Rudder Cable Systems Used in Modern Sailplanes

On 5/15/2012 12:35 AM, Ramy wrote:

When checking the rudder cables for broken strands it is best to
use a soft tissue which will readily snag on the broken strand. Of
course you can use your fingers if you like and if you have any
broken strands they can be easliy seen by the bloody drippings on
the cable.

Checked the rudder cables on my 27 - looking good. But as JJ
described, loosening the tension on one side causes a hard over to
the other side! I would like to hear how glider manufactures defends
this design! I wonder how many were killed by this design, giving
many unexplained spins into the ground from higher altitude. A glider
may still be landable without rudder control, but not with a full
rudder. 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.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

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