9/28/07
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This edition of letters deals with the John Force incident in Dallas and chassis and safety issues.
SOMETHING’S GOT TO GIVE
Regarding your "Chassis Safety" article...
Hmmm, a correction. It was stated: “Also mentioned was that the chassis is ‘designed to break apart in a crash’. This of course is all nonsense. The loads on a top fuel dragster chassis, while higher than an average race car, are by no means tremendous. And in a crash, containment is always preferred to non-containment. The reasons for many of the failures are due to poor, or lack of, proper structural design.”
SFI rulesets require "splice joints" at the rear of the cage on a T/F chassis and the same joints directly to the rear of the motorplate on ALL front engined race car chassis. This rule was put into the book waaaay back in the late 1960's after it was decided that the combination of engine/driver's cage created a mass that a human body inside (as a passenger) wouldn't tolerate. Given, at that time, most crashes were caused by oil fires washing back into the cockpit and/or striking solid objects in the vicinity of the racetrack.
The idea was to allow the chassis to shear off at the joint and free the engine from the cage and rear tires, the idea to contain the driver in his own protective cage, without the added weight and momentum of the engine/drive train... and if noted, most dragster chassis that we have seen come apart, usually come apart at the "splice", right behind the cage, lower chord first, pretty much as intended. That's the "Tension Chord", in theory, although in design practicality, it is no more than one member of a very flexible boom, or truss, constructed to do exactly that, flex... within limitations.
To the average viewer or even a structural engineer, a tubular framed racecar of any type will tend to be seen as simple and of course, the frame of a funny car or altered roadster IS, compared to perhaps, Buckminster Fuller’s space frames or the Maseratis of the ‘50s... however, apparent simplicity is no more than that.
Having worked as an Architectural Designer for a period of time and having designed and built several race cars (at one time I held a SFI # and an AAR welding certification) I can tell anyone that the design of a successful drag racing chassis is anything but simple. The movements acting on a chassis anytime during its operation is unbelievable, and at best challenging in trying to estimate and calculate. Type of car is important because different horsepowers and drive trains require different approaches to type of tubular truss that is to be constructed. E.G. In the case of a long wheelbase dragster, the truss is a long flexible lever, or counterweight. In the case of a funny car or altered roadster, it’s a platform... where many attempts to create, by mechanics or variations of tubing size, a suspension of sorts have been accomplished. Currently, in funny car chassis science, the slider chassis is being used to some success, a variation on a design by Woody Gilmore from back in the late 60's.
Problem at the bottom line is this... and NHRA doesn’t like to hear it. Rough tracks, especially at the top end and in the shutdown areas, aren’t good for any kind of short travel suspension, and even worse for cars with only steel tube trusses for a suspension... And over the years, I have been to very few tracks that had a smooth shutdown area. It’s almost a joke, and one, still, after 30 years, has a stop sign and a street crossing it!
John Largent
Pueblo, Colorado
