Pitot system
Posted: Fri Feb 17, 2012 8:27 pm
Hi Jim !!
Congratulations !! Another Rebel in the air !!! :-)
Rebels ALL seem to have problems with the ASI system -
might be something to do with the incredible speed range they
can fly through !! ;-)
The static system might be a problem - my new one has little
"shields" in front of the outlets on the fuse sides - and still
isn't accurate at the low end. The old one just uses cockpit air,
and is MUCH better !
On Rebel no. 3, we just ran the tubing up the strut, out the
top, through a hole in the fairing, onto the back of a 5/16" ID tube
that could be clamped to the strut fairing with a couple of upside-
down "U" shaped strips of aluminum. One problem was getting the right
angle - the tube appears to be pointing slightly down when in the
right position. The larger the diameter of the tube, the better,
as this seems to reduce the error caused by higher angles.
One consideration - I would ALWAYS go for an instrument
calibrated in MPH, rather than knots, and preferrably one with
markings for 20, 30, 40 mph., because the Rebel CAN fly down there !!
Glad you're enjoying your Rebel - have fun exploring the
large flight envelope !!
....bobp
------------------------------orig.--------------------------------------
At 07:56 PM 10/23/00 +0100, you wrote:
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Congratulations !! Another Rebel in the air !!! :-)
Rebels ALL seem to have problems with the ASI system -
might be something to do with the incredible speed range they
can fly through !! ;-)
The static system might be a problem - my new one has little
"shields" in front of the outlets on the fuse sides - and still
isn't accurate at the low end. The old one just uses cockpit air,
and is MUCH better !
On Rebel no. 3, we just ran the tubing up the strut, out the
top, through a hole in the fairing, onto the back of a 5/16" ID tube
that could be clamped to the strut fairing with a couple of upside-
down "U" shaped strips of aluminum. One problem was getting the right
angle - the tube appears to be pointing slightly down when in the
right position. The larger the diameter of the tube, the better,
as this seems to reduce the error caused by higher angles.
One consideration - I would ALWAYS go for an instrument
calibrated in MPH, rather than knots, and preferrably one with
markings for 20, 30, 40 mph., because the Rebel CAN fly down there !!
Glad you're enjoying your Rebel - have fun exploring the
large flight envelope !!
....bobp
------------------------------orig.--------------------------------------
At 07:56 PM 10/23/00 +0100, you wrote:
---------*I finally got Rebel #180R off the ground yesterday. No surprises: tracks
very straight (on gravel), got off the ground in a hurry, climbs about
1100 fpm, flies straight, control forces/responses feel fine, etc.
However, I do have a problem with air speed indication, which I had
noticed during a couple of high speed taxi runs, when compared to GPS
ground speeds. I was hoping things would improve at flying speeds, but
the ASI continues showing 20-30 Kts. slower than GPS. The indicator was
overhauled/certified prior to installation, so I suspect my pitot setup.
It's simply a straight 1/4" tube through the leading edge and attached
to a bulkhead ftting through the front spar in the most outboard rib
bay. The plumbing from there back to the ASI is unnecessarily complex,
since it never occurred to me to route the connecting tubing down thru
the strut. I ran it all the way to the wing root, in above the door and
managed to force it through the tooling holes in the upper wing attach
fittings and down in front of the doorpost to the panel. I checked all
the fittings when I mounted the wings, but a leak is still a
possibility. I'll try to check that out with the rolled up surgical
tubing routine as soon as I can find a long enough piece. In the
meantime, I would appreciate any suggestions. I'd be particularly
interested in installation details for an under wing pitot tube near the
upper strut fitting. My static setup is pretty much like a Cessna - a
port on either side in the side panels forward of the door posts with an
interconnecting tube. Seems to work OK, but, considering the leaks
around my doors, it might work just as well if it was simply open to the
cabin.
Thanks
Jim Callahan
Rebel #180R
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between builders and owners of Murphy Rebel aircraft.
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*-----------------------------------------------------------------------------------*
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