Aluminium Wishbones

[Mudgey]

Hi guys, Hopefully soon i am going to start the design of my own GT40 (proper excited) and was wondering what are the pro's and cons of using aluminium for the tubular wishbones/radius arms on a GT40? I would have thought they would save a huge amount of weight over mild steel.

What material grades would be suitable and is it worth the cost, i can only imagine thats a reason why they arent being done already.

Is there a reason why RCR use machined lower wishbones over a tubular construction?

Regards,
Mudgey

 

[chuck smith]

aside from the advantages of aluminum weight wise, I think the reason many builders use aluminum is significant cost savings associated with CNC milling of billet aluminum. If you have the equipment, a CNC machine can produce a very accurate , strong unit with little labor. In your case, it would probably be much easier to use steel, or even already produced units from some other source.

 

[flatchat(Chris)]

"Authenticity" -- mainly for the use of tubular steel.
DRBs use corvette front end --all aluminium
RCR use custom billet machined components through out.

Some countries / motor engineers (Australian) are'nt excited about the idea of threaded rose joints hanging out of aluminium critical suspension components --greater chance of failure therefore liability issus etc.
Qualified people may have a better opinion ?

I use these:-

 

[Jac Mac]

I would doubt that the RCR wishbones are lighter than what could be fabricated from suitable steel. QC, a consistent product with known dimensional accuracy make it easier for RCR & client alike to 'make it fit' but even then some folk will try to fit them inside out & upside down. Too many 'Tim Taylors' in the 'Kit Kar' world---you know the type''' Real Men dont Need or Read instructions''''

 

[Phil]

Mudgey
I would doubt that a set of wishbones fabbed from 4130 tubing would be heavier than aluminum units. Besides the strength advantage, as Chris said I would worry about threads pulling out or possibly galling, and as many pieces as we have made from chromoly I have confidence in that material.
Aluminum tubing is light, but to gain the strength you require you would need a thick wall tube, thereby giving up some of your weight advantage...and still not as strong as the alloy steel. This is why all the billet units you see are very substantial with large cross sections. I will say they look great, but for me its the chromoly pieces. I would think a competent fabricator in your area could make a real nice set of wishbones for your project.
Cheers
Phil

 

[Mudgey]

Hi guys, thanks for your reply's and highlighting these issues to think about. I'm only in the early stages of my build atm and am still throwing ideas around, to save more weight what are the pro's and cons of building an aluminium tube/box section chassis?

For instance i was looking at T6085 alloy and apparently it has a tensile strength of 360gpa compared to 260 for mild steel, however i could not find equivilant price but it did say that the alloy was 35% that of steel. They mentioned that this alloy weakens around where its welded, is this the same for all aluminium alloys?

 

[Fred W Ballinger]

Difficult to design and fabricate a safe reliable aluminium tube chassis.

Comes up quite often on Locostbuilders.co.uk in a 7 contect, See typical thread here

LocostBuilders

Cheers

Fred W B

 

[Mudgey]

Sorry, i mean 35% weight of steel.
Thanks for the link, i shall check that out.

 

[Scott Calabro]

C/F wishbones would be the ultimate, :idea:
hmmmm......

 

[fostereast]

Several considerations are

Fatigue: Aluminum has no fixed stress limit for fatigue like steel
Corrosion: depending on the galvanic of touching materials
Failure: Mild steel may help prevent a catastrophic failure condition, where aluminum unless it's designed properly or clearly overdesigned can fail "all at once." Usually mild steel will bend and work harden and give you some time to realize something is not right. To make the wishbones out of aluminum tubing mght not be that practical when you look at the acceptable deflection, stresses and fatigue. Expansion and contraction may also play a part if anything gets hot when being run hard also.

I know Kirkham and many guys are making really nice billet aluminum suspensions and I suspect they put a pretty good amount of design work and analysis into them. Also, I suspect the mild steel cobra suspension Kirkham charges a bundle and then some for is as light as the aluminum billet suspension he sells

Regarding carbon fiber, the corvette has/had a fiberglass leaf spring, but I suspect millions of dollars went into the R&D and testing before it was put in a car, and carbon fiber tubes can probably break or explode if a rock propeled from a tire on a car in front of you can hit it just right and at just the right time.

 

[Scott Calabro]

Fostereast,

Tubes aren't the only option but I know they would work well!

A monolithic C/F layup could also be CNC machined to the appropriate dimensions.

S

 

[Randy V]

C/F wishbones would be the ultimate, :idea:
hmmmm......

Not for the street... Too brittle even for competition unless reinforced substantially with Kevlar..

But then - you knew that!

 

[Scott Calabro]

Nah, but that type of fabric does look cool!

Probably just some Mil-Spec C/F with stainless angles (read bungs/ends), and maybe some simple impact protection.

I really do like the idea of a monolithic cnc'd part as well, probably something with a 70 % - 30% fabric to matrix ratio...

S

 

[Ron Earp]

I know Kirkham and many guys are making really nice billet aluminum suspensions and I suspect they put a pretty good amount of design work and analysis into them.

I don't think I'd worry too much about aluminum arms/suspension failing. GM, Ford, and others use extensive amounts of aluminum arms in cars, from mini vans to Corvettes and the cars are much heavier than what we deal with. I just just admiring the nice aluminum pieces under a Buick minivan (SUV crossover thing) the other day.

On you get your design setup in CAD for CNC production you can easily send the same design out for finite analysis. Once all designed you'll be able to pop them out, identically and with high quality, quite easily with no worries about welding, cutting, etc. That way you'll be insured to have a high quality piece designed as you need with whatever strength you desire.

R

 

[Darnel A.]

Funny you should mention production cars using alum A arms. The first Ford GT's were recalled due to aluminum A-Arms failing. Also, production vehicles used FORGED A-Arms, much stronger!

 

[Andy Sheldon]

Forged is the only way to go with Aluminium suspension components and anything screwed in should have a corse thread and be Heli coiled.

 

[flatchat(Chris)]

Agreed Andy --- Corvette stuff is all forged.

For strength, durability and lightness the fabricated tubular chrome moly is probably the best -- its been done/around for at least 40 years

 

[Scott Calabro]

Damn!

So now we are not going with the 18oz. C/F arm with the carbon-carbon matrix :worried: ?

While we are at it, what happened to the uprights autoclaved from the monofilament silicon carbide fibres in a titanium matrix?

You know that material/process we saw last week at Lockheeds shop in California?

Ooops! :lipsrsealed:

Also are the uni-directional fiber, Boron/ceramic engine bay heat shields gone as well?

:shrug:

S

 

[flatchat(Chris)]

---- and all mysteriously created by laser fusion or the like ( it is happening) --like the way you're thinking Scott but we're only trying to recreate a 60s dinosaur here:worried:

 

[Scott Calabro]

Chris,

A little tomfoolery never hurt.

Besides, the paddock is not the only place humor is found on this website.

I just like to "push the envelope" so to speak.

Just to see if everyone is awake.

Cheers,
S