I have no iron in this fire as I do not have a motorcycle streamliner and have not run at SCTA ……Yet! Hopefully, this will make me an impartial observer.
Although I am a professional engineer with a degree in mechanical engineering, I have never practiced, nor am I qualified as a structural engineer, and it has been over 40 years since I graduated. Therefore the observations that I make here are not intended to imply that current or proposed structural requirements are adequate.
The first statement that raised a flag to me was the wording of the proposed rule change that reads as follows:
"Reason for Chg:
The current tubing sizes on some streamliners and side car streamliners "Speed X weight X Mass) is inadequate.."
I am not familiar with any formula that uses speed x weight x mass as a basis for determining structural requirements. Firstly, weight and mass are related quantities only differentiated the force of gravity, and on the surface of the earth (which I believe includes the Bonneville Salt Flats!) they can be used interchangeably in unitless comparisons. Therefore, the formula as given can be simplified as velocity x weight squared. Ironically, this would imply that a 4000 lb vehicle would have 4 times the structural requirement as a 2000 lb vehicle and the argument for motorcycle streamliners to have equal structural requirements as the usually heavier 4 wheel streamliners becomes suspect.
But I believe that a better formula for determining structural requirements should be that for kinetic energy, which is the energy that a moving vehicle possesses, and that which must be dissipated for the vehicle to come to a stop. This formula is relative to the mass (weight) of the vehicle x the velocity squared (KE=1/2mv squared). Although this energy cannot be lost, it can be converted to heat thru the process of force times distance. This force can be the friction of the vehicle with the ground, the friction of the air velocity on the vehicle hopefully aided by a parachute, and in worst case scenarios, by destruction of the vehicle thru crumple zones and energy absorbing wear pads. Using the kinetic energy formula, a vehicle that is twice as heavy will have twice the kinetic energy (not four times) as a vehicle half its weight traveling at a given speed. But, velocity is the more important factor here, because a vehicle traveling twice as fast as another one of the same weight will have four times the kinetic energy.
In any case, the force required to dissipate this energy due to friction with the surface, or destruction of the vehicle, will be proportional to its weight. The force of friction with the ground is classically determined by the weight times the friction factor, which indicates that a heavier vehicle will undergo more energy loss due to friction which will create more heat, and will probably undergo more structural damage due to the higher friction force. Furthermore, if the vehicle becomes airborne and returns to the ground at speed, more structural damage can be expected due to its heavier weight.
My conclusions are that SCTA and other governing bodies should be proposing structural improvements to vehicles solely based upon their weight and projected speed, and not on the number of wheels. I would suggest that making any change based on insufficient data would not be helpful. But it is probably important that these governing bodies take a serious look at all the structural requirements in view of the increasing speeds that are being generated and possible future speeds. Any serious accident based on insufficient structural requirements could have a devastating consequence on our privilege of using the Salt Flats, not to mention increasing insurance cost that may follow. The following table, if it prints as I have typed it, indicates vehicle comparisons, and the need for different structural requirements based on their relative kinetic energy. I do not propose any solutions to the tube size requirement, as it is only one component of the structural requirements. For purposes of comparing vehicles, I will use unit values of (1) for a 1250 lb vehicle, and (1) for 175 mph.
Relative Kinetic Energy of Vehicle at Speed (weight x velocity x velocity, unitless)
Vehicle weight 175mph 250mph 400mph
1250 lbs 1 2.05 5.22
2500 lbs 2 4.10 10.44
5000 lbs 4 8.20 20.88
This shows, for example, that a 5000 lb vehicle traveling at 400 mph will have twice (20.88/10.44) the kinetic energy as a 2500 lb vehicle traveling at the same speed, and four times the kinetic energy as a 1250 lb vehicle. More importantly, it shows that any vehicle in the list will have 5.22 times the kinetic energy at 400 mph as it does at 175mph.
I hope these observations can be used to help formulate future structural requirements for our vehicles, regardless of the number of wheels. It may also imply that we need tiered structural requirements based on the above. Increasing structural requirements for all vehicles, regardless of weight and speed, would be a mistake, as it would certainly drive up costs of construction, and reduce the number of participants who would be able to compete.
I invite constructive criticism.
D. Thomas Borcherdt, BSME, P.Eng
