FREE FLIGHT DURATION
Louis Joyner, 4221 Old Leeds Rd., Birmingham AL 35213
BUILDING BOXES
In the last column, I wrote about the need for model boxes in which to safely store and transport Free Flight (FF) models. Several ready-made model boxes were shown in a variety of sizes.
But what if you can't find a model box that's just the right size? That's easy—make one.
If you have basic home-workshop tools, putting a box together should be a good weekend project. Here are some guidelines:
- Unless you have access to the proper sheet-metal cutting and bending equipment, forget making an aluminum box. Wood is easier to work with for most of us.
- Perhaps the most popular choice for a wood box is a "door skin"—a 1/8-inch-thick, three-ply sheet material used to face flush doors. Typical sheet size is 3 x 7 feet, which is usually enough for a four-foot-long box. You can find door skins at many specialty lumberyards and cabinetmaker supply stores. I have never seen them in home-center stores.
- A birch-faced door skin is approximately $20. Other species of wood are available, but birch gives the best finish. I've used door skins for two boxes, both of which held up fairly well, but I'd opt for 1/8 aircraft plywood if I was going to build another box.
- Aircraft plywood is considerably more expensive than a door skin, but it has more plies—and all the plies are birch. On a door skin, only the ply on one face is birch; the other two layers are weaker lauan. Large sheets of aircraft plywood are available from select lumberyards or full-scale aircraft suppliers, such as Aircraft Spruce and Specialty.
- The best blade for cutting plywood is a fine-tooth plywood blade (which is also great for cutting balsa).
- Cut the top and bottom of the box to exact size, then rip full-height pieces for the sides and ends. Build the box solidly, then cut it apart to make the lid. I tried to build the lid separately on my first box, and never got a good fit. Building the box in one piece, then cutting it apart is much easier.
- If you don't have access to a table saw, use a hand-held circular saw and a long straightedge clamped to the plywood to produce straight cuts.
- Use 3/8-inch- or 1/2-inch-square wood to reinforce the corners. I have used square reinforcements glued and screwed in place. You can also use molding strips from a home-center store, but they are often out-of-square. Blaine Miller, who built one of the neatest boxes I've ever seen, used 3/8-inch-square spruce from the local hobby shop.
- With wood glue and a number of spring clamps, attach reinforcement strips to the inside face of the top and bottom, exactly 1/8 inch in from the edge. For a stronger box, use half-lap joints at the corners. After the glue dries, add the sides and ends, overlapping the corners pinwheel-style. You can trim the sides and ends to exact length later, with a saw or a flush-trimming bit in a router. Miter joints aren't worth the effort.
- You'll need a good supply of tape, bar clamps, and extra hands for this stage. Make sure everything is square, and let the glue dry.
- Cut the box apart with a table saw or a hand-held circular saw. Make shallow cuts on all four sides. It helps to tape each cut after it is made, before starting the next cut. Wide masking tape or duct tape will work.
- When the box is cut apart, add square strips of wood along the inside of the cut edges. The strips along the hinge line should be flush with the edge. The strips along the sides and front should be recessed approximately 1/8 inch into the top. The corresponding strips on the bottom half of the box should protrude above the sides and front approximately 1/8 inch, to help key the lid to the lower section of the box.
- Cut short strips of square stock to reinforce the corners and glue them in place. It's also a good idea to add two or three vertical pieces along the front and back. For extra strength, drive small flathead wood screws in from the outside, to fasten the plywood to the square strips.
- Use a full-length piano hinge along the back. A piano hinge is easier to install than a series of separate hinges, and it spreads the load along the entire box. Add local reinforcement on the inside where the handle and latches will be attached.
- Paint the box with white enamel or clear lacquer before installing the hardware. White will help reflect sunlight better, but the clear finish is easier to apply and won't show dirt. Add the handle and latches. I also installed stamped-brass reinforcements on the corners, in an effort to protect them. You should be able to find most of the supplies you need at a good hardware store.
- If desired, put your name and AMA number on the outside. As with any luggage, include a name-and-address tag. Another tag on the inside could prevent your box from being lost if the outer tag is torn off.
- For a more-durable box, reinforce the corners with fiberglass tape. You could also cover the entire box with heavy glass cloth and epoxy resin.
- A third approach is to use a lighter material for the box, such as rigid foam or balsa, then reinforce it inside and out with fiberglass cloth, or even aramid cloth.
FITTING OUT
Now that you have a box—purchased or homemade—fit it with partitions, hooks, and straps, to help hold everything in place.
- Partitions separate heavier items, such as fuselages, from lighter, more-easily damaged parts, such as wings and tails. The partitions will also help give the box greater strength and rigidity.
- You can use leftover pieces of plywood or door skin for the partitions, although a lighter choice is 1/4-inch Fome-Cor® sheet. This material is available at most art supply or craft stores, and it's easy to cut with a sharp knife. Make sure any partition is glued securely in place.
There are two approaches to packing:
- Use clips, hooks, straps, screws, or rubber bands to hold heavier parts in place. This method takes up less room but requires more effort in fitting out the box and is less flexible—changes in model design may require a box redo.
- Use foam rubber or blister-packing material to cushion and contain the parts. The foam method is quick, easy, and flexible, though not as elegant as custom clipped layouts.
Test your box before heading off to an important contest. Pack the box with your models, close it up, and shake it gently. Open it and take a look. Make any needed adjustments to the packing, then shake it harder. Work your way up to shaking it as hard as you dare; some airline-baggage handlers will give it a much harder test.
REELING IN THE TURNS, PART TWO
My mention in the August column of Paul Crowley's rubber winder made from a spinning reel prompted a note and several photos from former World Champion Bob White. Here's what Bob wrote:
"I saw Paul Crowley's spinning-reel winder last summer. Here is my version. The reel was bought new at K-Mart®; gear ratio is 4.9 to 1. It is an excellent winder and very smooth. You can wind up to 14 strands of line rich rubber. You can feel the rubber better with any winder that I have ever used."
Bob added a U-shaped aluminum strap handle and a 21-inch-long extension shaft. The long shaft allows him to wind by using a blast tube in the model, then to slip the tube out of the model and over the extension after the motor is wound. This saves several steps compared to using a separate winder hook to remove the blast tube.
(A blast tube is made of aluminum or heavy plastic and is slightly smaller than the inside diameter of the motor tube or fuselage. The blast tube's job is to absorb the shock when a rubber motor breaks. It protects the fuselage from damage and makes removing broken motors much easier.)
Bob's mention of being able to feel the rubber motor during winding is an important point. Torque meters and turn counters are valuable aids, but only experience and a good winding feel lets you know when the motor is wound as tightly as you dare to wind it. Even then, motors break—especially when you are trying to get the utmost from the motor. That's the reason for blast tubes.
FREE FLIGHT FORUM 2000
Each year, the British Model Flying Association (BMFA) conducts a Free Flight seminar, then publishes the papers. This year's Free Flight Forum 2000 includes a wide range of articles, from the theoretical to the practical.
Topics include:
- "A Practical Approach to Propeller Design at Model Scale" by John Gibbons
- "The Use of Boost-Glider Rocket Structures in Free Flight" by Nigel Bathe
- "Two-Stroke Engine Design and Development for Free Flight" by Gordon Cornell
- "Free Flight Scale Trimming and Trouble Shooting" by Andrew Hewitt
- "Design Implications of the New F1D Rules" by Bob Bailey
- "Trimming F1Cs" by John Cuthbert — a must-read for anyone who flies contest-power models of any class; John's discussion of model setup and safe trimming of these high-performance models is worth the purchase price of the Forum
- "Structures for Open Rubber" by Phil Ball — includes construction ideas for lighter and stronger models using carbon fiber and Kevlar™, plus a sketch of a simple fixture for making diamond-section fuselages using carbon-rod longerons, wing-construction ideas, and a simple way to mold propellers using Kevlar™ cloth, carbon tow, and a foam core
Order your copy of Free Flight Forum 2000 from Martin Dilly, 20 Links Rd., West Wickham, Kent BR4 0QW, UK, or E-mail [email protected]. Martin's fax number is (44)-(0)181-777-5533.
The 86-page book is 11.00 pounds Sterling, which is approximately $16 in US funds, postage included. Checks should be payable to BMFA F/F Team Support Fund, in pounds Sterling only and drawn on a bank with a branch in the UK. You can also order by credit card.
Transcribed from original scans by AI. Minor OCR errors may remain.
