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

[JeepNmpg2]

I don't know XJguy, Basjoos drives a lot faster than Darin and he hasn't related anything to us about relative "takeoffs". If anything he writes about how stable his car drives. I digress that sidewinds will plague him more with his increased lengthwise cross-section, but there is always a trade off right?

[RobertSmalls]

Originally Posted by JeepNmpg2

I digress that sidewinds will plague him more with his increased lengthwise cross-section, but there is always a trade off right?

If crosswind stability becomes a hazard, there is a remedy:

Designing a tail extension for the first-gen Insight

[MetroMPG]

Matt - just saw your question. Probably to late to be useful on your project, but I could shake the car pretty vigorously wiggling from the tail.

Low frequency shaking though. I probably would have pulled some tape off with fast shaking.

[3-Wheeler]

Originally Posted by Blogpostwriter

Nice project. I suggest you use a thin plywood for your tail.Its better than plastic because its more durable. It is best also to use contact adhesive in joining ends than to use epoxy. Contact adhesive sticks harder.

I'm a little reluctant to agree about with the statement above about contact adhesive.

Is this the same stuff that you spray on and let set for 20 minutes before bringing the two halves together?

I use epoxy on all sorts of stuff such as wood and foam, and once you get a good bond, it is permanent.

My experience with contact cement has not been as highly rated, due to delamination of layers over time, and the forces were low to-boot.

Jim.

[3-Wheeler]

Actually, MetroMPG's project gets my vote for mod of 2010.

There are several reasons:

1) First complete tail extension that I remember reading for last year.
2) First example of the video cam-on-a-stick. I was amazed upon seeing this.
3) Beautifully done rear wheel strakes.
4) Showed the true worth of the tail addition in the form of a 15% mileage increase.
5) Fabulous tuft testing, showing the air efficiency gains of the structure.
6) Very well designed AND lightweight structure from, what else, cardboard !!
7) Nicely crafted tight fit around the leading edge of the tail piece.
---- this is not easy, since if you cut too much off, it's hard to add back on.
8) This tail was the motivation to make one for the Insight.

Overall, an excellent example of how to build a beautiful tail extension.

Jim.

[MetroMPG]

Thanks for the kind words, Jim!

But my tail doesn't qualify on a technicality: I did all the building/testing in the early winter of late 2009.

This is my only picture of the tail I took in 2010, when it went out with the recycling.

(OK, I kept the aluminum tubing.)

Darin

[3-Wheeler]

Originally Posted by MetroMPG

...But my tail doesn't qualify on a technicality: I did all the building/testing in the early winter of late 2009....

Darin,

Then let's hope that I get a chance to vote on your project for 2011 !!

Jim.

[jtbo]

Originally Posted by Funny

Fortunately, Darin's need for speed brings him up to a whole 55 mph....

Therefore I see zero possibility of catastrophic incidents at this time, at least caused by D.

Sorry for being late from the party. I have been reading these threads with great interest, have been learning many things from all of you.

This quoted comment above deserves bit more thinking, imo.

Speed of driving is one thing, then we have the wind.
If driving against the wind, in gusts it is not rare to reach total aero speed of 100mph and violent gusts are really sudden danger to be aware of.

That is reason why I think mods should be planned speeds above 100mph in mind, to avoid any possible problems, parts becoming loose or car becoming airborne.

In here roads mostly have only one lane to each direction and nothing separating lanes instead of paint on tarmac, so I have to take account of gusts that oncoming big rigs are causing, it is easy to hear and feel that air which they move.

So I think it is misleading to think that driving at low speed does not require design to be working at higher speeds, but of course driving higher speeds say 100mph requires designer to think how to make shape work in speeds around 150-160mph because of normal wind, add storm and wind speeds of 100mph to be absolutely sure and there starts to be a challenge to design working mod.

What do you think, will it be effort wasted or is my thinking reasonable?

[basjoos]

I've tested my aeromods at speeds up to 100mph.

[MetroMPG]

Whereas my car's unaeromodded flat-out top speed is 100 mph. (~50 hp. )

There's no way I'd be attempting to drive 50 mph into a 50 mph headwind - accelerator floored in 3rd or 4th gear or whatever it would take. I never need to drive anywhere that badly.

Of course if someone else is planning to mod a car to drive in those conditions, then of course higher apparent wind speeds need to be taken into account and/or tested. I only drove this proof-of-concept tail at road speeds up to 100 km/h, in let's say ~15 km/h winds (guess).