Installing a real air filter in a 173

["James F. Agnew" <RRT0162@IBM.NET>]

I wanted a real air filter in my 173 that would provide well filtered
air and easy maintenance.  I decided to use a Brackett model 6210 foam
filter based on its high filtration and easy maintenance.  The #6210 is
the aluminum housing, a filter (2" thick) bolts and the cover screens. 
This is the same filter used on Mooney's with IO-360 engines and
provides about 40 sq.in. of filter area.  This was also the area
recommended by Brackett in their literature for 360 ci. 200 HP engines. 
Solving the place to put it was more of a challenge.  Since I have the
173 wing and after reading Alan Shaw's notes on wing mounted oil coolers
I decided that this was a good place to put it.  I started 1" behind the
rudder conduit and cut our an opening in the web leaving 1" all around
for a flange.  Layup a 2 bid flange on this cutout out piece.  The
opening is about 6" front to back and the wing surfaces determine the
height.  Since the filter housing is about 8" long I tunneled into the
wing 9" and left a consistent 1" of foam on the upper and lower wing
surfaces.  I next measured back 3 1/2"  from the wing spar and cut a
round end slot parallel to the spar 1 1/4" high x 8" long.  This size is
based on the injector total intake area and is a little larger.  You
then cut and form a sloping and curving plenum back toward the front
face of the foam cutout to form the intake plenum.  The air filter
assembly stands upright against the front of the wing cutout.  After
filling the foam with microballoon and glassing you are ready to install
the filter (do it backwards for maintenance purposes and remember to
reverse the element).  Add some nutplates to the wing flange to mount
the cutout piece.  On the cutout piece add an appropriate flange for a
piece of Scat duct to the fuel injector and I suggest that you construct
a pop door with a light spring in case the filter plugs then the door
will open by suction and the engine will keep running.

You will note that I did not add an external lip or scoop since Alan
said that this is a very high pressure area I will try it without the
lip scoop.  If it works as expected you will have less drag and when in
ground effect on takeoff & landing you should get some additional boost
pressure and additional power.  Maybe not much but at high density
altitude every little bit helps.

I will send a picture to Scott & VV so you can see how this is done and
many thanks to Alan Shaw for all of his help.

Jim 





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//------10--------20--------30--------40--------50--------60--------70--------80
// James F. Agnew
// Tampa, FL
// Velocity 173 FG Elite ( http://www.VelocityAircraft.com/ ) under
construction