X-Mozilla-Keys:                                                                                 
Jeff Spitzer wrote:

At 01:53 PM 7/26/99 -0700, you wrote:

2; The E-Racer design uses an NACA bottom inlet duct with a horizontal

bottom

location radiator similar to your design.  It seems that a sufficiently

large

enough NACA inlet duct would create less drag than a scoop.  How about NACA
inlet ducts?  Wow well do they perform?  Could a Velocity be modified to

use a

NACA type duct as on the E-Racer?

Yes. My only question is if a horzontal  rad is too close to the NACA
duct I don't know how well that would work as the NACA duct is designed
to roll up the boundry layer and provide an internal airstream
parallel to the direction of flight and not at right angles to it,
if you get my drift. I also don't know what pressure the NACA type
scoop can work into. I suspect it will stop working at some
pressure well below dynamic pressure or not too far above
static pressure.

The claim is that the NACA scoop can recover nearly 100% of dynamic
pressure when done right.  That means following the length, ramp angle and
aspect ratio guidelines.

I am suitably impressed. I did not think it was quite that good. PL

A P51 type scoop on the other hand would merely pressurizes the
chamber below the horzontally mounted radiator and above
the scoop with dynamic pressure if, for some reason,
the radiator became completely plugged up with say
....bugs or debre.

BTW dynamic pressure is that pressure you would measure
at the center of a flat plate held perpendicular to the
airstream. The pressure in pounds per square foot is
0.0026 times velocity in MPH squared. Static pressure is
15 pounds per square inch at sea level and reduces
with altitude of course.

.0026 is really dense air.  Sea level standard is more like .00238.  You
also forgot the 1/2 multiplier.  Formula at sea level is 1/2*.00238*V^2 in
lb/ft^2.

I think we had this discussion before. My formula yields 26 pounds per
square foot at 100 MPH which is indeed correct. Obviously different V's. 

100 MPH is 146.666 FPS so your V is in feet per second 
while my V is in MPH. 146.666 squared is 21,511.012. Times .00238 is
51.196. Divided by two is 25.598 pounds per square foot. So I lied
slightly.

I can see why a lot of new engineering students throw up their
hands in frustration with all the different systems and constants in
use. There was nothing wrong with the old English system. After
all they invented it. Newton! Now we have stupid things
like Hertz instead of cycles per second. PL

I would say the NACA duct might work if it was well
ahead of the horzontally mounted, low aero pressure drop
(thin), radiator and probably provide less aerodynamic drag.
You would of course then have to cut into the
rear seat area/volume of the canard to install the NACA duct.

That's the problem with NACA ducts for radiators.  They are extremely long.

This is just another illustration of why large frontal area thin
rads are lower drag than small frontal area thick rads. Thin rads
are now universally used in cars and trucks.

3; Regarding cooling while setting on the ground:  On a Velocity, it

seems a

small NACA outlet duct on each side of the engine cowling might work well.
Airflow over the cowling created by the prop would certainly create a

partial

vacuum and reasonable air flow.  The duct could have an inside offset

bottom

plate an inch or two deep to prevent water from entering the engine
compartment.

There's no such thing as a "NACA outlet duct"

Jeff Spitzer

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