Powerin Posted October 9, 2011 Posted October 9, 2011 I know nothing about tailwheels Pud, but I'll bet a crook bearing would have a bearing () on the shimmy. Either by causing a bit of play or drag in the tailwheel.
turboplanner Posted October 9, 2011 Posted October 9, 2011 Steve and I checked out the tail wheel today to see if we could nail the cause of the shimmy. The photos here show the tail wheel assemblies on all 3 Thrusters in the hangar - I must confess I don't see any difference to the castor angle on any of them (other minor differences are evident), with only mine having the shimmy. See what you think. There is a difference PUd (assuming constant camera angle), and I'd expect the centre one to travel the best. Yours has a steeper angle so the wheel centreline is closer to the pivot centreline, so there is less castor. One way to investigate further is to drop a plumb bob from the pivot and check the distance from the pivot to the wheel CL on all three, then work out the percentage difference. For example if one was 400 mm and one was 450 mm, the 450 mm, the 450 mm one has 12.5% better leverage, and that may be just enough to make the difference. However, the posts above outline a lot of things to do before changing the angle/extending the leg. 2
Tomo Posted October 9, 2011 Posted October 9, 2011 If the wheel isn't square with the aircraft it will do a shimmy I would imagine also. Have you checked that? i.e. if you look from the back on is the tired parallel with the rudder?
turboplanner Posted October 9, 2011 Posted October 9, 2011 If the wheel isn't square with the aircraft it will do a shimmy I would imagine also. Have you checked that? i.e. if you look from the back on is the tired parallel with the rudder? Good point Tomo, it would be trying to track out of true, then being flicked back.
Tomo Posted October 9, 2011 Posted October 9, 2011 Good point Tomo, it would be trying to track out of true, then being flicked back. Yep, which is what happens to shopping trolleys, the wheels get bent in a bit from mad... *cough*... drivers hitting the gutter etc... which then causes grief to the poor old lady trying to do her shopping
pudestcon Posted October 11, 2011 Author Posted October 11, 2011 Thanks guys, My understanding is that all 3 assemblies are exactly the same dimensions - but I'll check that next weekend. I'll nail it!! just might take some time. I have the new bearings and will make up the shims this arvo. A coat of paint and back on the aircraft on Saturday for a test run. Pud
turboplanner Posted October 11, 2011 Posted October 11, 2011 Bearings first, it could well be that bearing wear on one side is allowing the axle/wheel to drag back against the smaller balls on that side creating the alignment issue Tomo mentioned. Then, if that doesn't solve the problem: Check the #337 dimensions I mentioned, and with a fine string plumb bob and mark the floor with engineers chalk. You need to work to +- 1 mm They may all be identical components but they are sitting at different angles, so what you are measuring is castor length on the ground from pivot CL to axle CL - you can plumb bob from the side of the pivot and side of the axle if the diagonal is small, otherwise one set of measurements each side and average them. Geez 341 posts to get you cruising Pud, that must be a record.
Guernsey Posted October 11, 2011 Posted October 11, 2011 Well Pud I believe that so much work and helpful advice has gone into what will be the best Thruster in the world and will be worth a fortune if you sell it. Alan 342
pudestcon Posted October 11, 2011 Author Posted October 11, 2011 Well Pud I believe that so much work and helpful advice has gone into what will be the best Thruster in the world and will be worth a fortune if you sell it.Alan 342 SELL MY GAYGIRL!! Wash your mouth out with soap Guernsey. This little aircraft is here to stay:smile: Pud 1
pudestcon Posted October 11, 2011 Author Posted October 11, 2011 Bearings first, it could well be that bearing wear on one side is allowing the axle/wheel to drag back against the smaller balls on that side creating the alignment issue Tomo mentioned.Then, if that doesn't solve the problem: Check the #337 dimensions I mentioned, and with a fine string plumb bob and mark the floor with engineers chalk. You need to work to +- 1 mm They may all be identical components but they are sitting at different angles, so what you are measuring is castor length on the ground from pivot CL to axle CL - you can plumb bob from the side of the pivot and side of the axle if the diagonal is small, otherwise one set of measurements each side and average them. Geez 341 posts to get you cruising Pud, that must be a record. Yep, one thing at a time eh turbz? That way I'll be able to report exactly what the problem was - maybe the new coat of paint on the tail wheel components will do the trick:wink: 341 posts - it's a few eh? I must sit down and write the story of this journey; Could be a story for the magazine, as the story has already been told here on this thread. Pud
turboplanner Posted October 11, 2011 Posted October 11, 2011 No, write a trip story on the next flight, on one of the other threads people are asking for them.
Guernsey Posted October 11, 2011 Posted October 11, 2011 SELL MY GAYGIRL!! Wash your mouth out with soap Guernsey. This little aircraft is here to stay:smile:Pud Fantastic news! it's good to know that the Pudster will go down in history as being the oldest surviving Thruster in the world. Good on ya Pud. Alan.
Guernsey Posted October 12, 2011 Posted October 12, 2011 Further to the above Pud, my Mum used to use that expression although I never took her up on it, so I thought I would give it a try. Absolute dissaster.....went flying and had to get my passenger to use the radio because every time I spoke the cockpit filled with bubbles. Alan.
pudestcon Posted October 12, 2011 Author Posted October 12, 2011 Further to the above Pud, my Mum used to use that expression although I never took her up on it, so I thought I would give it a try.Absolute dissaster.....went flying and had to get my passenger to use the radio because every time I spoke the cockpit filled with bubbles. Alan. Hehehe
pudestcon Posted October 16, 2011 Author Posted October 16, 2011 No more tail shimmy. You were correct in thinking it was the bearings turbz, although I did straighten out a minor curve in both spring leaves as well. I replaced the 1/2" pivot bolt and nut for good measure as well. Costs - 2 bearings at $16.50 each and pivot bolt and nut (high tensile) $3.00. Cheap as chips really to get the desired result. I'm happy. Did some more circuit bashing yesterday, and then my mate Poll did a few circuits with Steve just to start getting his flying legs back after not flying for a couple of years - interesting that he was able to nail the last 2 landings considering he hadn't quite 'got' the landings 2 years ago. The weather at Northam yesterday was a bit windier than what we normally fly in (still onjy 8kts or so), and a few thermals to boot, which made it very interesting for Poll. Pud
Powerin Posted October 16, 2011 Posted October 16, 2011 No more tail shimmy. You were correct in thinking it was the bearings turbz,Pud What? Tubz gets the credit?? What about my post #336 way before Tubz thought of it???? But seriously, glad you got it sorted Pud!
sfGnome Posted October 16, 2011 Posted October 16, 2011 ...then my mate Poll did a few circuits with Steve just to start getting his flying legs back after not flying for a couple of years - interesting that he was able to nail the last 2 landings considering he hadn't quite 'got' the landings 2 years ago. Makes some sense to me. I reckon that some times the best thing to do when you just can't 'get' something is to go away and sleep on it for a while - let your subconscious work on it in the background. Mind you, 2 years may be a bit longer than I'd normally suggest...
Tomo Posted October 16, 2011 Posted October 16, 2011 You always do it better when flying your 'mates' plane, as you try very hard not to break it!
turboplanner Posted October 16, 2011 Posted October 16, 2011 What? Tubz gets the credit?? What about my post #336 way before Tubz thought of it???? But seriously, glad you got it sorted Pud! You were too far ahead of your time Pow!
pudestcon Posted October 16, 2011 Author Posted October 16, 2011 What? Tubz gets the credit?? What about my post #336 way before Tubz thought of it???? But seriously, glad you got it sorted Pud! Shite!! I'm gonna have to start reading all the posts in this thread again before I go answering anyone now. Onya Pow, you had it sussed long before I did - you must be one switched on high roller (bearing that is). On second thoughts, you are just a down to earth, logically thinking cocky - that's why you had it nailed all the time eh? Pud
turboplanner Posted October 16, 2011 Posted October 16, 2011 ....or he leaves his bearing maintenance until the harrows run into the next paddock.....
Powerin Posted October 17, 2011 Posted October 17, 2011 ....or he leaves his bearing maintenance until the harrows run into the next paddock..... Yep!
pudestcon Posted October 21, 2011 Author Posted October 21, 2011 Makes some sense to me. I reckon that some times the best thing to do when you just can't 'get' something is to go away and sleep on it for a while - let your subconscious work on it in the background. Mind you, 2 years may be a bit longer than I'd normally suggest... Here's a video of the first 2 landings from Poll's flight last week - somehow I've managed to lose some footage so I can't show the best landing. Sorry Poll!! Pud
turboplanner Posted October 21, 2011 Posted October 21, 2011 Never mind Pud, it also happens to people who take photos of UFO's, Yetis and Big Cats 1
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