Paul:
Are you aware of an research done on the effects of using induction
tubing of square or rectangular x-section?

You've mentioned using rectangular exhaust tubing in the past, I know,
but I've been thinking that fabrication of intake systems would be
easier if one could make critical components from sheet goods instead of
buying/making all sorts of sophisticated bends from stainless or
aluminum tubing.

R. Berglund

It should work. For a given cross sectional area there is more skin friction
drag.

I found a much cheaper source for tubing.
http://www.siliconeintakes.com/

Half the price of Burns stainless.

Paul Lamar



R. Berglund:

Round duct is preferred over rectangular duct for moving air.
Rectangular duct weighs more, for the same flow rate, than round duct
does.  It's not a matter of just matching the area of the round tube to
the area of the rectangular tube to get the same flow rate.  Like an
airplane with sharp intersections between the wing and the fuselage the
interior corners of the rectangular tube suffer from interference drag.

Now, while I'm typing about flow rate and drag, any kind of directional
change in the intake system will increase restriction and decrease flow
rate.  The most efficient intake system will have straight round pipe
straight into the engine ports.  No elbows or turns of any kind.

A bellmouth at the inlet of the tubes will reduce pressure loss in the
system as well also contributing to improved flow rate.

I've seen a lot of pictures of intake systems on Wankel powered aircraft
with pretty swooping bends across the top of the engine or tight elbows
right at the intake ports.  Both of these are really bad news for the
air flow.  Elbows, no matter how pretty they are, cause turbulence in
the airflow, using up energy, and resulting in restricted flow into the
engine.

If a change in direction can not be avoided it is best to use a mandrel
bent round elbow with a throat radius equal to the diameter of the tube.
The elbow should be followed by straight tubing have a length equal to
at least three times the diameter of the tube to allow the air flow time
to straighten out after being upset by the elbow.

If a required change in direction is more than 90 degrees it is best to
use two elbows with a length of straight between them.  Best practice is
to divide any direction change into two equal elbows with sufficient
straight between them to allow the airflow time to straighten out.

 Mark LaPierre

Jatin Khatri & geleem