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Static Wick

Posted: Mon Apr 02, 2018 12:13 am
by putthoff
How are static wicks attached to the wings and rudders? Are they difficult to replace? I understand that some airlines require that a certain amount be intact to fly.

Re: Static Wick

Posted: Mon Apr 02, 2018 12:32 am
by Starlionblue
Having a certain number of wicks is not really an airline requirement. It is a regulatory requirement stemming from the manufacturer's master MEL/CDL.

I don't really know how they're attached, but I don't think they're that hard to replace.

Re: Static Wick

Posted: Mon Apr 02, 2018 12:47 am
by e38
Quoting puthoff (thread starter), "How are static wicks attached to the wings and rudders?"

puthoff, it depends on the aircraft. Many years ago when I flew Citation I aircraft, the ailerons and rudders were manufactured with receptacles and the static wicks had threads which you would simply screw into the receptacles. When the aircraft would RON, it was standard procedure at the company I worked for to remove the static wicks from the rudder and ailerons to preclude damage to them; in the morning, we would re-attach them, of course. Fortunately, the aircraft was small enough that you could reach all the static wicks on the rudder without the use of a ladder. As Starlionblue mentioned, they can be deferred by MEL/CDL depending on the aircraft, but as I remember on the Citation I, we were not able to MEL/CDL those on the ailerons because they were integral to the proper balance of the ailerons.
Obviously, on the Citation I, no, they were not difficult to replace.

On the aircraft I currently fly (not the Citation I anymore), yes, you can have a certain number of static wicks missing.

e38

Re: Static Wick

Posted: Mon Apr 02, 2018 12:53 am
by Dalmd88
The base is riveted to the control surface. Typically they are 'blind' rivets, commercial called cherry max. Basically an expensive strong pop rivet. The wick itself is attached to the base with an allen screw. So if the wick breaks off many times you just screw a replacement. With a lightening strike the wick and base is usually burned off and a new base has to be installed. I would say it takes longer to position the lift truck than to do the replacement.

Re: Static Wick

Posted: Mon Apr 02, 2018 1:02 am
by CCGPV
On citations they are screwed into a base like a lightbulb. There can be 3 missing total and no more than 2 in a row on the aircraft I'm familiar with (Citation XLS).

Re: Static Wick

Posted: Mon Apr 02, 2018 5:46 am
by Lpbri
Per the 737 CDL, up to 2 may be missing, the outermost ones must always be present.

Re: Static Wick

Posted: Mon Apr 02, 2018 6:55 pm
by gregorygoodwin
Putthoff,

Just had an interesting experience with static wicks last week at work. I do structures and composite work on the FDX fleet in IND. We had a 767 in one bay with a wing tip strike that broke off one of the static wicks and its base from the outboard aileron. It, the base, was secured with small screws (6-32 thread) into inserts in carbon fiber. The screws were sheared leaving a stud in the inserts, difficult to extract. You don't want to mess up, as this would require a composite repair to the aileron, which is a balanced surface and anything you do to it must require a weight and balance correction, even small areas of paint touch-up must be accounted for. Fortunately, all went well on the 767. In the other bay we had a 757 that had numerous failed static wick resistance checks. If you get too many wicks that do not work it will interfere with communications and other systems. One of the outboard ailerons was replaced due to failed static wick checks. Amazingly the replacement aileron also failed. It was discovered that the wick bases were not contacting the underlying carbon fiber, but were sitting slightly above it on the inserts, and the inserts potting compound acted like an insulator and thus no pathway for conductivity. We came up with a metallic sealant that goes under the base and conducts, problem solved. Ironically, this type of sealant was called for on our 727's, but is not on any other aircraft. Usually, static wick bases are installed with rivets into the underlying structure, but on some of the newer ships you can see small screws, especially if the base is on a balanced flight surface. In the case of a lighting strike, if you get lucky, you can simply replace the base and wick. Sometimes though, the base gets completely burned off and the underlying skin is gone also, time to get a time consuming repair going.

Gregory

Re: Static Wick

Posted: Thu Apr 05, 2018 2:04 am
by CanadianNorth
Replace them all the time in winter on the 748s, the wing covers tend to win. Those ones are attached with two screws, just regular aircraft 10-32 screws. We buy them about a dozen at a time and it usually takes longer to go find a ladder than it does to replace the static wick.

As mentioned previously most airliners in the MEL or CDL it will let you have a given number missing.

Re: Static Wick

Posted: Mon Apr 09, 2018 1:36 pm
by pugman211
Interestingly, recently I've noticed that new A320 neo's were being manufactured without the static wicks on the trailing edge of the fairings. At first, we thought it was a mod for the neo's, but even ceo's don't have them on the fairings anymore. The ones fitted to the ailerons are still present.

Re: Static Wick

Posted: Mon Apr 09, 2018 4:07 pm
by LH707330
pugman211 wrote:
Interestingly, recently I've noticed that new A320 neo's were being manufactured without the static wicks on the trailing edge of the fairings. At first, we thought it was a mod for the neo's, but even ceo's don't have them on the fairings anymore. The ones fitted to the ailerons are still present.

On the flaptrack canoes? I always wondered about those, I thought they were plastic anyway.

Re: Static Wick

Posted: Mon Apr 09, 2018 4:41 pm
by pugman211
LH707330 wrote:
pugman211 wrote:
Interestingly, recently I've noticed that new A320 neo's were being manufactured without the static wicks on the trailing edge of the fairings. At first, we thought it was a mod for the neo's, but even ceo's don't have them on the fairings anymore. The ones fitted to the ailerons are still present.

On the flaptrack canoes? I always wondered about those, I thought they were plastic anyway.



Yes on the flaptrack canoes. They are a composite material, and used to have a static wick on the end of them, same as all others, screwed on by an Allen key. But the new wings rolling off the lines don't have static wicks fitted to them anymore, atleast not on the fairings.

Re: Static Wick

Posted: Tue Apr 10, 2018 2:46 am
by fdxtulmech
Some planes, like the EMB-135/140/145 the wicks themselves are threaded on the end and screw into the base. The base however is basically, glued to the aircraft and is usually what gets blown of during a lighting strike or knocked off. They are easy to replace, but require cure time.