Grounding of control tubes/cables

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

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

On Feb 29, 8:20*am, Mike the Strike wrote:

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!

I've found the nasty noises on the radio and the fact that I get a
shock off anything metallic I touch is a good sign too. Must be an
Arizona thing. Trouble is that in monsoon season hugging in tight
against a Cb may be a better choice than landing out in a place that's
about to be flooded. The lift under the storm shelf can be as good as
the nearby lightning is disturbing.

In the 2 Schleichers I've owned the metal parts in the cockpit are
seem to be bonded together but independent of the electrical ground.
The wing control rods are not bonded but they are not insulated
either.


Andy

On my '27 there is a bond wire connecting between the front tow hook,
the rudder pedal assembly and the control column assembly. Then the
bond wire heads south behind the seat where I suspect it is connected
to the aft tow hook.

I'm thinking that the bond wire is not so much about protecting the
structure as it is about protecting the gooey dielectric that
interconnects between the rudder pedals and the control column and the
tow release while on tow. Providing some level of easily achieved
protection for the gooey dielectric might ultimately be effective in
protecting the structure as a whole when a lightning strike is not
exceedingly energetic.

Cowering into as small a target as possible and not holding onto any
controls that don't need to be held onto has always seemed like a
sensible strategy to me. Of course, not flying near to lightning
activity is also a sensible strategy when that is feasible.

I appreciate all of your responses, guys.

Mike, I think your point on controlling static during winch launch
using a wire is the true reason why the previous owner of my ship did
the bonding. I hadn't thought about it, but of course the Tost release
is bonded to the rudder assembly by virtue of the Bowden cable. The
electrical system was probably bonded to the rudder assembly so that
the VHF antenna could discharge static to ground if necessary. So in
my plane only the control column isn't bonded - but perhaps the PTT
switch wiring accomplishes this task.

I've not experienced static discharges like you guys talk about, but
I'd much rather learn from others than do it myself. Assuming that the
rudder assembly, the control column, the Tost release and the
electrical system are bonded, that leaves the spoiler rod (and the
canopy latching rods) as the only metal near me that isn't bonded. Is
this ever done, or is it overkill?

One last question - the bonding in my plane was not done at the
factory. Was the bonding you guys speak of done by the factory?

-John

Mike the Strike wrote:
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

One last question - the bonding in my plane was not done at the
factory. Was the bonding you guys speak of done by the factory?

Yes, factory on the '27.

Steve, Mike,

Again, I appreciate your answers. It's strange, though - the grounding
in my 1984 ASW19 is clearly home-made. I wonder why Schleicher would
do the -20s, and not the -19s.

-John

On Mar 1, 11:51 pm, Steve Koerner wrote:
One last question - the bonding in my plane was not done at the
factory. Was the bonding you guys speak of done by the factory?

Yes, factory on the '27.

On Mar 2, 7:23 pm, Mike the Strike wrote:
John:

Both my present glider (2001 Discus 2) and the previous one (1980
ASW20) had similar factory-installed grounding straps.

Mike

jcarlyle wrote:

On Mar 1, 11:51 pm, Steve Koerner wrote:
One last question - the bonding in my plane was not done at the
factory. Was the bonding you guys speak of done by the factory?
Yes, factory on the '27.

On Mar 2, 7:23 pm, Mike the Strike wrote:
John:

Both my present glider (2001 Discus 2) and the previous one (1980
ASW20) had similar factory-installed grounding straps.

Steve, Mike,

Again, I appreciate your answers. It's strange, though - the grounding
in my 1984 ASW19 is clearly home-made. I wonder why Schleicher would
do the -20s, and not the -19s.

Is it possible that the ASW 20 with the bonding straps was built for a
country in Europe where cloud flying was common? I don't recall bonding
straps on my ASW 20 C. Our Blanik had them, though.

--
Eric Greenwell - Washington State, USA
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* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Mar 2, 8:38*pm, jcarlyle wrote:
Steve, Mike,

Again, I appreciate your answers. It's strange, though - the grounding
in my 1984 ASW19 is clearly home-made. I wonder why Schleicher would
do the -20s, and not the -19s.

I have no reason to think the bonding in my 19b (19356) was not
factory original. The bonding on my 28 certainly is. Some Schleicher
factory stuff looks home made. Don't let that make you think it's
not factory original. Glider manufacture is a cottage industry. Didn't
you notice the German garden hose fittings in the water ballast
system?

How Schleicher got away with joining ballast valve control cables
with electrical terminal blocks in the 28 is beyond me.

I may have some photos that show the bonding in 19356. I'll check
tonight.

Andy

John:

Both my present glider (2001 Discus 2) and the previous one (1980
ASW20) had similar factory-installed grounding straps.

Mike


One last question - the bonding in my plane was not done at the
factory. Was the bonding you guys speak of done by the factory?

-John