Frame question

[andrewb]

First, this is a rear engine chassis but you guys the ones that know this stuff. Back story. Purchased this chassis for my wife to run a rear engine Ford Flathead. Really only need to go 9.99 and slower but would like to see if I can get it certified for 7.50 and slower. Original builder did a great job on the moly chassis but last owner was a hack.

My question is in regards to the lower frame rail. As you can see by the photo, the rear frame rail (#3) is butt welded to a cross brace the front seat support (#1) and its butt welded to the front frame rail (#2).

I’ve read the General Regs and the the 7.50 regs and (other than pictures) it doesn’t mention that the lower frame rail needs to be a continuous piece in the roll cage area.

Before I get too excited about working on this, I want to verify if this is a NHRA legal setup. I’m been trying to contact our local Tech guy but he just doesn’t seem to want to return calls. It’s worth the $100 to have him do an initial inspection before I continue.

Thanks,

Andrew

[dreracecar]

Step back and take another pic, hard to define what I am looking at. A butt weld is when 2 pieces of the same dia are welded together inline

[andrewb]

OK, I'll take a few better pictures tonight.

Andrew

[rooman]

I guess that what you are saying is that the seat cross member is at the end of the forward lower frame rails and ties them together and then the rear rails attach to the back side of that seat cross member. If that is the front seat cross member where do the rear cockpit uprights attach? There was some discussion at the SFI meeting that I attended on Friday morning about permissible locations for a lower rail splice (inboard or outboard of the cockpit) but this is a whole different can of worms.

Roo

[andrewb]

Here's a better pic Bruce.

[rooman]

Andrew,
            apart from the frame layout I can see another problem. The seat belt mount bolt is tilted the wrong way. With the driver in the car the belt should pass across the hip and angle back at approx a 45 degree angle (depending on seat configuration). A better install would have a tube running from the lower rail to the diagonal to achieve that. As it is now the belt basically holds the driver down but not back in the seat. Also the crotch belt mount is way too far forward to be effective.
  Has this car ever been certified?  Neither of the photos show enough of the lower bay to see if there is a diagonal but there is obviously not a "K" in that area and even the spec for 10 seconds and slower calls for one or the other. That said, I think that the non contiguous lower rail is a deal breaker as the junction is in the "spec" area of the frame.

Roo

[andrewb]

Hi Roo,

Not sure if it’s ever been certified in the past. Yes, there are several changes that need to be made, many of which you pointed out.

To your last statement that the junction is in the spec area of the frame and is non-contiguous. I’ve read most of the SFI Chassis specs as well as the General Regs numerous times and haven’t found anything stating that this design is not permissible. Can you point me to where I’d find information regarding this?

Thanks,
Andrew

[andrewb]

If i'm reading the second sentence below right, which is found in all SFI Chassis Roll Cage specs. Anything other than the upper roll cage can be repaired.

II. Basic Construction Practices

9. No components may be clam-shelled in order to satisfy nominal outside diameter or nominal wall thickness requirements. Roll cage components (#1) above the upper frame rails (#4) may not be repaired by splicing, patching, clam-shelling, etc. according to generally accepted aircraft repair procedures.

Andrew

[dreracecar]

No where in the spec does it say that the lower rail has to be continuous all the way to the rear. Its not the way its normally done or the way the picture spec shows it, but I dont find it that bad. The rail and cross member although welded without an inner sleeve is still supported buy another tube welded on top and the offset welding of the rear bottom rail is so close that for structure it did not lose enough to make a difference. It was prob done to keep the rails close together with out bending them back to a real narrow R/E housing. As long as the required tube dia and wall thickness meet minimums that junction should pass