Following indications on this Forum that the above problem could be cured by
cleaning of the flap motor brushes, and a request for feedback on the work
involved, here's a summary plus long version of what's involved:
Summary:
Cleaning the flap motor commutator and brushes cures intermittent flap motor
operation and speeds up flap movement..
Long Version:
The commutator and brushes of the (early type) flap motor can become
contaminated with lubricant from the tail bearing of the motor. This bearing
is a micro-ball race with a labyrinth seal; any excess or additional
lubricant drip-fed into the bearing will pass straight down on to the
commutator.
The flap motor/servo does not need to be taken off the aircraft and the work
can be done in situ, gaining access through the D-cover in the back of the
cockpit. A pile of cushions in the back of the cockpit provides some comfort
while doing the work. In particular a very thick blanket draped over the
edge of the D-cover aperture provides relief to the armpits when leaning
through the aperture.
There are two Phillips-headed screws on top of the motor casing; these
screws pass the full length of the motor and hold everything together.
Remove the screws. Withdraw the end housing (which retains the tail bearing)
and brush holder. The spring loaded brushes will pop out of the holder, but
are electrically connected by wire tails, so won't fall out on to the floor.
The casing of the motor (which holds the permanent field magnets) can also
be withdrawn, but this is not essential. The armature is captured at the
gearbox end of the servo, so won't come out. However, there are a number of
steel shims on the tail-end of the armature that can be dislodged as the end
housing is withdrawn; these shims can fall off and become 'stuck' to the
field magnets in the outer casing; with poor light, it's difficult to spot
that this has happened. There is one insulating washer under the stack of
shims.
Commutator and brushes can now be cleaned; Q-tip (cotton bud) helps with the
latter.
Now the fiddly bit of holding back the brush-springs while getting the
brushes back into the holder. This can be easily achieved with a 1/2" to
5/8" wide strip of stiff card inserted edgewise between the springs, holding
the springs back while the brushes are reinserted into the holder. There is
a convenient slot in the brush holder provided for this purpose and prevents
the piece of stiff card from slipping out during this operation.The brush
holder can now be placed back in position over the commutator and, when in
place, the strip of stiff card withdrawn allowing the springs to push the
brushes down on to the commutator.
Reseat end housing, reinsert the two Phillips-headed screws and retreat from
aircraft.
Done.
Duncan McF.
|