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Nose wheel shimmy

 
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rickw(at)lifepointministr
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PostPosted: Tue Feb 28, 2006 7:37 pm    Post subject: Nose wheel shimmy Reply with quote

Hey all

I just purchased an AA5 N6542L with wheel pants and when I set the nose
wheel down on landing she shimmies and I have to pull it up as long as I can
then set it down. Is there a fix for this that some one may know about!!
hope for help
Rick


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GrummanDude



Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

PostPosted: Tue Feb 28, 2006 11:28 pm    Post subject: Nose wheel shimmy Reply with quote

two things to look at

1) with the nose off the ground, first spin the tire by hand. It should
spin no more than 1 revolution. That is, LESS than one revolution. If not,
tighten the axle bolt nuts (you'll need two 1/2 inch sockets/ratchets.)

2) try pushing the the nose gear wheel pant side to side. Push from
anywhere near the back of the wheel pant. Technically, you need to rig up a fish
scale, tighten (or loosen, as required) the nose fork bolt until you reach
somethin like 22 in-lbs (or was it ft-lbs?). THe truth is, there is nothing
magical about the fish scale. Google search Belville washers, do your own
research, whatever. What you need to do is compress the the washers roughly 75%.

As it turns out, there are many ways to install the washers. 22 fish-scales
will get you various amounts of compression depending on how you do the
washers.

Before you get started, take it all apart. Clean up everything. INSIDE
the nose fork, you need one thich and one thin thrust washer (two washers total)
A new "O" ring. Grease everthing with No. 22 Aeroshell grease. on the
OUTSIDE, I use one large area flat washer against the nose fork. You need to
protect the aluminum. Then, 4 Belville washers. Then, one small area
washer against the nut.

Like this. | <<>> | nut. Put a thin film of grease on these too. They
are steel and they will rust.

Assemble the washers and nut. Tighten until you fell the washers
compressing. They'll compress a lot. Push on the back of the wheel pant (as ytou
tighten) until you feel a fair amount of drag on the wheel pant. If you tighten
it all the way until the washers are compressed, just back off on the nut to
where 22 fish-scales are.

Gary


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AuCountry Aviation
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FLYaDIVE(at)aol.com
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PostPosted: Wed Mar 01, 2006 4:19 am    Post subject: Nose wheel shimmy Reply with quote

In a message dated 3/1/06 1:56:08 AM Eastern Standard Time,
rickw(at)lifepointministries.com writes:

Quote:
Hey all

I just purchased an AA5 N6542L with wheel pants and when I set the nose
wheel down on landing she shimmies and I have to pull it up as long as I
can

Quote:
then set it down. Is there a fix for this that some one may know about!!
hope for help
Rick
==============================

HMmmmmmm Sort of a built in ... This is the way you are spouse to land device!

Hey Rick, a couple three things:
1 - Any idea what your speed was during rollout?
Too high a speed when the nose wheel touches down sure can cause shimmy.
2 - Yes, Grumman's sure like keeping the nose wheel up, it is not only the
way you should land, but it sure LQQKs impressive
3 - Now, just in case, the nose wheel was not addressed during the annual
there is a maintenance procedure to properly set the nose wheel:
a> Jack up the plane - Simple method is to place a 2x6xwidth of plane right
at the firewall edge and use a hydraulic jack.
b> Put a clean piece of cardboard under the nose wheel. This is to catch any
parts that you will drop.
c> Slide the nose wheel pant up and out of the way. Good idea to tie it up
there.
d> Get a NEW cotter pin for the castle nut on the bottom of the nose fork.
e> Remove the castle nut and remove the nose fork.

Note: YES, there is a simpler method BUT you just said you were the new
owner and because of that YOU do not know the condition of the nose fork bearing
or the cupped washers.

f> Wash all the parts using Mineral - GAS is NOT a cleaner!
g> O! You do have the Maintenance Manual open and on the correct page? If
you do not have the correct page give a call to Fletcher Aviation
(1-800-329-4647, FAX: 713-649-6060) and request the Nose Wheel Washer Assembly Instructions.
h> Inspect the parts make sure you have ALL the proper parts and that they
are stacked in the proper order.
j> GREASE each and every washer ALL OVER.
k> CLEAN the nose wheel bearing and the nose strut spindle.
m> GREASE both these parts TOTALLY. The maintenance Manual has identifies
the proper grease to use. Though I prefer MOLY-GREASE for the washers.
n> Reassemble in the proper order.
p> Now you could have skipped all of the above and just done this step but
you would not know the condition of your nose wheel assembly ... With the nose
wheel straight, put a wrench on the castle nut, [DON'T USE VICE GRIPS OR
CHANNEL-LOCK] tighten the nut ... How much?
q> Until you develop a calibrated arm, you will need a simple spring scale,
like a fish scale. With the scale attached to the AXLE tighten the nut until
you have about 20 to 30 Lbs of drag as you try to pull the nose wheel off of
straight. Yea, Yea, Yea ... I know the manual says only 20 Lbs. But I have
found in more cases than not it does take as much as 30 Lbs. I attribute that to
either stronger or weaker cupped washers and internal bearing ware. Hey, IF
it works at 20 Lbs ... Go for it! BIG IF ! ! !
r> Align the castle nut with the cotter pin hole and install the cotter pin
.. NEW COTTER PIN. And the head of the pin faces forward.
s> Install the wheel pant.

Good idea to have a A&P look over your shoulder the first time you do this
and once trained have him sign off your log book as being trained. Oh, this is
also true for Oil Changes and Spark Plug Cleaning and Installations.

Go FLY but! Just because you did all the maintenance to stop the shimmy does
NOT mean you come in hot or drop the nose. After all, you are NOT a Cessna
pilot. You fly a Grumman! Wink

Barry
"Chop'd Liver"
PS
Good luck with your plane and welcome to the GG. Did you also join the AYA?


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david(at)carneyaviation.c
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PostPosted: Wed Mar 01, 2006 5:29 am    Post subject: Nose wheel shimmy Reply with quote

# when I set the nose wheel down on landing
# ...
# I have to pull it up as long as I can then set it down.

If you can pull the nose back up, you might want to consider not forcing the
nose wheel onto the ground at high speed.

Also check the tensions (Gary's answer).

This email has been scanned by the MessageLabs Email Security System.
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FLYaDIVE(at)AOL.COM
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PostPosted: Wed Mar 01, 2006 5:31 am    Post subject: Nose wheel shimmy Reply with quote

In a message dated 3/1/06 1:56:08 AM Eastern Standard Time,
rickw(at)lifepointministries.com writes:

Quote:
Hey all

I just purchased an AA5 N6542L with wheel pants and when I set the nose
wheel down on landing she shimmies and I have to pull it up as long as I
can

Quote:
then set it down. Is there a fix for this that some one may know about!!
hope for help
Rick
==============================

HMmmmmmm Sort of a built in ... This is the way you are spouse to land device!

Hey Rick, a couple three things:
1 - Any idea what your speed was during rollout?
Too high a speed when the nose wheel touches down sure can cause shimmy.
2 - Yes, Grumman's sure like keeping the nose wheel up, it is not only the
way you should land, but it sure LQQKs impressive
3 - Now, just in case, the nose wheel was not addressed during the annual
there is a maintenance procedure to properly set the nose wheel:
a> Jack up the plane - Simple method is to place a 2x6xwidth of plane right
at the firewall edge and use a hydraulic jack.
b> Put a clean piece of cardboard under the nose wheel. This is to catch any
parts that you will drop.
c> Slide the nose wheel pant up and out of the way. Good idea to tie it up
there.
d> Get a NEW cotter pin for the castle nut on the bottom of the nose fork.
e> Remove the castle nut and remove the nose fork.

Note: YES, there is a simpler method BUT you just said you were the new
owner and because of that YOU do not know the condition of the nose fork bearing
or the cupped washers.

f> Wash all the parts using Mineral - GAS is NOT a cleaner!
g> O! You do have the Maintenance Manual open and on the correct page? If
you do not have the correct page give a call to Fletcher Aviation
(1-800-329-4647, FAX: 713-649-6060) and request the Nose Wheel Washer Assembly Instructions.
h> Inspect the parts make sure you have ALL the proper parts and that they
are stacked in the proper order.
j> GREASE each and every washer ALL OVER.
k> CLEAN the nose wheel bearing and the nose strut spindle.
m> GREASE both these parts TOTALLY. The maintenance Manual has identifies
the proper grease to use. Though I prefer MOLY-GREASE for the washers.
n> Reassemble in the proper order.
p> Now you could have skipped all of the above and just done this step but
you would not know the condition of your nose wheel assembly ... With the nose
wheel straight, put a wrench on the castle nut, [DON'T USE VICE GRIPS OR
CHANNEL-LOCK] tighten the nut ... How much?
q> Until you develop a calibrated arm, you will need a simple spring scale,
like a fish scale. With the scale attached to the AXLE tighten the nut until
you have about 20 to 30 Lbs of drag as you try to pull the nose wheel off of
straight. Yea, Yea, Yea ... I know the manual says only 20 Lbs. But I have
found in more cases than not it does take as much as 30 Lbs. I attribute that to
either stronger or weaker cupped washers and internal bearing ware. Hey, IF
it works at 20 Lbs ... Go for it! BIG IF ! ! !
r> Align the castle nut with the cotter pin hole and install the cotter pin
.. NEW COTTER PIN. And the head of the pin faces forward.
s> Install the wheel pant.

Good idea to have a A&P look over your shoulder the first time you do this
and once trained have him sign off your log book as being trained. Oh, this is
also true for Oil Changes and Spark Plug Cleaning and Installations.

Go FLY but! Just because you did all the maintenance to stop the shimmy does
NOT mean you come in hot or drop the nose. After all, you are NOT a Cessna
pilot. You fly a Grumman! Wink

Barry
"Chop'd Liver"
PS
Good luck with your plane and welcome to the TG & GG. Did you also join the
AYA?


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flyv35b(at)ashcreekwirele
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PostPosted: Wed Mar 01, 2006 5:56 am    Post subject: Nose wheel shimmy Reply with quote

In addition to Gary's comments, the manual says 10-22 lb pull sideways
(perpendicular to the longitudinal axis of the nose fairing or fork) at the
axle centerline. 10 lb is to low and will almost always shimmy. 20-25 lb.
is a good range to shoot for. Even there the Belville washers are nearly
totally compressed where the spring rate is drastically changing, which
makes it hard to adjust with the limitation of the two cross-drilled holes
for the cotter key. If problems still persist there is probably a problem
with the tire and/or tire pressure. The tire may be worn abnormally from
past shimmying and have to be replaced.

Cliff
---


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BDDenham(at)lasd.org
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PostPosted: Wed Mar 01, 2006 7:49 am    Post subject: Nose wheel shimmy Reply with quote

It's common to find the washers are not installed properly. Make sure you
check that.

Bob

--


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gilalex(at)earthlink.net
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PostPosted: Wed Mar 01, 2006 9:57 pm    Post subject: Nose wheel shimmy Reply with quote

A picture is here that shows the washer layout much better than the manuals....

http://www.sbw.org/nosestrut/

gil in Tucson
At 08:48 AM 3/1/2006, you wrote:
Quote:


It's common to find the washers are not installed properly. Make sure you
check that.

Bob


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