Roll cage material

[walkingpace]

Gday all,

Back again with another rookie question

This time it's about the all important roll cage. I'm pursuing a goal that may be more trouble than it's worth in that I'm trying to build my streamliner to meet both DLRA and ANDRA rules so that I can run at Sydney Dragway for "testing" purposes (or to simply alleviate boredom). Now naturally there are some deviations between the rules which can be easily accounted for but no blatant contradictions....until now...

DLRA requires a roll cage made from 1 5/8" tube with a .120" wall for all parts of the cage however has limited material requirements other than mild steel tube. (forget about chromoly. I'm not interested in trying to bend it) I understand some people are even using black pipe...

Now ANDRA and SFI specifies all steel tube MUST be Cold Drawn Seamless or Cold Drawn Welded (as a side issue, I got this stuff quoted. Almost cheaper to pay for chromoly ) however they specify different material thicknesses for different parts of the cage. These are as follows;

Hoops over divers head: 1 5/8" x 0.116". (I'm happy to use the ever so slightly thicker wall DLRA spec stuff here)

Shoulder hoop: 1 1/4" x 0.075"

Uprights (Chassis to shoulder hoop) 1 1/4" x 0.075"

Diagonals (chassis to shoulder hoop) 7/8" x 0.065"

Now the cage design will be as per SFI spec for dragsters running faster than 7.5sec 1/4 mile including tube spacing and angles as this cage is designed to take a roll over at around 300MPH

Will this however be enough to pass DLRA tech inspection given that on a strict viewing of the rules, all the tubes below the top hoops are too light not withstanding the higher grade of tubing. My concern is the SFI spec has been carefully designed to spread the load in a crash and using heavier tube in some areas will affect the way it does this and may focus stress on areas improperly, ultimately leading to failure. Basically someone REALLY smart designed this cage and I don't want to start bumbling around trying to "fix" it.

[DLRA]

G'Day WalkingPace,
Please take this in a constructive way, I understand where you are coming from and what you are trying to achieve, and this is not the first time that this question has been asked.
I won't be discussing the technical aspects of roll cage design. Rather I ask you to consider why the specifications are different and how they got that way.
Each form of motorsport has been around for a long time and has developed rules and regulations specific to each sport based upon the collective learning of the participants.
We all tend to learn by experience, we cut our finger, it hurts, we resolve not to do that again and put in place measures to try and not do it again.
So it is with chassis design and safety. Each sport (Drag Racing and Land Speed Racing) has developed a set of rules and regulations based upon lessons learnt.
After each incident, it would have been reviewed and in many cases new rules put in place to try and limit or reduce the likeyhood of it occuring again.
There are some simularities between the 2 sports, like the performance of the motors and high speeds attained. But the circumstances under which they are attained are vastly different.
- Drag strip, 1/4 mile or 1/8 mile, bitumen track, barriers on each side of the track. Emergency vehicles located at either end and within seconds of attending in a crash. Weight is seen to be of a disadvantage and reducing weight can aid performance.
- Land Speed Racing 9 miles of track, on salt or clay, nothing around for miles and miles. Emergency vehicles at either end and may be in the middle, will take many minutes to arrive just because of the distances involved. Weight is your friend and is keenly sought after to give more traction and stability.

So when you have spun and rolled your lakester after having lost traction, skidding for hundreds of metres on a very abrasive salt surface, which diameter tube are you going to be wanting to save your life?

[walkingpace]

Thanks for the reply and I take it as the helpful advice I'm sure it was intended to be. I guess where I'm coming from is whilst ANDRA accepts a smaller size of tube, they require it to be a higher standard of material, whereas DLRA requires the larger size however will accept other types of material eg ERW steel tube or pipe (more prone to splitting along the seam I'm told). I suck at maths but I get the feeling the end result would be awful close to equal.

I kinda figured this might have come up before and that there might be a standard response. ie YES we think SFI spec cages are tops or NO you aint comin in here with that.

If there isn't a clear position regarding cages of this type then I'll just make the whole thing out of 42mm x 3mm seamless tube which is the best of everything and plead my case with the ANDRA tech boys that if a little is good, more must be better. If they say no then so be it. Their rule book is extremely unclear as to whether the tubing sizes are a minimum or an absolute requirement but then again most things about ANDRA aren't clear...

[DLRA]

Thanks for your understanding and appreation of the situation.
Every so often we get an enquiry from some guy, "I want to run this or that" which has been built for some other form of racing to a different set of specs to what we have and they fully expect us to let them run.
We are no different to any other form of motorsport.
Consider a belly tank wanting to run in a historic touring car race? Imagine what sort of response you'd get?

It also comes down to legal issues and responsabilities, we have rules and we let you run outside those rules, you have a accident and then sue us because we let you run.

I think you've already figured out what the answer is although I think I'd be wanting some agreement from ANDRA before you started sticking things together.

[penny]

A simple reason landspeed cars are built tougher than dragsters is that although there is nothing to hit on the salt but salt , sometimes the cars hit the salt 13 times or more .

Have a read of a similiar topic on landracing .com

heres the link
http://www.landracing.com/forum/index.p ... 814.0.html

[walkingpace]

Thanks for the link.

All of this has prompted me to have a look on youtube at some crashes from both drag racing and dry lakes and look at the difference. Whilst I had never noticed it before it seems as though most times a dragster looks like pencil rolling, it will catch the concrete barrier, and either bounce back level or at least drastically reduce the rate of rotation. Not so on the lakes. They just keep going over and over and over and over......often with tragic consequences...

Perhaps a quick reminder of my own mortality is not such a bad thing.

Cage will be DLRA spec. No question about it.

Complying with ANDRA as well, whilst theoretically possible looks like being a very complex and expensive exercise which would require parts of the car to be changed for different events. To be honest it would be a whole lot easier (and perhaps cheaper) to build just for LSR and then put together something else for the drags.

As always your assistance is greatly appreciated.

[momec3]

The less you have to comprimise on the easier it is to build.

Chris