Landracing Forum
Tech Information => Technical Discussion => Topic started by: Cajun Kid on December 05, 2010, 04:22:01 PM
-
By looking at a few still pictures, then finish line pics and videos can anyone tell if car is Lifting ? Has Down force ? or neutral?
The reason I ask is I remember the A2 commentary and the pics DW took of the Superbird. It was easy to see the lift and then the the corrective down force.
On my car, from both the drivers seat and the pics, I can not feel or see any lift. Looking at the pics, I use the moon disc realtionship to the fender openings as a referance point as well as the rocker panel and front spolier height.
What are your thoughts or observations?
Car at rest
(http://i261.photobucket.com/albums/ii43/cajunkid5690/Studebaker2010006.jpg)
(http://i261.photobucket.com/albums/ii43/cajunkid5690/DSC01027.jpg)
At 164 mph
(http://i261.photobucket.com/albums/ii43/cajunkid5690/Studebaker%20Racing/ECTAOCT697.jpg)
180 mph finish line video (click to launch then go full screen)
(http://i261.photobucket.com/albums/ii43/cajunkid5690/th_MVI_2284.jpg) (http://s261.photobucket.com/albums/ii43/cajunkid5690/?action=view¤t=MVI_2284.mp4)
-
Clever method . A piece of masking tape on the body above each wheel would add accuracy .
-
Charles the picture angles are different so its hard to tell, doesn't look like lift, you have a better view of car sitting in shop. It should be squatting some from spoiler downforce in rear depending on spring rate.
Looks good though :cheers:
JL222
-
Yes if the car has major lift, or down force changes in ride height you can see them on good telephoto shots of the car.
As you are doing that, the best way is to measure from fixed reference points, such as the top of the wheel (moon caps in your case) and the wheel arch.
A couple pieces of light colored masking tape (on a dark car) or dark tape on a light car, will greatly help you make the measurements.
There are a couple issues to consider however. During the heat of the day mirage can significantly distort the appearance of the bottom of the tires and the rocker panels.
This distortion makes measuring the air gap from rocker panel to the apparent racing surface highly suspect in some cases. By measuring from the top of the wheel (not tire) to the wheel arch you get above the worst of this distortion.
If you want to make more precision measurements take a chalk line and with tape mark reference points that are even with the top of the wheel.
On a good high resolution camera and long telephoto image you can resolve details down to about 1/2 inch wide, so use tape at least 1 inch wide to be sure you can pick it up in the image. The most important issue is visual contrast, ie white against dark or dark against white. The higher the contrast of the reference point the easier it will be to pick it up on the image. To scale it use the known diameter of your wheel as your ruler (measured horizonatally in the image if the image is shot from near 90 degrees to the path of the car. If the image is at a significant angle use the vertical measure from the center of the wheel to the top of the wheel to minimize distortion of your reference point.
Or you can put a tape ruler on the side of the car near the wheel well.
I will post a couple images in a bit to show what you can see with a good long telephoto and then blowing up the digital image on the computer.
Below is your image resized several times. As you can see if you had a hard white reference point above the wheel center it would be easy to measure the exact body lift. The blocky (pixilized) character of the image is due to the low resolution of your original. If you did the same with your original image the quality would be much better.
Larry
-
Charles are you data logging?
You can buy a linear potentiometer and data log if you are getting lift or down force, how much and at what speeds.
This one if from the Edelbrock Quickdata stuff (*expensive) but there are many out there and will work great.
(http://www.edelbrock.com/ecomm/detail/91127.jpg)
~JH
-
Looking at the enlarged pic, I can't say if you are lifting at the front, but you sure are letting a lot of air under the car... What is the measurement from the bottom of the air dam to the floor at ride height in the shop? What is the height of your tire sidewall? (the height of the dam at speed looks about the same height as the edge of the moon disc. As I think about it, it sure looks like the front is up. vic
-
The budget potentiometer is a piece of welding rod with two o-rings on it. Mount it to either the frame or an A-frame and an eye mounted on the other with an o-ring on each side of the eye. You'll soon know what your suspension travel is and you can figure your body lift or squat from that.
Pete
-
Ron Joliffe told me years ago that he quit racing the original Rocket Science '50 Olds after seeing pictures of it in the lights. As I recall, the top of the rear fender opening was about even with the top of the Moon disc while standing still. In the lights there were inches of clearance above the top of the tire. He had no sensation of lift, either, and is an experienced and sharp piloto.
-
Looking at the enlarged pic, I can't say if you are lifting at the front, but you sure are letting a lot of air under the car... What is the measurement from the bottom of the air dam to the floor at ride height in the shop? What is the height of your tire sidewall? (the height of the dam at speed looks about the same height as the edge of the moon disc. As I think about it, it sure looks like the front is up. vic
Yea Charles, if you take a card and square it with bottom of Hotrods foto the the air dam and rim look the same height, now all
you have to do is go measure :-D
And if Hodrod could blow up the rear tire 8-)
JL222
-
Thanks for that!
I used the "paperclip on the throttle linkage" to gain 15 mph in my mile speed (from totally shameful to merely embarrassing). Big help, and thank you again!
The budget potentiometer is a piece of welding rod with two o-rings on it. Mount it to either the frame or an A-frame and an eye mounted on the other with an o-ring on each side of the eye. You'll soon know what your suspension travel is and you can figure your body lift or squat from that.
Pete
-
Deducing aero forces from suspension travel is a dodgy endeavor unless the suspension rate is relatively low. Many LSR cars have very stiff suspension and/or travel limits for the express purpose of restricting body movement and attitude changes.
The problem with the o-ring or ty-wrap technique is what happens when driving over a bump.
For one-off testing and instead of an LVDT* and data system, one could inexpensively rig up a common rotary potentiometer and read or record the variation with an ohm meter.
*LVDT = Linear Variable Differential Transformer.
It is highly likely that the “linear potentiometer” shown earlier is, in fact, an LVDT.
-
On the Dallara Indy cars we ran we had load sensors on each corner that measured the load on each corner. Looking at that data after a run gave a pretty good indication of downforce. Those sensors are probably fairly available on the used market. The problem may be getting a data collection system that can read the results.
Pete
-
Charles are you data logging?
You can buy a linear potentiometer and data log if you are getting lift or down force, how much and at what speeds.
This one if from the Edelbrock Quickdata stuff (*expensive) but there are many out there and will work great.
(http://www.edelbrock.com/ecomm/detail/91127.jpg)
~JH
If you are logging a cheaper way to moniter lift, up or down, is to use throttle position sensors.
-
I have no data logging at all.
Looks like I may have to look into a logger.
For Maxton I raised the cars ride height as to make certain nothing hit the track or pit/return road.
Since nothing hit (in 4 passes) I am going to lower the car both front and rear another 1/2 inch to start. Keeping the same rake as the handling is great, the bumps seem to have no effect, car goes straight and the suspension takes up the bumps without even a wiggle from the car (the in car camera run shows my hands and sterring had no inputs other than to make the dogleg in shutdown).
One of the reasons I was trying to determine any front or rear lift is deciding on adding a Step Pan,,, and I can adjust the rear spolier lip angle. I have 0 , 15, 30 and 45 degree lips,,in 1 inch lip and 2 inch lip lengths from flat, all those runs used the 30 degree 2" lip. If I was not getting rear lift,, I could reduce rear angle from 30 degrees to 15 and that would also bring the nose down (if it was lifting some)
Charles
-
If you look at alot of the doorslammer cars that run in LSR they have a pretty hard rake. Just look at a pic of Mike Cooks Alpha. I have been told to rake my car because it's quite a handful.
-
Thanks for the note.
My hood bulges at highway speed and the steering feels light 130-150mph. I want to know if the front is lifting. Hitting a bump won't affect the "paperclip" that indicates lift, will it?
Deducing aero forces from suspension travel is a dodgy endeavor unless the suspension rate is relatively low. Many LSR cars have very stiff suspension and/or travel limits for the express purpose of restricting body movement and attitude changes.
The problem with the o-ring or ty-wrap technique is what happens when driving over a bump.
For one-off testing and instead of an LVDT* and data system, one could inexpensively rig up a common rotary potentiometer and read or record the variation with an ohm meter.
*LVDT = Linear Variable Differential Transformer.
It is highly likely that the “linear potentiometer” shown earlier is, in fact, an LVDT.
-
FWIW;
Putting a data logger in the car is not that much money now a days, 15 years ago was another story.
But, you would not believe the uses you can find for one besides the std tach/speed/temp and pressure logging/display.
With a standard 0-5v analog channel you can use std instruments, for instance, I monitored ram air inlet pressure to our car while on Cal Speedway (sports car).
With some of the talk about traction control, I could easily see throttle position/rpm/speed data as necessary.
John
-
any reccomendations on which data logger ? and then what I need to log ?
The only data I have ever gotten was from the
Seat of the Pants, Eyes, Ears, Hands and Right Foot. :cheers:
Maybe I need ELECTRONICS now ??
Charles
-
Charles,
I personally use Pi Research, this from investment 10+ years ago. Good equipment works for a long time, multiples of cars and karts.
A few years ago I worked with a fellow who ran CDS, Competition Data Systems eq. If and when, I will look this direction.
I have also been looking in the direction of Racepak, I believe the same folks as MSD in Tx. Or owned by the main company.
Not to advertise but these folks are very good www.veracitydata.com
One note: the software to anaylise the data is a tool, take a look at it also.
A very good book on data was published by the SAE, I forget the author. Can be usefull to show you what systems can do.
I will look up the author later today when I go to shop.
John
-
John thanks for the info.
Charles
-
Edelbrock has a system called Quick Data. Easy to use, windows based software, and $$ friendly. Has all the things you need and more.
-
Edelbrock has a system called Quick Data. Easy to use, windows based software, and $$ friendly. Has all the things you need and more.
Thanks Michael, talk to you tomorrow night on chat.
Charles
-
Charles,
the book is written by Jörge Segers, Analysis Techniques for racecar data acquisition
published by SAE
It goes from the basic data logging to full on theory and creating math channels.
Again, I will mention the anaylist software tool is a must.
I am very skeptical of any SW that is updated every month and a "free" download.
John
-
Charles...have you measured from the floor to bottom of front wheel rim and to bottom of body in front of wheel? This should answer half of your question.
JL222 :cheers:
-
^^Well?^^ vic
-
:? The distance from the bottom of the rim to the floor should not change much, not sure why that is a factor? Tire is not going to change much is it ? Now from bottom of front air dam to the ground is the ride height at rest, but at speed from the pictures it is hard to tell what that measurement is at the finish line.
To get the air dam to floor measurement I need to put the air dam back on and it is COLD and the air dam is in the nose of the trailer out on the back forty. Will get mounted and measured this weekend.
Charles
-
The tire could grow some at speed but assuming it doesn't if front end is higher in the shop than rim, you have lift
and downforce if less 8-) eyeball engineering :-P
-
The tire could grow some at speed but assuming it doesn't if front end is higher in the shop than rim, you have lift
and downforce if less 8-) eyeball engineering :-P
Hmm, I would have thought that if the bottom of the air dam was lower or even with the lower edge where moon meets rim at rest, then looking at the pics that would mean front end has lift at speed ?
I will get exact measurements over the weekend,,, But going through and zooming in on a dozen or so finish line pics and as many at rest as well,,, it looks like the front is lifting just a little (maybe 1/2 to 3/4 inch at the most) and the rear may have a bit of down force as it looks just a smidge down at speed.
I guess some precise measuring and a wind tunnel test is in order for Feb/Mar. That way I can try out my step pan and various spoiler lip length's and angles as well as adjusting rake.
Charles
-
Or you could install the data system, make a run and see how much lift/squat you have and at what speeds.............
Also, during the acceleration, you can see the amount of squat in the rear end.
Just an observation, John
-
IMO a little lift goes a long way, most time the wrong way.
-
"IMO a little lift goes a long way, most time the wrong way."
I admit it , I am a coward about body lift ever since my 65 160 mph Olds road walked--bad-- with out a substanal rake. The reason I like solid suspension on LSR cars I want to minimize the chance of the angle of attack changing. It doesn't much matter which is the cause, the spoiler creating down force, or the front end lifting because of pressuer changes. Without good data, which I do not have, I would rather put up with the problems of unsprung.
-
I too want to make sure I know what the car is doing on the big end...
On board data and wind tunnel data... seems to be the answer...
eye ball engineering and seat of the pants are only good up until the point that they aren't !!
Charles
-
spot on
-
You could run solid suspension until you want to run a production class. I believe the rulebook says "original running gear design" or something close to that.
-
But I'm not sure they check the "compliance" of the shock absorbers (nor do they want to).
Stan
-
But I'm not sure they check the "compliance" of the shock absorbers (nor do they want to).
Stan
In inspection at SW we made a car find some coilovers because he had A-arm suspension with solid struts in place of the shock/coilover.
-
I can only speak for myself in inspection, but we should be as throe as possible. I'm sure Dan has seen stuff thrown out of impound for less. It only takes the other guy(s) in your class to go snooping around to try and find some way to protest. Just saying.
Peter.
-
I prefer suspension, and my home track is Maxton, therfore suspension is a good thing. I just has some fine tuning to do.. Since those pics are from the Stude's firts runs at Maxton (where I had the car set up as high off the ground as I could) in order to make certain my air dam or other parts of the car did not hit the track or the return road. Now I can lower the front 1/2 to 3/4 inch which
will increase the rake and most probably reduce or eliminate the front lift. It lay however increase the rear down force, so then I would have to decrease the rear ride height, or spolier lip angle or spolier lip surface lenght or some combination of those 3.
Hmm,, looks like I better reserve an extra hour of wind tunnel time ?
Charles
-
Charles 1) You should have in your set up notes the distance from the bottom of the air dam to the ground (if not, bad boy, you need to know this and have other measurements recorded,too).
2) If this # was less than the sidewall height of your tire at set up pressure, it means that you have front lift (as jl222 said "eyeball engineering"). At the speeds you're running front tire growth is not going to have a big effect on the tire height.
3) I think you'll learn more in the tunnel (for the equivalent $$ spent on data acquisition, at least chassis-wise) than buying a data system for next year, unless you've got the $$ to spend on both. I'd gladly discuss this with you (we need to do lunch during the upcoming holiday season, anyway.)
4) I'd gladly help you with a plan of attack for the tunnel which will optimize your efforts (I do have some experience here), and accompany you to assist.
vic
-
Vic, yes I do have notes (and you know why I keep some data to myself)....
and yes when I go to the tunnel I will need some help and will keep you informed.
Call me and we can grab lunch next week or the following...
Charles