The uplock system in our Beech landing gear
has been with us for some time. It's essentially a mechanical blocking arm that
was engineered by Beech to keep the landing gear from coming out of the wing
under a high G load.
Bonanza owner and BT-er Rick T. has this
picture and narrative:
When the cable breaks (due to lack of proper tension - from a missing
spring)....the up lock arm can continue to rotate up.....till it contacts the
upper skin. When the arm contacts the upper skin....it either pokes a 1"
hole....or flops back.
There are varying opinions on whether this
system is really necessary or not. Nevertheless it is on many of our airplanes
and we have to deal with it.
Here is a narrative from a very experienced
Bonanza owner, John W, of Texas. While in the process of changing out an uplock
cable during annual:
"In the throws of
an annual. I have been installing a new uplock cable in the left main gear well.
That requires adjusting the rigging which is under way. In the photo is a
squiggly arrow pointing at the attach bolt for the turnbuckle at the end of the
cable. That bolt head needs to be on the aft side. Once the gear is up, the bolt
head just barely clears a rib. If it was the other side (castle nut) it would
likely catch. Just a point of emphasis. Anyway, for those with keen eyes, the
turnbuckle has not been safety wrapped yet as I'm still adjusting tension.
The bracket that
holds the end of the cable as well as the uplock block is made of aluminum and,
unfortunately, it has no bushings where it rotates about a bolt. In the photo,
you can see there is a crack extending out from the elongated hole although that
crack does not reach the edge. The bracket failed where the rotation point
simply elongated over time.
In other words, the
hole got too large and the bolt head could slip through (with help from a small
crack). I share this because one typically cannot see under the bolt head so as
to determine the condition of the bracket hole without removing it for
inspection. I will be installing new brackets on both mains.
I replaced an uplock cable on my prior
Vtail. Not a fun job at all. Anyway, I had a lot of trouble getting the uplock
block to move into position correctly at the end of the retract cycle. Try as I
may, If I approached to book value of the cable tension (which is REALLY high at
52 + and minus nothing) the block would move into place too early and end up
assisting in the lifting of the gear leg. That's not good. I queried a number of
sources that I trust and all came back with the same answer ... don't get too
wrapped up in that high number.
I believe the sequence of adjustment
should be to screw the turnbuckle into the end of the cable to a point where the
witness hole is well covered yet there are threads still visible. Then route the
cable in the gear well ( that will change tension by just adjusting the routing
a little) and then get to where the block moves into position correctly with w
.010 to .020 gap between the block and gear flange. Now, after everything is
working OK, go check the tension on the cable. If it is around 40 to 45 pounds,
I've heard from many sources that this is just fine. But as you say, I would
never personally vary from the book tension. No, not me.
Below is a picture of a damaged Uplock cable
which was hiding under the tubing
Here are pics of the bracket in serviceable
Below is a comment from Old Bob who forgot
more about Bonanza design and maintenance than any of us will ever know (grins)
"One thing I have found is that the mechanism will last longer if the
tension on the cable is a bit below the 52 pounds specified. It might work just
as well at only 35 or 40 pounds, but, of course, that would not be legal even
though it would reduce wear."
So remember, varying from book tension is
illegal and it will REDUCE the wear on your mechanism.
HERE is the Beech
Instruction for the uplock system.
Below is an image of the uplock cable and
bracket system for clarity
Here is an image of later model
Baron 55/58 landing gear that includes a DOWN LOCK as well. It is believed Beech
added this feature to guard against side loads of their heavier birds and this
can also be found on the Duke gear as well.