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Need advice on pitot replacement procedure

bill.hutchison

Well Known Member
The original builder of my RV used a pitot tube that doubles as a static source. Originally I thought this would be handy/helpful, since I'm replacing it with a Dynon heated Pitot/AOA unit to go with an upcoming HDX EFIS and ADAHARS unit.

The idea is that I'd use the lines already in the wing for pitot, use the existing static line for the AOA, and then plumb a couple of new static ports into the airplane - there are no other static lines in this RV.

However, I'm unsure about how to go about doing this now, and here's why:

In the first picture, you see the inspection mirror showing a couple of hard lines with AN fittings going all the way down into the mast. These lines arch up and go into the large hole, which, directionally is FORWARD, toward the leading edge. If I feel around in there, they then bend inboard and penetrate the next rib - the second and third photos show this a little more clearly.

This routing seems odd to me, because it seems like the lines are running through the fuel tank, or, if they're not, they're bending back around the rib and then going behind the tank but I can't tell that for sure. Either way, I can't get to them very easily and there is very little slack in them.

So...with the new pitot, does it make sense to cut the existing hard lines, cut the ones on the new pitot shorter and then splice them together with AN fittings? Or plastic tubing? Something from the Dynon plumbing kit?

EDIT - further thought....the mast is screwed into the wing on nutplates....maybe it makes sense to unscrew the mast, drop it low enough to access the AN fittings and unscrew them, and then remove the pitot? Then cut the lines on the new one and match them to the existing AN fittings?

I figure there are multiple ways to approach this, so I'd be interested in the advice of someone more experienced than I here. What say you?
 

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I think you’ll find the instructions from Dynon recommend not cutting the metal lines from the new pitot tube, if you’re transitioning to nylon or plastic. You need some free-air run of the metal lines to make sure you don’t melt the nylon or plastic ones.
I presume you’ll also have to run power out to that location; and find a spot to mount the temperature controller as well. If you need to pull a wire, may as well pull plastic tubing at the same time.
The heat can pull a pretty good current, don’t run the wire near a magnetometer.
 
I think you’ll find the instructions from Dynon recommend not cutting the metal lines from the new pitot tube, if you’re transitioning to nylon or plastic. You need some free-air run of the metal lines to make sure you don’t melt the nylon or plastic ones.
.

Well....that's sort of the problem...I can't GET to where they transition right now....that's why I'm trying to figure out what to do. I *really* don't want to pull the fuel tank.

Power is already there.
 
You didn’t say in your original post what airplane you have. I’m guessing either RV6, or RV4. The pitot line, and maybe in your case, the static line, runs behind the fuel tank, between the fuel tank aft baffle and forward side of the wing spar web, usually made out of 1/4” aluminum tubing. There’s about a 1” gap there. If that is so, then you don’t need to do anything other than use that static line for your AOA line, as you’ve said, and run a new static line (plastic) to the aft cabin somewhere. If you don’t want/need to have a dual port heated pitot tube, you could route that static line to a leading edge pop rivet (AKA) static port for use as your AOA dynamic feed. Works for several people here (including me).
 
You didn’t say in your original post what airplane you have. I’m guessing either RV6, or RV4. The pitot line, and maybe in your case, the static line, runs behind the fuel tank, between the fuel tank aft baffle and forward side of the wing spar web, usually made out of 1/4” aluminum tubing. There’s about a 1” gap there. If that is so, then you don’t need to do anything other than use that static line for your AOA line, as you’ve said, and run a new static line (plastic) to the aft cabin somewhere. If you don’t want/need to have a dual port heated pitot tube, you could route that static line to a leading edge pop rivet (AKA) static port for use as your AOA dynamic feed. Works for several people here (including me).

Yup. It's an RV-6A.

Yeah, the basic plan is to re-use the current static line for AOA and plumb a new one in. I'm just trying to figure out how to connect the new tube to the current aluminum tubes to do exactly that.

I *think* I can push the mast up enough to get to the AN fittings in it and disconnect them, and then cut/flare the tubes on the new tubes of the new pitot to the existing aluminum tubes in the wing.
 
Flexible connection

Access is very tight in there especially without removing the fuel tank and it will be a challenge for sure to fit flared connector fittings properly. Assuming the lines on the new pitot/AOA are the same diameter as the existing hard lines (1/4") then I wonder if there is any reason to not use a length of some flexible rubber vacuum or Tygon hose with spring clamps to join between the hard lines?
https://www.aircraftspruce.com/catalog/appages/tygon.php
 
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Well....that's sort of the problem...I can't GET to where they transition right now....that's why I'm trying to figure out what to do. I *really* don't want to pull the fuel tank. Power is already there.

Pulling the tank is not hard once empty of fuel - maybe a 20 minute job. If you need a paint cutter for the tank screws then that would add more time and cost of a cutter.

I pulled my RV6 tank when I changed to a new pitot but I also had to add AOA and power. Mine fits snug so I had to temporally use some thin material to help get the dimpled holes on the tank flange to slide back over the spar.
 
I would cut the existing line a splice with something flexible. Mine is spliced. Like Bob said...you just need to make sure there enough metal run from the new mast to dissipate any heat conducted from the pitot tube.
 
Pulling the tank is not hard once empty of fuel - maybe a 20 minute job. If you need a paint cutter for the tank screws then that would add more time and cost of a cutter.

I pulled my RV6 tank when I changed to a new pitot but I also had to add AOA and power. Mine fits snug so I had to temporally use some thin material to help get the dimpled holes on the tank flange to slide back over the spar.


I may look up a tutorial on how to remove the tank.

I didn't build my plane, but I seem to be trying to reverse-engineer my way into it, because I keep disassembling....everything. :)
 
pitot tubing

It isn't very hard to remove a tank. It is straight forward. Here is a picture of what I did. The large black tube under the pitot lines are for wiring.
You really need access, for the lines, wiring and just plain gittin in there.
ArtIMG_0436.jpg
 
Tank Removal

I may look up a tutorial on how to remove the tank.

I didn't build my plane, but I seem to be trying to reverse-engineer my way into it, because I keep disassembling....everything. :)

I don't know that you will find a tutorial but once you remove the wing root covering strip it will look straight forward. You can refer to drawings 18A and 21 for the RV6/6A.
With the wing root cover strip removed you will see there is only one bolt attaching the tank to to the fuselage. The bolt should be lockwired so you will need to cut that. Next there should be a -6 (3/8") Fuel line and a -4 (1/4") vent line to disconnect from the tank. There will be one fuel sender wire to disconnect which might be on the back side of the tank if you have a flop tube pickup in the left tank. See manual section 7 figure 7-6 for flop tube info.

After that removing all the perimeter screws on the fuel tank allows it to be removed. It may take some gentle force to get it started. Removing the fuel cap provides a handhold for pulling.
 
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Yup. It's an RV-6A.

Yeah, the basic plan is to re-use the current static line for AOA and plumb a new one in. I'm just trying to figure out how to connect the new tube to the current aluminum tubes to do exactly that.

I *think* I can push the mast up enough to get to the AN fittings in it and disconnect them, and then cut/flare the tubes on the new tubes of the new pitot to the existing aluminum tubes in the wing.

Bill,
Consider a push fitting for 1/4” tubing:

https://www.steinair.com/product/fitting-straight-pitot-union-connector/

This will seal around 1/4” plastic and aluminum tubing. For your aluminum tube, make sure you have a clean cut with no scratches on the aluminum tube. This is what I am doing on my RV6 build. I have a 1/8” ID 1/4” OD silicone tube going from my AOA port in the leading edge of my wing all the way to my EFIS instrument in the cockpit - no fittings. My pitot line is standard aluminum 1/4” OD tubing as per Vans plans. At the wing root I’ll transition that line to the silicone line with a fitting as shown, from there to the instrument. These lines both run behind the left fuel tank.
 
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Bill,
Consider a push fitting for 1/4” tubing:

https://www.steinair.com/product/fitting-straight-pitot-union-connector/

This will seal around 1/4” plastic and aluminum tubing. For your aluminum tube, make sure you have a clean cut with no scratches on the aluminum tube. This is what I am doing on my RV6 build. I have a 1/8” ID 1/4” OD silicone tube going from my AOA port in the leading edge of my wing all the way to my EFIS instrument in the cockpit - no fittings. My pitot line is standard aluminum 1/4” OD tubing as per Vans plans. At the wing root I’ll transition that line to the silicone line with a fitting as shown, from there to the instrument. These lines both run behind the left fuel tank.

This looks interesting. I'm not sure how hard it will be to remove the existing tube/mast. Once I can get it removed/disconnected from the AN fittings, I can figure out how I want to plumb the thing. Seems like removing the tank gives me options.

And, lets face it, gives me a reason to spend some time in the hangar, wrenching on the plane. With all the other avionics upgrades I'm doing, this might not be a bad idea. My fuel senders kind of suck and replacing them wouldn't be a bad idea either....hmmm....

As far as running a new static port/line...any thoughts on that? The full Dynon plumbing kit or a static port kit from Spruce or Stein?
 
I would opt for the static kit from Spruce, Stein, or Vans. Less money and relatively easy (other than crawling back into the tail cone - which you also have to do with the Dynon system).

If you want to “roll your own”, all you need is two LP4-4 pop rivets, some low pressure tubing, and one barbed plastic T-fitting, which you can get at Home Depot, Auto Zone, etc. If you need the tubing, let me know - I have plenty.
 
AOA port in wing skin

Bill,
Consider a push fitting for 1/4” tubing:

https://www.steinair.com/product/fitting-straight-pitot-union-connector/

This will seal around 1/4” plastic and aluminum tubing. For your aluminum tube, make sure you have a clean cut with no scratches on the aluminum tube. This is what I am doing on my RV6 build. I have a 1/8” ID 1/4” OD silicone tube going from my AOA port in the leading edge of my wing all the way to my EFIS instrument in the cockpit - no fittings. My pitot line is standard aluminum 1/4” OD tubing as per Vans plans. At the wing root I’ll transition that line to the silicone line with a fitting as shown, from there to the instrument. These lines both run behind the left fuel tank.

Hi Scott,
How did you attach the silicone tube to the AOA port rivet (probably like is done for the static- with some sealant?) and what exact measurement location did you decide on for the port in the -6 wing? Also assume you have an EFIS that doesn't require an ADAHRS module mounted back in the tailcone?

(Apologies Bill this is slightly off the original topic question)

Thx
Paul.
 
Static Port Location

As far as running a new static port/line...any thoughts on that?

Regardless of which static port you go with I would recommend you review Van's recommendation for the location. It is not shown on the drawings but it can be found in the fuselage section 8 of the main RV6/6A manual. Snapshot attached
 

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Regardless of which static port you go with I would recommend you review Van's recommendation for the location. It is not shown on the drawings but it can be found in the fuselage section 8 of the main RV6/6A manual. Snapshot attached

Wholeheartedly agree with Ralph - static ports, and their locations, take some time for a designer to pin down, and once they do, there is little reason to reinvent the wheel;. Use the standard location, and the standard (pop rivet) port, and you’ll get accurate static. Choose something else, and you’ll likely be chasing static errors for some time.

Paul
 
Replacing Fuel Senders ?

This looks interesting. I'm not sure how hard it will be to remove the existing tube/mast. Once I can get it removed/disconnected from the AN fittings, I can figure out how I want to plumb the thing. Seems like removing the tank gives me options.

And, lets face it, gives me a reason to spend some time in the hangar, wrenching on the plane. With all the other avionics upgrades I'm doing, this might not be a bad idea. My fuel senders kind of suck and replacing them wouldn't be a bad idea either....hmmm....

As far as running a new static port/line...any thoughts on that? The full Dynon plumbing kit or a static port kit from Spruce or Stein?

Replacing your fuel senders would greatly add time and most likely frustration to your project especially if they are prosealed in like most are. Not sure what you mean by they suck :confused:, but they are never linear because of the tank shape and dihedral.
If you monitor your fuel tank level via an EFIS or engine monitor system some of them have calibration procedures that helps make the readings more linear.
 
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Replacing your fuel senders would greatly add time and most likely frustration to your project especially if they are prosealed in like most are. Not sure what you mean by they suck :confused:, but they are never linear because of the tank shape and dihedral.
If you monitor your fuel tank level via an EFIS or engine monitor system some of them have calibration procedures that helps make the readings more linear.

It was an idle thought. Not going to do that. :)
 
Hi Scott,
How did you attach the silicone tube to the AOA port rivet (probably like is done for the static- with some sealant?) and what exact measurement location did you decide on for the port in the -6 wing? Also assume you have an EFIS that doesn't require an ADAHRS module mounted back in the tailcone?

(Apologies Bill this is slightly off the original topic question)

Thx
Paul.

Paul,
The silicone tube has a 1/8” ID, and fits snugly over the tail of the LP4 rivet (don’t forget to knock the mandrel out first). The -4 gives you a little more length for the tube to hang on to. I did also apply plenty of silicone sealant around the tube, and also held in place with a nearby adel clamp on the adjacent rib. I took measurements looking for a 30* location. The most forward rivet on the nose rib was a little aft of that location, but close enough, since this is something you program in the EFIS with flight testing, so I drilled that one out. Apparently Vans did a similar thing on the RV12 and found that a slightly more aft location created less turbulence around the port and gave more consistent results. At least that’s what I read on this forum. I’ll find out eventually. Of course my fuel tank was off for this installation. The silicone tube parallels the aluminum pitot line along the forward side of the wing spar, behind the fuel tank.
 
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“And, lets face it, gives me a reason to spend some time in the hangar, wrenching on the plane. With all the other avionics upgrades I'm doing, this might not be a bad idea. My fuel senders kind of suck and replacing them wouldn't be a bad idea either....hmmm....”

If you can just recalibrate the fuel gauges that might be a better option than replacing the fuel senders in the tank (if you can). I replaced both of them in my -4 (they were bad) and had to replace one in the -8 I fly now. I thought about replacing the one in my other -8 tank but all it needed was recalibration so maybe try that before you do anything drastic. I do not like working with proseal either.

As far as your other option- if you need parts get them from Stein not Dynon. Not saying anything bad about Dynon but they are a big company and I think it’s better to support small business like Stein. They are active participants in this forum and we need to keep sending business their way.

Just like supporting the VAF Forum!
 
Additional holes in ribs

It isn't very hard to remove a tank. It is straight forward. Here is a picture of what I did. The large black tube under the pitot lines are for wiring.
You really need access, for the lines, wiring and just plain gittin in there.
ArtView attachment 19338

The max allowable hole size for where the big black conduit goes is 5/8" per Vans. Here's the guide for where it is OK to drill:
https://www.vansaircraft.com/faq-technical-builder-items/wing-wiring-routing-wires-in-the-wings/

Good luck.
 
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