Halladay's feathering windmill turns sails about radial spindles to change their exposure to the wind. Levers connect the spindles to a head that slides along the main shaft. Explore this arrangement using an entered wind-to-feather-angle schedule, and compare projected sail width and wheel-tip speed. The schedule does not predict windmill power or governor response.
Feathering Windmill Interactive Calculator
Explore an explicit feathering command schedule on Halladay's patented arrangement: sails rotate on radial spindles as a governor shifts a linked head along the main shaft.
Equation Used
- All sails receive the same commanded spindle rotation.
- Feather command varies linearly between entered wind thresholds.
- Projected width uses a simple cosine projection.
- No aerodynamic, governor-dynamic, pump-load, stress or safe-speed model.
The entered wind thresholds prescribe the illustrated feather angle. They do not calculate the response of a hydraulic or flyball governor, aerodynamic torque, pump load or a safe operating speed.
Halladay's sliding-head governor
Patent 11,629 mounts each sail F on a radial spindle b that can turn in the wheel E. Levers connect those spindles to a head G sliding on the main shaft A. A governor moves the head, rotating the sails obliquely to the wind when speed rises and returning them toward broadside when speed falls.
This is blade feathering, not offset-yaw furling of the entire rotor.
Changing sail exposure
Turning the sails about their own spindles changes their angle to the wind while the wheel remains in the same plane. This is different from yawing the entire wheel out of the wind.
The model illustrates that motion and a chosen control schedule. It does not describe the performance or settings of a particular farm wind pump or modern turbine.
The entered feather-angle schedule
Between the entered begin and full-feather wind values, q = (V − Vbegin)/(Vfull − Vbegin). Values below zero are held at zero and values above one at one. The commanded feather angle is 90q degrees. Projected sail width is 100 cos(angle) percent of the broadside width.
Set the full-feather value above the begin value. If it is equal or lower, the calculator uses an effective full value 0.1 mph above the begin value to avoid division by zero.
Wheel-tip speed in mph is πDN/88 for wheel diameter D in feet and entered wheel speed N in rpm. Wheel speed is an independent input; it is not predicted from wind speed.
Example: halfway through the entered schedule
Set begin feather to 20 mph, full feather to 30 mph and wind speed to 25 mph. The schedule fraction is (25 − 20)/(30 − 20) = 0.5, giving a 45-degree feather angle. Projected width is 100 cos(45°), or about 70.7%.
For an 8 ft wheel entered at 20 rpm, wheel-tip speed is π × 8 × 20/88 = 5.71 mph. Raising the entered wind to 30 mph commands 90-degree feathering and zero projected width in the ideal projection. It does not automatically change the separately entered wheel speed.
These are illustrative command and geometry results, not operating thresholds or a shutdown recommendation for a real windmill.
Motion, control and power
The sliding head links the sail settings mechanically. A real governor must respond to the wheel and its load; aerodynamic forces, inertia, friction and linkage dimensions affect that response. The model supplies a command directly instead of solving those dynamics.
Projected sail width alone is not aerodynamic force or power. The calculator has no blade aerodynamic data, pump characteristics, tower loads or material-strength model. It cannot set a storm limit, select a pump or estimate water delivery.
Frequently asked questions
Do the sails pitch individually or does the whole wheel turn away?
The illustrated Halladay arrangement turns the sails about radial spindles through levers and a sliding head. It is not a whole-wheel yaw-furling model.
Are the wind thresholds actual windmill settings?
No. They define the linear command schedule shown here and do not predict the response of a physical governor.
What does projected sail width mean?
It is the cosine projection of the sail width relative to its broadside value. It is not a measure of aerodynamic power or thrust.
Why does the wheel-speed input remain independent of wind speed?
The model does not solve the balance of wind torque, mechanical load and governor response. Wheel rpm is entered separately.
Can the results predict pumped water volume?
No. There is no pump, lift-height, power or efficiency calculation.
What if full feather is set below begin feather?
Use a higher full-feather value. For that invalid ordering, the calculator substitutes an effective full value 0.1 mph above the begin value.
Primary reference
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
