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I have extracted from the archives some technical info & tips to assist folk with trim tab & trim cable installation & maintenance. These are in no particular order, and I have credited the writer where I could.
Pictures relate to a tool for relieving the spring tension, courtesy RonC.
Rob Lees
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
First, the trim crank is designed to be turned ONLY when the elevator is held
streamlined with the horizontal stabilizer, otherwise it can and will bind.
The mechanism:
The trim cable turns a vertically mounted pulley on the left elevator located
behind the access cover at the tail post. This pulley is connected to a
screw-jack (worm gear) inside a steel sleeve in the left elevator. The screw
jack pushes and pulls on a bellcrank which in turn pushes and pulls on the trim
push rod. This vertical pulley should turn freely if the trim cable is first
lifted off of it. Use care because the trim cable has a spring tensioner in
the fuselage and it may be difficult to lift the cable off the pulley.
Loosening the spring tensioner is a good idea before starting to work on the
pulley.
In my case, the screw jack was packed with ancient, dried-up grease and bound
up the whole system. There are several sources of play in the system. Check
the bolt holding the pushrod to the trim tab for looseness. A fluttering trim
tab can wallow out the small bellcrank on the tab itself. If the bellcrank
riveted to the trim tab is wallowed out, you can solder a brass bushing to the
steel bell crank. Make the bushing from thin-walled brass tubing available at
your hobby shop. Check the bolt holding the pushrod to the bellcrank inside
the elevator. This bolt will wear some and it is not hard to replace if you
have an inspection cover on the elevator. The screw jack won't have a lot of
play in it, and there is not much you can do there except lubricate it
properly. You probably can't get at the screw jack without uncovering the
corner of your elevator and re-covering later. A careful job would only
require some 2 inch fabric tape to re-cover the edge.
One last important source of play is the trim tab hinges. The trim tab is
fastened to the hinges using a long piece of spring steel wire (known as piano
wire at your local hobby shop). If the holes in the hinges have enlarged,
there will be slop at the hinge line. THIS is probably the cause of any
flutter! It was the source of significant flutter in my plane. Once I fixed
the slop at the hinge line and removed what play I could in the rest of the
linkage, the flutter disappeared. There is still some play at the trim tab,
and given the way the linkage is put together it probably will always have some
play in it.
In my case, the trim tab itself had the hinges wallowed out a little while the
hinge points on the plane were OK. A temporary fix is to pull out the hinge
piano wire, and curve it. Make a big smile in this piece of spring steel and
re-insert it in the hinge holes. The tension on the hinge wire will now take
up some of the slack, and in my case the fluttering stopped immediately. A
longer term fix is to bush the holes in the trim tab. I did this using thin
wall brass tubing available at the hobby shop. You can't solder the tubing to
the aluminum trim tab, but you can hold it in place with epoxy or with Loctite
Bearing Formula.
OK, now I have given away all my trade secrets.
Mark J
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Naturally once you-all started talking about
trim tabs going ptfffoofl, mine had to do it also. So I thought about it
twice and made a gadget. Picture attached. If you don't like the picture
don't look at it.
To use this gadget turn the trim crank until the trim stops are centered,
then you simply hook the ends of the gadget over the spring brackets and
pull the back bracket back and lock it with the set screw. This will
release tension on the trim system. Now turn the trim crank till the
needle is centered. Then go to the tail, reach in through the inspection
hole and spin the trim pulley until the trim tab is even with the elevator.
You don't need to center the control wheel because there will be not tension
on the cable.
I've pushed the hooks on the gadget to one end so that it would be easy to
photograph. You can make one of these out scrap, plans are free.
RonC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Das dopplenderextenderspringenthingen plans. (picture below).
Get a lightweight tube or rod (hickory ram rod - brake lining - TV antenna
rod , etc.,) .
Drill a 3/8" hole in a block of something ( plastic, hard wood, aluminum,
etc.,) and another hole to match your tube (figure A). Saw out a notch down
to the 3/8" hole to match the size and depth of your trim cable spring
about 3/4" (figure B). It would help if you filed another cross notch
(figure C). This notch will keep the hook from slipping off of the spring
attach block (?). Slip one hook on the tube with the claw pointed left and
fasten it in place on the end of the tube with a screw, a nail, JB weld, or
what ever. Drill and tap hole in the other hook so that a screw can be
threaded into the hook and against the tube. I like 1/4 X 20 thread. It
is common and easy. Other threads available in England. Fancy thumb screws
are available in this thread in case you are going to enter it in
competition at Oshkosh. Next (see illustration - no figure letter ) slip
the remaining hook over the right end of the tube with the claw facing right
; now you can sit on the edge of the bed and light up. You are finished.
Hand rubbed oil finish, powder coating, or chrome plating is optional.
You may use your dopplenderextenderspringenthingen to expand to your hearts
content.
RonC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The mechanism inside the elevator might be slack, but it won't slip. Problem may be with the cable/pulley side of things.
Set your cabin trim indicator to neutral (remember to have the control column pulled back to neutral while you do this). Then go and have a look at where the trim tab is on the elevator. If it is also in the neutral position, then I must be mistaking your problem.
However, if it is not, then you need to re-position the trim tab in relation to the trim indicator inside the cabin (in other words, in relation to the trim cable).
This is best done with the assistance of a willing assistant (if you don't have one, get an unwilling one). Get your assistant to kneel on the seat facing aft, and to take the tension off the trim cable spring. To do this, your assistant will need to
a) temporarily open up the headliner behind the pilot's head
b) turn the trim crank to bring the trim cable spring into reach
c) reach behind the opening of the headliner in an awkward and probably painful position so as to get hands at each end of the spring to relieve the tension on the spring.
In the meantime, you have of course removed the inspection panels either side of the aft trim pulley down at the tail. While your assistant is relieving the tension on the spring, you will find that with your fingers you can rotate the aft trim pulley, and it will "slide" past the trim cable.
This moves the trim tab back to its correct position, without moving the trim cable or the trim indicator.
Now you need to tell you assistant that he (or she) can release the tension of the spring inside the fuselage.
Rob L
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The elevator trim control micarta pulley on my first 2 Taylorcrafts
sometimes slipped. The fix for this is quite easy. It is one I learned
from my years of designing Westinghouse elevators. All elevator drives
which use cables use this to improve traction between the drive
sheave and the wire ropes by a factor of 5 or more!
And it works on Taylorcrafts too!
What you don't want is to have a groove in the pulley that matches the
wire diameter! What you want is groove where the wire rope never touches
the bottom of the pulley groove. For example the bottom should be "V"
shaped or even rectangular but the width of the rectangle must be less
than 50% of the wire diameter. Mechanically, what this does is it
squeezes the wire rope on both sides and magnifies the traction force by
2/cosine of the contacting angle between the pulley and wire rope. For
example if the angle is 75 degrees, the traction will be 2/.259 or 7.73
times what it would be in a worn pulley where the bottom of the pulley
has the same radius as the wire rope!
An easy way of (and proven) modifying the pulley is to remove the wire,
and using a hack saw blade pressed against the center of the pulley
groove, rotate the trim handle forward or backward about 10 times. Put
wire rope back on and problem is solved!
HankW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It is possible that the cable is polished where it "lives" most of the time, a smear of rosin will give it grip. Ask your local School Orchestra violin players (or Viola, Cello, Double-Bass, etc) for some redundant Rosin...after cleaning the pulley & cable, run this over the cable...slipping will become a thing in the past!
The hole for the lubrication of the trim screw can be seen at www.taylorcraft.org.uk/TrimLubeHole2.jpg . There are no teeth in the mechanism. The whole mechanism can be seen at www.taylorcraft.org.uk/trim_mech.jpg
You can also lubricate the jack screw thread mechanism using the access panel on the underside of the port elevator, using a gob of grease on a pipe cleaner... There is a bell-crank in there that should also be lubricated as part of the annual.
(and V-cutting, if necessary after the Rosin, should be with a very fine, narrow hacksaw blade, not a file, which will be too broad in the Vee of the pulley).
Rob L
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Rosin always worked great for me. Check with a local school with an orchestra. They may have messed up cakes. The kids take a while getting used to rosining their bows correctly. If not any good music store sells rosin. Don't over-do it. The stuff is sticky.
HankJ
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the past, someone had suggested to use violin bow rosin on the cable near the pulley -- works great.
Jerry in NC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
While we're on that subject, you can get violin bow resin cheap by
the pound if you check with somebody who supplies the
Amateur Telescope Making (ATM) trade. The resin is used
for lapping optical elements.
Mike
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The readjustment of the cable can be done without too much trouble if you have a friend to help:
1. Make access to the rear fuselage from the seat (unzip the headliner or whatever).
2. kneel on the seat facing aft and with two hands, grab either end of the tensioning spring and expand to relieve the tension on the cable.
3. Have friend rotate the aft trim pulley to correct the out-of-alignment
4. Release the tension on the spring, and check for correct elevator tab operation and front indicator operation.
5. Repeat as necessary.
6. Re-zip the headliner and take your kindly friend for a trip round the bay to thank him/her.
RobL
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If you don't remember to center the trim cable after you center
the trim indicator with the trim tab centered the cable crimps will hit the
stops in the fuselage and you won't get full trim movement! (I know this
from taking it apart and studying it, not because it actually happened to me
or anything like that) ;-0 YEA RIGHT!
The trim works because it has been apart a dozen times and rebuilt. Once
you get it right it seems to work forever.
Hank J
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The jackscrew is probably worn. It's made of bronze or brass and can easily be
reproduced on a lathe from a piece of stock. Mine had to be replaced because it
had so much slop in it. Either the trim-tab would hang up or it would walk in
flight, so that you would lose trim while flying. That's the most complicated
part to repair. The cable sometimes gets too loose, in which case you just
loosen the clamps and tighten it against its spring. Seems to me I had to
replace a pulley once too. Gotta have that poor man's auto-pilot.
James L S
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
However, there is an additional item not yet mentioned. Just before the
rear pulley, the cable rides in a little one inch by 3 inch plate which was
originally made of bakelite (early form of plastic). The cable actually
rides inside two hardened copper inserts which was probably pressed into
the bakelite. The problem: Over time the cable will eat into the copper
insert and cut a groove and eventually cause the cable to break strands
and bind. This happened to old 974. I built a new plate out of schedule 80
PVC, did not add the copper inserts. I'm watching it to see if the cable
eats into it. If it does, I will have to add inserts. I have heard you
can reverse this plate 180 degrees
and therefore cause the "cable sawing" to begin on a new surface of the
copper insert. Should last 40 years anyway. Check your tails gentlemen,
you could be sawing copper. John in N/Fla.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the jackscrew is sloppy with wear and the trim tab changes position in
flight against your will and in spite of the setting you just gave it with your
handy-dandy overhead trim roller handle, I had the same problem. I had to cut
into the fabric on the elevator and remove the brass jackscrew and from that,
Bill Fields, a talented friend with a lathe, turned a new one from round
bronze, or brass, stock. I greased it up, put it in, and it has always worked
perfectly. I have the old jackscrew in case anyone needs it to make a new
one. Plus a wooden trimtab blank, if anyone needs that.
I used to see a lot of T-Crafts at airshows with aluminum trimtabs. Not
original, but I guess they don't tend to rot like the wooden ones do, which
will rot -- guaranteed -- if you don't have weep-holes, one in each hollow of
the trimtab.
Larry S
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I am not sure what the type certificate requires for a trim cable, but
7x19 stranded cable is available from McMaster-Carr Supply Company,
Chicago, Illinois. Telephone 630-833-0300. They also have locations in Los
Angeles, Cleveland, Atlanta, and New York. In current catalog, #107, the
cable is listed as "Type 302 Stainless Steel Wire Rope, page 1236, part#
3458T75, has a breaking strength of 480 pounds, and meets Federal Spec.
RR-W-410 and is also listed as "Full Compliance Military Spec. MIL-W-83420.
Whether or not that meets the standards for the type certificate is not
something I know. But, it will be pretty difficult to place 480 pounds of
tension on that cable and not have everything else fail first. Plus, it is
stainless. I verified price and availability by telephone a few minutes
ago. Both 302 SS 7x19 and 7x7 are currently in stock. The 1/16" rope sells
for $0.59/ft. up to 99 feet, $0.51/ft over 99 feet, and $0.43/ft over 300
feet. They ship same day via UPS and if you are in their next day zone, you
will receive the order in 24 hours at no additional shipping charge. It is
also available with a Teflon coating for lower resistance and in >030" and
>038" diameter if the 1/16" (.032") will not fit perfectly. I should have
been more specific in my earlier reply. Sorry for the lack of detail.
Randall R
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1/16 (7x19) trim cable is readily
available from the mfgr Loos & Co, Pomfret Ctr, CT, 06259, U.S.A. The cable
is mil spec. Be sure to ask for a certificate of origin. 32' cost me around
$12 US. I'd like to suggest that you contact David Loos (related but not
the mfgr [email protected] ) to help you with your order. Loos & Co is one of
about five US companies making mil qualified cable supplying the industry
mostly through retailers like Spruce and others. David helps as a local
distributor
Jerry E
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
At any rate, my original trim cable was 7x7 and works OK.
Mark J
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
well the 696 TC calls for a trim tab movement of Up 25 degrees ; down
30 degrees so that when you have it 25 degrees down that will give you
the correct up elevator for minimum trim speed IF your Wt. & balance is
within limits...... bye Forrest
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The trim system is a high maintenance
item ; the cable needs to be cleaned maybe replaced, the pulleys need to be
cleaned, the screw needs to be lubed, the system needs to be set up
correctly on tension and adjustment; THEN if you want it to work, treat it
gently. On pre-flight I see that the tab is neutral; if NOT then have the
wheel back in level flight position and crank it neutral, I reset it after
landing going to the hangar.
After take-off and going into cruise make sure when you turn it that
it does something and is not slipping on a pulley ( you can end up with
full nose up trim quite easily, I have seen it so bad a guy had to put his
knee on the wheel to maintain level flight). I teach to only use trim as
necessary especially in the cold weather when it is prone to slipping
easily. One to two turns is plenty for any condition. On a warm day or
in a warm shop at annual time with someone watching for no slippage I do
crank the trim full both ways and lube it all. There are a lot of little
tricks learned out in the field. For certification each factory test did
show full nose up trim and release the wheel, the ship would glide power off
at 60-70 mph ( known as minimum trim speed). I use one to one & one half
turns nose up out of level flight on downwind and that is plenty to help out
on the glide to flare and should not cause any slippage then just crank it
back the way for take-off. bye Forrest
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
One thing I forgot to mention... Never ever oil or lube the wire rope that drives the elevator trim. If you do, it will slip on the pulleys and for sure the trim and the indicator will go out of sync, and with them, the spring. This spring is in the tail cone on the elevator trim drive cable and keeps taughtness in the wire rope. the spring cannot pass through two guides, one fore, one aft, and the distance between the guides is equal to full up/full down. When the indicator reaches full up, the spring must be at a guide, and the elevator trim must also be full up. When the indicator is full down, the spring must be at the other guide and the trim full down. My AME didn't know this and after an annual a couple of years ago, I had to resync the trim tab system in the air. That's how I found out... the interesting way.
Bruce U.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I have experienced a stuck trim tab also. It was because the tab was
turned on the ground without the elevator in neutral position, just as John
mentioned. I removed the inspection panel and my inspection panel cut-out is
just big enough that I can grab the cable to relieve some tension on the
pulley, and then manually reset the tab to neutral. Only takes a couple of
minutes.
Bob Mc
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On a BC-12, the tab is connected to a push rod which is connected to a 90 degree
bell crank. The bell crank is connected to a screw jack. The screw jack is
turned by the pulley which you can see at the tail post by the elevator control (leg bone connected to the thigh bone etc).
If the tab is jammed, there are a few likely causes:
1) Someone put heavy grease in the screw jack and it has set up on you. (I have first hand
experience with that)
2) The screw jack was screwed out so far that it disconnected.
3) Something got bent, perhaps a screw or the pin holding the
screw jack together.
Without seeing it, I believe your best bet will be to glue a reinforcing ring
on the bottom of the elevator at the bell crank. Cut out the new inspection
hole and have a look.
Mark J
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Pictures relate to a tool for relieving the spring tension, courtesy RonC.
Rob Lees
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
First, the trim crank is designed to be turned ONLY when the elevator is held
streamlined with the horizontal stabilizer, otherwise it can and will bind.
The mechanism:
The trim cable turns a vertically mounted pulley on the left elevator located
behind the access cover at the tail post. This pulley is connected to a
screw-jack (worm gear) inside a steel sleeve in the left elevator. The screw
jack pushes and pulls on a bellcrank which in turn pushes and pulls on the trim
push rod. This vertical pulley should turn freely if the trim cable is first
lifted off of it. Use care because the trim cable has a spring tensioner in
the fuselage and it may be difficult to lift the cable off the pulley.
Loosening the spring tensioner is a good idea before starting to work on the
pulley.
In my case, the screw jack was packed with ancient, dried-up grease and bound
up the whole system. There are several sources of play in the system. Check
the bolt holding the pushrod to the trim tab for looseness. A fluttering trim
tab can wallow out the small bellcrank on the tab itself. If the bellcrank
riveted to the trim tab is wallowed out, you can solder a brass bushing to the
steel bell crank. Make the bushing from thin-walled brass tubing available at
your hobby shop. Check the bolt holding the pushrod to the bellcrank inside
the elevator. This bolt will wear some and it is not hard to replace if you
have an inspection cover on the elevator. The screw jack won't have a lot of
play in it, and there is not much you can do there except lubricate it
properly. You probably can't get at the screw jack without uncovering the
corner of your elevator and re-covering later. A careful job would only
require some 2 inch fabric tape to re-cover the edge.
One last important source of play is the trim tab hinges. The trim tab is
fastened to the hinges using a long piece of spring steel wire (known as piano
wire at your local hobby shop). If the holes in the hinges have enlarged,
there will be slop at the hinge line. THIS is probably the cause of any
flutter! It was the source of significant flutter in my plane. Once I fixed
the slop at the hinge line and removed what play I could in the rest of the
linkage, the flutter disappeared. There is still some play at the trim tab,
and given the way the linkage is put together it probably will always have some
play in it.
In my case, the trim tab itself had the hinges wallowed out a little while the
hinge points on the plane were OK. A temporary fix is to pull out the hinge
piano wire, and curve it. Make a big smile in this piece of spring steel and
re-insert it in the hinge holes. The tension on the hinge wire will now take
up some of the slack, and in my case the fluttering stopped immediately. A
longer term fix is to bush the holes in the trim tab. I did this using thin
wall brass tubing available at the hobby shop. You can't solder the tubing to
the aluminum trim tab, but you can hold it in place with epoxy or with Loctite
Bearing Formula.
OK, now I have given away all my trade secrets.
Mark J
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Naturally once you-all started talking about
trim tabs going ptfffoofl, mine had to do it also. So I thought about it
twice and made a gadget. Picture attached. If you don't like the picture
don't look at it.
To use this gadget turn the trim crank until the trim stops are centered,
then you simply hook the ends of the gadget over the spring brackets and
pull the back bracket back and lock it with the set screw. This will
release tension on the trim system. Now turn the trim crank till the
needle is centered. Then go to the tail, reach in through the inspection
hole and spin the trim pulley until the trim tab is even with the elevator.
You don't need to center the control wheel because there will be not tension
on the cable.
I've pushed the hooks on the gadget to one end so that it would be easy to
photograph. You can make one of these out scrap, plans are free.
RonC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Das dopplenderextenderspringenthingen plans. (picture below).
Get a lightweight tube or rod (hickory ram rod - brake lining - TV antenna
rod , etc.,) .
Drill a 3/8" hole in a block of something ( plastic, hard wood, aluminum,
etc.,) and another hole to match your tube (figure A). Saw out a notch down
to the 3/8" hole to match the size and depth of your trim cable spring
about 3/4" (figure B). It would help if you filed another cross notch
(figure C). This notch will keep the hook from slipping off of the spring
attach block (?). Slip one hook on the tube with the claw pointed left and
fasten it in place on the end of the tube with a screw, a nail, JB weld, or
what ever. Drill and tap hole in the other hook so that a screw can be
threaded into the hook and against the tube. I like 1/4 X 20 thread. It
is common and easy. Other threads available in England. Fancy thumb screws
are available in this thread in case you are going to enter it in
competition at Oshkosh. Next (see illustration - no figure letter ) slip
the remaining hook over the right end of the tube with the claw facing right
; now you can sit on the edge of the bed and light up. You are finished.
Hand rubbed oil finish, powder coating, or chrome plating is optional.
You may use your dopplenderextenderspringenthingen to expand to your hearts
content.
RonC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The mechanism inside the elevator might be slack, but it won't slip. Problem may be with the cable/pulley side of things.
Set your cabin trim indicator to neutral (remember to have the control column pulled back to neutral while you do this). Then go and have a look at where the trim tab is on the elevator. If it is also in the neutral position, then I must be mistaking your problem.
However, if it is not, then you need to re-position the trim tab in relation to the trim indicator inside the cabin (in other words, in relation to the trim cable).
This is best done with the assistance of a willing assistant (if you don't have one, get an unwilling one). Get your assistant to kneel on the seat facing aft, and to take the tension off the trim cable spring. To do this, your assistant will need to
a) temporarily open up the headliner behind the pilot's head
b) turn the trim crank to bring the trim cable spring into reach
c) reach behind the opening of the headliner in an awkward and probably painful position so as to get hands at each end of the spring to relieve the tension on the spring.
In the meantime, you have of course removed the inspection panels either side of the aft trim pulley down at the tail. While your assistant is relieving the tension on the spring, you will find that with your fingers you can rotate the aft trim pulley, and it will "slide" past the trim cable.
This moves the trim tab back to its correct position, without moving the trim cable or the trim indicator.
Now you need to tell you assistant that he (or she) can release the tension of the spring inside the fuselage.
Rob L
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The elevator trim control micarta pulley on my first 2 Taylorcrafts
sometimes slipped. The fix for this is quite easy. It is one I learned
from my years of designing Westinghouse elevators. All elevator drives
which use cables use this to improve traction between the drive
sheave and the wire ropes by a factor of 5 or more!
And it works on Taylorcrafts too!
What you don't want is to have a groove in the pulley that matches the
wire diameter! What you want is groove where the wire rope never touches
the bottom of the pulley groove. For example the bottom should be "V"
shaped or even rectangular but the width of the rectangle must be less
than 50% of the wire diameter. Mechanically, what this does is it
squeezes the wire rope on both sides and magnifies the traction force by
2/cosine of the contacting angle between the pulley and wire rope. For
example if the angle is 75 degrees, the traction will be 2/.259 or 7.73
times what it would be in a worn pulley where the bottom of the pulley
has the same radius as the wire rope!
An easy way of (and proven) modifying the pulley is to remove the wire,
and using a hack saw blade pressed against the center of the pulley
groove, rotate the trim handle forward or backward about 10 times. Put
wire rope back on and problem is solved!
HankW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It is possible that the cable is polished where it "lives" most of the time, a smear of rosin will give it grip. Ask your local School Orchestra violin players (or Viola, Cello, Double-Bass, etc) for some redundant Rosin...after cleaning the pulley & cable, run this over the cable...slipping will become a thing in the past!
The hole for the lubrication of the trim screw can be seen at www.taylorcraft.org.uk/TrimLubeHole2.jpg . There are no teeth in the mechanism. The whole mechanism can be seen at www.taylorcraft.org.uk/trim_mech.jpg
You can also lubricate the jack screw thread mechanism using the access panel on the underside of the port elevator, using a gob of grease on a pipe cleaner... There is a bell-crank in there that should also be lubricated as part of the annual.
(and V-cutting, if necessary after the Rosin, should be with a very fine, narrow hacksaw blade, not a file, which will be too broad in the Vee of the pulley).
Rob L
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Rosin always worked great for me. Check with a local school with an orchestra. They may have messed up cakes. The kids take a while getting used to rosining their bows correctly. If not any good music store sells rosin. Don't over-do it. The stuff is sticky.
HankJ
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the past, someone had suggested to use violin bow rosin on the cable near the pulley -- works great.
Jerry in NC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
While we're on that subject, you can get violin bow resin cheap by
the pound if you check with somebody who supplies the
Amateur Telescope Making (ATM) trade. The resin is used
for lapping optical elements.
Mike
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The readjustment of the cable can be done without too much trouble if you have a friend to help:
1. Make access to the rear fuselage from the seat (unzip the headliner or whatever).
2. kneel on the seat facing aft and with two hands, grab either end of the tensioning spring and expand to relieve the tension on the cable.
3. Have friend rotate the aft trim pulley to correct the out-of-alignment
4. Release the tension on the spring, and check for correct elevator tab operation and front indicator operation.
5. Repeat as necessary.
6. Re-zip the headliner and take your kindly friend for a trip round the bay to thank him/her.
RobL
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If you don't remember to center the trim cable after you center
the trim indicator with the trim tab centered the cable crimps will hit the
stops in the fuselage and you won't get full trim movement! (I know this
from taking it apart and studying it, not because it actually happened to me
or anything like that) ;-0 YEA RIGHT!
The trim works because it has been apart a dozen times and rebuilt. Once
you get it right it seems to work forever.
Hank J
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The jackscrew is probably worn. It's made of bronze or brass and can easily be
reproduced on a lathe from a piece of stock. Mine had to be replaced because it
had so much slop in it. Either the trim-tab would hang up or it would walk in
flight, so that you would lose trim while flying. That's the most complicated
part to repair. The cable sometimes gets too loose, in which case you just
loosen the clamps and tighten it against its spring. Seems to me I had to
replace a pulley once too. Gotta have that poor man's auto-pilot.
James L S
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However, there is an additional item not yet mentioned. Just before the
rear pulley, the cable rides in a little one inch by 3 inch plate which was
originally made of bakelite (early form of plastic). The cable actually
rides inside two hardened copper inserts which was probably pressed into
the bakelite. The problem: Over time the cable will eat into the copper
insert and cut a groove and eventually cause the cable to break strands
and bind. This happened to old 974. I built a new plate out of schedule 80
PVC, did not add the copper inserts. I'm watching it to see if the cable
eats into it. If it does, I will have to add inserts. I have heard you
can reverse this plate 180 degrees
and therefore cause the "cable sawing" to begin on a new surface of the
copper insert. Should last 40 years anyway. Check your tails gentlemen,
you could be sawing copper. John in N/Fla.
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If the jackscrew is sloppy with wear and the trim tab changes position in
flight against your will and in spite of the setting you just gave it with your
handy-dandy overhead trim roller handle, I had the same problem. I had to cut
into the fabric on the elevator and remove the brass jackscrew and from that,
Bill Fields, a talented friend with a lathe, turned a new one from round
bronze, or brass, stock. I greased it up, put it in, and it has always worked
perfectly. I have the old jackscrew in case anyone needs it to make a new
one. Plus a wooden trimtab blank, if anyone needs that.
I used to see a lot of T-Crafts at airshows with aluminum trimtabs. Not
original, but I guess they don't tend to rot like the wooden ones do, which
will rot -- guaranteed -- if you don't have weep-holes, one in each hollow of
the trimtab.
Larry S
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I am not sure what the type certificate requires for a trim cable, but
7x19 stranded cable is available from McMaster-Carr Supply Company,
Chicago, Illinois. Telephone 630-833-0300. They also have locations in Los
Angeles, Cleveland, Atlanta, and New York. In current catalog, #107, the
cable is listed as "Type 302 Stainless Steel Wire Rope, page 1236, part#
3458T75, has a breaking strength of 480 pounds, and meets Federal Spec.
RR-W-410 and is also listed as "Full Compliance Military Spec. MIL-W-83420.
Whether or not that meets the standards for the type certificate is not
something I know. But, it will be pretty difficult to place 480 pounds of
tension on that cable and not have everything else fail first. Plus, it is
stainless. I verified price and availability by telephone a few minutes
ago. Both 302 SS 7x19 and 7x7 are currently in stock. The 1/16" rope sells
for $0.59/ft. up to 99 feet, $0.51/ft over 99 feet, and $0.43/ft over 300
feet. They ship same day via UPS and if you are in their next day zone, you
will receive the order in 24 hours at no additional shipping charge. It is
also available with a Teflon coating for lower resistance and in >030" and
>038" diameter if the 1/16" (.032") will not fit perfectly. I should have
been more specific in my earlier reply. Sorry for the lack of detail.
Randall R
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1/16 (7x19) trim cable is readily
available from the mfgr Loos & Co, Pomfret Ctr, CT, 06259, U.S.A. The cable
is mil spec. Be sure to ask for a certificate of origin. 32' cost me around
$12 US. I'd like to suggest that you contact David Loos (related but not
the mfgr [email protected] ) to help you with your order. Loos & Co is one of
about five US companies making mil qualified cable supplying the industry
mostly through retailers like Spruce and others. David helps as a local
distributor
Jerry E
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At any rate, my original trim cable was 7x7 and works OK.
Mark J
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well the 696 TC calls for a trim tab movement of Up 25 degrees ; down
30 degrees so that when you have it 25 degrees down that will give you
the correct up elevator for minimum trim speed IF your Wt. & balance is
within limits...... bye Forrest
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The trim system is a high maintenance
item ; the cable needs to be cleaned maybe replaced, the pulleys need to be
cleaned, the screw needs to be lubed, the system needs to be set up
correctly on tension and adjustment; THEN if you want it to work, treat it
gently. On pre-flight I see that the tab is neutral; if NOT then have the
wheel back in level flight position and crank it neutral, I reset it after
landing going to the hangar.
After take-off and going into cruise make sure when you turn it that
it does something and is not slipping on a pulley ( you can end up with
full nose up trim quite easily, I have seen it so bad a guy had to put his
knee on the wheel to maintain level flight). I teach to only use trim as
necessary especially in the cold weather when it is prone to slipping
easily. One to two turns is plenty for any condition. On a warm day or
in a warm shop at annual time with someone watching for no slippage I do
crank the trim full both ways and lube it all. There are a lot of little
tricks learned out in the field. For certification each factory test did
show full nose up trim and release the wheel, the ship would glide power off
at 60-70 mph ( known as minimum trim speed). I use one to one & one half
turns nose up out of level flight on downwind and that is plenty to help out
on the glide to flare and should not cause any slippage then just crank it
back the way for take-off. bye Forrest
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One thing I forgot to mention... Never ever oil or lube the wire rope that drives the elevator trim. If you do, it will slip on the pulleys and for sure the trim and the indicator will go out of sync, and with them, the spring. This spring is in the tail cone on the elevator trim drive cable and keeps taughtness in the wire rope. the spring cannot pass through two guides, one fore, one aft, and the distance between the guides is equal to full up/full down. When the indicator reaches full up, the spring must be at a guide, and the elevator trim must also be full up. When the indicator is full down, the spring must be at the other guide and the trim full down. My AME didn't know this and after an annual a couple of years ago, I had to resync the trim tab system in the air. That's how I found out... the interesting way.
Bruce U.
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I have experienced a stuck trim tab also. It was because the tab was
turned on the ground without the elevator in neutral position, just as John
mentioned. I removed the inspection panel and my inspection panel cut-out is
just big enough that I can grab the cable to relieve some tension on the
pulley, and then manually reset the tab to neutral. Only takes a couple of
minutes.
Bob Mc
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On a BC-12, the tab is connected to a push rod which is connected to a 90 degree
bell crank. The bell crank is connected to a screw jack. The screw jack is
turned by the pulley which you can see at the tail post by the elevator control (leg bone connected to the thigh bone etc).
If the tab is jammed, there are a few likely causes:
1) Someone put heavy grease in the screw jack and it has set up on you. (I have first hand
experience with that)
2) The screw jack was screwed out so far that it disconnected.
3) Something got bent, perhaps a screw or the pin holding the
screw jack together.
Without seeing it, I believe your best bet will be to glue a reinforcing ring
on the bottom of the elevator at the bell crank. Cut out the new inspection
hole and have a look.
Mark J
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