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Wing size and down force?

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Old 03-10-2014, 12:13 PM
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The_Iceman
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Default Wing size and down force?

Hello everyone, I'm trying to build a prototype Pinewood derby car with a fixed wing on the front. I've never seen it done before and I figured if anyone has the knowledge to find the wing size I need and Angle, this would be the place.

I would like a down force of 4.72 grams of downward force on the front (well at least a starting point anyway!)
Any help would be much appreciated.

Track = 42' time = 2.96 seconds (best car at last race)
The car weighs 5oz
Car dimensions = 7"Long X 1/4" tall X 2 and 3/4 wide"
speed = 9.67445 MPH or 20.81 feet/second
Location = indoors
Altitude =981 feet


Thanks
Ice

Last edited by The_Iceman; 03-10-2014 at 12:16 PM.
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Old 03-10-2014, 11:57 PM
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beepee
 
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Iceman,

First question is why? Do you expect directional instability due to insufficient load on the front wheels? ANY wing addition that will provide down force, will also provide drag. Unavoidable. If the cost (drag) is worth the gain, it will be by pure experimentation that you find the right size/shape/angle of attack. As a group, we think in terms of approximate mph, it is meaningless to us to carry this out five places past the decimal point.

Good luck and have fun.

Bedford
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Old 03-11-2014, 10:17 AM
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The_Iceman
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Quote:
Originally Posted by beepee View Post
Iceman,

First question is why? Do you expect directional instability due to insufficient load on the front wheels? ANY wing addition that will provide down force, will also provide drag. Unavoidable. If the cost (drag) is worth the gain, it will be by pure experimentation that you find the right size/shape/angle of attack. As a group, we think in terms of approximate mph, it is meaningless to us to carry this out five places past the decimal point.

Good luck and have fun.

Bedford
Thanks for responding Bedford. There are two reasons for a wing
1. Moving the weight farther back alows a faster run. but you loose stability.

2. I wasn't going to bring this up yet but I would like to try a verticle wing to that I may reduce toe on the single wheel.

Note: A few years ago someone figured out that the fastest cars seem to ride the rail and that brought about Railriding.

How to Railride = lift one front wheel off the ground or remove completely. Toe in the DFW (Dominant front wheel) wheel to make the car Ride the Center Rail. So if you would roll it on a table it would steer 4" every 4'

conclusion: So what it comes down to, is a wing worth the stability and could you remove a bunch of toe??? (Toe forces the single front wheel into the center rail, what if a wing did that?)

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Ice
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Old 03-12-2014, 12:07 AM
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OK, point taken. What you are trying to achieve is out of my (our?) league. The speeds are much lower and the size much smaller than anything I fly so the aerodynamics are in a different world than which I have any experience. It's a Reynolds number thing.

Bedford
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