Landracing Forum
Bonneville Salt Flats Discussion => Build Diaries => Topic started by: Milwaukee Midget on January 12, 2010, 11:51:30 PM
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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.
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/DSCN3415.jpg)
Here's the factory hardtop.
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/roll%20cage/DSCN3542.jpg)
And another view of the same top, only on a completed car.
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/roll%20cage/Midgettop.jpg)
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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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. :-D :cheers:
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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 :-D
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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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! :-D :-D
Pete
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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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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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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. :-D :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. :-)
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......
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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 :roll: There's a nice, long stretch in Racine County just south of town - straight, flat as a billiard table. Hmmm . . . :roll:
I appreciate everyone's honest opinions. This is a variable that I may wind up keeping in play.
The fool's errand continues . . .
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Chris,
I have bad news I'm afraid, Austin Healey Sprite , Mk III & IV Cd is listed as.... 0.5 :-o 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 :-D
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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Chris,
I have bad news I'm afraid, Austin Healey Sprite , Mk III & IV Cd is listed as.... 0.5 :-o 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 :-D
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. :-D
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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An old MG magazine I have shows the C/D as .5 also - Frontal area 1.24 M squared.
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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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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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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
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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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Dr Mayf- see home page- has some numbers:
http://www.mayfco.com/tbls.htm
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Chris, Gerald Davenport took his Crosley #1010 to Bonneville without a top and had to have one made to compete in the GT class.
pic from Maxton...
(http://www.crosley1010.com/photogallery?g2_view=core.DownloadItem&g2_itemId=314&g2_serialNumber=2&g2_GALLERYSID=c8bfe78c70ff0e6a34a1f91cae11b23c)
Pic with top, correct windshield and doors required by SCTA...
(http://www.frsengineering.com/m37.JPG)
He had to have the top/sidecurtains, correct doors and windshield to match OEM for the GT class.
I'm no expert on car classes, but this is just info I got from a conversation with Gerald.
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To add to what Rchop said . . . to run GT you MUST run a top.
I don't have a 2009 rule book handy but am pretty sure this still applies. Looking at the rules (in an older rule book) under Production Category and also specific GT class rules it is not real clear about this . . . but . . . if you skip to the rules under the Modified Category for Gas Coupe there is a specific reference to convertible tops. It clearly says that Convertible tops are only allowed in the Gas Coupe classes and in the Production Category (that includes GT). It also says that the top must be up during competition.
If you have a 2009 rule book I suggest you verify that this is still the case.
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And you can't chop the top in GT.
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Too many rules from the man in GT.....
Startin' to make MS look better all the time doesnt it....
A GSXR 1K and all the fun you can handle "ahead of and including the cowl".
My vote.....
MS all the way (*and who knows maybe a run for the H records in the future!)
LOL
~JH
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Jh --
Just look at GT as a Production class for sports cars, not a Gas or Altered class.
Stan
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Chris, Gerald Davenport took his Crosley #1010 to Bonneville without a top and had to have one made to compete in the GT class.
I remember Gerald was running a '48 Crosley about eight years ago in J/PRO. There's a picture of that car in the 2005 Rule book on page 67. He doesn't know it, but that car was one of my inspirations, and after reading his story, so is he.
The 1010 J/GT he and his team put together is a stunning piece, and there are more pics on his website -
http://www.crosley1010.com/index.php?option=com_gallery2&Itemid=4
So he was required to run a top at Maxton? The last GT Bugeye at Bonneville I was made aware of ran topless. I think Dan Warner forwarded me this pic, but if it was somebody else, let me know.
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/81_I_GT.jpg)
Don't know the year it ran - late '80's?
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Now you see Leroy( you need to listen to a CD MM plays on to get that one :wink:), a build diary is like floating your company........ You used to be able to turn up when you wanted , spend company funds on whatever "entertainment" you liked , keep a bottle under the desk and employ your relatives....NOW, you have to do an annual report, have a shareholders meeting, draw graphs and stuff and comply with company law....next thing you know there'll be some young dude share-raiding you and stacking your board.....
Just joking , but suddenly all this expertise rolls up and it gets real serious....... This project has been simmering away out of view , now it's broken cover everyone's weighing in and you're accountable, being compared to other cars, having to make the big decisions about which way you're gonna go........It's great to see you're well on the way to being a contender.....
Good one!
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Rchop -
Just re-read your post - SCTA said no - got it.
Yeah, the doors on Gerald's original build are not stock. Just pulled up a pick of an original Hotshot, and the rebuilt doors in the pic with the top on it are in keeping with the original lines. It's a shame they got that far and had to do a fix.
In section 5.E.3, the rule states that "Any tarps shall be non-rigid." I'd always interpreted that to mean that a soft tonneau was permissible, whereas a fiberglass or aluminum cover, like on a roadster, would be rejected. A full tonneau was an option in the Midget - maybe not on the Hotshot?
. . . but suddenly all this expertise rolls up and it gets real serious.......
Thanks to everyone for your input and encouragement. I repeat, this is the greatest brain-trust in racing, but Gray Baskerville said it best - "Don't take this s*#t too seriously". :cheers:
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I vote for leaving the top off and giving everybody rides.
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Ewww, get this horrible picture of a 6'6", white bellied man walking around with no shirt, orange and white shorts (tropical leaf pattern, of course), green flipflops, and pickles (Milwakee Midgets, naturally) dangling from a string draped around his neck.......ewwww.... :-o
Lynda
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Ewww, get this horrible picture of a 6'6", white bellied man walking around with no shirt, orange and white shorts (tropical leaf pattern, of course), green flipflops, and pickles (Milwakee Midgets, naturally) dangling from a string draped around his neck.......ewwww.... :-o
Lynda
:-D
Worry not, dear lady. My strong sense of fashion would never let me wear a tropical leaf pattern with flip-flops.
I'm thinking tiger stripes. :mrgreen:
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Just found this - a copy of "Auto Test", circa 1975. Topic - MG Midget.
"Open sports cars always suffer in performance at the top end when they run with the hood (top) down, and the Midget was no exception. Lowering the hood took the maximum speed down to 94 MPH."
The data sheet indicated a best top speed of 102 mph @ 6,200 RPM, about 700 RPM past the peak advertised horsepower of 66 at 5,500 RPM (DIN).
Granted, the top they were running was the soft top, but at this point, I'm thinking there's strong circumstantial evidence to go with the top on. It's a difference of ~ 7.8%.
It's still a long way from 122 mph, but it's a step in the right direction.
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When I was 16 I had a 63 Midget and got into a race with a VW. My tach was past redline in 4th gear and there was about 2" of daylight between the top of the windshield frame and the the soft top.
I thought the top was going come off, but the two little fasteners on the ends held.
Don
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I would have thought there was not enough time for you to be building it two ways without any class advantage.
Go the hard top, air will pass through smoother and join back together behind the car smoother with the sloping rear screen.
If you cannot change the windscreen then to make it better aero extend the rear screen so it takes longer to join the back.
I was interested in buying a Sprite when I was in my 20's, but when I finally got in one I found I could only get out walking on my hands wheelbarrow style. Ended up getting a Renault Floride instead, the inspiration for the MGB. I actually did lose my hardtop once when I failed to fix it on properly. eek
rH+
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When I was 16 I had a 63 Midget and got into a race with a VW. My tach was past redline in 4th gear and there was about 2" of daylight between the top of the windshield frame and the the soft top.
I thought the top was going come off, but the two little fasteners on the ends held.
Don
I actually did lose my hardtop once when I failed to fix it on properly. eek
rH+
Well, that would certainly solve any fresh air venting problems. :-o
I'm thinking I'll need to treat this like one would T-tops or a moon roof - tabs or straps.
Between what I've gathered here, what I've read over the last weekend, and my gut, I'm going with the top and will continue accordingly.
Thanks again, everyone, for your input and your encouragement. :cheers:
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Cool link indeed.
Your sharing is much appreciated.