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Author Topic: Rear Stabilizer Fin  (Read 1865 times)

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Offline John Burk

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Re: Rear Stabilizer Fin
« Reply #15 on: January 23, 2020, 03:14:27 PM »
Something anybody can do to learn about tail fins is bandsaw an 18" wooden model of your car , hang it from various points and blow an air hose at it with small , large and no tail fin to find the dangle point where it points into the air stream . Hang a weighted thread from the nose to keep it level . You may be surprised at how hard (impossible) it is to get the get the aerodynamic center back to a mid engine car's CG . The center of area in side view is close to the aero neutral point when a car is going sideways but pointed down track it's much further forward .

Offline Lemming Motors

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Re: Rear Stabilizer Fin
« Reply #16 on: January 24, 2020, 08:38:15 AM »
But it was Tom Burkland that found my Cp a couple inches ahead of Cg so we added three foot of cardboard to extend the rear and that helped.


John - if the cardboard tail extension worked well just make a cardboard fin. All this talk of tubing and fibre glass sounds like hard work :laugh:
A Bonneville Lakester please barman.
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A Squeeze of Lemming it is sir.

Offline ggl205

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Re: Rear Stabilizer Fin
« Reply #17 on: January 24, 2020, 11:53:20 AM »
John, that rear extension helped reduce Cd by .3 but did little to move the Cp rearward. Looks like I am stuck trying to affix some sort of fin to this new section. I will swing by Stainless?s place and we can noodle it out.

John
« Last Edit: January 24, 2020, 12:17:27 PM by ggl205 »

Offline Rex Schimmer

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Re: Rear Stabilizer Fin
« Reply #18 on: February 28, 2020, 11:48:14 PM »
John,
Duke and I may need to add a fin to our car, depending on what Woody comes up with but I am planning to use a piece of 1/4 inch aluminum plate cut to the area we need and having leading edge that lays back about 60+ degrees, I would also champfer the leading edge and make the the exact center of the champfers be a sharp edge. Read about "vortex lift in "Race Car Aerodynamics" by Joseph Katz which has a great section on it. As the car starts to spin side ways the sharp leading edge develops a vortex that runs down the back side of the plate, a vortex is low pressure so it makes a pressure differential on the tail that is pushing in the opposite direction to the spin. The amount of "lifting force" starts small but increase rapidly as the angle gets larger and will work fairly well at angles higher than 30 deg. This appears to me as being just what we need, easy to fabricate and mount, anti spin force rapidly increases as the car gets more side ways and probably not much more drag than an aerofoil shape.

Rex
Rex

Not much matters and the rest doesn't matter at all.

Offline jacksoni

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Re: Rear Stabilizer Fin
« Reply #19 on: February 29, 2020, 07:25:43 AM »
A perhaps not generally considered (and maybe has other disadvantages) method to help the Cp and Cg discrepancy is add weight to the front of the car. Your long lakester would have a big lever. Might not take too much lead.
Jack Iliff
 G/BGS-250.235 1987
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Offline ggl205

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Re: Rear Stabilizer Fin
« Reply #20 on: February 29, 2020, 03:11:58 PM »
Jack:

Probably wouldn?t hurt to have a bit more weight up front anyway. Before making battery and suspension modifications to the front, wind tunnel data said I had around 35 pounds of lift. Given the 525 pounds on front axle, I figured net weight of 490 would be enough to plant the front tires. So, maybe another 30 or 40 pounds of steel (lead is too expensive) along with added weight from battery and axle mods, will help move the Cp back a bit and kill the lift at speed.

John

Offline ggl205

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Re: Rear Stabilizer Fin
« Reply #21 on: February 29, 2020, 03:32:59 PM »
Rex:

Food for thought. Mounting a stabilizer was of paramount concern until I went over how Stainless did his. I may need to sharpen up my aluminum welding skills for this exercise, however.

John

Offline Stan Back

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Re: Rear Stabilizer Fin
« Reply #22 on: February 29, 2020, 05:18:28 PM »
We bought clean, used shot at $1 per pound.  Then enclosed it in a steel vessel that fit where I wanted it and bolted it down.  Easy to fit, easy to change.

This one is in a 1/2-inch steel enclosure.
« Last Edit: February 29, 2020, 05:19:59 PM by Stan Back »
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Offline ggl205

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Re: Rear Stabilizer Fin
« Reply #23 on: February 29, 2020, 05:24:06 PM »
Stan, unless I can get lead locally, shipping would negate any benefit.

There is quite a bit of dirt track racing here in Wichita so I may find what I need in lead.

John

Offline Speed Limit 1000

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Re: Rear Stabilizer Fin
« Reply #24 on: February 29, 2020, 06:50:30 PM »
Find a friendly tire shop and you can get used tire weights.

John Gowetski, red hat @ 221.183 MPH MSA Lakester, Bockscar #1000 60 ci normally aspirated w/N20

Offline aircap

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Re: Rear Stabilizer Fin
« Reply #25 on: February 29, 2020, 11:43:43 PM »
Quote
There is quite a bit of dirt track racing here in Wichita so I may find what I need in lead.

Tried all the Mexican tire repair places?
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Offline Stan Back

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Re: Rear Stabilizer Fin
« Reply #26 on: March 01, 2020, 11:11:53 AM »
I think the shot conforms and fills the container better than wheel weights.  I buy mine locally at a shotgun range that recycles and sells it.  It amazed me how clean it was, too.
« Last Edit: March 01, 2020, 11:56:31 AM by Stan Back »
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Offline Stainless1

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Re: Rear Stabilizer Fin
« Reply #27 on: March 01, 2020, 11:36:52 AM »
Stan, ya gotta melt down the wheel weights... the steel floats the lead is under the scum layer.  You get a lotta lead out of a 5 gallon bucket of weights... oops, the Dodge handle pulled off when you tried to move that bucket...
offer the kid $10 to put it in your car  :laugh:  :cheers:
Stainless
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MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.

Offline Stan Back

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Re: Rear Stabilizer Fin
« Reply #28 on: March 01, 2020, 12:09:03 PM »
Stainless ? the shot has other values, too.  One ? you don't have to melt it.  And, Two ? you can easily(?) adjust it.

I made an about 1-inch diameter entry in the containers (not shown) and just closed them off with an 1-1/2" circle of aluminum with a toggle bolt securing it.
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Offline ggl205

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Re: Rear Stabilizer Fin
« Reply #29 on: March 01, 2020, 03:26:19 PM »
Hmmm, recycled shooting range lead. Never thought of that. We have a few ranges out here in the heartland.

John