F1D "microfilm models", which are about 55 cm (22 inches) in wing span,
are powered by a long thin rubber band driving a large propellor.
They weigh so little that they use tiny amounts of energy to fly and so the propellor turns at only about one revolution a second.
They move so slowly that even small air disturbances can upset their flight (such as a person walking past while they are in the air).
In addition, because they need such a small amount of energy to fly, on one fully wound rubber motor they can stay in the air for up to 50 minutes at a time in a large airship hangar. Even in a small gymnasium, flights of 25 minutes are not uncommon.
View or download the F1D Rules (0,3 Mb pdf)
Maximum wingspan of the monoplane model aircraft: 550 mm
Maximum chord of the lifting surfaces: 200 mm
Maximum tail span: 450 mm
Minimum weight without rubber motor: 1.4 g
Maximum weight of the lubricated rubber motor: 0.4 g
Always check the plans against the current rules, as the rules changes almost every year!
A model for starters: de Moustique [860 KB]
. A tutorial (in dutch) [579 KB]
is also available.
Models for experienced indoor builders: the Free Spirit [336 KB] (cat. I), the Kagan [7 KB] (cat. IV).
A lot of plans, tips and articles on IndoorDuration.com