One of the most well engineered pieces of our
Beech Bonanzas, Barons and Travel Airs is the landing gear mechanism and the
symphony of coordination created by the landing gear transmission box and it's
gears, arms and drive motor.
Here is the story of my IA supervised
exploration into the depths of my landing gear transmission. Feel free to peruse
this page to educate or entertain yourself on the insight and learnings that I
have gained in doing this with my IA. Feel free to share it with your mechanic
if they are interested in these learnings. Some of these images contain
disturbing high resolution graphic images of Multi-thousand dollar parts that
have been ruined by poor landing gear rigging and/or poor or non-existent
dynamic braking function! If you are on a slow connection, please be patient to
allow the whole page to load!
Do NOT treat this as the end
all and be all of knowledge for servicing this part of the Beech landing gear
system. A failure in the landing gear system can create a total insurance loss
of your airplane. A licensed mechanic is required to do or to supervise any of
this work in this area and the factory issued IPC and Shop Manual for the
airplane SN are parts of the official guiding documents required. Users are
strongly urged to utilize all official resources in reinstalling the gear
transmission AND re-rigging the gear to factory specs. As a suggestion, the
ABS Landing Gear Rigging Guide is an invaluable resource for re-rigging the
Beech landing gear.
NOTHING IN THIS
PAGE SUPERSEDES YOUR
BE THE FINAL AUTHORITY ALONG WITH
MECHANIC AS TO THE AIRWORTHINESS OF
PARTS FOR YOUR CERTIFIED AIRCRAFT.
Sometime circa 1983BC (Before Caban) my
airplane was subjected to a gear up event. The log books show the gearbox having
been repaired and all new Beech skins installed and restored to flying service.
Fast forward to December 2017 when a gusher of a transmission fluid leak was
noticed on the hangar floor
at a time when the ambient temps had dropped below freezing. Initial thoughts
were that a seal had sprung a leak.
Upon deeper investigation it was found that
three screws, out of a total of 11 that hold the two case halves together, were
not safety wired and had loosened up to create a gaping opening in the case for
the fluid to gush out. The visibility of these three screws is severely limited
by the manual crank handle case portion of the housing and the wire bundle
running under the gear case pedestal while it is in it's mounted position.
Knowing that this day would come, several years ago I
acquired a low time Beech transmission gear box and was thrilled to have a
serviceable spare on the shelf. But WAIT, upon closer inspection and cranking of
the manual handle on the presumptive spare, it was found that there was much
harder cranking of the gear at both ends of travel while the unit was on the
bench. As it turns out, this sector gear in the spare was toast! It had been
abused much of it's life by being electrically wound into the mechanical stop
either by bad gear rigging or a bad dynamic brake relay. See the pictures below
for the gear teeth of this several thousand dollar sector gear that took the
pounding. Thankfully, my sector gear ran smoothly from stop to stop and is able
to be re-used for continued service.
The extraction of the landing gear
transmission was akin to seeing your first child being born - you can't believe
a thing of that size could come out of there!
(1) We put the plane up on jacks and a tail stand and
confirmed it secure.
(2) Even with master power off, we pulled the breaker
for the gear motor and relay
(3) We cranked open the inner gear doors with a few
clockwise turns (looking forward) of the manual crank and removed the inner gear
door bolts at the hinges and then placed hoses over the exposed rod ends so as
to protrude from the side of the fuselage. This insures that the rod end will go
in and out of the airframe without crashing into something immobile and bending
the rod or worse when we eventually test the system.
(4) We removed the main gear rod cotter pins and nuts
under the spider arm. We did use some movement of the manual crank to better
position the cotter pin for extraction. We applied the same philosophy to
removing the cotter pins and nuts on the inner gear door arm/uplock cable, just
a little manual cranking to get a good working position.
We were careful to note that there is a tiny bushing in the top of the inner
gear door arm that must be preserved for reassembly.
(5) We then removed the 4 bolts that connect to the base
of the flap motor and slid the metal plate outward toward the cockpit door.
(6) With the top arms out of the way we then had clear
access to remove the gear motor and the dynamic brake. We were sure to
photograph the wires from the motor and their positions on the dynamic brake.
Also the wires on the aft side of the dynamic brake were marked and photographed
to insure perfect reassembly. While the dynamic brake might not have been needed
to be removed for the tranny extraction, we chose to remove it to replace it
with a very low time unit and also most importantly to renew and refresh the
critical frame grounding that the dynamic brake relies upon to do the best job
of bringing that high torque 24V/7600RPM motor to an instant dead stop when the
up and down limit switches are tripped. While still in the top end of things we
removed the four screws that hold the micro switch mounting cradle to the
airframe. Moving this cradle to the side allowed more room to wrestle the tranny
out. If I didn't already have fairly new
(aka BZ-R31) micro switches, now would be a great time to replace the 50
year old switches. Scroll down
find info on the BZ-R31 switch sources.
(7) We then went under the belly to remove the nose gear
drive arm. This required us to manually crank a little of the mechanism to
position the arm in the opening such that the rod end bolt can drop free and the
arm can be pulled off the tranny shaft down through the opening. The snap ring
was removed and the arm was able to slide free and down. A helper comes in handy
to take some pressure off the nose gear to remove the tension on the rod end
bolt. At this point we then removed the four 7/16" nuts that hold the tranny to
the airframe. Some reports of corrosion of the transmission base and the
magnesium reinforcing plate in the bottom of the mounting cavity have caused
some people to have to use jacking pressure to break this loose. Thankfully, I
did not experience this corrosion issue during my extraction.
(8) Since we had all the cranking for optimum
positioning done we now removed the three screws holding the crank handle onto
the tranny housing.
(9) Now we began our lift and wiggling of the tranny
toward the cockpit door. The removal of the wood floor section immediately under
the crank handle was essential to us in getting the last few mm needed for the
tranny to clear the bottom of the seat support frame. My years of practicing
with Chinese puzzle rings have finally paid off!
Based on my experiences summarized here, I'll offer some of my non-mechanic "opinions/observations".
My 24V gearbox had slammed into the stop back in oh, 2006. Slammed so hard
into the stop it blew the circuit breaker (and was unable to unwind it with the
crank). By the grace of God, multiple breaker resets actuating in the down
position freed up the mechanism. Loose transmission mounting nuts were the cause
of this anomaly and possibly complete dynamic braking failure (the motor
internals were toasted after this event). After troubleshooting and parts
replacement and rejigging, the gear box continued to function normally for the
next 11 years.
When I finally pulled my original gearbox as outlined in the above narrative,
the sector gear was in fine shape. So, in my case, strictly applying the rule of
overhauling the box when it slams into the stop would have been completely
With a low time gearbox that I had on hand, I noticed that this low time box
had a significant change in hand crank resistance at the beginning and end of
crank travel. Sure enough, when I opened this gear box up to inspect the sector
gear, it was badly gouged. So, from this empirical physical observation, I could
offer that if one can detect rough or increased hand cranking forces at either
end of sector gear travel, you likely have something of a gouged sector gear on
your hands and THEN, in my humble opinion (shared by my IA), you would be
advised to pull the box and have it completely inspected and begin your search
for a viable sector gear (>$2,000 new).
So, if I were concerned about my sector gear being pranged by slamming into
the stop over a long period of time, instead of a complete pull of my box, I
would simply disconnect the inner gear doors from their rods and the main gear
rods and nose gear rod from the transmission, then freely crank the transmission
with the manual crank and feel for any cranking resistance change at the ends of
travel. You might also consider removing the gear motor itself, as it adds some
resistance to the manual cranking but you would surely notice the increased
force required by a pranged sector gear. I was certainly able to feel some ting
wrong when I was cranking the box with the badly gouged sector gear ends.
Some other thoughts to consider, taken from Kevin O.:
12V gear motors, by virtue of their speed and lower torque present a lower
risk to their sector gears.
Conversely, 24V motors by virtue of their speed and torque present a HIGH
risk to their sector gears in terms of gouging them when out of proper rig or
dynamic braking failure.
Just my $0.02 and worth what you paid for it!
The below pictures can help readers visualize my
gear transmission extraction experience and all the gory details of my process!