Adrian wrote:
3. Roll center height. Now I don’t see this as being supercritical in its actual height above ground. I think with the layout and style of the car the C of G is going to be very low. The only negative impact on C of G is going to be the transverse engine trans combo which will be relatively high and possibly worse give a steep C of G axis, up towards the rear. Obviously I don’t want it too high for jacking reasons and I don’t want it below ground as that would lead to the need for very stiff springs. I’m thinking 0-2” in the front with the rear at 3-4” This is something I definitely want input on. I’m also concerned about the roll axis inclination. With the high rear C of G, do I need a higher rear roll center and steeper R.A.I?
There are a lot of people with a lot of strong and conflicting opinions on roll centers. It seems to me that you’re taking a reasonable approach. Just from the way I was originally taught, I would probably set the front such that I would never expect it to go negative, even at full compression. So depending on how stiffly sprung the car is might be in the 2-3 inch range, then set the rear a ‘bit’ higher. As to exactly how much higher, well that involves some of those previously mentioned opinions, and I don’t think you’re going to be able to get a very specific answer from anybody…Including myself. But I would think you should be pretty safe at least up to the point where the distance from the CoG to the RC is the same both front and rear, of course assuming you know where exactly they are.
Adrian wrote:
5. For the rear I would follow basically the same process once I’d finished the front. Starting with whatever the final RC height came out at the front I’d start around 1” higher (Do I need a great roll center inclination, especially given the high rear CofG with the transvers engine?) I would also aim for a greater camber gain in the rear as there is no camber gain due to steering. Both upper and lower wishbones would have to be shorter due to engine packaging. This will also lead to greater roll center migration Is this an issue?
As noted above, with the higher rear CoG a somewhat higher rear RC probably won’t hurt. As to the RC migration, that’s always a balancing act which will go back to those dreaded opinions, including at what point you would consider something an issue. For the what it sounds like your intended purpose would be, within reason I would not expect it to be an issue or necessarily make the car unenjoyable to drive.
Adrian wrote:
7. Wheel frequencies, not sure right now, I’ll need to look into that. Suggestions?
Depends how much aero you plan to run. Without aero generally speaking you would probably be pretty safe in the 2.0-2.5ish Hz range, but might push closer to 3.0Hz depending on circumstances. With aero the sky is kind of the limit, depending how much downforce you’re making.
Adrian wrote:
13. Steering column. I’m assuming just a straight steel bar. Do single seaters have a collapsible column? If so I would imagine an outer tube with a very close tolerance inner rod. The inner rod would have a long flat machined in it with set screws through the outer. This concerns me though. Again this is something I need advice on. The lower joint would be a UJ to suit the rack. The upper would be supported from a Heim joint.
I don’t think I would be comfortable in any car unless it had multiple joints along the steering linkage that would allow it to ‘fold’ if the chassis were to collapse. There are also rods/tubes designed specifically for this type of use which give a stronger rotational interface, but little in the way of axial sliding.
Adrian wrote:
15. Reading the GCR (9.4.5) it appears that the front and rear hoops plus side brace between the two can be 1.0 x 0.080” seamless, It might be easier to use 1.375 x .08”. It looks like the hoops have to extend to the ground, although I’m unsure if they sit on the chassis rails or go all the way to the floor level.
Remember that you’re building to Production/GT specs more than IT/T/SM. I believe that for the tube frame classes, it is essentially specified that the hoops must simply be integrated into the chassis. That seems to leave it somewhat up to the tech inspection though. And unless I was well under the minimum weight I would probably anticipate building from the next level up cage tubing as that can only help your case.
Adrian wrote:
17. As the heavy engine is going to be offset to the right, I’d place the battery and radiator on the left to counter that. This would be a balancing act and I’d imagine final placement would be decided once partly built so I can check weight and F/R Vs. L/R balance. I’d want them as far back as possible to help the cross weights, but as far forward as possible to prevent a too rearward C of G. Advice?
I would probably focus more on getting the balance in a more desirable state than the rearward weight distribution, provided you're comfortable tackling a more rearward weight distribution of course.
Adrian wrote:
Thoughts? Have I lost the plot or do I have the basics of an idea?
Seems like you’re on a pretty good starting track so far. And while you seem to have done a good bit of research I’d just say to keep searching around for more specific information on this site, and any others you can find, for topics that go into more depth regarding specific information you seek, as many of these items have been the topic of considerable discussions before.
I hope that all makes sense, as I'm TWT (Typing While Tired), and is helpful even though it's not really giving you a lot of direct answers...Since the answer to most car design questions seems to be "it depends".