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<< Lancair Builders' Mail List >>
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From: n295v v
I have a comment on the safety of the Hydraulic Cylinder which actuates the
Flap Actuator Bell Crank on the LNC4, and this was brought to light by Bill
Maddox several years ago, with the factory not acknowledging that a problem
exists.
It is not safe, and everyone with a LNC4 should be looking at their plane.
Simply put, the length of the throw of the ram in the cylinder is incorrect
for the arc through which the bell crank is able to move. Incorrect by
several eighths of an inch.
The recent SB which requires reinforcement of the Flap Actuator Bell Crank
with a welded strap has been reported to be required because two pilots
extended their flaps at excessive speeds, causing failure. This may be so,
but I think the Cranks failed because the hydraulic ram had pushed or pulled
them past their limits of arc until they cracked, and high speed extensions
then failed them completely.
To examine your own planes, remove the 1/4" bolt attaching the ram to the
crank. Retract the ram, and look at the alignment of the holes in each.
Then extend the ram, and look at the alignment of the holes in each. If the
ram goes past the physical limitation of the swing in the crank in either
direction, you have a problem.
In my case, shortening or lengthening the screw adjustment in the rod end of
the ram makes no solution. Shortening it makes it bind in the extension
mode, lengthening it makes it bind in the retraction mode.
Bill Maddox, whom i highly respect for his problem solving and design
capabilities, said that the ram was making the walls of his gearbox flex in
and out. The only other direction to relieve the pressure is for the bell
crank to fail or the Fowler track to fail.....
In my own case, I found a rod in the left flap bent from the cylinder pushing
the flaps past their limits set by the Fowler tracks. This happened during
my recent attempt to adust the throw of the crank. Don't try to adjust it
before you check the throw by removing the 1/4" bolts.
I finally adjusted mine so the retract setting is correct, but if I extend
the flaps fully, I would be trying to bend the crank or worse, tear the
Fowler track apart.
Well, I look forward to your comments on this problem. It is a safety
issue. It was not acknowledged by the factory, but since I am claiming that
the SB caused by the Bell Crank failure was really caused by the Hydraulic
Ram being incorrect, the factory MUST look at it and re-engineer it.
By reinforcing the Bell Crank with a welded strap, they have simply made it
so the failure will ocurr someplace else--PROBABLY A FAILURE OF THE FOWLER
FLAP TRACK OR A FLAP PUSH ROD.
PS- Remember when the factory told us LNC4 builders to add several layers of
reinforcement of glass to the areas holding the Fowler Flap Tracks to the
wings and spar? I wondered why at the time, and now I think I have figured
out why they were getting a lot of bending and flexing in that area.....
David Jones, Pecatonica, Illinois
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LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
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