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

[Cd]

Originally Posted by RobertSmalls

Mine does. The oil pan is completely in contact with the coroplast. I also have coroplast in direct contact with my radiator. No damage yet.

Coroplast melts at 160°C = 320°F. Motor oil is expected to be a little bit hotter than coolant, so I figure no more than 220°F.

However, I have measured my cat at 560°F, and I'm sure it gets much hotter than that.

Well, what I meant, is that after looking at AndrewJs bellypan, I noticed that he even had the Coroplast touching the exaust pipe ( header ) at the front of the car.
It looked like MetroMPG had the front exaust touching as well in the pictures, but as I look closer, it seems that he may have done the area around the exaust pipe in something other than Coroplast.

O.K. back on topic. ( the boat tail )

[Bicycle Bob]

I've been working with the stuff for a long time without noticing that the minimum forming temperature is 150 C. Of the common plastics, only polycarbonate is higher, at 190.

[MetroMPG]

Re CAD...

Originally Posted by RobertSmalls

What kind of software are you using

Sorry, should have said "CAD", in quotes. With a nod to Craig Vetter, I was talking about "Cardboard Aided Design".

Originally Posted by aerohead

Darin,the tuft images look great.They may be a little "nervous" in places,but they're mostly pointed "back" which means attached flow and no circulation.

Thanks for the input, Phil.

I'm a little nervous about those nervous looking side tufts. It's clear I could increase the top taper - those tufts are laying almost still right to the transom.

What I don't know - and maybe you or Bob can tell me - is this: should my goal be to taper as much as possible until I actually see evidence of separation through circulation/reverse flow, and then back off a bit?

In other words, will we achieve favorable drag results even as we increase the amount of "nervousness" in the tufts (evidence of tubulence and a thickening boundary layer) through further tapering?

It's clear I can taper the top more. Not sure about the sides though. Maybe you can decide when I post some video this week.

Many of the concept cars have "apparent" angles which are pretty steep until you figure what happens with their active suspensions,with dropped noses kicking their hineys up to a "shallower" angle.

Given that Cd is supposedly constant in the range of speeds where road vehicles operate, why would a vehicle want to actively adjust its angle of attack? Is the nose up/tail down attitude a concession to low speed driving for clearance, making the top angle aerodynamically sub-optimal until the nose goes down?

[MetroMPG]

Originally Posted by Cd

It looked like MetroMPG had the front exaust touching as well in the pictures, but as I look closer, it seems that he may have done the area around the exaust pipe in something other than Coroplast.

In the front section, the coroplast is cut out ~1 inch around the pipe ahead of, around, and just aft of the catalytic converter.

In the middle section of the car, I've got aluminum immediately under the exhaust pipes (it touches the resonator).

[MetroMPG]

Due to inclement weather, CAD and further road testing will be delayed until conditions improve!



First dusting of the season. (Welcome to December!) Supposed to be warmer and the roads drier by Wed/Thu.

[wagonman76]

Originally Posted by Christ

wagonman76 -

The few companies I looked into for the opportunity to use Cara for some ad space had waivers that the drivers had to sign, basically absolving them of all responsibility for damage to the vehicle whether due to advertising materials or otherwise. I'm pretty sure it's not a liability for them, really.

Well that's cool. I was just thinking that by endorsing something homemade, they wouldn't have a leg to stand on in court if something happened, as opposed to something designed by a professional company.

[Piwoslaw]

Originally Posted by MetroMPG

Reminds me of the lightning scene from Back to the Future:

[Cd]

Originally Posted by MetroMPG

I'm a little nervous about those nervous looking side tufts. It's clear I could increase the top taper - those tufts are laying almost still right to the transom.

What I don't know - and maybe you or Bob can tell me - is this: should my goal be to taper as much as possible until I actually see evidence of separation through circulation/reverse flow, and then back off a bit?

In other words, will we achieve favorable drag results even as we increase the amount of "nervousness" in the tufts (evidence of turbulence and a thickening boundary layer) through further tapering?

It's clear I can taper the top more. Not sure about the sides though. Maybe you can decide when I post some video this week.

Metro, I'm assuming that the next tuft test that you do will incorporate an adjustable section on the sides of the tail.
Since you are working with CAD ( ) it would be really easy to do.
Not only will you be able to test the maximum amount of taper that you can have, but also you can verify if that flutter was indeed coming from upstream.

[Cd]

Oh wait ... I didn't think about the frame under the cardboard.
I guess you couldn't just cut an adjustable section out could you ?

[Frank Lee]

Right or wrong, I'd increase tapers until I see sign of turbulence, than increase until "laminar". Otherwise you may just end up with extra unneeded length. With unneeded length comes extra unwanted skin drag as noted in recent discussions re: crx and del sol tails.