#21
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Good evening Cameron:
By adding x-bracing only in the floor, you mainly add resistance to horizontal distortion (x & y components), but torsional resistance/strength requires an x, y AND z components. If you can visualize the 'birdcage' construction of the early Maserati's vs the large diameter tube 'ladder' chassis of the early Cobras, the difference should be readily apparent. The 'birdcage' design was FAR superior in cornering, and because of the triangulation factor, the 'birdcage' chassis is also able to be built slightly lighter as well.
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Will |
#22
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I'm thinking that if you can isolate the torsional rigidity issue to be within the passenger area, the rest should be easier. A strong firewall would take care of the front of the "box". A similar shear panel behind the seats would take care of the back of the box. These shear planes should extend down and attach to the bottom of the frame rails as well as the top of the rails. Now you just need to use as deep frame rails as you can fit in there and an X brace. I'm thinking this is going to be more of a cruiser than a corner carver so use very light anti-roll bars or none at all to hopefully be able to keep the doors shut when the car enters a driveway at an angle. Does your Solidworks program contain the FEA option?
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Bob Don't believe everything you think. Last edited by bobadame; 08-24-2015 at 09:35 PM. |
#23
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Bob, I agree with your approach, but this is really up to Jim, and I am thinking that he is leaning more towards authenticity in appearance than building a 'hot rod', but performance is also in his thinking. The current design of this Bugatti has a suitable strong front firewall, but the long doors and the fact that it is a four passenger convertible makes some of those ideas a little more difficult to achieve. Looking at some of the pictures already posted will show that Bugatti approached this by some VERY sturdy frame rails. I am just a 'helper' at best in this project, and my aim is to assist Jim achieve whatever he is interested in achieving. The large and VERY rigid motor and its mounting, along with the very strong firewall, rear motor mounts and the kick out at the front would seem to do a good job forward, but the fact that this car uses quite heavy quarter elliptical rear springs mounted clear to the rearmost corners of the chassis would seem to detract from the ability to corner, but it sure adds to the distance between suspension mountings providing smoother ride characteristics. The body is mounted by only four small mounting points and that does little to add to torsional rigidity.
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Will |
#24
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Maybe with only 4 mounting points the body will be somewhat isolated from torsional flex. 3 points would completely isolate it.
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Bob Don't believe everything you think. |
#25
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I only mentioned an X-member because of what I observed when straightening frames for other body shops for so many years. When over jacking (did so because of spring-back) a corner of a frame to remove twist I’d have to leave the doors slightly open because the door on one side would be hanging at the rear where the opposite side would be jacked up at the rear. Neither door could be closed when the frame was in this twisted condition I put it in to correct its twist damage. While my example surely is an extreme condition it showed me that it only takes a small amount of twist to make doors bang on their locks.
My other observation is I never saw a convertible from the fifties (that had a conventional ladder style frame) that didn’t have an X-member while the frames in same year sedan lacked them altogether. Later on when the manufacturers went to perimeter style frames so they could sink the floor boards lower there was no room for X-members anymore so they had to add Teflon & other plastic parts to the door locks to keep them from banging. ~ John Buchtenkirch
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John |
#26
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I understand each of your points, there, John, and have no argument with them, but No convertible is worth a crap as a road race / handling car, and no amount of cross bracing to only the chassis will increase its handing to any significant degree. I maintain my position that adding x-bracing in the horizontal frame rails only slightly adds to the torsional rigidity or 'truss strength' of the frame, but will make the chassis take a 'set' once deformed making it more difficult to repair. It is my observation that the diagonals were added to cars that had difficulty (for whatever reason) maintaining alignment from one side frame rail to the other caused by 'lozenging' due to the horizontally vectored force from hitting large bumps and potholes. Most convertible's would fall into that category.
Again, these are just thoughts from an old man!
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Will |
#27
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Updates on Bugatti chassis development
Here are some pictures, some of which may have appeared on another post, but belong in this post as well. These are miscellaneous pics of the gas tank progress.
This the top view of an original tank This is an end view SolidWorks drawing of the gas tank assembly Showing S/W drawing of gas tank end plates formed on the hammer form bucks Showing S/W drawing of gas baffle plates formed on the hammer form bucks S/W drawing file for water jet cutting of tank baffles S/W drawing of roll forming of tank exterior S/W drawing of water jet layout of tank components
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Will |
#28
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Updates for the front bumpers and muffler
S/W drawing of water jet cutout
Drawing of layout for bumper .dxf file Jim Hery found it necessary to pre-bolt the 14 gauge cutout to the buck that he made to control panel movement Jim at intermediate stage of the heat forming procesess More at the beginning of the forming This shows the condition of the bumper as Jim closes in on the final contour Here is the first one done, ready for plating - all done by hand - excellent work!
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Will |
#29
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More misc. Bugatti chassis upgrades.
S/W drawing of Rear view of the '35 Bugatti Stelvio dash panel
S/W drawing of Front view of the '35 Bugatti Stelvio dash panel S/W drawing of front shock mounting bracket Jim Hery and Teddy Hefner assembling the Bugatti muffler insides. Jim welding end mounting flange Preliminary folding of the upper chassis mounting brackets for the muffler S/W drawing of the Bugatti muffler assembly Muffler dimensions were taken by scaling the actual chassis to this page from an original Service manual Additional muffler hanging brackets details made by measuring the actual mounting holes in the frame and the picture of the original manual.
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Will |
#30
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Again, slow progress, but this is where I am currently in the drawings for the T57 Chassis. I still have some detailing to do on the frame forward of the firewall and then will get started making water jet drawings. After several trips to Tennessee there are still LOTS of details left.
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Will |
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