Another belly tanker, QLD

See cars and bikes being built for the salt

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Greg Watters
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Post by Greg Watters » Sat Jun 12, 2010 1:08 am

Doc how do you feel about no suspension after this years jolting ??

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Dr Goggles
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de Bono

Post by Dr Goggles » Sat Jun 12, 2010 1:52 am

OK Dave,
For simplicity lets assume a suspension event is a "lump" on the track ,a hole is the opposite event.

When you hit the bump ideally you hope the suspension movement slows to zero before the limit of travel is reached and that some of the energy is dissipated as heat in the spring , and then some in the dampener or shock absorber as the system rebounds.

Ideally, the "rate" or stiffness of the spring has to be such that it resists the force applied before the spring is fully compressed.The aim of the dampener is to stop the spring oscillating , but it too must be calculated to allow the spring to return as quickly as possible to allow it to follow the track surface.

The tire itself has an amount of compliance that assists this. As speed increases the required response rate rises .As tire pressures increase and psi on contact patches rises due to narrow tires and higher vehicle weights the compliance of the tire becomes less and there is further reliance on the suspension to have a more accurate response.

At worst the response is too slow, or the spring rate wrong and the suspension is literally a "step behind" similar to what happens on a corrugated road. This scenario is heightened in a short travel, the curve is parabolic, and a longer travel is much more forgiving.
a smart bloke called Greg Watters wrote:Doc how do you feel about no suspension after this years jolting ??
I get the feeling something along the lines of bags or a viscous system is probably closer to what we need than the classic spring and dampener system, for the reasons above, it would be nice to take out the "vibration". One side of my argument is a few responses above, we wanted simplicity, we got it . If we constructed our own suspension system and it DIDN'T work, then we'd have a can of worms.... :wink:I suspect this years ride was as much the toe in we ran..the only real nasties for the tank are when it bottoms out, when the floor hits the track, I got it airborne past the 7 mile marker and it was like being dropped on my arse from about three feet....

We're in a pretty small community here, my comments are based on my opinion and observations from my own driving experience, there is absolutely no conjecture or comparative comment here. If someone else who had a bellytank gave us the same we'd have a better idea of the different approaches.
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T-34
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Post by T-34 » Sat Jun 12, 2010 12:45 pm

penny wrote:t 34, mick dont even think about buying this paul http://www.racingjunk.com/category/17/A ... gster.html
Mnnn - looks like a good buy for some cheap racing, would cost double that to build yourself. Shame we don't have a real drag track anywhere near SA.

Gotta admit, I thing Burly's streamliner bug is a pretty unique idea, will be watching that one closely.

My original idea for a VW salt racer was to build a volks rod - I considered that it would be very much in keeping with the whole lakester / rod heritage of the event, and hopefully better aero than a fully fendered car, plus a bit of fun too. This is the car that originally inspired me

http://img3.image.hotrod.com/f/14274545 ... swagen.jpg

Maybe one day - lol.

RE suspension. Here's my 02c.

Suspension serves two purposes - to keep a nice ride for the passengers, and to ensure that the wheels stay in contact with the ground at all times - to provide 'grip' - this is important for both traction and handling. Generally these three are mutually exclusive, so in a race car the drivers needs are secondary to traction and handling

I think that there is a big difference in the applications between a circuit racer and straight line racing - this is demonstrated perfectly in a drag car, where the suspension is setup to ensure controlled weight transference - both during and after launch. Everyone knows - drag cars don't go round corners - this is for good reason - setting the car up for cornering would be a compromise - the better handling would compromise traction.

Geometry...

Straight - fixed axles are king for straight line racing - or at least maintaining a neutral camber through the suspension range is - no need to change camber as there is no body roll when racing in a in straight line. The more of the tyres width you maintain in contact with the ground - the more grip you have. A straight axle always maintains this - they are very good in a straight line, but piss poor when you introduce body roll into the equation - hence the need for IRS in cornering applications.

So in this respect, I think that the vee suspension may be a bit of overkill, it's main advantage in this application is simply that it's more aerodynamic than the stock VW setup - and you can copy the design - saving some time / headaches, but I'm not entirely convinced that it offers massive advantages.

RE Springs / shocks

The other thing to maintaining grip is to ensure that the rate and rebound of the suspension is correct - otherwise you will get the skip that's mentioned. The wheel will effectively 'bounce' over bumps - losing traction on the back side of the bump. Of course this is an extreme scenario, and not one that is necessarily present on the salt (can't comment there as I haven't run on it yet), but I would guess that the changes in surface topology are relatively small - the surface is chosen specifically for this purpose - very long and very flat. The surface is also prepared to get rid of the ripples too.

So - what to do?

With any setup, it will probably be set to a minimum travel, pretty stiff and likely have equal rate and rebound - my guess is that the few mm of travel required may be better handled by dialling in the tyre pressure.

I see the goal here is simply traction and aero - not handling nor ride quality.

Given the the surface is pretty constant, and applying what i know about suspension (probably not much I will confess - lol), I would guess that the adjustment gained in using suspension versus the potential aero gains by using a solid setup may not worth the time, effort and money.

I think that there will obviously be a compromise with using a fixed setup, but in actuality this compromise is only a small one - the compromise is simply the loss of adjustment, and to a degree this can still be catered for, albeit in a different manner. Even fixed suspension still has some travel (flex) and this can be controlled if designed correctly.

As an aside - if you look at the DR's setup - it will still have a little travel - due to the flex / rubber mounts, and the rate / rebound will probably be identical - for all intents and purposes it's probably not too far from where an ideal setup needs to be.

Of course - this is all conjecture on my part - I am far from an expert in these matters.

Mick.
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sammj
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Post by sammj » Sat Jun 12, 2010 10:18 pm

Wow! Thanks for the info and ideas. And that was only question number one :) Perhaps I should have started with a less controversal question rather than suspension.
I have been egerly searching formula vee sites etc for ideas. And I have read a few build dairys again.

Heres a nice Aussie one. If you rounded off the nose it is almost a tanker already (in profile anyway)

[img][img]http://i768.photobucket.com/albums/xx32 ... /image.jpg[/img][/img]

T34 here is one for you
[img][img]http://i768.photobucket.com/albums/xx32 ... VijA-O.jpg[/img][/img]

sammj
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Post by sammj » Sat Jun 12, 2010 10:27 pm

Heres some old school tankers that I have been admiring... Not sure I would like my head outside the car though.
[img][img]http://i768.photobucket.com/albums/xx32 ... /race2.jpg[/img][/img]
[img][img]http://i768.photobucket.com/albums/xx32 ... Bonnev.png[/img][/img]

I am looking forward to actually DOING some work now so I have some proper pics to post.

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Dr Goggles
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ship shape up

Post by Dr Goggles » Sun Jun 13, 2010 11:54 am

sammj wrote:Heres some old school tankers that I have been admiring... Not sure I would like my head outside the car though.
Image[/img]
I am looking forward to actually DOING some work now so I have some proper pics to post.
that's a garden ornament that one, there's a few floating around that are repro's, made to sit on the grass at shows.

When I wrote "The rules. There are very specific minimum requirements related to safety, learn them off by heart and begin your design there. They dictate the smallest possible area you can sit in."

What I specifically meant was that there are rules about the clearance you must have in your roll cage, fitting that in with the body design you have will be one of the more challenging parts of the job.Trust me , the chassis/driveline/suspension stuff is a walk in the park compared to shoehorning and drafting that you require to make everything fit into a space that comes close to being aero-dynamic. The armchair designers will sniff but when you get close to cutting the first piece of pipe you want to know this part of it backwards....you will have pictures of yourselves sitting there in the driving position with a mocked up steering wheel, roll cage and seat, helmet on..... It's easy to draw cool shapes but someone has to get in, and out and the clearances between the helmet and cage and the cage itself are dictated by very strict rules.There is also a good chance that between the first cut and the first run you will get fatter.........I weighed 73 kilos from 16 to 41, next thing I know I'm 84 :lol: , bending to get into the car is harder when your gut is bigger..

these, are beautiful tanks, the So-Cal of course,favorite of mine second only to the Brown Hooper tank..

Image


BTW everyone, there's no hard feelings between Dave L and I , we have a fairly robust conversation going usually in PMs where we disagree most of the time. He has raced and been around lots of different types of race cars, I haven't. I have a salt lake car, he doesn't. There is a healthy respect between us. :wink:
...few understand what I'm trying to do , but they vastly outnumber those who understand why..

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T-34
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Re: ship shape up

Post by T-34 » Sun Jun 13, 2010 12:31 pm

Dr Goggles wrote:There is also a good chance that between the first cut and the first run you will get fatter.........I weighed 73 kilos from 16 to 41, next thing I know I'm 84 :lol:
You forgot to point out that this is actually an advantage

(but only for one week - once a year)

:lol: :lol: :lol: :lol: :lol:
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David Leikvold
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bounce

Post by David Leikvold » Sun Jun 13, 2010 8:39 pm

The simplest solution to the suspension dilemma with swing axles is to build the rear end as per a current Formula Vee and have the transverse monoshock OR a solid rod (perhaps with height adjustment capability) between the pickups for the shock. That way both ideas could be tested back to back then Sam becomes the expert on whether suspension offers any advantage for HIS lakester. The only thing you'd have to do is make the pushrods and mounting points strong enough to withstand the shocks from being mounted solid, none of which would be difficult. The same thing would apply to the front end.

Cheers
Dave :D
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green

Post by David Leikvold » Sun Jun 13, 2010 8:59 pm

That green beetle is fabulous and would make a really interesting Competition Coupe, especially if the nose was extended to cover the H-beam again. Do it Mick, you know you want to :lol:!

Cheers
Dave :D
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or not

Post by David Leikvold » Sun Jun 13, 2010 9:17 pm

Actually Mick, now that I look at it again I'm sure there's a rule that says you can't section the body of a CC so that would rule it out. And it couldn't be a lakester because it is based on a production car. I wonder if the rule would let you use a fibreglass stylised replica of a beetle that shared no dimensions or body parts with an original? That way you could build one that looked like the green one in profile but was much narrower, a bit longer and much more aerodynamic. The next problem is that it looks like it is probably only just over 2ft tall and might be very difficult to fit inside especially if you rotated the engine and transaxle. What the hell, nothing's impossible. Check the rules and start dreaming!

Cheers
Dave :D
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T-34
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Post by T-34 » Mon Jun 14, 2010 12:31 am

I'm not 100% where sectioning the bodies put it. My thoughts were that the rules state pre '49? (I think) cars are allowed to be channeled but later are not, also repro / replica are allowed too - so I figured that a split oval channeled and chopped would be okay as this puts it in the correct time frame (prod 1936 > 1952).

Obviously couldn't chop up a real split to do it so would base it around a later (early 60's) body - to which there are not many major differences (dash / rear window + other minor differences only a buffer would spot - most of which can be sourced + added in).

So in effect it becomes a pre '49 replica with a channel and chop - legal according to the rules.

Who needs a lo-boy when you can roll one of these - lol :shock: :lol:
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Post by sammj » Tue Jun 15, 2010 11:50 am

Ok bit of info.
With mid mounting and "flipping the box" the Ring is swapped sides to maintain 4 forward gears. Final gear of swing axles is .89 (an overdrive).
now the interesting bit. Old combi gearboxes with reduction hubs had a final gear of .82 due to them using reduction hubs. Also they are already set up with the ring on the other side to compensate for the reduction hubs rotation.

So.... If i use a early Kombi box, meant for reduction hubs but setup without and in mid mount position, I don't need to worry about getting a box machined and i gain a taller top gear.

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Dr Goggles
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Flipper

Post by Dr Goggles » Tue Jun 15, 2010 11:55 am

So.... If i use a early Kombi box, meant for reduction hubs but setup without and in mid mount position, I don't need to worry about getting a box machined and i gain a taller top gear.
There is no end to his cunningness, I think he has the BUG :wink: :wink:
...few understand what I'm trying to do , but they vastly outnumber those who understand why..

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T-34
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Re: Flipper

Post by T-34 » Tue Jun 15, 2010 11:59 am

Dr Goggles wrote:
So.... If i use a early Kombi box, meant for reduction hubs but setup without and in mid mount position, I don't need to worry about getting a box machined and i gain a taller top gear.
There is no end to his cunningness, I think he has the BUG :wink: :wink:
mnn tis a great idea - IIRC the volks rod in the first pic I posted used reduction boxes to get the extra lowering benefit from the axle offset.

I'm pretty sure that there are a few different ratios available too.

So would you hide these within the body, or keep them out at the hubs?

/DM
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T-34
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Re: Flipper

Post by T-34 » Tue Jun 15, 2010 12:05 pm

T-34 wrote:
Dr Goggles wrote:
So.... If i use a early Kombi box, meant for reduction hubs but setup without and in mid mount position, I don't need to worry about getting a box machined and i gain a taller top gear.
There is no end to his cunningness, I think he has the BUG :wink: :wink:
mnn tis a great idea - IIRC the volks rod in the first pic I posted used reduction boxes to get the extra lowering benefit from the axle offset.

I'm pretty sure that there are a few different ratios available too.

So would you hide these within the body, or keep them out at the hubs?

/DM
HAHAH ignore me - I should read the post before replying.

Although.....

using redux boxes and flipping the gears is also an option :twisted:

Mick
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