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1. 07:25 AM - Re: Re: Wheel shimmy - solutions? (Bernard Melendez, Jr.)
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Subject: | Re: Wheel shimmy - solutions? |
Hi Selwyn and Clive,
Not trying to throw gasoline on the fire, but from my experience in tail wh
eel aircraft, and from general consensus and information I've read on the s
ubject, toe in is preferred. The reason is, is that toe out tends to make t
he plane wander from the center line. And from looking at the geometry of t
he Lightning landing gear, that is, trailing back (like the RV's), not stra
ight out to the sides, it would appear to me, and it makes sense that as th
e aircraft is loaded (as in landing and on roll out), the little bit of toe
in built onto the airframe when empty would cause the wheels to toe out, h
opefully parallel to the airplane center line, or thereabouts.
The REAL question in my mind, is how much toe in to build in when the wingl
ess (light weight) fuselage is in your shop so that the desired results are
achieved when the plane is finished and loaded. I'm planning to build in 1
or 2 degrees of toe IN on my plane when I get to that stage in my build.
On my Corby Starlet, the wheels are set at 1degree toe in, and it tracks st
raight. But the landing gear is vertical to the ground when the plane is in
a landing, or take off position, with the tail wheel off the ground. That
way, when my plane is loaded, the gear splays out, but the tracking does no
t change. Matter of fact, most tail wheel planes have a little toe in built
in.
The geometry of the landing gear when the rubber hits the road is what is i
mportant. I believe that wheel shimmy is caused by the wheels trying to go
in a different direction than the plane is going, and their propensity to g
rab, and then let go of the contact surface.
As stated, I'm not trying to confound the issue, and everyone is free to ch
oose their poison, but I'm pretty clear on how I will do mine.
Regards,
Bernardo Melendez, Kit # 110
--- On Mon, 1/24/11, James, Clive R <clive.james@uk.bp.com> wrote:
From: James, Clive R <clive.james@uk.bp.com>
Subject: RE: Lightning-List: Re: Wheel shimmy - solutions?
om>
Hi Selwyn, I haven't had any shimmy on the Esqual since I reset it and
before nothing that would worry me it was more as I thought the tyres
would wear.
However, I did wrestle with alignment on the Esqual after my Jabiru,
which was very carefully set as required, wore it's tyres out in 150
hrs.
I reset the toe after 5 years (3 sets of tyres) with the plane fully
fuelled but empty.
Initially when rolling the Esqual over a painted hangar floor it
squeaked.
I rolled it over some newspaper and the twist showed it was toed out. I
believe the recommended set was 2 degrees in? I obviously got it wrong
or...
Staring at the thing it looks to me like the aircraft would toe out the
heavier it got. This from the angle of the legs (same as the Jab).
I'd set the toe before it had the wings + engine on and was loaded.
So I did it again full of fuel and with barrels or water in the seats to
simulate 1 pilot.
I set it as straight as I could get it, not in or out.
Now it doesn't squeak.
My thoughts on the shimmy.
If it's out of toe when rolling surely the wheels will try and get
further apart (toed out), further together (toed in).
When the wheel rotates the rubber will flex and then release,- flex then
release, as it tries to steer the leg away from it opposite side leg (or
towards it-toed in). Ideal to set up a shimmy?
So my vote goes for parallel at middle weight which is why I did what I
did.
This at the risk of doing the subject to death a little more....sorry.
My question is? How are people repeatedly changing the tracking? Surely
you only get one shot and then you drill the holes, after they are
drilled how do you make adjustments?
Regards, Clive
-----Original Message-----
From: owner-lightning-list-server@matronics.com
[mailto:owner-lightning-list-server@matronics.com] On Behalf Of selwyn
Sent: 24 January 2011 06:59
Subject: Lightning-List: Re: Wheel shimmy - solutions?
--> <selwyn@ellisworks.com.au>
Hi Guys,
I didn't want to get into a debate about the merits of one or the other,
that's been done to death already.- I simply want to gather some data.
Is there anyone who has had significant shimmy problems with definite
toe out set?
--------
Cheers,- Selwyn
Kit 66
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