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Flap failure - broken wires

 
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aerosiam



Joined: 26 May 2008
Posts: 57

PostPosted: Tue Mar 23, 2010 1:26 am    Post subject: Flap failure - broken wires Reply with quote

There is a vertical post next to the flap motor with 3 microswitches to control flap travel. A computer ribbon with 9 wires is used to connect to it.
I have had 2 flap failures because of broken wires.

The problem is that the gage of the wire in the ribbon is very small . I fly from a grass strip that is not smooth and the solder joints can break especially the top ones which are longest and most affected by vibration.

One solution is to connect the ribbon to heavier 18 gage wire and solder that to the terminals which have a hole so they can be well secured.

When I checked all the joints before repairing, another joint broke just by touching it. This may be an issue for older planes or those not operating from smooth runways.

Paul


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hgmckay



Joined: 23 May 2006
Posts: 374

PostPosted: Tue Mar 23, 2010 6:09 am    Post subject: Flap failure - broken wires Reply with quote

Paul, Jim, Brad, Thom, et al,

Paul, thanks for your insight concerning the negative flap question I
posted. Mine will stay at 4.5 degrees negative.

Concerning the broken wire problem on the electric flap drive; I too fly out
of a turf runway and I have had the same broken wire problem, but only
once. However, another problem that I have had is related to the screw drive
for the flaps and the flexible metal plate that trips the micro switches.
When the screw drive motor engages the round vertical screw housing that
holds the flexible metal plate rotates slightly (slack) as the screw
engages. This slight rotation of course causes the attached flexible metal
plate to shift slightly. In my case this slight rotational slack caused the
metal plate to shift out of position just enough to cause the micro switch
to catch on the edge and bend the switch arm and break the switch. This
happened two times before I figured out what was happening. The flexible
metal plate was not wide enough to compensate for this rotational slack. My
solution to the problem was to fabricate a wider flexible metal plate. This
took care of the problem.

The original tires for the Allegro 2000 are cheap thin wall tires that have
poor rigidity, and yes the inner tubes are poor quality. I have had only one
flat tire in 3 years of flying, and that was a slow leak down over night
while sitting in the hanger. Thank goodness it was slow and while I was on
the ground. After taking the tire off and checking the tire and tube I found
that the side wall of the tire was cracked in three small places at the
points where the tire mould came together to form the outer shape of the
tire. One of the other tires was also beginning to crack at the mould seams.
This slight crack, combined with the already weak side wall strength which
allowed the tire itself to flex more than it should on normal on landings,
created a situation that allowed a slight pinching to occur on the inner
tube where the crack was located. This flexing of the side wall, the slight
crack in the side wall, and the resulting minute pinching on the inner tube
over time worked it's way through the tube resulting in the final leak down
over night.

As a result of this I changed all of my tires to 8 ply tires with tubes. I
suggest that everyone who has the original tires on their Allegro check them
carefully and on a regular basis before every flight. If you find any
visible cracking of the side wall, get new tires!

Hugh McKay
Allegro 2000
Rotax 912
N661WW

--------------------------------------------------
From: "aerosiam" <pk(at)aero-siam.com>
Sent: Tuesday, March 23, 2010 5:26 AM
To: <allegro-list(at)matronics.com>
Subject: Flap failure - broken wires

Quote:


There is a vertical post next to the flap motor with 3 microswitches to
control flap travel. A computer ribbon with 9 wires is used to connect to
it.
I have had 2 flap failures because of broken wires.

The problem is that the gage of the wire in the ribbon is very small . I
fly from a grass strip that is not smooth and the solder joints can break
especially the top ones which are longest and most affected by vibration.

One solution is to connect the ribbon to heavier 18 gage wire and solder
that to the terminals which have a hole so they can be well secured.

When I checked all the joints before repairing, another joint broke just
by touching it. This may be an issue for older planes or those not
operating from smooth runways.

Paul


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http://forums.matronics.com/viewtopic.php?p=291386#291386




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