes, a start lock for a zero-thrust blade angle is available.

The dual pressure propeller governor has two relief valves, operated by an electro-magnetic solenoid valve, which switches from standard pressure to high pressure mode on pilot's command. One relief valve is for normal servo pressure (constant speed), the other is for high servo pressure (reverse). The high servo pressure is not governed (overspeed protection) and will move the blades all the way into full reverse. The beta range can only be accessed below approximately 1500 RPM, when the propeller pistons are not locked together.

Schematics:

Dual Pressure Governor (Schematic)

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