Grounding of control tubes/cables

[jcarlyle]

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

[Mike the Strike]

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

[Andy[_1_]]

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

[Steve Koerner]

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.

[jcarlyle]

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

[Steve Koerner]

> 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.

[Mike the Strike]

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
>

[jcarlyle]

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

[Eric Greenwell]

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
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Andy[_1_]]

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

[Andy[_1_]]

On Mar 5, 3:53*pm, Andy > wrote:
> 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

I have a photo of 19356 rudder cable bonding. Email me and I'll send
it to you.

Andy

[JJ Sinclair]

> 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?

All the metal parts should be grounded to prevent static noise in your
radio receiver (which you will get any time an ungrounded control is
moved).

> 2. *If bonding is useful, shouldn't all of the glider's control tubes/
> cables be bonded?

Yes


> 3. *What would be the recommended method to effect a bond to aileron

The control tubes are usually grounded with a wire that goes to one of
the mounting bolts that hold the stick in place, the electrical
connection is then made through the stick into the aileron and
elevator pushrods.

Hope this helps,
JJ

[jcarlyle]

Hi, Andy,

My 19b is 19397, so if yours was bonded by the factory then mine
probably was, too. I appreciate the offer of a photo, I'll write you
off-line about that issue.

Reiterating, I'm talking about a wire that leads from the battery
negative side bus bar to the rudder assembly. This is probably not the
bonding that you and others are talking about. Now, I know for a fact
that the battery was put in by the previous owner. And the reason I
think the bonding was homemade is because the ring connector to wire
junction has been made the the mother of all cold solder joints! We're
talking ugly, dull and lumpy, to the nth degree.

-John

On Mar 5, 5:53 pm, Andy > wrote:
> 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?
>
> Andy

[jcarlyle]

Hi, JJ,

Your input is very much appreciated - thanks!

-John

On Mar 6, 9:13 am, JJ Sinclair > wrote:
> > 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?
>
> All the metal parts should be grounded to prevent static noise in your
> radio receiver (which you will get any time an ungrounded control is
> moved).
>
> > 2. If bonding is useful, shouldn't all of the glider's control tubes/
> > cables be bonded?
>
> Yes
>
> > 3. What would be the recommended method to effect a bond to aileron
>
> The control tubes are usually grounded with a wire that goes to one of
> the mounting bolts that hold the stick in place, the electrical
> connection is then made through the stick into the aileron and
> elevator pushrods.
>
> Hope this helps,
> JJ

[Steve Koerner]

Radio receive performance is important and the benefit arising from
bonding the controls would undoubtedly be a sufficient reason for
doing it. But the most compelling reason relates to crew safety and
airframe protection. FAR 23-867 requires bonding specifically for
lightning protection. See

http://www.risingup.com/fars/info/part23-867-FAR.shtml

Everyone knows that you should not fly a kite in a thunderstorm. It
would similarly be unwise to float your body near a thunderstorm with
your feet attached to one large electrode and your hands connected to
another large electrode. Any lightning that happens upon those
electrodes would want to flow through you, the gooey dielectric --
much better to have most of that current jolt going through a low
impedance bond wire.

[Mike the Strike]

On Mar 6, 4:06 pm, Steve Koerner > wrote:
> Radio receive performance is important and the benefit arising from
> bonding the controls would undoubtedly be a sufficient reason for
> doing it. But the most compelling reason relates to crew safety and
> airframe protection. FAR 23-867 requires bonding specifically for
> lightning protection. See
>
> http://www.risingup.com/fars/info/part23-867-FAR.shtml
>
> Everyone knows that you should not fly a kite in a thunderstorm. It
> would similarly be unwise to float your body near a thunderstorm with
> your feet attached to one large electrode and your hands connected to
> another large electrode. Any lightning that happens upon those
> electrodes would want to flow through you, the gooey dielectric --
> much better to have most of that current jolt going through a low
> impedance bond wire.

Steve:

No composite glider can comply with the FAR you quote nor would any
such plane survive a severe lightning strike. The bonding straps and
their connections are also clearly not robust enough to conduct
lightning currents. Lightning protection is generally only required
for IFR rated aircraft. Risks of lightning strikes while operating
VFR are small (although not zero).

The straps are clearly there to equalize potentials, but from what
source is anyone's guess.

My guess is atmospheric potentials resulting from wire cables during
winch launching.

Mike

[Papa3]

On Mar 6, 12:39*pm, jcarlyle > wrote:
> We're talking ugly, dull and lumpy, to the nth degree.
>
> -John
>

Awww John, you're not THAT bad...

P3

Is it GCup season yet?

[Steve Koerner]

First, the FAR that I quoted is not restricted to IFR aircraft, it is
generally applicable to certified airplanes in the normal category.

Mike is a noted expert in lighting and he can quote expert knowledge
as regarding the distribution in the intensity of lightning energy.
The distribution of lightning intensities is very wide. So when Mike
prefaces his discussion as relating to a severe lightning strike his
points are exactly right. A severe lightning strike is probably a
death sentence to one of us in a composite glider regardless of
bonding wires.

But my writing did not pertain to a severe lightning strike; quite the
opposite, in my 2/29 post I restricted the applicability of my remarks
to the case of lower energy levels.

Anyone who has ever seen a nice photograph of a lightning strike knows
that there are branches and tentacles of differing brightness. The
varying brightness of those lightning tentacles and their distribution
in 3-space must indicate that for an arbitrarily positioned glider
there is a very good chance that the lighting that he is most likely
to encounter will not be the main bolt but rather a lower intensity
tentacle.

Many gliders have survived lightning hits. Clearly lower intensity
lightning is a matter of interest and concern. My premise is that
bonding the controls in a glider is a low cost measure intended to
slide the survivability point in the spectrum of lightning intensities
that could be encountered. It is further my premise that the most
sensitive component in the airframe is the pilot and that bonding the
controls that the pilot is touching goes a long way towards protecting
that sensitive component. Even if the wings were to explode, the
pilot may have an opportunity to bail out if he is protected to a
degree that he is able to do so.

The bond wires in my glider look to be maybe 14 gauge which would
certainly fuse if the lightning energy is very great. But it would
be pointless to give the bond wires a lot more current handling
ability than the steel control cables and steel drive tubes. All the
bond wires need is a little bit more current handling ability than the
drives to be effective. Since copper is 10 times more conductive
than steel, that is probably what is being accomplished.

Mike is undoubtedly right that bonding will help to protect against
atmospheric potentials during a wire ground launch. JJ is surely
correct that bonding will make the radio work better in receive. I'm
still convinced that the foremost equation that gets the bond wires
installed in the first place is the lightning protection equation. As
I have pointed out, it is lightning protection which is the express
reason that the FARs require electrical bonding in certified aircraft.

[jcarlyle]

Oh, thanks, Erik! Thanks very much. My seconds will call upon your
seconds. Or......you can let me fly your LS-8 once....8-)

-John


On Mar 6, 10:52 pm, Papa3 > wrote:
> On Mar 6, 12:39 pm, jcarlyle > wrote:
>
> > We're talking ugly, dull and lumpy, to the nth degree.
>
> > -John
>
> Awww John, you're not THAT bad...
>
> P3
>
> Is it GCup season yet?

[Mike the Strike]

......and I should add I have seen a couple of gliders survive minor
lightning discharges, including an ASW-27. This suffered a strike
from nose to tail, the exit point leaving a little hole in the upper
rudder area, but no major structural damage. I spoke to the pilot and
he suffered no injury, but his electronic instruments were damaged.

I'll bet the requirement for bonding is in the German regulations.
Perhaps one of our readers over there could help us?

Mike