concentrate on sweeping the rear wing, and then add or subtract from the front wing appropriately. That is, if I add two degrees of rear wing, I add two degrees of front wing, and vice versa. This gives you your true drag polar. Before we leave the topic of
Figure 1: the section of the aeromap you obtain from race data
See equations: 1,2,3 and 4where, Fs
damper unit at the wheel s
x and s is the movement
is the force of the spring x
and velocity of the spring k is the spring rate or function c is the damper rate or damper function specified at the damper MR is the motion ratio of the spring expressed as damper / wheel movement di
is the total movement of the
corner of the car rh are the relevant ride heights To make thing easier on yourself,
Figure 2: what the locus of front and rear ride height maps needs to look like for aeromapping
Table 2 Test No Front rh Rear rh 1
2 3 4 5 6 7 8 9
Where, frh0
rrh0
frh0 frh0
frh0 frh0
frh0 frh0
frh0 – del_frh
frh0 – del_frh
frh0 – del_frh
rrh0
rrh0 + del_rrh
rrh0 +
2*del_rrh rrh0 +
3*del_rrh
rrh0 - del_rrh rrh0 –
2*del_rrh
rrh0 + del_rrh
rrh0 +
2*del_rrh rrh0 +
3*del_rrh
= initial front ride height = initial front ride height
Del_frh = delta of front ride height Del_rrh = delta of rear ride height
rh rh i
Equations 1,2,3 and 4 F
S = k xs + m
k w F=
d = si t
MR w x
+
f = rhf 0 − + d2 2
d1
r = rhr0 − + d4 2
d3 mi
( ( ) ( )) MRxc s S
⋅
zero the dampers on the ground. The point of this exercise is so that every time you do a data run you do an xy plot of front and rear ride height. This will give you a snapshot of what you have just done. Alternatively, you can use simulation tools to do this for you. The important thing is to actually look at it so you get an idea of the section of the aeromap you have categorised. In terms of the practicality of doing this, you can either do runway testing or at the track. Runway testing is ideal but, if you have to do it at the track, it’s in and out laps only. In my experience, it doesn’t take very long for racecar drivers to get bored and team managers to get grumpy doing this. Also choose a circuit with a long straight (say, 400m and above). The next step is to reset the car
to the nominated ride heights and sweep the wing settings. I generally sweep the wings to the drag polar specified in the racecar manual as it saves you time coming up with a test matrix. It also cross checks what’s in the manual. If it hasn’t been specified in the manual, I
aero testing, let us quickly discuss coastdown testing. There are some who are adamant about performing these tests, but my personal view is if you can test your engine on a rolling road dyno, you only need to do this step once to get a snapshot of the aero drag and rolling tyre resistance. Once you have this, the rest can be back calculated from engine power. If you don’t have this, I would recommend one coastdown to calibrate your engine losses. If you don’t do a lot of coastdown testing, though, it’s not the end of the world.
Tyre testing Now that we have the aero side of things out of the way, it’s time to focus our attention on the tyres, and our first port of call here is camber testing. What we do in this situation is
set the racecar to the recommended set up and sweep the front and rear camber. How do you determine the deltas you sweep in? Again, this is where a bit of simulation comes to our aid. To illustrate this, consider the plot of cambers for a given lap shown in figure 3. If you know what camber
variation you are looking at, you can plot the deltas you are looking for. To really focus on the effects, I would suggest doing the camber sweeps in isolation. This way, when you compare run to run you can see immediately what is affecting the lateral and longitudinal grip. This also allows you to refine your deltas. A rough rule of thumb here: if you make a change and the change in lateral acceleration is very large, back off the delta. This information is invaluable for determining camber sensitivity and invaluable for populating this curve. If you are dealing with an open wheeler / Sportscar, use 0.2 degree deltas, Touring Cars use 0.4 degrees. However, the operative word here is
10
www.racecarengineering.com • August 2011 67
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100