RC-assist Airfoiler replica

Model Airplane News, Jan 2001 by deBolt, Hal

The first Airfoiler was created in 1940, and the updated design presented here is legal for Society of Antique Modelers (SAM) competition. The second one was born in wartime. It was quite different in design and was kitted by Dmeco in 1947. In the prewar years, I was deeply into free flight. I had outgrown my '37-38 Blitzkrieg when Carl Goldberg impressed me with his Valkyrie. I had lost several Blitzs for lack of a proper dethermalizer. At the time, spoilers were the only known lift reducers. So with Carl's influence and a need for a new design, I designed the Thunderbolt. The spoilers did the trick; the T-Bolts kept on ticking. Winning contests without losing models gave me more time to look for things to improve.

Believing that a wider wing chord would perform better, I used a 5:1 aspect ratio with the T-Bolts. I did, however, have a desire to compare a higher ratio wing with the one I was using. Obviously, investigations do not require an exotic model; a simple box-style is sufficient. Bellanca's lifting-body ideas were also impressive. Regarding Bellanca: if the box had an airfoil shape, it could be added to the mix while adding some cosmetic appeal to my model.

Foresters were said to be fine engines then, and I wanted to try them. They came as a .29 and .305, so with a simple engine exchange, a single model could fly in two competition classes. So the Foresters dictated my model's size. Right off the board, the new model proved to be a very kind flyer-extremely easy to use and surprisingly competitive. However, the War terminated my freeflight activity, and I was unable to determine which of the new designs was superior.

Sometime in 1943, on a weekend home from the Navy, I learned that a local contest had been scheduled. I hadn't competed since my induction, so I had to fly my Toiler in this one. The model's performance at the meet was like something I'd never seen before! The weather was free-flight perfect, and the first two flights ended (dethermalized) on the field with excellent time. For the next flight, I locked the spoilers into place, and the Toiler sat sky-high, right over the field; it didn't want to come down. Eventually, it lost lift and landed less than 1/4 mile away. The flight time was hard to believe; one hour and five minutes! Fantastic? I was in free-flight utopia!

Recently, Fred Mulholland and Tom McCoy enticed me to seek SAM approval of my three designs: the Blitzkrieg, Thunderbolt and Airfoiler. All three were approved. As good friends will do, Fred and Tom agreed to produce the needed replicas of my models, so I give considerable credit to them for making this article possible. Fred built a Toiler replica and reported fine contest performance. Tom also built one that he now flies regularly.

CONSTRUCTION

The original Airfoiler was pure free-flight. Today, we have "RC-- assist," for which the needed control surfaces are shown. If you like vintage models, the Airfoiler structure is very common to the era. To build the free-flight version, simply omit the control surfaces.

The tail is the easiest place to start. The stabilizer and fin have curved profiles, so begin by producing the indicated outlines. These surfaces use "quick and dirty" cap-- strip-style ribs bent around a spar. The secret with these is first to soak them in water and to form the curves with your fingers before installation.

WING

Start by cutting out the ribs as shown on the plan. Note that the wing has rather robust leading and trailing edges. These are needed for strength and to prevent the wing from warping when the silk covering is shrunk tightly. All balsa is medium weight except for the spar, which is 8 to 10 pounds per cubic foot, straight grained. Today's obsession with excessive power might dictate 10- to 12-pound balsa or an equivalent. Tom and Fred capped the spars of their replicas with carbon fiber.

The spoilers are hinged at their front edges and are opened by a no. 16 rubber band to a maximum of V4 inch above the wing surface. I use an Austin timer with a suitable linkage to activate the spoilers after a desired time.

FUSELAGE

The basic structure uses balsa stick construction and is very easy. This is covered with lightweight 1/16-inch sheeting. Build the sides together (one on top of the other) and then sand their edges so they are identical. Place them vertical on the assembly board using a centerline as a guide while you join them with balsa crosspieces, as indicated. The wing pylon is built separately and then attached to the fuselage floor. The pylon post and ribs are then installed, followed by the sheet covering.

The construction of the pylon wing saddle is a neat trick. First, protect the bottom center of the wing with clear food wrap. The two halves of the wing-- mounting platform are cut oversize and placed between the wing and the pylon. After the wing has been properly aligned with the fuselage, the platform is glued into place and then trimmed to shape after the wing has been removed (see illustration). The advantage of this method is that the wing sits in a saddle that is an exact copy of the wing's shape; thus, the wing has little tendency to shift.