Dihedral Options

Free Flight Duration

By Louis Joyner | [email protected]

As seen in the February 2024 issue of Model Aviation.

DO YOU NOTICE anything unusual about Sarah Dalecki’s P-30 in the photograph on the next page? Here is a hint: It does not have one feature that nearly every Free Flight (FF) model has. FF aircraft typically have wings with dihedral to provide roll stability. For example, if a model starts to roll to the right, the lift will increase on the right wing and decrease on the left. Without dihedral, the model will spin into the ground.

Sarah Dalecki launches her P-30 Rubber model on a test flight. Tip plates provide roll stability.

The model in the photograph, a Three-Nite P-30, has a flat wing with no dihedral. Designed by Mike Jester and kitted by Volaré Products, it offers a good introduction to rubber-powered model competition.

Eliminating dihedral in the wing simplifies construction, while the larger, rudder-like tip plates provide roll stability, much like dihedral would. The flat wing also makes it easier to attach it to the fuselage. Flat wings with tip plates are frequently used for Indoor Science Olympiad events. J&H Aerospace offers a variety of entry-level, rubber-powered models with flat wings and tip plates. Tip plates are also used by full-scale aircraft, such as the Boeing 737 Max, not for ease of construction but to reduce aerodynamic vortex drag.

Wing dihedral can take many forms. (Bottom to top): The left half of a six-panel wing, the left half of a fourpanel wing, a V-dihedral wing, and a molded foam wing with elliptical dihedral.

Eliminating dihedral in the wing simplifies construction, while the larger, rudder-like tip plates provide roll stability, much like dihedral would. The flat wing also makes it easier to attach it to the fuselage. Flat wings with tip plates are frequently used for Indoor Science Olympiad events. J&H Aerospace offers a variety of entry-level, rubber-powered models with flat wings and tip plates. Tip plates are also used by full-scale aircraft, such as the Boeing 737 Max, not for ease of construction but to reduce aerodynamic vortex drag.

Dihedral dates back to the dawn of aviation. On August 18, 1871, Alphonse Pénaud launched his rubber-powered Planophore in the Jardin des Tuileries in Paris. The 11-second flight was the first flight of an inherently stable airplane. (Note that that this is an airplane—not a model airplane.) The principle of dihedral had been developed a few years earlier by British scientist Sir George Cayley. (Birds have used dihedral for millions of years.)

For FF models, there are many options for wing dihedral. Each has it’s own advantages and disadvantages.

Robert Sifleet’s F1Q electric model features a high-aspect-ratio six-panel, two-piece wing. Note the curved wingtips.

V-dihedral wings require only a center joint, but mounting them on a square fuselage requires rails on the top of the fuselage to accommodate the V. A round fuselage might require a pylon. Another workaround is to use a flat center panel with a width equal to that of the fuselage, with the wing attached on each side of the center panel.

Polyhedral wings have four wing panels. Typically, the two inboard panels are longer than the tip panels. One example is Gerald Ritz’s 1959 world champion Nordic glider that featured 36-inch inboard panels with two inches of dihedral and 7-inch tips with 4-3/4-inch dihedral. The short and steeply upturned tips function much like the vertical tip plates on the Three-Nite P-30.

Another wing dihedral option includes tip dihedral: a flat center panel with upturned tips. The center panel can be in one long piece or in two sections that are connected at the fuselage. Making the wing in two halves allows for easier transport and storage. The wing halves can be connected with a wire pin, and then strapped onto the fuselage or plugged into a pylon. Two-piece wings also offer another advantage—the incidence of each wing half can be adjusted separately to optimize glide turn.

The two-piece wing on Paul Crowley’s F1B Wakefield of his own design uses flat center panels with long, tapered tip panels.

A two-piece wing also allows for the use of a wing wiggler to control the model’s climb. For example, I use a wing wiggler on all of my F1G Coupes. At launch, the left wing is set at several degrees negative relative to the fixed right wing half. This allows for a straight climb pattern during the first four or five seconds of the motor run. A clockwork timer then moves the left wing back to the glide position for the rest of the flight. This is the only auto surface used.

In recent years, the aspect ratio of FF models has dramatically increased. New construction methods using carbon fiber molded over foam have allowed more accurate airfoils and stronger and longer wings.

A typical molded, carbon-fiber wing has six panels. For example, the Serge Vorvihost F1Q electric has a total span of 2,400mm (almost 8 feet). The inboard panels are 610mm (approximately 24 inches), the middle panels are 380mm (approximately 15 inches), and the tip panels measure 210mm (slightly more than 8 inches). The goal is to approximate elliptical dihedral with its smooth, upward curves from tip to tip.

In the 1950s, a few brave souls built elliptical dihedral Wakefields and Hand-Launch Gliders (HLGs). This involved bending balsa on curved jigs and was not for the faint of heart. Some examples can be found in Frank Zaic’s Model Aeronautics Year Books from that period.

While researching, I came across another type of dihedral: an asymmetric dihedral, circa 1960. It was developed by my older brother, Bud, for HLGs, to have one half of the wing as a single panel and the other as two panels. In other words, a V-dihedral on one side and polyhedral on the other. The idea was to glide with the polyhedral on the inside of the turn. The stabilizer featured a shallow, inverted V-dihedral. The stabilizer was set up with the right tip higher than the left tip.

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