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FLAPS:

Addendum to my letter yesterday. I was incorrect on the description of the
IV's flap cylinder stops, it has been a while since I rigged them. Here's how
I did mine.

The flap actuator cylinder (HC-09) is a reduced travel actuator, designed to
be the UP and DOWN stop at the end of it's range of travel, each way. The
center flap bellcrank (make sure you have the new reinforced one), is set to
travel an equal amount on either side of centerline, as per page 21-15. At
the UP position, I added a 1/2" or so, rigging wood block to stop the
bellcrank's travel, roughly keeping the top (long) arm of the bellcrank
parallel to the front member of the MG box. The block touches the cylindrical
end of the long arm of the bellcrank at full UP and is instant glued to the
backside of the front MG box member. The flap pushrods going out to the wings
can then be final adjusted with no fear of going further. Have a helper or
use duct tape to place the flaps in their full UP position, firmly against
the forward ends of the flap tracks, while you adjust the pushrods to the
center bellcrank.

The actuator can then be installed, set at it's full extension, with the rod
end about 3/4 screwed onto the shaft of the actuator and installed to the
bellcrank. The actuator at full extension then defines it's rear bracket
attach point. If all is well, the UP stop is the actuator at full extension,
with the DOWN stop the actuator fully retracted. You should have 1/8" left of
travel at the rear end of the flap tracks on the wings, in full DOWN, thereby
insuring that nothing is loaded in compression. You cycle the flaps a few
times, knock off the wood block; then recheck that at full UP, the wing
pushrod length is snug to the bellcrank, not in a forced position. Tighten
all the nuts, checknuts. A bit of grease on the bearings and years of good
service will follow. Do make sure that the pushrods coming in from the wings
have clearance for their full range of motion, especially where they
penetrate the fuselage. I had to enlarge the opening slightly on one side.

Finally, there is a service bulletin requiring the rear actuator attach
bracket to be inspected for cracks. Since the hydraulic shaft is retracted in
the DOWN position, I usually leave my flaps down in the hangar to keep it
retracted in fluid and not corroding. Note that this is the also the case
with the gear down: shafts are internal and clean.

Robert Forest, N295P.

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