12          Thompson Trophy Class Specifications

12.1        Introduction

The following rules and specifications are for the Thompson Trophy Class.  All Common Rules apply as appropriate.  The specifications are based on a scale factor method combining wingspan plus fuselage length for a total required 156" (with exceptions as noted).   The goal is to make a variety of aircraft from this "Golden Age" as similarly competitive as possible while keeping aircraft at a large scale and incorporating existing plans and kits.

12.2        General

12.2.1            All entries must be a scale representation of a full size aircraft that qualified, attempted to qualify or competed in the Thompson Trophy Races between the years of 1929 to 1939.  

12.2.2            Additional golden age aircraft may be added based on the race experience of this class.

12.3        Weight

12.3.1            Minimum aircraft weight is 22 lbs. (dry).  Maximum aircraft weight is 40 lbs. (wet).

12.3.2            Aircraft weight may be verified at any time during a race.

12.4        Scale Sizing Requirements

12.4.1            All aircraft must conform to basic scale outlines and meet a total minimum size of 156", calculated by adding the wingspan to the fuselage length.

12.4.2            EXCEPTIONS:  An 8" overall deviation (4" maximum on wingspan, 4" maximum on fuselage length) is allowed for use of existing kits and plans only.  Total minimum size for an existing kit or plan is 148".  Any existing plan or kit that falls under a total minimum size of 148" must be redesigned to 156".  (Note:  The 1/4 Scale Byron Original's Gee Bee R-2 is legal only with the 80" wing)

12.4.3            There is a 25% reduction rule allowed for biplanes so that the total size is 117" inches.  No other biplane reductions are allowed and wingspan is based on the larger (upper) wing.

12.5        Size Examples

11.5.1            Please refer to Thompson Trophy Specification Sheets.

12.6        Scale Details

11.6.1            Three views and/or other scale documentation is the responsibility of the pilot/owner and must be available to verify fidelity to scale for Technical Inspections.

12.6.2            Canopy or windscreen must be clear or tinted - not opaque.

12.6.3            A human-likeness pilot bust installed in the cockpit is required.

12.6.4            A minimum instrument panel with at least three scale size gauges is required.

12.6.5            Scale color paint schemes are not required; however typical schemes of the era, such as scallops, etc., are encouraged in order to help maintain the "feel" of the time.  The "look" of the era, such as fabric-covered structure (regardless of the material used) should be maintained / replicated where possible but is not a requirement.

11.7        Engine Specifications

12.7.1            4.88 cubic inch displacement (81 cc) maximum size reciprocating engine. No modifications of any kind are allowed. This includes the removal of chokes, piston ring heating, porting, polishing, etc.

12.7.2            Maximum engine displacement checks may be required before, during or after any sanctioned racing event.

12.7.3            Any commercial brand of replacement spark plugs is permitted.

12.7.4            The removal of the recoil spring starter is permitted. The resulting protruding crankshaft cannot be trimmed or altered in any way.

12.7.5            Any extension shaft length is acceptable.

12.7.6            Straightening of the crankshaft is permitted.

12.8        Exhaust Systems and Cowling

12.8.1            Exhaust systems should exit as close as possible to the scale location(s) where possible and should not exceed more than 8" inches from the manifold to the end of the header/pipe unless a large cowl requires excess length to exit.

12.8.2            Engines must be cowled. Narrow cowls require that single cylinder engines be mounted inside the natural line of the cowl.

12.8.3            No engine parts may protrude from the cowling except the carburetor, exhaust header, spark plug, spark plug wires or twin engine cylinder heads (if in a narrow cowl).

12.9        Airfoils and Planform

12.9.1            Wing and tail group airfoils suitable for model aircraft may be used.

12.9.2            Wing and tail surfaces must follow the scale planform of the full size aircraft. Slight modifications such as washout and small increases in both wing and tail surface dimensions may be used to enhance the flight characteristics of this era's aircraft.

12.9.3            Control surface dimensions may vary as long as the aircraft's outline is not affected.

12.10      Landing Gear

12.10.1          Aircraft must have and use scale-like landing gear for the aircraft modeled. Gear may be modified for simpler construction and operation; however, the overall scale appearance must be retained to include the use of wheel pants, etc., if used on the full size aircraft.

12.10.2          Tailwheels must be installed and steerable.

12.11      Thompson Trophy Class Aircraft

A list of Thompson Trophy Class aircraft (by year, type, finish position and race number with remarks) is available from the USRA together with a listing of available kits, plans and scale sources.  Information has been compiled from the EAA Aviation Foundation book, The Golden Age of Air Racing - Pre-1940, 2^nd Edition, 1991.  However, this listing contains some minor discrepancies.  It includes some of the aircraft (*) that were built for the Thompson Trophy Race but did not qualify or compete due to problems, schedules or crashes.   For example, "Wendell-Williams 45", the Pearson-Williams PW-1, "Mr. Smoothie" and the Hughes H-1 (short wing) are legal to race.  Note that several types raced in multiple years and that most of these aircraft underwent many improvements and revisions as well as changes in race and registration numbers year to year.   The Thompson Cup Race became the Thompson Trophy Race in 1930.

12.12      Thompson Trophy Specifications

The following information is referenced from "The National Air Racers In 3-Views 1929-1949" by Charles A. Mendenhall.  The associated model requirements at the required 156" (based on the prototype specs) are available from the USRA along with some of the known plans/kits that meet the requirements.  Modifications of plans and/or kits to meet the required minimums are the responsibility of the builder/pilot.  Note that specifications may vary slightly between published reference works, three views, etc.  Additionally, in order to support the use of existing kits and plans, an overall five percent (5%) deviation is allowed.  This allows a deviation of up to eight (8) inches (4" max wingspan, 4" max fuselage length).  Due to the unique nature of the very short-coupled GeeBee's and only one fiberglass kit being available, the Byron Original's 1/4 Scale GeeBee R-2 is legal only when built with the 80" wing.   A GeeBee "Z" is also legal with an 80" wing.

Thompson Trophy Class

*  Factor divider is 117"  (25% Biplane)

**  Due to likeness with the R Models, the same Model Specs, 91" + 65", is legal as would a scratch built model with an 80" wingspan, similar to the Byron R-2 sized kit