Today's Message Index:
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1. 01:35 PM - fun and games with a manometer (Lynn Matteson)
2. 09:28 PM - Re: fun and games with a manometer (zeprep251@aol.com)
Message 1
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| Subject: | fun and games with a manometer |
I built a U-tube water manometer this week, and finally got a chance
to try it out (flying) today. Prior to today, I had used it to find a
slight leak in my pitot system, which I fixed by tightening up the
Nylo-Seal fittings while watching the indicated leak disappear. Ever
wonder how much tightening is enough for those fittings? I have, and
now I know....just use a manometer on the system during the assembly
of the fittings, and you'll know when to quit tightening.
Today, I got a chance to fly briefly to test the Jabiru-dictated 2.4"
of water column difference between the inlet air ducts (each side
tested individually), and the exit-air area of the plane. I haven't
had any cooling problems, so I just wanted to test how close my
installation came to meeting that 2.4" measurement. My installation
was pretty close to right on the mark...it read about 2.3" to 2.6"
depending on the bounce of the water in the tube. Pretty happy with
that, I flew home to add a 1" lip to the bottom of my cowl exit. I
bent a 20" length of sheet aluminum to a 60 angle, letting 1" stick
out into the airstream below the cowl, and c-clamped it in place. (I
didn't want to rivet it in place just to test the theory.) I went up
and flew some more...windy day, didn't want to fly too much....and
now I saw about 2.5" to 3" on either of the two air ducts. But the
really interesting thing about the last test, was that I saw a mark
on the aluminum "lip" showing where it was contacting the left
exhaust pipe. Normally, this pipe cleared the cowl/lip by about 1/2",
but apparently during flight, my cowl flexes up enough to allow
contact with the exhaust pipe. No big deal you say, and I agree, but
if that lip is flexing up 1/2", what just happened to the carefully
engineered 3:1 ratio of exit air-to-inlet air that shouldn't change?
Kinda like having a wrong-way operating cowl flap for the exit air,
I'm thinking. So I need to stiffen up the lower cowl exit flange so
that it doesn't flex at all, and then do some more testing....maybe a
center support for the cowl is in order...something that will be
permanently attached to either the cowl or the airframe, but not
both, so as to allow for removing the cowl without having to deal
with another fastener down there.
If anybody's having trouble with overheating issues, yet you're sure
of the "correctness" of your installation, you might think about the
rigidity of things when air pressure gets applied.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062
Prince prop (64 x 30, P-tip)
Electroair direct-fire ignition system
Rotec TBI-40 injection (sleeved to 36mm)
Status: flying with "Ramcharger" intake manifold...1110 hrs (since
3-27-2006)
Message 2
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| Subject: | Re: fun and games with a manometer |
Lynn,
Are you certain that the engine torque at max throttle does not rotate the
engine in it's mounts far enough to cause contact with the cowl?
G.Aman
-----Original Message-----
From: Lynn Matteson <lynnmatt@jps.net>
e-list@matronics.com>
Sent: Sat, May 28, 2011 1:36 pm
Subject: JabiruEngine-List: fun and games with a manometer
I built a U-tube water manometer this week, and finally got a chance
to try it out (flying) today. Prior to today, I had used it to find a
slight leak in my pitot system, which I fixed by tightening up the
Nylo-Seal fittings while watching the indicated leak disappear. Ever
wonder how much tightening is enough for those fittings? I have, and
now I know....just use a manometer on the system during the assembly
of the fittings, and you'll know when to quit tightening.
Today, I got a chance to fly briefly to test the Jabiru-dictated 2.4"
of water column difference between the inlet air ducts (each side
tested individually), and the exit-air area of the plane. I haven't
had any cooling problems, so I just wanted to test how close my
installation came to meeting that 2.4" measurement. My installation
was pretty close to right on the mark...it read about 2.3" to 2.6"
depending on the bounce of the water in the tube. Pretty happy with
that, I flew home to add a 1" lip to the bottom of my cowl exit. I
bent a 20" length of sheet aluminum to a 60=C2=B0 angle, letting 1" stick
out into the airstream below the cowl, and c-clamped it in place. (I
didn't want to rivet it in place just to test the theory.) I went up
and flew some more...windy day, didn't want to fly too much....and
now I saw about 2.5" to 3" on either of the two air ducts. But the
really interesting thing about the last test, was that I saw a mark
on the aluminum "lip" showing where it was contacting the left
exhaust pipe. Normally, this pipe cleared the cowl/lip by about 1/2",
but apparently during flight, my cowl flexes up enough to allow
contact with the exhaust pipe. No big deal you say, and I agree, but
if that lip is flexing up 1/2", what just happened to the carefully
engineered 3:1 ratio of exit air-to-inlet air that shouldn't change?
Kinda like having a wrong-way operating cowl flap for the exit air,
I'm thinking. So I need to stiffen up the lower cowl exit flange so
that it doesn't flex at all, and then do some more testing....maybe a
center support for the cowl is in order...something that will be
permanently attached to either the cowl or the airframe, but not
both, so as to allow for removing the cowl without having to deal
with another fastener down there.
If anybody's having trouble with overheating issues, yet you're sure
of the "correctness" of your installation, you might think about the
rigidity of things when air pressure gets applied.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062
Prince prop (64 x 30, P-tip)
Electroair direct-fire ignition system
Rotec TBI-40 injection (sleeved to 36mm)
Status: flying with "Ramcharger" intake manifold...1110 hrs (since
3-27-2006)
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