The fully homologated Stohr, Piper and Citation cars all use large rear "spars" that are in fact big stressed-skin monocoque structures that take up a third (or so) of all structural loads being fed into the chassis. Even Van Diemen, with its' use of a large cast aluminum "bell housing" (a de facto spar), is doing the same.
Yet, F-1000 is intended as a "tube frame chassis class." How can this be?
I'm not asking rhetorically. It's a very primary design question in this terrific formula car class.
Going further: What if a builder decided to employ a "spar" at the front of his chassis as well as at the rear? That is, a front "spar" running from, say, the front bulkhead all the way back to the front roll bar bulkhead? If that's legal, then what if these two spar units then grew in size... all the way until they met a chassis-center? A chassis made up of just two spars linked together. And then, taking it further yet, what if those units were not fabricated from fastened aluminum plate, but rather from 2024 aluminum sheet, folded, bonded and riveted? You'd then have a damned Lotus 49!
The answer to this question must be quantified somewhere in the GCR, but I can't find it. And any help would be greatly appreciated.
The Z10, built from 1974 to 1978, was the last car with a tube frame that I was involved with, that you could remove the engine and transmission and still roll the car around. Since 1980 practically every car that I am aware of started to evolve to the point that the engine/bell housing/transmission became major structural members. Reynard has used a casting for the front major structural member as well. Reynard even cast their own transmission/bell housing that was the rear structural member of their car. You might call it rules creep.
As to FB, I think that getting sufficient structural strength and making minimum weight with an all tube structure is tough. I admire those who have accomplished it.
You still are using a tube structure to connect the front and rear of the car together. And tube structure still caries the driver and fuel. At the end of the day this is still a tube frame.
..... Since 1980 practically every car that I am aware of started to evolve to the point that the engine/bell housing/transmission became major structural members. Reynard has used a casting for the front major structural member as well. Reynard even cast their own transmission/bell housing that was the rear structural member of their car. You might call it rules creep.....
Yes he DID from 1987 to 1992. And woha onto those who damage one beyond repair. They are only available if somebody parts out a car.
Originally Posted by S Lathrop
.....As to FB, I think that getting sufficient structural strength and making minimum weight with an all tube structure is tough. I admire those who have accomplished it.....
As the early FB's were converted from (mostly) FC cars, they did away with the LD200 and MK 8/9 transaxles and went to a 'tube' type supporting structure for the chain drive differential.
Stohr, being the first factory built FB carried their D/SR design in to FB making the engine a stressed member with the differential and rear suspension supporting structure bolted directly to the engine.
The objective of the rule is not to necessarily state that ALL components on the car must be attached directly to the tube frame structure. Rather, to EXCLUDE a carbon fiber tub or, monocoque chassis.
To try and build a triangulated structure at the back of a 'tube' type formula car to take the loads off of the transaxle would be very complicated and make working on the car far more difficult as much of it would have to be a 'bolt together' design to allow removal. Castings at the front of the tube chassis are simply an easy way to get strength with reduced over all weight with a simpler structure.
This plus the use of shear plates and brackets helps protect the chassis from damage in the event of a shunt. A bent frame is the last thing you want to deal with if you're involved in something on track. EXCEPT in the 87 to 92 Reynard where the last thing you want is damage to the transaxle!
CREW for Jeff 89 Reynard or Flag & Comm.
Here is a picture of the steel fabricated version that I designed for the Phoenix F1K.09 and F1K.10.
In just about every crash I have ever seen where a sheer plate gets ripped from a chassis, the chassis also gets pretty badly damaged. This makes me wonder why we would even bother to use sheer plates.
I don't think anyone could design a car for SCCA racing with only the rule book to go by.
You have to know the history, the court rulings over the years, the intent and then decide how brave you want to be in pushing the envelope.
For instance, I think the Swift DB1 Formula Ford was the car that blew up the space frame rule. They semi-stressed the engine and the SCCA bought it. At a stroke that obseleted every FF built (for aerodynamic reasons) and made for a nice profit center for Swift. The car had several other questionable areas of legality, engine cover height and forward roll hoop braces as I recall. I fully admit I could be wrong on some of that, you really have to find an old timer to get the history - someone like Richard Pare.
So today I think the pan and transaxle are considered aluminum brackets in FF. I think Mike Sauce pushed it even further with aluminum tube structure in the engine bay of his FF's.
I personally have no problem with technical advances, that's why I like racing cars. Some people think otherwise.
The Stohr FB and DSR do not stress the engine anymore, that was done on the first gen DSR's.
Yes, I'm thankful for email and a very helpful member of the Comp Board...if I had designed our car strictly by the GCR we would be in big trouble! There is definitely a lot of history out there.
My understanding is that the main frame of the car, including main roll hoop, front roll hoop, lower main frame rails, and front bulkhead has to be of tube frame construction and meet the dimensions and limitations outlined in the GCR.
With the exception of the floor pan, front bulkhead, front roll hoop bulkhead, and main roll hoop bulkhead, no panels can be attached to this structure with centers closer than six inches.
Anything attached to the main frame (as a "bracket" if you will) can be built in any manner you like, including monocoque-type construction, as long as it isn't attached with centers closer than six inches. That's why cast and fabricated bell housings, stressed panel engine bay floors, etc are allowable.
I agree with Lee about technical advances...isn't that why we build cars?
Just a thank you to all those who weighed-in on the spar question. I guess a lot of people wish the rules were just a little bit more precise. But then these sorts of vagueries occur at all levels of motorsport. Always will and always have.