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Question: GT options for the Midget -  (Voting closed: January 19, 2010, 11:51:30 PM)
Yes, run with a roadster-style cage and a soft tonneau - you'll go faster. - 2 (9.5%)
No, go with the factory hardtop - you'll go faster. - 7 (33.3%)
Try it both ways - build the cage so you can still fit the top over it, but have your boat-buddy make you a tonneau, too. - 12 (57.1%)
Total Voters: 19

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Author Topic: Should I go Topless?  (Read 8968 times)
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Milwaukee Midget
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« on: January 12, 2010, 11:51:30 PM »

Okay, here's a thinker.  I guess I'd like to know which will get me the best aero.

Here's a 3/4 view of a Midget with the top down.  Imagine it with a roadster style cage and a soft tonneau.



Here's the factory hardtop.


And another view of the same top, only on a completed car.

GT requires I keep the windshield.  The hardtop has been okayed to race with.

The plan since inception has been to run the hardtop, but before I commit, I guess I'd like to hear from those of you who have opinions regarding the aerodynamics of either style.  The cage is going in this month, and I also haven't ruled out running it both ways. 

Thanking you all in advance, the greatest brain-trust in racing, for your input.

Chris
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« Reply #1 on: January 13, 2010, 12:20:25 AM »

Doesn't the quote go something like "without data , you're just another guy with an opinion"?
....so, run it both ways and tell US.

Five foot eighteen and you want to run with a roof ,ha ha, you won't need a rollbar coz your knees will be above your head. grin cheers
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« Reply #2 on: January 13, 2010, 12:45:52 AM »

You aughta know Doc.
"Five foot eighteen and you want to run with a roof ,ha ha, you won't need a rollbar coz your knees will be above your head" !
The thought "dog humping a cricket ball" comes to mind after seing you in the belly tank last year  grin
How are your plans progressing for 2010 ? I think Iv'e managed to contain my oil, at last, I'll run it tomorrow.
Tiny
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Tiny (in OZ)
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« Reply #3 on: January 13, 2010, 01:31:49 AM »

I'd run it both ways and find out the truth. Unfortunately, to my untrained eye, neither appears to have award winning aerodynamic properties. On the other hand it's my understanding that the whole idea is to be safe, go fast and have fun and that just may fulfill the bill. Good luck! grin grin

Pete
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McRat
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« Reply #4 on: January 13, 2010, 02:46:43 AM »

I would bet on the hardtop.  An extended cab pickup is more aero than a short cab pickup, I think the same thing will happen.

It's fairly easy to find out before the race.

If the car can made to appear street legal, put in a throttle stop that will limit you to a reasonable speed (no rev limiter), then go test in both directions down the highway.
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« Reply #5 on: January 13, 2010, 11:49:09 AM »

Or do a coast-down test somewhere.  A and B runs are hard to come by at BV.  Lots of time between runs, weather changes, etc. can effect the outcome.  Plus you'd be wasting runs you could use for other purposes.
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« Reply #6 on: January 13, 2010, 12:21:52 PM »

Doesn't the quote go something like "without data , you're just another guy with an opinion"?
....so, run it both ways and tell US.

Five foot eighteen and you want to run with a roof ,ha ha, you won't need a rollbar coz your knees will be above your head. grin cheers

Certainly a different car but the testing has already been done.

Before the Cobra "Daytona Coupe" they ran hard tops on the Cobras at Le Mans because it was more aero......
History is our friend.   smiley

The second picture is a cobra hard top, the third is a "coupe". I forgot to add a picture of the coupe from the rear so I did now.
The "hard top" cobras were ~10 mph faster than the roadster. The coupe was ~ 15 mph faster yet......


* Kirkham Summit 2007 028 (Small).jpg (46.46 KB, 640x480 - viewed 191 times.)

* Kirkham Summit 2007 006 (Small).jpg (75.26 KB, 640x480 - viewed 215 times.)

* IM000041(Small).JPG (55.87 KB, 640x480 - viewed 173 times.)

* IM000039(Small) (Small).JPG (59.24 KB, 640x480 - viewed 161 times.)
« Last Edit: January 13, 2010, 08:09:35 PM by Dynoroom » Logged

Michael LeFevers
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Without Data You're Just Another Guy With An Opinion!

Racing is just a series of "Problem Solving" events that allow you to spend money & make noise...
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« Reply #7 on: January 13, 2010, 06:25:56 PM »

Doc - Yeah, data.  I can't even find a published drag coefficient on a Spridget, so the starting point remains an unknown.  I've got nothing more than my gut feeling, and I'm hoping to glean an educated guess from this exercise.  And yes, I look like a Praying Mantis in this thing.

Peter Jack - Yup, you don't need to be a rocket surgeon (brain scientist?) to see that it is, at best, a brick, albeit a rather small one.

McRat - Thanks for your post - the pickup analogy was something I wouldn't have come up with, and that's why I've got this thread going.  And I do have plates for it . . . coast down test . . . hmmm  rolleyes There's a nice, long stretch in Racine County just south of town - straight, flat as a billiard table.  Hmmm . . . rolleyes

I appreciate everyone's honest opinions.  This is a variable that I may wind up keeping in play.

The fool's errand continues . . .
« Last Edit: January 13, 2010, 07:34:49 PM by Milwaukee Midget » Logged

"Problems are almost always a sign of progress."  Harold Bettes
Well, I guess we're making a LOT of progress . . .  rolleyes

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« Reply #8 on: January 13, 2010, 10:43:34 PM »

Chris,

I have bad news I'm afraid, Austin Healey Sprite , Mk III & IV Cd is listed as....  0.5  shocked My source does not say top up, top down or hardtop/soft top sorry.

If it helps any a Lotus Seven is listed as 0.7  grin

My money is on the hardtop over a mess of exposed tube and an open screen, coast down test sounds like the right plan to me.

Cheers,
Rob
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Milwaukee Midget
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« Reply #9 on: January 13, 2010, 11:48:07 PM »

Chris,

I have bad news I'm afraid, Austin Healey Sprite , Mk III & IV Cd is listed as....  0.5  shocked My source does not say top up, top down or hardtop/soft top sorry.

If it helps any a Lotus Seven is listed as 0.7  grin

My money is on the hardtop over a mess of exposed tube and an open screen, coast down test sounds like the right plan to me.

Cheers,

Rob

Maybe a bit more compression and a slick coat of wax will help. grin

Rob, thanks for ferreting out that info.  About what I expected - I know a shoe box when I see one.  Was the source on line?  I'd like to compare it to a Mini - I've read of a couple of guys who have hit the speed I'm looking for in a vintage Cooper, and my frontal area is about the same.

I appreciate the research - Thank You! cheers
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"Problems are almost always a sign of progress."  Harold Bettes
Well, I guess we're making a LOT of progress . . .  rolleyes

We are NOT rebuilding . . . We are reloading.

GOD SAVE MG - The Queen can take care of herself!
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« Reply #10 on: January 14, 2010, 12:02:06 AM »

An old MG magazine I have shows the C/D as .5 also - Frontal area 1.24 M squared.
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« Reply #11 on: January 14, 2010, 01:27:25 AM »

A top will be better than a whistle cage.
My vote is to keep the top and chop it as much as you can and still fit.

~JH
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« Reply #12 on: January 14, 2010, 01:52:43 AM »

I would design the bars so you could do either but start with the top.

Not so funny things can happen on a new build and not digging the playing surface up with a roll bar or having stray body parts potentially getting some road rash are both good things. Once it was sorted out... Yeah, it's fun to have the top down some days.
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« Reply #13 on: January 14, 2010, 03:14:37 AM »

Chris,

The only info I can find is quoted for the Leyland Mini, they don't qualify it with a year model. The later models of the early variant (Clubmans) had a flat, rectangular grill.

That aside, the quoted Cd figure is again 0.5. Given that the "new" Mini started at 0.48 this is probably correct. They have managed to get the new model down to 0.33 so there's hope for you yet. BTW yes I found both figures online by getting creative in Google.

I have a heap of Mini literature from my Cooper "S" days and will see if I can find anything more concrete for you.

Cheers,
Rob
« Last Edit: January 14, 2010, 05:23:14 AM by Rob » Logged
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« Reply #14 on: January 14, 2010, 04:56:54 AM »

Chris, more of the same in this link, good 'ol wikipedia, actually, there's a lot of vehicles listed here.

http://en.wikipedia.org/wiki/Automobile_drag_coefficient

Tiny (in OZ)
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Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE
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