Daily Archives: December 5, 2017

Spitballing other gas tank options for the TGS2

I have been thinking about other places to put the gas tanks than inside the body with me.

One place they will have an aerodynamic effect is between the wheels to fair them in aerodynamically and keep the undercar and top of the car separate aerodynamically. This design would basically be a wall instead of a fence keeping the high-pressure flow constrained to the top and not letting it spill over into the low pressure flow under the car, and also clean up the wake from the tires. This will increase downforce and reduce drag at freeway speeds which will help the gas mileage. Now the bad parts, the tanks will be pretty vulnerable stuck out on the far edge of the car even if I put a protective cage around them. Also putting the fuel out there does bad things to the polar moment of inertia, which is a measurement of how much energy needs to be expended to change direction of the car. The further away the tanks are from the center of gravity the higher the polar moment and the harder it will be to make sudden changes in direction. I could make this work for me in setting up the car for highway use where a high polar moment is good for stability, and run pretty much empty tanks for racing and a low polar moment for a car that changes direction almost telepathically.

A quick punching of numbers on the calculator app gave me over 700 pounds of E85 for near coast-to-coast unrefueled range (2900 miles), so I don’t need to use the entire volume available for fuel, some could be empty space for strictly aero purposes, or the tanks partitioned for ballast use to make the polar moment higher when I want it to be high. But with the tanks out on the edge I’m still stuck with the vulnerable in a wreck scenario. Now the other setup with the tanks inside the body with me but outside the frame gives me a low polar moment with tanks full and even lower with race levels (almost empty) than the outrigger tanks because even the empty outriggers have some weight and so does the support structure even without crash bars.

Something else that occurred to me was that I could use a 1 gallon fuel cell as a surge tank when in street mode and the total fuel capacity in race mode. On the street or even in race mode there wouldn’t be any time that I would drain a 1 gallon tank. In an autocross the longest courses I would run are less than 2 minutes long, while on the street even frequent stop-and-go traffic would not use fuel faster than a low-pressure pump could refill the surge tank, or gravity if the level in the main tanks was higher than the surge tank. There are several models in the current JAZ catalog from a quart to 3 gallons capacity set up for use as a surge tank so I don’t have to design this bit from scratch, just buy and attach the plumbing and drive it, NBD. And looking at the catalog I could easily stuff 2 10 Gallon cells per side into the outriggers without much effort. The only thing that might make it tough is the 9″ width getting towards the front of the enclosure where the tire it’s chasing is only 7″ wide. But a 9″ wide tank can fill the wake just as good as a 7″ one, if not better.

OK then, the fuel system is 4, 10 Gallon fuel cells with foam, 2 per side inside the wheel fairings on the outside of the car with the low pressure fuel pumps mounted between the tanks on each side, connected to a 3 gallon Pro Mod cell with foam as a reserve/surge tank feeding the high pressure injection pump. This gives me a system with enough range to get to El Paso from Dallas with reserve for adverse winds and also use crash-resistant containers to prevent leaks in case of a wreck. Also, dividing the fuel load between several containers limits the amount of fuel spilled in a wreck. Still subject to revision in case of a different donor vehicle, because changing the location of the engine changes everything else, and changing the donor vehicle can change the end of the vehicle the engine is placed in.