Pickups enter the jet age.
Although Smith had designed a number of jet-propelled promotional cars, he was determined to create a jet-powered pickup truck. "I wanted to design a jet truck that would resemble a conventional pickup as much as possible, so I requested a body from Dodge", Smith said. He was given a Dodge Rain Club Cab, a truck that has an extended cab and shortened bed.
Smith selected the Pratt & Whitney J-60 turbojet engine, used on the T-39 Sabre Liner and Lockheed Jet Star executive aircraft, to power the vehicle. "We chose the 7,200-horsepower J-60 because its power-to-weight ratio was the best among the engines specified by the National and International Hot Rod associations," Smith said. "When the afterburner is scheduled, the engine produces 5,500 pounds of thrust."
The chassis of the Dodge Ramjet was made of 4130 chrome molybdenum tubing, which is also specified for funny cars. ThermoDynamics engineers laid the two bottom frame rails of the chassis inside the body, and set the engine on a Jig stand that was positioned so the engine would sit far enough forward to get intake air through the fire wall and let only 12 inches of tailpipe through the tailgate. "We did this to balance the engine on the chassis and to make it look like an ordinary pickup," Smith said.
The tailpipe was customized out of 316L stainless steel. The designers borrowed the four-stage nozzles from a General Electric J-79 engine and part of the J-79 flame holder. "We removed two of the outer rings on the flame holder, leaving only the two center rings, and then machined new mounts to attach it to the tailpipe," Smith said. K-1 kerosene fuel is supplied by a 29-gallon aluminum tank. "This fuel leaves no residue, is relatively clean-smelling to audiences, unlike diesel, and creates a pretty white cloud when we burn it," he added.
Weight reduction was an integral design consideration for the Dodge RamJet, because its initial weight was a hefty 2,200 pounds. According to Smith, "We had to put it on a diet in a hurry." George Link at GTS Fiberglass in Wentzville, Mo., who was originally commissioned to make Smith a fiberglass hood that would not flex at high speeds, offered to make fiberglass doors, bed sides, and a tailgate as well. This cut the weight down to 1,900 pounds.
In the truck's first track speed test last November, as Rosberg hit 180 miles per hour, air tumbling over the truck bed created a low-pressure area while air flowing beneath the truck created a high-pressure area. When Rosberg tried to stop, the pressure differential lifted the rear of the truck from the road. It bounced back down on its rear tires and barrel-rolled.
Smith and company had already put a 3-degree rake in the body and a 5-degree rake in the engine to keep the truck on the ground. "After the barrel roll, we also cut slots in the tailgate to relieve air from under the deck, and we added an aerodynamic `wing' to create a downforce on the rear," Smith said.
At the truck's professional racing debut in April, Smith found that air coming off the windshield was creating an area of low pressure over the door. Combined with a ram effect through the grill, this pressurized the cab and nearly broke the doors at the window post. The pressure differential was too strong to use cam locks, so the ThermoDynamics crew cut three 12-inch pentagons in the back cab window to draw the cab pressure out. "We have not had the chance to test this in a race, but we think it will do the trick," Smith said.
Smith is trying to cut 280 more pounds from the vehicle to improve its starting speed, "because for the first 60 feet, it's a slug." One way is to tackle the lighting system.
Unlike most jet funny cars, the Dodge Ramjet uses factory lights, brake lights, and taillights (which strobe to impart an aviation look). In another departure from funny-car tradition, the RamJet is a self-starter, and as far as Smith knows it is the only jet-propelled vehicle that does not require a plugged-in power source on the track. "This means we have a 180-pound battery pack on the truck. But if we reduce that weight, it will look less like a truck," said Smith, considering another one of those compromises that differentiate idle dreamers from engineers.
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|Title Annotation:||turbojet-powered pickups|
|Date:||Sep 1, 1997|
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