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

[MetroMPG]

Did some housecleaning and removed recent off-topic/juvenile posts (to which I contributed) after receiving a complaint (justified) via PM.

Let's keep comments on topic please: more substance, less banter.

[Tango Charlie]

Gee, I don't log on for a day and look at all the fun I miss. Ha ha!

Darin, will the raw footage show underbody tuft testing with the wheel spats in place? Curious how much they helped underneath. Even with the full under tray on, the yarns right behind the tire were showing detached flow.

[Nerys]

No complaint is justified. nobody got antagonistic or angry or argumentative. FUN is the name of the game folks. If its not fun you really should find something else to do.

I am curious though metrompg. was there any difference with the plastic wrap versus just the raw cardboard? the paper is a rougher surface than the plastic. Not sure if tuft testing is even capable of showing such a small difference but it is a curiosity.

I have a feeling even if there is a difference we won't be able to see it since if the forward tufts themselves don't cause problems for the tufts downstream from them I doubt we can measure the difference in surface drag with paper versus plastic.

[MetroMPG]

No complaint is justified.

Disagree - it distracted from the topic. The lounge is the area for the "light stuff" and unrelated banter, not members' project threads.

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About the plastic: I put it on mainly for aesthetics and to make tuft testing easier to record (contrast). It may have made a marginal improvement in aero because it stretched across & leveled out many uneven dips in the cardboard.

Terry: unfortunately, I didn't tuft test the bottom with the wheel fairing in place. It would have been interesting to see, but I only actually made one.

[thatguitarguy]

I've heard people mention concerns about skin friction before, and I really don't think it's an issue at the speeds we travel. It is an issue for the SR-71, but that plane isn't a very good example of an eco-friendly vehicle.

This isn't a very good picture - just a screen shot of of a youtube video, but if you watch the video, you can see that the air stays attached better on this wing made of fabric tubes, than on a comparably shaped conventional wing. Again, this wing is not designed to fly at anywhere close to the speed of sound, and neither are our cars.




By the time you separate all the forces that a car has to overcome to be put into motion and remain in motion - aerodynamics, rolling resistance, etc. - the drag coefficient of the difference of paint jobs, or plastic, or paper, is infinitesimally small.

This video shows that it is more about the aerodynamic shape than about the materials. Take a look at the Aerocivic. On close inspection, that car looks pretty rough. There are a lot of irregularities in the surface, despite all of the gap fillers and such. It doesn't look like something that the car manufacturers would put out as a concept car, until you stand back and look at the car from the bigger perspective, then it really does look like a concept car, and basjoos has put the miles in to prove his concept.

http://www.youtube.com/watch?v=WZbR3...eature=related

[orange4boy]

I wonder about the rough surface issue. On the one hand, a rough top wing surface will stall much sooner than a smooth one. But then you have the application of vortex generators on the leading edge of many aircraft, golf ball dimples (not the dreaded golf ball dimples). There are also rough surfaces for lower drag in water as in the Americas cup boats and sharks. I guess it's the type of roughness that matters.

In any event I think canvas on the back end would be fine and kind of vintage. You might need some decals on the side. You car already looks like an aircraft. I can see you now, driving with goggles and a scarf.

Thanks for cleaning up our mess. I got a little carried away. *it was fun though* but a bit much.

[Nerys]

OK that inflatable wing. THATS BAD ASS!! but note he said low reynolds numbers.

Remember when they said a bee aerodynamically could not fly? well they are right. It can't. IF you apply normal aerodynamic laws to the situation.

what they later discovered is that when you drop the reynolds numbers (IE small things) the rules do not apply the same way. its a "different" set of rules in force on smaller scales.

that wing would not be as aerodynamic on a 747 since the reynolds number of a 747 puts it into the realm of NORMAL aero rules.

I believe our cars would definately be in the "normal" realm.

that wing is also taking advantage of the same process a golf ball uses. if you make the air more turbulent IE add "energy" it can remain attached over a greater divergent angle IE the round shape of the golf ball or this inflatable wing.

metrompg already has attached flow so he would gain NO advantage from adding energy to the air stream. it would only hurt him.

what is interesting is that you might be able to make a boat tail HALF as long as metrompg's and yet be ALMOST as effective as his if you add the dimples on the latter half of your tail. the increase energy would allow the airstream to approximate the effect of his longer tail without the need for the longer tail.

whether this is possible how much effect it would have and how precise you would need to be I have no idea. BUT thats the idea anyway.

I am really stoked about that inflatable wing! I am already envisioning my L1 project using those! got to see if I can figure out how they made it rigid!

[3-Wheeler]

Originally Posted by Nerys

...I am really stoked about that inflatable wing! I am already envisioning my L1 project using those! got to see if I can figure out how they made it rigid!...

Nerys,

You may want to write to Craig Vetter, and ask how he got the tail on his step-through motorcycle to work. It too was inflatable.

Check about half-way through his chapters to find some nice pictures with the sun showing through. You can easily make out that it is indeed air filled.

Jim.

[Nerys]

I will definately look him up. for my L1 project I have decided it must be a Glider. inflatable wings would allow me to boost a SERIOUSLY large glider with the same motor impulse :-) (sorry WAY WAY off topic but it is Aero :-)

[yanlapanic]

ugly and that it

probably dangerous when its windy and not really ''cool ''

but its a concept!