Two posts ago I speculated on moving the seat forward and putting the gas tank behind the seat. Well without making a custom tank or severely cutting the body, or both it won’t work. I just spent an hour climbing in and out of the bare body with the steering wheel. If I put the steering wheel inside the passenger compartment on the normal side of the dashboard even with the steering wheel in my chest there’s no room for a commercial fuel cell between my butt and the back of the car, except the 3 gallon tank , which would be great for racing, but pretty crappy for driving to and from the races. Especially with E85 which isn’t common. There is room for a big tank behind the driver’s seat, but it would have to be built custom for the space. I roughly estimated that a 30 gallon tank would fit with room to spare. If I got really crazy it would be over 40 gallons, but that would require basically making the inside of the body part of the gas tank, which like I wrote, would be really crazy.
Another alternative is to make a race-car like cockpit like this Lotus 49.
Basically the cowl would be cut away where the windshield is on the Lotus in the picture, and my head will be just back of the original location of the dash. There’s lots of room to play with out front once the gas tank(s) is(are) gone, but almost none behind the body because of the engine and its systems. The bad part of this would be my feet would be right up against the radiator. The good part would be there would be room for a 32 gallon fuel cell behind me which would mean 700 miles between highway fill ups with some cushion for crossing Wyoming or west TX running E85. How often I would be doing that is unknown. The only thing I could think of would be the Goodguys Shootout for the year-end champion in autocross held in AZ.
Well I have about run out of words but not ideas which continue to run through my brain but not in a complete enough form that I can post them to this blog.
Still thinking about making the TGS2 lighter and simpler to build and I had a minor revelation. If I lower the 3″ tube until it is on the axle centerline that will reduce the bending moment enough to not need any bracing other than what is provided by the double-shear spring mounts (that’s a plate on either side of the coilover heim with the mounting bolt going through both plates) welded to the top. That unloads the top radius rod on the 4 link allowing for higher loads from restraining the brake rotation etc.
Someone asked me IRL how I know there is going to be so much weight in the back of the car. That one is simple: The engine and trans combined weigh 620 pounds with the CG about 10″ in front of the rear axle centerline on a car with a 100″ wheelbase that will weigh about 1600 pounds. I’ll let you do the math yourself, after I set the equation up for you. The arm for the drivetrain is 90″ and the weight is 620. The arm for the rest of the car is going to be 40″ if we are incredibly lucky, probably real close to 50″ split the difference and call it 45″ and the weight is 980. Moment is weight times arm. Add the moments together and divide by weight. That is the total arm of the car, between 63 and 65.5 and since we used the front axle as zero datum and we have a 100″ wheelbase that makes the rear percentage equal to the
momentarm, I.E. between 63 and 65.5 percent. I learned this one when I was taught weights and balances for flying. Yes, I used to be a pilot before the wreck. Sioux this one was for you 😀 Math IRL for your students. Oh and the reason I don’t know the exact arm for the rest of the car is there are a bunch of parts I don’t know the exact weight for nor where they will go on the car when it’s finished. So I had to use a SWAG for the arm of the car without engine.
Excuse me I zoned out for a moment listening to an old piece from the ’70s on YTM; Mike Oldfield’s “Tubular Bells (Pt.I)”. They had just gotten to a part of the piece I call “The Procession of the Instruments” that starts about 17:00 into the piece, and continues to the end of Side One of the LP. This was one of my first experiences listening to polyrhythmic music, which my mind finds very relaxing. Anyway, Mike says the name of the instrument and they bring it up in the right channel then mix it over to the center front then over to the left and back but still up enough to hear if you focus on the sound. I didn’t know this at the time but polyrhythmic music has a calming effect on people with ADHD and PTSD. At the time there wasn’t any such thing as PTSD by that name, it was “Shell Shock” and didn’t happen to kids (that they knew), but I had been diagnosed with “something” tied to my high IQ, that we now know as ADHD. Anywho, when I listen to polyrhythmic music I zone a bit and get real calm.
Back to the car, I’m really feeling torn between totally enclosing the roof and windows and saving weight. Putting a roof and windows on it will make the car look more complete, but will need A/C in the summer. Or I could figure out some other way to keep dew and rain off the instruments and save about 50 pounds, most of it off the back of the car, by leaving the A/C in the donor vehicle and cooling the car by leaving the windows off. That would save even more weight but lower the gas mileage on the Interstate a bit. Basically all I really need is something to cover the cluster and seat when I’m not driving. I could make a snap-on cover like old hot rods and sports cars used in the ’40s and ’50s, called a tonneau. These days a tonneau is basically the thing that goes over the pickup bed when it’s empty, but back then it kept the interior clean and dry when the roof was down or if there wasn’t any roof at all. I bet I could make something with the HDPE sheet and some Velcro™ and get the same effect and roll it up inside the car when I was driving.
And I think I have meandered across the screen enough for today.
My main guide to engineering is the math, but after that is my sense of engineering esthetics. And sometimes that gets in the way of finishing a design. Seriously, the single 3″ tube would have worked fine for the de Dion suspension, but a truss would weigh less and be stiffer, by a small amount on both counts. And the new truss is much simpler both to build and to mount than the previous truss of 0.5″ thinwall tubing with a plethora of tiny triangles in two planes as it is just 7, 1.5″ X 0.120 wall round tubes in a single plane. The tube diameter and wall thickness are enough to hold the toe and camber alignment while the truss is strong enough to take all the vertical and horizontal forces with a huge safety margin. The truss weighs 20 pounds with brackets, not including the filler wire from the welds. This compares to the 3″ tube which comes to exactly the same weight but not as stiff vertically. Or as pretty to look at, which as I wrote earlier is an equal criteria after weight.
I mean face it, the 3″ tube would work just fine and probably less than 3 people out of 100 would be able to feel the difference in stiffness compared to the truss. Even fewer than that would care about the looks of the truss compared to the single tube. TBH even I am just the slightest bit ambivalent about the difference in appearance between the truss and the single tube. There is the simplicity of the single tube across the back of the car, but on the other hand there is the zen-ness of the collection of triangles running across the back of the car, even if it is hidden by the bodywork for aerodynamic reasons. There is also the fact that I can lower the roll center by almost 2″ in the rear to reduce oversteer slightly with the truss. And finally there is the cost issue, a single 58″ 3″ X 0.120 wall tube is less than half the price of the 132″ of 1″ X 0.120 I would need for the truss.
And even while I’m thinking about the rear suspension I’m still thinking about the cockpit and a possible roof and side windows. Mrs. the Poet is still saying there is no way I’m going to be able to get in and out going through the top of the roll cage after climbing the side of the frame. I have zero doubts about getting in and out of my own car, if for no other reason than I will have lots of time to use the frame as exercise gear to get my upper body strength up. Or I could screw together some black pipe for a dipping rig and chinup bar and continuously build my upper body every day. 😀
And I think I need to go to bed now, and so become the Nighty Knight.
I was thinking while walking again, and I wondered if a single 3″ OD 0.120 wall tube weighed more or less than the complex truss of half-inch tubing I designed for the de Dion suspension that still needed more work to actually support putting a spring on it. So when I got home I looked up my truss calculations and found I was putting just shy of 15 pounds of tubes in the version that just kept the rear wheels pointed in the right direction.
Then I ran a quick bending load calculation on the 3″ tube and it won’t need any extra support aside from the gusseting action of the spring mount (I mount coilovers in double shear mounts and tie them with bulkheads). Then I looked up how much it would weigh…18 pounds for just the bare tube, 20 with the brackets to make the upright adjustable.
Five pounds, I spent hours with a calculator, and paper and pencil for a design that saved 5 pounds and still needed more work to get right. Five freaking pounds, at minimum wage those pounds cost me about $20 each, maybe more. Probably more. A classic case of over-design. Now granted it would take a huge shunt to make a rear wheel point in the wrong direction and there is a good chance the tire would get knocked off the rim or the rim bend or break first, but the fact remains I couldn’t mount a spring anywhere except the upright or trailing arm without redesigning the truss, and adding weight, when I discovered that there was no way to balance the handling without moving the rear springs inboard. Now the fun part is moving the spring mounts on the frame inboard to prevent frame flex.
There are a couple of ways I can move those mounts in to get the springs off the ends of the axle. One is just change the mounting point to the crossmember and make that a truss to handle the bending load. Or I could continue to mount the springs to the heavily triangulated intersection of the upper frame rail, lower frame rail, center top hoop of the roll cage to upper frame rail brace, crossmember, lower crossmember to watt’s link center mount brace and taillight mount (that’s the intersection of 5 tubes in 3 different planes triangulating the mount to kingdom come) and move that complex intersection inboard a few inches as needed. Right now that intersection exists only on paper, not in steel, so moving it is just a matter of changing a drawing. This would also have an effect on the engine mounts as the tubes they mount on get moved inboard an as yet to be determined amount.
Now I’m going to open up a beer and eventually go to bed.
Opus the Unkillable