I've been doing nothing much lately other than looking at the ends of the car and thinking about aero. I've also been thinking about the great header test, CRVtec's, flared fenders and real race tires. I've been thinking about how many times I can make it to TCRA at ButtonWillow and Willow Springs. Enough. Here's the new plan:

I leave the motor alone in 2002.

I resume suspension analysis at a higher and yet more practical level. The primary thing we are interested in (and can measure only so very imperfectly) is what is happening with our tire temps. Drivers sense the balance of the car, but rely on the stopwatch for analysis of speed. Changes to chassis setup under even a fairly sophisticated club racer data acquisition scheme are still not good enough. I'm going to spend 2002 cutting to the heart of things. My friend with the shock dyno is a dealer for both SPA and Stack and is developing pretty good familiarity with the systems. He said Pi used to have infrared sensor accessories that could be adapted for use for real time tire temps - we are going to put together apparatus to sample this data. I'll buy all the sensors, transducers, and fab all necessary hardware, he'll donate the base setup for testing - and we'll both learn what we can. We will have to sort out issues like available input channels and it will be unlikely that we can log 3 points each on all 4 tires simultaneously.

One of the largest challenges will be the construction of testing methodology. I wrote about the series running in Racecar Engineering titled "Design of Experiment". I believe that this will be key to learning more economically.

Mechanical changes and investigations that I intend to make in 2002:

Fab my own adjustable front upper a-arms ala the DC cars, with discrete multi castor settings, discrete shim style camber adjustments (so that a table tying shim to turns on the front tie rods can be made, making changes quicker), and better clearances to the inner fender.

Revisit front bump steer and rework my RTR clone kit.

Analyze the effect of different length rear toe links. As the car goes lower into bump, the rear view virtual swing arm IC gets shorter - this must have an effect on the rear bump steer curve since the toe link length is fixed. Even though we have very little travel with 900+ rates this looks like an interesting way to find more rear end predictability. Guys running adjustable toe links made of heim joints without regard for link length may be making a mistake here. I will also rig up apparatus to subject the rear axle to longitudinal load and evaluate toe change under deflection (or I may just model the geometry if that suffices), and try to tie that back to toe link length too. I realize the vertical location of the inboard end of the toe link should be considered too - and I will try. This may well turn out to be worth very little.

Fab motorcycle yoke style chain adjuster type rear toe link adjusters so that rear toe changes can be more discretely and positively made.

Full cage - SCCA IT IL-Legal - I'm going to tie it in to the A and B pillars for the expressed purpose of stiffening the chassis as much as possible. I may not penetrate the firewall. I am going to ape alot of European cages in that I will triangulate the top of the A pillar viewed from the side. Of course it will pass for ITE.

Adjustable sway bar end links to make zeroing the bars after corner weighting possible. I may fab a rear sway bar to run across the rear towers inside the car to be worked by long vertical links to make it possible to have a driver adjustable rear bar.

I may add a remote oil filter and Accusump, and relocate the battery. I want to preserve the usefulness of the passenger seat so placement of these items will be a challenge. The battery will not go to the back of the car - I don't want any more polar moment of inertia than I already have.

I will be running one of Andy's lips and be fabing my own tray which will incorporate as much rear kick up as possible - even if this means a shorter throat. Material selection and cost containment will be a problem here.

I will be fabricating a rear diffuser that will have a throat that runs rearward from the rear of the gas tank as wide as the span of the inner lower control arm pivots. The length of the throat will be dependent on the divergence curve required to terminate cleanly at the edge of an early G3 rear bumper cover. Those sections of the rear bumper cover outboard of the diffuser and below the bumper re-bar will be vented. I've already started drawing the frame for the mold.

I'll have to clear some room currently occupied by the stock muffler. I'll probably make a new axle back section using one of those small oval Borla's. I hope it end's up sounding good without being too loud.

Scott, who thinks that if he can put this all together, maybe I'll be ready to do a little racing in 2003 - course I'll have to save up a bodywork fund.....

 

 

Can that be possible?

Thanks again for your post.

Will

[sp]


[Modified by Willard, 2:19 PM 12/18/2001]

 

thats what i'm talking about!

 

may all your wet dreams come true!

 

holy crap, scott.

you're a friggin' animal. i shoulda spent more time in your analytical glow at the expo. (:

-k-b0t, who pops up like a whack-a-mole when yoshi pushes me into it... (:

 

can you provide some defintions?

Kick-up

Throat

-Mike

 

Picture a typical venturi: Convergent cone - throat - divergent cone.

Cut it in half horizontally. That could be a splitter and tray. Usually you don't have much of a convergence at the leading edge and the focus is on the lip being a shelf for high pressure to act on from above.

The flat part is the throat - this is the high velocity low pressure section over which downforce is exerted. The amount of force generated is roughly proportional to its area.

The divergent part - called the diffuser - is sometimes called "kick-up". It should be a curve that is gradual enough to prevent seperation of airflow and so maintain the maximum draw on the throat.

I've been paying alot of attention to DTM cars lately, and so I've become trapped in the conviction that I must do this.

Scott, who like so many people is a victim of TV programming....

 

Damned metaphors....ok, so this thing has two hearts, only one of which I can get to.

We can measure tire temps somehow to discover how happy our tires are in the sense of dynamic alignment so to speak. The part that's really hard is to optimize tire force variation thru spring rate and damping selection (though I could qualify this sentence by saying that spring rate selection can be dominated by geometric control and vehicle response rate requirements).

Bucks up people buy lots of time on 7-post shaker rigs with mega channels and load cells (though often their testing might be aimed at accomodating a critical section of track and eliminating the effect of this accomodation elsewhere on the track - nothing is ever perfect everywhere - though the day is coming when a team of systems engineers and a bank of computers effect realtime control over suspension, alignment and steering variables).

The only club racers I know who've rigged up linear potentiometers (wheel position sensors) have done little more than gathered alot of data and scratched their heads alot (even after talking to their shock reps).

When I said cut to the heart - I was really only getting at one part of this gigantic challenge - the part that I can approach. I don't expect to be able to make any decently founded suppositions about TFV from tire heat data - though I hope to be able to see differences in the heat generation rates in response to large changes in low speed damping levels and curve shapes. People don't pay good money on those shake rigs for no good reason.

So, I hope to do a better job of keeping the tires happing in their orientation thru DAQ and maybe gain insight into damping curve effects. As to how happy they are about their vertical force inputs, well I'll just have to try to be a more thoughtful caveman than the next guy.

Scott, who is just a caveman.....your world confuses and frightens me.......yeah, lets race!.........


[Modified by RR98ITR, 7:39 AM 12/19/2001]