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Can I run AOA tubing in this conduit?

MacCool

Well Known Member
I need to run some 1/4" blue AOA tubing from my pitot mast to the cockpit. Hard to do after the build...options include fishing it down to the root in some abrasion sleeve through the lightening holes right behind the pushrod.

BUT...I'm wondering if I can just cut a little access hole in the 3/4" nylon conduit and run the AOA tubing root-ward inside of that? The only other stuff in that conduit AFAIK is the wiring for the wingtip strobes and navigation lights.
 

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I want to say yes but the real answer is maybe.

Is there enough room in the conduit?

Will tubing slide through the conduit without pulling the wires out?

Can you cut the conduit with the wires inside and not damage the wires?

The other option that I see would be to take the access covers off and see if you can made new holes that "snap bushings" can go in to run the tubing in.
 
Sure. If you cut into it with a knife, then switch to snips after a hole is made you have little chance of damaging wires.
 
I swapped out all my lights for LEDs last year and pulled all new wiring thru the conduit. The wiring didn't appear to take much room in that conduit. Should be enough space for the AOA tubing.
Might make a small incision in conduit and check with borescope.
Much better option than trying to snake tubing in front of fuel tank.

Ken
 
AOA tubing through conduit

I did exactly what you are describing on my RV8. The only difference was that I used 3/16" (-3) aluminum tubing so as to take up less space in the conduit. I also lubricated the conduit with a spray of dry lubricant to ease the sliding of the tube through the conduit.
 
I did exactly what you are describing on my RV8. The only difference was that I used 3/16" (-3) aluminum tubing so as to take up less space in the conduit. I also lubricated the conduit with a spray of dry lubricant to ease the sliding of the tube through the conduit.

Good tip. I'm hoping to vacuum a string down the tubing from the cockpit entry point of the conduit and pull the tubing back to the pitot.

Do you think there's any reason to be concerned that that AOA tubing running in the same conduit with wiring might abrade the wiring and cause a short someday?
 
I swapped out all my lights for LEDs last year and pulled all new wiring thru the conduit. The wiring didn't appear to take much room in that conduit. Should be enough space for the AOA tubing.
Might make a small incision in conduit and check with borescope.
Much better option than trying to snake tubing in front of fuel tank.

Ken

Where did you find the cockpit end of the black conduit? I've been guessing it enters the cockpit underneath F-940 left fwd seat floor. Haven't pulled the seat floor yet. I didn't want to squander all the fun at one time....I want to drag it out...:)
 
That's exactly what I did. I used 3/16" tubing within the wing conduit. Out of the pitot tube's AOA port, I used a 1/4"-to-3/16" push reducing union to 3/16" tubing.

DSCN4028.JPG


From there the 3/16" tubing easily slid inside of the conduit already in the wing.
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I believe the conduit ended just at the wing root and did not extend thru the sidewall. If memory serves, the wiring then traveled thru grommets in the fuselage wall.
 
off topic

This thread reminded me of a time waay back when I tied a 30 foot long string to my neighbors cat's collar then put the cat into the air duct feeding back into the neighbors apartment from my place. The cat was lured home with a shake of the treat jar. We then tied coax cable to the string and pulled it back into my apartment. Voila, free cable TV.
 
I believe the conduit ended just at the wing root and did not extend thru the sidewall. If memory serves, the wiring then traveled thru grommets in the fuselage wall.

Yeah...pulled the floor today and note that that's how mine was constructed too....the entry into the cockpit is a grommet.

On the positive side....that grommet will easily accommodate some 1/4" OD AOA tubing. Unfortunately I have to find a way to leap the gap between grommet and end of conduit. I'm going to try some piano wire from one end or the other....hope to then be able to pull some string.
 
Yeah...pulled the floor today and note that that's how mine was constructed too....the entry into the cockpit is a grommet.

On the positive side....that grommet will easily accommodate some 1/4" OD AOA tubing. Unfortunately I have to find a way to leap the gap between grommet and end of conduit. I'm going to try some piano wire from one end or the other....hope to then be able to pull some string.

This is what my engineer and I did. Conduit stops in the wing root. We took the fairing off and with a combination of teamwork, expletives, beer, and needle-nosed pliers managed to thread it through the same grommets the lighting wiring went through. Easily achievable.
 
This is what my engineer and I did. Conduit stops in the wing root. We took the fairing off and with a combination of teamwork, expletives, beer, and needle-nosed pliers managed to thread it through the same grommets the lighting wiring went through. Easily achievable.

DOH! Didn't think about pulling the fairing :eek: (did think about the beer, though). Thanks for the tip.

Looks like the wing fairing comes off with just a bunch of screws into nutplates, along with the rubber gasket?
 
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If the conduit is unbroken end to end, you might be able to use a vacuum cleaner on the outboard end, and feed a string in the other end. Pretty impressive how well that works, at least inside long tubes without wires!
 
Pulling wire

Wow. 30 years in Telecom. Pulling a wire 8' is not even a 2.0 on my Oh ****-O-Meter. I've pulled Romex into an insulated wall with no conduit into an insulated attic!:eek:
Pulled several 200 pair voice cables under crawl spaces. Once had my head light fail. I could hear the **** racoons growling around me in the pitch black!

Snag about 20' of telecom wire. Cat 3, 4, or 5. Not 6. It's got a separator inside. Tape off the end so it's nice and round and slide that puppy in. Strip off 3" of jacket and tape the victim to the 4-pair. Slide it through. No problem. Done it several times already.

Or, disconnect the existing cable. Tape the telecom wire to it. Pull it through. Tape everything back on and pull it back. Add string for future. Needless to say, my airplane and home have pull strings for future use. House is wired for 7.2 sound system.

Drill a hole in that black conduit carefully with pen soldering tool. Makes a nice round hole.
 
I appreciate the input, but pulling the AOA tubing through the conduit isn't the problem...that will be easy. Getting it across the gap between the end of the conduit and the fuselage entry point is going to be the challenge. Pulling the wing root fairing may get me there, though...
 
I had the wing tip off and used a tool I purchased from Harbor Freight, The tool is a bunch of fiberglass (maybe plastic) rods 15" long that you thread one into the next to pull or push wire or tubing.


For fishing the wires out between the side of the fuselage and the wing butt rib I used another tool from Harbor Freight: a 18" long locking forceps.
 
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I had the wing tip off and used a tool I purchased from Harbor Freight, The tool is a bunch of fiberglass (maybe plastic) rods 15" long that you thread one into the next to pull or push wire or tubing.
If I can't use the black nylon conduit for some reason, with the wingtip off, can I just slide a 12 foot length of PVC conduit into the second lightening hole and run it from tip to root? I'd then push the AOA tubing down the PVC, then slide the PVC back out leaving the AOA tubing in place?
 

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Putting a hole in the corrugated conduit

If there is room , yes run the AOA tube in the conduit. Enter the conduit via hole in the conduit. To put a hole in that conduit, use a soldering iron to melt a hole without cutting the wires inside. Once the hole is melted, insert a rubber grommet to prevent chafing. I would also add an abrasion sleeve over the tube as it passes into the conduit.

I read about this process on this forum and tried it. It works well.

I am sure there are other options too.
Enjoy
 
Pitot and AOA tubing

An alternate solution for you. Please find three photographs of my installation of the plastic tubing from the Dynon pitot tube using the holes in the ribs just behind the main spar.

The first photo shows the location of the pitot tube and AOA red and blue plastic tubing running through plastic grommets in the ribs. Plus it shows my installation of the wiring conduit for the wing tip lighting.

The second photo shows how the two plastic tubes are connected to the pitot tube.

The third photo shows the bracket I manufactured to ensure clearance with the aileron bellcrank.

https://www.flickr.com/photos/189412597@N04/shares/2M68qc

https://www.flickr.com/photos/189412597@N04/shares/879819

https://www.flickr.com/photos/189412597@N04/shares/jb77B3

An alternate for you to think about.

Cheers,
 
If I can't use the black nylon conduit for some reason, with the wingtip off, can I just slide a 12 foot length of PVC conduit into the second lightening hole and run it from tip to root? I'd then push the AOA tubing down the PVC, then slide the PVC back out leaving the AOA tubing in place?

Sure you can, but don't you want to keep that line from flopping around? Rubbing on the edges of the ribs?

I installed my AoA after all the other installs and just about ready for first flight. You can each pretty far through the inspection plates. I made some stand offs (another research topic) and drilled, pull-riveted them to the rib and ran the 1/4" through there. Where I could not reach I installed a length of aluminum tube to suspend it over the ribs close to the root and into the fuse. It was 3003 tubing, don't recall what size.

That tubing is stiff as elephant hair. I use a heat gun to straighten and bend to a nice shape. Some stress free radius bends can be made a lot smaller that way.

Just be sure to vacuum out all the chips if you drill in there. It is a big puzzle, have fun with it. Cheat if you need to. :D
 
I had the wing tip off and used a tool I purchased from Harbor Freight, The tool is a bunch of fiberglass (maybe plastic) rods 15" long that you thread one into the next to pull or push wire or tubing.

For fishing the wires out between the side of the fuselage and the wing butt rib I used another tool from Harbor Freight: a 18" long locking forceps.

Heh...I was at Harbor Freight yesterday to get the forceps, and stumbled onto those rods right next to them. The forceps....well...I won’t be doing any surgery with them, but they were $6. Likewise, the extending rods, which appear to be perfect for the task at hand, were $6. The only thing that’s keeping me from completing this task now is sufficient kerosene to run the pair of bullet heaters. It’s -2F in my hangar right now. Hard to get enthusiastic about airplane maintenance.
 
Sure you can, but don't you want to keep that line from flopping around? Rubbing on the edges of the ribs?

I installed my AoA after all the other installs and just about ready for first flight. You can each pretty far through the inspection plates. I made some stand offs (another research topic) and drilled, pull-riveted them to the rib and ran the 1/4" through there. Where I could not reach I installed a length of aluminum tube to suspend it over the ribs close to the root and into the fuse. It was 3003 tubing, don't recall what size.

That tubing is stiff as elephant hair. I use a heat gun to straighten and bend to a nice shape. Some stress free radius bends can be made a lot smaller that way.

Just be sure to vacuum out all the chips if you drill in there. It is a big puzzle, have fun with it. Cheat if you need to. :D
If I have to run the tubing free in the ribs, my plan is zip-tie standoffs and anti-chafe tubing, but Plan A is the hole in the tubing at the inspection plate, feeding it to the root, and guiding it into the fuselage grommet with forceps after removing the wing fairing. My kerosene heaters, which look, smell, and sound like jet engines, are also ideal for heating up the tubing. The consensus at the avionics shop across the taxiway is that anti-chafe won’t be needed in the conduit, but might be a good idea and the entry and exit points
 
Wirejock’s done this before

I’m liking wirejock’s thoughts. Along those lines... Thinking a little out of the box, and definitely beyond my RV build experience....
If the wingtip wire isn’t super expensive, is it possible to disconnect the tip light wire at the wingtip, tape it up carefully in a snagless manner to a pull string, and then pull the fuselage end of the wing light wires into the fuse where you can get to it. Now you have a pull string from the wings to the fuse for whatever you want. Then pull new wing light wires, the aoa tube, and a pull string for future use.
 
An alternate solution for you. Please find three photographs of my installation of the plastic tubing from the Dynon pitot tube using the holes in the ribs just behind the main spar.

The first photo shows the location of the pitot tube and AOA red and blue plastic tubing running through plastic grommets in the ribs. Plus it shows my installation of the wiring conduit for the wing tip lighting.

The second photo shows how the two plastic tubes are connected to the pitot tube.

The third photo shows the bracket I manufactured to ensure clearance with the aileron bellcrank.

https://www.flickr.com/photos/189412597@N04/shares/2M68qc

https://www.flickr.com/photos/189412597@N04/shares/879819

https://www.flickr.com/photos/189412597@N04/shares/jb77B3

An alternate for you to think about.

Cheers,

The original pitot tube ran the line like that...through grommets in each rib...very nice. The previous owner wanted the plane to be IFR-certified, so a couple of years ago he had a Dynon heated pitot installed. That unit also has a port for AOA, but the A&P that installed it didn't plumb that because a) it was hard, and b) it was unneeded since the EFIS already had AOA coming from a wing port in the right wing. Unfortunately, my new AFS/Dynon EFIS doesn't accommodate a wing port for AOA, but does work with the AOA port on the Dynon pitot. So now, if I want AOA (and I do), then my options are either AOA display mounted on the glare shield and hooked up to the wing port, or use my existing AOA in the pitot and spend a few $$ for plumbing, and suffer the hassles of running new AOA tubing from the pitot...which is where I am now. I think it's do-able to feed that tubing one way or another....this post is about finding the easiest way to do that and avoid spending $1100 on a glareshield-mounted display.

This kind of project is probably old-hat to most of you here, but even though I've been a pilot for decades, I've never built an airplane...I've never even disassembled one anywhere near as far as I've disassembled this one. I'm an utter noob at this. Four months ago I had no idea how RVs are constructed, but boy am I learning fast. It's very cool, and I really appreciate everyone's help.
 
I’m liking wirejock’s thoughts. Along those lines... Thinking a little out of the box, and definitely beyond my RV build experience....
If the wingtip wire isn’t super expensive, is it possible to disconnect the tip light wire at the wingtip, tape it up carefully in a snagless manner to a pull string, and then pull the fuselage end of the wing light wires into the fuse where you can get to it. Now you have a pull string from the wings to the fuse for whatever you want. Then pull new wing light wires, the aoa tube, and a pull string for future use.

I'm hopeful that Harbor Freight has solved my problem. And for $6.

.
 

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Well, the answer to the question I originally posed is "yes".

I used a Dremel to cut a hole in the conduit...it was mostly empty. I fed the Harbor Freight fiberglass fish rod down toward the fuse...it went easily until it exited the tubing in the root gap and hit the fuselage. I removed the upper half of the wing fairing, was able to see the brass end of the fish rod and the fuse entry point of the wire bundle. I used the 12" Pean hemostat to nudge the brass end of the rod forward about 1/2" and up about 1/2", and it easily entered the fuselage. I heated the tubing end, forced it over the brass end, and drove a little pin through it..cut off flush. I also taped some Mason's twine to the tubing. Then I pulled gently on the fish tape...it brought the AOA tubing and the Mason's twine out through the hole in the conduit. I used the Mason's twine because I'm going to mount the new OAT sensor there and I want to be able to pull the wires for it back down the conduit and into the fuselage.

All-in-all, it took me about 20 minutes and was pretty easy. Next step is feeding the ADAHARS cable from the tail cone to the panel, and the AOA tubing, Pitot tubing and OAT wiring back to the ADAHRS. It's already pretty busy in that tunnel and I'm not sure those items will all fit through the room I have left in the grommets. I appreciate everyone's help. It turned out to be a one-man job, and neither beer nor expletives were required.
 

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