In this article, we explain how the V-22 control system works.
Other tiltrotor aircraft will likely take a similar approach.
We focus on how pilot stick movements affect aerodynamic control surfaces, only briefly touching on software and electronics.
As you might guess, the V-22 uses a combination of traditional helicopter and fixed wing controls.
The effect that a stick movement has on control surfaces depends on the flight mode.
The V-22 is in “helicopter mode” when the nacelles are vertical and “airplane mode” when the nacelles are tilted down (horizontal) like an airplane.
Between these extremes is the “transition mode.”
- The angle of the nacelle is referenced as 0 when horizontal, in airplane mode.
- Above zero, through 75 degrees (15 deg forward of vertical), is called conversion mode.
- Above 75 degrees to the 97.5 deg limit (7.5 deg aft of vertical) is helicopter mode.
Below, we first discuss the primary controls that the pilot moves.
We then discuss the aircraft surfaces that can move in response to pilot controls.
Finally, we put these together and discuss which surfaces move with which pilot controls.
Primary pilot controls
There are four primary pilot controls: the thrust control lever (TCL), longitudinal cyclic, lateral cyclic and pedals.
There is a single cyclic stick, but it represents two degrees of freedom with longitudinal (fore/aft) and lateral (left/right) movements (like a game joystick).
There are two pedals, one under each foot, but they represent a single degree of freedom and move as one unit—pressing
one down makes the other raise by the same amount.
Thrust control lever
The TCL is mounted to the left side of the pilot and is gripped by the pilot’s left hand.
A picture is provided below.
It’s generally pushed forward to increase power and aft to decrease power.
This is most closely related to the collective on a traditional helicopter, but there’s a reason for the difference in name (as we’ll see).
The cyclic stick is located between the pilot's legs. It’s typically gripped with the pilot’s right hand.
Fore/aft movement of this stick is called longitudinal cyclic, and is used for pitch control.
Left/right movement of this stick is called lateral cyclic, and used for roll control.
A pedal is located under each of the pilot’s feet. The two pedals move together as a single unit—pressing the left pedal down raises the right pedal by the same amount (and vice versa).
Pedals are used for yaw control—to turn the nose of the V-22 left or right.
Pilot control movements cause control surfaces like the rotor blades or wing flaps to move.
These movements change the aerodynamic forces and moments that push and turn the aircraft.
In the case of the V-22, the following surfaces are used.
Both rotors have a swashplate that governs blade feathering.
Each swashplate has three degrees of freedom: it can move up/down to change the feathering of all blades collectively, and it can be tilted in any direction by a varying amount (cyclic) to induce flapping.
For more information, please see our article on swashplates.
The aft end of the tail is a movable surface called an elevator, highlighted red in the diagram below.
With forward speed, air pressure on the elevator pushes the tail up and down, primarily pitching the aircraft.
If the aft end of the tail is rotated down, as in the picture, it will increase lift on the tail and pitch the V-22 nose down.
Raising the aft end of the tail causes aerodynamic forces to push the tail down, and pitches the nose of the V-22 up.
Flaperons are much like the elevator discussed above, but they are located on the aft end of the wings.
They, too, rotate in a pitching motion, with the aft end of the flaperon moving up and down.
Turning the trailing edge down, as in the picture below, increases the lift of a wing when flying with forward speed.
If one wing flaperon is turned down, and the other up, there will be substantially more lift on one wing relative to the other.
This will roll the V-22 with the higher lift wing moving up.
Rudders are located on the aft end of the vertical surfaces at the tail of the V-22.
They are highlighted red in the diagram above.
These surfaces pivot left/right to effectively push the tail laterally in forward flight.
When the tail end is turned to the pilot’s right (down in the lower diagram) the tail is pushed to the pilot’s left.
This primarily yaws the V-22 nose right.
Likewise, when the rudders turn the other direction, the tail is pushed right and the aircraft yaws nose left.
Unlike traditional helicopters, V-22 pilot controls are not mechanically linked to the control surfaces.
Instead, pilot control movements are fed to a computer.
This computer uses the pilot control movements, along with the flight mode (helicopter/airplane/conversion) and other data,
to determine desired control surface movements.
The computer outputs electrical signals via wires to actuators that move the surfaces. This is called a fly-by-wire system.
How pilot controls impact control surfaces
Control surface movement in the V-22 depends on flight data beyond the pilot control inputs.
Probably the most significant driver is the flight mode described above (hover/transition/airplane).
Control surface movements associated with pilot control movements are drastically different depending on this mode.
For this reason, we describe the control behavior in two sections below, one for helicopter mode, and another for airplane mode.
Unlike the other axes, pitch is accomplished like a traditional helicopter (only with two rotors).
When the pilot pushes the cyclic stick forward, the swashplates in both rotors are tilted to make them flap forward.
The forward flapping primarily provides a nose down pitch moment, but also a force to accelerate the V-22 forward.
This is exactly what longitudinal cyclic does with the main rotor of a traditional helicopter.
The initial plan was to link lateral cyclic with differential collective on the two rotors.
When the pilot moved the cyclic right, the left rotor would increase collective while the right would decrease collective.
Higher thrust on the left side would therefore roll the V-22, right wing down.
Early flight tests revealed that the differential collective concept was too clumsy.
Lateral, side-to-side, flight was difficult, and a phenomenon called pilot induced oscillations was rampant.
Engineers decided to reduce the differential collective magnitude (not eliminate it) and augment it with traditional
helicopter lateral cyclic to improve handling qualities.
This combination is apparently good: many pilots have applauded precise lateral control in helicopter mode.
When a pilot presses the left pedal, aft cyclic is applied to the left rotor and forward cyclic to the right rotor.
In effect, the left rotor is pushed aft while the right is pushed forward.
The result: the V-22 yaws nose left.
If you want to know more about how cyclic control works, see our
article on cyclic control.
Of course, with the right pedal the opposite effect is applied: forward cyclic on the left rotor, aft on the right rotor, and hence a nose right yaw.
Vertical control is accomplished using the TCL.
Increasing the TCL increases engine power.
Added power would normally increase rotor speed, but a rotor speed governor is used on the V-22.
This governor modulates collective pitch (in both rotors) to maintain rotor speed.
Hence, increased TCL generally increases collective pitch (like a traditional collective control), but the path to this change is different.
Likewise, decreasing TCL reduces power and therefore the collective pitch to prevent rotor speed reduction.
In airplane mode, the pilot still uses longitudinal cyclic for pitch control.
However, the computer commands the control surfaces in a much different way.
Rather than tilting rotor swashplates, the computer commands the elevators on the tail to move.
Forward cyclic causes the aft end of the tail to turn down.
Since the V-22 will be moving with significant forward speed in airplane mode, aerodynamic forces
will push the tail up, creating a nose down pitch moment.
Of course, aft cyclic does the opposite: it raises the elevator, pushes the tail down and pitches the nose up.
The pilot moves the cyclic right to command a right wing down roll.
In airplane mode, the V-22 control system will respond by commanding the flaperons
on the right wing to move up, and the flaperons on the left wing to move down.
This decreases lift on the right wing and increases lift on the left wing, effectively rolling the helicopter as desired.
Left cyclic has the opposite effect, increasing lift on the right wing and decreasing it on the left by
lowering the right flaperon and raising the left.
Again, this works because, in airplane mode, the V-22 must be moving with significant forward speed.
Without forward speed, flaperon movement will have a negligible effect.
The pilot presses the left pedal to turn the nose of the helicopter to the left.
The control system commands the rudders to pivot, moving their aft end left.
This rudder movement increases aerodynamic forces pushing the tail right, and therefore turns the nose left.
Of course, pushing the right pedal accomplishes the opposite, moving the nose to the right by pivoting the rudders right.
The pilot can push the TCL forward for increased thrust.
For example, the pilot may do this to accelerate or, with aft cyclic, to initiate a climb.
This movement results in increased engine power and, if necessary to maintain rotor speed, collective feathering of all blades on both rotors.
Pulling the TCL aft has the opposite behavior, and could be used to slow down or level out after a climb.