Measuring Aero Forces through Track Testing

[boyracer]

Hi everyone,

As part of my masters thesis I am investigating methods that can be used to determine the aerodynamic forces (primarily lift and drag) through track testing alone - ie without using wind tunnels or CFD.

I have established several different potential methods. It appears that the 'standard' method which most F1 teams use is through pitot tubes and pressure tappings. I am quite familiar with this method having studied it before, though it strikes me as quite a complicated and expensive method.

I am interested in your thoughts on some alternative methods, in particular how accurate and how feasibile they would be. One interesting idea I've read about is using Pressure Sensitive Paint. As far as I know, no F1 teams use this (to actually measure forces rather than 'flo-vis' to see flow patterns), is this because it is too complicated and inaccurate? Other ideas are using strain gauges and load cells to measure the force directly, or using spatial pressure averaging techniques.

I am yet to fully research how these ideas could be implemented, though if anyone has any insight on these it would be very much appreciated

[Muulka]

I suppose that you could use the suspension travel to measure the downforce- if you know the spring rates and the speed.... The only problem would be bumps, but this would give a ballpark figure, and I'm sure you could adjust for track surface...

As for drag, I have no idea. Maybe use the car's acceleration at a certain speed? If you knew the power and the car's weight, you could use Newton's Second Law, but does weight from downforce make a car accelerate slower? I've always wondered that.

I think that the problem with using track testing as supposed to a wind tunnel is that a track isn't a sterile, clinical environment, but it would give you more accurate performance figures, if not accurate L/D figures.

[boyracer]

Cheers for the response. Just to clarify, the reason for using track testing is this is aimed at club racing - ie individual competitors who don't have the facilities or finances to go wind tunnel testing and want some relatively inexpensive way of establishing their aero forces. The idea is to create a standardised wing which can then be rented out at a one-off cost for the day enabling competitors to test and measure the lift and drag of the car.

[bettonracing]

As alluded to by Muulka: linear potentiometers @ the springs/ dampers, coastdown tests, & a big ass parking lot (out-of-service airports preferred). Bumps are usually easy to filter out using numerous different methods: electronic, software, mechanical (e.g. stiff damper settings) and the good ole eyeball filtering. Obviously rising rate/ falling rate suspension geometry makes it marginally more difficult to translate (into downforce).

With a proper test plan/ protocol You should be able to filter out Your sources of 'noise' (or figure out when You need to stop testing & find another place/ time). Keep in mind the more tightclad Your test protocol, the more likely for Mother Nature to play unfairly. And she's got some helluva lungs.

Not to dishearten your efforts, but the setup above (the linear pots at least) actually pretty common practice in both amatuer and professional racing circles. The low cost to implement, accuracy of end-results & ease of installation/ removal make it a hard combnation to beat.

The pitot tubes You commonly see on F1 cars in testing is to correlate flow patterns around the vehicle to their CFD data. Technically they're using it to measure downforce, but measuring pressure/ flow is an indirect method to measure downforce, and is a bit beyond the means/ interest of the average amatuer.

Regards,

HKB

[Belatti]

I use linear potentiometers to gather suspension movement data and optimize mechanical grip. Downforce calculation is a secondary use that I give to them, however I take those numbers with a pinch of salt...

To measure drag I do coasting runs but they also include friction (tyres, brakes, bearings, etc)
While doing this, I check weather with a device similar to the ones you can buy in any nautical store: