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No, Bill, they do not have bell mounths,
because the primary and secondary runners are essentially one piece (like
an upside down "U") inside the plastic housing.
Here are a couple of photos of the process.
Basically, I cut a half-moon shape out of a piece of 3 " high density
foam. I then close up the sides with other pieces of foam including
cutting out any thing needed like the flat portion of the front for mounting the
Throttle body. I then form two silicon cores by pouring the silicon
core two part liquid mix into some "U" shaped aluminum tubing of the right
size. I extract the silicon cores from their tubes and suspend them upside
down in the 3" void, mix up a two part polyurethane casting resin - pour it in
and wait 15 minutes. Then remove the plastic casting which has the tunnels
and openings for the four aluminum runners which get inserted through a 3/8"
aluminum plate into the plastic casting. This plate is held to the plastic
(or vice versa) through bolts through the plate into inserts placed in the
plastic (I place the inserts after the casting by drilling holes and pressing
them in - the right kind or citical).
I use a hole saw to cut through the front of the casting
the dia of my 65 mm throttle body until I just interesect the tunnels cast into
the plastic. Then I hand sand/die grind the intersection of the TB hole
with the runner tunnels to a smooth interface between the two. Drill holes
and place inserts for the throttle body and your are done.
It takes me an hour or so now to make a mold, cast the
resin. About another couple of hours to cut the 3/8' plate drill the holes
for the tubes and mounting bolts, etc. Then you have to braze the aluminum
tubes to the plate and that's it for the top half of the manifold. The
bottom half (I use telescoping tubes for ease of construction and tuning)
has slightly smaller tubes to fit up into the tubes brazed to the 3/8" mounting
plate.
I cut off the heavy cast aluminum runners from an 88 or
earlier N/A lower manifold, mill out the holds to the dia of the lower tubes and
then assembly the top and bottom structure before brazing in the tubes to the
aluminum casting of the lower manifold.
When you get it all done you have the assembly I showed in
the previous e mail photograph
Hope that helps explain it a bit
Ed
Sent: Saturday, April 30, 2011 10:44 AM
Subject: [FlyRotary] Re: Intakes old and new
Ed,
Do the intake runners
have bell mouths at the top inside the plastic plenum? If so, how
did you construct them?
Bill
B
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Saturday, April 30, 2011 9:49
AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Intakes old and
new
Here is the induction system set up
I first flew with Phtos MVC-007F JPG). 4 injectors into a TWM dual throat
Webber Throttle body (2" dia throats) into a two into four manifold. The
engine started easily and operated fine - with the exception it was low on
power. Top speed was 185 MPH TAS.
The apparently problem was that
while this set up did well for the rotary racing crowd when theirengines hit
9000 rpm - it sucked (but not very well) at the lower rpms like 5000. So I
swap it out for my current design using an 65mm dia mustang throttle body and
smaller diameter runners and immedately picked up 10 MPH top airspeed and 400
ft/min improvement in Rate of climb.
It was the beginning of my
understanding that what works well for one environment and set of operating
conditions may provide lousy results under different circumstances. The
other two photos show the intake that produced the best results for my
installation and which has now been on the aircraft for over 6 years, top speed
achieved with this intake was 196 MPH TAS with the old 2.17:1 and 68x72
prop. Same intake with the 2:85:1 and 74x88 prop topped out at 200 MPH
TAS.
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