Rudder Cable Systems Used in Modern Sailplanes

On 16/05/2012 15:06, Eric Greenwell wrote:
On 5/15/2012 12:35 AM, Ramy wrote:


...Couldn't they come up with a design with a more graceful mode
of failure??

Since it's something that gradually goes bad (many flights from the
first strand breaking until cable failure) and is easily checked during
preflight, I don't think it's an issue. If not caught during preflight,
I think it would last till the annual inspection.

I'd agree with you except for the JS-1 which began this discussion. I
find it hard to believe (and unacceptable) that a glider which can only
be a year or so old has had a broken rudder cable from normal wear and tear.

Perhaps there was wear against the top of the S-tube - maybe the plastic
insert had migrated down. Otherwise, something failed which isn't
expected to wear or break - a swage slipped, anchor fitting broke - I'll
be interested to read the report.

Also, with great respect to Bob K and his experience, I'm not convinced
airflow will sufficiently straighten a rudder with a broken cable. Even
in the best case there will be residual deflection where the airflow
balances the other spring. This could be quite large.

GC

On May 16, 2:10*am, GC wrote:
Also, with great respect to Bob K and his experience, I'm not convinced
airflow will sufficiently straighten a rudder with a broken cable. *Even
in the best case there will be residual deflection where the airflow
balances the other spring. *This could be quite large.

Isn't that something that can be easily (and safely) verified? In many
gliders, rudder cables are accessible in the cockpit. Take a high tow,
grab one cable and pull it. This simulates broken spring or broken
cable on one side. If the glider becomes uncontrollable, just release
the cable.

Bart