Landracing Forum
Tech Information => Technical Discussion => Topic started by: Sumner on October 10, 2005, 03:55:18 PM
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I have a question that I hope I can explain clearly enough that someone can help me with an answer or a good guess.
(http://purplesagetradingpost.com/sumner/temp-pictures/air%20foils.jpg)
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
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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.
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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
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Before you build those foils why don't you talk to Seth. He has flown helicopters :lol: , airplanes 8) and a lakester. :cry:
FREUD
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And as they say Seth is still learning (as we all are), and building a new lakester (did i say that too).
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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
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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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(http://purplesagetradingpost.com/sumner/bvillecar/rear%20control%20arms-29.jpg)
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.
(http://purplesagetradingpost.com/sumner/temp-pictures/38-39%20Ford%20Pickup-1.jpg)
And of course there is the Ford pickup I dug up in the desert waiting for me.
(http://purplesagetradingpost.com/sumner/temp-pictures/desoto-1.jpg)
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
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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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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.
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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.
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
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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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(http://purplesagetradingpost.com/sumner/temp-pictures/rear%20suspension-1.jpg)
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
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Sum,
It is a 39. Check the photos on this site, 38's seem to have a double bar in the middle.
Doug
http://members.aol.com/rasloto/gallery.html
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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.
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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.
Thanks for that link. They have lots of stuff that can be used in our cars. I spent way too much time looking at their catalog on line. Ordered one, but it seems they are out until Dec.. I liked the info they supplied on the downforce and drag of the air foils.
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.
Out of the different books I have on aero only one, THE LEADING EDGE -- Aerodynamic Design of Ultra-streamlined Land Vehicles, has much to say about the radius of the area where an appendage attaches to a body. They say:
The optimum radius was found to be about 4-6% of the chord. For example, for an airfoil strut with a chord of 30", the optimum root radius is about 1.5".
For me with a chord thickness of only 7 inches it would be about 3/8 of an inch. I'm wondering if the radius is a linear amount for different thicknesses of chords? Maybe I'll go down to the airport here and try and measure the radius vs. the chord of some of the small planes there like you suggested.
I hear you about the long flat areas and worry about that also. The bottom of the body will be rounded for that reason. I'm thinking about having the pods 8 inches thick at the attachment point to the body and then tapering them 1/2 inch on the tops and bottoms across their widths so that they are 7 inches width at their outer edges. Even though they won't be a true airfoil viewed from the side they will be formed at the leading edge (front of the car) and trailing edge (at the rear of the car) in the shape of an inverted airfoil.
At this point I'm not too concerned about traction with the 750 cc motor. I think even with a turbo on it traction won't be an issue. Now if later I put in a 1000 cc or 'Busa that might be an issue.
I appreciate your thoughts on this,
Sum
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I?m new to this so bear with me.
I?m wondering why you are building independent suspension on a lakester? Cool but not KISS and maybe overkill. I have mulled over a lakester in my mind and the best I could come up with (IMHO) was a streamlined tube front axle suspended inside of the body. It would only present one shape to the air. Something similar at the rear. A solid, streamlined axle tube mounted and suspended inside of the body. Again, only one shape presented to the air.
Some idea I?ve wondered about
? What is the optimum distance between the wheels and the body? From what I?ve read on airplane stuff you get ?interference? drag. As I understand it the air is getting squeezed between the two shapes (the body and the wheels) and creates a high pressure area that presents an even bigger interference to the air. I?ve wondered if mounting the wheels farther out would give it a larger area and hence less compression and drag. On the other hand when you see drawings of the air after something that isn?t streamlined it shows a huge wake that they say is where the drag really comes from. With that thought I wonder if mounting the wheels with the inside edge lined up with the outside of the body would help decrease the wake?
? What is the optimum wheel size? I always thought tall and skinny but with it just sitting out there in the wind I wonder if the airplane style wheels may present less interference to the wind with less wake and drag.
Just some thoughts. Thanks!
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I?m new to this so bear with me.
I?m wondering why you are building independent suspension on a lakester? Cool but not KISS and maybe overkill. I have mulled over a lakester in my mind and the best I could come up with (IMHO) was a streamlined tube front axle suspended inside of the body. It would only present one shape to the air. Something similar at the rear. A solid, streamlined axle tube mounted and suspended inside of the body. Again, only one shape presented to the air.
I'm not a KISS kind of guy :D . Actually I want suspension after the way the course was in the mid-90's and this last year. I think it can also help avoid wheel spin if the springs/shocks are set-up right. I can't seem to find a way to hang a tube axle with the suspension inside a narrow body with no radius bars, etc. outside of the body to locate the axle and suspension, especially if you go with the wheels/tires away from the body sides.
One other thing in my case running a bike motor and having to drive the rear axle with a chain left me with few options in the back if I wanted some suspension there. The Datsun IRS rear allows me to locate the center section in a fixed position for the chain drive, but allows via the 1/2 shafts suspension movement for the wheels/tires. My other option was to drive a rearend similar to the way they do with a legend car (motor turned sideways driving a driveshaft off the countershaft). I didn't like that since I wouldn't have the flexibiltiy of gearing I have with the option of changing front and rear sprockets (a poor man's quick change). With my current rear sprocket I could run, if there was enough power, anywhere from 150 mph to 210 mph at the same final 12,000 rpm by changing the front drive sprocket on the motor (2.77 to 2.00 final gearing). Then I still have the option of changing the rear sprocket around. If I would have went the "legend" way I would have been stuck with one final gear.
In the back the axle has to be located someway unless it is solid to the frame, so unless you are running a solid suspension chances are you are going to have other parts hanging out there in the air with the axles. Then a rear axle is going to probably have to be at least 3 inches in diameter. I feel I can develope a lower Cd even considering the increased thickness of the pods covering all of those parts with what I'm doing vs. having the axles and locator parts hanging out in the wind naked. Of course both set-ups have been successful in the past. I just have it in my mind to try it this way.
Some idea I?ve wondered about
? What is the optimum distance between the wheels and the body? From what I?ve read on airplane stuff you get ?interference? drag. As I understand it the air is getting squeezed between the two shapes (the body and the wheels) and creates a high pressure area that presents an even bigger interference to the air. I?ve wondered if mounting the wheels farther out would give it a larger area and hence less compression and drag. On the other hand when you see drawings of the air after something that isn?t streamlined it shows a huge wake that they say is where the drag really comes from. With that thought I wonder if mounting the wheels with the inside edge lined up with the outside of the body would help decrease the wake?
There again you see record setting lakesters both with the wheels/tires up against the body and out away from the body. I want to go with the latter. Seems that I've read somewhere, but don't hold me to it that the wheels/tires have to be at least 12 inches from the body for the body to be in more or less free air. I'll be 14 to 15 inches from the body with mine.
What is the optimum wheel size? I always thought tall and skinny but with it just sitting out there in the wind I wonder if the airplane style wheels may present less interference to the wind with less wake and drag.
Just some thoughts. Thanks!
From what I read the air is going to see the largest tire if they are in line with each other, so having a skinny/short little tire up front might not offer an advantage if the rear tire is larger. I orginally was going to run a sbc so a year or so ago when tires were becoming scarce I bought my rear 300 mph landspeed tires and got them in the size I wanted for the way the car would have been geared. So I'm stuck with them, at least for now. So I bought front runners in as close to the same size as possible for the front. There again using the car rearend and ride height, etc. I probably don't have many other options for wheels/tires.
The reason I picked a lakester is that they and streamliners allow you the most freedom in design. So I suggest doing what you feel comfortable with as far as your designing/building skills and what your budget allows. No matter what you do some people will applaud you and others will think you are out of your mind :wink: .
Have fun and see if you can go fast,
Sum
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Utahfab
I was advised that if the tires are less than one tire's width away from the body it's as if the gap was added to the frontal area .
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Sum
If the pivots of the trailing arm are inside the body and the fairing pivoted on a front to rear axis it might only cut a 2" slice through the air . In that case there would be seperate fairings for the front and rear suspention .
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The rear design from an ATV can be made very strong and have all the features you want without hanging a lot if stuff out in the wind.
The front doesn't have to be any larger than the material strength requires and the steering arm can be hidden from the air with it.
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JackD beat me to it. An ATV style rear end could handle the rear. After seeing some photos from the new, HEAVY, V-twin ATVs jumping I have no doubt that you could even use the parts right off the shelf and bolt it to a shorter swing arm. Even use the axle!
For a rear axle fairing I wondered about a fairing bolted to the swing arm so it would only be big enough to cover the axle. The problem is it would move in relation to the body creating a need for some sort of sliding joint and it would change it?s angle of attack thru the suspension?s travel. How about mounting an airfoil on the axle (each side) with bearings? It would automatically turn the right direction to the wind (even if because of the bodywork that angle isn?t parallel with the ground!) and be the smallest section possible. Weird but it might work! On the down side it wouldn?t have a radius where it met the body but I guarantee with it being less than 1/4th the size of the other option it would still have far less drag.
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There is a lot of ATV stuff available that can take a huge amount of power in an LSR application.
Flaps on aircraft wings have been going up and down hext to bodies for a long time and are almost perfected.
Aero loading on an LSR vehicle will make it more subject to side winds that can change a lot during a run.
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An ATV rear might work, but I have two Datsun rears free and if I would ever get the chance to put in a blown Busa that could put out 400-500 hp I feel better about this rear/u-joints, etc. dealing with that. There are a number of Datsuns running SBC's. Besides I have 6 months into this now. It will be a good comparison when you guys build one the other way. I also wanted the wider track and I don't think you have that with the ATV. What is the thickness of one at the outer axle with any locator that you might need.
I think I'll leave movable airfoils to the airplanes. Seems like they are there to change directions :( .
Like I said the other day "some people will applaud you and some people will think you are crazy". Seems like someone, maybe you Jack, said something to the effect "if you build your car the same as everyone else it will run like everyone else".
c ya, Sum
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I didn?t mean a controllable foil. Instead one that moves in the wind like a weather vane. Always pointed into the apparent wind.
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Little or no problem in a cross wind. 8)