Re: PT-23 Shimmy

Michael Denest · Post by **Michael Denest** » Mon Jul 08, 2019 2:06 pm

'Running the tire pressure in the tailwheel that low is not good, making it possible for the tire to slip on the wheel and shear the stem on the inner tube. From: fairchildclub@yahoogroups.com [mailto:fairchildclub@yahoogroups.com]
Sent: Monday, July 8, 2019 3:56 PM
To: fairchildclub@yahoogroups.com
Subject: Re: [fairchildclub] PT-23 Shimmy
Hi I run my tyre pressure low as 25 psi, seems to solve it for me. If it does start it’s right at the end of the landing roll.CheersSent from my iPhone
On 8 Jul 2019, at 20:32, Thomas Rood tdrood@yahoo.com [fairchildclub] wrote:

Definitely check cable tension. Also check for anything bent back there, if the pivot axis is not tipped sufficiently aft at the top, it will shake violently (kind of like a defective shopping cart castor). Check this article. Interesting article on tailwheel shimmy - Backcountry PilotInteresting article on tailwheel shimmy - Backcountry PilotThis interesting look at what actually causes tailwheel shimmy was written by Gilbert Pierce of Pierce Aero. Tail Wheel Shimmy I noticed when flying my Piper Clipper heavily loaded I experience tail wheel shimmy on my Scott 3200 when landing on a h Yes, I realize it would take some doing to change the angle of the tail wheel on these airplanes, but you never know what they have been through in previous lives - of which these planes have had many...Sent from Yahoo Mail on Android On Mon, Jul 8, 2019 at 10:04, ozzie@arearealestate.com [fairchildclub] wrote:
I know this has been answered many times. After setting the tail wheel down. violent shimmy. We have rebuilt with bushings. Please point me to previous suggestions

'

Richard Ellingworth · Post by **Richard Ellingworth** » Mon Jul 08, 2019 2:41 pm

'

I’ve been doing it for the last 7 years without a problem, solves the shimmy.

Sent from my iPhone

On 8 Jul 2019, at 21:05, 'Michael Denest' mjd12k@yahoo.com [fairchildclub] wrote:

Running the tire pressure in the tailwheel that low is not good, making it possible for the tire to slip on the wheel and shear the stem on the inner tube.

From:
fairchildclub@yahoogroups.com [fairchildclub@yahoogroups.com]

Sent: Monday, July 8, 2019 3:56 PM
To: fairchildclub@yahoogroups.com
Subject: Re: [fairchildclub] PT-23 Shimmy

Hi

I run my tyre pressure low as 25 psi, seems to solve it for me. If it does start it’s right at the end of the landing roll.

Cheers

Sent from my iPhone

On 8 Jul 2019, at 20:32, Thomas Rood tdrood@yahoo.com [fairchildclub] wrote:

Definitely check cable tension. Also check for anything bent back there, if the pivot axis is not tipped sufficiently aft at the top, it will shake violently (kind of like a defective shopping cart castor). Check this article. Interesting
article on tailwheel shimmy - Backcountry Pilot

Interesting article on tailwheel shimmy - Backcountry Pilot
This interesting look at what actually causes tailwheel shimmy was written by Gilbert Pierce of Pierce Aero. Tail Wheel Shimmy I noticed when flying my Piper Clipper heavily loaded I experience
tail wheel shimmy on my Scott 3200 when landing on a h

Yes, I realize it would take some doing to change the angle of the tail wheel on these airplanes, but you never know what they have been through in previous lives - of which these planes have had many...

Sent from Yahoo Mail on Android

On Mon, Jul 8, 2019 at 10:04,
ozzie@arearealestate.com [fairchildclub]

wrote:

I know this has been answered many times. After setting the tail wheel down. violent shimmy. We have rebuilt with bushings. Please point me to previous suggestions

'

tonylowe2 · Post by **tonylowe2** » Mon Jul 08, 2019 4:22 pm

'Isn’t the answer to make sure, 1) there aren’t any worn parts with excessive play, 2) make sure tailwheel geometry is right – plenty of trail – that is the distance from where the pivot axis touches the ground to where the wheel touches the ground – more trail is better, and finally 3) keep the weight off the tailwheel as much as possible, and especially at speed – that means learn to wheel-land the airplane – keep the tail wheel off as long as possible on rollout. Question – are you having tailwheel shimmy on takeoff or just on landing? The answer tells you something. Very few complain of shimmy on takeoff, or even during fairly rapid taxi. Shimmy starts when tailwheels meet the ground with some force and with quite a bit of speed over the ground. Once started, it isn’t going to stop unless almost all the load is removed, or unless there is a major geometry change, which is not likely. Normally, trail decreases with tailwheel deflection. Set that tail down easy.

From: fairchildclub@yahoogroups.com
Sent: Monday, July 8, 2019 11:28 AM
To: ozzie@arearealestate.com [fairchildclub]
Subject: Re: [fairchildclub] PT-23 Shimmy

To tell you the truth, I don't know of a fix. My only guess is that somewhere down the line that you had someone put the fork from a F-24 on your tail wheel strut. I really don't know of a 24 that hasn't had a shimmy problem. One possible cure that I know of, is to not lubricate the bottom of the strut. Keep it dry, which would add friction to the bottom end. That is what my 24's previous owner did. But of your motor leaks a fair amount of oil, that may be hard to do. You also have an oval tire? That won't help the problem. I have a bit of film footage, from 40 years ago, and it was a local Iowa guy landing on grass. His tail wheel was swinging at least 60 deg. from side to side. He had an oval profile tire. I did use a square shoulder tire on my 24, and it worked well. I don't know what kind of a problem that would cause on a Pt. The only guess that I would have is to put friction in the collar at the bottom of the strut. Another thing that I heard from many years ago, was the owner increase the angle of the fork. Just thinking about that gave me a headache. You can do much of anything with the fork casting, but he may have done something with the bottom end of the strut. Bottom line, I think that most will say that is the nature of the beast...…..Just live with it.

Boy.... I am a lot of help. The last PT that I was in didn't have working brakes, the tail wheel strut was complete worn out. The top end moved but the bottom didn't. That PT was completely reworked and is back flying this spring. Within a year after my ride, it made a forced landing on a highway and it was force off the ride by an oncoming driver. the Right main strut bottom end failed and tore up and across the center section. The cause for that was Magneto issues.

Good Luck. I would send a photo of my project, but it would only get scrambled

Bob

On ?Monday?, ?July? ?8?, ?2019? ?07?:?04?:?06? ?AM? ?PDT, ozzie@arearealestate.com [fairchildclub] wrote:

I know this has been answered many times. After setting the tail wheel down. violent shimmy. We have rebuilt with bushings. Please point me to previous suggestions

[Non-text portions of this message have been removed]

'

dave@hadfield.ca · Post by **dave@hadfield.ca** » Mon Jul 08, 2019 5:05 pm

'On the 24 you can take off the bronze collar and make it slightly smaller. Then it grips the post harder, which doesn't shimmy.
Jack up the tail, take off the collar by undoing the 2 bolts, clean them, then lay the mating surfaces on a piece of very fine sandpaper, and take off an educated 2-thou or so. Then clean and reassemble.
It's not a perfect fix. It's better to reduce play throughout the system. But it'll get you through a season, costs nothing, and takes :20 min.
The PT-19/26 does not have that collar, I believe. Different arrangement.'

robert Etter · Post by **robert Etter** » Mon Jul 08, 2019 10:45 pm

' After all that probable crap that I sent earlier. I would assume that you have the strut that uses 2 splines. You can see a line of rivets running up the front and rear of the out strut shell. The splines that are riveted to the inside. If you jack the tail completely off the ground, you can see how much play between the inner strut (that which the fork is attached to) and the riveted splines. They are about 1/2" wide, they could be worn or loose and or the inner strut guides could be worn. The old cow that I once rode in, when I looked at the strut, the splines were gone. Some of the rivet part were still in the holes. Replacing the splines are fun. You must put the rivets from the inside to the outside. I used a large 1/2" socket to buck the rivets on the inside. It was a very snug fit. Flattened the rivet on the outside. This truthfully, is just about most all that I remember. I know that there were multi spline struts out there. I never took it apart, so the guts are an unknown. I did make a parts break down of the 2 spline strut. I don't know how it compared to what may be on a CD. I know that the only time that I had a problem with the 24's tail wheel was when the pressure got low. The tire went flat, the tire spun on the wheel and popped the stem off. I would say, jack the back end up off the ground, and see if you can find something that wiggles to much. I would think with the torque tube steering, when the tail wheel wiggled, the rudder peddles should be trying to beat up your feet. If the splines are your problem, I think that I may still have a pair of OE splines. Rivets, I don't think that they were anything special. Anyway, most everything wears out after 70+ years.My 24 is virtually brand new. I reused only 7 minor pieces of wood. I guess that I did something unusual, I covered each side, top and bottom of the horizontal, with single pieces of 1/16" plywood. The last bay has a compound curve, it sure turned out pretty. I have about a hard month of work and she is flyable. My body isn't cooperating.
Good Luck Hope this is more help than what I sent earlier.Bob

On ?Monday?, ?July? ?8?, ?2019? ?04?:?09?:?29? ?PM? ?PDT, dave@hadfield.ca [fairchildclub] wrote:

On the 24 you can take off the bronze collar and make it slightly smaller. Then it grips the post harder, which doesn't shimmy.
Jack up the tail, take off the collar by undoing the 2 bolts, clean them, then lay the mating surfaces on a piece of very fine sandpaper, and take off an educated 2-thou or so. Then clean and reassemble.
It's not a perfect fix. It's better to reduce play throughout the system. But it'll get you through a season, costs nothing, and takes :20 min.
The PT-19/26 does not have that collar, I believe. 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