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7/23/06

GT_Jet - Exciting new way to race pancake motors

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By Steve Medanic

The GT-Jet Project
A Lexan bodied alternative to the Resin Bodied Fray Style cars

The intent of the proposed GT-Jet class is to establish a fast, easy to tech Lexan bodied T-jet class with few simple rules. The chassis rules would be the same as the current NITRO class slip on tire cars. The NITRO cars are based on the Fray rules with certain additional restrictions.

Why another Fray class? Good question. In my opinion good race worthy resin bodies are becoming less commercially available as time passes. There is currently one supplier in the Midwest. Some of the "Fray legal" bodies look nothing like the car they represent. Cost of a typical resin body is $15 for an out of the mold special to $40 or more for a fully detailed RTR body. Even the best RTR resin body needs additional work before being ready to race. Most of this work involves lightening the inside of the body to distribute weight properly or reworking the wheelwell openings to fit the tires. One mistake and the body is history. Lexan eliminates all this. At last count Lexan was $2-3 (clear) to less than $15 for a really nice painted body. Going to full width Lexan bodies eliminates the go kart look of a typical Fray style T-jet. The wider bodies eliminate the tire nerf making for better side by side, door handle to door handle racing. Lexan does offer alternatives as NASCAR, Trans-Am, Sports and Prototype Lexan bodies will fit onto a T-jet chassis. While sharp eye will notice that the two cars in the photo above are not on T-jet chassis the above bodies will accommodate a T-jet chassis and not look much different than the ones shown above.

Faster or slower? Definitely faster! The best CRR slip on tire class time of 5.65 was set this November during the NITRO Turkey Trot with a full tilt electronic controller. In that race and this test the same chassis was used. The yellow inside lane was used for the test. The only difference between November and now is the body and body mounts. With a simple resistor controller the mule turned laps under 6.000 at will with a best lap of 5.500. On its second test run with my “Trek” controller the fast lap dropped to 5.476 with a backup of 5.487. The 5.476 ties or is just under the best FRAY lap time set at CRR with silicone sponge tires. So far the GT-Jet is approximately 0.2 sec/lap faster than a NITRO class resin car and just as fast as a full tilt FRAY car. The mule was incredibly easy to drive in the 5.6-5.7 range. Obviously when you get close to the limit it gets more difficult. On a twisty track the difference in times would be greater.

The minimum weight was determined by building a NITRO chassis with the lightest current setup borrowed from Andrew, Dennis and Tony. This setup has RTHO Plastic Fronts and a JW Ti Rear axle. 0.225” rear rims and Wizzard Lo-Lo Pro tires were used. Lightweight versions of the Figure1 and 2 body mounts were added along with an unpainted MaDD Porsche 917K Lexan Body. The weight of that chassis was 17.8g. This was rounded up to 18.0g to account for paint, parachute tape and decals. Using silicone sponge tires the minimum weight would go down as the Fray tires are lighter than slip on silicones.

Complete car rules
1. The complete "car" shall not weigh less than 18.0 grams and no more than 22.0 grams.
2. The complete "Car" shall not exceed the maximum allowed width of 1.3125" (1-5/16"). The car shall slide without force though a standard tech block.

3. No additional pans or weights of any kind are allowed.

GT-Jet Body rules
4. Bodies shall be full width, commercially available, clear plastic 0.010” “Lexan” bodies. Bodies shall have a minimum width between the centerlines of the axles of 1-1/4” (1.250”). Material thickness of the body shall be less than 0.015”.

5. The chassis shall be entirely covered by the body when viewed from directly above.

6. No window, lubrication or ventilation openings may be cut in the body. (Windows, engine covers, radiator openings, pickup bed covers, etc. shall remain in place and unopened.)

7. Windows and headlight openings may be left clear. All other areas of the body shall be painted.

8. The front body mount shall be a brass 1/16” pin tube mount in accordance with Figure 1. Configuration and maximum dimensions of the front body mount are shown below.
9. Acceptable rear body mounts are as shown below.

A. Plastic, Aluminum or Brass 1/16" pin tube mount in accordance with Figure 1. Configuration and maximum dimensions of the rear body mount are shown in the above figure.

B. Plastic, Aluminum or Brass 1/16" pin tube mount in accordance with Figure 2. Configuration and maximum dimensions of the rear body mount are shown in the above figure.

10. The total number of body mounting points (front and rear) cannot exceed four.

11. The body may be reinforced with clear and/or parachute tape at body mounting points.

12. The body mounts shall be secured to the chassis with self tapping or 1-72 or 2-56 machine screws. The mount may be tapped to receive the screw. One nut and washer can be used with each screw. Screws and nuts can be steel, brass, aluminum or plastic.