Author Topic: Need some aero advice..........  (Read 9595 times)

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Offline Sumner

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Need some aero advice..........
« on: October 10, 2005, 03:55:18 PM »
I have a question that I hope I can explain clearly enough that someone can help me with an answer or a good guess.

   

The body on my lakester will resemble some of the motorcyle liners, such as Ack Attack and EZ-Hook.  But being a lakester the wheels/tires will be expose and will be moved out from the body so that their inner most planes will be at least 12-14 inchs from the body sides.  I will have a neutral wing, kind of like, pod going down the body sides that will cover the axles, control arms and suspension components similar to the now gone Hammond lakester or like the bottom airfoil in the drawing above.

Now the longer this gets the more surface drag I'm going to have.  If I broke it up into two shorter airfoils like at the top of the drawing and the airfoils were very close together (tail to nose) then I think that would have more drag than the one longer one.  But if you moved the two airfoils apart a certain distance ( |<---- A ---->| ), then I would think that the overall drag would be lower than the one long one with the long top and bottom component.

So the question is how far apart would the two airfoils have to be from each other before I would derive a benifit?

The airfoils wil be about 7 inches thick and would have to be a minimum of about 3 feet long to cover the axles, etc. with an average width of about 12-14 inches.   They would also be in the same plane with each other and the same size.  The long one right now is about 12-14 feet long from it's leading edge to the trailing edge.  That means the way I'm setup now there could possibly be 6-8 feet between them.

The long single one does have the benifit of giving me more room on the car for things like intercooler icewater, cooling water, and/or fire extinguishers.

Thanks and c ya,

Sum

Offline Rex Schimmer

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Need some aero advice..........
« Reply #1 on: October 10, 2005, 06:08:49 PM »
Sum,
If it were only so easy! I personally think that the two airfoil concept is the lowest drag but of course you have to make sure that the leading airfoil is designed such that the air is always attached and even then there will probably be some type of turbulent flow shedding off of the trailing edge and that certainly may an affect on the rear airfoil.  The one long shape probably will have more skin friction as the laminar boundary layer becomes turbulent the longer it runs along the surface and if the turbulent air should become un attached then the shape is very dirty.

With the availability of some of the new CDF programs that are now around  you would think that a guy could give someone a fairly general definition of the shape of his car and the CDF could tell us which is best. LSR cars, anyway lakesters and streamliners are so simple from a aero standpoint, as compared to a F-1 car or even a NASCAR tin top. Simple but still very complex to figure out for most of us "regular" guys to really get a handle on.
Rex

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Offline 1212FBGS

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Need some aero advice..........
« Reply #2 on: October 10, 2005, 08:43:12 PM »
do both airfoils have to be the same size? if the rear is larger it could stabilize the turbulent wash from the front. but why go to all the trouble? seems to me you could get the steering rod behind and close enough to almost touch the axle making the aero covering one shape. if the axle is 3" and the steering link is 1" with a 1" air gap between the axle and rod, all would fit into a 1X3 aspect ratio wing (3" tall X 9" long wing). 12 to 14 wide is not much but why is this covering 7" tall.  your exposed axles or covers will cause little drag its the exposed spinning turbulent tires that will slow ya down. But nothing ya can do about that. so dont trip out on whats the lowest drag on these little foils cuz there gonna get lost in all the turbulent wash from the front tires. just make something that looks cool and fast . Put trip lips, vortex generators and zig tape tape all over it and make it look like ya spent a lot of time researching Afro stuff. maybe they can be big enough to hide something in like a 6 pack of bud so when the tech guys open the access door they get a big surprise. When we were first running the twin engine car we ran with the rear motor only. Vesco put a lawn chair in where the front motor was suppose to go. so we get to tech and pulled the rear canopy off and the tech guy said "Whats that for?" "I said that's where the tuner rides so he can tune the motor!" The tech guy threw a fit "you cant do that, you cant have anyone ride back there, that's dangerous, you cant do that!" We all about pee'd our pants. Ya gotta have fun, and stop thinkin 2 much, get R done and come out and race with us remember KISS
kent

Offline Freud

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Need some aero advice..........
« Reply #3 on: October 10, 2005, 10:36:26 PM »
Before you build those foils why don't you talk to Seth. He has flown helicopters  :lol: , airplanes  8)  and a lakester. :cry:

FREUD
Since '63

Offline Dynoroom

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Need some aero advice..........
« Reply #4 on: October 11, 2005, 12:33:23 AM »
And as they say Seth is still learning (as we all are), and building a new lakester (did i say that too).
Michael LeFevers
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Without Data You're Just Another Guy With An Opinion!

Racing is just a series of "Problem Solving" events that allow you to spend money & make noise...

Offline RichFox

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Need some aero advice..........
« Reply #5 on: October 11, 2005, 12:10:50 PM »
If you have ever seen my roadster, my drag link is covered in the form of an airfoil, and placed just in front of the round axle. Kind of like the old PBY wing struts being used to build cars on the old days.  RF

Offline JackD

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Yup
« Reply #6 on: October 11, 2005, 05:13:32 PM »
Airfoil shaped 4130 is still available.
A PBY is like the Ross Milk Truck steering box. "Gone but not forgotten." 8)
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Offline Sumner

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Need some aero advice..........
« Reply #7 on: October 11, 2005, 06:11:04 PM »
   

Quote from: 1212FBGS
12 to 14 wide is not much but why is this covering 7" tall.  your exposed axles or covers will cause little drag its the exposed spinning turbulent tires that will slow ya down. .............. Ya gotta have fun, and stop thinkin 2 much, get R done and come out and race with us remember KISS
kent


Thanks for the input guys.  

Kent the reason the covering is 7 inches tall is to cover up all of that stuff in the picture above.  The trailing arm (control arm, a-arm or whatever it is called) is just a little over 4 inches in height.  I want to end up with 2 inches of suspension travel, about 5/8 in rebound and about 1 3/8 in compression.  Add that to the 4 inches and another inch  for the suspension to stop on its bumpstops and body thickness and I'll be at about 7 inches.  I'm hoping, but will never know, that I'll be able to get the Cd on the side pods down to .2 or so.  Even if it is .3 I want to see if that is better than having all of the axle stuff out in the wind.  I've always wanted to try this approach, so we'll see.

I do belive in the KISS principle I just like complicated KISSES  :roll: .  Building this car is probably the most important and most enjoyable part of the whole racing deal so I don't want to have it end too soon.  Of course I already have plans to change some of this a year or so down the road to try out some other ideas.

 

And of course there is the Ford pickup I dug up in the desert waiting for me.  

   

And the Desoto I drug back from Missouri would also like to get on the road.  And my GMC needs a complete re-do.  Wow that wore me out just thinking of what I'll have to work on if I ever get this racecar done   :shock: .

c ya, Sum

Offline JackD

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38 Pig Nose
« Reply #8 on: October 11, 2005, 06:22:31 PM »
I have one of those with a 53 Merc put away from my High School days.
Why make the aero features any larger than the part ?
Unless your are building some load into them with the air going by, make them as small as you can and let them travel with the wheels.
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Offline 1212FBGS

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Need some aero advice..........
« Reply #9 on: October 11, 2005, 07:22:09 PM »
wow Sum thats lots of stuff ta hide :shock: ! now I see why ya need 7+ cord. maybe it should be sprung and swing, is the shock gonna mount to that thingy? whats the front stuff look like?The zoto looks cool bet you could put a king size bed in the back.

Offline Sumner

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Re: 38 Pig Nose
« Reply #10 on: October 11, 2005, 07:29:28 PM »
Quote from: JackD
I have one of those with a 53 Merc put away from my High School days.


One of which, the pickup or the Desoto.  I've been trying to figure out if the Ford is a '38 or '39.

Quote from: JackD
Why make the aero features any larger than the part ?
Unless your are building some load into them with the air going by, make them as small as you can and let them travel with the wheels.


That could possible be a solution if I had one airfoil over the front axle/suspension and another over the rear as I posted at the beginning of this post.  

Still Seth went mighty fast with a car that had a somewhat similar design to what I'm doing.  I talked to him a little about the accident, but he was reluctant at the time to share what he thought was the cause of it.  I'd like to know and haven't really had a good chance to bring it up with him again.

c ya, Sum

Offline JackD

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38 and 39
« Reply #11 on: October 11, 2005, 07:40:18 PM »
The Pig Nose Ford PU was a 38 and early 39. The 40 style was started as a second edition 39
Just like GM did in 55..
There is a joke about that lakester that says it seats 8, and every year somebody gets out and into the 2 club.
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Offline Sumner

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Need some aero advice..........
« Reply #12 on: October 11, 2005, 08:38:35 PM »
   

Quote from: 1212FBGS
wow Sum thats lots of stuff ta hide :shock: ! now I see why ya need 7+ cord. maybe it should be sprung and swing, is the shock gonna mount to that thingy? whats the front stuff look like?The zoto looks cool bet you could put a king size bed in the back.


The rear of the Desoto was for the 3 dogs.  They are hoping I finish it so they can go on trips with us again.

Now don't laugh at my sketch above (you can laugh at the engineering).  There will be inboard shocks and springs that will be tied to the outboard hubs with the tube that will have lever arms on each end.  I'm starting on that part now.  My latest version will have aluminum bearings (that I'll machine) inside of the tube with a piece of 1 inch cold rolled steel going through the bearings/tube and supported on both ends.  The springs will be setup with jack type screws to set the ride height.  I won't get the springs until the car is about done and I can get a weight on it.  I have a couple more hours work on the right rear control arm and then I'll strart on the tube with the bearings and lever arms.  The tube and outboard lever arm will fit into the 7 inch height of the side pods.  The out-board lever arm will ride on a 3/4 inch bolt that goes in the back of the control arm.  You can see the hole for it in the post above or on my web page ( http://purplesagetradingpost.com/sumner/bvillecar/construction%20page-28.html )

The front will be somewhat similar as far as the lever arms and inboard shock/springs.  I've made the bosses for the end of the front axle, but wanted to finish up the rear so I know exactly what the front track width will end up being so that the front and rear tires are lined up.  I still haven't made up my mind yet if the front axle is going to be a single straight axle or two seperate axles similar to Ford's twin I-beam setup.  I have to make sure it isn't too simple  :wink: .

c ya, Sum

Offline sirstude

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Need some aero advice..........
« Reply #13 on: October 12, 2005, 05:23:43 PM »
Sum,

It is a 39.  Check the photos on this site,  38's seem to have a double bar in the middle.

Doug

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Offline ack

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Need some aero advice..........
« Reply #14 on: October 16, 2005, 06:36:53 PM »
Just a couple of my thoughts on your streamlining question:

I like the idea of a single streamlined faring purely from an aerodynamic perspective.  However depending upon how fast you are planning to go I would begin to worry about presenting a large flat surface to the air stream.  You might consider using the two separate faring concept and if you are looking for down force for traction airfoils can be very efficient in providing down force with little drag penalty. The airfoils we have but have not used since the 04 BUB event are readably available from several sources.  The following link (page 17) has the airfoils we have and the corresponding force and drag data. http://www.chassisshop.com/pdf/fabrication.pdf  Just multiply any of the data for the speeds given by 4 to determine the force and drag at double the speed.  These airfoils will not work for your application but will give you an idea of what you could do. Which ever way you go it is very important to have a generous radius at the point that the airfoil or faring meets the body to minimize drag.  Look at any of the low wing aircraft at your local airport to get an idea of how this should look. I just don?t know what effect the front airfoil would have on the back one.