> The Pantera design was done without a wind tunnel.
> Performance information was never forthcoming from "the factory".
Also, Ford tested a Pantera in a wind tunnel and the results were published
in the Italian design magazine "Style Auto" (Issue #29). Front, rear and
total lift along with the total drag was presented for 5 speeds from 130 to
260 KPH. This info is also reproduced in the PI new member packet I just got
from Paige Adler. If I did my SI unit conversions correctly, here's the data
from the wind tunnel test published in Style Auto Issue 29:
Vehicle Speed Speed Lift Lift Lift Drag HP required
(KPH) (MPH) Front Rear Total (lb) due to drag
(lb) (lb) (lb)
-----------------------------------------------------------------
260 162 300 112 412 556 238
225 140 229 86 315 426 159
Pantera 190 118 170 62 232 313 100
160 99 115 49 164 218 58
130 81 75 33 108 139 30
-----------------------------------------------------------------
260 162 265 -31 234 509 217
225 140 203 -24 179 390 146
GT40 190 118 150 -18 132 287 92
160 99 97 -11 86 201 54
130 81 60 - 7 53 132 28
-----------------------------------------------------------------
260 162 560 -165 395 758 324
Mustang 225 140 428 -126 302 580 217
Boss 302 190 118 315 -93 222 426 137
160 99 218 -64 154 302 81
130 81 132 -42 90 196 42
-----------------------------------------------------------------
The article was about the Pantera and the photos show the original
pushbutton Pantera prototype sitting visually level.
> The information I have is from racers like Gary Hall, when he did race.
> I know that Gary used flexable ducting from the bat ears to the carb(s).
You do want to isolate the incoming air from the engine bay air for both
temperature and pressure reasons. Smooth tubing with a flexible coupling
will result in a lower pressure drop within the ducting.
> I think it was more of a cold air source than a ram air effect.
Yes, though at high speeds speeds the ram air effect can be significant.
The conversion of dynamic to static pressure is a linear function of
density (which is itself a function of temperature) and a function of the
velocity squared. It's quite eaay to calculate the static pressure rise.
Below 100 MPH, the ram effect is pretty small and the cooler air is the
stronger effect. As the speed goes above 100 MPH, the ram air effect
increases more rapidly and becomes dominant since it is a function of the
velocity squared. Glancing at the tables in my Gas Dynamics book, it looks
like a 2% pressure rise would be possible at around 112 knots which is
something like 129 MPH. On a 400 HP engine, you'd need over 190 MPH to see
a potential 20 HP (5%) increase. You have to balance this against the drag
penalty, of course.
> The only ones that work are the ones that look like bat ears.
You first need to determine whether the flow has separated. If the flow
remains attached, you need to get the scoop out of the boundary layer. Air
near a surface, tends to cling to the surface and slows down. The farther
back on the body, the thicker the boundary layer becomes. It's best to be
at the leading edge of the hood or bumper to stay out of the boundary layer.
Alternatively, you can raise the scoop out of the boundary layer. When we
tufted a 1987 Mustang hatchback, we used a hang glider airspeed indicator on
a pole to measure the boundary layer thickness across the roof. The boundary
layer was attached and approximately one inch thick. If, for example, the
boundary layer is 2" thick, then a scoop less than 2" tall will be less
effective than one 4" tall. There will be no "ram-air" effect for a scoop
within the boundary layer but you may still get a benefit from cooler air.
You can also use yarn tufts to visualize the flowfield. I've been
corresponding with Mad Dog Antenucci on this subject and he says he plans
to test the boundary layer thickness on his Pantera.
If the scoops are in clean air, they don't need to be overly large. If you
look at IRL and F1 air inlets, they are sized for their speed and engine
power. The total area isn't large though they feed 700+ HP (F1 is down to
2.4L normally aspirated) but they are in clean air (inlet just above drivers
head).
> Hall was quoted as saying that his race car was .2 seconds faster in the
> 1/4 mile with the bat ear scoops.
That's in the right ball park.
> I don't know if anyone has scientific information that proves or disproves
> anything.
Somewhere in the database, I have some info on 76 individual wind tunnel
tests that were carried out in the Maryland University wind tunnel on
a 3/8 scale model to arrive at the original GT40 MKI body shape. Nothing
directly related to the bats ears question but some interesting info,
none-the-less. Based upon those tests, a full-size model was built and
tested at Ford's own wind tunnel in Dearborn. Ford used the Lola GT as a
baseline, comparing it to various revisions of the baseline GT40 shape.
Some results are presented below:
Vehicle Yaw Speed Lift Lift Lift Drag
(MPH) Front Rear Total (lb)
(lb) (lb) (lb)
-----------------------------------------------------------------
Lola GT 0 200 528 168 696 503
15 200 768 384 1152
-----------------------------------------------------------------
GT40 with 0 200 540 108 648 519
High Nose 15 200 844 362 1206 614
-----------------------------------------------------------------
GT40 with 0 200 445 199 644 507
Low Nose 15 200 704 422 1126 596
-----------------------------------------------------------------
Front Spoiler 0 200 326 266 592 513
#1
-----------------------------------------------------------------
Front Spoiler - 200 --- --- --- 531
#2
-----------------------------------------------------------------
Front Spoiler 0 200 236 272 508 488
#3 15 200 309 343 652 591
-----------------------------------------------------------------
Front spoiler #1 was 2.67 tall and was added below nose, behind the
air intake. Front spoiler #2 was in the same location but twice as
tall. It reduced lift but was deemed to not have enough ground
clearance. Front spoiler #3 was 3 1/2" tall and faired in. Recessed
headlights were chosen as raised headlights resulted in "marked increases
in lift and drag".
Many of the tests were directed towards trying to find the lowest drag
way to provide air flow for the cooling system, the induction, engine
compartment ventilation, interior ventilation, and brake and shock
absorber cooling air. The designers originally wanted to use twin side
radiators mounted in the engine compartment but tests on the full scale
wind tunnel model indicated 8000 CFM would be required which was deemed
not possible with the side intake duct layout. A conventional front
mounted radiator with intake and outlet beneath the nose was a little
better. The final solution was to take air in at the high pressure
region below the nose, let it flow past an angled radiator and exhaust
out the low pressure region at the top of the nose bodywork. Anti-dive
and squat were designed into the suspension to keep the cars more level
so as to not upset the aerodynamics.
Even with all the wind tunnel work, Ford was learning as they went and
the GT40's airflow management proved insufficient once the cars got out
in the field. The wind tunnel models were not fitted with the internal
ducting so it was only later discovered that 76 horsepower were being
consumed up just trying to ram air through the car at high speed. The
cars were modified in the field to fix one problem like cooling only
to change another, like the aerodynamic balance resulting in yet another
problem. Ken Miles spoke of the problem:
"The aerodynamic problems we've had with the car were essentially ones of
air flow within the car being affected by external details. For example
we were getting very little air flow to the brakes, although they had huge
ducts ostensibly directing vast quantities of air at them. In fact, the
brakes were overheating badly. The engine was getting too hot. The
engine compartment itself was getting too hot. The cooling water was
getting too hot. The engine and gearbox oil was gettting too hot. All
this in spite of a large number of aperatures which should have supplied
them with more than enough air. We discovered that what was happening was
that due to design changes that had been made over a period of time,
probably without reference to the original specifications practically all
of the ductwork was at a "stall " condition" i.e. no air was moving in the
ducts".
Ford's aerospace division Aeronutronics was brought in to instrument a
GT40 with pressure and temerature sensors on various parts of the body
(externally and inside the ducts). From this data, the Shelby team was
able to modify the cars properly. Even when the MKII's appeared, Ford
still had some aerodynamic lessons to learn. Phil Hill wrote "The second
year at LeMans we were in deep trouble when we first arrived, thanks
to a diabolical instability that had been supposedly eliminated in
stateside testing. The MKII's were simply terrifying down the Mulsanne
Straight. We ended up tacking on little eyebrow spoilers as well as an
additional little spoiler across the back to solve the problem. I also
remember early Ferraris with so much front end lift that the steering
became progressively lighter as speed climbed until finally the rebound
stops were a factor... we could have called it up-force."
Dan Jones
just joking
