This is a recording.
Again the fundamental problem is: NACA ducts are not designed to

work with

heat exchangers. The boundry layer is not the problem.
A P51 style duct is called for on pushers for feeding heat

exchangers.

Paul Lamar

a word about recorded messages:
Greg's plane comes off the runway like it was catapulted and

continues to accelerate  then it hits

a point where the drag of the (3) P-51 scoops just stops the

acceleration and no amount of more

applied power will budge it. He and anouther pilot that has flown it

agree there is a need for a

bit more prop but both agree the drag is kiling the performance.
...Chrissi

Cozy Mk-IV 13B-turbo
www.CozyGirrrl.com
Chrissi@BlueMountainAvionics.com

Really? Have you tried 2000 HP? Perhaps you need to squirt some of

that

hot air aft and gain a bit of thrust :-)

I don't buy that Chrissi. Not all P51 duct systems are created equal.
Here is a picture of a liquid cooled engine powered airplane with P51

duct that

is just about the fastest canard in the world. Right behind Klause.
236 MPH. No were near 2000 HP.  Just 250 HP like Greg's airplane.

Paul Lamar

Paul, Regarding your recorded message, there are hundreds of EZs flying

successfully with NACA flush

inlets - a baffled air cooled engine with finned cylinders is a heat

exchanger. A properly designed

flush NACA inlet can recover 85% of the available pressure as compared

to a free air ram inlet of same

size.

That being said, I am using a downdraft ram air inlet on my Velo project

and expect it to get as fast as

other fixed gear Velocitys.

Greg is flying without wheelpants or gear leg fairings, has a way too

lumpy cowl with too much inlet

area, has a 3" exhaust pipe sticking out perpendicular  to centerline

just in front of the prop and has

not corrected any of the obvious things he could to make it go faster.

He could easily speed up that

Cozy by 25 mph with minor expense and some labor to recowl. He must be

too busy with the Blue Mtn

Avionics to play with the Cozy.
Herb Sanders

Yes and I have also said over and over again the pressure drop through a
air cooled engine is way less than a real heat exchanger such as
an oil cooler or a water radiator. Glance at the fin spacing for example.
Besides that many don't cool all that well.

Water cooling aircraft engines is a whole new ball game and not easy.
Why handicap yourself by using s NACA scoop that the inventors say
should not be used with oil coolers and water radiators. How specific
to you want them to get? It is too easy to build static pressure in the
radiator scoop to 80% of dynamic pressure. In a case like that
the air will simply refuse to go into a NACA duct.

Paul Lamar

Hi, Paul....I noted that NASA says that "Submerged inlets do not appear to
have desireable recovery characteristics for use in supplying air to oil
coolers, radiators or CARBURETORS of conventional recip engines"
     I have to say it worked GREAT on my LongEZ for carburetor air.  NASA
also said they were going to find that missing sattelite.  Still waiting.
Not trying to start an arguement here....I'm just not so sure NASA knows
everything even though they designed it. I know my NACA inlet worked very
well for carburetion, regardless of what they say. Just my 2 cents worth.
Paul Conner

Yes I agree it works well with carb air. Apparently those NACA engineers
made a mistake on that point. Perhaps they were aerodynamic engineers and not
engine engineers. It does not change anything however.
A radiator on the other hand does not suck air like an engine.

Let me translate this into layman's terms. I want people to thoroughly
understand this. Perhaps it is too obscure for people to understand.

"The required diffusion of the air and the range of inlet velocity ratios
is too great to give desirable characteristics for all flight conditions."

"diffusion" The conversion of air mass speed to air pressure. 
This is what is supposed to happen in a heat exchanger duct.
It does not necessarily happen in an engine combustion air intake.

"velocity ratios" The ratio of forward speed of the airplane to that
of the air speed out of the back of the radiator. As I just measured
with my rad test box setup it is typically 40% for a two inch thick radiator. 
Less for a evap core or a thicker rad.

Paul Lamar
 
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