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Static Dischargers

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steveadams

Joined: 10 Jan 2006
Posts: 191

Posted: Mon Feb 27, 2006 8:10 am Post subject: Static Dischargers

Hopefully some of you can help me out. Last week I finally got to fly in some actual IMC in my plane (total of 4 hours actual). After about 15 minutes in the clouds, my radio transmissions became more and more filled with static. Still understandable, but not very clear. No static when just listenning to controllers or talking without transmitting. Slowly cleared up after exiting clouds. I think this is a static build up problem and wondered what others thought. My airplane is an CH640 and I have braided grounding straps across rudder and horizontal tail hinges. They didn't specify static wicks in the design. I know that static dischargers should be out and back as far as possible, but otherwise am not sure about placement and how many I may need. Is there any general advise concerning placement and number, or is it basically a trial and error process to see what works?

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nuckollsr(at)cox.net
Guest

Posted: Mon Feb 27, 2006 2:48 pm Post subject: Static Dischargers

At 08:10 AM 2/27/2006 -0800, you wrote:



 	  Quote: 	
		  

<dr_steve_adams(at)yahoo.com>



Hopefully some of you can help me out. Last week I finally got to fly in 

some actual IMC in my plane (total of 4 hours actual). After about 15 

minutes in the clouds, my radio transmissions became more and more filled 

with static. Still understandable, but not very clear. No static when just 

listenning to controllers or talking without transmitting. Slowly cleared 

up after exiting clouds. I think this is a static build up problem and 

wondered what others thought. My airplane is an CH640 and I have braided 

grounding straps across rudder and horizontal tail hinges. They didn't 

specify static wicks in the design. I know that static dischargers should 

be out and back as far as possible, but otherwise am not sure about 

placement and how many I may need. Is there any general advise concerning 

placement and number, or is it basically a trial and error process to see 

what works?


	


    Pretty much. P-static mitigation is a combination of science and

    art . . . but without the 200Kv hot spot chaser wand we use at

    RAC, a bit of luck doesn't hurt.



    Fortunately your airplane is slow and your time in the clouds

    probably limited. If you query the usual suspects for aircraft

    quality static wicks, you'll find listing like:



http://www.aircraftspruce.com/catalog/elpages/staticwick.php



http://www.texair.com/aircraftparts/Dayton-Granger.asp



     . . . and occasionally you might even find them on Ebay. See

    item 4612427645



    You can try three minimum. One on trailing edge of each

    aileron and one on the rudder. It's a cut-n-try sort of

    thing without a purposeful testing facility but you

    have nothing to loose and an experimental airplane to

    try things on.



    Here's an article that speaks to the science of crafting

    and installing static wicks for terrestrial applications:



http://www.repeater-builder.com/pdf/staticbusterarticlecomplete.pdf



    In a Google search I ran across this note. I was 3/4th through

    the thing before I realized it was one I wrote some years ago:



                                 Stat Wicks



Static wicks have nothing to do with radio quality or

reliability. EVERY time dissimilar materials slide across each

other, there is a tendency for one material with a stronger affinity

for electrons than the other to acquire a negative charge.

Common manifestations include sparks that jump between

fingertip and doorknob after walking across carpet. In the winter

especially, I have to remind myself to keep part of my body

touching the frame of my 1" vertical belt sander while sculpting a

piece of metal . . . the Van DeGraff like nature of the belt sander

will charge the ol' bod with a significant kick if I don't bleed it off

during the sanding operations.



Precipitation static is unique to airborne particles sliding

past any conductor. Radio receivers can be severely affected by

dust storms usually associated with high winds. I used to work

with an amateur radio repeater installation 1200 feet up on

KTVH-TV in Hutchinson, KS. A blowing snowstorm would

severely de-sense our receivers.



Airplanes have unique problems in that they generate their

own wind. Airplanes flying through dust, rain or snow can pick

up significant charges. When the charge reaches sufficient

magnitude, it begins to form coronas at the sharp (usually trailing

edges) of wings and flight control surfaces.



The static wick is a sharp-ended conductor (enhances

tendency for charge to concentrate and form corona) connected to

the airframe through some nominal but rather high resistance.

The idea is to put sufficient static wicks in the right places so that

they force lots of small, low current discharges to form and

dissipate the energy at much lower (read less noisy) levels than if

the wicks were not present.



The faster the airplane flies, the more likely it is to

experience the effects of p-static. Further, the finish and skin

materials have an influence on tendency to build and concentrate

static charges. These effects are present and potentially

troublesome irrespective of the vintage of radios carried aboard

the airplane.



VHF radios are less susceptible than HF or ADF receivers.

Grounded antennas are quieter than isolated antennas. There are

some modern digital signal processing techniques that can reduce

the audible effects of p-static but ultimately, locally generated

static noises will overwhelm a receiver looking for weaker

signals.



The number, style and placement of static wicks on our

bizjets is as much an art as a science. We spent a great deal of

$time$ selecting the right products and installations. Further,

there's a comprehensive incoming inspection of static wicks . . .

seems that a performance of a static wick is very sensitive to

production variability.



If your airplane suffers from the effects of p-static, it may

take a lot of effort over a long period of time to deduce the

optimum solution

    I might add to this that a static wick is not

    a simple sharp-tipped conductor tacked to the trailing

    edge of a wing. It has a high resistance . . on the

    order of tens of megohms. Not easy to build. This

    long, linear resistance element is necessary to keep

    the wick from becoming an efficient concentrator

    and radiator of noise at it's 1/4 wave resonance

    frequency. It's also necessary to mitigate the

    ability of the discharge at the tip to generate

    noise.



    Your best source for "real" wicks is probably Ebay.

    They'll come already built . . . but with no guarantees.

    Bob . . .

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rshannon(at)cruzcom.com
Guest

Posted: Mon Feb 27, 2006 4:32 pm Post subject: Static Dischargers

Slightly tangential, but....



Early research on P-static and how to deal with it was carried out

during WWII by a team led by Bob Buck. In a B-17, they intentionally

sought and charged (sorry about that one) into major storm clouds all

over the world -- for the benefit of science. He writes about it in

fascinating detail in "North Star Over My Shoulder", a memoir of his

extraordinary life in aviation (early biplanes to Chief Pilot for TWA

driving 747's, etc.) and a good read all around.



Ron

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Mon Feb 27, 2006 5:27 pm Post subject: Static Dischargers

steveadams wrote:



 	  Quote: 	
		   ...After about 15 minutes in the clouds, my radio transmissions became more and more filled with static. Still understandable, but not very clear. No static when just listenning to controllers or talking without transmitting. 


	


While the fact that it happens in the cloud and clears up when you leave

the cloud certainly implies p-static, I have *never* heard of p-static

having an effect on transmission. I have been in p-static so bad (dry

snow) that not a single receiver in the aircraft worked (well, they

worked but the noise was greater than any signal). Through that my

transmissions were clear to receivers.



Is there anything else you turned on while in the clag? Pitot heat?

Another (remote) possibility is that the base of your antenna is not

bonded well and the water changed the characteristic of your ground

plane connection.



And of course it could be just a bad lobe on your antenna radiation

pattern. Did you make any turns or were you motoring straight and level?



-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

dcarter11(at)sbcglobal.ne
Guest

Posted: Mon Feb 27, 2006 8:12 pm Post subject: Static Dischargers

I believe p-static is principally the noise created by static electricity 

jumping from skin panel to skin panel on the way aft and finally off of the 

plane in elevator and rudders.  I think fiberglass stuff up front is a big 

source of buildup. You could try running a wire from nose to tail, with good 

electrical connection at each end - this might let the static build up on 

fiberglass cowl (I'm thinking RV series aircraft) bleed off by going from 

front to back without jumping a lot of little skin gaps along the way (don't 

ask me why the fore-aft longerons wouldn't do the same).



David



---

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Bruce(at)glasair.org
Guest

Posted: Mon Feb 27, 2006 8:27 pm Post subject: Static Dischargers

Yes, we know of p-static. It's a real problem in our fast plastic airplanes.

The only solution the factory ever came up with was a copper mesh imbedded

in the glass close to the surface, this was also their solution to lightning

protection. I believe the same solution was used on the SR-20/22. Others

(builders) have had some success with conductive primer. Static wicks won't

work on our airplanes. 



Bruce

www.glasair.org

 



--

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steveadams

Joined: 10 Jan 2006
Posts: 191

Posted: Tue Feb 28, 2006 4:22 am Post subject: Re: Static Dischargers

Thanks for all the suggestions. I have over 150 hours flying, and this never happened before. I was flying down to Florida, straight and level when it first happened. As I said, it cleared slowly after leaving the clouds. I then took a few flights VFR and everything was fine. Then again coming home I was in the clouds and it happened again, but not as bad. On my plane the cowl is fiberglass, but the cabin is carbon fiber and the rest of the plane is metal. Com 1 antenna is on top, and com 2 is on the bottom. Static was worse on #1, but also present on com 2, again, only with transmission. Maybe it is something other than p-static. The CH640 airframe is the same as the Alarus, which does not have static wicks, and from people I have talked to it has no p-static problems. The 640 is about 30 KTS faster though, which could make a difference. I guess it is worth finding a few static wicks and seeing if it makes a difference.

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nuckollsr(at)cox.net
Guest

Posted: Tue Feb 28, 2006 5:11 am Post subject: Static Dischargers

At 04:22 AM 2/28/2006 -0800, you wrote:



 	  Quote: 	
		  

<dr_steve_adams(at)yahoo.com>



Thanks for all the suggestions. I have over 150 hours flying, and this 

never happened before. I was flying down to Florida, straight and level 

when it first happened. As I said, it cleared slowly after leaving the 

clouds. I then took a few flights VFR and everything was fine. Then again 

coming home I was in the clouds and it happened again, but not as bad. On 

my plane the cowl is fiberglass, but the cabin is carbon fiber and the 

rest of the plane is metal. Com 1 antenna is on top, and com 2 is on the 

bottom. Static was worse on #1, but also present on com 2, again, only 

with transmission. Maybe it is something other than p-static. The CH640 

airframe is the same as the Alarus, which does not have static wicks, and 

from people I have talked to it has no p-static problems. The 640 is about 

30 KTS faster though, which could make a difference. I guess it is worth 

finding a few static wicks and seeing if it makes a difference.


	


   You bring up an interesting point. Not every owner

   of a particular airplane has p-static problems to

   report . . .



   It's a HIGHLY variable phenomenon. EVERY airplane has

   a p-static charge on it to some degree or another, it's

   only in the right combination of variables that noise

   levels rise sufficiently to be heard on radios. In severe

   cases, we've had p-static eat away at structural parts of

   the airplane . . . e.g. window glazing. The results

   of your experimenting may not be known until you seem

   to have slain the dragon by not having problems over a

   series of similar conditions . . . which could take years.

   It's quite disappointing than to have a solution

   in place for a couple of years and encounter conditions

   further out on the bell-curve and find that you're only

   partially successful.



   What you're experiencing is not new/startling. In fact,

   it's so commonplace and has such a problematic history

   of solutions that first response from those who have

   wrestled with it is sympathy and best wishes for a lucky

   break. Folks who do this professionally have access to

   expensive test and development tools and techniques

   that are not going to be available to the OBAM aircraft

   community. So, please do experiment and let us know of

   your findings. But I would also caution that what works

   for you may only be a starting point for determining

   what mitigates someone else's problems at a later date.



   Good luck!



   Bob . . .

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