tailwheel nut tension

[Buckeyejim]

The videos on rebuilding the Scott 3200 tailwheel say to wait till the tailwheel is back on the plane before adjusting the tension nut at the bottom.
But they don't go into how to do that. I assume this is done with the tail jacked up. Any suggestions as to how to go about adjusting that nut?

[n2582d]

Jim,
The C-185 Service Manual and the C-100 Series ‘62-‘68 Service Manual say virtually the same thing:

Tailwheel Friction Check.png

See also Service Newsletter 10-24-50.

[Buckeyejim]

Thanks, Gary. When I click on that link about the newsletter, I get: You are not authorised to read this forum.

[Buckeyejim]

The newsletter finally opened up. This site is really really slow, at least on my computer. Anyhow, 5 to 6 pounds is what I need.
Thanks again, Gary.

[GAHorn]

The newsletter finally opened up. This site is really really slow, at least on my computer. Anyhow, 5 to 6 pounds is what I need.
Thanks again, Gary.

For reasons yet un-known….this site has been V E R Y S L O W …for the last two days. It appears to be cleared up now.

[n2582d]

You're welcome Jim.

There's a third set of instructions for torquing that kingpin castle nut here. This is from Scott Aviation, the manufacturer of the tailwheel assembly. There, on page two -- entitled "Shimmy Checklist / 3200 Tailwheel" -- item #6, gives the castle nut torque to be 15 in./lbs. and then tighten to align cotter pin hole. 15 in./lbs. is about finger tight which is surprisingly low in my opinion. I wonder if that is a misprint and should instead read 15 ft./lbs. (180 in./lbs.).

So, take your pick:
1.) 5-6 lbs. pull on the steering arm.
2.) Tighten "in increments in 1/6 of a turn until the tailwheel starts to bind when rotated by hand. Then back off 1/6 of a turn for correct tension on the shimmy dampener."
3.) 15 in./lbs. on the castle nut then tighten to as needed to install cotter pin.

[Buckeyejim]

Thanks, Gary. I see it says: Force required should be 5 to 6 pounds (approximately 23 to 28 pound inches of torque). I wonder what torque
they're talking about?

Anyhow, the reason this came up is that I usually jack the tail up and swivel the wheel 180 degrees prior to winching it into the hangar.
Recently it all of a sudden became extremely difficult to do the swiveling. We took the unit apart and didn't see anything amiss - plenty of
grease. The only thing I could think of was that the tiny coil springs had weakened. Spruce sold me 3 replacements. Guess I'll wait on those
before re assembly.

Now I wish I'd tinkered with that castellated nut a bit before removing the tailwheel and disassembling it.

[n2582d]

If 5-6 lbs. pull at the chain attach point results in 23-28 in/lbs. of torque at the pivot point — the kingpin — that seems to indicate that the arm on the C-180/185 that they’re measuring is about 4.6”. On my Scott 3214 tailwheel arm assembly with the upturned arms I measured 3.5” from center to the chain attach point. So, to get the same torque with this shorter arm, one should be looking for 6.5-8 lbs.

IMG_1315.jpeg

[Buckeyejim]

Interesting! The arm on my Scott 3200 is also 3.5", so maybe the spring scale should read a bit more than 5 to 6 pounds, but not much.

There were only 3 of the tiny coil springs in my unit. A friend with a 170 says he went to 5 springs - what do you think?

[n2582d]

3 or 5 springs has been debated here. The Service Newsletter 10-24-50 that I linked in my first post says there are 3 compression springs. As a side note, that Service Newsletter text has a typo. It actually reads, “… Then back off 1/6 of a turn for correct tension … .” The typo reads “1/16 of a turn”.

[Buckeyejim]

Many thanks for the link, Gary - I've got a bunch of reading to do.

[Bruce Fenstermacher]

The little coil springs put basic pressure on the damper plates. The tighter you make the pin the more pressure the springs make. 3 spring is less pressure than 5 springs. So if you could measure the drag of the damper plates when the tailwheel is functioning properly and you added two more springs for a total of 5, you would't have to tighten the king pin nut as much as it was with 3 springs. Following the instructions 3 or 5 springs you tighten the king pin the minumum and try it and add more pressure by turning the king pin nut in until the tail wheel works and you stop. So it makes no difference really if you use 3 or 5 springs so long as you can adjust the nut to get the tailwheel to work

What usually gets fouled up in a 3200 is the paw, which is a flat spring breaks on leg. The side that breaks will not lock. If the broken paw part jams the innards it may not swival in either direction. The other thing that kills 3200 tailwheels is plan old wear and the resulting uneven pressures and misalignment. The last a long time but they don't last for ever.

[Buckeyejim]

Thanks for the info, Bruce.