A constant-speed propeller system changes blade pitch to oppose a speed departure from a selected setting. This illustration shows a flyweight governor’s spring, hinged weights, inward toes and pilot-valve stem, followed by a separate propeller view. Its calculator is an ideal force comparison, not a governor calibration tool.
Constant-speed Propeller Mechanism Interactive Calculator
Explore the direction of a propeller governor’s response and compare ideal flyweight forces at selected and actual shaft speeds. Change shaft speeds, flyweight mass, reference radius and equivalent spring rate to compare their effects. The worksheet does not predict an aircraft’s blade angle or actual pilot-valve travel.
Equation Used
- Two equal point masses at one fixed reference radius; actual and selected speeds are compared at that same radius.
- The mass/radius worksheet is separate from the schematic flyweight tilt, which only shows overspeed, on-speed and underspeed response direction.
- No lever ratio, governor gearing, port geometry, hydraulic pressure, propeller torque or airflow model is provided.
- No valve travel or blade angle can be calibrated from these five inputs. The propeller depiction uses an explicitly illustrative blade pose.
Compare actual RPM with the selected RPM. Dividing the ideal force difference by spring rate gives a spring-equivalent displacement; it does not determine valve lift or blade pitch.
Governor response and the drawing
The FAA governor cutaways identify the speeder spring, flyweights, their toes and the pilot valve. Above selected speed, the weights tilt outward and the toes raise the valve linkage. The pitch response tends coarser; below selected speed the response reverses. At equilibrium, the governor holds the required pitch within its governing range.
The drawing makes that mechanical arrangement visible. Each weight and toe is a rigid L-shaped member hinged to a rotating carrier. Their central contact supports a sliding collar and stem. The housing stays fixed while the carrier turns. The propeller is drawn separately, and the pitch change is illustrative.
The view does not depict the pump, complete oil passages or the exact governor-to-propeller gearing. Different propeller systems route oil differently. Consult the applicable system documentation for those details.
An educational force worksheet
The inputs let you compare the effects of mass, reference radius and shaft speed on two ideal rotating weights. They also show how an assumed spring rate changes a force-equivalent displacement.
This is a useful way to explore proportionality: radial force scales with mass and radius, and with the square of rotational speed. It does not turn a radial-force sum into the axial load delivered through a real toe or bearing. That conversion requires the actual geometry.
What is calculated
For each ideal point mass, radial-force magnitude is mr omega², where omega = 2 pi N/60. The displayed two-weight sum is 2mr omega². With equal opposite weights, the vector sum of their radial forces is zero; the result is explicitly the sum of magnitudes.
The force difference is evaluated at the same mass and reference radius: ΔF = 2mr[(2 pi Nactual/60)² − (2 pi Nselected/60)²]. The speed-error result is Nactual − Nselected in RPM.
The fourth result is ΔF/k, in millimetres when k is entered in N/mm. This is the displacement of a hypothetical linear spring driven directly by that scalar force difference. It is not the valve lift of a governor: no toe lever arms, contact angles or spring preload have been provided.
The drawing illustrates the direction of the governor response. Calculating a blade angle or valve travel would also require the hydraulic system, linkage calibration and operating limits.
Example: changing actual speed
With two 35 g weights, a reference radius of 18 mm and 2,400 RPM, the radial-force magnitude sum is approximately 79.6 N. If selected speed is also 2,400 RPM, the force difference, speed error and ideal spring-equivalent shift are all zero.
At an actual speed of 2,600 RPM, with the other entries unchanged, the sum is approximately 93.4 N and the difference from the selected-speed value is approximately 13.8 N. With an equivalent spring rate of 20 N/mm, ΔF/k is approximately 0.69 mm. This number is a worksheet comparison, not a pilot-valve measurement.
Doubling mass or reference radius doubles both force values. Doubling k halves the ideal shift. When actual and selected speeds are equal, the force difference remains zero for any of those three inputs.
Model boundaries
A fixed-radius centrifugal-force calculation cannot determine blade pitch. The same selected RPM can be maintained at different blade angles under different aerodynamic and engine conditions. A numerical prediction would require those conditions and the propeller’s characteristics.
Likewise, actual pilot-valve travel depends on linkage geometry and the governor’s construction. The schematic tilt is chosen to show response direction clearly. It is not dimensioned by the reference-radius input and must not be used to derive a lever ratio.
The animation keeps entered actual speed fixed; it is not a dynamic simulation that accelerates an engine back to its selected setting. These results are educational and do not specify aircraft operating, maintenance or adjustment limits.
Governor model questions
Does the displayed force act axially on the pilot valve?
No. It is the sum of two ideal radial-force magnitudes. The linkage’s geometry is needed to relate those forces to the valve.
Why is there no calculated blade angle?
The inputs do not describe propeller aerodynamics, torque, hydraulic motion or linkage calibration. A numerical blade-angle prediction requires those relationships to be specified.
Why can spring-rate changes have no effect at matched speeds?
The force difference is zero then, and zero divided by any positive spring rate is still zero.
Does the animation simulate the return to selected RPM?
No. Actual speed is an input held fixed. The view shows the corrective direction rather than a closed-loop engine simulation.
What does the governor animation illustrate?
It shows how flyweight motion opposes the speeder spring and moves the pilot-valve linkage. Blade pitch indicates the direction of response, not a calculated angle.
Governor construction reference
FAA Aviation Maintenance Technician Handbook—Powerplant, chapter 7: Propellers, figures 7-15 and 7-16, pages 7-9 and 7-10. The cutaway photograph and diagram show the spring, flyweight toes, carrier and pilot-valve arrangement.
The force worksheet above is explicitly derived from the ideal point-mass relation mr omega² and an assumed linear spring. It is not a formula or calibration supplied by the FAA for a specific governor.
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