Pig Page

Pig Page

by Mike Sandlin
The Pig is my latest biplane airchair design....

Last update......

May 5, 2010 (text revision)

Flying the Pig is simple, a two axis system like a hang glider, "fast-slow, right-left", not requiring any coordination between the yaw and roll axes as does the three axis system. There is no yaw string, and the general instruction is: "nose level, turn with your feet".
The initial use of the rudder induces a skid, quickly followed by banking of the wing. Generally, the control feel is quick and stable, and the controls function just as well as on any of the three axis airchairs. There are special two axis procedures, such as keeping the nose low while ground rolling in a cross wind, so the weight of the glider on the wheels will keep the wings level.
The photo at the very top of the page serves as an illustration of the mechanics of aerodynamic yaw/roll coupling as related to the dihedral angle of the wing. Imagine that the pilot is turning right and so has just yawed to the right, and the oncoming air is reaching the wing exactly from the direction of the camera view. You can see the bottom of the left wing but only the top of the right wing, so the oncoming air has a higher angle of attack on the left wing than on the right wing. (This is exactly the condition the would have been achieved by applying right aileron, if ailerons had been present.) Now there is more lift on the left than on the right, so the wing rolls to the right, as desired for a right turn. (A big turn is not something you would actually do at this low altitude, but I hope you can get the idea from this example.)

The eight main wing struts are mounted on swiveling eye bolts, so that during disassembly the struts can be detached at one end and rotated ninety degrees on the other. This allows each upper wing half to be lowered onto the lower wing half, making a compact stack for car top transport.

The wing airfoil is a simple utility type that I made up (Pigfoil 3012, 12% thick at 30% chord) with a completely flat bottom. This airfoil is similar to that of some radio controlled trainer gliders, and much like a Piper Cub. From this I expect good low speed flying characteristics and easy construction. This airfoil can also provide a strong and stiff trailing edge which will tolerate rough assembly on irregular terrain (the wing section is assembled with the trailing edge on the ground).

Room has been reserved behind the the pilot to allow for installation of a small motor, presumably with a pusher propeller at about the trailing edge of the wings. The engine frame might replace the two centerline struts, and there are other hard points nearby if required. The prop wash can exit through the box tail without hitting any control surface, avoiding a common source of vibration and drag. Adding a motor to the Pig would create a "motor floater", a self launching airchair which could play the game of minimal power flight to the nearest thermal. Right now I'm not doing anything with motors, but someone with those interests might want want to take a look at it.