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Aluminum frame - Is this a bad idea?

Discussion in 'The Hokey Ass Message Board' started by oldcarmike, Sep 4, 2007.

  1. OK, here's the question: Can a frame and cross members be made of aluminum or is that material just too prone to fatigue to be safe?

    I'm thinking about a lightweight 4 cylinder streamliner for the streets; aluminum skinned with an aluminum skeleton like an aircraft or cloth doped covering. Very lightweight and narrow. I'd like to keep the thing under 1,000 pounds. Would the weight savings of aluminum be worth it?

    I'm figuring that this is a bad idea due to fatigue and resulting catastrophic failure, but I could be wrong. Wadda ya think?
     
  2. oktr6r
    Joined: Feb 14, 2006
    Posts: 724

    oktr6r
    Member
    from Tulsa

    I'd avoid it myself. Depending on the donor engine / transmission, you should be able to build a car that weights less than 1,000 lbs using steel for the frame. I'm building a single seater to look like an early Indy car. The major components weight in as follows:

    Frame 125 lbs (calculated from tubing used and rounded up)
    Engine and trans axle 300 lbs (estimates provided by Fiat fanatics)
    Front suspension 75 lbs (My estimate, can easily pick up one handed)
    Tires and wheels 75 lbs (My estimated, 13" wheels and tires)

    I should be under 600 lbs at this point. My goal was 800 lbs, I may go over that some.
     
  3. Les, that's what I was thinking too. The frame takes up such little space that it wouldn't be worth it. But, I had to ask and now I know.

    I can't get this little one seater out of my head so I'm doing all the fab work and calculating in my mind's eye.
     
  4. xlr8
    Joined: Jun 26, 2006
    Posts: 700

    xlr8
    Member
    from Idaho

    One of the big name rod builders built a couple, I think they were called the Alumatub and Alumatruck (?). Virtually every part on them was Aluminum, it can be done.
     
  5. mpls|cafe|racer
    Joined: Jun 18, 2006
    Posts: 1,323

    mpls|cafe|racer
    BANNED

    I think airplanes are made of aluminum.... and they take more abuse, power, and fatigue than any car ever will. ;)

    It's all in how its built. :cool:
     
  6. DrJ
    Joined: Mar 3, 2001
    Posts: 9,419

    DrJ
    Member

    Focker triplanes were titanium upgraded design copies of (I think) a spruce framed Sopwith triplane they captured.
    I've been contemplating a Bamboo framed and airframe cloth covered trike myself, a HPV.
    It's all in the triangulation of the stressed parts, and adequate road impact isolation.
     
  7. I hear what everyone is saying but an airframe, I assume (there's that word) would take less vibrations and stress than a road going vehicle. My major concern would be suspension mounting points receiving vibration and work fatiguing.

    I'd sure hate a spring perch to let go at 80 MPH on the highway. When I build this thing it's going to be a driver.

    Would the weight savings be that dramatic to justify the use of aluminum?

    The means of making the body are open to ideas but the chassis needs to be safe and reliable.
     
  8. Unkl Ian
    Joined: Mar 29, 2001
    Posts: 13,509

    Unkl Ian

    If it was designed correctly,stressed skins riveted together
    would be fine.Construction adhesive also helps.

    Aluminum Monoque construction was commonly used in Formula car chassis.Labor internsive to make and assemble,but the strength to weight ratio is impressive.The other down side is they are bulky.

    DO NOT copy the Aluminum Tub chassis that Boyd's gang threw together.They didn't scale up the cross sections on the chassis,
    and their welding is suspect.

    Research aircraft construction before going too far.
     
  9. oktr6r
    Joined: Feb 14, 2006
    Posts: 724

    oktr6r
    Member
    from Tulsa

    You're headed down the same road I was. It took me 4 years of building it in my mind before I found the donor. I've actually extended the wheelbase from 79.8" to 100", but the overall length of the car will be very close to stock, 12' 6" approximately.

    I brought the donor home just about 1 1/2 months ago, this is where the project is right now...

    [​IMG]
     
  10. xlr8
    Joined: Jun 26, 2006
    Posts: 700

    xlr8
    Member
    from Idaho

  11. Unkl Ian
    Joined: Mar 29, 2001
    Posts: 13,509

    Unkl Ian

    The easy answer is to rivet Aluminum skins on a tubular space frame.

    Check out what the Locost sports car guys are doing with space frames.
     
  12. Stressed skin aircraft style construction is the way I'm leaning and I would be doing lots of research before I start any fab work.

    Rest easy, I will NOT be trying to duplicate anything the Boyd boys did. I'm thinking streamliner style, kinda like an Airstream trailer or an aluminum Twinkie with 100 HP.


    And xlr8 - that is THE longest fucking link I have ever seen.
    :eek:
     
  13. Prop Strike
    Joined: Feb 18, 2006
    Posts: 651

    Prop Strike
    Member

    For the small size and weight of your project, seems like a well designed aluminum frame would work fine. I'm no engineer but plenty of smart fellas on here that could recommend the best alloys to use.
    In the same breath, for the small size and weight of your project, seems like weight savings for aluminum over mild steel frame is probably negligible.
    Sweet sounding project, can't wait to see you build it.
     
  14. Appleseed
    Joined: Feb 21, 2005
    Posts: 1,053

    Appleseed
    Member

    Close. Fokker used steel tube in place of wire braced wood. Titanium and its alloys wern't used outside of the lab untill 1946.

    But I'd like to see an aluminum frame polished. That'd be rad.
     
  15. Appleseed - seeing the construction technique of the B-17 on the Reliability Run really got the wheel turning. Do you know of any good sources of info re: the Hows and Whys of this style of construction?
     
  16. telecaster_6
    Joined: Dec 8, 2001
    Posts: 657

    telecaster_6
    Member

    It definitely can be done. There are many subframe assemblies in current production cars made from aluminum....but you need to be very carefull with your design in both material and weld cross sections, as well as the grade of alumium, as well as your filler wires. I'd recommend buying some books on aluminum weldment fabrication and study up first. Properly designed, an aluminum weldment vs. mild steel, will yeild a weight of 2/3's that of its steel counterpart while still retaining its strentgh characteristics. Keep in mind though that aluminum has much different fatique characteristics than that of steel, so your design will have to be very well thought out. Also.....the biggest factor when welding aluminum is heat imput. Heat affected zones (the areas adjacent to the welds) are the weak links in a aluminum weldments..
     
  17. Unkl Ian
    Joined: Mar 29, 2001
    Posts: 13,509

    Unkl Ian

    The stock Prowler chassis is Aluminum.
    And the frames on a lot of Japanese Sport Bikes are Aluminum.

    The difference is, they have lots of Engineers
    and fancy Computers to make sure the frames will live.
     
  18. I'm a smart guy but I'm not an engineer (yet) so I'm thinking that a steel frame will be the easiest and safest way to go for my project. Saving 25 pounds at the risk of life and limb isn't worth rolling the bones on.
     
  19. 32v
    Joined: May 20, 2007
    Posts: 952

    32v
    Member
    from v.i.

    chrysler prowlers have alum frame
     
  20. Rootie Kazoootie
    Joined: Nov 27, 2006
    Posts: 8,130

    Rootie Kazoootie
    Member
    from Colorado

    Telecaster pretty much got it. Higher grades of ali are tempered (i.e. t-4 t-6 etc.) welding on these grades of ali. will affect the final strength of the weldment. A more practical material for the home builder would be small o.d., thin wall chrome-moly tubing in a space frame design (think birdcage Maserati.) JMO.
     
  21. sheepdog
    Joined: Jul 17, 2006
    Posts: 27

    sheepdog
    Member

    Some of these frames come in around 50 pounds.
    That will be tough to beat regardless of material.
     
  22. Appleseed
    Joined: Feb 21, 2005
    Posts: 1,053

    Appleseed
    Member

    Hey Mike,

    I'd try the EAA. They have tons of books that go over this stuff. From the basic to the advanced. Or try some books by this guy, Tony Bingelis. www.actechbooks.com/Bingelis. This dude wrote a load of stuff for the EAA's Sport Aviation.

    (why the hell is this green?)
     
  23. Of course!! The EAA... great idea! Thanks
     
  24. Flexicoker
    Joined: Apr 17, 2004
    Posts: 1,416

    Flexicoker
    Member

    It all depends on how you design it. Nothing in bending, double shear for all tabs/mounts, and NOT a ladder frame. An aluminum spaceframe would be bulkier than a steel spaceframe, with little weight savings. An aluminum monocoque is where its at. Look at old F1/Indy cars, airplanes, can-am cars, etc.
     
  25. If you are good you could build a frame from chrome-moly that weights in between 50 and 100 pounds. Rust resistant, welds nicely and will polish up like chrome.
     
  26. Ralph Moore
    Joined: May 1, 2007
    Posts: 663

    Ralph Moore
    Member

    Seen a lot of failures of aluminum frames on trailers. Just cant take the stress. I would stay away from alum if you plan to drive it more than once a year.
     
  27. zman
    Joined: Apr 2, 2001
    Posts: 16,790

    zman
    Member
    from Garner, NC

    If it has any flex aluminum will "work harden" and become extremely brittle.
     
  28. Kenworth had aluminium chassis rails as an option on highway trucks for years.
    I would lean towards good ol 4130 myself
     
  29. nexxussian
    Joined: Mar 14, 2007
    Posts: 3,237

    nexxussian
    Member

    All these are good points, if you want to check on Aluminum structure that was intended for high vibration and high impact, check any of the radial powered carrier aircraft. Anywhere near any of the attach points, landing gear to fuselage, fuselage to wing, engine to firewall. All had to be beefed significantly to take the vibration of the engine and the pounding it received on landing.
     
  30. I'd have to recommend the steel or Chromoly birdcage myself.
    My Locost frame, without the suspension and floor, weighs 35#.
    Thats 16ga one inch, rectangular Hollow steel.
    Take a look at an older Sopwith or DeHaviland, Space frame with cloth.
    Now, I'm off to check out the EAA website. Sounds interesing and my brother is getting into the R/C stuff, So it might come in handy.
     

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