4             Common Class Rules

4.1          Introduction

The following rules and specifications apply to all racing classes. Specific requirements and exceptions are detailed in the Specific Class Rules for each class.

4.2          Control Surfaces, Pushrods, Linkages & Servos

4.2.1               Each flight control surface shall be powered by servos of sufficient torque for the size, weight and speed of the aircraft and shall not be less than 69 in-oz torque as rated by the manufacturer.

4.2.2               Elevators must use one servo that meets or exceeds a 105 in-oz torque rating or two servos that each meet or exceed a 69 in-oz torque rating as rated by the manufacturer.

4.2.3               Ailerons must use one servo that meets or exceeds a 105 in-oz torque rating or two servos that each meet or exceed a 69 in-oz torque rating as rated by the manufacturer.

4.2.4               All flight control surface pushrods must have linkage and clevises at least 4-40 size.

4.2.5               Control linkages, horns, etc., shall be of sufficient size and strength to handle the aerodynamic forces at speed and have minimal play. Each clevis must have a "keeper" mechanism installed.

4.2.6               Fairings over control linkages are permitted provided that control integrity can be visually confirmed by the USRA Technical Inspectors.

4.3          Radio Batteries

Minimum acceptable battery capacity rating is based upon the number of servos used, multiplied by 200 mAh per servo. For example: 9 servos x 200 mAh = 1800 mAh battery capacity rating.  Battery capacity must be rated at 1200 mAh or greater, even if less than six servos are used. Multiple battery packs operated in parallel may be used to achieve the required capacity.

4.3.1               Use of a 5 cell, 6-volt battery pack(s) to power the receiver is strongly recommended.

4.3.2               All major flight control servos and actuators must be visible for inspection with the wing removed and/or through access panels.

4.3.3               The aircraft owner/operator is to verify the integrity of the flight pack batteries prior to installation and, thereafter, at least annually prior to racing. This check is to include load testing and, discharge capacity of the battery pack(s), with notation in the logbook to indicate the date of the last battery check or replacement with a new battery pack.

4.4          Propellers

4.4.1               Propellers allowed are any fixed pitch propeller, constructed in one piece of any suitable material except metal. Component propeller systems, those composed of separate hub and blade elements, will not be permitted in any USRA sanctioned class.


4.4.2               Injection molded propellers, regardless of manufacturer or material composition, are not to be modified except for diameter reduction and/or minor blade chord narrowing at the trailing edge only. The blades are not to be thinned by sanding or any other method to achieve balance, nor will holes be drilled in the hub. Static balancing is to be accomplished by adding material to the lighter blade rather than removing material from the heavy one. Lead tape can be applied near the blade root to balance the propeller, or thin coats of clear paint or CA may be used. The strength of any injection-molded propeller depends upon the integrity of its outer skin, therefore, it is important to inspect the propeller surfaces for scratches or other damage before starting the engine.

4.4.3               The gray injected molded APC propellers specified for racing in the AT-6 and F-1GT classes may not be used on airplanes with engines of greater displacement or power than specified for the F-1GT Class. The AT-6 and F-1GT propellers are not legal for racing in any class that permits engine modifications or fuel other than gasoline. F-1GT class airplanes entered in Formula One class may use the APC F-1GT propeller if all stipulations of the F-1GT class are maintained, including exclusive use of USRA supplied gasoline. When using a gray plastic, injection-molded APC propeller in any class, no modifications other than de-flashing and balancing will be allowed

4.4.4               AT-6 and F-1GT Class Propeller Specification           USRA will annually specify the propeller to be used by all contestants in this class during every sanctioned race on the schedule for the year. Certified race propellers will be available in new condition to each T-6 and F-1GT class entrant at the event registration table.           Propellers needed for practice or testing are available for purchase from USRA or directly from the manufacturer.           The specified propellers will be available from USRA at the races and the event organizers will obtain race propellers directly from USRA until further notice.           The current racing propellers are manufactured by Landing Products (APC) and are identified as “T-6 Racing Propeller” or “F-1GT Racing Propeller” by Landing Products and USRA. These propellers are available for purchase by USRA members direct from Landing Products, 1222 Harter Ave. Woodland, CA 95776. Telephone (530) 661-0399 during business hours (Pacific time zone) or, the APC web site: www.apcprop.com/ or, e-mail: apcprop@aol.com           These propellers are the current standard for USRA AT-6 and F-1GT Class racing and will remain so until further notice.           No modifications to the specified propellers are allowed. Mold flashing around the blade edges may be removed if care is taken not to alter the blade shape or size. Race propellers are customarily marked for identification by USRA officials or the race promoter and no other propeller will be used by AT-6 and F-1GT Class contestants at that race. Waxing or polishing of the propellers is prohibited.  Race propellers will be administered by the Chief Technical Officer (Typically the Vice President of the USRA). The Chief Technical Officer or Chief Technical Inspector or his designated representative will be the source for all replacement propellers during the course of each event.

4.4.5               AT-6 and F-1GT Class Propeller Pool - USRA will provide propellers for the T6 and F-1GT classes.  During the registration process of each race the competitor will be issued an appropriately marked propeller after providing a $20 deposit per propeller. In the event the propeller becomes damaged or unserviceable during the racing event he is to return the damaged propeller and be reissued another propeller prior to the next round at no additional expense.  Following completion of competition he is to return the issued propeller to the race promoter and the $20 deposit will be returned to the pilot.  Between the racing events the returned propellers will be re-inspected, remarked and any unserviceable propellers will be replaced with new propellers to provide an adequate supply of race propellers for the next race.  Propellers not returned at the end of the event in which it was originally issued cannot be reused at any other event.

4.5          Engine Control & Security

4.5.1               All engines must be able to be shut down from the transmitter.  For non-ignition engines, a positive fuel line shutoff is mandatory.  Venting only of the fuel system is not considered sufficient for engine shutdown.  All aircraft utilizing gasoline engines must have a manual emergency ignition kill switch (momentary push and hold pushbuttons are not permitted) visibly mounted on the exterior of the aircraft.  Marking of the kill switch location is encouraged.

4.5.2               All airplanes with gasoline/ignition engines are required to use an on-board ignition kill switch operable from the transmitter, preferably operated by a dedicated servo. If a separate radio channel is not available the ignition switch servo may be slaved to throttle command via a "Y" harness however one servo cannot perform both functions.

4.5.3               It is mandatory that engines be secured in a secondary manner to a major airframe component such as the firewall, wing spar or landing gear structure through the use of a cable or safety strap of at least 200 lbs. tensile strength.

4.6          Radio

4.6.1               All radios will be on 2.4 MHZ . Radios that are failsafe capable are required to be programmed for engine shut off, fuel shut off or low throttle position when the transmitter is turned off. Inspection of the failsafe function is to be done during the airframe safety inspection with the wing off. Ground testing of the radio failsafe function is not to be done with the engine running on airplanes equipped with retractable landing gear.

4.7          Exhaust Systems

4.7.1               Exhaust systems (headers/pipes) may not exceed 8" measured along the centerline. The inside diameter from the end of the exhaust to within 1 1/2" of the header plate must remain constant. (1 1/2" allows fit to rectangular exhaust port shape)

4.7.2               No tuned pipes or augmenting methods of any kind are allowed.

4.7.3               The Experimental and Unlimited classes are exempt from these rules. See Specific Class Rules for further details.

4.8          Technical Inspection & Test Flights

4.8.1               All aircraft must pass an initial airframe certification inspection before approval to race is granted. Authorized USRA Technical Inspectors are USRA District Representatives and selected designees. The technical inspection certifies that the airplane meets all dimensional and current rule requirements for racing in the class intended. Documentation includes issuance of a permanent logbook for the airplane with serial numbered stickers affixed to the fuselage and wing(s) for identification. It is the responsibility of the aircraft owner/pilot to have available a pre-approved USRA specification sheet, if applicable, for the airframe type prior to inspection. The aircraft need not have flown prior to this inspection but will be presented in complete, ready to fly condition, less fuel.  It is the competitors’ responsibility to maintain their race plane in the same configuration it passed initial airframe certification. Adding or removing parts to gain a performance advantage is prohibited.

4.8.2               All aircraft must have been flown successfully prior to racing, regardless of inspection status. To complete the pre-race safety inspection, the pilot is required to certify that he or she has safely flown the aircraft two times in its present configuration.

4.8.3               To qualify for racing, all aircraft/pilot combinations must exhibit controlled and predictable handling characteristics on the racecourse and on the ground. Erratic or unsafe flying in any stage of the event may be cause for disqualification. The Contest Director has authority to ground any pilot or airplane when conditions are deemed to be unsafe.

4.8.4               Aircraft shall be fabricated in a sound manner using quality workmanship, construction practices and materials. Please be prepared to answer questions regarding construction methods, materials, etc.

4.8.5               Unless otherwise specified, wing thickness will have a straight taper from root to an area near the wing tip that is not affected by the wing tip shape. Wing root thickness, if defined at the centerline of an aircraft, may be calculated at the centerline from projected lines. Belly pans, fairings or other discontinuities are not part of a wing thickness measurement.

4.8.6               Statically balanced control surfaces and the use of selected full-size construction practices are strongly recommended.

4.8.7               Aircraft must race in the same configuration as passed in technical inspection. Spinners, cowls, canopies, etc., cannot be removed for racing. Exception: Wheel pants that become damaged beyond convenient repair or lost during an event may be temporarily removed for the duration of the event. The minimum weight requirement for the class will still apply when wheel pants are removed. Damaged or missing wheel pants must be repaired or replaced prior to technical inspection for the next race event.

If an aircraft sustains structural damage to one or more major airframe components, or is involved in a mid-air collision, the aircraft is grounded pending a damage assessment inspection by the aircraft owner and USRA Technical Staff, with the findings noted in the aircraft logbook. Upon completion of repairs, the aircraft must be re-inspected by a USRA Technical Inspector with the inspections noted and signed in the aircraft logbook prior to resumption of racing. The USRA Technical Staff may require the accomplishment of a radio range check and/or an observed test flight prior to approval for racing.

4.8.8               All decisions made by the USRA Technical Staff are final.


4.9          Airframe Details

4.9.1               Aircraft are meant to be reasonably accurate scale models, which conform to scale outlines. For those classes that do not require published aircraft specification sheets, deviations from documented scale proportions regarding overall length or wingspan shall not exceed 5%. Questions regarding scale fidelity should be submitted to the USRA Technical Staff well in advance of planned competition with the airplane. It is the responsibility of the pilot/owner to produce scale documentation that supports the dimensions or details of the modeled aircraft. Refer to Specific Class Rules and/or aircraft specification sheets for further details. Minimum dimensions contained there are not subject to deviation.

4.9.2               Aircraft must compete in the same configuration as it passed technical inspection. No airframe components may be interchanged unless approved and re-inspected by a USRA Technical Inspector.  At least one major airframe component, (Fuselage or Wing) must be retained from the original aircraft that passed technical inspection.

4.9.3               Wing dihedral, if appropriate to the model, may be reduced to one half the angle of the full-scale prototype, but will not be eliminated.

4.9.4               Aircraft may have either a clear plastic or fiberglass canopy.  If an opaque canopy is used, it needs to be painted in a near-scale outline for that aircraft.  If a pilot figure is installed, it needs to be of near-scale size to the aircraft.

4.9.5               Scale color schemes are not required and personalized schemes are highly encouraged to aid in aircraft identification. Exact cosmetic scale detail need not be followed, e.g., rivets, sliding canopies, etc. Non-scale wing tip skids are limited to 1/2" total height.

4.9.6               Scoops, blisters and air intakes necessary for full size operation must be included unless otherwise specified by the Aircraft Specification Sheet or Specific Class Rules.

4.9.7               If the engine does not fit completely within the cowl, the natural lines of the cowl will not be altered to cover any projection of the engine or its components. Covering these projections by application of non-scale fairings or tape to the cowl or obvious distortion of the cowl shape is not allowed.

4.10        Fuels and Fuel Handling

4.10.1            Any glow fuel may be used, with the exception that hydrazine, nitrobenzene or tetranitromethane fuel additives are not allowed. Nitrous oxide systems are not allowed.

4.10.2            Fuel for the classes requiring standardized gasoline/oil mixtures is the responsibility of the USRA. The specified gasoline/oil mixture will be dispensed using USRA fueling equipment at a designated fuel dock during all sanctioned events.

4.10.3            A fire extinguisher must be present during fueling operations at the fuel dock and in the engine run up area during radio range checks. Contestants are expected to have a fire extinguisher or water nearby whenever glow fuel is being mixed or dispensed in the pits.

4.10.4            AT-6 & F-1GT Class Fuel Specification         In order to provide a consistent fuel mix for the AT-6 & F-1GT Classes the following instructions are provided:         GASOLINE: Fresh, Regular Grade automotive unleaded pump gasoline of the lowest octane rating available locally will be used. Typical octane rating for gasoline of this grade should be in the range of 86 to 88 (R+M) and may or may not be oxygenated. Aviation or commercial racing fuels are not to be supplied for this class.         OIL: Any major brand two-cycle chain saw oil formulated for air-cooled engines, such as, Zenoah, Echo, Stihl, Husqvarna, Red Max, or Homelite, that are commonly available across the nation. No substitution for the above oil specification is allowed. Oil packages not intended for use in air-cooled engines, including all outboard motor oils or pre-mix, are not to be used.         MIXING INSTRUCTIONS: The specified gasoline/oil mix ratio is 25.6 to 1, which is 5 oz. of oil to each gallon of gasoline. It is acceptable to use a mix ratio of 25 to 1 if the oil packaging makes this more convenient. For example, if the oil container says it is for a 50 to 1 mix ratio in a given amount of gasoline, simply double the amount of oil to obtain the desired 25 to 1 mix ratio. Please insure that the oil is thoroughly mixed with the gasoline and kept in a clean container with clear, identifying markings for the fuel mix condition.

4.10.5            Any questions concerning the above instructions should be directed to your USRA Technical Representative.

4.11        Logbooks

The logbook issued upon airframe certification is a permanent historical record of the airframe.  It remains valid for the life of the airplane and certifies that the airframe has met USRA standards for racing competition. The logbook is to be transferred with the airframe in the event of sale. Supplemental logbooks should be stapled to the original if additional space is required.  Along with the logbook, the corresponding serial-numbered stickers attached to the airframe must be preserved in a legible condition. Failure to provide the logbook or legible identification stickers at a race site will require a complete re-inspection of the airframe before a new logbook or stickers can be issued.  The pre-race airframe safety inspection and radio range verification shall be initialed in the logbook by a USRA Technical Inspector.  Damage affecting airworthiness and the corresponding corrective repair(s) shall be annotated in the logbook and, upon completion of safety and range checks, signed off by a USRA Technical Inspector prior to racing.  Pictures in the logbook are to reflect the current paint or color scheme used on the aircraft, including the race number.

4.12        Pilot and Crew Requirements

4.12.1            All pilots must be a current USRA member, show proof of Small UAS Certificate of Registration, and, when required, AMA members in good standing in order to participate in USRA sanctioned events. It is highly recommended that all flight line team members join both organizations.

4.12.2            Valid proof of membership is required and will be checked at Registration.

4.12.3            While on the flight line ALL pilots and callers are required to wear an approved (i.e., DOT, ANSI, etc.) helmet.

4.12.4            All pilots and crewmembers must conduct themselves in a professional manner displaying high standards of good sportsmanship.

4.12.5            Pilots must possess and demonstrate sufficient skill necessary to maintain and operate a giant scale race aircraft on the racecourse at race speeds.

4.12.6            The pilot and caller must demonstrate acute awareness of other aircraft on the course and on the ground. They must be willing to yield to dangerous situations in support of safety, even at the expense of their aircraft.

4.12.7            Rookie pilots are defined as pilots who have never competed in a USRA sanctioned racing event. Rookie pilots must complete one flight with a USRA legal race plane demonstrating satisfactory control of the plane in all of its flight regimes as witnessed by any member of the USRA Board of Directors or a delegate under their authority. This flight can be completed prior to arrival at the race venue or the flight can be completed at the race site the afternoon prior to the race. In the event of inclement weather the race promoter will allow the demonstration flight prior to the commencement of round one on race day

4.13        Official Protests

4.13.1            During a race, only official protests will be accepted concerning USRA rules and specifications and it must meet the following requirements:

4.13.2            Filed in writing by either the pilot or owner and given to the USRA Chief Technical Inspector. Any additional supporting information will be included at the time the protest is filed.

4.13.3            Accompanied by a $100.00 cash fee. If the protest is upheld, the fee is returned. If the protest is denied, one half of the fee is retained by the USRA and the other half is awarded to the party protested.

4.13.4            Filed within one hour of incident in question. No protests will be accepted within one hour prior to a Trophy Race.

4.13.5            The protest will be reviewed by a committee (not less than 3 persons) comprised of USRA officials and, if necessary, the race promoter/event organizer.

4.13.6            All decisions are final and are not open to appeal or any other action.

4.14        Race Numbers

4.14.1            Each aircraft must clearly display its assigned race number in visible, contrasting color - separate from any other artwork, on both sides of the fuselage between the wing and tail section and/or on the tail section. Numbers should be standard type, easily read numbers. See Appendix A.

4.14.2            The race numbers on the fuselage and/or tail shall be appropriately sized (either location is acceptable) so that they are as large as possible. The race number shall also be displayed on the lower surface of the right wing (as viewed from the cockpit) with the top of the wing number nearest the wing tip and each number of the race number shall be a minimum of 10" tall.

Appendix A