horizenjob wrote:
My take on this is try and look at the bigger picture then just the tunnel. I think you a re trying to also. So among all the things you would like to accomplish I would prioritize occupant safety, which pushes me to put more material on the outside of the car. A simple thought experiment here is that if you remove one piece of 1" square tube from the tunnel, that's enough material to increase the size of the chassis rails by 25%. That would increase their stiffness and strength by a factor of 2.5X.
You can see where this is going. Using material to increase the diameter of chassis rails swamps any other effort. There is enough material in the tunnel tubes to both increase the diameter and the section of the chassis rails. Also to raise the upper rail a bit.
Protection from the driveshaft can be provided by 1"x1/4" hoops with an attractive bend on their top. These hoops make a nice way to bolt in a sheet metal cover welded to them. Less mounting hardware because the sheet can be well attached with welds to the hoop and the hoops are strong enough for fewer bolts.
That's thinking outside the tunnel!
That's a very interesting point of view, Marcus. That's a very interesting figure, the 2.5X one, that I've never seen before. It's pretty dramatic and I'm going to assume you've done your homework and accept it. I see lots of people obsessing about weight. I understand the argument and if you're building a race car 30 pounds can make a big difference, all other things being equal, with respect to your competitors. Most of us are building street cars and I think strength and safety are the first concerns and an extra 30 pounds (what I added in steel including size and gauge of outside rails) is not a big issue
in that context.
First, we could all lose 15 pounds and get half back immediately and be healthier too. Second, we can probably all get 15 HP by careful and minor work on the engines and still be ahead in terms of the most basic indicator of performance.
Case 1) 1600 lb/ 150 HP = 10.67 lb/HP
Case 2) 1600 + 30 -15 = 1615 lb/(150 + 15) = 165 HP = 9.79 lb/HP
My other "back woods" reasoning is that with a better tunnel (compared to a simple, quasi-structural sheet metal one) you are essentially taking the worst performing area of the Locost chassis, the passenger compartment, and turning it into two improved "cells" that will be obliged to give you better over-all chassis performance no matter what the particular numbers in bending and torsion prove to be. I'm assuming you do something sensible and not totally silly with the tunnel.
I also accept that someone could come up with a nice, sheet metal structure that would accomplish the same thing. I just haven't seen one yet on a Locost.
Cheers,