What to Build?

Free Flight Duration

By Louis Joyner | [email protected]\

As seen in the October 2023 issue of Model Aviation.

THE NEW Vintage Coupe d’Hiver event is for small, rubber-powered models designed before 1970. Unlike the F1G Coupe d’Hiver event, vintage Coupes will be low-tech models—no auto surfaces, no delayed or instant propeller release, and no carbon-fiber wings. In other words, it is a back-to-basics event. The models are less expensive and, for the most part, easy to build.

The My Coupe (left) was quicker to build than the Hat Band. Both designs were NFFS Model of the Year selections.

The Coupe event was developed in France in the 1940s as a small-field contest, often flown in the winter. Coupe d’Hiver, the official name, means Winter Cup.

The rules were simple and still are, with a maximum rubber motor weight of 10 grams and a minimum airframe weight of 70 grams. Back then, rise-off-ground (ROG) was required, as well as a minimum fuselage cross section. Throughout the years, the rules have changed. By the 1960s, both the cross-section rule and the ROG requirement had been eliminated.

There are plenty of Coupes that were designed before 1970. Not surprisingly, most are French. There are also a few American, British, Italian, and Czechoslovakian designs. Free Flight Quarterly’s two-volume Coupe d’Hiver Survey is an excellent source of information. The 1964-65 Model Aeronautic Year Book by Frank Zaic includes an introduction to the event, as well as a number of Coupe three-views from France and the US.

Before I started looking for a design to build for the new Vintage class, I made a list of all of the features I wanted in the model. The most important was a two-blade propeller. (The Vintage rules require using the type and diameter of the original design.)

Next was the contest record of the original design. I discovered two designs that fit my criteria. Both had been chosen as National Free Flight Society (NFFS) models of the year. Bill Vanderbeek’s My Coupe first won Senior Coupe at the 1967, 1968, and 1971 Nats. At the 1969 Nats, it won the Dick Black trophy for all age groups. It is a simple and quick-to-build design.

John O’Donnell’s Hat Band was a 1970 Model of the Year. Unfortunately, there were no drawings, but there were three photos of the model and a detailed description in the text. The wing had a 4.25-inch wing chord and a 34-inch wingspan. The wing airfoil was from Mike Borrows’ A/2 glider. I found three-views of the glider in the 1964-65 Model Aeronautic Year Book and was able to scan and enlarge the airfoil.

Knowing the wing chord, I was able to determine most of the other dimensions. As far as I know, no drawings of the Hat Band are available. Both the wing and stabilizer use the Union Jack construction method. This is a mix of straight and angled ribs, which results in a stiffer wing. Surprisingly, the wing was only a couple of grams heavier than the My Coupe wing.

The Hat Band’s fatter fuselage required a wider propeller hanger to allow the blades to fold flush against the fuselage sides. The original propeller hanger is shown for comparison.

Both models use a laminated balsa and plywood nose block with a large center hole to hold the Ukrainian F1G front end. The F1G front end allows the motors to be wound outside of the model.

The front fuselage construction for both models is a balsa box. They use 3/32-inch square longerons running the full length of the fuselages. The diagonal bracing on the My Coupe proved stiffer than the bracing on the Hat Band boom, but the Union Jack wing construction on the Hat Band was stiffer than the straight ribs on the My Coupe.

The fuselage construction for both models was similar. The front section that contains the rubber motor is a square box made from 3/32-inch balsa (use the lightest wood you can find!). The corners of the box are 3/32-inch square balsa (use the hardest you can find). These longerons extend all the way to the rear. Balsa spacers tie the four longerons together. The Hat Band used vertical and horizontal spacers. The My Coupe used diagonal spacers. After covering and doping the booms, both models were quite stiff.

Both models use Ukrainian F1G front ends. These are designed to fit rather small carbon-fiber motor tubes. I made traditional laminated balsa and plywood nose blocks, and then drilled a large hole in the center to receive the front ends. The propellers are homemade laminated balsa covered with light fiberglass cloth and coated with epoxy resin. These are the same blades I use on my F1Gs. The tips were trimmed to the same diameter as the original model.

The only problem that I encountered was the propeller fold for the Hat Band. The fuselage is considerably fatter than the My Coupe fuselage. The solution was to remove the bent-wire propeller hanger and bend a wider one out of 1mm wire.

After covering, the airframe weights were 74.5 grams for My Coupe and a rather porky 89 grams for the Hat Band. Most of this excess was from the 3/32-inch balsa that was used for the front fuselage section. (Rules state that you must use the original material thickness or thicker.) Try to find the lightest 3/32-inch balsa that you can.

To keep the weight down, I use a fuse timer in each model. My F1Gs use two-function mechanical timers that weigh approximately 6 grams to trigger the wing wiggler and dethermalizer (DT). Using a fuse DT saves roughly 5 grams. I mounted an aluminum snuffer tube sideways in the pylon of each model at the center of gravity. An 8-pound test monofilament line runs through several plastic guides and through a bent aluminum tube up to the stabilizer. At the front end, the line has a small loop for the DT rubber band.

After the two models were finished, I started looking for a third Vintage Coupe to build. The previously mentioned 1964-65 Model Aeronautic Year Book article included a small three-view of Charles Sotich’s Dwarf Dip Mk II Coupe.

The construction looked simple, but it used a one-blade propeller. Some searching on the internet uncovered an Mk III version with a two-blade propeller and a better wing construction than the Mk II version. Fullsize plans of the Dwarf Dip are available from the AMA Plans Service. The original three-views were published in the 1969 American Aircraft Modeler Annual.