Thermoelectric Aircraft Control Surfaces

If you want to go flying about in an aeroplane, it's nice to be able to control that flight. To do this, several methods have been developed. You can change the engine thrust to go faster or slower, but this might not be enough control if you're pointed at a mountain.

The solution is control surfaces which come in a variety of flavors. Perhaps the most obvious to a casual airline passenger is the ailerons. These are movable surfaces mounted on the trailing edge of the outer portion of the wing. Move it down, and the effect is to modify the aerofoil shape of the wing to provide more lift. On the opposite wing, the other aileron moves up, reducing the lift of that wing and there is a net force rolling the aircraft. The same principle is in play with the rudder and elevator on the tail of the aircraft, with some modifications. Elevators usually work together, and they may be split into an all-moving horizontal stabilizer with elevators on the trailing edge. The point being that changing the pitch/roll/yaw of an aircraft requires changing the shape of the related aerodynamic surfaces*.

Movable control surfaces are UNdesirable for a number of reasons:

They require moving parts, these wear out and require servos/jacks/cables etc. to be routed throughout the aircraft.

They mess with stealth. Stealth requires VERY careful control of the aircraft shape and movable control surfaces hurt this badly and mitigation is tricky. The B2 for example has gone to great lengths to remove traditional control surfaces and mitigate movement of the remaining ones.

So how can we achieve the effect of movable control surfaces without movable control surfaces? What is the basic effect we are trying to achieve? Well, an aileron moving down increases the pressure under that portion of the wing and decreases it above the wing. The pressure difference creates extra lift. Can we change the pressure by other means? Yes!

If we place thermoelectric/Peltier elements in-between the upper and lower surfaces of a wing and apply a current, the Peltier will cool the upper surface and heat the lower surface, effectively pumping the heat from top to bottom (with some excess heat from the element inefficiency.). PV-nRt demonstrates that cooling the air will reduce pressure/volume and heating it will increase pressure/volume causing a bigger difference between the two and therefore increased lift. We do the opposite on the other wing and now we have our rolling moment with no change in wing shape.

The same principle can be applied to all the control surfaces. Furthermore, there are opportunities to subtly modify the properties of aerofoils. For example, Peltiers could be used to locally heat & cool parts of a wing aerofoil to make it behave as if it were thicker/thinner or a different profile, e.g. moving the point of maximum thickness back for more efficient high speed flight. For more robust effects, the fuel can be used as a heat sink/source, which would allow other control options, for example in a flying wing, one wing could be cooled and the heat pumped via the fuel to the other. Aerodynamically, one wing would behave as if it were thicker than the other giving a drag difference and a yaw moment - no rudder required.

I'm under no illusions that the forces generated would be small compared to conventional movable control surfaces, but I'm not suggesting this for a dogfighter. Applications like the B2/B21 and small stealthy drones where subtle control inputs are all that's required are most suitable.

*Two notable exceptions to this: 1. Vectored thrust, e.g. the F22 uses movable jet exhaust nozzles to direct thrust up or down to change pitch. 2. Center of gravity manipulation, e.g. Concorde pumped fuel rearward during supersonic flight to avoid the drag associated with elevon deflection as the center of lift moved back.