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Welding

Fabrication-fueled ambitions

By Gretchen Salois

Fulfilling a promise, one welder sets his sights on breaking speed record

October 2013 - Unlike vehicles that come off the assembly line, Challenger II, a custom-fabricated and engineered car, will attempt to break the piston driven world land speed record. “Only 11 people have ever gone over 400 mph in a piston powered car—our streamliner needs to exceed that mark without compromising safety,” says Danny Thompson, the fabricator restoring the Challenger II.

In 1960, Danny Thompson’s father, Mickey Thompson, became the first American to break the 400 mph speed barrier, reaching 406.60 mph in the Challenger I. Its successor, the Challenger II, was originally constructed in 1968 by Mickey. In 1988, he recruited his son, Danny, to drive the vehicle he was building to beat the record. Just weeks later he and his wife, Trudy, were murdered in front of their home in Bradbury, Calif.

“[Mickey] wanted us to run the Challenger II together as a father/son team,” says Danny Thompson. “For a long time I didn’t feel like doing it without him but realized it needed to be done.”

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Thompson wants the restored Challenger II to reach at least 450 mph, comfortably above the current record of 439.562 mph held by American George Poteet. To achieve this goal, he brought together engineering expert Tim Gibson and a team of metalworkers. 

We go through a lot of cardboard before metal. Its a fabricators dream because everything is done by hand, from design to machined, finished part, Thompson says. You cant go out and buy this stuff. We template everything. Besides being the hardest project Ive ever worked on, its also been the most satisfying thing Ive ever done.” 

No shortage of obstacles

Steering gave the team its first challenge. It needed a complete overhaul due to changes in safety regulations. “Our car has four-wheel drive and two engines,” Thompson says. “The front of the car used to have wagon wheel steering, which is outdated and dangerous. We had to rethink the design entirely.”

The complex packaging requirements required several months of diligent planning. “Because the car is only 34 in. wide, the necessary components had to be aligned in a uniquely compact manner,” Thompson says. “It’s pretty esoteric stuff.”

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All front-end parts were made from either maraging 300M steel or 4130 chromoly steel. The maraging steel parts were then heat treated to 52 to 55 on the Rockwell C hardness scale. The rest of the parts were normalized 4130 welded with ER80S-D2 welding rod, with those components heat treated to 28 to 32 Rockwell C.

Thompson uses a Miller Dynasty welder and is sponsored by the company. When he welded the 4130 parts, they were preheated to 225 F and kept at that temperature during the multihour weld process to prevent cracking, then cooled in a specially constructed box that allowed them to shed heat gradually. 

“For the more complex stuff, we often weld for several hours at a stretch in teams of two,” Thompson says. “One guy welds, the other keeps the material at the proper temperature.”

Thompsons team TIG welds the vehicle because they use 4130 and TIG welding allows for better heat handling. You can control your heat in small areas, Thompson says. Some of the parts were making are from 0.032 in. material, and you can get in there using TIG with good control and penetration. Thompson uses a broad range of thicknesses, from 0.032 in. to 0.5 in. The team uses 3003 H14 aluminum for body work and 2024 T351 aluminum for the engine plates. 

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Machinist Dave Hadley, of San Diego-based S-K Specialties, machined a box out of billet 7075 aluminum that ties the two engines together. The drive shafts are new and among some of the innovations Thompson and his team designed and prototyped before machining the parts out of aluminum. 

The back of the car houses parachute tubes that release the parachute, which serves as the car’s brakes. “You have to engineer where that parachute is connected to the car so it doesn’t lift the nose of the car off the ground,” Thompson says. “The center of the parachute has to be at the centerline of the car, so we had to keep that in mind as we fabricated parts.”

Details make the difference

The completed car will be raced at the Bonneville Salt Flats in Utah, an environment that complicates the already difficult endeavor. “One big problem there is you’re driving on a tire that’s 4 in. wide,” Thompson says. “It’s 100 miles of flat salt that’s so flat you can actually see the curvature of the earth.”

Unlike jet cars, which are powered by thrust, all the power in a piston-driven car is delivered through the wheels. “So we have 2,000 horsepower for the front tires and the same for the rear. If there’s all spin and no traction, you don’t go anywhere,” Thompson says. For that reason, wheels and tires are critical.

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The team constructed custom-made wheels because they have to be a two-piece mount design. The reason for the two-piece wheel design is because the tires we use are specifically constructed to withstand 570 mph, Thompson says. Tires are tested on a spinning machine, so we know these tires can withstand these types of stresses.

The tire uses a 5/16 in. wire that runs around the inside and outside bead of the tire. “So the only way you can mount it is by using a two-piece mount design,” Thompson says. “By doing this you don’t have to stretch the 5/16 wire and take a chance of hurting its integrity.

“A typical car or truck tire has about half the rubber on the tire when new,” he says. “Land Speed Tires we use, built by Mickey Thompson Tire Company, use only 1/32 in. of rubber. The reason for this is rubber weighs a lot and will expand at high rpm causing the tire to grow on the outside diameter and create excess heat—none of this is good. We’re basically painting rubber onto these tires to make ourselves feel good. That’s how thin they are.”

The team will test the car this winter and plans to attempt a record speed in August 2014.

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For more information on fabrication of the Challenger II:

Thompsonslr.com - Facebook - Instagram 

 

Video - Mickey Thompson at Bonneville from Danny Thompson on Vimeo.

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