Wright Stuff

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The Event

Wright Stuff (WS) is an event where participants try to make, test, and fly an airplane powered by twisted rubber band(s) for the goal of longest flight duration. The airplane can be of any design, though it must conform to rules regarding maximum wing and stabilizer dimensions, as well as a minimum mass limit (of the entire airplane, not including the rubber loop) and a maximum rubber mass limit.

The Average Airplane

An average Wright Stuff airplane contains six parts:

Wing assembly
A frame made of sticks of low-density balsa wood glued together, covered and glued with a thin covering made of paper or plastic. One or two sets of these are glued to tougher (higher-density balsa or basswood) sticks, and inserted into paper tubes on the fuselage of the airplane (so that the wings can be disassembled from the fuselage for storage/transportation). There are also other ways of mounting the wings on the motorstick besides the tubes. The sticks running perpendicular to the motorstick are called spars. The front spar is called the Leading edge and the back spar is the Trailing edge. The ones running parallel to the motorstick are called ribs, and are usually curved (cambered) to increase the lift of the wing. Ribs are usually created using a simplex foil. The higher the simplex, the harder it is for the plane to climb. The wing usually has a slightly higher simplex than the stab as well.
Motorstick ("MS" or "stick")
The fuselage or "body" of the plane. This is either a length of fairly thick and relatively (relative to the wing spars anyways) denser balsa, or a thin, long sheet of light balsa rolled along its length and glued so that it becomes a thin-walled balsa tube. Either way, the motorstick serves to hold the twisted rubber between the propeller assembly (at the front) and the motor hook (at the back of the MS) and to hold the wing tubes. A single stick fuselage can have advantages as well such as being flexible.
Tailboom ("TB" or "boom")
The "tail" of the plane. This is another length of solid balsa, usually lighter than the MS and sometimes tapered to save weight, or a thinner, lighter balsa tube, which can be tapered as well, but usually not worth the effort. The boom serves to support the vertical and horizontal stabilizers. Since it doesn't do not have to support the rubber, it is usually lighter and weaker than the motorstick.
Propeller assembly
The propeller ("prop"), the thrust bearing, and the wire propeller shaft.
Horizontal stabilizer
The horizontal stab has a similar structure to the wing with the exception that it's smaller. It is the second lifting surface and is usually located in the rear of the plane, except in canards.
Vertical stabilizer
Usually located near the horizontal stab, the vertical stab controls the yaw of a plane. It can act as a rudder to induce turn.

Trimming a Plane

For inexperience fliers, focus on building a working airplane to weight and trimming (adjusting) it until it flies around in circles before worrying too much about advance techniques or bonuses. A simple, well-trimmed plane with lots of practice flights will do better than a poorly trimmed pusher canard with a torque burner, ribbon drop, and other bells and whistles.


On a well trimmed plane, the wing has a positive incidence and stab has a small negative angle of incidence. Raising the leading edge of the wing or lowering the trailing edge can cause the plane to climb. Raising the trailing edge of the stab, or lowering the leading edge can also do the same. If your plane tends to stall, do the reverse of the above. Some modelers have a small amount of down thrust and left thrust in their propeller by angling the thrust bearing.

The whole point of trimming is to set the moments of the plane to 0. This means having the (wing lift)*(distance from Center of gravity) = (lift of stab)*(distance from CoG)

Turning

There are, in general, two methods for controlling turn:

  • Setting the wing's angle relative to the horizontal stabilizer so they they are skewed, causing the plane to roll. This works because the lift vectors are directly perpendicular to the surfaces that generate them. So, since the wing and stab are slanting in opposite directions, their lift vectors have components in opposite directions. Since they are on opposite ends of the fuselage, this causes the plane to turn.
  • Turning the rudder/vertical stabilizer so that the entire plane yaws. The plane is now moving forward, but pointing slightly to the side. One tip of the wing is now pointing more forwards than it was before. Because of dihedral, this causes that end of the wing to rise, and thus causing the plane to roll. This is known as slipping and sliding because the plane is never pointed in the same direction that it is traveling in, so it is always skidding a little.

Dihedral vs. Tip plates Dihedral is angling both ends of the wing upward. This causes the plane to have more stability from rolling. It has to do with the plane sliding when one side of the wing goes lower than the other. When the plane slides, there is a horizontal force on the lower wing that corrects it until both sides are balanced again. Tip plates accomplish the same goal, however I believe there is less sliding during flight with tip plates.

Propeller Pitch

Usually propeller (prop) pitch can be measured in degrees using a protractor or a pitch meter. The pitch angle refers to the angle of the prop blades as they rotate. At steeper pitch angle the prop will revolve at a slower rpm, and at a lower pitch angle the prop will speed up. Some broad blade props are designed to be natural flexing props, meaning that at high torque the blades will flex to a steeper pitch angle slowing the climb, yet they flex to a lower pitch angle later in flight.

Rubber

Rubber is the source of potential energy that is transfered into thrust. Rubber is often measured with its cross section. A band with a bigger cross section will take less winds than a smaller band before it breaks. However, the bigger cross section will spin the prop faster, considering prop pitch is constant in both cases. Matching propeller pitch with cross section to make the longest endurance can take much testing.

Making Flights

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Finding a Flying Spot

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Winding Rubber

A rubber winder is important to a free flight modeler. Winding an Ikara prop 1500 times can be both damaging to the prop and time consuming. When winding rubber, first stretch the rubber 4-8 times its original/relaxed length. After entering around half the desired winds, slowly move in, decreasing the length of the stretched rubber, while still putting in some more winds. The key to winding is to place as many winds as possible without the band breaking. It takes a true feel to know when you are on the edge and when you can still put in a few more winds, so practice helps. After one gets the desired number of winds, dewinding might be useful. Dewinding decreases the launch torque so you can avoid hitting the hazardous ceiling.

Launching

Indoor flight planes are not meant to be thrown, just released. Simply walk with the plane to its normal flight speed, and release. In small ceilings, launch your plane with a smaller torque than in high ceilings.

Logs

Serious indoor fliers keep very accurate logs so they can test and record what makes their plane most efficient. Some suggested data are rubber size, rubber weight, number of winds, number of dewinds, launch torque, circle radius, max height, number of winds left, prop diameter/pitch/width, duration time, etc.

A List of Supplies

Here is a list of supplies you need:

  • Balsa
    • (1) 18" sheet A grain, thickness between .045" and .050", density not more than 5.5 pcf (for wing and stab spars)
    • (1) 18" sheet C grain, thickness between .020" and .030", density not more than 5.5 pcf (for rolled motor stick if used)
    • (1) 18" sheet any grain any density around .030" thick (for ribs)
  • Winder: yellow plastic 15:1
  • Torque meter: the torque meter must have a range to at least 1.0 in-oz. You can make this if you'd rather do it that way.
  • Covering plastic
    • Covering: Indoor Mylar, clear. .000059 x 12" 35 ft roll
  • Propeller assembly
    • Plastic Prop or Ikara SO model propeller
    • Ray Harlan Penny Plane bearing (NOT the SO model bearing) .019 or .020"
  • Music wire and Teflon washers
  • Glue; Ambroid or Duco glues
  • Glue Thinner; Acetone from hardware or home improvement store
  • Glue Bottle: with steel needle nose and cap
  • Glue for wing covering Super 77 spray glue
  • Rubber for motors
  • Tool box: fishing tackle boxes are nice esp. the 747 model.
  • Table: folding but get one big enough to have some weight when winding
  • Building Board; cork or 3 inch or more thick styrofoam from home improvement store
  • Wax Paper: to cover building board with plans in between from food store
  • Pins: to hold wood on building board in place to glue. Regular straight pins or T shape are better from
  • Knife: Exacto type
  • Razors Single edge: for striping wood
  • Ruler: for straight edge to cut wood
  • Scale: Best bet is to borrow the schools or get a digital scale with 0.01 gram accuracy.

Alternatives

  • Balsa Cutting: Master Airscrew balsa stripper
  • Thrust Bearing:
  • Winders:
  • Pitch Gauge: for pitching the prop blades
  • Scale: not digital but more accurate than most. You need to measure to 0.01 grams
  • Knife: thin bladed Surgeon's type for cutting ribs
  • Sand Paper: very fine grain for smoothing wood; usually 220-320+

List of Supply Sources

Ready Made

Build Your Own

Info Links

New York Coaches Conference [1]