Keeping Track of Your FF Model

Free Flight Duration

BY DEFINITION, Free Flight (FF) models fly without any direct control from someone on the ground. The flight pattern is preprogrammed into the model by design and adjustments to the flying surfaces.

Wind and thermals can affect the flight. Launching the model into a thermal usually ensures a maximum flight time, but if the wind speed is up, the model can be off of the field in a matter of minutes. Throughout the years, the maximum flight time for a contest flight has been reduced a number of times to help keep the model on the field. A variety of methods have been developed to terminate the flight when it reaches the maximum time and to bring the model safely to the ground.

The pop-up stabilizer dethermalizer (DT) has been the most popular method for more than 70 years, but small and lightweight models, such as P-30s, F1Gs, Coupe d’Hivers, and Hand-Launch Gliders, need a more effective DT system. Pop-up wings, folding wings, and pop-off wings attached to the fuselage with a line all work.

Several methods are used to activate the DT. A slow-burning fuse is lightweight and easy to install, but accuracy can vary. Clockwork timers provide more accuracy, but with a weight penalty. Viscous timers are lighter, and with practice, they can be surprisingly accurate.

Electronic timers provide maximum accuracy and are often lighter than mechanical timers. Similar to mechanical timers, electronic timers can provide other functions in addition to DT. For example, the timers used for F1B Wakefield control the movable surface during the flight. Similar timers are used for F1C Power and F1A Towline Glider.

(L-R): The GPS transmitter goes in the model and sends location data back to the receiver. Information includes the direction and distance.

Electronic timers often offer a remote dethermalizer (RDT) option. This allows the model to dethermalize at any time during the flight. For safety, F1C rules require an RDT system that can shut off the engine and dethermalize the model if it goes off pattern.

One big advantage of an RDT is that the flight can be terminated at any time during it. Test-flying on a small field is one obvious advantage. If the model is headed for a tree line, you can dethermalize early or overfly the trees and dethermalize on the other side.

Standalone RDT systems consist of a receiver, battery, and small servo in the model. A transmitter held by the flier sends a coded signal to the receiver to trip the DT. The typical weight of the onboard unit is less than 10 grams, which is lighter than most timers.

Color and Visibility

While the model is in the air, the flier and the person timing the flight need to see it to the ground. A good pair of binoculars is important, but the model’s color scheme might be even more valuable.

Ross Jahnke’s paper in the 1998 National Free Flight Society (NFFS) Symposium studied the relationship between the color and visibility of FF models. When a model is above the horizon and silhouetted against the sky, fluorescent orange, red, black, and blue were the best color choices. When a model is silhouetted against trees, fluorescent orange is the best choice, with red being second. Orange and white also scored well.

When the model is on the ground (or in a tree), it needs to be accurately located. For years, modelers depended on good eyesight and a compass to walk a line from the launch site to the last sighting of the model. The introduction of radio tracking systems provided a more accurate method of locating the model.

A small transmitter in the model sent out a signal to a handheld receiver. (The system was developed for tracking birds.) Models could be tracked and found 20 miles or more downwind, but it often involved a lot of driving and walking as you slowly narrowed the search area. You had to be patient.

There was a learning curve to using a tracker. The best advice I received was to keep turning the gain (volume) down until you could barely hear the beep. The signal would get louder as you approached the model. It would also become louder if you pointed it at the model. The most important thing, however, was to use fresh batteries, install them in the transmitter, and tune the receiver to the transmitted signal.

Faust Parker uses the Pyxis GPS system to track his F1C Power models. A lanyard keeps the receiver handy. GPS tracker systems are becoming a popular alternative to using tracking radios.

While waiting for a thermal, Alexander Andrukov adds hand turns to his F1B Wakefield model. Bright colors on the wingtips increase visibility. An electronic timer in the model operates the auto surfaces. The timer also has an RDT function.

Although the GPS system has been around for 40 years, it has only recently become a viable alternative to the radio tracking system. In some ways, GPS trackers are similar to the familiar radio tracker. They both send out a signal from the model to a receiver. The big advantage of a GPS system is that it sends out useful information, such as the direction and distance to the model. Another advantage is that the receiver is much smaller and lighter than a radio tracker with its big Yagi antenna.

There are at least two different GPS tracker systems in use by modelers. The Pyxis GPS model tracker from FFelectronics in Italy, and the FlexiDisplay GPS Locator System from BMK in the UK.

Last but not least, put an easy-to-see label on each model. I print mine on thin typing paper and attach it to the top of the wing and the top of the fuselage. (Whatever you do, don’t hide the label on top of the pylon where it is hidden by the wing.) My labels reads, "If found please call," followed by my name and cellphone number. Be sure to carry your cellphone with you at all times. Make sure your flying buddies know your number.

A Century of British Free Flight History

In its more than 150 color and black and white pages, A Century of British Free Flight History traces the development of our sport from before Blériot flew the English Channel in 1909 up to the present day and marks the centenary of the British Model Flying Association (BMFA), the world’s oldest model flying organization.

With chapters by specialists such as Mike Fantham and Bob Bailey, who cover Rubber, gliders, Power, electrics, Scale, Indoor, electronics, and the vintage movement, the book is one you will refer to again and again as you discover how FF became the international sport that it is today.

The book is available from Martin Dilly; his email is listed in "Sources." The book is £22.00 GBP. You can order by credit card or PayPal; checks should be payable to the BMFA FF Team Support Fund in British Pound Sterling only and drawn on a bank with a branch in the U.K.