A 25-foot gentle giant

Model Airplane News, Jan 2000 by Krapp, Tom

Almost 20 years ago, I began flying radio control model aircraft. My first plane was a Carl Goldberg Eaglet 50, and I've had many other powered aircraft. But as much as I enjoy designing, building and flying these models, I've always had a soft spot for gliders. So in 1981, 1 purchased a Carl Goldberg Gentle Lady. Ever since then, I've flown it off hills, power pods, high starts and Lake Michigan's sand dunes, as well as by winch and piggyback off my Eliminator 40 and Big Eliminator planes.

As the years went by, I had an increasing urge to design and build a 25-foot glider, but every time I looked at the cost of building this monster, I put the project on hold. There is an inexpensive and easy way to do it, though: just use 1/2-inch foam for the wing skin.

I originally thought of putting brown paper over the wing, but I later found foam with brown paper and silver foil already applied to use. To complete the 2S-foot-span wing, I needed eight sheets, so I bought nine-just in case-because they only cost $6.50 apiece. I also picked up a plain sheet of 3/4-inch foam for the ribs, supported by Russian birch ply along with 1/2 x 3/8-inch maple for the spars. I then grabbed furnace tape at Wal-Mart and spray adhesive from a lumber company. Using these materials, I put together a 25-foot wing for about $80.

The fuselage is 1/8-inch Russian birch ply and lite-ply, and the stabilizers are 5/8-inch balsa and maple. I knew that I would need to be able to transport this monster, so I designed a fourpiece wing and a two-piece fuselage with removable stabilizers. Four brass hinges with bolts going into 6-32 T-nuts and locknuts soldered to the backs hold the fuselage together. I also used a 6-32 threaded rod that I glued into the vertical stabilizer and passed through the horizontal stabilizer and fuselage into nuts on the bottom. I also included boost tabs on the rudder and elevator.

One of the most interesting phases of the glider's development was the stress test for the wing. For my test, I clamped one of the inside wing panels to my workbench using a thick board and an 80-pound bag of cement for counterbalance. Then I loaded up the wing with 50 pounds of plywood. It bent 1/4 inch and tilted my workbench four inches-success!

Six weeks after starting this project, I was ready for the first flight. I loaded up the truck and headed to the airport. It was a cold, cloudy day with low ceilings and 20mph winds gusting to 25mph. My dad, my friends and I put the glider together but had some trouble putting enough air pressure into the Du-Bro 6-inch tire that held up the 54-pound glider. A friend got a big tire nipple and put it on the end of my pump then used an air bottle to fill the tire. We put the glider at the end of the takeoff spot and started up the Quadra 50. A friend held the wingtip as I advanced the throttle. Fifty feet down the runway, the glider leapt into the air flapping its massive wings like a bird. The air was very bumpy, and it looked as though the dihedral braces were flexing a little, but after getting about two or three hundred feet up, the air smoothed out, and the glider flew great with no trim adjustments. I came down for a flyby and again the wings flapped, so I went back up. When I saw a cloud go under the glider, it reminded me that this was not your standard two-meter glider, and I knew I had to be more mindful of the altitude. I came down after 15 minutes. We saw the huge shadow of the 66.5-square-foot wing on the ground, and it came in for a perfect landing.

I am in the process of putting carbon fiber on the dihedral braces and a bigger servo on the elevator, but besides these minor modifications, I don't need to do anything to make this monster fly like a 747-size Carl Goldberg Gentle Lady.