Lakester frame in 3 parts

[Tman]

Thanks, I looked all over for that thread and wanted to read it myself!

My current project involves a 170" wb lakester chassis too long to easily get in and out of my small shop.  I'd like to do it in 3 sections ("bolted together") the center of which is a cage structure pretty close to figure 4B on page 27 of the 2011 rule book.  My question is how to best make the connections to the nose section and the rear section (with motor and drive train).  Both sections have similar 4 tube rectangular layout as the cage.  All work in mild steel; 1-3/4" dia cage tubing. Est'd car weight 1800 lbs dry.
Should I design my own connectors for each of the tube intersections (external tube sleeves with cross bolts)  This doesn't thrill me.
How about the weld-on machined steel roll cage connectors that the off road folks use?
I could make it more elaborate with additional bolts, plates and cross bracing in the two end sections where they connect.
Who has done this before besides Al Teague?  Legend has it that his liner frame was in two sections; so it would fit in his garage.  True?   Anyone know how Al did his?
Ed Weldon
 
Some images in this post from 2007.      ( http://www.landracing.com/forum/index.php/topic,2629.msg31129.html#msg31129 )

[edweldon]

old gringo -- Much appreciate your finding that lakester thread. It has some very instructive photos showing structural details.  Bolts through reinforced sections of the tubes to bring the two halves together looks interesting.  It does put a lot of loading on two bolts.  But the calculation the stresses in the bolts is pretty straightforward. 
I think I would make sure the contact surfaces were in a good single plane when assembled.  A 24" x 24" piece of MIC 6 aluminum jig plate or a similar scrap of countertop granite and feeler gauges would work. I'd shoot for 20-30 mils flatness across each side of the joint and maybe add stainless steel (for salt resistance) shims at selected points to make that up.  Then I'd carefully torque up each bolt-nut combination using a micrometer to measure bolt stress.  That way the bolt preload takes away the effect of fatigue on the bolts. (much the same way as cylinder head bolts work).  Nice thing in this case is that the ability to measure bolt length easily gives a good preventative maintenance check point on the bolted joint.
Here's one of the pics from that thread showing the features I'm referring to:

An interesting question in the analysis of this design is what G forces would the frame see during normal operation over the Bonneville surface at speed.  Really it's about what  frequency and what G levels would cause the driver to think "this thing is shaking too much" and lift his foot. ............... Ed Weldon

[Ron Gibson]

After looking at some old pictures, when Al changed from lakester to streamliner, he did make the front end to come apart. I don't think he ever had it apart after and it wasn't necessary other than as described, to get it into the garage.

Ron

[Rex Schimmer]

Ed,
If your chassis is a basic 4 tubes in a square/rectangular pattern wouldn't it really be easier to machine some accurate clevis connections with a 5/8 inch dia reamed hole and use 5/8 inch shoulder bolts? If you make the clevis parts accurate and ream the holes for a good slip fit. The bolts are then in double shear and if you use a 5/8 dia they would have a double shear strength of around 50,000 lbs ( using a conservative sheer strength of 50% of the tensile strength of 160,000 psi). This would be the equal to a distributed load on your 1-3/4 x .120 wall tubing of about 33,000 psi tension load which is slightly less than the yield strength of mild steel tubing (assuming 36,000 psi yield strength). Now you have a joint that is very easy to build and very easy to align and assemble plus very simple to fabricate. If you made the clevis pin 3/4 inch the strength would be approx 70,000 lbs and the tube stress would be approx 46,000 psi which is above the material yield strength.

I saw a nostalgia fuel dragster built by Sterling that was done this way, it was split just in front of the motor. They brought the car to the strip in two parts in a small Ford pickup, the engine, rear end, tires and cage were rolled onto the  pickup bed and the front section, with the fuel tank, front axle, wheels etc were on the lumber rack. Took them about 15 minutes to bolt the thing together and run.

I don't especially care for the way the old gringo chassis is done as the load paths from the connection bolts to the main structure put the bulk head rings in bending, if you do it this way I would highly recommend additional gussets or diagonal tubing that goes from the bolted joint to the main longitudinal structure. The little gussets that they have at the corners are nothing but welding practice, they have minimal affect on the strength of the structure. The larger square tube gussets do contribute to the structure's strength and stiffness but they should extend closer to the bolted connection. (In my opinion. Which with a buck fifty you can get a small cup of coffee at Starbucks!)


Rex

[Tman]

Rex, those small gussets appear to have threaded holes in them and are actually mounting tabs.

[Peter Jack]

Ed

PM sent.

I do agree with Rex that the bolted connections in this particular application are in the middle of the tube causing rather large bending loads in the bulkhead tubes. Hopefully the tubes are of sufficient wall thickness to allow for this The saving grace in a design like this is any failure is probably going to be rather slow and should be noticeable long before catastrophe occurred.

Pete

[edweldon]

Pete - Got your off list email.  More comments after I get rid of the family birthday event later this evening.
Reference  "I do agree with Rex that the bolted connections in this particular application are in the middle of the tube causing rather large bending loads in the bulkhead tubes."  I don't like that exposure to bending of the frame tubes either.  But they'll get the first indication of problems likely when the belly pan starts scraping the high point of the trailer when they are loading it.  "Failsafe" would be when when it sags enough that the belly pan actually drags on the salt. ............. Ed Weldon

[kiwi belly tank]

The bolt on front section of Al's chassis (Betsy) was originally done that way because Al wasn't sure how stable the staggered set up would be. The plan was, if it didn't work out he could go back to the lakester front end & not miss a season.
We did take it appart one time back in the 90's to repair the damage after the front tire explosion episode. 97 I think.
The 5/8 Allen bolts came from the back & screwed into welded bungs in the horizontal tubes of the front section then there was two more 1/2" Allens in the top & in the bottom. The heads of the Allen bolts were beside the horizontals on the rear section with gussets & diagonals in the frame as well.
When the nose bit the ground back then at 380-ish, none of the bolt up show'd any adverse affect. It was just easier to take it off to repair the damage on the bottom & we gave it a fresh set of bolts.
Betsy was a tough ol girl.
  Sid.

[edweldon]

Rex - You've got some interesting comments about relative stresses and the two piece dragster description.  Again, excellent data points.  But I'm not too enthusiastic about close fitting clevises.  I expect to take this thing apart several times.  Some movement or welding stress relief in the frame could turn an effort of taking apart into a pain and putting back together into a crying session.
I don't like the placement of bolts away from the fairly ridged tube connections on the #575AGL either.
http://www.landracing.com/forum/index.php/topic,2629.msg31129.html#msg31129
I think I could use their approach or something similar on my project and put the connections closer to the corner tube intersections.  So their setup has me thinking.
Thank you for your comments and you engineering based numbers on relative stresses and proportions. 
This is one of those situations in engineering where one component, in this case 1-3/4" dia 1/8" wall mild steel tubing has a long and valid experience set supporting it (and a codified rule as well).  Other pieces of this structural "chain" are well selected to be stronger "links" than the tubing.  But some elegance in the design is desirable.  This means that the strength of these new components like nuts and bolts ought to be "better" than the tubing; but not so much so as to add parasitic load (cost is also a "load") that adds no real value to the design. ............................. Ed

[edweldon]

Sid (kiwi belly tank) - Thanks for the info on Al Teague's car.  If I understand you description correctly Al's frame had different spacing on the horizontal tubes between the two sections such that a bolt could be driven through a cross tube close to the joint and into an insert in the end of the tube in the frame other section.  This sounds neat but isn't so great for me since it I'd just as well prefer not to change the existing frame width between the sections due to the existance of some very nice aluminum body work that would have to change if the frame were widened and the very real concern with narrowing a proven design.  The one exception to this line of thinking is in the rear section where I may choose to push the rear section frame rails out a bit to ease maintenance on the engine and transmission, especially the stock Ford flathead starter which is a bear to remove and the possibility of eventually goinf to a dry sump system that could use the space.
With all the talk in the abstract I think it would be helpful to post a picture of the car as it was running about 20 years ago.  Trouble is I haven't yet figured out how to insert or attach a .jpg file from my own computer. ............ Ed

[edweldon]

Hmmmmmmmmmm ...... That didn't show up in the preview.  But I see it attached...  OK, now I know how it works.   Ed

[Tman]

Ed, thanks for bringin this thread up. My front and rear suspension will be using similar "pods" that also hold the bodywork, chute tubes etc. as well as the axles. All this discussion is helping me finalize some ideas on how to do it.

[kiwi belly tank]

Ed,
  To not re-engineer your wheel so to speak, if you just run some diagonals out from the bolt location to the opposite corners, that'll triangulate it & stiffen that baby right up. Smaller tube will do the job.
  Sid.

[edweldon]

Sid - There are a couple of places where diagonals may be the right answer.  Certainly an option if a connection point has to be away from a frame corner joint. 
Right now the frame with some sheet metal components is still sitting out in the rain.  Won't hurt it any since it is all powder coated.  But weather conditions are not particularly inviting for working out there and taking closeup photos, which I now know how to post. Later this week, I think...........Ed

[Peter Jack]

Too bad about the powder coating Ed. I don't like the process simply because it makes repairs and modifications difficult. That being said I definitely use it when I know there aren't going to be any modifications to the project I'm building. No race car falls in that category.

Be sure you get the areas where you're going to be welded sand blasted well back from the area where you're going to work. That's probably about twice as far as you think. The powder or the plastic coating melts at about 450 deg. F if I remember correctly and will surely run back to where you're working, so don't let the parts still coated get that hot. The good thing about the coating is that if you're planning on using the same color you don't have to remove all the coating as the old stuff will just remelt and blend with the new.

Good luck with the mods.

Pete