Radio Control: Giant Scale
Bob Beckman
Plan reviews
#### JB Special Convertaplane It's plan review time. This month I'm looking at a couple of plans by Jerry Behrens. The first is an interesting (although non-scale) design called the JB Special Convertaplane. This is a Quadra-powered aircraft that can be built and flown as a monoplane or a biplane, or both. (No, Mortimer — not at the same time.) The biplane version is very reminiscent of the Aeromaster, and in the flying instructions Jerry says that it flies much like one. The monoplane version does away with the top wing and the cabane struts and substitutes a larger surface for the lower wing. You can, of course, set it up permanently in either configuration. The overall length is 69.5 in., the monoplane span is 84 in., biplane span 78 in. (upper) and 72 in. (lower), and the weight is approximately 18 lb.
The plans are on two sheets, each approximately 3 by 7 ft. The drawings are clear and uncluttered. There is a very good exploded view of the fuselage, but only half of the wing(s) are shown. It turns out you don't really need a full wing drawing, because you don't build the wings by pinning them over the plans. You do have to remember to make right and left panels!
Construction is simple, but rugged. Spruce, plywood, and pine are the main ingredients, with some balsa. The wings employ a spruce-and-plywood box spar. This makes a very strong structure for its weight, but it's a tedious job cutting the spar holes in the ribs. Most of the ribs are balsa, with plywood at the strut locations. (The balsa ribs could be replaced with foam-core board to cut the cost a bit. The same applies to the fuselage turtledeck formers.)
As with most plans, the control installation is left pretty much up to the builder — i.e., selection and installation of hinges, horns, pushrods or cables, etc. The plans do indicate that receiver, servos and batteries are to be mounted near the tail. I don't know if this is for balance, or to keep the pushrods short, or both.
I was interested in Jerry's interplane strut attachment method. He uses Du-Bro links — the standard size, not the newer larger ones. The plastic socket ends are drilled and tapped to take a 4-40 stud, which in turn is anchored in the wing. The balls used are the type made to take a 4-40 screw, and they are attached to the side of the strut. Now the struts simply snap into the sockets in the wings, and the strut length can be adjusted to a small extent by running the sockets in and out on the screws. I like the idea of using the 4-40's rather than 2-56 hardware, but I wonder about that drilled-out plastic socket. They are apparently working for Jerry, and actual use is what counts in anything like this.
The plans and instructions that come with them are pretty good, but there are a couple of areas that I think could be clearer. The two different CG locations, one for the monoplane and one for the biplane, are marked on the plans, but I don't remember seeing anything about how to manage the change if you are shifting from one configuration to the other at the field. Another feature dictated by the convertible nature of the design is an incidence shim to be mounted on the upper center section of the biplane's lower wing. On the plans, this shim is shown on a drawing of the wing rib at the aileron, which had me confused for a bit.
I haven't actually seen this model fly, but it certainly looks capable enough. It would be a good design for an experienced modeler who wants to move into Giant Scale. The construction techniques will feel quite familiar, even though there is more spruce than balsa used.
#### Behrens TravelAire 2000 The Behrens TravelAire 2000 is, to me, a prime example of what Giant Scale is all about. This is one of the classics from the Twenties, and modeled in this size it can be uncannily realistic in appearance and performance.
The model's design and construction is very similar to the JB Special, but it is a bit larger. Span is 105 in., length 73 in., and projected weight 23 lb. It should fly well on a Quadra, but this is getting toward the upper limit, weight-wise. One of the newer, slightly larger engines might be a good bet to ensure top performance in the air.
The plans are on two sheets, each approximately 3 by 7 ft. Just about everything said about the JB Special applies here. Again, an experienced modeler will find no surprises, once he trades in most of his balsa for spruce. I would consider either one of these designs a good entry point into Giant Scale.
Plans are available from:
- Behrens Plan Service, 31-27 Healy Ave., Far Rockaway, NY 11691.
- JB Special Mk III: $21.95
- TravelAire 2000: $22.95
- Add $2.00 for postage and handling.
Smoke makers
I have several times mentioned Don Harris and his smoker/mufflers. These are the ones that have an inner chamber into which the diesel smoke fuel is pumped. Since the inner chamber reaches red-hot temperatures, the smoke fuel is well vaporized before it mixes with the exhaust. As a result, almost all of it produces smoke, instead of just being blown away. He now has units available for several different engines, and every one that I've seen has been very effective at producing smoke.
Don apparently was not satisfied, however. He recently sent me the Quadra muffler shown in the photo. At first glance I thought it was just like the one I already had, but then I noticed the coil of tubing in the center. On the old one, there was a piece of tubing of about 3/8 in. diameter that served as the vaporizing chamber. On this new one, the coil of 1/8-in. tubing does the same job — but even better. The smoke fuel is fed into the coil at the center, where it starts to vaporize. A row of slits in the tubing allows some of the vapor to escape into the main muffler chamber as the rest of the fuel, vaporizing as it goes, is forced toward the ends of the coil. The coil provides a more efficient transfer of heat from the exhaust to the smoke fuel. The result is that more of the smoke fuel is vaporized before mixing with the exhaust, so you get even more smoke than before. And I thought the original setup did a great job!
Don also sent along one of his new pumps, which comes with a miniature switch. His system works best with a pump supplying the needed volume of smoke fuel to the muffler. The pump runs off two pen cells and can be mounted almost anywhere inside the plane. Its few ounces won't be noticed by our aircraft. The miniature switch can be easily mounted to a small servo for controlling the smoke.
Here's everything you need to get smoke from a Quadra:
- Harris muffler (with coil-style vaporizer) and electric pump — Don Harris, 23668 Shadow Dr., Auburn, CA 95603.
- 16-oz. tank — US Quadra, 1032 E. Manitowoc Ave., Oak Creek, WI 53154.
- Fuel line ("Aqua Blue" gasoline and diesel fuel line) — AeroTrend Products, 44 West Prospect St., New Haven, CT 06515.
B-I-G B-29
Last year, Bob Campbell of RC Kits showed up at Toledo with a twin-Quadra-powered Grumman Tigercat. Later in the year, he demonstrated that it was not just for show. At several events, including the IMAA Fun Fly Festival in Louisville, he proved to everyone that it flew, and flew very, very well.
This year for Toledo he plans to have on display his 16.5-ft. span B-29. This is getting to be too much for me even to contemplate, but I admire Bob's imagination and perseverance. Powered by four 2.4 Kioritz engines, the projected weight is 125–150 lb. Retracts are custom made by Aeromarine. The wings and stab are foam, and the fuselage built-up. The entire aircraft is sheeted with 3/32 balsa and then 1/64 ply. I don't know how he plans to transport it; the wings break down, but that fuselage is 11 ft. long!
Fly-ins scheduled
- Radio Control Club of Connecticut Giant Scale Fly-in
- Date: Sunday, June 6
- Site: Sikorsky Memorial Airport, Stratford, CT
- More info: Ray Hinds, 140 Edna Ave., Bridgeport, CT 06610; phone (203) 334-7207.
- Second Annual 1/4-Scale/Giant Size Fly-in (Winnebago RC Fliers)
- Date: August 29
- More info: Hugh Ziebell, 338 West 20th Ave., Oshkosh, WI 54901; phone (414) 235-2316.
There is also a list of IMAA-sanctioned fly-ins scheduled throughout the year. It's a bare-bones list, just for quick reference. For more details, check the Spring '82 issue of the IMAA High Flight, or write to Don Godfrey, 254 Washington St., Binghamton, NY 13901.
Bob Beckman 8248 Holly Grove Ct., Manassas, VA 22110.
Transcribed from original scans by AI. Minor OCR errors may remain.
