A carbon wing I made for a friend recently had a run. Due to mechanical maladies with the car testing was non existent so the only real testing was during practice. The current wing is 100mm wider then the old one and since we did not know how well it would work we mounted it at approx 1 deg AoA instead of the 9 degrees of the old alloy wing. The results were 9kph faster top speed and persistent understeer in the faster corners, where the car usually had neutral entry leading to oversteer. This seems to be indicating an improvement, however what data is usually used to monitor aero changes in more professional situations?

I assume its a rear wing?

All together now after 3,
1 2 3,
a stopwatch!

ooops, yes a rear wing.
Double ooops...lap times, yes.

Speed traces through corners, latacc, stringpots would all be helpful (if you have them before and after). Anyway, sounds like a good result.

Also record ride height and steering wheel angle if possible.
They'll tell you the change in downforce (change in ride height) and the amount of change of understeer. (steering wheel angle, more in the same corner on the same line is more understeer, etc)

Mmmmmm. I'm guessing I was getting preachy?

The best data to monitor these types of changes is load cells in the suspension someplace that allow you to see how the suspension loads have changed. Damper travel is also a useful, if less accurate, alternative. Your driver comments seem telling to me. If the report now is understeer, then add front downforce in some manner to balance it. If you add front wing and return to the previous handling balance, you pretty much know that you've added downforce. The other sure tell is if you have to raise the ride height to reduce bottoming issues that didn't previously exist.

It's tough to get more downforce and a higher top speed. You've done well.

Nah, it cut to the chase.

We're starting to use twin head differential GPS instead of our usual twin Correvit/gyro/accelerometer setup, looks really good so far.

Bill steering angle we're starting to do to do understeer...but was Phillip Island in the rain last run and full wets were not really enough - so you can imagine that you cannot compare data. We tried a new front splitter there too - a very cut and shut raised centre airfoil just to try something. Reports were it was 'more pointy' at speed, but ground clearance was 50mm too high and we could not adjust it lower on the day...and it was the only day as head gasket failed. Well try it lower and see what happens and if there is some change well invest more into it. The car has a limited life ahead of it, but is a useful learning tool...when it works.
Fat Boy thanks for the comment but I cannot claim any credit. The wing uses an Enrico Benzing profile used on the Lancia LC2 sportscar and it would have to be more effecient than what was on there. It's simply the old story of easy improvements when starting from a low base. Front end downforce is much harder on a sedan.
Load cells? This sort of thing: http://cgi.ebay.com/INDY-LOLA-RACE-CAR-SUS...=item5636e0d71d

Front end downforce....Vent the front fenders on the top....probably you'll call them 'wings'...like this.




The loads cells you've found on ebay are exactly what I'm talking about.

Sorry to let this slide but I had to get the next issue done and dusted.
Fatboy we actually call them guards...I knew about the venting as shown, unfortunately it is against the rules for the class.
I've been told the load cells need an amplifier of some sort, what sort of data system have you seen with such things? I also pulled out the rapid switching manometer I had under the bench - I think it is dead. However is there a cheapish commercial pressure transducer system that would allow measurement of surface area pressure - say 20 channels?
In the mean time I have purchased two GoPro HD cameras and we'll be using these to do some active flow visualisation work (the usual oil or tuft). I'm interested to see how the aero changes with speed and yaw etc, after all we really want the aero to work in the corners and under braking and virtually disappear on the straight for min. drag.

Yes, you will need amplifiers for loadcells unless they are already built into your loadcell or logger. This is one external version I have used, there are plenty of others available: http://www.firstsensors.co.uk/page9/index.html

Take a look at an old post here: http://forums.autosport.com/index.php?show...t&p=3283578 it might help you.

Regards, Ian

Most data systems do not have internal amps, and the ones that do are probably out of your price range. I actually prefer to amp the strain gauges as close as possible to the gauge itself. Strain gauges give millivolt outputs, and shipping that around the car is a really good way to induce noise in the signal. If you have the signal amp'd at the gauge, then you're passing volt level signals around the car and whatever electrical noise it picks up will be less of a deal.

Pressure sensors are tricky. You can get multiple pressure tap sensors in neat packages, or you can build them. It's not really all that tricky to build a multiple pressure tap system. When you do go down the pressure tap road, make sure they all have a common reference pressure. A cheap approach is to route all the reference pressures into a 2 liter bottle with a small puncture wound. You get a resistor-capacitor effect that calms the pressure fluctuations a little bit and gives a better signal.

Thanks for that Ian, I had forgotten about that old post. For some reason I cannot activate the NRoshier ID, anyway I'd be interested in your car and findings - after all I have a 750cc test car in planning. Thanks for the link, I will contact them about the amplifiers.
Fat Boy I have seen the gauges with plugs on them, which I assume plug into an amp. What sort of signal rate would you use? BTW would there be any advantage in using the gauge in the wing mount itself?
Thanks for the idea on pressure sensors. I went and got the latest version of Katz and saw the multi-channel sensors - looks very handy.

The best source of info on what we did with the Gould GR55 is the November 2008 issue of Race Tech magazine, in which I did a write-up of the aero development programme.

A good, cheap, differential pressure transducer is the Freescale MPX5010DP (http://www.freescale.com/files/sensors/doc/data_sheet/MPX5010.pdf). They are as good as the various multichannel sensors out there that don't cost $thousands, i.e. they need TLC and frequent zeroing and calibration checks if you use them as absolute sensors but they are very linear as differential sensors.

Plumb one side of all your sensors to a common static reference then the other side will meaure +/- 10kPa from that. That's all you need to develop a racecar.

Regards, Ian

If you were doing a series of wing tests, then gauging the wing mount would be interesting, but only only as an addition to the pushrod load cells, not in place of them. In short, it's just not necessary. You can get amps installed under the heat-shrink on the pushrod and that's the easiest way to do it. Outta sight, outta mind.

If you're doing aero testing, then depending on what you're doing, 250 Hz logging is more than enough. 100Hz would work fine. The aero stuff you're doing is very low frequency, so Nyquist doesn't raise his head. You will still get thousands of samples for each test and you aren't doing any high level maths with the numbers. It will kind of depend on what kind of memory you have on board and how often you can download, but don't stress about logging rates.

Thanks for the link Ian. I sort of meant changes if any since the article (which I could not get btw). I keep a close eye on Howells GR55b which is local to me and was interested to see the addition of a new wing and barge boards.
Fat Boy thanks I think we have a spare channel in the Motec M800 and we can sample at those rates. I will have a close look at the second hands Indy stuff that comes up on ebay. Have you read any of Buddy Fey's writing? http://buddyfey.blogspot.com/ or had a read of Warren Rowley's book?

I'm a little out of the loop on the release schedule for the various GR55 mods. I think the latest front wing stuff hasn't come out yet - at the moment the GR55 is still the car to beat so until another manufacturer gets on the pace there is little customer demand.

What was interesting (and I'm not sure it happened in time to make the magazine article last year) was that the last set of front wing tests found solutions which gave more overall downforce. I.e. a front wing flow was found which enhanced the diffuser, much like a lot of current F1 development direction.

100Hz is about right to log pushrod loads if you can manage 2 or 3 seconds of constant speed at your test venue. I would use 250Hz for on-track purposes, and make sure the correct anti-alias filtering is in use.

Regards, Ian

Howell would like to sell his GR55 but you can imagine that the market is not strong. I believe he has the new wing, but many venues simply may not be fast enough to use it properly...things are a bit bumpy, cambered and tight locally compared to what I have seen in the UK and on Youtube. There is a Carbon Force over here too that is starting to do well.
We can log over 300Hz so I'll have a chat to Simon and seen what we can do. The more I think of it the more I like the idea of a load cell in the mount, but I'll follow up Fat Boys advice.