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PostPosted: Fri Feb 15, 2019 11:25 am 
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Joined: Fri Dec 23, 2011 6:59 am
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Location: Spring Hill, FL.
Lots of cars like this in SCCA.
A couple ways of coming into actual compliance; A short gusset tube inside the bend , while not technically correct, should be deemed compliant.
Add a X cross braced rear structure . Many cars have crossed rear braces, removing those long tubes from consideration.

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PostPosted: Fri Feb 15, 2019 1:04 pm 
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Joined: Wed Sep 08, 2010 8:01 am
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zChris wrote:
yes they have bends at the bottom.

Ignoring personal opinion about cage building, nothing in the rules disallows bends in the rear braces. I have built several cages where I have put a short bend in the end of the tube to facilitate being able to weld it properly.

Jesse has a good point about the horizontal seat brace. It looks undersized. Unless there is a complete horizontal bar under the tin, that would need to be addressed.

"c. Cars must have 2 braces extending to the rear from the main hoop and attaching to the frame or chassis. Braces must be attached as near as possible to the top of the main hoop (not more than 6 inches below the top), and at an included angle of at least 30 degrees."


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PostPosted: Fri Feb 15, 2019 1:31 pm 
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Joined: Thu Nov 12, 2009 6:01 am
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Two things are missing from the current GCR that were included previously. No more limit in number of bends for main hoop, as well as the restriction on no bends in main hoop bracing.


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PostPosted: Sat Feb 16, 2019 6:06 am 
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Joined: Sun Aug 18, 2002 6:52 pm
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Location: Topeka, Kansas
I think that's it Steve. My history on building cages goes back pretty far and I didn't know those rules weren't still in there. I know you can also submit photos/drawings for what you want to do so maybe some additional bars would fix this. Either way, still not a big deal to fix.

Jason, pro racing is the same thing as we do but with more travel and money. Oh yeah and you get to sign autographs..

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PostPosted: Sat Feb 16, 2019 9:40 am 
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Joined: Thu Oct 03, 2002 10:34 am
Posts: 2869
Location: Wauwatosa, WI
Sometimes I get a bit more crazier when reading the GCR/Rules/Roll Cage rules. I knew I had read the bends rule. The roll cage bend requirements disappeared from the 2008 GCR forward. A question would be, were the bend rules haphazardly eliminated or was there an engineering study completed before they were eliminated? Said with a grin, Rick where are you?

They were:
Main Hoop: 4 bends max., totaling 180* +/- 10*
Front Hoop: 4 bends max. or
Front downtubes: 2 bends max.
Rear hoop supports: No bends.

If any of the above bend requirements cannot be met, all components of the roll cage shall be fabricated from tubing size(s) listed for the next heavier category of automobiles.

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PostPosted: Sat Feb 16, 2019 10:48 am 
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Joined: Fri Nov 13, 2009 5:51 pm
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During roll bar wars of the '80s, I wrote numerous letters to SCCA regarding bends in roll bar braces. Crickets!

Both Rankine's and Euler's laws regarding support columns apply. Major consideration in long, telescoping, hydraulic cylinders, like cranes.

Basically, if centerline between applied compressive forces goes outside profile of supporting column, no real support exists! Failure occurs at bend! Easily demonstrated with a book and a soda straw!

Apparently ease of fabrication is more important than actual safety.

This will drive Rick nuts!

RJS


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PostPosted: Sat Feb 16, 2019 1:21 pm 
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Joined: Wed Sep 08, 2010 8:01 am
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R. J. Sorensen wrote:
During roll bar wars of the '80s, I wrote numerous letters to SCCA regarding bends in roll bar braces. Crickets!

Both Rankine's and Euler's laws regarding support columns apply. Major consideration in long, telescoping, hydraulic cylinders, like cranes.

Basically, if centerline between applied compressive forces goes outside profile of supporting column, no real support exists! Failure occurs at bend! Easily demonstrated with a book and a soda straw!

Apparently ease of fabrication is more important than actual safety.

This will drive Rick nuts!

RJS



That was some dry reading. I guess they had a lot of free time back in the 1700s.

While I can agree that a bend in the middle 4/5s of the bars length is a bad thing, having a short radius bend on one end isn't going to ruin the bars load carrying capability to a great extent. Especially given the rear brace bar's typical short length. A subpar weld is the greater danger in my book.. The rear support bar is there to assure the main hoop doesn't fold backwards and it is being assisted by the front hoops/brace presence. It is up to the main hoop to carry the bulk of the load in a rollover.


I would think that there is a far greater chance of tubing failure due to load when the car takes a side impact.


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PostPosted: Sun Feb 17, 2019 5:46 am 
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Joined: Thu Aug 18, 2011 10:46 am
Posts: 208
Car was pulled from ebay on last day as "no longer available" suggesting it has either been sold privately or owner was unwilling to accept the no reserve auction results ...last bid was still $4050 which is pretty low for a car like that. I need another racecar like a hole in the head but I was considering putting a bid in for the car.
Jim


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PostPosted: Mon Feb 18, 2019 11:24 am 
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Joined: Mon Feb 18, 2019 10:45 am
Posts: 1
Brett W wrote:
Apparently Blackbird doesn't understand proper cage fabrication techniques.

Blackbird Fabworx owner here, we understand proper cage geometry just fine, you'll never find bent rear legs on anything we ever built.
This cage was not of our doing, all we did with it is make a couple of small changes to fit the driver better and additional work like the Aluminum work around the cockpit and some mechanical stuff.
You are welcome to check out our work in the many galleries we have on FB page - https://www.facebook.com/pg/BlackbirdFa ... e_internal

Image

Image

Image

Cheers!


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PostPosted: Mon Feb 18, 2019 8:41 pm 
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Joined: Tue Dec 31, 2013 10:40 am
Posts: 345
Location: Huntsville, AL
My apologies. Looks like you understand physics and proper cage construction. A beer or dozen when we meet at a race track sometime.

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