Wright Stuff is a Division B event for the 2017 and 2018 seasons and a Division C event for the 2019 season. The event involves making, testing, and flying an airplane powered by a twisted rubber band, with the goal of achieving the 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). However, there is no longer a mass requirement for the rubber motor.
- 1 Basic Plane Design
- 2 Using a Kit
- 3 Trimming a Plane
- 4 Making Flights
- 5 A List of Supplies
- 6 List of Supply Sources
- 7 Past Results
- 8 Info Links
Basic Plane Design
A typical Wright Stuff airplane contains six major 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 a length of fairly thick balsa wood. It is often mistaken that balsa needs to be dense, but actually, it happens to be sturdier if made of the least dense (but with the biggest cross-section) piece. Or it can be made of a thin, dense, 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 have to support the rubber, it is usually lighter and weaker than the motorstick.
- Propeller assembly ("prop")
- The propeller, 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.
Using a Kit
Using a kit is often the best course of action for inexperienced fliers. Kits are often easy to assemble and trim, and make Wright Stuff a much less intimidating event. However, certain kits are more complicated than others. Laser Cut Planes has very simple, affordable kits that are easy for kids to put together. Freedom Flight kits are great planes, but are very delicate and more expensive. Buying multiple kits is also a good idea, as planes are very fragile and can be broken easily. Having multiple planes is a great way to test what works and what doesn't, and provides a back-up in case one plane is lost or broken.
Most kits come with instructions, but the way the plane flies depends on how accurately it's put together. Taking the time to sand off burn marks from the edges of laser-cut kits makes your plane a little lighter, and helps it look better. Putting the plane together straight or angling the stabilizer so it turns is essential to making sure you get the best flight time possible with your kit. Many competitors post their results with certain kits on the Science Olympiad forums, so comparing times to other people with the same planes can give you an idea of how to better improve your plane.
Kits are easy to build, but they aren't always be the most optimal planes. Once you know what you're doing, building your own plane from scratch can be a good way to get the best times possible for the season's rules.
Trimming a Plane
For inexperienced fliers, focus on building a working airplane to weight and trimming (adjusting) it until it flies around in circles before worrying too much about advanced 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)
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.
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 is the source of potential energy that is transferred 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. Lubricating the rubber with Armor-All or something similar can also increase the longevity of the motor and make it less likely to snap the more winds are put in.
When making flights, follow the directions in this wiki for finding a flying spot, transporting your plane, winding, launching, and trimming. Always have a toolkit for making minor repairs, so if something goes wrong your entire day won't go to waste. Also, regardless of how well your plane flies, keep a log. This is not only for competition purposes but also to help you decide what adjustments to make (winds, torque, rubber size) when flying in a new ceiling height at competition.
Finding a Flying Spot
Obviously, you would want to find a place where you can keep the doors from opening unnecessarily, and a place with little or no air condition. Most people only have access to your school's gym, which will do if the competition is in a similar ceiling height. For state (and maybe nationals) if you live in the area and it is easy to get to the site of the competition, they will probably let you fly your plane if nothing else is going on in the building. (For example, the University of Tennessee allows access to Neyland-Thompson Sports Center, their indoor football facility where the event is held at state, and you can make flights there over the weekend.) Check with the site owner/manager, and if you are nice and explain your love for science, they can be nice and allow you in. Once inside, stay away from wires, hanging scoreboards (ouch, those are plane-killers), basketball hoops, and places where the rafters extend downward. Don't wind your plane up too much the first time you fly it, because if it gets stuck, you are out of luck. You also should see the radius in which your plane turns. Use this to determine where to launch from. (If your plane gets stuck, wet paper towel balls can dislodge it from a low ceiling such as a gym, but anywhere else will require a balloon and a stick taped to it to dislodge it. Caution: these methods, especially the paper towel balls, may injure your airplane, however you may find it worth the risk to get it back.) Also, you may want to try to find a model airplane group in your area. Often, they will get gym time from colleges or other places, and if you explain what you're doing, chances are they will let you join them.
After spending effort building, being able to safely transport your plane(s) to practice sites and competitions is crucial. A cardboard box works, but be careful if it's open flapped. There's been cases where people using cardboard boxes had their plane ruined because they left the box lying around and their cat got to it. A plastic sweater box with a lid would be safer. Place a few plastic grocery bags inside the box, surrounding the plane. This avoids the need to make jigs and supports so the parts of the plane hold in place, and the bags will prevent the model from sliding around and getting damaged.
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.
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. Also, in small ceilings, it may prove beneficial to launch your plane while laying or kneeling on the floor. That way, you may be able to add 3-5 feet to the ceiling height and prevent your plane from colliding with the ceiling. This technique isn't as useful in very high ceiling areas.
Serious indoor fliers keep very accurate logs so they can test and record what makes their plane most efficient. A log is also required by the 2018-2019 rules. Logs must include the motor size, number of winds, and the flight time, in addition to three more data parameters. Some suggested data are rubber weight, 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 might need:
- (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" or the bearing included with ikara props.
- Music wire and Teflon washers
- Glue; Ambroid, Duco, or cyanoacrylate (super glue)
- 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
- X-acto Type/Hobby Knife: for general purpose cutting
- Single Edge Razor Blades: for striping wood, and general purpose cutting
- Metal Ruler: for a straight edge to cut wood
- Scale: the best bet is to borrow the school's or get a digital scale with 0.01 gram accuracy.
- Balsa Cutting: Master Airscrew balsa stripper
- Thrust Bearing: music wire pigtail bearing
- Winders: (You really probably don't want anything other than the 10:1 or 15:1 yellow plastic type)
- Pitch Gauge: for pitching the prop blades
- Scale: not digital but more accurate than most. You need to measure to 0.01 grams. You can also build your own, look under the "build your own" section
- Knife: thin bladed Surgeon's type for cutting (human) ribs
- Sand Paper: very fine grain for smoothing wood; usually 220-320+
List of Supply Sources
- Model Research Labs
- FAI Model Supply
- Ray Harlan
- Freedom Flight Models
- Laser-Cut Planes
- Guru Engineering Tech
- J&H Aerospace
Build Your Own
- Torque Meter: www.indoorduration-gbr.co.uk/#/manage-rubber/4572563487
- Thrust Bearing: Pigtail bearing out of music wire.
- Pitch Gauge: www.indoorduration.com/ftp/LaurieBarrPitchGauge.pdf
- Scale: build it yourself from Here. It is a simple scale. [Here] is another type of scale, it is also simple (know weight) scale or add a graduation points for how much the music wire bends.
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