Constant Speed Propeller System

Variable Pitch

With a variable pitch propeller, you really have choices.  To use the automobile analogy, your car now has a real gearbox that you can change gear with on the go.  In addition, rather than being limited to 4 or 5 gears, you can utilize any pitch along the continuum from maximum to minimum. The pitch of the propeller may be controlled in flight to provide improved performance in each phase of flight. Typically you would take-off in a fine pitch (low gear) allowing your engine to develop reasonable revs, before increasing the pitch (change up gears) as you accelerated to your cruising speed. You’ll end up with the propeller at a relatively coarse pitch, (high gear) allowing the miles to pass beneath you at a rapid rate, while your engine is gently ticking over at a comfortable speed.

This feature of a variable pitch/constant speed propeller will provide you with performance advantages, including:

• Reduced Take-Off Roll and Improved Climb Performance. Fine (low) pitch allows the engine to reach maximum speed and hence maximum power at low air speeds. Vital for take-off, climb, and for a go-around on landing.
• Improved Fuel Efficiency and Greater Range. Coarse (high) pitch allows the desired aircraft speed to be maintained with a lower throttle setting and slower propeller speed, maintaining efficiency and improving range.
• Higher Top Speed. Coarse (high) pitch will ensure your engine does not overspeed while the propeller absorbs high power, producing a higher top speed.
• Steeper Descent and Shorter Landing Roll.  With a fine (low) pitch and low throttle setting, a slow turning propeller is able to add to the aircraft’s drag, slowing the aircraft quicker on landing.

            Constant Speed Propeller

The constant speed propeller is a case of variable pitch, which is considered in a family of its own, and offers particular operating benefits.

With constant speed control, the pitch of the variable pitch propeller is changed automatically by a governor. After the pilot sets the desired engine/propeller speed with the propeller speed control, the governor acts to keep the propeller speed at the same value. If the governor detects the propeller speed increasing, it increases the pitch a little to bring the speed back within limits. If the governor detects the propeller speed decreasing, it decreases the pitch a little to bring the speed again back within limits. This operation may be compared to an automatic gearbox in an automobile, where the gears are changed automatically to keep the engine operating at a reasonable speed.

A constant speed propeller will automatically deliver the advantages outlined above for variable pitch propellers, with almost no control required from the pilot. Once a propeller/engine speed is selected, the pilot is able to control the power purely with the throttle (actually controlling manifold pressure, which then determines power output) and the governor will act to keep the propeller/engine speed at the selected setting.

While allowing the pilot to ignore the propeller for most of the time, the pilot must still choose the most appropriate engine/propeller speed for the different phases of flight.

• Take-Off, Go Around and Landing. A high speed setting is used when maximum power is needed for a short time such as on take-off. The high speed setting may also be used to keep the propeller pitch low during approach and landing, to provide the desired drag and be ready for a go-around should it be required.
• Climb and High Speed Cruise. A medium speed setting is used when high power is needed on a continuous basis, such as during an extended climb, or high-speed cruise.
• Economic Cruise. A low speed setting is used for a comfortable cruise with a low engine speed. This operation produces low fuel consumption and longer range, while the advantages of low noise and low engine wear are also enjoyed.