How to install bonding straps?

Mouser · #1 10-12-2009, 12:37 AM

I'd like to install some static wicks on my trailing edges. If I do that, I should really put braided copper bonding straps between the various moving control surfaces and their static counterparts. Since I am now getting to the point of riveting together my vertical stabilizer, I need to finalize how to attach a grounding strap or two to the aft end of the rear spar in the vicinity of the hinges.

Has anyone done this who could provide some guidance on how they did it, or better yet photos?

pierre smith · #2 10-12-2009, 05:08 AM

We used bonding straps in the '70's on our ag airplanes when we put out sulphur dust because it could catch fire and burn to the airplane's hopper. We drilled into the inside of the wing tip rib and attached a wire from the wing to the moveable control surface because the bearings didn't provide an electrical path. We did not, however, have static wicks like you see on some high performance jets.

Regards,

GAHco · #3 10-12-2009, 09:34 AM

Quote:

Originally Posted by Mouser

I'd like to install some static wicks on my trailing edges. If I do that, I should really put braided copper bonding straps between the various moving control surfaces and their static counterparts. Since I am now getting to the point of riveting together my vertical stabilizer, I need to finalize how to attach a grounding strap or two to the aft end of the rear spar in the vicinity of the hinges.

Has anyone done this who could provide some guidance on how they did it, or better yet photos?

The terminals are aluminum and the wire is a flexible braided aluminum.

There is an MS Spec for these. I will try to look up and come back when I can post it.

I suspect they do this to keep the weight down and lessen the chance of abrasion and dissimilar metal corrosion when the wire touches the airframe during its normal motions of travel or blowing around in the breeze.

MJarreau · #4 10-12-2009, 03:33 PM

GAHco,

I would have thought the braid was to increase the surface area of the current carrying capacity.

Can anyone else chime in on this?

PCHunt · #5 10-12-2009, 03:48 PM

I always thought that the braids were for long-term flexibility, since they are attached to a moving object. On my T-6G, the grounding straps to the flight controls are braided, whereas the grounding straps to the cowl are not braided.

$0.02

flyeyes · #6 10-12-2009, 04:55 PM

Quote:

Originally Posted by Mouser

I'd like to install some static wicks on my trailing edges.

I'm sorry this is non-responsive to your question, but I'm curious as to why you want bonding strips..

We've owned and operated a number of IFR aircraft of the years, only one of which had bonding straps and static wicks (a Loran and ADF equipped twin Cessna). I've never missed them on the other airplanes that i can recall.

Unless you're planning a loran as your primary nav, I'd suggest flying the airplane first to see if you have a problem.

kevinh · #7 10-12-2009, 05:08 PM

Quote:

Originally Posted by flyeyes

Unless you're planning a loran as your primary nav, I'd suggest flying the airplane first to see if you have a problem.

Yes! Simplification is good.

apkp777 · #8 10-12-2009, 06:52 PM

Large commercial aircraft are entirely electrically bonded. Mostly because of speed, weather and electronics. All the carbon fiber components are coated with a "conductive coating" making them conductive. A typical Boeing aircraft could probably power your entire neighborhood during Christmas. Bonding makes sense with what they are dealing with.

I doubt you would ever suffer for NOT having any bonding. The all aluminum structure of most rv's should be suitable bonding by itself. Aluminum is a pretty good conductor. If you painted (enameled) every part on your plane, you could have some issues, still doubtful though.

That being said you can make bonding straps by using a length of heavy gauge wire with aluminum lugs crimped on both ends. Use a Bonding Brush to prep the hole on both spars (aileron and rear wing). The resistance of the bonding strap has to be EXTREMELY low for it to function with any value so that is why a "braided strap" is usually preferred. We used both types at UAL.

Mouser · #9 10-13-2009, 07:43 AM

The reason I'm thinking about bonding straps is that I have read several reports on this website regarding dramatic reductions in radio static with the addition of static wicks and bond straps. I'm thinking about installing an HF system in my plane, and HF radios are more prone to static than VHF.

Regarding trying it without the wicks and then adding them after the fact if necessary, installing them before the skin is all buttoned up would be easier and would lead to a more aesthetically pleasing installation. The wicks and bonding straps are pretty simple, so I don't feel like I'm hopelessly complicating my project even if it turns out to be of minimal value.

apkp777 · #10 10-13-2009, 10:07 AM

It won't hurt anything to install them that's for sure. Yes, HF will pick up lot's of static/noise, most sources will be from random radio wave interference from distant transmissions (like an AM radio). I would say do it. Let us know if it works well. Others may want to do the same. You really need VERY low resistance between the wicks and aircraft ground. Even a small amount of corrosion, alodine, alclad or primer/paint will limit the effectiveness. Make sure your bonding is really good. You can paint over the top of everything, just between the sandwich.