Project: Geo Metro boat tail prototype - 15% MPG improvement @ 90 kph / 56 mph

[3-Wheeler]

Originally Posted by MetroMPG

I think I'm going to aim for a 6 degree bottom angle, approximately what's shown there (don't do the photoshop measurement to check my work on this image - it's 5 degrees there.)

Bicycle Bob advocates for no more than a 4 degree angle. Unfortunately, that will leave the end of the tail a bit lower than I'd like for departing slope angles from the back tire.

Hi Metro,

When I read your post, the first thing that came to mind was to use Vortex generators to supplant the 6 degree angle. Then I read Bicycle Bob's comments and it seemed like a confirmation.

Jim.

[MetroMPG]

Didn't do a whole lot today other than set up the strings & rear "transom" you see below. Obviously if I follow the strings, I'm not aiming for curvature (going fore/aft) on the cardboard prototype.

Next step will be to cut out two more intermediate cardboard "bulkheads" that will help support the outer skin and the overall structure. There will be some triangulation in the aluminum frame too. Basically I'm winging it.





Should have more time to work on this tomorrow.

[Sorrow Six Star]

awesomeness embodied! looks very cool!

[MetroMPG]

Hopefully the shape/angles are OK. Because it's no small task. Tuft testing will reveal all...

Tomorrow I need to make 1 more bulkhead, then find some thinner cardboard to skin it. The stuff I've used so far is double ply. Good for structural bits, but heavy and harder to cut/form.

Oh, and I should probably pick up another roll of duct tape.

[KJSatz]

Can't wait to see how it goes! Encouragement encouragement encouragement!

[MetroMPG]

Originally Posted by Bicycle Bob

Wheels are the 1st thing that come to mind, but they create point loads I try to stay away from.

Good point, that.

[orange4boy]

Darin,

You are a string artist! Looks cool just the way it is. Makes me think a tent designer could do something with fiberglass poles and ripstop nylon.

If and when I get around to my collapsable boat tail, I will make it four framed coroplast flaps that fold flat against the back of the van. Hinged on the trailing edges and joined with quick connectors. Unfortunately that pretty much makes it a square edged design to keep it simple and the dimensions would be restricted by the area available for the folded flaps when stowed.

Exciting work.

[Nerys]

Hmmm collapsing this SHOULD be very easy. use FABRIC to skin it and then have those aluminum polles in 3 sections that Telescope into each other with locking pins (or pop buttons like on EZ up tents if you can manage the fabrication or find the poles.

you could collapse the poles into each other FOLD them into the center and now you have something nice soft and FLAT to stow in the car.

the trick would be the frame ON the car. the easiest but most finicky would be welded SPIKES a few inches long that the tubes would insert ONTO to hold them at the right angle and stiff. then a couple bungies on the INSIDE of the tail to hold it all taunt.

Looking VERY nice so far.

[Funny]

OMG, why didn't I see this thread before!!!!! Subscribed... Look forward to the sweetness that we should soon behold!

[MetroMPG]

No sweetness today - all I managed to do was pick up a large box made of lighter cardboard that will mean making the skin will be easier.

Tomorrow I should have more time to fiddle with it...