Chrissi wrote>

Paul, Welcome back!
While you were absent this came across one of the canard lists and just

seemed more within your realm of knowledge and experience:

Ram air box truths (real PSI gain)
Gentlemen,
This issue has been explored and many of us have spent hundreds of

dollars

or many hours to install a RAM air box in our aircraft to gain an

expected

increase in performance. Truth be told, there isn't much gain under 200
mph. At least not enough to even register on the airspeed indicator.

I'll

explain why and you can decide for yourself.  This is probably why no

one

will quote any increase in speed when you purchase a RAM airbox from

them,

because there won't be any.
Here are the true hard facts using the following criteria:

(Publication:

Aerodynamics and Flight)
At   MSL Pressure 14.7 psi  (densest air possible on the planet)
At   200 MPH (if your plane will go this fast) direct air flow (non
obstructed, perfect flow)
At   59.02 degrees F  (15 degrees C)  Standard aeronautical calculation
temp at MSL

TOTAL INCREASE IN PRESSURE =  0.710 psi

By the way, any performance increase is assuming that there are zero

bends,

curves, voids, filters elements or any other disturbance/blockage of the
flow into the cylinder head ports. And we all know that isn't the case

in

our aircraft or engine induction design.  Now, go ahead and factor in
actual conditions and temp at 2000 to 8000 ft MSL along with your actual
airspeed (indicated pressure) and the fact that you are not getting
true/undisturbed RAM air into your PERFORMANCE DESIGNED Lycoming

induction system.

You might see 1.5 HP at 2900 RPM's on an 0-320 engine running Wide
open Throttle.  Just don't pack a lunch before flight, you'll get the

same

results.
Just passing along mathematical facts.

Mark wrote:
Funny how this article has all the facts but comes to a pretty bogus
conclusion.

The assumptions made here are misleading as they imply the potential
pressure rise is only the difference between static and dynamic pressure.
Given that the existing intake won't deliver full static pressure to the
chamber, the potential difference is really the difference between whatever
you currently have, and dynamic. This could be substantial.

It is probably correct that bolting a ram air box on an existing tortuous
intake system is of little value, but a more valuable conclusion whould be
"you should attempt to optimise your flow path right through into the
chamber", but he dosn't even allude to that.

"At   MSL Pressure 14.7 psi  (densest air possible on the planet)" This guy
has never been to El Centro, or the dead sea.

The shame here is that he sounds like an eggspurt, and many would take this
at face value.
Mark Wrathall

 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org