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Tim Olson
Joined: 25 Jan 2007
Posts: 2872
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 Posted: Tue Oct 16, 2007 7:53 am Post subject: Shimmy comments |
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I've been wanting to wait a bit and write up a little on tire
balancing and such, because my tires are not at all balanced
and I want to see how much better things gets once they are.
But, I did have a curve to throw into the wheel shimmy thing
we hear about with the RV-10.
First, its ESSENTIAL that you take your nosewheel and re-torque
the axle bolt and the large fork to gear leg nut on the nosewheel
once you hit 40-75 hours. You will find that the required 26lbs of
breakout force has dropped to almost nothing on that large nut.
This will cause a lot of extra shake. Remember that Anh tightened
his 3 full flats to get it back to spec. You will prevent a lot
of problems by using the new nosewheel spacers, and keeping
everything tight for the first 100 hours or more.
But, the curveball is, I think a lot of people who are feeling
shimmy are mis-diagnosing it. I was once told by John that my
main gear was where he saw the shimmy when I taxied. I believed
him, but I also know I feel some in the nose as well. Keep in mind
that none of the tires are balanced yet, and my mains are now
in the process of wearing the outer tread on the opposite side
of the tire.
Well, this weekend I had shimmy on landing and I decided to hold
the nosewheel ALL the way off the ground as I had a perfect CG
balance to do it with, having baggage and rear passengers.
What I found was that I felt my normal shimmy on landing at
35-40kts, but I only had the mains on the ground. Don't ask
me why, just yet, but I can tell you without a doubt that some
of the shimmy people are complaining about is main gear
shimmy, not nose. It may be a while but I'll report back once
I've balanced my tires, and I'll also report back next spring
once I've swapped in new tires and balanced them.
--
Tim Olson - RV-10 N104CD - Flying
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wvu(at)ameritel.net
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| Posted: Tue Oct 16, 2007 7:06 pm Post subject: Shimmy comments |
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Tim,
I should also mention, which I forgot before, that by tightening the the
large fork to nose gear leg nut it took care of 80% of the need for right
rudder input during cruise. At the end before tightening this nut I had to
give so much right rudder that my foot got tired. Once a gust of wind hit
during cruise I went from right rudder input to left rudder input to center
the ball. After tightening only resting my foot on the pedal was required.
Probably 3-5lbs at most. I decided that rudder trim is not even necessary.
Anh
N591VU - 102 hours
---
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billderou(at)yahoo.com
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| Posted: Wed Oct 17, 2007 8:23 am Post subject: Shimmy comments |
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I have also been very suspicious that the nose wheel is creating the need for rudder trim. Just yesterday I removed the fairing and tightened the big nut. With the fairing off took the plane for a test flight and now it needed left trim instead of right trim. Shook it back and forth with rudder deflection and it centered the ball with feet on the floor.
Apparently too loose is bad and too tight is bad. Has anyone considered adding a fin to the nose wheel fairing, much like the Piper Archer, that would de-sensitize the big nut torque?
I am having difficulty understanding why too loose is a problem. This is what is holding me up from adding the fin.
Bill DeRouchey
N939SB, flying
DejaVu <wvu(at)ameritel.net> wrote:
[quote]--> RV10-List message posted by: "DejaVu"
Tim,
I should also mention, which I forgot before, that by tightening the the
large fork to nose gear leg nut it took care of 80% of the need for right
rudder input during cruise. At the end before tightening this nut I had to
give so much right rudder that my foot got tired. Once a gust of wind hit
during cruise I went from right rudder input to left rudder input to center
the ball. After tightening only resting my foot on the pedal was required.
Probably 3-5lbs at most. I decided that rudder trim is not even necessary.
Anh
N591VU - 102 hours
---
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pitts_pilot(at)bellsouth.
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| Posted: Wed Oct 17, 2007 10:36 am Post subject: Shimmy comments |
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Bill DeRouchey wrote:
| Quote: | I have also been very suspicious that the nose wheel is creating the
need for rudder trim.
|
Very well could be.
| Quote: | Just yesterday I removed the fairing and tightened the big nut. With
the fairing off took the plane for a test flight and now it needed
left trim instead of right trim. Shook it back and forth with rudder
deflection and it centered the ball with feet on the floor.
|
Seems like it worked .... at least for the tirm problem.
| Quote: | Apparently too loose is bad and too tight is bad.
|
Didn't know that too tight was bad except when you're trying to park the
airplane without the help of a towbar. 
| Quote: | Has anyone considered adding a fin to the nose wheel fairing, much
like the Piper Archer, that would de-sensitize the big nut torque?
|
It would work to 'straighten' out the nose gear.
| Quote: | I am having difficulty understanding why too loose is a problem. This
is what is holding me up from adding the fin.
|
Too loose generally causes shimmy of the nosewheel on landing. I've
been a Grumman (AA-1B) owner for 35 years, and they have the same
problems with the castering nosewheel and shimmy. This shimmy is the
side/side motion as opposed to a balance problem which is an up/down
motion. The Grumman nose gear has a stack of belleville washers
(they're cupped, not flat) that causes more drag as the big nut is
tightened. The Grumman maintenance book says to apply 25 Lbs of force
sideways at the wheel axle and if it doesn't move, it's tight enough.
That 25 Lvs appears to be a minimum, and 28 to 30 is better.
Since I haven't seen my nosegear yet, I haven't got a clue as to it's
assembly ..... but you can bet I'll use my Grumman experience to get it
right.
I also think some of the ground 'vibrations' are caused by the mains
'walking' fore/aft while taxiing. I've given much thought to replacing
the std. main gear with a spring aluminum gear, but will probably end up
with the std -10 gear. However, by the time I get there, there will be
a whole lot of operational info out there that might cause me to revisit
the idea.
Linn
| Quote: |
Bill DeRouchey
N939SB, flying
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Tim Olson
Joined: 25 Jan 2007
Posts: 2872
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| Posted: Wed Oct 17, 2007 12:09 pm Post subject: Shimmy comments |
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Linn,
You're Grumman is almost identical in setup to the RV-10 on the
nose gear. Same washer type, same torque ranges...everything.
As for the mains, you're accurate there too...it's a fore
and aft walking vibration. I don't think that particular
vibration is as common as the shimmy though, but it is
one of those things people will experience. What remains
to be seen is if that walking can be eased by proper inflation
and good balance, or not, because it's related to the
wheel angle or toe. Either way, I don't think the mains
have any problem large enough to be worth spending a lot of
worry on. I know I need to check my pressure again now that
it's cooling off, but that'll be about it for the mains.
(other than balance)
Tim Olson - RV-10 N104CD - Flying
do not archive
linn Walters wrote:
| Quote: |
Bill DeRouchey wrote:
> I have also been very suspicious that the nose wheel is creating the
> need for rudder trim.
Very well could be.
> Just yesterday I removed the fairing and tightened the big nut. With
> the fairing off took the plane for a test flight and now it needed
> left trim instead of right trim. Shook it back and forth with rudder
> deflection and it centered the ball with feet on the floor.
Seems like it worked .... at least for the tirm problem.
> Apparently too loose is bad and too tight is bad.
Didn't know that too tight was bad except when you're trying to park the
airplane without the help of a towbar.
> Has anyone considered adding a fin to the nose wheel fairing, much
> like the Piper Archer, that would de-sensitize the big nut torque?
It would work to 'straighten' out the nose gear.
> I am having difficulty understanding why too loose is a problem. This
> is what is holding me up from adding the fin.
Too loose generally causes shimmy of the nosewheel on landing. I've
been a Grumman (AA-1B) owner for 35 years, and they have the same
problems with the castering nosewheel and shimmy. This shimmy is the
side/side motion as opposed to a balance problem which is an up/down
motion. The Grumman nose gear has a stack of belleville washers
(they're cupped, not flat) that causes more drag as the big nut is
tightened. The Grumman maintenance book says to apply 25 Lbs of force
sideways at the wheel axle and if it doesn't move, it's tight enough.
That 25 Lvs appears to be a minimum, and 28 to 30 is better.
Since I haven't seen my nosegear yet, I haven't got a clue as to it's
assembly ..... but you can bet I'll use my Grumman experience to get it
right.
I also think some of the ground 'vibrations' are caused by the mains
'walking' fore/aft while taxiing. I've given much thought to replacing
the std. main gear with a spring aluminum gear, but will probably end up
with the std -10 gear. However, by the time I get there, there will be
a whole lot of operational info out there that might cause me to revisit
the idea.
Linn
>
> Bill DeRouchey
> N939SB, flying
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acs(at)acspropeller.com.a
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