From: JOSCALES@aol.com
Message-ID: <82.50d9420.2784beb2@aol.com>
Date: Wed, 3 Jan 2001 12:43:14 EST
Subject: Yaw oscillation
To: charliesiv@yahoo.com, lancair.list@olsusa.com, lancen@lancair.com,
        penneysam@msn.com, orinr@lancair.com, KayLueck@aol.com
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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Guys,

I have a problem with my Super ES that I have not been able to solve.  
Hopefully, one or all of you can enlighten me and send me in the right 
direction. 

Background:  I have been flying the plane for just over a year and have about 
150 hours on it.  Previous to the last 10 hours or so, it has not had any 
handling or flying problems.  With the exception of adding gap seals to 
ailerons, elevator and rudder and moving my datalink antenna from inside the 
fuselage to the underside, I have made no changes in the exterior of the 
plane.

Problem:  The plane has developed an irregular yaw oscillation at high cruise 
speed.  The oscillation is different from ones I have felt in certified 
airplanes.  It doesn't move very much (estimate the tail to move 2-3" total, 
side to side) but is very noticeable and seems to be speed sensitive.  The 
difference from other experiences is its irregularity (frequency changes 
practically on every cycle) and the way it feels.  Other airplanes that I 
have flown yaw like a pendulum swinging, with the movement going to one side 
and slowing to a stop then reversing and moving to the other side and slowing 
to a stop before repeating the process.  This movement has always been on a 
fairly regular frequency.

The yaw I am experiencing, as I said, is irregular.  It also feels as though 
different things are happening at each end of the yaw cycle.  When it (the 
tail) moves to the right, it seems to slow to a stop and reverse as in the 
other yaw description.  When the tail moves to the left it seems as if it 
"bumps" to a stop (sorry, but that's the best description I can give) then 
reverses.  When I try to visualize the problem, it feels as if there is 
something changing or moving at the end of the movement to the left that 
causes the tail to start back the other way.  The difference in the way the 
plane acts on each end of the cycle is able to be felt in the pilot seat.

I have flown the plane with various CG's and find no difference.  I have 
tried different weights, from gross to 700 under gross, still no difference.  
Speed makes a difference.  Cruising at 190 kts or greater the yaw is bad. 
High speed descent in the 200 range is worse. Slowing to 180 or so greatly 
reduces the feel.  It disappears completely below about 165-170.

I have tried other things to stop the yaw.  Holding constant pressure on both 
rudder pedals at the same time (in effect, locking the rudder in place) made 
no difference.  Trimming excess rudder (severe skid) seemed to reduce it.  
Yaw problem didn't change between auto pilot and manual flying.  I discovered 
I could stop it by anticipating the movement and tapping the rudder pedals as 
needed.  This didn't work very well, though, because of the irregularity of 
the cycles and I found myself causing a new yaw oscillation to go with the 
one I already had.

The yaw is not noticeable in greater than standard rate turns but is felt in 
turns less than standard rate.

What I have done:  I have thoroughly inspected all gap seals, control 
surfaces, hinge bolts, trim tabs, wheel pants, nose gear, rudder cables, 
rudder hinges and cable attachment brackets.  I have checked for any thing 
that might be moving or rolling around in the fuselage.  I have looked at 
inspection panels, doors and anything else that might be loose and moving in 
response to change in air pressure.  I have inspected the engine and prop 
and, though I found engine mount firewall attachment bolts to be less than 
fully torqued, I could see no sign of movement.  Engine mounting bolts are 
fine.  I have not yet set the plane on jacks to check if anything in the main 
gear could be moving.

I am baffled and concerned.  I am beginning the annual even though it is not 
yet due.  I could certainly use some input.  I will check out any and all 
suggestions.  If any of you has questions or would like some further 
description of the problem in order to form an opinion, I would welcome your 
phone call at 812-853-9800.

Thanks in advance for your help.

Jim Scales 98AF  
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