New metal, thickness?

[Tinkley]

My point is that actually you can have light modern cars - just use composites. Stronger/stiffer and with the ability to put in structural deformation ie crumple on impact. I would not mind 'jumping' to say a fuel cell powered carbon/glass structured vehicle at all. Personally I'm not convinced by the heavy battery carrying 'Hybrids' as they are a halfway house. Would quite like to try the Cyclone 5 steam powered engine in a composite car, I could even make my own wood pellets!

Agree on visibility being good on a BX. You don't notice it much till you drive something else like a C4 or are a passenger when the pillars and positioning create much larger blind spots. My old Chrysler (later Talbot) Sunbeam was very good for visibility, much like a shorter BX.

Another little gripe is the boot width - 1.25m plywood - straight into a BX. Try that on a few modern ones especially VW group cars. Guess its the same roof strength problem. But a good tubular or specially formed tube structure could take the load quite easily as could a hollow composite tube.

Thanks for the imput on steels, like other materials the alloys and heat treating make very significant changes to the tensile strength etc of the material. Note that molybdenum steel m/cycle frames have a life of 3-4 years.... Classic 'E' modulus fall off after so many cycles.

Of course if the MOT tester found steel in the body of the new McLaren in the rear sub frame area...!

[KevR]

If you're going to weld galvanized, don't forget to grind (or better, use a flap wheel so as not to thin the edge too much) all the galvanizing off the bit you're actually welding. Treat with a weld-through coating before welding.

[mat_fenwick]

The thread was supposed to be about steel thicknesses however!

True, but we're not all that good at staying on topic here! To my mind it doesn't really matter once the original question is answered - the thread can drift off at a tangent like a conversation in the pub would...

One of the downsides to higher strength alloy steels is that corrosion protection becomes even more important - once rust starts it obviously takes less time to eat through a thinner/lighter section. And what about the fatigue life of aluminium cars like top end Audis? Aluminium alloys have significantly poorer fatigue strength than steels.

[Tinkley]

XM trailing arms? The BX got ductile cast iron but the XM to save weight got ...... aluminium.
Suzuki used AL on a lot of early GSX750's in the 80's, don't know how they fared. AL is fine on body non structural panels, hell my old mans Rover 90 had AL panels in 1959!. Copied by Citroen on C4 and C5 but as much to do with pedestrian crush zones as saving weight. Pesky Euro NCAP ratings.

[Vanny]

Aluminium alloys have significantly poorer fatigue strength than steels.

But when structured correctly, are much more flexible. Just look at an air craft wing, they spend there entire life bending up and down, and don't tend crack/fatigue/fall off. There have been high power alloy cars on the road for over 10 years without too much of a problem.

[mat_fenwick]

Just look at an air craft wing, they spend there entire life bending up and down, and don't tend crack/fatigue/fall off.

But when they do...

Yeah, I'm not saying it's a bad thing at all - I was just thinking it would be interesting to know whether fatigue is a realistic consideration in the lifespan of an aluminium bodied car. I'm talking 30-40 years down the line - is it likely to be an equally big problem as rust would be on a steel bodied car?

[Way2go]

Just look at an air craft wing, they spend there entire life bending up and down, and don't tend crack/fatigue/fall off.

Not strictly true is it? A number of aircraft have been taken out of service due to cracks developing.

I remember being marooned in Edinburgh for a day years ago when BA grounded the entire Trident Fleet for checks as fatigue cracks had been detected in their wings. Although they subsequently patched this it didn't last very long before the whole Trident Fleet was scrapped, not sold to a 3rd world country, such was the likely severity of the problem.

Concorde also suffered quite large cracks in all it's wings and probably many other aircraft types did too.

[Vanny]

Not strictly true is it?

I'm not sure what you think is 'not strictly true'. Perhaps you don't like the use of the word tend? It's not a great word, having different interpretations, but statistically of all the ally flying machines that have ever been in the air, have fallen out of it due to a metal defect? I cant imagine it's many! (actually i hope to hell its not many, i do a lot of flying)


I suspect on an all ally car there will be problems with repairs making the car brittle in places, and a lot of problems with galvanic corrosion. And ally will still oxidise in salt, and at a fair old rate when it gets going. I guess that's part of why they paint planes so often.

[Way2go]

Not strictly true is it?

I'm not sure what you think is 'not strictly true'. Perhaps you don't like the use of the word tend? It's not a great word, having different interpretations, but statistically of all the ally flying machines that have ever been in the air, have fallen out of it due to a metal defect? I cant imagine it's many! (actually i hope to hell its not many, i do a lot of flying)

No problem with the word "tend" but I gave you actual cases of Trident and Concorde that were grounded as a fleet due to wing fatigue initiating cracks that were serious enough that there were fears that they (& their passengers) could come to grief in flight.

So two conditions were not true but the wings actually falling off have not been reported. However, they would not have been expensively repaired before being allowed to resume flight if that was not a possible prognosis.

Aluminium is used because it is light and apart from getting off the ground obviously allows a larger payload than a heavier infrastructure. Dreamliner has gone lighter still with a higher proportion of plastics etc - I wonder how that will fare for stresses after it gets millions of miles into its service?

[citsncycles]

When I worked for BAe Aviation Services we used to have to modify the wing roots of A300's as they were prone to cracking round the mounting bolts. They apparently modified the design for the A320 series, only to leave them prone to spar cracks.

Concorde's biggest problem was cracking at the base of the tail fin. They had a prototype at Filton that they ended salvaging the fittings from in order to keep the BA fleet flying a little longer.