Alternate Frame?

[Shadow Dreamer]

I'm playing with an idea in my head and was wondering what others think...See, I know I'm not the greatest welder in the world, but I can do a bang up job with fiberglass. So, with that in mind, I'm toying with the idea of using carbon fiber weave and epoxy resin to build my frame. What do YOU think?

 

[Loner]

I for one appreciate the attributes of the carbon fiber weave and similar materials. I worked with military designers and test labs for years coming up with all types of components for missiles and other applications. I also owned NovaTrikes and did stress analyses and tests on frame designs. The biggest stress area(s) on a trike (or most any motorcycle) are in the tubes supporting the neck. These primary stress points are a few inches from the neck itself, both on the backbone and the downtubes. Stresses in these areas could easily reach 8-10 thousand pounds laterally.

DOM tubing .125" thickness and 1.250" OD is rated exceeding 63,000 pounds stress. With those numbers in consideration, I would strongly question whether the high strength weaves could stand those dynamic stresses. Perhaps if machine-rolled carbon fiber thread over a tubing shaped mandrel with continuous resin flow (that's how high-burst rocket engine containers were made, but even then that was burst strength, not lateral stress.

If you know the technical attributes of carbon fiber and feel like a nominal size tube can handle high lateral stress then you may can manufacture something that works.

My numbers are somewhat simplified and summarized (you don't want to see a true stress analysis - it can make one's eyes cross), bit my advice would be to use a good heavy DOM for your frame and use your composites skills for body-work and other components.

 

[Shadow Dreamer]

I for one appreciate the attributes of the carbon fiber weave and similar materials. I worked with military designers and test labs for years coming up with all types of components for missiles and other applications.

That's actually where I got the idea in the first place. While I was in the Army, I serviced the AH-64A and got to work with the guys in the "body shop" on the airfield. Since then, in civilian life, I've had multiple opportunities to apply that same technology. That led me to the thought that it has to be possible. I know that a group of Swedish college kids built a carbon fiber bike, but that was a crotch rocket and used a unibody approach.

DOM tubing .125" thickness and 1.250" OD is rated exceeding 63,000 pounds stress. With those numbers in consideration, I would strongly question whether the high strength weaves could stand those dynamic stresses. Perhaps if machine-rolled carbon fiber thread over a tubing shaped mandrel with continuous resin flow (that's how high-burst rocket engine containers were made, but even then that was burst strength, not lateral stress.

Well...I talked with one manufacturer of carbon fiber weave and epoxy. The attached pic is a screen shot of the stress test information he had available. The problem is that it is ONLY for 10 ply, flat test pieces, cured at room temp (no autoclave or vacuum). He's specifically asked the engineering group (I only got to talk to a salesman) but they haven't done any testing on tubular uses, even though they sell a tubular weave (think Chinese finger cuffs...that's how their weave is).

If you know the technical attributes of carbon fiber and feel like a nominal size tube can handle high lateral stress then you may can manufacture something that works.

My numbers are somewhat simplified and summarized (you don't want to see a true stress analysis - it can make one's eyes cross), bit my advice would be to use a good heavy DOM for your frame and use your composites skills for body-work and other components.

Thank you for the input Loner. I'm a touch shy of going through with it yet, due to the "unknown" stresses involved and the fact that CF has awesome strength in one direction, but can be absolutely lousy in a different direction.
~SD

 

[stacebg]

just a thought....
why not get your frame tacked together and have a pro welder finish welding it

 

[Shadow Dreamer]

just a thought....
why not get your frame tacked together and have a pro welder finish welding it

Cost mostly....my area is mostly tourist based consumerism. There aren't any real industrial places here, which translates to having to make at least an hour drive to find a welder I would trust enough to do a better job than I could. That's not to say there aren't any welders close by, but they're all stick-jockeys who taught themselves how to weld their trailers back together after flipping their boat on the way home from a drunk fest on one of the lakes. Of course, there's the option of buying a MIG welder, but the cost for gas in my area is prohibitive, and I'd have to make that same hour drive to pick it up.

I also like the idea of the weight to thrust ratio. Since I'm using a Fiero as my donor, the Iron Duke (2.5l) only produced 92 hp, stock. 1.25" x 0.125 DOM steel has a weight to length ratio of approximately 1.45lbs/ft. vs. 0.143lbs/ft. for commercially produced tubing (meaning hand laying my own would probably be closer to 0.3-0.4 lbs/ft if I'm realistic about it). When considering just the main rails, 2 pieces of 10-12' pipe or tubing, the weight difference is dramatic:

DOM steel pipe: 14.5 - 17.4 lbs per pipe or 29 - 34.8 lbs for both
CF tubing: 1.43 - 4.8 lbs per tube or 2.86 - 9.6 lbs for both

Depending on whom you ask, those main rails account for anywhere from 1/4 to 1/3 of the entire weight of the frame (not including engine mounting), which takes the weight of the trike up to somewhere around 104 - 139.2 lbs for the steel frame, but you're still around 8.58 - 38.4 lbs for the CF.

The Fiero had a curb weight of 2462 lbs, or just over 1 American ton. IF I can get that weight down to 1% of the "original" weight, that SHOULD increase my MPG from the stock Fiero's 21MPG up to close to, if not over, 40 MPG (approximate adjustments for wind resistance calculated in), where sticking with the steel frame, IF I did my math right (which I am almost always right when it comes to math) I'll only see around 29-32 MPG.

Since I am forced to live on the limited budget (married family father of 4 kids) disability affords me, I have to think more than twice about every penny spent. That extra 8-11+ MPG will actually go a long way for me when you consider the price of gas. Yesterday had to fill up our only vehicle at a price of $2.35/gal.

That's why I'm interested in seeing if there's a safe way to do it with carbon fiber, stacebg

 

[vwbug72501]

I'm by NO means an expert on the subject, but it sounds like you are trying to approach your CF frame using metal tube designs. How about a monocoque chassis approach? I would think that CF lends itself better to that approach. There might be some good information on chassis design on the Society of Automotive Engineers Student Competitions sites.

 

[Shadow Dreamer]

I'm by NO means an expert on the subject, but it sounds like you are trying to approach your CF frame using metal tube designs. How about a monocoque chassis approach? I would think that CF lends itself better to that approach. There might be some good information on chassis design on the Society of Automotive Engineers Student Competitions sites.

I know a group of university students in Sweden made a uni-body-ish motorcycle (after reading THEIR article again and taking a much closer look at their build), and it seems as though they used a modified monocoque chassis. I had considered that, but to be honest, I'm a little scared that my design might not work doing it that way.

Now, I've got...looks like 20 tabs open and am researching it through the avenue you suggested, vwbug. THANK YOU! This is sparking all kinds of new ideas, just seeing how others have approached a similar issue. I'm on my 5th article/paper about race car frames, and I'm beginning to think I may want to keep my focus on their designs, issues and ideas, since the end effect isn't to build something that I can turn into a production model, but rather turn into a custom, one-off machine that will give me the performance I'm hoping for. Again, thank you for directing my attention....sometimes I get stuck on an idea and can't see the forest for the trees.
~sd