8 Formula One GT Class Specifications
The following rules and specifications are for the 42% Formula One GT (F-1GT) Class. All Common Rules apply as appropriate. The dimensions of Formula One GT Class aircraft are based on the Formula One Class Rules that follow.
8.2.1 All entries must be a 42% scale representation (aircraft are not meant to be precision scale) of a full size aircraft that qualified to race during any year at the Cleveland National Air Races or Reno National Air Races.
8.2.2 Three-view drawings of the aircraft modeled (or at least a side view and top view) and basic scale dimensions, must be approved by the USRA Board and available, when required, from the pilot/owner during initial certification (Logbook) inspection. Any further changes or modifications to the aircraft that would affect the planform and/or scale outline of the model must also be approved by the USRA Board
8.3.1 Minimum aircraft weight is 27 lbs. (dry). Maximum aircraft weight is 40 lbs. (wet).
8.3.2 Aircraft weight may be verified at any time during a race.
8.4 Scale and Wing Area
8.4.1 All aircraft must be scaled to a minimum of 42% of the full size prototype by dimension with a minimum wing area of 1675 square inches.
8.5 Engine Specifications
8.5.1 Aircraft must use a stock 4.8 cu. in. (80cc), magneto ignition, Zenoah GT80TM. No modifications of any kind are allowed. This includes removal of chokes, piston ring heating, porting, polishing, etc.
8.5.2 Any commercial brands of replacement spark plugs are permitted.
8.5.3 Indexing of the spark plugs by using various thickness washers is permitted.
8.5.4 The removal of the Zenoah recoil spring starter is permitted. The resulting protruding crankshaft cannot be trimmed or altered in any way.
8.5.5 Any extension shaft length is acceptable.
8.5.6 Straightening of the crankshaft is permitted.
8.6.1 USRA-specified propellers will be supplied by the race event organizer.
8.6.2 No modifications may be made to the propeller or propeller hub.
8.7 Bottom Scoops
8.7.1 Bottom scoops are required if present on the full size subject unless an inverted engine installation prevents modeling.
8.8 Landing Gear and Wheel Pants
8.8.1 Aircraft must have and use fixed scale landing gear and wheel pants.
8.8.2 Wheel/tire assembly must be a minimum of 4 1/2" diameter and 1" wide.
8.8.3 Wheel pant minimum width is 2 1/2" at the axle centerline. Axle hardware will not be included in width measurement.
8.8.4 Wheel pant contours from leading to trailing edge and top to bottom must be smoothly curved to represent the scale shape as appropriate to the aircraft. Non-scale projections or bumps will not be used to affect the required minimum dimensions of the wheel pant shape.
8.8.5 Tail wheels must be installed and steerable.
8.9 Airfoil Thickness and Planform
8.9.1 Airfoil thickness shall be no less than 10% of the root and tip chords. In the case of round tips or elliptical wings, the thickness will be 10% to within 5 inches of the extreme tip of the wing. At that point, it can taper to the tip in a scale fashion.
8.9.2 Wing and tail group airfoils suitable for model aircraft may be used.
8.9.3 Tail surfaces must follow the scale planform of the full size subject but may be enlarged to provide adequate stability and control.
8.9.4 Control surface dimensions may vary as long as the aircraft outline is not affected.
8.9.5 Separate flap surfaces may not be used if the full-scale subject did not have flaps.
8.10.1 If the engine cylinder does not fit in the cowl when side mounted, the natural lines of the cowl will not be altered to cover any such projection of the engine or its components.
8.10.2 The minimum width across the cowl at the location of the full size prototype engine must be no less the 13.5 inches.
8.11.1 Engine fuel will be the only liquid carried in the aircraft. Any foreign liquid, other than provided fuel, will be grounds for disqualification.
8.11.2 Fuel will be supplied by the race promoter/event organizer. Fuel will be formulated and mixed according to the USRA F1-GT Class fuel specification as stipulated in paragraph 4.10.4 of the Common Class Rules.
8.11.3 A means of defueling through the fuel supply line to the engine must be provided.