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roverman
Art Gertz
Winchester, CA.
(2909 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Tube chassis with F-glass Body, 914 ish
Posted by: roverman
Date: April 30, 2014 01:59PM

My WAG. is F-glass to a multi tube space frame, should NOT be considered as a torsion/stessed member ? Considering a back-burner project of "Beck 914 kit",(best known for replica Speedsters), with other needed glass parts. This would culminate in a very light, exceptional powered and handling, 914 hybrid. Powertrain likey to be de-tuned 4.1L,stage II Buick V6,(273"), coupled to Toyota turbo MR2 t-axle,(transverse). I'm not yet ready for a Rest Home, but I do like to rest at home, Is that so bad ? roverman.



Edited 1 time(s). Last edit at 04/30/2014 02:04PM by roverman.


Moderator
Curtis Jacobson
Portland Oregon
(4372 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: Moderator
Date: April 30, 2014 03:08PM

There's no fundamental reason why your project couldn't include stressed fiberglass bodywork, but it's just so much simpler to create a stressed skin by joining sheet aluminum to your steel space frame using strong adhesives. Use Clecos for alignment and clamping during the fabrication process, and then replace the Clecos with blind rivets even while knowing it's the adhesive that really matters. Then, your fiberglass bodywork can very thin and light, it can be made removable/serviceable/easily-modifiable, AND its form can be so much more freely designed (in terms of styling, aero, etc.).

Structural composites are fantastic, but to get full advantage from them will require sophisticated design and fabrication techniques. You're talking about a one-off build, aren't you? If you have to create molds, you'll want to build multiple cars so you can spread out that up-front investment.

Do you pay any attention to "Formula SAE" cars? You should. They'll help keep your imagination youthful. Buy yourself a plane ticket and go to a Formula SAE competition. Formula SAE is THE place to see composites used without regard to practicality or cost! Check out this example! [www.michigandaily.com]


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5648 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: BlownMGB-V8
Date: April 30, 2014 11:45PM

Art, for light weight and strength look into composite honeycombed panels similar to what are used on aircraft. All flat panels of course but there is quite a lot you can do with flat panels.

Jim


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: DiDueColpi
Date: May 01, 2014 02:03AM

Art, I would adopt the original Colin Chapman mantra.
" simplify, then add lightness"
"adding power makes you faster on the straights. Subtracting weight makes you faster everywhere".
Every part must perform at least two functions,
it must be comprised of the lightest possible construction,
if it doesn't make you accelerate, turn or stop then get rid of it.
In that that vein, I would look more towards a monocoque construction.
Ditch the birdcage design and embrace the "origamicar".
Folded metal or composite panels are the pathway to eternal lightness.
In particular with a vehicle as square as the 914.
Did I mention that we have one with a ZR1 in it.
It's "stoopidfast" (my hotmail name) and as reliable as a timex.

Cheers
Fred


roverman
Art Gertz
Winchester, CA.
(2909 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Tube chassis with F-glass Body, 914 ish
Posted by: roverman
Date: May 01, 2014 11:19AM

Perhaps I should mention, this has a somewhat limited budget ? A sufficient stiffness, multi tube would weigh 120lbs/max ? Max car weight of 1,600/less ? Using oem targa and glass. Minium fab/ maximum return. I haven't seen a transverse 914, but I like the concept. Toyota t-axle should be up to the task and has oem.Gleason type posi. V6 should produce 400+ streetable hp. Onward, roverman.


Preform Resources
Dave Craddock
Redford,Michigan
(357 posts)

Registered:
12/20/2008 05:46PM

Main British Car:
72 MGB V6 3.4

Re: Tube chassis with F-glass Body, 914 ish
Posted by: Preform Resources
Date: May 03, 2014 08:19AM

Art, I think Curtis nailed it, the most economical way to build your chassis would be to rivet and bond aluminum panels to your
multitube frame, the next would be to fab carbon fiber honey comb cored panels bonded to the chassis BUT,,,, there goes your budget! I am assuming you mean multi tube as in the description in Costin & Phipps book, sorta like the old Cooper race cars, large diameter heavier gauge tubes ?
Dave


roverman
Art Gertz
Winchester, CA.
(2909 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Tube chassis with F-glass Body, 914 ish
Posted by: roverman
Date: May 05, 2014 11:43AM

Dave and clan, yes, no Masser-bird cage-here. Another wag, square tube, with adequate corner radius, same diag. dim. as dia. of round tube, rotated 45deg., to align with major loads, will be lighter stronger,(same material/wall thickness). Why not s-glass, or alum. honeycom,(floor/bukheads, for strength/weight/cost ? As one might guess, radiator over,or behind engine. I would like to see a novel design, for multi-point/stressed locking mechanisms. This to make doors, easy open/close, stressed members,(no dzus fasteners). Cheers, roverman.



Moderator
Curtis Jacobson
Portland Oregon
(4372 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: Moderator
Date: May 05, 2014 02:56PM

I think you're kidding yourself if you think square tubing is ever "lighter stronger" for a proper space frame. Not only is "round" the more efficient shape, but it's also economical to buy in various seamless and redrawn forms whereas box tubing is significantly (and sometimes unpredictably) weakened by a weld seam.

However, the aluminum stressed skin (which I mentioned earlier) really tilts the table in favor of box tubing: nice big, flat surface areas for applying adhesive! I also like working with box tubing because joints are easier to jig and because it's easier to attach brackets.

As for rotating tubes to align with loads... all significant loads should enter at tube intersections! Always.

Now here's an idea for you: aluminum stressed skins on BOTH sides of steel tubes with two-part expanding foam injected to fill the voids (a.k.a. "sandwich" construction).


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5648 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: BlownMGB-V8
Date: May 05, 2014 04:25PM

Be aware though, expanding foam continues to grow for a LONG time. Ever see an old Igloo cooler bursting it's seams because the foam kept growing? Very common. 6 months is not too short a period for it to stop by any means. So be very particular about what sort of foam you use.

Jim


roverman
Art Gertz
Winchester, CA.
(2909 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Tube chassis with F-glass Body, 914 ish
Posted by: roverman
Date: May 06, 2014 11:50AM

I agree, for area/ volume, round /sphere is most efficient shape. Shortest distance between two points, is straight line. Square is essentially two triangles, back/back. We know the triangle is best for strength/weight. My theory is, when square and round are same dimension overall, same wall,material and hardness, when rotated 45 deg., the square should prevail in flexure strength,(triangulation of load bearing walls). Just theory, at this point. Update: A500/low carbon steel, grade "C", round, yield=46ksi, square, yield=50ksi. FWIW, roverman.



Edited 1 time(s). Last edit at 05/07/2014 11:27AM by roverman.


Moderator
Curtis Jacobson
Portland Oregon
(4372 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: Moderator
Date: May 06, 2014 01:01PM

I hadn't thought about foam continuing to expand long term, but I have a split open cooler right here!

So a square tube is equal to two triangular tubes, but lighter? I'm not really following...

In any case, round tubes still have the advantage in true space frames where by definition tubes can only ever be loaded in pure tension or pure compression. (If flexing exists in a space frame, someone did something wrong.) In other multi-tube (non space frame) structures, round tubes have a different advantage: it's comparatively easy to bend a round tube. (Think roll hoop.) A round tube is also preferred for pure torsional loading. (Think driveshaft.)


MGBV8
Carl Floyd
Kingsport, TN
(3496 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: MGBV8
Date: May 07, 2014 12:13PM

Quote:
So a square tube is equal to two triangular tubes, but lighter?

Gonna have to do some convincing, Art. I can't quite grasp that, either.


roverman
Art Gertz
Winchester, CA.
(2909 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Tube chassis with F-glass Body, 914 ish
Posted by: roverman
Date: May 08, 2014 11:23AM

"Essentially" vs "Equal", because there is no "bridge" in the middle of the square tube, it is weaker and lighter than two triangular tubes, attached back/back. Square tube is rotated 45deg., to better vector horizontal/vertical loads. It's likely the square tube, rotated 45 deg., is more difficult to bend than round tube. It should have no more wall reduction, on outside of radii, than round tube with identical cross section. I'm not convinced a round/multi- tube frame, has zero flexure, as Curtis suggest. Top Fuel and Funny cars, could not funtion properly, without it,(suspension). Off road, multi tube cars, do indeed flex. Would a straight/square tube axle, rotated 45 deg., act stronger, in verticle and horizontal loads ? Yes. Same weight? Yes. Why ? Span of the tube, receiving major load, has increased by 1.414, minus the corner radius. I'm not suggesting anyone throw-away their round tubing, and tooling. It certainly has its place. I am suggesting, under a few applications, it might have merit. A rear end housing comes to mind. Bonding stressed aluminum skin, on to square, might have an advantage. Onward, roverman.


Moderator
Curtis Jacobson
Portland Oregon
(4372 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: Moderator
Date: May 08, 2014 02:49PM

quote: "I'm not convinced a round/multi- tube frame, has zero flexure, as Curtis suggest."

I wrote that bit about flex in reference to a "true space frame". That's a theoretical design of the sort that's probably not practical for anyone to build. Top Fuel and Funny cars CERTAINLY AREN'T true space frames. One of the key features that makes a true space frame work is that loads are never ever applied anywhere except at the intersections between tubes. Also, tube intersections aren't gusseted in any way whatsoever and in theory they could (should?) all be replaced with "pins". For the overall structure to flex at all, a tube has to either stretch or compress along its length.

Earlier in this thread, Dave mentioned a wonderful book by Costin and Phipps. It's called "Racing & Sports Car Chassis Design." It was out of print for years and early editions can command three-figure price tags, but it's a great read. The guy who designed frames for Lotus (with Colin Chapman) back in the late fifties explains the theories behind them. (They were trying to build space frames, and they probably came as close as anyone.) And he analyzes competitors too. Fascinating stuff! Very thought provoking.


Something else to think about... the British racing sportscar builders of the early sixties went back and forth on this "round vs. square" thing. Elva, Ginetta, etc. - a lot of those really fantastic cars - were built with one type of tubing for awhile and then the builders switched to the other.


I've already said, square tubing with stressed skins and bulkheads is how I'd build a stiff and lightweight custom chassis. It probably wouldn't be as light as a Lotus Seven but it probably would have more "crashworthiness". Cheap. Easy to fabricate with few and simple jigs.


roverman
Art Gertz
Winchester, CA.
(2909 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Tube chassis with F-glass Body, 914 ish
Posted by: roverman
Date: May 08, 2014 05:16PM

As a porous side note, as what point does foam stop expanding ? I suspect the cooler skins crack, because "a", foam absorbed water, or "b" plastic stressed skin, succumed to UV rays and aging, being polymer based. ALL plastics age at an accerated rate, compaired to metals/etc. I think plastics were "part" of the formula for designed obsolescence. Hell, even paint holds-up, better than plastics, but where would we be without them ? Onward, roverman.



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5648 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Tube chassis with F-glass Body, 914 ish
Posted by: BlownMGB-V8
Date: May 08, 2014 07:03PM

Same as with the "Touch-N-Foam" in a spray can. You squirt it in a hole in the wall and next day you tear off the extra that sticks out but it keeps growing. How long? Hard to say, it'd be different with different types of foam. Don't know if water would have any effect on it at all. Seems like the rigid foam insulation doesn't grow but has anybody ever measured it? Any way of knowing if it's been "aged" before it's distributed? Just saying you ought to take that into account.

Jim


Preform Resources
Dave Craddock
Redford,Michigan
(357 posts)

Registered:
12/20/2008 05:46PM

Main British Car:
72 MGB V6 3.4

Re: Tube chassis with F-glass Body, 914 ish
Posted by: Preform Resources
Date: May 08, 2014 08:43PM

Here are some examples of space frame and a quasi multi tubular/ space frame design. the first is a Stohr D-Sports chassis ,square tube with a large carbon panel in the cockpit area and very little triangulation, the other is a Jay Novak designed formula 600 chassis using both large section square and rectangular tubes and some triangulation, I have asked on the DSR forum if anyone had stiffness figures on the Stohr , no response, the weakest link is in the mechanical attachments holding the engine rear diff assy my guess is that this setup probably does about 3200 lbs per ft. per degree in torsion, Novaks' would probably approach 5000 maybe a little more, while the average carbon tub formula I or LMP car would be at a minimum of
20000 once again the weakest link in many cases being the attachment method for the engine gearbox since they are largely run as stressed units.
Dave
Stohr D-sports.jpg
image-1.jpg
Left%20Front.jpg


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