Steve Pierce
BENEFACTOR
I need to take the time to cover some more common issues, wear items etc to add to these videos. Hopefully have time in a few weeks.
The shimmy is because of your head angle not the tightness of the nut. You are keeping it from shimmying by making it harder to swivel. On Cubs I set it up loose so it is easy to turn and break over. It is all by feel for me.I was hoping that one of the assembly videos might have a secret, cut-and-dried method of adjusting the bottom nut.
I've always had to rely on trial-and-error,
too loose and you got shimmy and too tight and it didn't want to steer well or kick out to full swivel.
I've been counting how many turns to full tight before disassembling,
then tighten to the same point when reassembling after cleaning & inspecting.
Just did that with my C180: it was one full turn looser than full tight.
But got a little shimmy after reassembly, so pulled the wheel back off & tightened that nut 2 flats worth.
Seems to have done the trick.
I was hoping that one of the assembly videos might have a secret, cut-and-dried method of adjusting the bottom nut.
I've always had to rely on trial-and-error,
too loose and you got shimmy and too tight and it didn't want to steer well or kick out to full swivel.
I've been counting how many turns to full tight before disassembling,
then tighten to the same point when reassembling after cleaning & inspecting.
Just did that with my C180: it was one full turn looser than full tight.
But got a little shimmy after reassembly, so pulled the wheel back off & tightened that nut 2 flats worth.
Seems to have done the trick.
So you're both saying that the tension on that nut doesn't matter? I don't buy that.
I have enough experience with 3200's to know that head angle is often the cause of shimmy,
but also enough to believe that the tension on the kingpin nut can be & often is also a factor.
BTW this is a 10" 3400-series t/w on a C180, & the t/w head angle is fine.
I don't think I've ever seen a C180/185 stinger that put an 8" or 10" t/w at a shimmy-inducing trailing angle.
The torque on the swivel bolt is to preload the bearing. The drag that's felt when trying to swivel the tailwheel is a function of the five (or whatever number you like to use) springs that apply pressure against the thrust washer, up inside the tailwheel head.
Sure, the head tension will help but if you had a good caster angle it would not shimmy. Post a picture of the head angle when loaded at the point that it shimmies.
Was it a plastic mudflap instead of rubber? I'm sure rubber would be a bit too squishy.Bill got a big truck mud flap and cut a bunch of spacers out of it for that purpose last time he was here.
Hard rubber from an 18 wheeler mud flap. Doesn't compress.Was it a plastic mudflap instead of rubber? I'm sure rubber would be a bit too squishy.
I was hoping that one of the assembly videos might have a secret, cut-and-dried method of adjusting the bottom nut.
I've always had to rely on trial-and-error,
too loose and you got shimmy and too tight and it didn't want to steer well or kick out to full swivel.
I've been counting how many turns to full tight before disassembling,
then tighten to the same point when reassembling after cleaning & inspecting.
Just did that with my C180: it was one full turn looser than full tight.
But got a little shimmy after reassembly, so pulled the wheel back off & tightened that nut 2 flats worth.
Seems to have done the trick.
you NEED TO ADD more shims under your bearing if tightening the nut stops swiveling on a cessna style scott
Sure, the head tension will help but if you had a good caster angle it would not shimmy. Post a picture of the head angle when loaded at the point that it shimmies.
Here's a pic of the tailwheel angle, parked in the hangar.
Same load as usual for day-to-day local ops, minus the pilot.
Tailwheel head angle looks about level or maybe even leading a little (vs trailing).
Camera (phone) is flat -- on the floor, atop a 4x4 block.
View attachment 44344
That works great except for a cub type aircraft that has a 200+# tail weight, and then all bets are off. 3" extended gear and a short mount and 31" tires causes all kinds of things to break, like the pins on the thrust plate, the fork casting where the pin for the lock spring goes is broke, everything wants to come loose! My taylorcraft weighs 68# and I dont break anything, but tripple that and you will find all sorts of problems if you fly a lot and your tail is heavy. TimThe shimmy is because of your head angle not the tightness of the nut. You are keeping it from shimmying by making it harder to swivel. On Cubs I set it up loose so it is easy to turn and break over. It is all by feel for me.
then you have not spent enough time in Alaska, they get bent up there all the time...So you're both saying that the tension on that nut doesn't matter? I don't buy that.
I have enough experience with 3200's to know that head angle is often the cause of shimmy,
but also enough to believe that the tension on the kingpin nut can be & often is also a factor.
BTW this is a 10" 3400-series t/w on a C180, & the t/w head angle is fine.
I don't think I've ever seen a C180/185 stinger that put an 8" or 10" t/w at a shimmy-inducing trailing angle.
Owner bought a 2 bolt spring, I tried to get them to convert from Nyloc to castlated nuts, changed the angle, went from 3 springs to 5 and still will get a shimmy after about 10-30 hours out from the annual. Every year it is a thrust plate replacement due to broken pins, if I leave the king pin nut with any looseness, instant shimmy. I have had the kingpin caster angle anywhere from 0 degrees to 15 positive with leaf spring changes and it will still shimmy with weight on the tail. I am to the point that a really heavy tail will just do that.I am not having those issues. My head would get loose on the spring but I solved that with a 2 bolt head. Reached springs at the truck spring shop and shimmy went away even when loaded heavy on asphalt.