Replacing the MKIV yaw string - tips

On Dec 1, 5:24*pm, Martin Gregorie
wrote:
On Sat, 01 Dec 2012 14:29:59 -0800, Mike Mike Ground wrote:
The MKIV is clearly the pinnacle of yaw string technology.
Meticulously crafted, it looks great on my glider. * *However, it
suffers from the same problem I have noticed on all yaw strings I have
flown. * *In flight, it constantly swings off the centerline 10, 20,
sometimes even 30 degrees, particularly while thermalling. * What’s up
with that?

How careful were you to place it on the center-line?

The tighter the curvature of your canopy near the centre line the more
critical yaw string placement is. For instance I think that, on a
Libelle, you need to place it within 5mm (1/4") or better of the exact
centre line, but probably canopies that aren't so sharply curved near the
centre line would make the string placement less critical. I stretched a
thread from the exact top of the fin down to the nose and took a lot of
care that both ends were correctly placed and that it wasn't deflected by
the top of the canopy before marking that line and fitting the yaw
string.

By contrast, I suspect that aligning the axis of symmetry of the
transparent sticky bit with the glider's centre line is more important
for aesthetics than for the yaw string's operation. In any case, by using
pencil marks on masking tape placed before and behind the sticky bit and
taking care, you should be able to align it well enough that errors can't
be seen once the masking tap and thread are removed.

You say the string is often deflected to one side: of course, it should
be tail out in a properly flown thermal turn and dead straight when you
cruise straight between thermals.

If it doesn't do that, it might be that:

1) its mounted off to one side. Check with a thin line as I did to see
* *if its not accurately on the centre line.

2) you've picked up the habit of flying sideways.

Either could make it hang consistently to one side. Either way you need
to work out what's causing it and correct the problem.

--
martin@ * | Martin Gregorie
gregorie. | Essex, UK
org * * * |

I carefully leveled Uniform Fox, then used a laser level to 'draw' a
line perfectly centered line on the fuselage from the nose to the TE
probe on the tail. I'm quite certain I netted a 10% performance gain
with the MkIV.