Aluminum frame sports racer?

I'm thinking about building a budget mid engine track car. Think along the lines of a LMP2 looking and sized car, but the low bucks version. Powered by a simple SBC or SBF. I like the idea of a two seater.

I think some sort of backbone frame might be best. I've been poking around for designs but haven't seen any yet on the web. I've also been reading up on the various methods of bonding aluminum.

Anyone have any thoughts on this? Doing most of the work myself, I wonder if $15K is a reasonable budget. All comments welcome, including you're crazy

J

something along the lines on a Radical?

The fatigue properties of Aluminum make this a harder project than a steel frame. If you are building your own frame I'd say go with steel.

Steel is a helluva lot easier to fabricate. "Bonding" aluminum is spelled TIG, not an easy art to learn. Aluminum is also a good bit more expensive. Body panels can be easily made of aluminum, or FRP, to save weight.

You could scale-up a LeGrand pretty easily. It's an all aluminum monocoque center section that is formed out of .050" 6061 T4 aluminum sheet that is riveted together. The monocoque is then riveted to front and rear steel bulkheads/rollhoops.

Front roll hoop ties into front steel 1" square framework that supports front suspension. Rear (main) roll hoop ties into rear 1" steel framework that supports drivetrain and rear suspension.

cwh wrote: Steel is a helluva lot easier to fabricate. "Bonding" aluminum is spelled TIG, not an easy art to learn. Aluminum is also a good bit more expensive. Body panels can be easily made of aluminum, or FRP, to save weight.

Ehhh, I wouldn't worry about the tig part... Besides MIG can do aluminum too.

I would worry to some degree about the fatigue as mentioned before... But mostly about the fact that as soon as you weld it the HAZ is effectively normalized and has to be re heat treated.

Heat treating an entire frame does not sound "budget" to me...

RedS13Coupe wrote: Heat treating an entire frame does not sound "budget" to me...

Depends on just how good a kitchen oven he has.

For the average goober like me, I'd go mild steel too. Aluminum is great stuff but IMHO a bit tough to make a complete frame of, unless you can cast bulkheads and stuff like that. Toyman and I have been bouncing A Mod ideas around and keep coming back to a tube steel roll cage with suspension attachment points, think a rail dune buggy frame.

A backbone or monocoque type frame is certaily doable, but you have to carefully consider the loads a roll cage would pass and would those loads punch through sheet aluminum?

If you are set on such a project, there are structural adhesives out there to bond aluminum together. That and some serious rivets (like aircraft rivets) would make for a very strong tub.

What's your prioritiy?

Do you want to build something and drive it fast, or do just want to drive fast?

Without knowing your answer, I'll suggest an existing car can easily get you on track within your stated budget. There are any number of Sport Renaults/Fords, S2000's and C-D/sr's on the market.

Get a car, sort it out, get it on the track, then make the changes you desire. Unless you already have the knowledge, skills, time, money and resources to build a car, go with one that's already built.

YMMV!

Per Schroeder wrote: You could scale-up a LeGrand pretty easily...

That would be called a Quasar. Built by Paul Van Valkenburgh. Very similar construction to a LeGrand Mk18 or Mk25, but scaled up a bit. Oddly, it used 10" diameter front wheels to reduce frontal area.

Check out this aluminum monocoque build by a University from Oz.

Trev Part 1

Trev Part 2

Basically an aluminum honeycomb monocoque bonded together with epoxy. I doesn't take too long to draw it up in Solidworks and have it run some basic FEA on the the suspension points. I have a vision for a road going 3 wheeler with a 600/750cc sport bike engine instead of the dinky electric motor. The thing weighs less than 600lbs so 100+hp would be wild.

Forget welding, take a look at how aluminum airplanes are designed and built. Do you have access to airframe maintenance equipment: Large shear, large bending brake, riveting tools? Do you know how to properly install rivets? Do you know how to design aluminum monocoque structures? Do you know where and how stiffening ribs should be placed? Do you know how to properly design a riveted joint, including the size, placement, and number of rivets? Do you know how to calculate the centroid and radius of gyration of an extruded aluminum stiffener in order to determine if it is correct for the structure? Do you know what the various aluminum alloys are, and which ones should be used for a particular purpose? If you have an off, and tweak your monocoque, are you prepeared to write it off and build a new one?

Just sayin ....

Carter

I think it can be done. I don't think it takes a PE to design a chassis that will serve well. Will it be optimized? No. It's the naysayers like the above (apologies, brother, but come on- how many people who build locosts actually know how to weld? How many chassis fail? How many people die?) that make me want to join you. I'd go with the solid structural rivet- learn from an A&P and some epoxy bonding material a la Elise.

And to add to my "how many" parenthetical rant, there are plenty of homebuilt aircraft by amateurs who don't have welding certs. I don't believe that real people can't do it. They just can't do it with the high $$ assistance that most F1/commercial entities have. Ever heard of Britten motorcycles? This guy started from pretty modest beginnings.

http://www.britten.co.nz/

Robin Hood in the UK made a Seven with aluminum - not sure how well regarded it was.

Wisdon is gained through experience. Experience is gained through a lack of wisdom.

Real smart people told Mr Chapman that a all fiberglass coupe would never work. While it might be a correct statment, he went and did it anyways. Once. Was not a wise thing to do. Dude still did ok with his life.

Draw the thing up. I would do it out of flat sections welded together. Tig welders are not very expensive and will serve you for the rest of your life, so a good nvestment.

Once you draw this thing out, have someone water jet cut the parts. Once again, not that expensive for the results you get. Water jets are not the oddity they were five years ago and prices are down due to lack of work in manufacturing.

Buy a good set of dimple dies; you are going to want a few access holes and these look good and keep some rigidity in the panel.

Panel adhesive where you don't want to weld.

Never heard of heat treating aluminum after welding. Have had to preheat to get the stuff to weld, but not heat stress relief like with chrome molly and DOM mild steel. Would love to learn more about that.

Sorry, but I would not MIG anything aluminum if it were structural. Just me but I dont see the penetration like with TIG. Not saying it wont work, just that I have no experience with it.

So start drawing and post up so we can see what you are thinking.

Pete

Thanks for the feedback so far.

Can you braze aluminum? I don't think so, but just asking. Could you bond the frame with a combination of that, adhesive, and rivets?

I'm still fleshing out this idea myself. Don't know what I'd do with the car when done, track days, autocross, who knows. I've loved sports cars since I can remember, Can Am (I was to young for the heyday), IMSA prototypes (I got to sit in the late Al Holbert's 962 once), and now the current LMP cars. I just want to do this if it can be done and I can do it.

Herb Adams in his Chassis Engineering book has an aluminum backbone frame that weighs less than 200 lbs and was designed to fit under Cobra bodywork. That's what got me thinking.

I'll try to get some drawings up sometime soon.

Start with an Elise. Not too much wrong with that chassis. There is room in any car for a V8. You can do it, but it will be way easier and cheaper to start with a known quantity. -Brian

NOHOME wrote: Wisdon is gained through experience. Experience is gained through a lack of wisdom. Real smart people told Mr Chapman that a all fiberglass coupe would never work. While it might be a correct statment, he went and did it anyways. Once. Was not a wise thing to do. Dude still did ok with his life. Draw the thing up. I would do it out of flat sections welded together. Tig welders are not very expensive and will serve you for the rest of your life, so a good nvestment. Once you draw this thing out, have someone water jet cut the parts. Once again, not that expensive for the results you get. Water jets are not the oddity they were five years ago and prices are down due to lack of work in manufacturing. Buy a good set of dimple dies; you are going to want a few access holes and these look good and keep some rigidity in the panel. Panel adhesive where you don't want to weld. Never heard of heat treating aluminum after welding. Have had to preheat to get the stuff to weld, but not heat stress relief like with chrome molly and DOM mild steel. Would love to learn more about that. Sorry, but I would not MIG anything aluminum if it were structural. Just me but I dont see the penetration like with TIG. Not saying it wont work, just that I have no experience with it. So start drawing and post up so we can see what you are thinking. Pete

Re-heat treating aluminum is not the same as stress relieving steel post weld. With out heat treatment even fancy alloys of aluminum are pretty damn weak for a structural member. When you weld the aluminum you kill the prior heat treatment, and wind up with severely weakened spots around the welds.

I agree he shouldn't be discouraged by the nay sayers...

But he shouldn't start dumping money into water jetting and barrels of industrial adhesives when he doesn't doesn't understand what he is up against. Colin didn't just run with some crazy idea simply because they told him not too, he did it because his experience and knowledge told him he could. Very different things.

YaNi wrote: Check out this aluminum monocoque build by a University from Oz. Trev Part 1 Trev Part 2 Basically an aluminum honeycomb monocoque bonded together with epoxy. I doesn't take too long to draw it up in Solidworks and have it run some basic FEA on the the suspension points. I have a vision for a road going 3 wheeler with a 600/750cc sport bike engine instead of the dinky electric motor. The thing weighs less than 600lbs so 100+hp would be wild.

Very cool, but I don't know that it proves much. They show no numbers for torsional rigidity, and have no info on how well it holds up to miles of rattles.

Its just a bunch of engineering students at school trying something, that doesn't mean it works well, or better then standard methods.

I can go to school, open our lab and start gluing together compressed saw dust talking about how it forms a composite material with the resin and going on about the strength of a single cellulose fiber of spruce.... They aren't really making a race car, they are making a super mileage cruiser, so what is good stiffness for them may not be good for corner carving either.

It seems like making an aluminum frame for the sake of making an aluminum frame. If you just want to do something different, I guess go ahead... but if you want something that works well at least START OFF with what has been proven, building any car is a major undertaking and there is time to try other ideas on future iterations.

In reply to Brust: The point of my posting is not that it can't be done, but that it takes a lot more than just throwing some aluminum sheets together into something that 'looks right' to get a good result. Building an aluminum monocoque is basically technology from the 1940's and 50's. It's been figured out, to the Nth degree. But it's not simple, it's the result of millions of man hours of trial and error, mistakes, and analysis of crash results. Let's be clear here, do it wrong, and someone can get hurt or killed. There are good reasons why the majority of purpose built racecars in the world use welded steel tubes: Steel tubing is tough and strong in several dimensions - aluminum skin only in tension and shear. Steel tubing is easy to design into structures, easy to build, and easy to fix - aluminum skin requires more complex analysis and design, more tooling and labor to construct, and is more difficult to fix. Steel prototypes are more forgiving of changes, cut off the localized mistake, and weld in the solution - aluminum skin may require scrapping, re-engineering, and start over.

The OP asked for feedback and opinions, (to quote, 'Anyone have any thoughts on this?'). I raised several practical issues that he will have to address in order to be successful. There is a similar list, should he choose to go with steel tubes.

As for homebuilt aircraft, I believe you will find that none of them are allowed to fly before a series of thorough inspections and certifications for airworthyness are performed.

The OP will make his own choice. If he's really got the fire down below, he will do the hard work of learning enough to make his project a working reality.

Carter

You'll need a 6' shear and brake, dimpling dies (which you can fake sometimes) rivet setting tools, and practice. TIG welder is all but essential, painstaking layout skills.

I design stuff made of sheet metal for a living, and it has to be unbelievably cheap to manufacture and hold pretty tight tolerances. I'm in awe of the quality sheet metal shops are capable of thats consistent over 10s or 100s of thousands of parts, and they do it so cheaply.

I've got a 4' shear and brake at work and little 1950s DiAcro shear, brake and notcher at home. Still it takes me freakin' forever to make stuff that fits perfectly and looks like it came from a good race shop.

My next car is stacked in the garage and it's a pile of 1" and 3/4" 16ga wall 1020 square tube.

Dude, I'm a professional pilot (with an ME degree) who flies an aluminum battle tested airplane (c-130- you may have heard of it) designed in 1950. I know the issues. I also know that rocket scientists didn't build it and don't maintain it. I also don't believe that someone will get killed with a well thought-out and less than FEA perfect design. I agree that its been figured out- why do you think that most vehicles on the road are essentially monocoque construction- unibody. Why not tell the guy- yeah, there's certainly some challenges, yes, probably not the best $$/benefit ratio, try to design it safe and go for it. Seriously- compare to some of the well-meaning amateurs building locosts (again, not to bag on these guys, cause I'm partially one of them) and tell me about safety.

My opinion- we didn't build this country on people playing it safe. One man's monocoque changed the automotive industry. And I think you'd be pretty surprised what those aircraft inspections entail. Yes, they're thorough, but they aren't comprehensive (NDI, etc).

Them more people who tell you that you can't do it, them more it satisfying it is to prove them wrong.

NBS2005 wrote: Can you braze aluminum? I don't think so, but just asking.

Yes - http://www.weldguru.com/braze-aluminum.html

As for heat treating aluminum, even professional and experienced shops can utterly destroy parts. Several years ago, I did design support for the Columbia accident investigation. We sent some aluminum parts (I forget the spec.) to a vendor for heat treat. The parts came back with surface bubbles and as fragile as glass. Say goodbye to $20k of taxpayer dollars.

With extremely rare exceptions, NASA does not allow welding of aluminum because of post process heat treatment, weld inspection, porosity, etc.

One exception is friction stir welding: http://en.wikipedia.org/wiki/Friction_stir_welding

The weight advantage of aluminum is more than offset by the robustness, strength, cost, and construction simplicity of steel.

With the economy as it is, race cars can be had stupid cheap. I saw a race ready Formula Renault for under $4k the other day. Another friend sold his Race Camaro for less than he paid for the shocks. Build if that's what turns you on, but realize that's the much more difficult road to travel - especially going aluminum.

In reply to Brust: First off, I never said that the PO couldn't, or shouldn't do it. Second, as an ME, you ought to know better; the reason the Herc is so good is precisely because the Lockheed 'rocket scientists' throughly understood the problem domain, and invested the engineering time and effort to make it perform and be maintainable in the battle environment. Third, I never said anything about it being perfect, I just hope it's safe enough not to fold and ball the dude up into an aluminum coffin the first time it drops a wheel into a chuckhole in a 1G corner. Fourth, Most vehicles on the road today are welded pressed steel unibodies, not aluminum monocoques. Take a look at the millions of $$ worth of man-hours to design them, the millions of $$ worth of presses used to make the panels, and the sheer number of units built, and then explain to me how that relates to what the PO wants to do? Fifth, the last time I looked, most Locosts were based on steel tube frames, with some stressed skins. Sixth, Colin Chapman was a gifted, degreed engineer and pilot who served in the RAF, and worked in the aeronautical industry before making Lotus his fulltime gig. Lotus designed and built many tube framed cars before the 1958 Elite, and only afterwards in 1962 did the monocoque racecars follow. Given his training and years of experience in the automotive problem domain designing, building, and racing, he is probably as far from the 'one man, gifted amatuer against the nay-saying world' that you could find. Even so, the Elite was a wonderful example of innovative high tech engineering that was a commercial failure. If the method was so great, why didn't Lotus continue with it? Why are so few cars built that way, even today? Seventh, I think that the USA (I assume you are American) was built on success, which is often the result of well informed risk taking. But we are currently suffering an economic disaster which is due to a lot of folks ignoring the risk, even when they really did know better.

I didn't start this post as a rant, and I don't mean it that way.

Building any car from scratch is a major undertaking. If the OP has his heart set on building an aluminum monocoque, so be it. But he asked for our comments and advice.

Carter