Pig Page

Pig Page
The Pig is my latest biplane airchair design....
by Mike Sandlin
Last update......August 19, 2008
(added a new photo)

The Pig (Primary Instruction Glider) is my current flying project, a biplane airchair with a two axis control system (rudders & elevator, but no ailerons). Its first flight was made in October, 2007.

The Pig is intended to be simple, safe, slow and soarable. It has already proven to be practical to transport and assemble, and I hope that more flying will show it to be an easy glider in which to roll launch and a satisfying soaring machine.
In addition to launching by rolling down slopes and line towing, the Pig design is intended to allow for installation of a self launch motor, with the propeller facing rearward behind the pilot. The idea would be for this "motorfloater" type of airplane to operate from small rural airports instead of hang gliding sites (as the microtrike, powered paraglider, and powered harness hang glider are already doing). The motorfloater, as compared to the existing self launch ultralights, could offer superior stability, easier control, and improved crash safety.

The Pig has a lot of the usual airchair features:

low wing loading for forgiving flight characteristics and rolling launches
open air pilot seating (allows hand thrown emergency parachute)
center of lift landing gear (16" diam. standard kite buggy wheels, 8 ft. separation)
car top transport (major sections separate, folding wings and tail)
one person assembly (37 minute setup for me in my backyard)
light weight airframe (120 lbs., but emergency parachute not yet installed )
nose skid for quick stops, nose down attitude for take off or landing
garage technology (simple construction from readily available materials, no molds, no welding, no special machining, no spray rig, no sail making, no sheet metal, etc.)
airframe made of bolted aluminum tubing with braided steel cables, covered with a light grade of conventional aircraft fabric (polyester fabric is cemented on, heat shrunk, then adhesive sealant is applied by brush)
secondary structure (small ribs) of foam, carbon, & fiberglass tape composite

Test flying with the two wheel, rudder and elevator controlled glider has been fun and eventful. Flying speed feels something like sitting in a moderate breeze. The turn response is good, but quick and active use of the rudders can cause a noticeable amount of drag, slowing the glider down and costing some altitude. I'm still adapting to this new control system, having a hard time relaxing in a bank with a stick that will not move sideways. My guideline to steady state flight is something like "nose level, steer with the feet, look where you want to go".
Launching makes me feel like a kid again, scooting down the family driveway in my little red wagon. When I got fast in the wagon, I just held on and tried to keep it under control, but now I pull up and fly.

Toward the end of the launch roll I have to stay nose down and accelerating until I'm I'm fast enough to lift off, then I rotate the nose up and get airborne promptly. If I had rolled more nose up and floated off more smoothly, as I might have with a three axis controlled glider like the Goat, I could have had trouble in the Pig because during the ground roll the wheels are the only thing holding the wings level. If there was much of a cross wind during the launch or landing roll, one wing might rise up and cause loss of steering control if I didn't hold the wheels firmly down on the ground by keeping the nose low. Once I get into the air, the crosswind is no longer an issue as I start steering in the ordinary manner, which will rotate me into a crab angle as I fly out from the hill.

For landing, I've decided just to steer where I want to go and not to worry about sideways drift or the wing not being quite level. Usually, one wheel will touch down first and will be skidding a little sideways, but it doesn't amount to anything after a little momentary roughness.

Two big tricks have been played to create the main wing structure of the Pig. First, the nose section has been rigged in such a way as to create a rigid wing structure, even though there is a strut missing where the pilot sits. The airframe is not rigid until the nose section is fully installed, sweep cables and all. Second, the eight main wing struts are mounted on swiveling eyebolts, so they can be swung back and rotated ninety degrees during disassembly. With the wing halves and landing cables disconnected, this allows the upper wing to swing back over the lower wing to a zero stagger position, and then (after strut rotation) to be folded sideways with the struts still attached, to make 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, see assembly photos above).

Here is the August 2008 rudder setup, big simple rudders with the control lines routed back along the upper tail tubes.

Test flying will continue.

I have nothing for sale and no commercial intentions. There are no Pig drawings available yet, but I intend to post some (as I did for the Goat and Bug) if things go as planned, hopefully this year. See my Airchair Update Page for my current status.

[END]