Author Topic: Tailfin basics...  (Read 7065 times)

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Offline Jack Gifford

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Tailfin basics...
« on: September 26, 2014, 01:06:56 AM »
My lakester (see avatar) trades-off aero considerations for vintage appearance. But when/if I ever finish the engine and drivetrain, I might decide to alter that trade-off in the interest of safety; especially since it appears that the center-of-pressure (laterally) won't be much (if at all) behind the center-of-mass. So... I may want to add vertical fin(s) (one or more) at the rear. Question: would such fin(s) possibly reduce the vehicles's drag coefficient? If so, what sort of minimum dimensions (length/width) would be required to make a not-insignificant difference? And what position(s) in relation to the rear of the tank?
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Offline bbarn

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Re: Tailfin basics...
« Reply #1 on: September 26, 2014, 07:35:39 AM »
Can you post a better picture of the car? Preferably a straight on side shot as well as the one you have as your avatar or an iso angle of the vehicle.

Also, what is the relationship now of your CP to CG? Are they right on top of each other, is CP ahead or behind the CG and by how much?
I almost never wake up cranky, I usually just let her sleep in.

Offline Jack Gifford

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Re: Tailfin basics...
« Reply #2 on: October 17, 2014, 11:24:39 PM »
Perhaps I didn't ask the question correctly. What I was thinking about was, say, a pair of fins symmetrical about the center of the car, each spaced some distance (?) out from the body/chute-pack. It seems to me these could possibly help the coefficient of drag in that area by cleaning up what I'm guessing is pretty turbulent air movement there.

Any thoughts?
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Offline Sumner

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Re: Tailfin basics...
« Reply #3 on: October 18, 2014, 06:56:16 AM »
...Any thoughts?

Personally I wouldn't go with more than one fin unless I wanted to also have a wing, just more drag, although the drag from a 'somewhat' aero fin is not a lot.  Then I'd only go with the one fin if I needed it to help with the center of pressure which looking at your cars profile it might need depending on anticipated speeds.

Is the added drag going to be less than possibly making the overall drag of the car lower?  I would guess not, but that might only get answered in a wind tunnel or by Woody.  The back of the car looks pretty clean to me so I don't see how the fin would help the overall Cd but that is purely a guess. 

Keeping the angles that the sides go in and the top of the car tapers down to less than 7 degrees will always help as it is my understanding that angles of 7 degrees or less will help to keep turbulence  down.  That is what I've used for the whole back of my lakester.

Good luck,

Sumner

Offline 8

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Re: Tailfin basics...
« Reply #4 on: October 18, 2014, 10:46:09 AM »
If you have traction, the tires will keep the car straight. Why would you want to add the drag of a tailfin. Make the car hook up and let the tires do their job.

Offline Ron Gibson

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Re: Tailfin basics...
« Reply #5 on: October 18, 2014, 10:56:45 AM »
And due to track or horsepower, you lose traction?????????

Ron
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Offline BHR301

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Re: Tailfin basics...
« Reply #6 on: October 18, 2014, 11:32:41 AM »
8  You have the answer..."If you have traction"

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Offline Glen

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Re: Tailfin basics...
« Reply #7 on: October 18, 2014, 03:42:03 PM »
8 it would help if you told us about yourself and racing background,OK.
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Offline Seldom Seen Slim

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Re: Tailfin basics...
« Reply #8 on: October 18, 2014, 04:34:23 PM »
Glen, you can tell by looking from whence he comes -- that he must be a merciful and laid back kind of guy.  I wonder what part of Kentucky is his home area. . . :roll:
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Offline Jack Gifford

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Re: Tailfin basics...
« Reply #9 on: October 18, 2014, 10:56:48 PM »
Thanks for the inputs.
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Offline kiwi belly tank

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Re: Tailfin basics...
« Reply #10 on: October 19, 2014, 12:10:21 AM »
Jack, if the avitar pic is a some what accurate depiction of your tank, you are correct in guessing there will be a lot of turbulance & drag behing the canopy. About the only way to clean that up will be to use of a long fin/fence to prevent the transfer from side to side.
We put this style of fin on Betsy for the same reason.
https://www.google.com/search?q=al+teague+streamliner&biw=1258&bih=600&tbm=isch&tbo=u&source=univ&sa=X&ei=DUNDVOerKqv2iQLQzoCYBA&ved=0CB0QsAQ
Putting a Cessna or 747 tail fin on won't stop the turbulance, only increase the drag.
You could always make it a bolt-on so you don't have to live with the spoiled look when you get back to the bragging area.
  Sid.

Offline sofadriver

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Re: Tailfin basics...
« Reply #11 on: October 19, 2014, 10:18:33 AM »
 
We put this style of fin on Betsy for the same reason.
https://www.google.com/search?q=al+teague+streamliner&biw=1258&bih=600&tbm=isch&tbo=u&source=univ&sa=X&ei=DUNDVOerKqv2iQLQzoCYBA&ved=0CB0QsAQ
Putting a Cessna or 747 tail fin on won't stop the turbulance, only increase the drag.
  Sid.


Thank you!
I'm anticipating a similar issue with the new APS bike.
I saved the first pic for reference.
So many good ideas on this forum!
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Offline floydjer

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Re: Tailfin basics...
« Reply #12 on: October 22, 2014, 02:12:40 PM »
Glen, you can tell by looking from whence he comes -- that he must be a merciful and laid back kind of guy.  I wonder what part of Kentucky is his home area. . . :roll:
Remind to stay on Jon`s good side...Once I get there.............
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