Grounding of control tubes/cables

On Feb 27, 4:14 pm, jcarlyle wrote:
Poking around inside my fiberglass glider, I discovered a ground lead
from the rudder pedal/cable assembly to the negative electrical system
bus bar. Interestingly, there was no corresponding ground lead to the
metal aileron/elevator control rods.

Searching past posts to RAS, I discovered threads talking about the
lightning induced destruction of the London Gliding Club K21. In this
incident it appears that the metal aileron control rods were the prime
cause of the glider's disintegration. In the safety recommendation
section Schliecher was quoted as saying non-conducting aileron tubes
near the ends of the control circuits might be benefical. Another
thread mentioned the factory insertion of metallic mesh into the outer
skin layers of the Beech Starships to lessen the effect of lightning
strikes. But I couldn't find anything about bonding metal control
tubes/cables to the ground of the electrical system.

Questions:
1. What is the purpose of such bonding? Would it help at all with
lightning protection, or is it intended only to lessen static
discharge noise in the radio and other electrical systems?
2. If bonding is useful, shouldn't all of the glider's control tubes/
cables be bonded?
3. What would be the recommended method to effect a bond to aileron
and elevator rods?

-John

As one of the lightning guys in this forum, I'm afraid I can't throw
much light on this. I have owned several gliders that had a similar
arrangement - all the metalwork around the pilot was grounded or
bonded, but not the control rods.

The only reason I can think of is to control static electric charges
involved with winch launching with a wire, as this can result in the
flow of significant electric currents, especially under clouds.

Any lightning strike to a non-metallic glider is going to have
significant parts of the discharge path through non-conducting parts
of the structure or across air gaps. Structural damage will depend on
the magnitude and duration of the lightning current. I've seen
everything from small holes to complete destruction. Gliders just
aren't capable of conducting lightning without damage.

Composite aircraft that are required to pass certification for flight
in cloud have to pass the appropriate lightning discharge tests and
the structure is modified with conducting material to enable this. No
glider has been so modified to my knowledge.

As a final remark, I have noted that I get sparks from my tow release
cable to my leg when I fly under electrified clouds. I use this as a
sign that I should be flying somewhere else!

Mike