Front nose of car, shape, aero, thin to win ?

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Stan Pope
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Re: Front nose of car, shape, aero, thin to win ?

Post by Stan Pope »

LightninBoy wrote:
Stan Pope wrote:It is interesting (to me, at least) that, whereas the picture shows air flow going above and below the wheel, the fenders on the fastest cars in the recently posted video appear to deflect the air flow mostly sideways. This makes sense to me since the deflection distance sideways is 1/3 to 1/2 of he vertical distance, depending on if the deflection is purely sideways or has both horizontal and vertical components!
:nod:

We live in a 3D world. Need to think in 3D.
Not sure if that is addressed to me? Or as a general reminder to those who don't think in 3D and 4D!?

The object appears to be a cylinder as indicated by the near-side machine marks. But, maybe, it is a sphere as suggested by the upper quadrant reflections?

I looked for smoke trails on the near side of the object, but none were apparent.

I could not view it as a wheel or fender viewed from the top, since the profile did not look like either.
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Re: Front nose of car, shape, aero, thin to win ?

Post by ngyoung »

Just came across this DIY wind tunnel setup. You can't set the MPH but you can find the drag force to compare your own cars.
http://pinewood-derby.blogspot.com/2013 ... n.html?m=1
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Re: Front nose of car, shape, aero, thin to win ?

Post by sporty »

Thanks for sharing link.
Its to bad all that nice work and effort and didn't place a piece of track under the car to get accurate wind tests.


Maybe he still has it and can use a piece of track. And can find a way to mimic the wind of a actual race speeds.

.that's been my fears, real testing. That can simulate the air of a actual race. The wind from that blower would be way over the limit of real track condition. But a pointometer, variable speed switch on the motor and a way to measure the air speed.

Darn so close, yet so far away.
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Re: Front nose of car, shape, aero, thin to win ?

Post by whodathunkit »

sporty wrote: The wind from that blower would be way over the limit of real track condition. But a pointometer, variable speed switch on the motor and a way to measure the air speed.
Darn so close, yet so far away.
Fluke air flow meters..
Or perhaps one from Extech insteruments for metering AC duct air flows might work.
What type of automobile can be spelled the same forwards & backwards?
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Re: Front nose of car, shape, aero, thin to win ?

Post by sporty »

whodathunkit wrote:
sporty wrote: The wind from that blower would be way over the limit of real track condition. But a pointometer, variable speed switch on the motor and a way to measure the air speed.
Darn so close, yet so far away.
Fluke air flow meters..
Or perhaps one from Extech insteruments for metering AC duct air flows might work.
:thumbup: :bigups: :lol:
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Re: Front nose of car, shape, aero, thin to win ?

Post by Stan Pope »

Regarding the Wind Tunnel Blower ... most such blowers are rated at CFM ... Cubic Feet per Minute. If you build the "tunnel" with a 12"X12" opening, then the conversion to MPH is easy.

Or, reverse the computation to select a blower rating that produces 11 MPH!

Next, some finer adjustments are available by selecting a specific cross section of the air coming out of the blower. For instance, if it has a 12X12 area, pick a 6x6 area and expand the "shute" to 12X12 ahead of the baffle to reduce the MPH to 1/4 original. Route the remainder of the output through a comparable shaft so as to keep pressures comparable.
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Re: Front nose of car, shape, aero, thin to win ?

Post by Laserman »

Hi fellas,
What a great thread!
Love that Sporty Spoon design.
Especially the way that it puts the front axles at about the highest point on the car and then dips down low.
I started building a wind tunnel a while back but got side tracked with other projects. Hopefully I will be able to post photos of the finished product before the end of winter.
It has two high powered 4" fans that funnel into a wind straightener made from straws.
Using an anemometer I was coming up with wind speeds of about 12mph.
After reading thru this thread I am starting to wonder how analogous it would be for certain testing.
As stated earlier, in reality the car is actually cutting thru the still air, not air moving fast over the car standing still like in a wind tunnel.
Laminar air traveling just beyond the edge of the boundary layer will most likely skew the results pretty fiercely when such small details can make big differences on these delicate little timepieces.
I wonder if dunking the car into a bucket of water and filming it at high speed would offer more.
Sporty mentioned downforce in his design of the spoon.
This idea is fascinating to me.
Can you tell us more about it Sporty?
Thanks
Last edited by Laserman on Sat Oct 04, 2014 9:35 pm, edited 1 time in total.
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Re: Front nose of car, shape, aero, thin to win ?

Post by Laserman »

Vitamin K wrote:So, one thought I had was, if I am doing full-length fenders (Nellie-Faye-esque), can I go thinner on the body, since the fenders will give rigidity when epoxied to the sides of the car? Balsawood is fairly rigid for its density, isn't it?

Here's the template I've been poking at for this years' cars: https://drive.google.com/file/d/0B3v2pe ... sp=sharing

Since the balsa fenders will add some weight, looking to shave as much off the body as I can, but I don't know if I want to go the hassle of a ladder chassis. The plan is to have my kids do as much work as possible, and routing out the chassis (or scrollsawing it) is not a lot of fun.

Hi Vitamin K,


Yes.

It forms something of an I-beam shape that will stiffen things up.

I really like your design based off the X-3, and have similar sketches on the drawing boards. (with a few twists here and there)

The trailing fenders are totally where it's at.


Hi LB,

Congrats again on that beautiful car. and the amazing times it is putting up.

Joe
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Re: Front nose of car, shape, aero, thin to win ?

Post by sporty »

Laserman wrote:Hi fellas,
What a great thread!
Love that Sporty Spoon design.
Especially the way that it puts the front axles at about the highest point on the car and then dips down low.
I started building a wind tunnel a while back but got side tracked with other projects. Hopefully I will be able to post photos of the finished product before the end of winter.
It has two high powered 4" fans that funnel into a wind straightener made from straws.
Using an anemometer I was coming up with wind speeds of about 12mph.
After reading thru this thread I am starting to wonder how analogous it would be for certain testing.
As stated earlier, in reality the car is actually cutting thru the still air, not air moving fast over the car standing still like in a wind tunnel.
Laminar air traveling just beyond the edge of the boundary layer will most likely skew the results pretty fiercely when such small details can make big differences on these delicate little timepieces.
I wonder if dunking the car into a bucket of water and filming it at high speed would offer more.
Sporty mentioned downforce in his design of the spoon.
This idea is fascinating to me.
Can you tell us more about it Sporty?
Thanks

Sure, I thought I had, I's sorry If I had not.

Early on, I realized, more weight placed farther in the back. , back when people said, nope that's to far, you get stability issues, need to much drift to keep it to the rail, and thus loosing some potential speed.

So I think I said this a few times, im trying to recall how I all worded it. I may end up saying the opposite of a previous post I did. Hope not. Sorry if I do. lol.

The nose being so low and then there in the front, that's the lowest point on the car, that front edge, unless you add wood underneath it, but the center guide rail and many doing the axles location as high up as they can, and still have a tiny amount of clearance under the rail.

well, this means, and what I seen back then, air don't go under the center guide rail / under the nose there.


So, this is also the area that has the most wind / air, what ever we want to call it. (im tired at the moment).

So, its at its lowest point, with the least amount of resistance of air. with that design.

Now Iy you seen a few variations of my spoon design. I have played with it a bit and sometimes, Im just not consistently repeating the same shape. but close to it.

So, any how. with that out of the way.

The higher up axle slots, how the angle is done up and over that and the slope back down just past the axle area under the wood. gives a bit of downforce there.

That little bit of downforce, allowed me/kids. to have a farther back weight balance point, well back then, people thought I was wrong and crazy.

But, now, I did not have to do as much drift as my other ways did, and the front end would not micro bounce as much, running rail rider, with just one wheel touching.

I was not able to wind tunnel my design, it was one of the results of what I seen with the wind tunnel.

So I was only able to see visually and track times and less drift changes.


There is a bit of a trick to it, To much back slope going down behind the axle height or not enough drop, it does not work as well.

I should add in, our pack required 4 wheels down, very tiny amount of cant. and tiny mount of toe allowed. This design, helped us huge in scouts with the rules, we had to work with.

In factors of adult racing. Its probably a tiny amount of help. but should and has proven to do something. I forget and I might not have kept track.

I had not ever, planned on really seeing this design, become so popular with people. and it has worked well for a few on here and the scouts in the area that used it.

I see allot of great cars, well built cars, by great builders. talented people. They just got it !

I and my kids worked hard for a very long time. And I worked very very hard for a few years for myself. nothing came quick or easy for me, allot of hard work and time.

I think the difference, is my view was share it, help others. racing for those who want to win or work at doing a better car. should be able to find the information and understand it well enough to try and use the information.

Back on track, I hope that gave you a good reply there, tried my best.


Sporty
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