[DeTomaso] Kurt Busch Pantera

[Daniel C Jones]

> What specific "scoop" are you talking about?

The Mickey Mouse ear ones I assumed you were referring to but it applies to
most any inlet that is perpendicular to the air flow, including one
positioned just above the roof.

> at higher speeds, the airflow at those locations become more stagnant due
to how the air tries to go around the car.

I'm not exactly sure of what you mean by "more stagnant".  Do you mean the
boundary layer has gotten thicker, the flow has separated from the body or
the flow has somehow slowed down?  The boundary layer should not have
gotten thicker.  In fact, it should get thinner as speed increases, though
the difference between 120 MPH and 160 MPH isn't all that much.

> The shorter side scoops (ears) didn't work as well at the higher speeds
because the airflow changes around the car.

For a scoop to work for pressure recovery, it needs to be in flowing air
whose speed can be reduced to increase pressure.  If the flow is, as you
implied earlier, a laminar boundary layer it is attached to the body.  In
that case, you don't need to make the scoop larger, you just need to raise
the inlet off the body a few inches into the free stream air.  See how the
inlet on this F-22 is raised off of the fuselage here:


https://en.wikipedia.org/wiki/Diverterless_supersonic_inlet#/media/File:Raptor-ElmendorfAFB-2009.JPG

Raising the inlet off the body generally allows the inlet to be designed
with less drag as the area between the frontal area between the body and
the duct can be made smaller (minimum duct area is smaller than the inlet
opening area).  However, if pressure separation has occurred, then the
inlet may need to be considerably farther out to reach flowing air.  The
flow might detach for some reason but why that would occur on the
relatively flat side of the car is not immediately obvious to my naked
eye.  Hmmm, was this perhaps with the windows down instead of up?

I'm not familiar with the specifics of Mad Dawg's change in inlets but
there can be other factors involved.  For instance, if the system is sealed
and the duct opening improperly sized/shaped, spillage can occur around the
inlet which can muck things up.  Also, carb tuning can be adversely
affected.  Note that the area of a properly designed inlet isn't all that
large.  Look at the inlets on a Formula 1 or Indy car for the size required
for the horsepower they make.

> To help settle this debate about inlet air temperatures and air flow, we
can do some testing with my car at the next fun rally

You can use an adjustable hang glider airspeed indicator like I mentioned.
You move it farther out from the body until the speed measured begins to
match the vehicle speed.  A lower tech way to visualize the situation is to
simply attach a rod perpendicular to the body at the point of interest with
yarn tufts at one inch intervals.  In the wind tunnel, we used to use smoke
to visualize the flow.  Now we just use pressure transducers scattered
about and a computer to create the image.  It will be interesting to see if
a pressure transducer was used to find a favorable pressure gradient to
place the duct opening on the Busch Pantera.   Back in the early days of
the GT40 program, when race car aerodynamics was in it's infancy, they
found that at speed, flow was going out of some of the ducts it was
expected it to flow into.

Dan Jones
-------------- next part --------------
   > What specific "scoop" are you talking about?
   The Mickey Mouse ear ones I assumed you were referring to but it
   applies to most any inlet that is perpendicular to the air flow,
   including one positioned just above the roof.
   > at higher speeds, the airflow at those locations become more stagnant
   due to how the air tries to go around the car.
   I'm not exactly sure of what you mean by "more stagnant".A  Do you mean
   the boundary layer has gotten thicker, the flow has separated from the
   body or the flow has somehow slowed down?A  The boundary layer should
   not have gotten thicker.A  In fact, it should get thinner as speed
   increases, though the difference between 120 MPH and 160 MPH isn't all
   that much.
   > The shorter side scoops (ears) didn't work as well at the higher
   speeds because the airflow changes around the car.
   For a scoop to work for pressure recovery, it needs to be in flowing
   air whose speed can be reduced to increase pressure.A  If the flow is,
   as you implied earlier, a laminar boundary layer it is attached to the
   body.A  In that case, you don't need to make the scoop larger, you just
   need to raise the inlet off the body a few inches into the free stream
   air.A  See how the inlet on this F-22 is raised off of the fuselage
   here:
   A [1]https://en.wikipedia.org/wiki/Diverterless_supersonic_inlet#/media
   /File:Raptor-ElmendorfAFB-2009.JPG
   Raising the inlet off the body generally allows the inlet to be
   designed with less drag as the area between the frontal area between
   the body and the duct can be made smaller (minimum duct area is smaller
   than the inlet opening area).A  However, if pressure separation has
   occurred, then the inlet may need to be considerably farther out to
   reach flowing air.A  The flow might detach for some reason but why that
   would occur on the relatively flat side of the car is not immediately
   obvious to my naked eye.A  Hmmm, was this perhaps with the windows down
   instead of up?
   I'm not familiar with the specifics of Mad Dawg's change in inlets but
   there can be other factors involved.A  For instance, if the system is
   sealed and the duct opening improperly sized/shaped, spillage can occur
   around the inlet which can muck things up.A  Also, carb tuning can be
   adversely affected.A  Note that the area of a properly designed inlet
   isn't all that large.A  Look at the inlets on a Formula 1 or Indy car
   for the size required for the horsepower they make.
   > To help settle this debate about inlet air temperatures and air flow,
   we can do some testing with my car at the next fun rally
   You can use an adjustable hang glider airspeed indicator like I
   mentioned.A  You move it farther out from the body until the speed
   measured begins to match the vehicle speed.A  A lower tech way to
   visualize the situation is to simply attach a rod perpendicular to the
   body at the point of interest with yarn tufts at one inch intervals.A
   In the wind tunnel, we used to use smoke to visualize the flow.A  Now
   we just use pressure transducers scattered about and a computer to
   create the image.A  It will be interesting to see if a pressure
   transducer was used to find a favorable pressure gradient to place the
   duct opening on the Busch Pantera.A A  Back in the early days of the
   GT40 program, when race car aerodynamics was in it's infancy, they
   found that at speed, flow was going out of some of the ducts it was
   expected it to flow into.
   Dan Jones

References

   1. https://en.wikipedia.org/wiki/Diverterless_supersonic_inlet#/media/File:Raptor-ElmendorfAFB-2009.JPG