[rebel-builders] Bloody Rotten Tailwheel Shimy !!! :o(

Ken · Post by **Ken** » Sun Feb 19, 2012 11:52 am

FWIW Rick

I run MAM's solid tailwheel with no damping in the pivot.
2 leaf steel spring
pivot angle is vertical without the plane loaded and it tilts very
slightly (top of pivot forward) when at gross weight.
I have never (knock on wood...) had a hint of shimmy so far as I come up
to 60 hours and about 160 landings
steering springs are screen door compression type and they are slightly
loose

Don't forget that a badly out of balance wheel will shimmy no matter
what you do....
A scalloped tire wouldn't help either.

Ken

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Bob Patterson · Post by **Bob Patterson** » Sun Feb 19, 2012 11:52 am

Hi Rick !

I went through this a few years ago with our Scott 3200 - I did
find an exploded view of the whole assembly somewhere on the net ...
it could be that your damping washers are badly worn & need
replacement .... 45 - 50 lb. pressure sounds about right.
If you put a foot on top of the tire & push down, you should
get just a small bulge at the bottom - enough to show that
the tire is 'giving' a bit - for cushioning.

Tightening that big nut on the bottom should do it. Many say
the pivot bolt should be vertical - our is, or slightly tilted rearward
at the bottom when really loaded.

Scott were very specific that you MUST use their TENSION
springs, (NOT compression springs) and there must be NO
slack in the chains. Ours have a very little bit of slack ...
maybe less that 1/4" sag ...
Tightening the nut solved the shimmy - so maybe you have
something worn out in there. Also ... avoid too much grease !

Personally, I avoid steel springs - years of bad experiences !
Maybe 2 leaves wouldn't bounce so much, and might let the
pivot get to vertical.

--
......bobp
http://www.prosumers.ca
http://bpatterson.qhealthbeauty.com
http://apatterson2.qhealthzone.com

-------------------------------orig.-------------------------
On Sunday 25 February 2007 23:54, Rick Harper wrote:

G'day All ....

H...E....L....P..... !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The plane is going GREAT again !!!

BUT .........................................

The tailwheel is driving me NUTS - with shimmy :o(

Please note :

I currently have about 50ish Lbs PSI in the tyre ...
The pivot bolt is angled BACKWARDS by about 10 degrees at the top
AND ... it is done up about as tight as I dare do it !
(but - there is little or no damping / friction within the pivoting motion)
My connecting springs & chains are "loosish"
I have different spring strengths on either side
I have a 2" wide , 3 leaf STEEL tailspring

Could I possibly get you guys 'n' gals (I assume here that we DO actually

HAVE "some girl builders" ?!?) .... to tell me a few HOW & WHYS with YOUR
tailwheel setups :

( BTW - I am running a SCOTT 3400 tailwheel - 10" dia' pneumatic tyre)

1) What Tyre pressure do you use ? ....................

2) What angle is the pivot pin for the yoke

at ? ...........................................

... (this is the vertical axis pin / bolt, that holds the wheel yoke to

the body of the Tailwheel assembly - around which the yoke & wheel
pivot) ... (I need to know whether your pin is dead vertical, leaning
forward at the top (and how many degrees if so ? .......... ) or leaning
backwards at the top (and how many degrees if so ? .... )

3) Do you have the connecting springs & chains to the rudder arms
TIGHT or LOOSE ? ............................................
(if they are LOOSE - the HOW loose are

they ? ...................................... )

4) Do you use different spring strengths on either

side ? ...............................

(if so, what sort of difference in strength is

there ? ...................................

5) ANY other tips or points of interest that I should be looking out

for ? ......

Many Thanks Everyone !

Rick "Biggus" Harper
541R "Flying again"

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Drew Dalgleish · Post by **Drew Dalgleish** » Sun Feb 19, 2012 11:52 am

Hi Rick is it possible that your tire has developed a flat spot after not
moving for several months with low pressure?

At 10:54 AM 2/26/2007 +1100, you wrote:

G'day All ....

H...E....L....P..... !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The plane is going GREAT again !!!

BUT .........................................

The tailwheel is driving me NUTS - with shimmy :o(

Please note :

I currently have about 50ish Lbs PSI in the tyre ...
The pivot bolt is angled BACKWARDS by about 10 degrees at the top
AND ... it is done up about as tight as I dare do it !
(but - there is little or no damping / friction within the pivoting motion)
My connecting springs & chains are "loosish"
I have different spring strengths on either side
I have a 2" wide , 3 leaf STEEL tailspring

Could I possibly get you guys 'n' gals (I assume here that we DO actually

HAVE "some girl builders" ?!?) .... to tell me a few HOW & WHYS with
YOUR tailwheel setups :

( BTW - I am running a SCOTT 3400 tailwheel - 10" dia' pneumatic tyre)

1) What Tyre pressure do you use ? ....................

2) What angle is the pivot pin for the yoke at ?

...........................................

... (this is the vertical axis pin / bolt, that holds the wheel yoke to

the body of the Tailwheel assembly - around which the yoke & wheel
pivot) ... (I need to know whether your pin is dead vertical,
leaning forward at the top (and how many degrees if so ?
.......... ) or leaning backwards at the top (and how many degrees
if so ? .... )

3) Do you have the connecting springs & chains to the rudder arms
TIGHT or LOOSE ? ............................................
(if they are LOOSE - the HOW loose are they ?

...................................... )

4) Do you use different spring strengths on either side ?

...............................

(if so, what sort of difference in strength is there ?

...................................

5) ANY other tips or points of interest that I should be looking out for

? ......

Many Thanks Everyone !

Rick "Biggus" Harper
541R "Flying again"

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Drew

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Rick Harper · Post by **Rick Harper** » Sun Feb 19, 2012 11:52 am

Thanks Ken ..... I haven't checked the balance of the wheel as yet !

Biggus
----- Original Message -----
From: Ken
To: rebel-builders@dcsol.com
Sent: Monday, February 26, 2007 11:56 AM
Subject: Re: [rebel-builders] Bloody Rotten Tailwheel Shimy !!! :o(

FWIW Rick

I run MAM's solid tailwheel with no damping in the pivot.
2 leaf steel spring
pivot angle is vertical without the plane loaded and it tilts very
slightly (top of pivot forward) when at gross weight.
I have never (knock on wood...) had a hint of shimmy so far as I come up
to 60 hours and about 160 landings
steering springs are screen door compression type and they are slightly
loose

Don't forget that a badly out of balance wheel will shimmy no matter
what you do....
A scalloped tire wouldn't help either.

Ken

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Rick Harper · Post by **Rick Harper** » Sun Feb 19, 2012 11:52 am

G'day Bob !

I replaced ALL the guts of the pivot mechanism when I rebuilt it .....
But I'll take it all apart & check those friction washers again ..
(I am guilty of regularly regreasing the pivot pin though ! :o(

I did NOT realise that SCOTT says to use tension spring either !

Thanks

Biggus
----- Original Message -----
From: Bob Patterson
To: rebel-builders@dcsol.com
Sent: Monday, February 26, 2007 12:38 PM
Subject: Re: [rebel-builders] Bloody Rotten Tailwheel Shimy !!! :o(

Hi Rick !

I went through this a few years ago with our Scott 3200 - I did
find an exploded view of the whole assembly somewhere on the net ...
it could be that your damping washers are badly worn & need
replacement .... 45 - 50 lb. pressure sounds about right.
If you put a foot on top of the tire & push down, you should
get just a small bulge at the bottom - enough to show that
the tire is 'giving' a bit - for cushioning.

Tightening that big nut on the bottom should do it. Many say
the pivot bolt should be vertical - our is, or slightly tilted rearward
at the bottom when really loaded.

Scott were very specific that you MUST use their TENSION
springs, (NOT compression springs) and there must be NO
slack in the chains. Ours have a very little bit of slack ...
maybe less that 1/4" sag ...
Tightening the nut solved the shimmy - so maybe you have
something worn out in there. Also ... avoid too much grease !

Personally, I avoid steel springs - years of bad experiences !
Maybe 2 leaves wouldn't bounce so much, and might let the
pivot get to vertical.

--
......bobp
http://www.prosumers.ca
http://bpatterson.qhealthbeauty.com
http://apatterson2.qhealthzone.com

-------------------------------orig.-------------------------
On Sunday 25 February 2007 23:54, Rick Harper wrote:

G'day All ....

H...E....L....P..... !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The plane is going GREAT again !!!

BUT .........................................

The tailwheel is driving me NUTS - with shimmy :o(

Please note :

I currently have about 50ish Lbs PSI in the tyre ...
The pivot bolt is angled BACKWARDS by about 10 degrees at the top
AND ... it is done up about as tight as I dare do it !
(but - there is little or no damping / friction within the pivoting motion)
My connecting springs & chains are "loosish"
I have different spring strengths on either side
I have a 2" wide , 3 leaf STEEL tailspring

Could I possibly get you guys 'n' gals (I assume here that we DO actually

HAVE "some girl builders" ?!?) .... to tell me a few HOW & WHYS with YOUR
tailwheel setups :

( BTW - I am running a SCOTT 3400 tailwheel - 10" dia' pneumatic tyre)

1) What Tyre pressure do you use ? ....................

2) What angle is the pivot pin for the yoke

at ? ...........................................

... (this is the vertical axis pin / bolt, that holds the wheel yoke to

the body of the Tailwheel assembly - around which the yoke & wheel
pivot) ... (I need to know whether your pin is dead vertical, leaning
forward at the top (and how many degrees if so ? .......... ) or leaning
backwards at the top (and how many degrees if so ? .... )

3) Do you have the connecting springs & chains to the rudder arms
TIGHT or LOOSE ? ............................................
(if they are LOOSE - the HOW loose are

they ? ...................................... )

4) Do you use different spring strengths on either

side ? ...............................

(if so, what sort of difference in strength is

there ? ...................................

5) ANY other tips or points of interest that I should be looking out

for ? ......

Many Thanks Everyone !

Rick "Biggus" Harper
541R "Flying again"

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Rick Harper · Post by **Rick Harper** » Sun Feb 19, 2012 11:52 am

G'day Ken ....

Nope,... the tailwheel doesn't have any flat spots ... but I haven't checked it's balance as yet .... so That is now on my list !

Thanks

Biggus
541R
----- Original Message -----
From: Drew Dalgleish
To: rebel-builders@dcsol.com
Sent: Monday, February 26, 2007 2:11 PM
Subject: Re: [rebel-builders] Bloody Rotten Tailwheel Shimy !!! :o(

Hi Rick is it possible that your tire has developed a flat spot after not
moving for several months with low pressure?

At 10:54 AM 2/26/2007 +1100, you wrote:

G'day All ....

H...E....L....P..... !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The plane is going GREAT again !!!

BUT .........................................

The tailwheel is driving me NUTS - with shimmy :o(

Please note :

I currently have about 50ish Lbs PSI in the tyre ...
The pivot bolt is angled BACKWARDS by about 10 degrees at the top
AND ... it is done up about as tight as I dare do it !
(but - there is little or no damping / friction within the pivoting motion)
My connecting springs & chains are "loosish"
I have different spring strengths on either side
I have a 2" wide , 3 leaf STEEL tailspring

Could I possibly get you guys 'n' gals (I assume here that we DO actually

HAVE "some girl builders" ?!?) .... to tell me a few HOW & WHYS with
YOUR tailwheel setups :

( BTW - I am running a SCOTT 3400 tailwheel - 10" dia' pneumatic tyre)

1) What Tyre pressure do you use ? ....................

2) What angle is the pivot pin for the yoke at ?

...........................................

... (this is the vertical axis pin / bolt, that holds the wheel yoke to

the body of the Tailwheel assembly - around which the yoke & wheel
pivot) ... (I need to know whether your pin is dead vertical,
leaning forward at the top (and how many degrees if so ?
.......... ) or leaning backwards at the top (and how many degrees
if so ? .... )

3) Do you have the connecting springs & chains to the rudder arms
TIGHT or LOOSE ? ............................................
(if they are LOOSE - the HOW loose are they ?

...................................... )

4) Do you use different spring strengths on either side ?

...............................

(if so, what sort of difference in strength is there ?

...................................

5) ANY other tips or points of interest that I should be looking out for

? ......

Many Thanks Everyone !

Rick "Biggus" Harper
541R "Flying again"

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Drew

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