Clear Yaw string tape?

I've always felt (but have no evidence) that positioning a yaw string on
the canopy is not optimal, and that you really want it in clean,
undisturbed, air (yeah, like the 2-33). There could be 2 problems with
the canopy mount. One, it is flush with a compound curve surface and who
knows that the air is doing there. Two, it is in the boundary layer
between the canopy surface and the airflow and who knows that the air is
doing there.

I wonder if any one has experimented with a "normally" mounted yaw
string and one placed on a post several cm higher.

Tony V.

Yep, done that. The string on the canopy surface is about twice as
sensitive to yaw angles as the one on a one inch tall post. In other words,
the string on the canopy surface 'over-indicates' by about 2:1. I think
that's a good thing.

As another poster noted, getting the string placed exactly on the centerline
is the key. I've found that tailors cloth measuring tape is useful for
making those measurements since it won't scratch the canopy.

Despite the aversion expressed to drilling a hole for the yaw string, that
approach has some advantages.
1. It is a very 'clean' attachment with no tape blocking the pilots forward
view.
2. If the measurements are made precisely before the hole is drilled, the
positioning will always be exact.
3. The string is easily removed/replaced for cleaning and polishing the
canopy.
4. There is NO chance of the string blowing off in flight.

Note: If you decide to drill, you MUST use a sharp new drill made
specifically for drilling plastic.

Bill Daniels

"Tony Verhulst" wrote in message
...

I've always felt (but have no evidence) that positioning a yaw string on
the canopy is not optimal, and that you really want it in clean,
undisturbed, air (yeah, like the 2-33). There could be 2 problems with the
canopy mount. One, it is flush with a compound curve surface and who knows
that the air is doing there. Two, it is in the boundary layer between the
canopy surface and the airflow and who knows that the air is doing there.

I wonder if any one has experimented with a "normally" mounted yaw string
and one placed on a post several cm higher.

Tony V.

On Thu, 13 Apr 2006 08:25:44 -0600, "Bill Daniels"
bildan@comcast-dot-net wrote:

Yep, done that. The string on the canopy surface is about twice as
sensitive to yaw angles as the one on a one inch tall post. In other words,
the string on the canopy surface 'over-indicates' by about 2:1. I think
that's a good thing.

I'm not so sure...there seems to be a definite hysteresis effect in
the boundary layer. I've experimented with two strings, one on a 3/4"
post and one at its base, and they did NOT respond in sync. I found I
could deflect one left, the other right, and hold it that way for a
second or two.

Note: If you decide to drill, you MUST use a sharp new drill made
specifically for drilling plastic.

Better, I think, to poke it with a hot piece of wire to avoid
stress-raising tool marks. Push from the outside in and pull the wire
on through from the inside...that way you don't get a raised lip on
the outside. It works well for stopping cracks, too.

rj

Tony Verhulst wrote:

I've always felt (but have no evidence) that positioning a yaw string on
the canopy is not optimal, and that you really want it in clean,
undisturbed, air (yeah, like the 2-33). There could be 2 problems with
the canopy mount. One, it is flush with a compound curve surface and who
knows that the air is doing there. Two, it is in the boundary layer
between the canopy surface and the airflow and who knows that the air is
doing there.

I wonder if any one has experimented with a "normally" mounted yaw
string and one placed on a post several cm higher.

Tony V.
Our club gliders all had or still have the yaw string mounted some centimetres
off the fuselage.
The Blanik L13 has its on a TE probe about 5cm long, the two BergFalkes have
wire standoffs on the nose. In all cases the string in the free stream tends to
flap like a flag, which can be a little irritating. They also easily drape
around the support and inattentive pilots then end up flying with no yaw
indication. We recently moved the string to the canopy on one of the Bergies,
and the result is an improvement.

In my experience the canopy mounted string is a stabler, and in most situations
better, tool. The small area occluded by the attachment is not significant as
long as you do move your head when scanning. Otherwise it can obscure other
aircraft.
--
Bruce Greeff
Std Cirrus #57
I'm no-T at the address above.

In article , Tony Verhulst
writes

I've always felt (but have no evidence) that positioning a yaw string on
the canopy is not optimal, and that you really want it in clean,
undisturbed, air (yeah, like the 2-33). There could be 2 problems with
the canopy mount. One, it is flush with a compound curve surface and who
knows that the air is doing there. Two, it is in the boundary layer
between the canopy surface and the airflow and who knows that the air is
doing there.

I wonder if any one has experimented with a "normally" mounted yaw
string and one placed on a post several cm higher.

Tony V.

There used to be a burble round the canopy on my sailplane,
which meant there was only a narrow speed range where the yaw string was
anything like stable.

I wanted to update the TE system from a diaphragm type to a
Braunsweig tube. It occurred to me that if I put the tube immediately
ahead of the canopy I could kill two birds with one stone. Worked a
treat!

I thought maybe I could use the tube as a radio antenna, too, (3
birds?) but never got around to trying it.
--
Mike Lindsay