Lift or Down Force ?

[SaltRat]

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.

[johnneilson]

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

[Cajun Kid]

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.   

Maybe I need ELECTRONICS now ??

Charles

[johnneilson]

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

[Cajun Kid]

John thanks for the info.

Charles

[Dynoroom]

Edelbrock has a system called Quick Data. Easy to use, windows based software, and $$ friendly. Has all the things you need and more.

[Cajun Kid]

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

[johnneilson]

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

[jl222]

   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

[krusty]

^^Well?^^     vic

[Cajun Kid]

   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

[jl222]

  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  eyeball engineering

[Cajun Kid]

  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   eyeball engineering

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

[johnneilson]

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

[MAZDA1807]

IMO a little lift goes a long way, most time the wrong way.