Box Plate Chassis

[Bobber]

As you know, I’ve been experimenting with an aluminum plate box chassis (similar to an aluminum boat). I sent the attached sketch (with CAD files) to Waterjet West and got a price for supplying all the aluminum plates, waterjet cut to size ready for welding for US $950.

[mkejim]

What is the weight?

[TooBusy]

Check out Pirate 7
http://www.pirate7.com/9.html

I think Lance still has a couple of flat pack kits available. The issue I had with the Centaur was being able to shoehorn in something other than a Mazda rotary. I managed to squeeze a 2TC in after modifying the cross member and tunnel.

[wrightcomputing]

Be aware that an aluminum chassis is not legal for most Motorsport clubs including SCCA. The chassis needs to be ferrous metal for nearly all classes.

[rx7locost]

I can't comment one way or the other. IIWM, I would be very nervous. 1st with the monocoque design; 2nd using aluminum; and 3rd welding it. But if you do a search on this site, you can find more knowledgeable comments on building with aluminum. It has been discussed many times before.

You might want to check out Kartracer47's build. It may be of some inspiration. He built an Aluminum monocoque middy some years back. It used a more traditional steel-tube front and rear sub-frames. It was a great non-traditional build! This is the only aluminum build that comes to mind.

http://www.locostusa.com/forums/viewtopic.php?f=36&t=10658

[KB58]

A couple more things:

1. No rollover protection, where's that going to come from? If it's a steel tube, does it extend to the floor?
2. Aluminum expands a lot with heat, how will you maintain alignment during welding?
2. Aluminum goes dead-soft when welded, are you planning on heat-treating it?
3. When being heat-treated, the chassis will undergo major warpage; how do you plan to rigidly hold the chassis as it heat cycles?

[RichardSIA]

Welding?

Maybe better bonded and riveted?

[Bobber]

Good comments all.

To further our aluminum discussion:
As a structural engineer I used to design aluminum equipment used for our underwater diving operations: underwater access platforms, equipment positioning booms, etc. Aluminum has it do’s and don’ts and I learned them over the years. There are aluminum design codes and I follow them religiously. Gentlemen, do not be afraid of aluminum!

The design of this thing is controlled by torsion. This creates the highest stress and deflection. In this design, all stresses are kept below Aluminum Association allowable limits for welded structures and structures subject to fatigue. Allowable stresses are also below the buckling limits for the individual panels so buckling will not occur (this is important for stiffness and additionally provides post-buckling energy absorption). The maximum stress in this structure is axial shear along the longitudinal joints parallel to the chassis, with the highest stress at the driveshaft tunnel. These joints could be welded, bolted or riveted; welding is the cheapest. There will be access openings (not shown) for access to all joints for welding or riveting (bucking). Munson Boat Works in Seattle showed me how they weld boats to avoid distortion so that’s no problem.

Details on the chassis: Current weight as shown, about 200 lbs. I have designed access openings (not shown) that will reduce this. Torsional rigidity as shown is 12,000 ft lb per degree. This will also be reduced with the access openings. On my designs, I design for excess strength first, then start trimming weight to reach the minimal required strength.
I have a roll cage designed (1.75” x 0.120” DOM per rules) but it looks funny and I need to improve it. I didn’t know about the prohibition of aluminum in SCCA. Well, there are venues just across the border in TJ.
I’ve also set this up to use that Camaro IRS cradle that I posted somewhere else. I have a similar cradle for the front suspension. This would be similar to the Kartracer build.
I’ll attach a drawing of this later.

This is really just a mental exercise for an old engineer. Neuropathy (thank you agent orange) is starting to make anything unbuildable for this old body, so now I just build ‘em in my head. I just bought a new drill press because I can barely hold a hand drill. But with years of hand drafting, I can still scribe a fine line in Dykem.

Keep Building!

[horizenjob]

Every approach has it's down sides. They weld large aluminum boats so I don't think that will ruin it. Putting rivits in involves drilling holes in the structure, that will weaken it too - it's just allowed for in the design.

I was going to mention you could weld items like channels and square tubes to the plates, but now I see there may be something like that around the cockpit already.

[Lonnie-S]

It's a very interesting concept, Bob. Because I don't have the equipment or skill to weld aluminum, I would be inclined to do adhesives and rivets if it were for myself. The big issue as I understand monocoque is handling the point loads and integrating them into the "pure" chassis. For example, the mounting locations of the suspension arms and coilovers, etc.

But, if you're building it in your head, no problem [SMILE].

Cheers,

[Bobber]

Here’s the box chassis with the Camaro IRS cradle. I did a similar cradle for the front suspension. These are based on the cradles I’m designing for rat rod guy so they are heavy iron right now. I will redesign them in aluminum and make them lighter.

[BHRmotorsport]

Be aware that an aluminum chassis is not legal for most Motorsport clubs including SCCA. The chassis needs to be ferrous metal for nearly all classes.

What is SCCA doing about the current Corvette, Ferrari, Lotus (and maybe other) cars that are aluminum? There have been aluminum monocoque chassis sports racers and formula cars racing for decades. Has something changed?

[BHRmotorsport]

You might want to check out Kartracer47's build. It may be of some inspiration. He built an Aluminum monocoque middy some years back.

Don't forget airframe fixer's build....it was/is incredible!!

[wrightcomputing]

Below is the actual rules that I was referring to. This is in the Solo II modified section (Autocross) where our cars compete. Here is a link for the entire rule section.
http://cdn.growassets.net/user_files/sc ... 1458857794

18. 3. Materials (all tubs)
a. Ferrous metal (containing iron) must be used for all primary load
bearing structures of the car. The primary load bearing structure is
the main tub or chassis and its connections to the suspension. No
aluminum cages or roll bars are allowed. Any ferrous or aluminum
alloy is permitted for suspension arms, location links, and uprights/
spindles. Beryllium and beryllium alloys are not allowed anywhere
on the car.
b. The exceptions to the above are parts of the donor production cars
that were originally non-metal. In all cases, replacement of these
parts or addition of more load bearing structure must be by metal.
Lighter replacement sections may not be used between bulkheads in
a Stock Tub without it becoming a Modified Tub.

[cs3tcr]

wrightcomputing,
I interpret those rules as, if the car is a Lotus 7 clone then it can't have aluminium as its structure. But if it's not a Lotus 7 clone, but a special, then it is allowed to have aluminium or any other material for the chassis provided it's not a tube frame chassis. If this isn't the case, then any carbon fibre/etc formula car/sports racer isn't allowed to run, which I find highly unlikely.