A collective-pitch linkage changes the feathering angle of all rotor blades together. In the arrangement shown here, the swashplate translates along the mast without tilting. Its rotating ring carries pitch links to the blade horns while its stationary ring receives the control input. This calculator illustrates a defined, generic linkage geometry rather than a particular aircraft.
Collective Pitch Control Linkage Interactive Calculator
Explore a generic collective linkage with three equal blade pitch angles. Control travel and gain set the swashplate rise; horn and pitch-link lengths determine the exact attainable angle. The pitch link is vertical at the selected neutral angle. This is an educational linkage model, not aircraft rigging or flight-performance data.
Equation Used
- Pitch link starts vertical at the selected neutral horn angle.
- All three blade stations have identical geometry and a level swashplate.
- Gain represents an ideal upstream transmission; direct drive uses G = 1.
- Fixed pin-to-pin lengths; no compliance, joint offsets, cyclic input or blade dynamics.
- Endpoints beyond the continuous branch are reported as unreachable.
Exact rigid horn/rod closure in a generic collective-only rotor, with a visible branch limit. No aircraft operating limits or rigging guidance.
How collective pitch is transmitted
The stationary and rotating portions of a swashplate move axially together. A bearing permits relative rotation; the rotating part follows the rotor through its drive linkage. Pitch links connect that rotating part to horns on the blade grips. Equal axial movement at all blade stations produces equal feathering changes in a symmetric model.
The animation shows three blade stations. Blue links and the upper ring rotate with the hub; the bronze lower ring and control rods retain their azimuth. The ring stays level because only collective input is included. The blade-end detail exposes the rigid horn and fixed-length pitch link so their motion can be checked directly.
The numerical model starts with each pitch link vertical. Changing the neutral horn angle also changes the neutral lower-joint location. An ideal upstream gain scales the entered control travel before it reaches the ring. For direct swashplate travel, set gain to 1. Drive-scissor, bearing internals, flapping and lead-lag articulation are omitted from the simplified illustration.
Where this mechanism appears
Collective feathering is used in helicopter main-rotor control and other variable-pitch rotor systems. Details differ among aircraft and rotor heads. This generic model is useful for understanding the relationship between slider travel, a pitch link and a horn, and for contrasting collective translation with cyclic swashplate tilt.
Exact geometry used by the calculator
Let L be horn length, R pitch-link length, θ₀ the neutral horn angle, z entered control travel and G the upstream gain. The feathering pivot is the origin in the blade-end view. At neutral, the rod is vertical:
y = y₀ + Gz; d = √(x² + y²)
θ = atan2(y, x) + acos[(L² + d² − R²)/(2Ld)]
This circle-intersection solution follows the branch connected to the neutral position. Pitch change is θ − θ₀. Average pitch gain is that change divided by z; at zero travel the local gain is G/(L cos θ₀), with radians converted to degrees.
The model reports an unreachable endpoint when the chosen rise reaches the branch limit. The preview stops just short of that toggle, with the rod length and assembly branch held constant. The circle-intersection solution accounts for the changing rod angle throughout the motion.
Worked educational example
Set control travel to 30 mm, gain to 1, horn length to 50 mm, neutral angle to 0° and pitch-link length to 150 mm. The lower joint starts at (50, −150) mm and rises to (50, −120) mm. The endpoint pitch is approximately 36.42°; the fixed rod is still 150 mm long and the horn 50 mm long.
This example illustrates linkage geometry only. A mechanically attainable angle is not evidence of a permissible flight pitch, aerodynamic operating limit or approved rigging setting.
What the model includes
Exact rigid-link closure makes the loss of travel near a toggle visible and avoids extending a small-angle approximation across the full slider range. It requires the pitch-link length as well as the horn length. Real installations also depend on three-dimensional joint positions, horn indexing, mixers, clearances, stops, elasticity and blade dynamics, none of which is inferred here.
Questions about the model
Why does pitch-link length affect the result?
A horn tip moves on a circle while the lower joint follows a straight path. A fixed-length rod connecting them swings as it moves. Its length is needed to solve this geometry exactly.
Why does the result say unreachable?
The selected travel exceeds the continuous assembly branch from neutral. The preview shows the connected portion of travel; an endpoint angle is unavailable beyond that limit.
Does the animation predict lift or safe rotor pitch?
No. It models rigid linkage geometry only. Aircraft-specific rigging, inspection and operation require the applicable approved documentation.
What does gain represent?
Gain is an ideal upstream travel ratio. Ring rise equals entered control travel multiplied by gain. Use 1 when entering the ring travel itself; the upstream transmission is not drawn.
References and model definition
- FAA Helicopter Flying Handbook, chapter 4, pages 4-6–4-7 and figure 4-11: stationary and rotating swashplate components, control rods, pitch links and drive links.
- The calculator uses the explicitly stated circle-intersection geometry above; its dimensions are illustrative and are not taken from an aircraft maintenance manual.
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