Chassis Rigidity - Replicas v. Origianls

[Cliff Beer]

With regard to the clamping of stainless fuel hose.

If the hose is rubber with just a stainless braid covering then it is alright to use hose clamps.

If it is the Teflon inner hose then as you tighten up the clamp it causes the Teflon to extrude out from under the clamp.

If the fitting on the tank has a ridge to grip the hose, when you tighten the hose clamp the ridge will cut through the Teflon due to the amount of pressure the clamp exerts and the minute surface area of the ridge.

Even though it feels secure because of the stainless braid the Teflon hose will leak where it has been damaged by the clamp allowing either fumes or fuel to escape.

Dimi.

+1. Best to have a proper hose fitting installed at your local hydraulic shop - one that is compatible with the type of hose (and obviously fits the fitting on the tank). I have all kinds of hoses made up at my local hydraulic shop and they're not that expensive. Nicely made, appropriate for the type of hose and liquid being carried. We have very good hydraulic shops in Seattle here with all the aerospace influence.

Incidentally, regarding chassis flex, I bet any original GT40 chassis that hasn't been rebuilt over the years is about as stiff as a wet pasta noodle. Take a look inside the original sponson of a 40 year old GT40 and you'll see a lot of rust and diminished integrity. Moisture held between the bag and the pressed ribs and such is a killer, especially when there wasn't rust proofing as in the originals. Of course, most have been rebuilt over the years however.

 

[Seymour Snerd]

This is a 8AN hose for cross-connecting the two tanks. It's not teflon.

>>>Best to have a proper hose fitting installed at your local hydraulic shop...

Whoa, Cliff, you come over and disassemble my front suspension and pull out both tanks.... I'll give you a beer. :heart:

About having hoses made at a hydraulic shop...... Really? For anything under a few hundred psi, I just buy hose ends from Summit or Jegs or my local Aeroquip distributor and make my own. It takes about 2 minutes and costs about 30 bucks, and if it's not *exactly* the length I want I can redo it in another four minutes and make it perfect.

What I *really* want to do is replace the whole stupid thing with stainless tubing. But I have to draw the line somewhere or it's never getting on the road. OTOH after Alex's comment I'm going to pull the hose off and find out what's under there... Maybe I'll get lucky and find they put a hose clamp over AN male.

Oh yeah, thread drift.... That piece of tubing would raise my torsional rigidity by 3 oz-microns per radian.

 

[Dalton Veitch]

I think it would be more like 3.2 oz-microns per radian.

 

[Ian Clark]

I wonder about the variance in chassis rigidity between original cars. Alan Mann had a couple of aluminium tubs, yes? The Mk11s had firewall mods to make room for the big mill, the X1 Roadsters had no roof, late JWAs and Mirage had light roofs and cowl revisions, Mk111s had no central tunnel. All of these effect the numbers. We do know the chassis was good enough to win just about every major endurance race going. They weren't fond of crashing though.

This is where modern race cars and road cars are built to a different standard. Things are not as they were. We lost a lot of great drivers in crashes that in todays racers they'd have walked away from.

What that means in response questions about things like how are the tanks mounted, uses of side ribs, data on torsional ridigity etc comes back to minimising harm when things go bad.

About the CAV monocoque, yes it is not as complicated or accurate as the SPF but I can tell you we've had a couple of bent ones on the surface plate, these cars are tough. There are pics on the forum of a CAV that went into a tree at something above 30mph. True to form, the tree didn't move.

However the CAV chassis did not collapse around the driver or companion, nor did the bladder fuel tanks burst. Fortunately they were wearing five point harnesses. I suspect in the majority of modern road cars, they would not have survived. We looked at pulling it back to shape but ultimately decided it wasn't a good idea.

CAVs have a tubular substructure additional to the folded sheet steel monocoque main structure. You can take out the extra tubing and still have a chassis but it was designed in.

The firewall has rectangular and square tube roll bar structure integral, the sill boxes have square tube outriggers welded in during manuacture as do the sides of the foot box and the rear of the chassis between the firewall and rear "horse collar" bracket. It's well done.

Chassis rigidity as it pertains to handling, so long as the suspension geometry is not effected by normal travel and knocks like curbs when cutting the apex or on corner exit, it's stiff enough. If the suspension deflects from intended paths the chassis has to be made more rigid. Alternately you can design the chassis to flex in a complimentary manner or at least not detrimental to the handling, or stay off the curbs and bumpy surfaces

Cheers

 

[Bob Putnam]

I suspect that the roof added very little to the overall chassis rigidity. Look at the path that the strain must take: Up the pillars into a very narrow center section. Not much there.

 

[Ian Clark]

Bob, gotta agree with you on that if we're talking impact protection.

I do recall something about the roadsters not working out as well as hoped at Targa Floria because of reduced stiffness in the chassis.

If that was the case an original chassis (without the roof) would flex under suspension loads... just speculating. For that to happen a lot more is going on than simply loosing a couple of windsheild posts.

I believe the roof structure plays a major role in joining the two sill boxes together on original tubs. It is a large double wall arch extending over the top of the firewall and rear (bulkhead) window. There is a stamped rectangular section spot welded below the bulkhead window above the access panel openning as well. Plus the windsheild was bonded in place acting as a structural component, not floating in a rubber gasket as was common back then. I wouldn't attribute any strength to the access panel however.

In the case of original chassis then, my suspicion is that by removing the roof there's only the stamped rectangular section above the access panel left to tie the sill boxes together. The horse collar and triangular section behind the seats are still there of course so they do not contribute to the (speculated) loss of torsional ridigity. From the pictures (thanks Jimmy, John) a roadster would be closer to an incomplete tub in terms of stiffness.

I wonder if in the Mk11 roadsters (X1s) there was reiforcement added in the remaining firewall area to beef it up. The X1 did win Sebring and that's not exactly a smooth circuit...

Cheers

 

[Rick Muck- Mark IV]

Ian,

I agree about the roof. While the front "A" looks thin, they are quite robust behind the windscreen as most is hidden. While what you see outside is less than a 1/2", the depth and width inside are enough to transfer a fair load. Plus add that the rood is double walled and you have some capacity for loads to be handled both fore/aft and transversly.

We shall see when one of my Superformance customers tranforms his car into a roadster with one of the original roadster windscreens he has.

 

[Ron R.]

I seem to recall that the handling of the GT40 with the roof cut off for the filming of "le mans" was termed "diabolical." Aerodynamics may have been a factor, but I suspect chassis flex had something to do with it.

 

[David]

Hard to tell if the film car suffered due to the lack of roof or the missing front clip (along with the wacking great camera bolted on).

 

[Mick Ridley]

David,

I wondered how long it would take you to find this thread.....

Taken on its own, ie, not fitted to the car, the roof section has very little ridgitity due to the narrow section at the top, and will twist very easily..

But when fitted to the car, the loads on that narrow section, are no longer twisting loads ,but the loads on that narrow section, become shear loads, and therefore the roof section would add quite a lot of stiffnes to the chassis, in the same way that a roll cage would add stiffness

 

[David]

Mick,

Found it by searching for something unrelated but I'm not one to shy away from commenting on an old thread!

I totally agree though. Just making the point that in that example it wasn't just a missing roof that could have affected the handling.