Page 2 - Combined_57_OCR

Page 2.

Performance of 1969 Dodge Charger 500 at Daytona International
Speedway

Discussion (cont3 d)

The cir, end as result is somewhat affected by the 10-15 mph., wind
conditions that existed during the test.

For analysis the particular lap chosen was the third lap of
test number 10, which had a lap speed of 136.119 mph. Curve sheet
#1 gives the epgine speed and yaw measured fo'r this lap together
with car speed and car acceleration derived from the engine speed.
The engine speed data has been smoothed to eliminate some roughnes
but the small amount of wheel spin that occiirs coming out of turn 2
and turn 4 has been left in. The wheelspin in these two locations
occurs during almost all of the laps recorded. It occurs just at
the end of the banking.

During the particular lap plotted the wind was about 10-15 mph.
blowing from an easterly direction. This accounts for the greater
speed on the front straight than the back straight. The wind also
accounts for difference in handling of the car between the two turns.
The yaw trace is reproduced only slightly smoothed! with the lower
frequency oscilatiohs left in. 'These yaw variations vary from lap
to lap, but similar frequency yaw changes"are present in each lap.
In all cases the yaw angles measured are less in turns 1 and 2 than
in 3 and 4. This is in agreement with the driver" s comments that the
car had more understeer in turns 1 and 2 during the whole test period.
In turns 3 and 4 the yaw angle is higher since an oversteer condition
was experienced there. Also in turns 3 and 4 the amplitude of the
oscilations in yaw are greater, possibly indicating that the car was
closer to breaking loose completely. With the wind direction as it
was during most of the test the number 3 and 4 turns are well shielded
from the wind by the banking, sc that the measured yaw is probably
very close to the actual yaw. In turns 1 and 2 the car experiences
considerable wind effects, so the yaw angles measured here are less
reliable. The yaw angles shown for the tri-oval turn are consider­
ably less than for the other turns..
Figure 2 shows the forces acting on the car for the lap plotted-,
as well as the locations on the race track. The top plot on the
curve shows the banking angle around the race track as well as the
locations of the straights, turns and transitions. This is from data
on the design of the race track obtained from Mr. C.H. Moneypenny the
truck designer. Also on the same sheet are plots of the normal and
lateral forces acting on the car during the lap. These are the total
gravitational forces acting on the car perpendicular and parallel
to the road surface at a given point. These are calculated from the
track data and the speed data and from data on the assumed line that
the car travels entering and leaving the turns. It will be noted that
the normal force exceeds 9000 lbs. entering turn number 1. The forces
entering turn 3 are slightly less due to the lower speed at this point
because of the headwind on the back straight. Also plotted on this
sheet is the ratio of the lateral force to the normal force. Tire
slip angle and car yaw angle are generally a function of this ratio.
The ratio is the equivalent of the lateral acceleration in terms of
’’G" as measured on a flat turn.