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Author Topic: P-38 Bellytank build  (Read 14365 times)
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awelker
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« on: July 26, 2007, 04:21:32 PM »

I'm starting a P-38 tank build and I thought I would post some pics of my CAD design to date (I'm a mechanical engineer with access to the software).  I currently am getting ready to start building the frame which I'm having the main rails and cross members being fabricated at a local machine shop.  Hopefully months of measuring and planning will pay off. 

It will be flathead v8 powered w/side shift 3 speed transmission, model A ford front axle, halibrand quick change.

Any advice or opinions are appreciated.

Andy



* frame fit assem 2.jpg (85 KB, 1593x971 - viewed 505 times.)

* frame fit assem.jpg (119.31 KB, 1593x971 - viewed 1319 times.)
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JackD
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« Reply #1 on: July 26, 2007, 06:25:00 PM »

Consider making the firewall and skin in that area join in such a fashion that fluids and gases must go outside and forward before they get to you as opposed to trying to seal the skin to the bulkhead.
This is a place where steel sheet can be your friend.
I don't quite understand in what direction you plan to exit and I don't see any diagonal bracing for at least the cage area.
Consider in sizing the driver area that safety equipment must hold you,  isolate you within the protective envelope, and if an extremity is already folded to the max, the next thing is break.
Plan for crashing at home and that will leave more time for racing. wink
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revolutionary
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« Reply #2 on: July 26, 2007, 08:30:26 PM »

Pretty cool.  I'm sure you've spent some time reading and looking at the pix of the Aussie bellytanker buildup.  Plenty of good hard-leaned info in there.
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t russell
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« Reply #3 on: July 26, 2007, 09:26:08 PM »

Dodge cool
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Dr Goggles
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« Reply #4 on: July 26, 2007, 11:49:34 PM »

Hi Andy
nice trad lookin' thing you're up to there .Jack is , as usual , right on the money. In the build of our tank we were very keen on the look of the early stuff and found over the time we designed and built that the rules that have been made since the fifties make it increasingly difficult to duplicate the look of those cars but that doesn't mean it can't be done.if you plate-in the drivers compartment you will achieve a lot of what Jack is talking about and strengthen the cage as well.

We won't be any use to you in making your car go faster but when it comes to making a decision on which way to go when you get to certain parts of the build let me tell you we've done lots of thinking about it. Are you going flathead because you "know" them or just for the traditional angle?For my money it won't change the outside look of the car and you can go really fast a whole lot cheaper with some later iron.

Keep up the good work.
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Glen
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« Reply #5 on: July 27, 2007, 09:20:09 AM »

Andy, like Jack said about roll bar bracing etc. Make sure you read the rule book. The same goes for the area below the driver and foot area. All of this needs protection. When fitting controls in the car make sure they are placed where you can reach them with a full fire suit and helmet on. This is a must do part of the build up.
Where do you live in case we have someone in the area to look at the car during build up. Also send construction pictures they really help us to see a possible problem area.
Glen smiley
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Rex Schimmer
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« Reply #6 on: July 27, 2007, 09:51:24 AM »

You want to consider adding 15-20 inches to your tank to be able to get room for the driver to be able to get out. The tech guys are are really strict on being able to get out with in a pretty short time and if your car is on fire you will see why! As Jack said you need some diagonals and also some gussets. You should try to make it to the salt and really look at some of the cars, specifically lakesters, that are running and spend some time at tech to see what is required to have a safe car.

I once thought about building a lakester that was a replica of Stu Hilborn's car but once you get some of the dimensions of that car and then try to design it with todays safty requirements you can't make it work. Stu was pretty skinny when he ran that car and he was a tight fit!

Rex
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« Reply #7 on: July 27, 2007, 10:54:50 AM »

Please take the time before you get your frame rails complete to make sure you can fit everything in the vehicle to meet your and the SCTA needs. Jack Kelly's tank fits that bill and was lengthened to do it. Your flathead idea could change and the trans to rear dimension can make everything very tight. Water tanks, oil tanks, fire bottles, fuel tanks etc. take up room.

I like your idea and enthusiasm Please continue and good luck...
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« Reply #8 on: July 27, 2007, 10:57:45 AM »

The added length can be done in the area of the seat and the contour of the body will not be altered beyond the appreciation of those that care.
This is a good place to make the finish skin from steel sheet that will not only make it much stronger, but help keep all the important juices on their side of the fence. and require them to go outside in the wind before bothering the neighbor.
That area can be as permanent as you make anything and it should never be in he way of any access.
Moisture that results in corrosion from the inside , and cracks are the most difficult to keep track of.
During assembly. the tubular frame components can all be interconnected with a tiny hole at the intersections and be pressurized with dry nitrogen.
You will need two !/8"npt bungs and one fitted with a screw in Schrader valve and the other with a cheap deal gauge like on a $10 home fire bottle.
Now with a hand spray bottle of soap and a rag it will clean outside stuff as you search for bubbles that indicate cracks you might otherwise never see.
If the gauge drops, it is probably a good time to get the soap and the rag.
It works the best and still looks cool. wink

 wink
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« Reply #9 on: July 27, 2007, 12:22:21 PM »

Andy,
   Great look! Reminds me a lot of Tom Beatty's tank, maybe because it is blue, or that the head fairing and front axle look alot like his. Anyway good luck and keep up the good work.

Tom G.
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« Reply #10 on: July 27, 2007, 01:12:05 PM »

Thanks everyone for the input so far.  Just to clear a few things up:

As for the the roll cage bracing, it can be a pain to draw and I've been modifying the cage shape so much I haven't spent the time to do that yet.  As for the cage itself, what I have shown is the concept, which will most likely change during the build.  To exit the tank a portion of the tank and the windshield will hinge front and be able to exit in front of the forward head loop through the cage.  I was part of a team previously where we built & raced a dune buggy type car for a competition that had very similar rules and requirements for getting out in a timely fashion.  Never had to get out from a fire but did make numerous upside down trips. 

The reason for the flathead is a combination of vintage coolness and the fact I have a bunch lying around waiting to be put in something.  I have measured a few other engines just in case a change of heart. 

As for stretching the tank, I don't think that is in the plans. I know things will be quite cramped, but I think I can deal with the space I have. Plus I like the look of the un-stretched tank as it is now.

I do have to remember to drill holes to be able to pressure check the cage, sounds like that would work well.

Thanks for all the advice, keep it coming.
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Dr Goggles
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« Reply #11 on: July 27, 2007, 07:42:42 PM »

I once thought about building a lakester that was a replica of Stu Hilborn's car but once you get some of the dimensions of that car and then try to design it with todays safty requirements you can't make it work. Stu was pretty skinny when he ran that car and he was a tight fit! Rex

There's that great shot of Stu Hilborn squeezing into the car with his hips twisted grin , and then the story of him getting it upside down , yikes!!!

Quote
Reminds me a lot of Tom Beatty's tank,

.....one of the prettiest , a beautiful car..............

Quote
I currently am getting ready to start building the frame which I'm having the main rails and cross members being fabricated at a local machine shop.

On the build of our car we reasoned that the use of a "chassis" type structure with frame rails was counter productive as we had no use for a flat platform .That type of frame is a progressive development from road cars and has been through all sorts of variations but when you look at what a tank requires it doesn't really do it.As a tank body narrows toward the bottom the room you need to make a rail type chassis rigid is lacking .If you , as we did , elect to keep the body as short as possible as much for aero as cosmetic reasons then you're gonna need as much room as you can get .To keep it brief we built a canoe , yeah a canoe , and sat it all inside that .The end result might look a bit primitive but it's really strong , gave us more space and because of the cage nature of the structure there's always somewhere to attach whatever it is that you're trying to attach .We spent a long time designing the frame ....then we chopped and changed merrily as we went through the build , expect the same if you're pushed for room because it's not until you've got everything in there that you see places where you can improve .

An Italian scooter nut saw our car and said ...."is like sandwich " ...I looked at him curiously and he held his hands flat together and said "no space!"

When someone is looking at the car and asks" why didn't you put that( for eg. sometimes I wish we'd built "boat" exhaust headers over the top and put the water tank underneath which would have lowered the CG and got the heat up top) , there"...the answer is always complicated because "everything" would have to be somewhere else!!! rolleyes
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Few understand what I'm trying to do but they vastly outnumber those who understand why...................

http://thespiritofsunshine.blogspot.com/

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THE LUCKIEST MAN IN SLOW BUSINESS.
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« Reply #12 on: July 27, 2007, 08:43:38 PM »

You have 51 weeks to prepare, 1 week to run., and their are always changes you want to make.
Q: Where does that time go ?
A;  Exactly where it is best.

PROCEED wink
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« Reply #13 on: August 05, 2007, 01:49:45 PM »

 Hey Andy,
 It looks like you took a good look at my chassis design.  It's a good design and it works well for hiding the roll cage.
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« Reply #14 on: August 05, 2007, 01:53:36 PM »

Here's another pic of my door design, it works well too.


 Good luck with your build.  I'll keep an eye out for updates.
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