Interesting Frame Comparison

Lex · Dec 22, 2009

People often ask, Why should I buy a Factory Five Racing Cobra or Other Factory Five Kit car over some other brand??

There are probably many answers that one could give including value for money, modern design and manufacturing materials and methods, not to mention their overall success.
But for me what REALLY sums it all up is when I look at the Factory Five Frame compared to the other guys frames. Check out the following photos to see what I mean.

This Photo shows the FFR Mk III Bare Frame done up in a black powder coat. Notice the extensive superstructure above the main 4 inch thick wall round tube frame. Of particular interest is the extensive use of triangulated steel which provides incredible strength and rigidity to the FFR Frame. Note also the strong round tube steel foot well protection as well as the extensive steel cage surrounding the passenger compartment

Starting with the bare frame one of the first steps is to glue and rivit the first of more than 40 Panels onto the frame. Every panel that gets added increases the already rigid frames rigidity. This construction method has beem employed by the aircraft industry since its inception and is employed on the Space Shuttle today. Compare this frame and construction method to the other cobra frames pictured below

This is a what we refer to as the "Bed Frame Construction style". Notice on this frame that other then the uprights for the front suspension the frame is devoid of any supporting structure that will provide the torsional rigidity required to keep the wheels on the road and provide a solid handling car.With this method of construction the fiberglass body will weigh upwards of 700 Lbs and is bolted onto the frame in the hope that the fiberglass itself will provide the torsional rigidity that the frame is incapable of. Problem is, fiberglass does not take well to flexing and is a poor material for this purpose. End result is a car handles poorly, Weighs a ton, and provides little or no occupant protection in the event of an accident since fiberglass shatters when hit rather than deforming and absorbing the impact like a steel chassis would do. Over time this Car will develop stress cracks that not only look bad but if left too long can comprimise the cars ability to work properly. Overall this style of build is not a good investment and is definitly not a safe car in the event of an accident.

This is a variation on the Bed frame construction style. Note that this is an improvement over the frame shown above in that this frame at least has a small amount of superstructure above the main frame rails both in front of and behind the passenger compartment.

Still in the event of a side hit this frame is going to crush almost into the center of the car since like Example B below there is nothing but the Fiberglass body to absorb the force of the impact in the passenger seating area, and with no triangulated steel crush zones built into the frame a front or rear end collision will not fare much better.

As for handling due to the built in flex that this style of frame has neither of these cars will handle very well when compared to the Factory Five Chassis.

BS · Dec 26, 2009

Yes, it will. Except in rare instances or a specific design, a welded connection will be much stronger/stiffer than a bolted connection.

trevor · Dec 26, 2009

thomas, the side bars have to be welded to the full width roll bar and 2x3 door hinge frame bar. Also, the bars have to intersect at frame nodes or nothing is really strengthened. So, swinging and detachable stuff doesnt add to the frame stiffness but will definately help protect you. Also, the side bars need an x-brace or something to connect the bottom to the top side bars.
The spec frame has a top and bottom side bar with bars connecting them:

This frame shows a perfect example of all bars joining at nodes (blue heated areas):

289FIA_Cobra · Dec 26, 2009

just my $wooden nickels worth but why do you think modern race cars have moved to monoque chassis instead of staying with ANY tubed chassis, round or otherwise.

I got my car, I'm happy so I don't really care anymore. ... where's that dead horse ...

George H · Dec 27, 2009

A big part of that, both for race cars and for street cars, is safety. Tube chassis are strong and resist flexing, but they are a LOT harder to make effective crumple zones work in.

FFRs hold up well in front-end collisions because the structure of the front of the car is fairly weak and crumples right away. Thats good for safety, good for ease-of-repair, but bad in lower speed crashes that can buckle the frame more easily then they should (the "bumpers" wouldn't take a 5mph hit, I'd be willing to bet).

ROADRACER83 · Dec 27, 2009

VSE monocoque frame

Once upon a time back in the 70's Herb Adams son Matt was building a monocoque C**^% frame that was really stiff. They built maybe only maybe 20 or so but there is a cult that is still talking about that frame and the replicas that were built on that platform.

http://www.vsecobra.com/phpBB3/viewtopic.php?f=1&t=10

I'm not sure if Matt Adams is still building the things or can provide drawings to DIY. They made some of them in steel and a few in aluminum. There is some information on them on the web. Just Google VSE Cobra and get a history lesson.

Ron

2FAST4U · Dec 27, 2009

This frame is superior to all

clutt gt · Dec 27, 2009

How about this frame design

Just wondering what the people think

Interesting Frame Comparison

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