Tail Wheel Patent 2,396,277

If you would like to know how the designer of the Scott tailwheel thought it worked here is his patent 2396277 by Richard Ledwin filed 18 August 1943.  Don't read this when you're sleepy.

Tailwheel Details

This simple little Scott 2000 tail wheel which has followed me in several airplanes, Fly Baby, Taylorcraft, Champ, Cub, etc. has been quite a bundle of learning.  I started with 2 complete (?) assemblies and assumed I should end with at least one good one and one re-buildable one.  I have one good assembly now and a few parts.  This exploded assembly drawing does not show all the parts and several parts it shows I didn't have.

Let's start with the wheel.  The part at the left (12) is a felt grease seal.  It has a piece of felt about 1/8" thick trapped between a washer and a dish shaped piece which is rolled on the edge to trap the felt and washer.  The felt needs to be oiled.  I'll get to that later.  The ones I had were both so warn that there was no felt sticking out into the hole for the shaft.  As a result neither would provide any seal to keep the grease in, and keep out dirt or water.  They had probably been that way for a while since all the bearings were shot.  The rolling surfaces of the races were furrowed like a plowed field.  I'm shocked the wheels didn't shake to high heaven.

The part (11) to the right of the seal is just a short piece of tubing 1-3/8" O.D. x .050" wall and 5/32" tall.  It's a spacer to keep the grease retainer/seal in the right place on the step on the the fork shaft.  This spacer is pressed against the bearing outer race and the grease seal is pressed in against the spacer. Next are the bearing inner race and rollers and then the outer race.  Between the 4 bearing sets I had 3 Timken A4050 inner assemblies and 1 from Bower.  For the outer races I had 3 from Bower and one Timken A4138.  For what it's worth both of these part numbers, made by National, are available in from Advance Auto.  They can get them in 2 days, no shipping and a cheaper price.  The wheel half for this side has the grease fitting and hex shaped sockets for the nuts.  The tires tend to dry out and become lose in the wheel.  New ones are about $60, if the tire is lose get rid of it.  The outer half of the wheel has counter bores for the screw heads and threaded holes at the edge for the 4-40 screws which hold the hub cap on.  The drawing does not show the spacer on this wheel and it would serve no purpose but both my wheels have them, go figure.  The 3 screws, washer, nut, and cotter pin are all standard AN hardware. 

The next part has no call out but is a felt grease seal under the hub cap. I made mine with 3 layers of 1/16" felt glued together. I made it that thick because the boss on the wheel for holding the seal centered is that tall. I made the O.D. 2-1/2" to clear the screws for the hub cap.  To get it to seal out dirt and water I worked wheel bearing grease into it.  Just push it down over the boss and the hub cap squashes it down into a nice seal.  Speaking of wheel bearing grease.  The grease called out for the tail wheel is AN-G-15 which is a general purpose grease not wheel bearing grease.

For the seal on the other side of the wheel the part comes from Univair without any oil.  There is only about 1/16" of felt sticking out from the metal housing so working grease into it didn't seam a practical idea.  What I really wanted was for it to be well oiled.  After all grease is just a carrier with oil added.  It's the oil that does the work of lubricating.  I thought of just soaking it in oil but wasn't sure it would get further in than just the little bit of felt sticking out.  Instead I soaked it in 200 degree 5W30 motor oil like an Oilite bearing.  The coolest thing happened when I added the bearing to the hot oil.  The air trapped in the felt expanded and blew out so after soaking it about 15 minutes I just removed the heat and let it cool to room temperature to draw in as much oil as it could.
I didn't find and obvious wear or play in the Bracket (1) bushing (4) for the Fork (5) spindle so not much to say there.  I have no Idea what the acceptable limits for this are.
The next part at the top of the tailwheel is the magical Arm and Cam assembly (6).  It is riveted together so normally no one opens it.  One of mine had been opened and reassembled with screws by threading the lower plate.  The other assembly snagged when moving the arms so both were taken apart.  I'm glad I did because the screwed together one had the better parts but some were missing, never good.

The missing parts were the 2 little spacers I made in an earlier posting.  The first picture shows all the parts inside with the lower bushing installed as well as the 2 spacers. Inside the housing are 3 bronze bushings, 2 spacers and 2 arms.  The bushings are all identical and the arms are left and right based on the bend tipping the arm up slightly.  The stack-up of parts is: bushing, left arm, bushing, right arm, bushing.  The spacers which hold the covers solid also act as stops for the 2 arms.

When the arms are aft, straight out, the shaft hole is open and the tailwheel swivels freely.  Without the springs holding 25-30 pounds on the end of the arms there is no steering.

When the arms are held forward by the springs the hole becomes sort of triangular shaped which matches the angled slots cut in the spindle of the fork.  That little clamping force on the spindle is what allows the steering.  If you push the tail to the side the spring load on one side releases and the arm moves to open it's half of the hole and the tailwheel starts to swivel freely.

The arms in the assembly have to line up with the slots in the spindle so they made shims to put between the bushing in the bracket and the face on the fork as the bushing wears down.  I have one shim but it was not needed to line all this up correctly.  The last piece which I just figured out, and have none of, is a spacer which goes on top of the end of the spindle.  It allows the nut to be properly torqued while maintaining the needed clearance for everything to move.  It also provides a bearing surface for the top of the Arm and Cam assembly.  I'll see if I have one on the Fly Baby which I can copy or if I need to make 2 of them.
The tail wheel is back on but I still can't sign it off until I solve this last problem.

Tail Wheel Spring Back Off

After downloading and reading Neal Wright's article on tailwheel springs I took the spring back off.  At least I have the correct springs.  There were 2 parts missing, the aluminum steering spring guard and the steel piece inside the abrasion strip.  Those have been fabricated and installed.  Also the pin on the shackle assembly which goes in the 1/4" hole in the 3rd spring was ground off years ago when someone installed a spring without the hole.  The hole keeps the shackle from sliding off the spring stack.  Rather than machine a new riveted pin I used an 8-32 socket head cap screw and AN365-832 nut.  The 8-32 screw fit the 5/32" rivet hole in the shackle piece and by just turning the knurle off the head of the screw it fit a 17/64" hole in the spring.  Since there was no hole I decided it was as easy to dirll it to to have the same clearance with a hole 1/64" larger.  If the screw wears it is easy to replace it.  As suggested in Neal's article, I also replaced the main 5/16" bolt with a 3/8" bolt.  Since the hole in the support was 3/8" it seamed better to have a snug fit.  All this required longer bolts to fit properly.  The cross bolt in the shackle is now an AN4-22A.  The main bolt is an AN6-22A and the bolts in the rear support are AN3-18A with the heads down. It's all back on the plane.  On to the tailwheel.

Tail Wheel Spring Back On

The spring parts have all been grit blasted, primed, and painted.  Along with new hardware I fabricated new rubber pads for the spring mounts.  I used 1/16" sheet to cut pieces and laminate pads to fit.  I'm not sure I have the correct durometer rubber since I've found nothing on what rubber was used to make the originals, long since gone from this plane.  We'll see how they last in service and get harder rubber if needed.  By laminating them with contact cement I was able to make them fit around rivets and things like that better than using solid pieces.  The aft spring clamp uses a "U" shaped piece of rubber 1/4" thick.  By laminating it I was able to glue the pieces together to form the "U" to fit very well.  I'm still waiting on a couple parts to assemble the tail wheel.

Tailwheel Parts

All the parts for the tailwheel are cleaned, inspected and painted. The tailwheel spring mounting bracket at the tail of the fuselage is cleaned up and painted. Once I have the rest of the new parts needed, all this can go back together. The tailwheel steering arm and cam assembly is one of the parts for which there seems to be no information on repairing it. The Scott factory riveted it together, so no internal parts are available. Once you un-rivet it, it's a very simple design. I'll write a short explanation before putting all this back together.


 There are 2 bushings which act as stops for the arms and prevent the covers from being crushed when the assembly is riveted together.  I could have drilled out the rivets, but it seemed easier to make new bushings.  The bushings are 3/8" long, 1/4" outside and 3/16" inside diameter.  I have some 1/4" x .028" wall 4130 tubing for the Waco project so I clamped a piece of it between some wood blocks and carefully drilled the ID to 3/16".  To cut off a short piece I used the end of the 3/16" drill to hold the end being cut off.




To square the ends of the bushing I ground one end before each cut was made by holding it against the miter gauge and spinning it while gently pushing it against the belt.  After cutting the bushings slip each one on the drill bit to hold the drill level. Use a gentle finger pressure to push the cut end against the belt while spinning it on the drill shank.  Spinning evens out any slight alignment error and a light pressure allows you to take off less than .oo1" in a cut.  With a little care the 2 bushings can be made within .0005" of the 3/8".

A light deburing after grinding and the bushings are ready to rivet in.

Tail Wheel in Pieces

I've removed the tail wheel now that the plane is back on the mains.  I think I'm shocked at the neglect.  It has been so long since being greased that the grease had dried out back to paraffin.  Grease is made by melting paraffin wax and adding #30 oil to the mix and letting it cool.  It takes a very long time to dry out this bad in a closed space like the wheel or arm and cam assembly.  Fortunately the plane came with 2 tail wheel assemblies.  Like all steel parts the springs were rusty but they cleaned up fine.  One tire is dead and the other is serviceable.  The wheel bearings are all shot.  I'll save one set as an example of just how bad bearings can get.  The inner races on one wheel are like furrows in a plowed field.  I've found new Timken A4050 bearings on e-bay for about $55 shipped so hopefully they really are new as advertised.  The rest should be a matter of cleaning, painting, greasing, and new hardware.  I'll have to fabricate new rubber pads for the springs.  I have some 70 durometer rubber which should work fine.  The tubular rubber piece which goes around the bolt in the spring holes is fine so that's good news.  I should have everything ready by the time the bearings arrive.  This is the same tail wheel we have on the Fly Baby so any serviceable spare parts will always be welcome.

On The Gear Again

After a rainy day yesterday it finally cleared this afternoon. The last wedge went in fine. This would have all been easier using a 7/16" universal socket. It's shorter than a socket and a universal joint, all 1/4" drive. There is not much space to work.

As the sun sets it's nice to have it starting to look like a plane again. Now I can get the remaining control cable pulley brackets out to clean up, re-grease the pulleys and check all the cables. All the brackets are rusty so I'm sure I'll find more problems but they should all be minor.

Gear Back On

The gear is finally back on. I still have 3 rivets to install on the skins around the gear. They need some modified bucking bars to get them in and I need to crawl in the fuselage to figure out what is needed. I haven't wanted to crawl in until the plane was off the stand. The rivets are also easy to get at with the gear on. I still need to install one of the wedges and torque the 2 attachment bolts.Someone had modified the skin on the left side to get at the wedge bolts better. I did those 2 wedges first without realizing how much easier it was with some room to work and being able to see what was happening. The right side has not been modified and is tough. On top of that the slight amount of primer I put on the gear, 2 coats, prevents the wedges from going in as far as they did in the factory. This requires longer bolts which adds to the problem. I did not repaint the wedges for that reason and wiped off any primer on the channels with MEK. The wedges are a very shallow taper so it doesn't take much to make a big difference. I got each wedge lined up with the bolt hole and then started the bolt in to assure it would be lined up free to turn it in. Then I pounded the wedge in tight per the Cessna 100 Series manual and tightened the bolt. Once I was convinced I had the wedge as far as it would go I checked the bolt with the mirror and found I had 1 - 2 threads through the nut plate, perfect. I don't trust that the wedges are in as far as they should be since I used AN4-10A bolts and the parts list shows AN4-5A. The bolts I removed were AN4-6A, but even then 1/4" longer bolts leaves me believing the wedges can go in further. I'll recheck them as we move forward and also after we start flying just to see if they can be wedged in further. I quit when it got dark and I got tired. It's still very cool to have the gear back on.

Painting Engine Parts and Brake Problems

I've started painting the black parts for the engine, rocker covers, intake tubes, etc. The cylinders are next. I wasn't happy with the Cleveland wheels I had cleaned up and installed so I could get this thing back on the gear. The plane came with a mismatched set of Goodyear wheels and 4 brake calipers. I found wheels to match the Goodyears so I decided to clean up the brake calipers. After degreasing and stripping the old paint I quickly condemned all 4 calipers. All four have cracks in the casting at the edge of the machined area and the closest hole. Each is only cracked on one hole. I'm sure if I thought about how the braking loads are applied it would be obvious which were on the right and which were on the left. But who cares, I have more metal for the recycling bin. I've drawn arrows to the crack to help anyone else looking at their parts.

Brake Lines In Gear Box

The new brake lines are fabricated and installed in the gear box. It took a few hours of careful work to get them so they follow the correct path and attach where they are supposed to. Fortunately 1/4" tubing is easy to work with.

I'm priming the fuselage under the 2 skin panels before I rivet them back on. After the riveting is done the gear can finally go back on.

Landing Gear Wedge Bolt Nut Plates

While removing the landing gear legs I had a problem removing the 2 bolts holding the wedges tight on the left side. The nut plates and bolts had rusted enough to bind the bolts and shear the rivets holding the nut plates. The bolts came loose enough to get the wedges out before I realized there was a problem. I should have gotten some oil on them before I started removing them. I had no problem on the right side but they were also rusty. The nut plates are riveted into the steel channel which is the upper gear support. I needed to get in enough to replace the nutplates on both the right and left gear. It also seemed a good chance to clean up any light rust and re-prime as needed. I thought about trying to remove the floor above the supports but removing the skin piece (0411611) covering the area was easier. I'll also replace the short piece of brake line which looks like it gets wet from water around the gear leg. Most of what looks rusty there is really primer sprayed in through the leg hole in the past. The bolts were easily cut off with a Dremel tool with a cut off disk. Now I know what to use to cut off a lock. It really went quickly through the 1/4" AN bolt. . The next step is to clean things up, epoxy prime and put in new nut plates. It looks like the skin can be riveted with the gear leg installed, but I'll probably rivet first.

Wheels Ready to Assemble

All the parts are painted ready to reassemble, after the paint drys a little more. New brake pads had been installed so I have new o-rings, felt seals and bolts. The wheel bearings will be repacked. It will be nice to put this plane back on it's own legs.

Priming Wheels & Parts

Business has finally slowed enough to get back to the landing gear. All the parts are cleaned and the first coat of epoxy primer sprayed.

I found a nice little airbrush at Michael's craft store for $25. It is set up to work with expensive little air cans. With a piece of 1/8" tubing and a couple fittings I modified it to work with the air compressor or my little portable air tank.

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I cut off the can fitting at the end of the thin tube on the brush. Then I opened one end of the 1/8" tube, with the tube fitting I used on the other end, so I could slip the small tube into it. A little super clue and some heat shrink tubing over the joint and it is tight past the 50 psi limit for the brush. With a quick disconnect fitting on the 1/8" tube I can hook it up to any air source. It works very well with 30 psi at the regulator and about 6 ft. of tubing. It atomizes the primer very fine so you get a nice smooth coat. I mix the primer in an 8 oz. jar so it pours easily into the small jar on the brush. I put any extra in the freezer until the next coat can be sprayed. I found it takes about 2 months in the freezer before you see it even start to thicken so a couple days in the freezer slows the epoxy's reaction enough to save wasting much primer.

Gear Legs Primed

Both wings have now been sanded and resprayed with Poly-Spray. If the weather holds I'll start spraying color with Poly-Tone. The gear legs are cleaned up and the step rivet holes inspected for cracks, fortunately none were found. I've sprayed the first coat of epoxy primer on the legs. I like epoxy primer better than zinc chromate. They'll get one more coat before putting them back on the fuselage. I have 2 sets of wheels and brakes with the project, one set of Goodyear and one set of Cleveland. We'll try using the Cleveland assuming they clean up to be serviceable. I've started bead blasting the parts to remove paint and corrosion. At least the rotors cleaned up fine.

Removed The Main Gear

The past three weeks have been very busy in the embroidery shop. Things have slowed enough to get some time on the fuselage. It's been to cold to spray on the wings. We may have to move them back up to the attic for the winter. Most everything has already been removed from the fuselage. There are a few steel parts which need to be removed and repainted, rusty. The gear legs are one of those and it seemed better to start there. We needed to remove them to properly clean them and epoxy prime the metal.

To remove the gear you need to get at the main bolt in the fuselage. The Bolts that hold the wedges in are easy to get at from outside. The wedges jam the spring steel tight in the frame so the legs don't rattle around on landing. To hold up the fuselage and get the doors open the easiest place to support it is at the rear spar attach fittings, behind the doors. Two 2x4 rails were laid on the ground and vertical pieces cut to fit over the spar fittings. Diagonal braces were added to stabilize the posts and everything is screwed together. I put a bolt through the 2 cross braces just to make it more rigid.

Some weight was needed on the tail even without the engine or anything in the cabin. I used a 5/16" bolt so there wouldn't be any severe loads on the spar fittings. The fuselage just sets on the bolts.

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With the doors open it was easy to get to the bolts. You need a 3/8" allen wrench for the bolt and a 12 point 9/16" wrench for the nut. A little tapping on the inside of the gear leg with a soft mallet got the wedges out and then it's just a matter of sliding the leg out. I thought I might need to support the gear but they don't move once the bolts are out.

The mains are off and in the shop for cleaning and painting. I'll also clean up the wheels and repack the bearings so once it's all done we won't need to take any of it apart before the plane flys.