What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RV-7A rudder penetration for tail light

LettersFromFlyoverCountry

LettersFromFlyoverCountry

Well Known Member
In addition to allowing me the opportunity to move up my annual inspection date to typical "no fly" months, the recent service bulletin and subsequent removal of the tail has given me the opportunity to correct some wrongs when I built.

On my RV7A I didn't want to drill through both the tie down bracket and rudder spar to run the wires for the tail light and strobe. So I had to cockeye it off to one side.

tail_bushing.jpg


The mistake is I then went into the rudder fairing, choosing to use a grommet for the entry point.

This was dumb for many reasons. First, using the AMP connector means I'd have to cut wires to remove the rudder anyway and, second, you get a lot of flexing in the wire between the rudder and the vertical stabilizer.

I'm thinking about a two inch wide rectangular "slit" in the fairing would make more sense and I'm wondering what other folks have done here?
 
No pics fully assembled, but I drilled through the hinge bracket and used a spacer between the hinge bracket so I could install an adel clamp on the bracket to hold the wires underneath the hinge bracket. I used 3 layers of heat shrink and dropped the wires down the front of the lower fiberglass fairing. The wire seems to stay in place via the adel clamp and the rudder rotates around it, I'm sure it's rubbing on the bottom of the rudder fairing but doubt it rubs through the heat shrink. I left enough extra wire so I can remove the taillight from the rear and disconnect it.
4CF58DD9-80BF-4CFA-B861-18E9E4D7514C-5782-000002B18EFCC2E9_zpsab828edf.jpg
 
When running wires to a moveable control surface, i always try to run the wires vertical for a short distance on the "fixed" side. This gives more of a rotation of the wires as opposed to bending at one point.

I hope this makes sense. I can visualize it, but it's difficult to put into words.
 
Slot in the rudder cap works well

I put a slot in the rudder cab about 2" or so wide and about 1/2" tall. I cemented a split piece of small diameter tygon tubing onto the bottom edge of the slot as a friction reducer. I also put 3 layers of heat shrink on the wire bundle where it passes into the rudder cap. Sorry, but I have no pics.
 
That's an area I check very closely an annual time .... to see if there's any evidence of chafing or wear. So far, none found. :)
 
Bob,

I routed my tail light wires the same as in your first picture coming out of the empennage but then I routed the wires straight up and through an adel clamp on one of the rudder bracket nuts and then curved it over the top of the "entrance" to the rudder fairing. No slot required. It's then attached to the bottom of the rudder soon after it enters the fairing. It's wrapped in shrink tubing and spiral wrap but it doesn't touch or bind anywhere through all angles of the rudder and is very secure. Hope that makes some sense. I'll try to get a picture tonight.
 
I have the exact same exit as you from the fuselage. Here is the slot I cut in the lower rudder cap, directly across from the exit.

IMG_2747-M.jpg


I sized the slot big enough to get a 3 pin Molex connector through the slot.

A rubber grommet can be squished in place in the slot to protect the shielded wires for the tail light and strobe.

IMG_2746-M.jpg
 
In past experience with robotics, we often would put a 90 deg turn (kinda like Mel was saying) such that the motion of the wire was not a flex but rather a twist over a distance. Stranded conductors generally can tolerate a limited twist more than a flex.

Worst case is a flex which is occurring at a hard fixed junction (forming a physical discontinuity if you will). The flex gets concentrated at the physical discontinuity and wire breakage is likely to occur there over time.
 
Grumpy-Hodge said:
In past experience with robotics, we often would put a 90 deg turn (kinda like Mel was saying) such that the motion of the wire was not a flex but rather a twist over a distance. Stranded conductors generally can tolerate a limited twist more than a flex.
Worst case is a flex which is occurring at a hard fixed junction (forming a physical discontinuity if you will). The flex gets concentrated at the physical discontinuity and wire breakage is likely to occur there over time.
Click to expand...

Actually that's EXACTLY what I was trying to say. Just not that good with words.
 
I drilled a hole in the rudder bottom so I could insert a snap bushing and cut a vertical slot up from that hole to the edge of the rudder bottom.

My rudder is attached with #6 screws so it can be easily removed, the snap bushing pushed out and the wires remove. Also, you can cut the snap bushing so you can remove it from the wires, if needed.
 
I installed a piece of plywood with a slot for removal of the wires in the rudder bottom covered, strengthened and weatherproofed with glass. A hole with a grommet is at the hinge line, so the wires don?t move a lot. A good thing would have been to round and smooth the rudder bottom with flox for anti chafing.
The wires go through the lower hinge bracket and the rear bulkhead. The rear bulkead has a larger hole than the hinge bracket. There are connectors inside the fuselage and inside the rudder bottom, so whenever I remove the vertical stab the wires stay with the stab (the connector in the fuse slides throug the larger hole in the rear bulkhead.



 
Bob, because you have routed the wiring through the bottom of the rear bulkhead (and to one side) I thought this solution might be of interest to you. In this case after the wiring comes through the rear bulkhead is is routed vertically and clamped to the rear bulkhead with an adel clamp. It then spills over the rear of the rudder fairing. In this case the rear of the rudder fairing has been cut down a bit to allow this to happen. You can see what I mean in the photo. Once inside the rudder fairing the wiring is clamped to the bottom of the fairing. There is no possible wire rubbing with this arrangement.

Incidentally my rudder fairing is attached with nutplates for removal. There is a Mate n Lock connector inside the rudder fairing. So it is relatively easy to remove the rudder and rear nav light while leaving the wiring intact.

Being clamped to the rear bulkhead, the wiring cannot "work" at the rear bulkhead penetration as the rudder swings. I like that.

Anyway just another possibility.

However you do it, don't forget to drill a hole in the bottom of the rudder fairing for water to escape.


imgurl
 
Mine looks more or less like Bob B.'s above. I just used extra headshrink and small diameter corrugated chafe tubing in the unlikely event it rubbed anywhere.
 
I ended up adding the Adel clamp on a bolt I have going through the hinge bracket. It is, indeed, a much better situation to "go vertical.".the only problem is on full left deflection, the front of the fiberglass fairing hits the clamp. I'll have to cut that down a bit.
 
LettersFromFlyoverCountry said:
I ended up adding the Adel clamp on a bolt I have going through the hinge bracket. It is, indeed, a much better situation to "go vertical.".the only problem is on full left deflection, the front of the fiberglass fairing hits the clamp. I'll have to cut that down a bit.
Click to expand...

Bob, there's no problem with cutting the fairing down. Give yourself plenty of clearance. Don't forget the drainage hole at the low point in the bottom of the fairing. That's not an area you want to accumulate water (weight and balance).
 
Mine is like Bob B's too. With the small difference that I used 2 Adels (one on each bolt) and the wire curve is over on the right side a little (still within trail of the fuselage so it is not sticking out in the wind as you would think)
 
Captain Avgas said:
Bob, there's no problem with cutting the fairing down. Give yourself plenty of clearance. Don't forget the drainage hole at the low point in the bottom of the fairing. That's not an area you want to accumulate water (weight and balance).
Click to expand...

I don't understand. The adel clamp is attached to the bolt under the bracket. On full left deflection the top front of the fairing hits the rubber on the clamp. I don't know how to give myself plenty of clearance without cutting the front of the fairing to allow full deflection of the rudder. I got the wire down into the fairing itself just fine.
 
PM sent

Bob,

I sent you a PM the other day. It should solve your issue. Did you get it?
 
LettersFromFlyoverCountry said:
I don't understand. The adel clamp is attached to the bolt under the bracket. On full left deflection the top front of the fairing hits the rubber on the clamp. I don't know how to give myself plenty of clearance without cutting the front of the fairing to allow full deflection of the rudder. I got the wire down into the fairing itself just fine.
Click to expand...

Bob, I think you must be misreading my previous post. Of course you have to cut the front of the fairing. You can see I've done exactly that in my previous photo. I'm just saying that you should cut off fully sufficient to give yourself plenty of clearance (ie. there's no need to scrimp on the fairing cut).
 
Ah, I see. I read your comment as "There's no REASON to cut the fairing down..." Rather than what it actually said, which was , "there's no PROBLEM cutting the fairing down."

This is happening more often with me these days and I'd rather not think about what this means at my advancing age.
 
You must log in or register to reply here.
Back
Top