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Originally Posted by aerohead
...an exo-duct diverging nozzle...
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Whenever I think I understand things, I just go read that again.
Like a lot of others, I started by comparing The Template to the side view of my car. I was dismayed to find that the boat-tail would be 98" long—about equal to the wheelbase of the car.
Oppan Tropfenwagen Style
Working only in plan, from a belt-line width at the back of the doors of 56", I find that a complete boat-tail would terminate ~36" from the present back bumper, making a 14' car 17' long.
I ran into a stumbling block on another project, so rather than be thwarted, I grabbed two 12' pieces of Redwood bender board, bungied them to my bike rack and clamped the tips together. The vertical stake holds the end at a height that is just out of sight in the rear-view mirror.
It appears that 10" lengths would have been better and I'm not sure about the acute angle at the very rear.
Then I made measurements and took them home to compare with <<template MRT1022.jpg>>. It has a fineness ratio of 2.5 and a max width 30% back from the tip.
I consider 3 stations on the shape. Setting the rear length to 7/4ths of max width (56") gives 98". At 41" behind that the very ends of the drip rails are 41" apart, slightly narrower than the template line. At 61" back we find the bike rack at 36" wide, slightly wider than the template line. 98" less 61" leaves only 37" from the inside of the bumper (it's curve and thickness add ~12" to the overall length) to an un-truncated tip.
I'm curious about the Template compared to the Dymaxion and Schlorwagen. The line in plan on the Dymaxion falls between the other two, but the Tropfenwagen looks to be pretty sharp.
I'm thinking that a backlight like a Studebaker Starlight coupe would be easy to fabricate with two sheets of lexan and a center divider; but I also like the idea of leaving the stock backlight exposed with a little triangular Redwood deck below it.
The next mock-up will have pieces cut to the angle of the drip rail, and have a properly angled wedge at the back. Aluminum flashing sandwiched behind the fender beading will offer an opportunity for mounting points below the drip rail, leaving the stock fenders and tail-lights un-modified.
I'm not seeing a lot of collapsible at this iteration. The trailer frame and wheel are starting to look like a lot of dead weight. I can make a curved triangle from 1" or 1 3/8" tubing that will plug right in like the bike rack does.
An update on gas mileage: Early in October I did 106 miles, mostly in convoy at 55mph, and saw 21.8mpg. Needless to say I was a little bummed. I filled up again on the 31st. Once again I traced my route in Google Maps and got a distance I can compare with my odometer. There is some uncertainty because I may have made one 22 mile round trip 4 times instead of three. Google says 259.9 or [282] miles. The odometer says 390 miles. So my actual mileage is either 66% or 75% of the odometer reading, and my gas mileage, driving normally (freeway mixed with intown and two-lane shortcuts through the hills, e.g. pretty average for me), is either 26.8 or 28.8 mpg. Or I could be stupid and say I'm getting 40.2 already!
I'm pretty OK with that. When I refilled it was with E85 regular. I've been been burning Ethanol-free Premium, which is down from $5.19 to $4.69 within this month. I'll probably alternate tanks to compare the differences.