Welding to A-arms? 2

[bvanhiel]

I have an 88' Civic that we are using in the 24 Hours of LeMons, a race for cars ostensibly worth less than $500.

We have a mildly dangerous idea for creating extra downforce that involves a large fan, a motorcycle motor, and a large vacuum manifold that is attached to car's suspension. Essentially we are mimicing Chaparral's 2J car, but have the additional lattitude of directing the forces directly into the suspension rather than the body.

Our current puzzle is figuring out how to attach to the lower links. The front link appears to be forged. The rear link is formed sheet metal. Is it folly to attempt to weld to a production car suspension member? Should I expect that the metal is hardened and that welding would destroy its temper?

The welder we have available is MIG and will be weilded by a somewhat practiced hobbyist. If complicated pre- or post-treatment is required we'll look for another way.

Thanks,

-b

 

[MikeHalloran]

The bigger danger is introducing a substantial bending moment into a part that was designed to be stressed primarily in tension or compression only, e.g. your typical pressed steel suspension link.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I think Jack Brabham tried it with his F1 car, ut it was banned as a sudden loss of down force in a corner or the braking area would result in a serious excursion off track.

At least the motor driving it should be considered part of the cars engine.

To apply the down force to all 4 wheels in controlled proportion as the wheels move up and down over uneven surfaces and to do it with structural integrity, then to control the air gap between the bottom of the car and the ground so you have reasonably predictable traction seems a universe away from your most probable resources.

Regards
Pat
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[bvanhiel]

Mike: These lower arms have the shock mount about 1/3 of the way along, so they are designed for bending. I realize that the way I referred to them in my OP was misleading. I am referring to the main lower link of the front and rear wheels. This link is the one that carries the shock/spring attachment for the Civic. Here's an image of the front:

http://www.suspension.com/civic.JPG

.

Pat: Brabham's design was limited, as they had the same constriant as Chaparral: the rules. I do not share that limitation. Safety is somewhat of a concern, but this is a slow race (40-70mph) on a flat track. An excursion may destroy the manifold underneath the car, but is unlikely to result in injury. Check out 24hoursoflemons.com to get an idea of what this race is about. It's less about winning than it is losing with style.

I agree that controlling the air gap is the primary difficulty, hence our plan to connect it directly to the suspension members as close to the wheel as feasible. The track is very flat, but hitting a kerb will probably mean bending something.

I don't understand this: "At least the motor driving it should be considered part of the cars engine." I have a completely separate motor to drive the fan ala Chaparral.

I understand both of your concerns, but the question is: can I weld a bracket to the lower link?

 

[patprimmer]

As the separate motor contributes to the cars performance it should be included as part of the motor for the car. Are you allowed to run 2 engines or to substantially increase capacity. It comes under the same principal of using an additional electric motor and a big battery and methods to charge it.

In my opinion you can weld to the arm if you know what your doing and do not create any notches. A correctly designed mount will strengthen the arm despite the effects of welding.

Regards
Pat
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[bvanhiel]

Pat: You're assuming some sort of normal racing rules apply. This race offers as one of the prizes the "Dangerous Banned Technology" award. One of the previous winners used a pivoting ironing board counterbalanced by a bowling ball to create "active" aerodynamics. We're just trying to take it up a notch.

I just wanted to make sure we weren't doing a very bad thing by trying to weld to the lower link and end up with a car that immediately collapsed under its own weight.

 

[JohnLear]

I have welded onto stressed forged components a number of times with no problems, and if it were my project I'd be happy to do it.

I very much doubt there is any heat treatment (i.e. hardening / tempering) of the control arm forgings, but I could be wrong.

It might not be a bad idea to heat the forging with a torch prior to any electrical welding as this might lessen thermal shocks should this be a significant risk.

You might want to consider brazing (nickel bronze would probably be strongest) rather than welding.

I'd be trying to place any brackets as close as possible to the ends of the control arms to minimise bending moments, but it might be possible to attach even in the middle of the control arms if the bracket design spread the loading far enough along the length of the arms (i.e. as patprimmer says, more or less, if the brackets also act as reinforcement for the arms). Also avoid creating stress risers, blend any joints.

 

[patprimmer]

I would preheat and weld with a TIG if at all possible

Regards
Pat
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[bvanhiel]

What do you guys think of the rear wheel's lower arm? It's formed sheetmetal. Would you have the same confidence welding to it?

It is considerably taller (1-3/4"). It's section is an upside down 'U'. I'm considering drilling a hole through it parallel to the vehicle cl along the its neutral stress plane and then inserting a sleeve to use as a pivot.

-b

 

[patprimmer]

Channel sections can be beefed up quite a bit by welding a plate over the open side to form a box section.

If you need to drill a hole through the pressed metal arm, you can compensate for a loss of strength by designing a reinforcing plate around the hole. Take care that it does not end abruptly across the load, but tapers out so as not to create a stress concentration.

Regards
Pat
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[evelrod]

First---If its steel, stampings, forgings, whatever, it can be welded, period! Will it be safe or, rather, is safety all that important in a race where "dangerous, banned technology" gets an award?

Second---$500? Your gonna do all this on $500?

Third--- I raced a back up race the day that Jim Hall brought the 2J to RIR so I got a close look at it and watched it on the track. Ck out the specs for yourself. You don't stand a snowballs chance in hell of generating enough suction to make ANY difference in handling, except to make it worse!

Rod

 

[bvanhiel]

Evelrod:
1) I know I can weld it, but the question is whether or not the degree of heat treat/cold work/etc that I destroy in the process makes any appreciable difference for a car that basically only needs to last for a day of hard (very hard) use. I felt like this was more a question for you guys with practical experience with suspension members than for the welding forum.

2) It is a $35 dollar fan and a $100 motorcycle motor. The fan was miltary surplus. The Grassroots Motorsports $2007 challenge winners accomplished something similar for an '84 vette. Google "Cheaparral".

3) It's rated for 11inH20 static pressure at 12000cfm. Spread that over a 40"x98" manifold and I should have in the neighborhood of 1300lb of downforce. I think it will make a difference. I'm familiar with the 2J specs. I believe it only generated on the order of 1000lb, although it probably weighs a little less than a Civic with an extra 400lb of fans, motor and manifold.

 

[evelrod]

One: Just weld it. The chances of some hidden flaw surfacing well down the road just does not apply to your project.

Two: $500? Your gonna do all this for $500?

Three: Jim Hall is a brilliant engineer/inventor/innovator/race car driver...If he could not get the 2J to work more than a few minutes at a time...???? While it was working, though...I could take T-9 at RIR at ~100 mph, the McLarens and Lolas could go through ~120 mph and, the 2J went through so fast I could not get my watch on it!!! The technology worked, all right---when it was working!

Oh yeah, one more thing...Be sure the "exhaust" is pointed some where you want to be totally covered up by the dust/oil dry/dirt/rocks, etc. They came out the back of the 2J with a ferocity one had to see to believe!!!

Rod

 

[bvanhiel]

I don't think I'm smarter than Jim Hall, just less constrained by rules and trying to accomplish a lot less. I'm not racing against can-am cars, they're just other $500 junkers. But, like Jim, I want to come at them with something they didn't expect to see.

We are a little concerned with the volume of debris we're going to toss around. Although after a few laps we probably will have completely swept the track! At the moment it's blowing out the back after taking a 90 degree turn. We'll have the sprocket to attach the fan on Wednesday and find out just how fearsome it is. In the end we may have to run the civic without the fan and manifold, but we'll still have the "Dangerous Banned Technology" award in the bag.

 

[patprimmer]

Put a huge cyclone in the exhaust?

It will be an excellent track cleaner if it works. The Brabham car was referred to as the vacuum cleaner. From memory it exhausted straight up.

Regards
Pat
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[evelrod]

Maybe one of the John Deere "yard vacuum" bags? ;-)

Rod

 

[MikeHalloran]

Remember that the downforce is applied to the manifold, so it needs some rigidity of its own between the attaching points. Sort of like building a carbody under the carbody. Which is probably why the Chaparral used skirts on the carbody that was already there (and already doing double duty as primary structure anyway).




Mike Halloran
Pembroke Pines, FL, USA

 

[bvanhiel]

Mike: We've got some ridiculously heavy steel to build the manifold. It'll probably weigh 200lb without the downforce. When we started down this path I imagined we'd build the manifold like a plywood boat. Thin walls, ribs and fiberglass tape to reinforce corners - very light. That was before we realized just how shallow it would need to be.

-b

 

[GregLocock]

I'd rather you took the extra load in via the spring seats or shocks, but it is a very smooth load, I think in a race like this you can risk welding. Everyone always bleats on about rocks being hurled about at high speed, have these people ever sat trackside at a Sprint race? That's an 800 hp gravel gun. Annoying when it hits your beer, admittedly.




Cheers

Greg Locock

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