Measuring static charge on an aircraft
chris paterson
its surface as a result of said flying.
My question is this: Is there any way of measuring this charge whilst the
aircraft is still in the air rather than waiting until it is back on the
tarmac to make a measurement?
Mark Kinsler
About the only thing you can measure is voltage, and voltages are measured
with respect to something else--the earth, in this case.
I'd be surprised if someone hasn't done this sort of thing with a wire
trailed from the aircraft. I'd like to measure the charge off of a
weather balloon sometime.
M Kinsler
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Cortland Richmond
> An fighter aircraft is flying along and picks up a sizeable static charge on
> its surface as a result of said flying.
>
> My question is this: Is there any way of measuring this charge whilst the
> aircraft is still in the air rather than waiting until it is back on the
> tarmac to make a measurement?
How about a variety of foil electrometer? Place two movable plates, connected to
the aircraft structure, near each other so the charge on each will repel the
other. Measure the force created by this repulsion. Knowledge of the force leads
directly to the charge involved.
Cortland Richmond
Science Hobbyist
"chris paterson" <chris.p...@baesystems.com> wrote:
> An fighter aircraft is flying along and picks up a sizeable static
charge on
> its surface as a result of said flying.
>
> My question is this: Is there any way of measuring this charge whilst
the
> aircraft is still in the air rather than waiting until it is back on
the
> tarmac to make a measurement?
The e-field at the surface of a charged aircraft will
be non-zero. Some sort of e-field meter mounted on the
flat surface of the wing would work. There would be
two problems with this: calibrating the field strength
against the total charge on the flying aircraft, and
also environmental e-fields can throw your measurements
off. The constant 100v/meter clear weather vertical
e-field could be rejected by mounting your sensing
device on a vertical surface of the aircraft. But
if it flew within a few tens of miles of a thunderstorm,
the distored e-fields of the storm would throw your
measurements off.
And if you get this thing working, and you measure
10KV per meter field strength at the aircraft surface,
how many nanocoulombs of charge has the aircraft
picked up? The e-field will be proportional to the
accumulated charge, but you'll need some way to determine
the proportionality factor.
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Before you buy.
Dr John Stockton
11:44:41 seen in news:sci.physics.electromag, chris paterson <chris.pate
rs...@baesystems.com> wrote:
>An fighter aircraft is flying along and picks up a sizeable static charge on
>its surface as a result of said flying.
>
>My question is this: Is there any way of measuring this charge whilst the
>aircraft is still in the air rather than waiting until it is back on the
>tarmac to make a measurement?
Fly it through a double-walled hangar, isolate the inner wall at mid-
passage, then after exit measure the charge on the inner. You might be
able to replace the hangar with a large loop of wire, between towers;
and perhaps measure the induced current into (not round) the loop.
Otherwise, as has been said, charge as such is difficult to measure.
Voltage is proportional to charge, and the capacitance to ground while
in flight (and any dependence on altitude) can be estimated; but for
voltage you need a reference.
Is the sign of the charge known & fixed? If it is positive, one might
think of finding how hard an electron gun had to shoot to get its
electrons away, but how to determine that? see whether returning
electrons come to an adjacent isolated plate? but a flying aircraft is
not /in vacuo/.
An all-important consideration for any measurement - what accuracy do
you envisage? Is instrumental precision needed, or do you just want to
know whether it will spark to ground before the wheels touch? Also,
have you any idea, also essential, of the expected magnitude of charge
or voltage?
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chris paterson
thunderstorm - like weather and make some real time measurements of static
build up in specific areas on the skin of the aircraft, wings, tail etc.
This followed by an assessment of the overall condition of charge build up
on the aircraft. The charge itself will probably be positive although there
could be some instances where this is not the case. As to accuracy, I don't
think that being able to measure V will be required, more like kV...
Dr John Stockton wrote in message ...
Ed Price
FWIW, the US Navy had installed some type of "charge neutralizer" on some of
their helicopters (maybe Sea Stallion?) in the 1980's. IIRC, the equipment
was mounted in an external pod. The purpose was to neutralize or counter the
effect of airframe charging (which is a rather huge problem if you are about
to dangle a lift cable to a swimmer).
I had heard that the systems were not very successful, and that they were
ultimately removed. I don't know how the charge was sensed or how a reverse
charge was applied to the airframe.
Ed
"chris paterson" <chris.p...@baesystems.com> wrote in message
news:39a4fba6$1...@pull.gecm.com...
Cortland Richmond
electrometer I described. You don't have a second terminal for your measuring
equipment, but like charges DO repel, and this may be measured without recourse
to a return circuit.
The usefulness of such a device is limited by your ability to measure repulsive
force. If laser interferometry is used, then minute deflections become quite
readable. Another method is to make the parallel plates part of a free-running
oscillator and measure the frequency change as the plates move. No doubt
mechanical noise of the airframe will be a problem, but the plates need not be
firmly fastened to the aircraft; all they need is an electrical connection..
However they WILL have to be outside.
Cortland Richmond
Cortland Richmond
We used similar generators on CH-47's. They worked well. If you didn't turn 'em
on, you would get a BIG arc on landing or dropping a hook. Dangerous, very.
Cortland
(ka...@saber.net)
Dr John Stockton
seen in news:sci.physics.electromag, chris paterson <chris.paterson@baes
ystems.com> wrote:
>Dr John Stockton wrote in message ...
>>An all-important consideration for any measurement - what accuracy do
>>you envisage? Is instrumental precision needed, or do you just want to
>>know whether it will spark to ground before the wheels touch? Also,
>>have you any idea, also essential, of the expected magnitude of charge
>>or voltage?
>What I want to be able to do is fly an aircraft through unpleasant
>thunderstorm - like weather and make some real time measurements of static
>build up in specific areas on the skin of the aircraft, wings, tail etc.
>This followed by an assessment of the overall condition of charge build up
>on the aircraft. The charge itself will probably be positive although there
>could be some instances where this is not the case. As to accuracy, I don't
>think that being able to measure V will be required, more like kV...
You really need to think about the difference between accuracy, which
can often usefully be expressed as a percentage (or as parts per
million) and range. Evidently in this case the range needed is itself
uncertain, and probably an accuracy of 10% of value would be of at least
some initial use.
For thunderstorms, you may need to think about megavolts, if struck;
though I'd guess that sort of voltage would rapidly decay by discharge
off the pointy bits. Not really my field.
ISTM that if the aircraft surface is made up of interconnected metal,
then the charge distribution may be constant, just varying in strength.
OTOH if the plane is going fast enough to build up plasma in front, as
the shuttle does; or if the engine efflux is significant ...
Have you consulted electrical measurement experts? NPL, Leatherhead,
and IIRC the Univ. of Southampton? And the RAF still have some planes
...
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Peter Somlo
>What I want to be able to do is fly an aircraft through unpleasant
>thunderstorm - like weather and make some real time measurements of static
>build up in specific areas on the skin of the aircraft, wings, tail etc.
>This followed by an assessment of the overall condition of charge build up
>on the aircraft. The charge itself will probably be positive although there
>could be some instances where this is not the case. As to accuracy, I don't
>think that being able to measure V will be required, more like kV...
>
>Dr John Stockton wrote in message ...
>
>
>>An all-important consideration for any measurement - what accuracy do
>>you envisage? Is instrumental precision needed, or do you just want to
>>know whether it will spark to ground before the wheels touch? Also,
>>have you any idea, also essential, of the expected magnitude of charge
>>or voltage?
>
>
>
Once I have asked on a plane "what are those little 'pencils' sticking
out of the back of the wing?" and was told by the steward that it is
to get rid of charge build-up on the plane. If this is the case,
measuring the current (nA?) through these would be proportional to the
charge on the plane (relative to its surroundings, which is not the
full story..).
Peter
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Cortland Richmond
charge, but also on the condition of the discharge wicks and the airspeed.
Cortland
Peter Somlo
>Problem is, they use sharp wicks - loaded fiberglass. I think current flow will depend not only on teh
>charge, but also on the condition of the discharge wicks and the airspeed.
>
>Cortland
I agree, but nevertheless the current would be proportional to the
charge, - so once the proportianilty factor were found (?) we'd be OK.
chris paterson
Is it a commercially available item?
Chris
ps. What is a CH-47?
Cortland Richmond wrote in message <39A6CDBC...@usa.alcatel.com>...
Cortland Richmond
modifications -- helicopter. It has two rotors, one on a pylon in the front, and
one on a pylon on the rear, operated by two engines mounted in nacelles beside
the rear pylon. It is a similar to, but bigger than the Navy and Marine Corps
CH-46, and has four landing wheels, longer sponsons and other differences.
As I recall -- I was a radio guy, not an airframe electrical repairman -- the
CH-47 anti-static discharger unit was about three or four ARINC shelves wide,
and heavy. One thing is, I understand you almost never had to change the
polarity. This is probably because tribolelectric charging due to air moving
over the painted rotors and fuselage would generate the same polarity all the
time. And yes, I understand they could take a lot of power. Of course, when the
rotors weren't moving, you didn't NEED them.
I don't know if civilian fixed-wing aircraft use them, but I would imagine large
helicopters do. Why not call up Boeing and ask? Whoops, that's Lockheed Martin,
now isn't it?
Cortland
John C. Polasek
to discharging it.
I have found it useful to use any simple very sharp point to automatically
discharge static electricity, at least down to some ionization level.
It's simple electrostatics: the field intensity is inverse to the radius (or
r²) of the point. A very sharp point will nicely remove a lot of charge by
ionization. The finest points could be subject to erosion and rounding.
I have taped a stick pin to my swivel chair sliding around on a plastic mat,
and since doing so, I do not experience shocks. I tested it with a neon test
light, after dark adaptation, and could see the slight sparking.
The use of those giant dischargers sounds like a true government job. They
can't cost less than $10,000 apiece.
John C. Polasek