Need some aero advice..........

[Sumner]

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

[Utahfab]

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!

[Sumner]

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 .  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   .

Have fun and see if you can go fast,

Sum

[John Burk]

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 .

[John Burk]

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 .

[JackD]

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.

[Utahfab]

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.

[JackD]

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.

[Sumner]

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

[Utahfab]

I didn?t mean a controllable foil.  Instead one that moves in the wind like a weather vane.  Always pointed into the apparent wind.

[JackD]

Little or no problem in a cross wind.