FREE FLIGHT: DURATION
Louis Joyner, 4257 Old Leeds Road, Birmingham AL 35213
Two-piece wing variations
Last month we discussed some of the basics of building two-piece wings. This time we'll look at some of the variations.
Straight wing wires are a lot simpler to make and install than bent ones, but what if you don't want a wing with flat center panels? If the wing is thick enough, you can angle the tubes slightly to give some dihedral in the mains. Usually the tubes are located tight against the top of the lower spar at the wing center, and against the bottom of the upper spar a few inches out.
Building the main spar subassembly
The easiest way to do this is to make the main spar as a separate, full-depth subassembly, with hardwood or carbon-fiber top and bottom spars and a balsa filler in between.
- Make both main spars and trim to length.
- Bevel the ends for the desired dihedral.
- Pin the spars down to a flat surface with the fronts of the spars down and the centers about 1/4 inch apart. The outer ends should be up at the desired dihedral.
- Cut a single aluminum tube to length. It should be about 1/8 inch longer than the total length of the wing wire, minus the width of the pylon. Position this over the spar and mark its location.
- Carefully cut away the balsa web until you can fit the wing tube in place. It should be flush with the back of the spar and level with the building board. Epoxy in place.
- After that dries, saw through the exposed section of aluminum tube and remove the finished spars.
This is the simplest method I have found to build in the aluminum wing tubes, even for a flat center-section model. It consistently results in an accurate two-piece wing.
Bent wing wires
If there is not enough depth in the wing to use a straight wing wire, the biggest problem is installing bent wires.
- For shallow bends, use a short section of brass tubing on the center section of the wing wire (the part that goes through the pylon). Bend the wire up at both ends just past the brass tubing. Use a piece of brass tubing in the pylon with the same inside diameter as the outside diameter of the tubing on the wing wire. This gives just enough clearance to insert the wing wire into the pylon.
- For deeper bends (for example, V-dihedral models), consider the method Jim Wilson used on his Simple Toy Nordic gliders: glue the bent wing wires firmly into the fuselage, then slice off the top inch or so of the fuselage (the part with the wing wires). Reattach this piece with two nylon bolts. This allows the wing wires to be removed for storage and provides some "give" in a crash. (Plans for the Simple Toy are still available from Model Aviation.)
Three-piece wings and removable tips
A different approach is to make a three-piece wing with a flat or slightly dihedraled center section and removable tips. Lothar Doring and Reiner Hofsass used this method on their Espada solid-wing Wakefields in the 1980s.
- The one-piece center panel is rubber-banded on the pylon in the usual manner.
- Each tip is removable, held in place with a small-diameter wire at the high point and a clip at the trailing edge.
A variation used by several Dutch glider fliers breaks the wing a few inches inboard of the dihedral break. The one-piece center section is bolted to the top of the fuselage. Total weight on a three-piece system probably comes out a little less than a two-piece wing, since the outboard wing wires can be considerably smaller. It can also result in a very compact model box.
Securing the wing halves
You need some way to hold the two wing halves together—slipping off the wing wires in flight could be disastrous. Common methods:
- Use a small rubber band (#8 will do) running from hooks on each wing half. Use a single band near the main wing wire or two bands—one at the leading edge and one at the trailing edge.
- Use nylon screws and a tab mounted on the top of the pylon that engage blind mounting nuts in the wing trailing edge. Position the tab either above the wing, with blind mounting nuts in the wing, or below the wing and run screws up through the wing into threaded holes in the tab. You'll also need a rubber band at the leading edge. This system allows easy adjustment of wing differential warps by adding shims between the tab and the wing.
Other two-piece wings will require some beefing-up to withstand the concentrated loads at the ends of the wing wire.
Center ribs and composite construction
- In traditional stick-and-tissue construction, center ribs usually are made with the first three or four ribs out of plywood instead of balsa, with holes accurately drilled for the aluminum tubes. I also like a faced root rib—a plywood rib cut full airfoil size, with notches for the spars, leading edge and trailing edge.
- For composite construction, the tube for the wing wire between the top and bottom spar needs wrapping with Kevlar thread to hold it together. A wide balsa root rib capped with carbon maintains the airfoil shape.
FAI Model Supply
For about as long as I can remember, FAI Supply has been the source for rubber and other related hardware. The owner, Ed Dolby, has worked long and hard to give us rubber that returns higher and higher energy.
Thirty years ago, 2,000 foot-pounds per pound was considered good stuff. Now we are seeing double that specific energy. It would be safe to say that Ed's Tan II rubber has done more to improve the performance of today's Wakefields than any other single thing. (Perhaps it has helped too much—rumors abound of rules changes to reduce the allowable rubber weight from 40 grams to 30.)
Along the way Ed has come up with other workshop staples, such as the Zona Saw. The FAI Supply catalog has also been a source of kits and parts you can't find in the average hobby shop.
After almost 30 years in the business, Ed decided it was time to retire. The new owner is a longtime friend of Ed's: John Clapp. John and his wife Sally will be operating FAI Supply from Sayre, Pennsylvania. In addition to keeping us supplied with better and better rubber, John plans to expand the catalog offerings.
For a copy of the new catalog, send $2 and a stamped, self-addressed envelope to: FAI Model Supply, Box 366, Sayre PA 18840-0366 Tel./fax: (717) 882-9873
Thin highly cambered wing construction (E. Jedelsky method)
This construction was developed more than 30 years ago by E. Jedelsky.
- The front third of the wing is carved, hand-launched-glider style, from 1/8" sheet; the rest of the wing is 1/32" sheet, curved slightly over 1/16" ribs. (The wing is not covered.)
- This results in a very thin, highly cambered wing that can withstand a lot of abuse.
The fuselage is a rolled balsa tube with Tyvek from a FedEx envelope spiral-wrapped on the outside. Although the extra weight of the all-balsa construction might keep this from being a competitive P-30, it would be a good beginner's model.
Easy Wakefield wiring (commercial wing)
After building a half-dozen carbon-fiber wings for Wakefields, I decided to try the easy (some might say lazy) way: I wrote a check to Starline International. A few weeks later I received a finished wing, ready to cover—no vacuum bagging, no carbon dust all over the workshop, no work.
The wing, built by a Ukrainian husband and wife, is at least as good as I can do—maybe better. It features a D-box formed from a single thickness of woven carbon cloth, with carbon-fiber spars and a carbon trailing edge.
- The 1 mm balsa ribs are spaced 10 mm apart in the D-box and 30 mm apart at the tips. The ribs are capped with carbon.
- The spar is wrapped with aramid thread all the way out to the tip.
- The root rib is 1 mm carbon. Epoxy resin was used for assembly.
The finished (uncovered) weight is just under 42 grams. Covered with Starline's Polysalyn, the all-up weight should be about 52–54 g. Total span for the two-piece wing is about 1.6 meters (63 inches), with a projected area of 16.18 sq dm.
I can't quite place the airfoil, but it is a bit thinner and slightly more cambered than the typical Ukrainian/Russian Wake. Thickness at the root is 5.6 mm; chord is 113.5 mm. At the break the numbers are 5.15 mm and 100 mm; at the tip it's 3.5 mm and 78.5 mm. Glide should be excellent.
Price: $160 plus shipping, from Starline International, 6146 E. Cactus Wren Rd., Scottsdale AZ 85253; Tel: (602) 948-5798. You might want to call Sal Fruciano first to double-check availability.
Transcribed from original scans by AI. Minor OCR errors may remain.
