Tuning fork design

[justin.wills]

I've been toying with the idea of building a tuning fork car for some time. many designs such as the GVP have been successful in the states, but there is one part of the way people are building them that just doesn't make sense to me.

most people are using a set of .062 fork rails inside either round or square tubing at the front. that is how the car twists. however, they then go and tie the nosepiece to the motor bracket with a second set of rails (whatever size they want to use). I see this then as just a single rail car with a fork that does pretty much nothing other than (maybe) apply some tortional force against the twisting that a single rail car would normally have.

looking at the rules, our local rules don't say anything about how the car must be held together. however, the IRRA rules clearly state that the front and rear must be tied together via the rails.

C - chassis
3i. Wire or tubing rails must connect the front
and rear sections of the chassis. Using metal
strip for this purpose is not permitted. A rail is
defined as that which connects the motor
bracket to the front of the chassis.

This rule clearly indicates that the front and rear must be connected. There are other ways to hold the front and back together, via the pans for instance.

If I were to build a car not connected from nosepiece to motor bracket, would it be considered legal or "in the spirit of the rules" ? I won't bother if the reaction is going to be "you can't race that" and I'd rather find out now instead of being told at tech. I'm not trying to build something that can change its length, just something that isn't bound up by a single rail design

There are a billion discussions on other forums as to whether this is a centerline hinge design, and it has been deemed that the forks aren't down the center, so it's OK in that respect.

I'm only concerned with the legality of such a chassis. whether or not it will work I'm prepared to find out for myself.

comments ?

[Timmy Tyler]

It's not the clearest rule in the world, which doesn't help. Even so, I think the key point is the first sentence which states that "Wire or tubing rails must connect the front and rear sections of the chassis" (emphasis added). To me, that seems like a pretty clear statement which they are enforcing over there.

However, if our rules don't have such an requirement, then I don't see how anybody could reasonably object. I have had a re-read of our regulations and I can't see any provision that could be applied to render your proposal illegal. As a result, I can't see a technical problem. Whether somebody objects is a different matter though!

As to the "centreline hinge" issue, I think the original intent of that rule was to prevent the use of "flexi-board" type chassis designs. Flexi-boards were invented in the UK in the mid 1970's by Ian Fisher and they marked the first successful departure from the traditional drop-arm chassis designs. They had made the side-rails much more flexible to improve the mechanical grip of the car but they tended to sag in the middle and touch the track. The centreline hinge was installed to stop the car from decking out. What they didn't expect was that it would transform the handling of the car.

I believe the tuning fork cars work on the same principle: the so-called tuning fork provides very good anti-decking while leaving the torsional stiffness to be unaffected. It is the flexi-board principle but it is implemented slightly differently. Personally, I don't think that they are within the spirit of the rules, but that's just my opinion.

[SlotBaker]

I read it as being connected in some way. Either soldered and/or loosely.
Could be soldered solidly at either/both ends, or pin/wire located (longitudinally) loosely in a tube.

A door in your house is connected to the door frame via a hinge. So does that satisfy the definition of "connect"?
Semantics...

I'm not sure how the "flexi-board' works, so not sure how if relates to centreline hinges.

If a frame has a centreline rail with pans attached to it with loose fitting tubes, then that is a centreline hinge, and not acceptable.

If the pans are soldered to the rail and can't rotate, then that is not a centreline hinge and is acceptable.
It can be flexible via bending.

I really don't think anyone here techs Retro cars to that degree anyway.

There are/were plenty of illegal cars around when I last raced.
I believe that most Race Directors don't know what is legal or not, other than widths and clearances.

[Timmy Tyler]

I think you are right on all counts, Steve. As for how a flexi-board works, I wouldn't worry about it. Although they were the dominant design in scale racing for about about 20 years, they have gone the way of the dinosaur. There are now much more elegant and simple ways of separating the torsional flex from the anti-decking, and they can certainly be implemented on retro chassis without violating any spirit of the rules. That's if you want to, but I think retros work fine as they are.

I would like to see Justin build a new and innovative chassis, and if it complies with the rules then he should be allowed to race it. End of story.

[justin.wills]

A door in your house is connected to the door frame via a hinge. So does that satisfy the definition of "connect"?

I love that explination. this is one of the methods I've been thinking about and unsure whether this constitutes a "connection". when used in the door example, it most definitely is "connected" to the door frame.

I know the intent is to be as close to the US rules as possible. so not much point doing it if our rules were to be re-written to make it clearer and illegal.

if the "door hinge" idea is legal, then the requirement for the fork probably becomes unneccessary as you can put all the flex you need into a single rail design.

[SlotBaker]

Justin, I posted a link on SlotBlog to get their take on it.

[justin.wills]

thx. I'll keep an eye on it.

I think we know the answer to that though, which is why GVP style are soldered both ends on the outside rail.

many are using hinges, etc and then a .032 tie rail so that there is a solid connection front to rear. I have done this with my "spoon" chassis which doesn't have forks, but double .062 straight rails with opposite ends floating in 3/32 tubing.

this makes the .032 rail the "main" rail. however, it can get in the way of other things like pan hangers, depending on how the pans are mounted

[SlotBaker]

Following on from that.... how thin can the 'rails' be??

Does 0.005" dia pass?

[Timmy Tyler]

Nice work, Steve, posting on Slotblog. You and Justin appear to have homed in on the critical issue here. Does .005" count? According to the rules, yes it does. There is no minimum rail thickness specified. I'll be interested in any feedback through Slotblog. Once again, good on both of you for your perceptive analysis of the issue. I am really interested to see how it works out.

[justin.wills]

Following on from that.... how thin can the 'rails' be??

Does 0.005" dia pass?

sure does. There is NO minimum rail thickness

[SlotBaker]

Response from Noose;

"Some rails need to be soldered, both front and rear.
No min diameter for the rails."

[justin.wills]

Yeah, I saw

Explains peopke using tie rails to hold it all together.