“TRIKE TALK” By Dick & Jim

What is a “TRIKE” anyhow?  Ultralight aircraft which looks a lot like Hang Gliders with a tricycle undercarriage suspended below that the pilot sits in.  Weight-shift rather than aerodynamic control and have flexible, rather than rigid wings, and have no tails.

Why is it called a “Trike” not a powered Hang Glider?  While sharing similar technology, modern Trikes are not Hang Gliders.  Calling them Hang Gliders leads to some difficulties in such things as sales tax. Aircraft (other than gliders and hang gliders are exempt in Australia from sales tax and import duties.  Therefore, “Trike” (derived from the tricycle undercarriage) or “Weight-Shift Ultralight” are the Politically Correct terms.

Why Fly A Trike?  The performance of modern Trikes compares favorably with “conventional” Ultralights. Cruise speeds range from 30 to 70+ mph, and have among the most spectacular climb rates of all Ultralights.  New Trikes are generally cheaper than new “conventional” Ultralights.  There are less moving parts to go wrong.  Trikes have an enviable safety record.

Why Fly A Trike? (cont.)  Can be assembled or disassembled within half an hour and easily transported.  You can store it in your garage and still have room for your car.  They’re the motorcycles of the air.  Can do most anything or go anywhere in a Trike that you can in any “conventional” Ultralight  ….AND HAVE MORE FUN DOING IT!

The Main Bits

The Main Bits (cont.)

So, How the Heck Does it Fly?  The controls, what there are of them :  The Control Bar is the primary control. With it, you can move the whole Trike undercarriage fore & aft and side to side under the wing. This will control Pitch and Roll.  You have a throttle, but unlike conventional aircraft, it’s a foot throttle – just like a car.  Your left foot has a nose wheel brake pedal.  And apart from the ignition switch & choke, that’s basically all there is!

 Aerodynamics of the flexible wing:  The flexible swept wing airfoil provides high lift, a high L/D, a small pitching moment and subdued stall characteristics.  The undercarriage (trike body) is suspended from a pitch & roll joint attached to the wing structure.  Angle of Attack and Roll are controlled entirely by shifting the trike body either to the sides or fore and aft via pilot pressure on the control bar (A-frame).  This action effectively shifts the CG in relation to the wing aerodynamic center, hence “Weight Shift”. So, How the Heck Does it Fly?

 Pitch Stability (without a tail)?  The wing is aerodynamically balanced in pitch because a download is applied at the rear of the wing by a reflexed airfoil (the T/E is bent up – reverse cambered) and the outer wing sections are washed out.  Wing is flexible, root cord always has highest AOA, and the tips the lowest.  Pitch stability is derived from the reversed CP movement – as AOA increases the CP moves backward which pitches the nose down (see next page) So, How the Heck Does it Fly?

Pitch Dynamics: So, How the Heck Does it Fly? Wing root high AOA, wing tips low AOA. Spanwise tension tries to keep the tips as flat as possible. Tip AOA increases, root already close to max lift. When root stalls tips still lifting. Tips behind you forces nose down (positive “nose-over”) Speed up, the tips dump load, the root is major contributor of lift. Since the roots aerodynamic center is FWD, you get bar pressure that opposes the speedup.

So, How the Heck Does it Fly?  How a Flex Wing turns:  With roll input from pilot, the Cross-bar (spreader) is allowed to float slightly w/respect to the keel, and allows the sail to “billow shift” (example: On ground, grab T/E of one wing, and push up, you would notice the other wing become tighter).  The extra load on the inboard wing causes sail to shift to that side. That tightens the sail on the outside wing, increasing AOA, while decreasing the AOA on the inboard wing (see diagram below).

3-Axis Conversions Are you a 3-Axis pilot thinking converting to (or trying) Weight-Shift?  Trikes have reverse sense controls compared with 3-Axis aircraft.  Pull control bar toward you to speed up, and away to slow down.  Move control bar right to turn left and vice versa.  Nosewheel steering is “billy-cart” style. Push right, go left. You can be a “Bi-Wingual” Pilot

Questions?