On Jul 13, 7:47*pm, Eric Greenwell wrote:
I don't recall ever seeing an estimate of the performance loss in a
glider as a function of yaw string deflection. Does anyone know what it is?


Actually I have pondered this quite a bit. My ASW 28 has a very
annoying loud noise after being cold soaked at altitude and if flown
at greater than 90 kts. I found that slight rudder pedal pressure in
either direction would kill the noise. The higher the speed the more
pedal input is needed required and the greater the yaw string
deflection.

I have long suspected that the noise came from the rudder fairing
mylar strips. On the 28 the mylars attach to the fins skins aft of
the the fin rear spar. The skins are much thinner at the top of the
fin than in the same area of the ASW 27 and ASG 29 and on my glider
have warped outward so that there is a slight gap between the mylars
and the rudder at the top of the mylar strips. The area of warping is
above the upper rudder hinge.

I did an experiment that seems to confirm the noise is caused by a
mylar seal resonance. I attached an additional mylar seal as an
extension of the width of the existing seal and at the top 6 inches or
so on each side. The additional width and the curvature keeps the
strips in contact over full rudder deflection whereas before there was
seal separation even with the rudder centered. I found that the noise
frequency was reduced and the onset airspeed was increased.

Until I find out why the 28 uses thinner skins, and get a factory
appoval to stiffen this area, I'll have to keep flying sideways or
wear earplugs. So I need the yaw string calibration chart.

Andy
28048