Page 8 - Combined_26_OCR

DISCUSSION

RECOnU^Ur^D REAR DECK AIRFOIL 7JiD TTP! VERTICAL STABILIZERS

After considering-many different airfoil sections, it was decided to use a
GLARN-Y section for the rear deck airfoil and an 1IACA-OO12 section for the
vertical stabilizers. Both of these sections are considered to be quite
ancient having been used on many of the very early aircraft. Although lower
drag - laminar flow airfoils have been developed in recent years, the
expected surface roughness of the control surfaces on the race vehicles due
to dust and other particles and imperfections nullifies the advantage of
the more modern airfoils, ie. - surface roughness increases the drag of
laminar flow type airfoils to a level comparable to the more traditional
sections selected•
Figure 1 shows the fore and aft locations and approximate dimensions of the
recommended airfoil stabilizers. The stabilizers are placed as far from
the vehicle center line as practical to reduce the effects of the greenhouse
on the air flow at the stabilizers. Tuft studies on wind tunnel models
indicate the flow is relatively straight in this region. The high airfoil,
position was selected to maintain airfoil control in ’’drafting” situations by
placing the control surface above the relatively stagnant region between the two
vehicles.

Figures 2 and b shew the dimensional parameters for the two airfoil sections
while Figures 3 and 5 contain information on the sectional lift and drag coeffi­
cients. In both cases, the lift and drag coefficient curves have been
corrected for Reynolds Number and surface roughness effects at race speeds.
Aspect Ratios of both stabilizers and airfoils have been assumed to be 6 even
though the actual geometry of the recommended sections results in Aspect
Ratios of 2 and 6 for the stabilizers and airfoil respectively. This is
explained by the fact that the stabilizer to quarter panel and stabilizer
to airfoil junctures tend to modify the effective Aspect Ratios upwards by
some unknown amount because of the effects on tip vortices $ above Aspect
Ratios of 6, airfoil characteristics do not change markedly. Taper and sweep
corrections were also considered -for the stabilizers but were found to be
negligible. The interference effects between rear quarter and stabilizers
were also neglected because no theoretical solution was readily applicable .

Because the rear deck airfoil and the stabilizers are located at the rear of
the car a considerable distance from the tire to road contact points, the
moment arms tend to magnify the control effects at the road. Figure 6
illustrates the combined effects of the recommended aerodynamic handling
package at various vehicle body rake angles, yaw angles., and airfoil angles
of attack. All data is related to a base vehicle, namely the recommended
°F” Charger Race configuration discussed in reference 1. With the airfoil
set at -10° angle of attack, the airfcil-stabilizer combination increases
.axial force coefficient by .Oil; throughout the body rake schedule which means
that the lap speed of the vehicle, based on drag alone, will be. reduced by
approximately 1 MPH. In the process of reducing rear lift with the airfoil,
the front lift increases by approximately 1 pound for every k pounds of rear '
lift reduction. Thus, if a large front to rear lift differential is to be
maintained with the front lift essentially reduced to zero, the body rake
will have to be increased or a larger front spoiler employed. As in the
lift case, as the rear wheel side force is increased the front side force is
reduced, by approximately a h to 1 ratio. Although front and roar side force

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