Re recent thread on wishbone failure, it strikes me the Locost market id big enough to support the manufacture of cast alloy wishbones. The pattern wouldn't be difficult and made in heatreated LM25 or similar they could be made more than strong enough without looking crude.

I'm no expert but wouldn't they be heavier than tubular jobies? Also, heat treated or no I think casting tend to snap in crashes rather than bending (& thus absorbing the impact), don't they?

My primary consideration would be the cyclic fatigue of aluminium control arms. Granted many manufacturers use them these days, but they also have vast testing budgets. Seems you could design closer the the limit, and thus lighter with steel, whihc below a certain load has pretty much infinite fatigue strength. But if its within your capabilities, more power to you and best of luck! Cheers!

Fair point, the materials are rather different in fatigue, alloy a bit less predictable in this application.

We use aluminium alloys for wheels without worry -- Although I have seem fatigue cracks in a wheels -- ancient Brabham single seater wheels that had done a lot of racing miles on a car heavier than it was designd for.

I mentioned LM25 because it is heat treatable -- and perhaps the best cast alloy where toughness is required, and the fatigue life should be very long provided there is proper attention to detail particularly finish and corner radi

Didnt the e type have cast alloy wishbones?

All manner of cars have had alloy wishbones (Corvette, Subaru Impreza etc etc ) but they are the same weight as well designed steel ones, if not heavier. Same with wheels, alloy ones with the same strength as steel ones are heavier than the steel ones! Always puzzled me, the "light alloy" wheel!! (I know there are many light ones, but most cast alloy road car wheels weigh a ton!)

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Originally posted by NS Dev
All manner of cars have had alloy wishbones (Corvette, Subaru Impreza etc etc ) but they are the same weight as well designed steel ones, if not heavier. Same with wheels, alloy ones with the same strength as steel ones are heavier than the steel ones! Always puzzled me, the "light alloy" wheel!! (I know there are many light ones, but most cast alloy road car wheels weigh a ton!)

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I would tend to agree with your arguments about it being stronger in bending due to the higher I (second moment of area) value dominating the equations....

By making it 3 times thicker you increase I by a factor of almost 30 times! (In sheet anyways) This more than accounts for the 3 times reduction in youngs modulus between aluminium and steel! But then you have wishbones that weigh the same as steel ones and if they were cast you cant make them hollow...they would be solid so would weigh even more!....what thickness would these ali wishbones be?

You could make some welded ali wishbones from 3mm wall tube maybe? (they would be lighter and stiffer) Or does the welding have too much of an effect on the structure and properties of the material to do this?

But i would be dubious about the fatigue properties of aluminium, that would be my only concern.

Cheers,
David

[Edited on 23/5/04 by flak monkey]

I cannot imagine that a 3 mm wall Al. tube wishbone would be as "strong",whatever that may mean,as a mild steel tube of 2 mm wall.
With proper (heat) treatment welded Al. can be brought "close" to it's original condition.
It is possible to cast hollow sections...but not at a locost price!
Titanium was develloped to overcome the "misleading weight" advantages of Al. in structural parts and even that is not the "magic" material!
I believe Titanium has about the same elasticy modulus as mild steel so that's not something to bragg with aldo the permanent distortion factor is much higher...i think

For the homebuilder, to many unpredictable factors are involved in the developement of cast wishbones so i would not spend money/time in such a thing,but...who am i?

You are quite right, that's who you are!!

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Originally posted by flak monkey
...if they were cast you cant make them hollow...they would be solid so would weigh even more!....

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Yes what you say is very true and something i hadnt really considered....

But to be honest I would rather stick to steel wishbones that have been tried and tested and save weight elsewhere with alloy components. (Uprights, floor etc)

Just IMO...i see nothing wrong with the idea however...

Cheers,
David

Very good note Aloupol, excellent suggestion. Thinking back, I believe a manufacturer or two does that exact thing. Cheers!

When dismanteling the rear end for my diff/halfshafts/uprights from the Mercedes in noticed that there were some short sort of trailing arms in steel shaped in I form.
Those things are stroooooooong!!!!

For the flexion I-shaped section is perfect. Poor in torsion but there's no torsion here. For buckling nothing is beter than a rould tube..
I think welded steel tubes can do it perfectly but why not..