The F1D Model

The F1D Model

FAI F1D Rules states …


3.4.1. Definition
Model aircraft which can only be flown in an enclosed space and which are powered by
extensible motors and in which lift is generated by aerodynamic forces acting on surfaces
remaining fixed in flight, except for changes of camber or incidence.

3.4.2. Characteristics of Indoor Model Aircraft F1D
Maximum wingspan of the monoplane model ………………..550 mm, (21.65″)
Maximum chord of the lifting surfaces …………………………200 mm  (7.87″)
Maximum tail span …………………………………………………450 mm  (17.7″)
Minimum weight without rubber motor ………………………….1,2 g,
Maximum weight of the lubricated rubber motor ……………..0,6 g.

A U.S. dollar bill weighs 1g.  With a typical F1D model length of 33″, how can a model be built to 1.2g?  A typical F1D model has the following component weights:

  • Wing                   .35 g
  • Motor Stick          .30 g
  • Tailboom              .16 g
  • Stabilizer              .14 g
  • Propeller               .25 g
  • Total                   1.20 g

These are typical weights, but each model is slightly different.

How do you build one of these ships?  Here is an excellent “build” thread at the Hip Pocket Aeronautics forum by Tim Haynes Brown of Australia, with many of the world’s top builders contributing:

Rubber motor

The rubber motor is limited to 0.6g.  The length of the rubber motor depends on the flying site and propeller set up, and it ranges from 8.5″ to 9.5″.  Because the motor weight is limited to 0.6g, the motor is wound to its maximum capacity in order to maximize energy.  A typical motor that is 9″ long is wound with 1600 turns.  When wound to the max, the rubber motor is rock hard.  It is not atypical for a top flier to break 5 motors before successfully winding one to max.  Even then, the danger is not over.  The wound motor often breaks while it is being loaded onto the model, and it will also break while the model is flying.  Every turn that is put into the motor counts, as the F1D model flies with a slow RPM of 50.

Top fliers use Tan II rubber, May 1999 or March 2002.

Model Styles

A typical European style F1D has a stab with tip dihedral, with no rudder used.  This is perhaps made popular by the models of Bernie Hunt (England) and Jim Richmond (USA).  A typical American F1D has a flat stab and a rudder at the end of the tailboom, made popular by American flier John Kagan.

European style F1D by Ivan Treger (click to enlarge image)Image

American style F1D by John Kagan

ImageLutz Schramm’s F1D with elliptical dihedral

Videos of F1D’s in flight

Here is a wonderful video showing two of Europe’s top fliers, Jonas Romblad of Sweden and Lutz Schramm of Germany.  Lutz’s model employs the latest high-tech features and is a beauty in flight.

The next video shows Mark Benns’s model just after launch.  Note how slow the propeller turns, resulting in a very slow, energy conserving climb.  You can see how that the propeller has very high pitch at the start of the flight — the propeller blade almost appears perpendicular to the direction of rotation.‘s


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