I would like to ask a unibody engineer some questions

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Re: I would like to ask a unibody engineer some questions

Post by pdq67 » Sat Feb 17, 2018 6:02 am

Isn't an old '53 Chevy convert. frame one of the most rigid because it was a full frame plus an "X" frame in the middle??

Frame was used for the 'Vette's up to'62 before they went IRS. It also had the old style center steering design in the frames front end.

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Re: I would like to ask a unibody engineer some questions

Post by Brian P » Sat Feb 17, 2018 9:03 am

Open cross-section frame members (C-channel) mean they would have had little torsional stiffness. The "X" triangulates against fore/aft distortion of one side relative to the other, but it does little to stop the front from twisting relative to the rear (the whole structure deforming by warping).

Boxing in frame members greatly improves torsional stiffness but you are ultimately still dealing with a relatively flat structure. A large cross-sectional tube, even with thin walls (i.e. a unibody) is much stiffer than a small tube. The stiffness goes up exponentially with the cross-section.

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Re: I would like to ask a unibody engineer some questions

Post by pdq67 » Sun Feb 18, 2018 8:44 am

Brian,

Are you saying to 100 percent box the '53 Chevy convertible frame and it will be made about as stiff as possible?

For all channel formed steel, box the forth side and for any I-Beam formed steel, box both sides.

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Re: I would like to ask a unibody engineer some questions

Post by Brian P » Sun Feb 18, 2018 4:41 pm

The aftermarket builds aftermarket frames for some of those older cars, and you'll see two types: the "period correct" type which is stuck with the original design because that's what is period-correct, and the "hot-rod" type ... which use boxed sections.

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Re: I would like to ask a unibody engineer some questions

Post by Ratu » Mon Mar 05, 2018 1:35 am

Mk e

THAT is outstanding.

Art.

Is it still around?

Bula!

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Re: I would like to ask a unibody engineer some questions

Post by mk e » Mon Mar 05, 2018 7:27 am

Thanks.

That was my first attempt at something like that. Mostly 1" x 0.028" wall 4130 ....it weighed 28lb. In the next version a lot of 1" was to be replaced with .75" and a few other changes to get it to 22lbs with nearly the same stiffness, but that car was never built. The car sat in the lobby of the engineering department for a long time but I think its since been dismantled as they saw it as dangererous.....a student was nearly killed and suffered permanent brain damage in a testing accident when he drove it bouncing off the rev limiter in 1st gear so like 60mph into the back of a guardrail in a parking lot....I never saw anything like it, it was like he just froze, never tied to steer or brake that we could tell, foot to the floor and straight into the guardrail. The guardrail was not installed properly and not attached to the 2 posts the car went between which let the rail lift up over the front roll bar and since it was the back of the guardrail not the front it had expessed edges that cut through the drivers helmet. It was a horrible day, the car was impounded as evidence for expected law suits and we didn't race that year. We built a new one to race the next year but there was no time for any real redesign, the first car had taken 6 of us 2 years to build but now we had 1 year and with just 4 people left on the team. We got it to the race with almost no testing of any kind and everything worked all weekend but it really needed some time tuning on the suspension, a lot of understeer. We managed 17th out of 110 so not terrible and performance wise we did top 10 on most everything performance wise but it is an engineering competition more than it is a race and we were not prepared....the top teams had slides and posters to present, we were luckly to have matching shirts :)
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Re: I would like to ask a unibody engineer some questions

Post by Ratu » Mon Mar 05, 2018 12:45 pm

Awful accident. By the sound of it the guy panicked. People respond in strange ways in situations to which they are unaccustomed sometimes. Perhaps the guy had not experienced the rawness of a race car and the sensations it provides (like the acceleration forces, noises, vibrations etc) so his mind just shut off in some sort of overload condition.

Did the lawsuits occur or did it all quiet down on that front in the end?

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Re: I would like to ask a unibody engineer some questions

Post by mk e » Mon Mar 05, 2018 1:57 pm

It was just one of those days. This was our first fsae car but the college acros town had done several and we talked. They had reserved a parking lot for testing and asked us to join so we met them there, but there car wasn't ready. So it seemed letting them have a drive in ours was the right thing to do, towards the end of the rotation I saw 1 guy left and I popint to the car, he stepped forward, put on the helpmet and crashed.

It turned out he wasn't on anyones team, just saw the car and stopped to watch. I don't thing he'd ever even driven a standard trans anything and had no business at all in the driver's seat. The car was about 450lb and about 90hp, it moved.

The law suit went on for years. The other school settled after about a year, my school was still fighting it when I left so I don't know the outcome beyond the car was locked up and we couldn't get near it. I know nothing was ever found to have malfuncitoned, nothing failed on the frame beyond some crushed tubes where the guardrail slid up but the roll hoops were in place, all weld intact and wouldn't have taken me more than 3-4 hours to get back in shape....which I imagine is why the college wasn't too interested in settling. The other college owned the defective guadrail and the parking lot and had approved the event so they had a harder case on their hands, but I'd been to 3-4 autocrosses in that lot in the past which is technically what was going on the day of the crash.
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Re: I would like to ask a unibody engineer some questions

Post by midnightbluS10 » Tue Mar 06, 2018 3:05 pm

MadBill wrote:
Sat Jan 20, 2018 10:42 pm
Back in the mid-seventies, my pal had his new GMC van recalled because they discovered the jacks wouldn't fit under the trucks if the tire was flat.. #-o
My drunk neighbors Silverado sat for 2 weeks without a tire because of something similar. He had a flat one day and jacked it up to take the tire off to go get it plugged. He jacked it up, took the flat off, and went to put the tire back on after getting it repaired. The jack wouldn't jack the truck up high enough to get it on and he didn't have the fortitude to take the 2x6 in the bed, cut it in half, stack the pieces and put the jack on them.

Maybe this belongs in the "some people shouldn't use tools..." thread lol

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Re: I would like to ask a unibody engineer some questions

Post by Ratu » Sun Mar 11, 2018 1:50 pm

Mk e

It sounds as if the car may still exist. What happened to it after the litigation was over?

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Re: I would like to ask a unibody engineer some questions

Post by mk e » Mon Mar 12, 2018 8:38 am

Ratu wrote:
Sun Mar 11, 2018 1:50 pm
Mk e

It sounds as if the car may still exist. What happened to it after the litigation was over?
There were 2 very similar cars....i know the intent was both would be destroyed, but destroyed often just means disassembled and parts stored in case they are good for something, so it may very well be on the shelves in the ME lab....no way to know as it been 20 years since I had a key to the lab.

I keep thinking I'll build a Dsports or F1000 based on the same basic design....a chassis like that takes me 80-100 hours so not too bad.
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Re: I would like to ask a unibody engineer some questions

Post by Ratu » Thu Mar 15, 2018 5:58 am

If you did do that, what engine/trans do you reckon you'd go for?

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Re: I would like to ask a unibody engineer some questions

Post by mk e » Thu Mar 15, 2018 7:10 am

Ratu wrote:
Thu Mar 15, 2018 5:58 am
If you did do that, what engine/trans do you reckon you'd go for?
I'm not sure exactly. The thought I was having is I could build a single car that was legal in both classes with just a body change, so 1000cc motorcycle or some sort is the most obvious choice and means the basic chassis design is basically good to go. I'm not really sure I have time for a project like that though....garage needs to be finished which will mean redoing part of the patio, FrankenFerrari still needs a lot of work, wifey wants the basement finished.....time is not my friend at the moment.
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Re: I would like to ask a unibody engineer some questions

Post by Ratu » Fri Mar 23, 2018 2:54 am

Sad to say, time is no-one's friend, although it is reputed to bring some benefit on occasion.

Years ago (more than I care to admit) a guy I knew at Uni built a frame around a BBC. It was a compact single-seat tube-frame chassis type of vehicle. He never did put a body on it. Nevertheless the thing was road registered. It was really quick. It was quick enough to scare super-bike riders. Jone died at night in his sleep. The story that got about was that he must have been having a dream about racing around in his car and suffered a fatal off in it. So the deal was he supposedly died doing what he loved to do.

Anyway, his frame was not as good as yours. Nowhere near really. What about a larger engine like a contemporary automotive V-6 say? I notice Lotus trying this approach. Long reliable life and good low-end torque...

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Re: I would like to ask a unibody engineer some questions

Post by mk e » Fri Mar 23, 2018 5:34 pm

Ratu wrote:
Fri Mar 23, 2018 2:54 am

Anyway, his frame was not as good as yours. Nowhere near really. What about a larger engine like a contemporary automotive V-6 say? I notice Lotus trying this approach. Long reliable life and good low-end torque...
Thanks. Any engine could be used....I sketched up a version for a 33 Ford to use the Lincoln V12 I have sitting in the basement so anything can be done, it just takes time :(
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