/A Professional told me that there is controversy about
/the airframe used as a ground due to corrosion
/possiblities at joints, around rivets, etc. He
/said that one manufacture (Piper I believe) traced
/corrosion troubles airframe grounding.
/Is this a possiblity or -----?
This subject has come up over the years but I've never
seen a definitive study that confirmed it. I can tell you
that tons of airborne aluminum is shipped out of Raytheon
(Beech) every year wherein EVERYTHING grounds to airframe
in order to pick up the power return path.
One of the problems I have with "professionsals" is that
they happily participate in the circulation of aviation
legends too. I'll readily concede that there are cases
of demonstrated airframe damage due to POOR grounding
technique . . . I reported one such case myself. At this
time, I wouldn't double up on wires in a metal airplane
to avoid "airframe corrosion." It has certainly not been
a barn-burner or we'd have heard a lot more about it. I
suspect someone, somewhere posted a service difficulty report
where a line mechanic observed and diagnosed the cause for
some form of corrosion problem. Service difficulty reports
stuck up on bulletin boards are responsable for generating
a LOT of aviation legends.
/From the postings I have read and the above possiblity
/we should be running ground wires for everything, right?
I can't recommend it except to the extent that I've discussed
for ground loop avoidance . . . virtually all techniques
I describe go to performance and noise issues . . . not
airframe corrosion.
/A number of people building things like Ezes and Berkuts--
/where you have the battery in the nose and the starter etc.
/back in the tail--have bonded aluminum or copper strip to the
/fuselage to use as main power leads.
Nothing wrong with this as long as they've done their homework
and calculated sufficient cross section to control voltage drops
and further, taken care to keep out and return power paths as
close together as possible for magenetic field cancellation.
The biggest problem I have with this is how do you connect to
the strips? You've created a metalic quasi-airframe that
requires bolts, bonding techniques and terminals to attach
wires to these strips at both ends. . . . LOTS of new, unnecessary,
power-robbing joints not to mention the labor of installing
the strips in the first place.
Do a component count and compare hours for installation.
As a general rule, very few design philosophies with increased
hours or complexity can be justified over simpler techniques.
Ask yourself which of the techniques is easiest to implement;
it's quite likely that the simplest is also the best.
/I seem to recall someone else using copper plumbing pipe--I
/think it was 3/4 inch--for primary power, while at the same
/time using it as a conduit for running other smaller wires to
/the back of the airplane.
I did a black hole project about ten years ago using a Long-Eze
where we installed a conduit ground system. The airplane was to
carry some sophisticated electronic countermeasures
equipment and we went to a lot of trouble to get things very
QUIET. In early revisions to my book I described this system
and a number of readers installed conduit grounds. There are
two advantages: Noise reduction and ease of pulling in new wires
at a later time. Turns out both reasons were marginal justification
for all the extra work on ordinary transportation/pleasure airplanes.
If you've got a conduit ground system in place, don't rip it out.
If you've yet to install a ground system in a canard-pusher,
I recommend you use parallel paths of 2AWG wire and take pains
to control ground loops per other techniques already on record.
You'll save HOURS of work with no perceivable degredation to
performance.
Bob . . .
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