Beech Bonanza, Baron & Travel Air Landing Gear Transmission
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!
Where the gear transmission lives and all it's neighbors.
Removing dynamic brake relay for clearance and access.
Photographing the connections and marking them is a really good idea.
Inner gear door arm bushing and bolts. Note significant wear
in 50 year old bolt shaft.
Removing nose gear drive arm. Gear must be wound to a retract
position to allow the arm to come down through opening. An assistant is helpful
to take the load off nose gear while removing the rod end bolt. Simple snap ring
removal and then wiggling of arm off splined shaft.
The beginning of extraction/birth of the gear transmission.
Note the removal of the 4 bolts in the silver plate that provides the mounting
base for the flap motor.
After removing the aft floorboard just behind the transmission
mounting area and a few judicious wiggles the baby was out!
The 24V Dynamic Brake Relay PN: 6046H39A
Gear motor wiring locations onto dynamic brake relay.
Cutler Hammer PN: 6049H39A or NSN: 5945-00-258-1408
Below is a video
of Kevin testing dynamic braking of one of his
refurbished 12V motors. Notice
the torque his hand experiences when the motor is stopped. Don't even think
about holding a 24V landing gear motor in your hand while testing dynamic
If you lost your "VIP" washer, it is PN: 10509CR032-3E Item #37
If You Can't Pay Attention
Pay an Expert Beech Mechanic
To Install Your Gear Motor!
This poor soul did not
install his VIP Gear Motor washer and the gouging of the motor case was
causing huge amp draw and CB tripping !
The transmission sector gear PN: 35-810117
A Gear Motor with a bad armature can
also lead to ineffective dynamic brake performance!
The above images show the
mechanical stop that is mounted in the case housing. This is what the opposing
curved sides of the sector gear gets forcefully wound into by the worm gear when
the gear is not rigged properly or the dynamic brake relay is not functioning
properly. Another critical reassembly tip from Del L.
is that the proper sector gear orientation in the case housing is with the cast
PN facing upwards toward the sky in the as installed orientation.
Per Del: "The sector gear has a slight offset, and there are 2 "bosses"
machined; one in each case half. If the sector gear is installed upside down, it
is still possible to rig (albeit a PITA....ask me how I know), but the longer
term effect is teeth wear due to side loading which causes some minor binding.
But over time you'll note wear on all teeth. Typically, a braking action issue
will just present on the last 3 or 4 teeth of either or both ends."
Baron IPC extract (Bonanza and Travel Air may
be similar but ALWAYS CHECK YOUR IPC FOR YOUR AIRFRAME
AND SN) Item #22 is the gear transmission bearing (x2) K21B. Item #23 is
gear transmission oil seal (x2) PN: 450273 (available from many Auto Parts stores).
Click image above or
HERE to see my
landing gear transmission IPC extract pages for the Baron 55-Series.
Oil Seal PN:
Bearing PN: KP21B
The bearing and seal was removed by using a
large impact socket on a 6" extension with a diameter slightly smaller than the
OD of the bearing and whacking said implement with a BFH (Big Fierce Hammer) from the outside of the
case half (using blocks of wood under the inside of the housing will insulate
the cast housing from the whacks) or one could also use a bearing press.
You might find a replacement bearing PN: K21B at
LocateBallBearings.com for about $8 (January 2018 price) and the PN: 450273
seals at the same place also at about $8 each. The FAFNIR KP21B bearing is very
pricey at $60-$80 each.
Images above show the worm gear drive
slot shaft that the manual crank engages to lower the gear manually.
An over greased gear motor
Bonanza owner Paul S. adds: With re-assembly of the gearbox, about the
only item to be adjusted is the worm gear lash. It controls the play noted in the "nosegear kick test".
The "nut" calls for a spanner wrench, but I've found with the gearbox installed a modified socket is easier
to get proper leverage on it.
... from the ABS gear supplement....
Worm drive gear end play
When the aircraft is on jacks and the landing gear is part way down, move
nose gear fore and aft while
watching main gear for movement. The main gear should not move, but inboard
gear doors will. If the
main gear also moves:
(1) Remove the oil service plug on the top of the gearbox.
(2) With the landing gear 20 handcrank turns from the down position, have
someone move a main landing gear strut left to right while you watch the worm
drive gear through the service port.
(3) Check end play - there should be no fore or aft movement. If movement is
(4) Remove the emergency hand crank assembly. Use an absorbent towel under
the under the assembly, as some gearbox lube will leak out during the process.
(5) Tighten the thrust bearing retainer nut with a spanner wrench and re-stake
(6) NOTE: On very early gear boxes, end play is controlled by shims and the
bearing is held in place with a snap ring.
(7) Reinstall and safety the hand crank assembly.
I hope you have enjoyed
learning more about the Beech gear transmission as much as I have!
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