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Some pitot questions

N546RV

Well Known Member
#1: Location. I see from previous discussions that at least one person has mounted the pitot tube in the most outboard wing bay (vs the more common ~mid-span location). I'm very interested in using this location; it seems to provide some solid benefits vs the mid-span location. Specifically, maintenance access is simple (accessed with the wingtip off), and there's no concern whatsoever of interference with the aileron control system (not that I'd consider this a major concern).

The setup I'm considering is to have the pitot mount on the inboard side of that outboard bay. The hard lines from the tube would bend to outboard, and be secured to a piece of angle that would bridge the lightening hole. This would provide really easy access to the pitot/AoA line and electrical connections.

The main thing I'd need to figure out is how to brace the mount against the rib - the little piece of angle provided by Dynon with their mount doesn't work on the flange side of the rib.

Photo to help clear up what "inboard side of outboard" means: :)

EG5WUu0l.jpg


#2 involves routing of the pitot/AoA lines. Rather than drilling dedicated holes through the ribs for these lines, I've been intending to run those lines through the conduit with the wiring. "Conduit" in this case will be 3/4" PEX tubing, so there will be plenty of room in there. I guess the one issue I can think of is that if there was a short in those wires that got things really hot, it'd have a greater chance of destroying my airspeed reference than if the lines were routed elsewhere.

Any thoughts on either of these ideas? I spent an inordinate amount of time today just staring at the mount clamped to the spar web and using my imagination...
 
Ive got a -10, but mounted mine near one of the access holes. I cannot imagine that you?re going to need to do so much maintenance on these things that its worth putting it in the end rib.

That said, I?m not sure it would hurt anything either...
 
On our club RV9A we installed the probe inboard of the aileron bellcrank access bay. It's was a right prick to get in past the rib and required removal of the aileron-to-control column pushrod, and some creative techniques to dimple the skin.

From a club perspective we had to account for the tiedow
rope's arc of movement and therefore needed to mitigate the risk of it getting caught up with the Pitot probe should a member not consider the possibility.

There is sufficient nylon tubing to allow the probe to be pulled out far enough to access the pneumatic fittings, although the controller itself was mounted onto the aileron bellcrank access panel for serviceability assuming electrical things would need attention before pneumatics.

If it were my own aircraft I would have installed it directly into the aileron bellcrank bay.
 
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Why not mount it on the other side of the rib and use the Dynon supplied bracket?

Definitely a possibility I've considered. It'd remove that one bit of complication, at the cost of making accessibility a little worse (but probably not substantially so). I'd probably also have to rethink my strain-relief idea for the connections, but again, not substantially so.
 
Maintenance wise, pitot heads rarely need maintaining. I have changed out 4 pitot heads, in over the 50 or so RVs I've worked on. One for a failed heating element, one where the builder drilled a mounting hole thru a static line inside the head. The other 2 for warranty replacement (long time ago issue Dynon rectified with a recall). Each time the swap out took about a half hour, easily accessible through the stock bellcrank cover location. I would rather deal with the 12 cover screws than 50 or so wingtip screws to access something that rarely needs maintaining. As for the alternate mounting location, go for it, if you like the extra work it involves.
Additional suggestions,
- use a .040 doubler plate, approx 5x6" that rivets to the spar/skin/rib with a airfoil shaped hole through it and the skin so the pitot mount tube can be installed from the inside and held in place with screws upwards thru the skin/doubler, nutplates riveted to the pitot mount flange. Reasoning, this is how other brands install them, also you don't have a permanent pipe sticking out the bottom skin asking to be damaged or do damage to your knee while the wing is waiting to be installed.
-pitot head tubing to 1/4" plastic tubing coupler- I recommend not using the efis plumbing kit supplied couplers with GREEN plastic lock rings, their internal metal barb locking jaws do not like to come apart again after they are engaged. The couplers with BLACK plastic lock rings sold by Cleaveland (Safeair fittings) easily disengage, are reusable & seal perfectly.
 
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Conduit

You may want to think the conduit thought through again. If you are using AOA, you will need TWO 1/4" tubes, plus any wiring for lights, strobes, aileron trim, roll servo, etc. You may find that 3/4" doesn't provide as much space as you think...
 
AOA Considerations

If you want to accurately measure AOA, consider placing the tip of the probe aft of 25% chord (the mount in the picture will get a Dynon tube close to that), outside the propeller arc but inboard from the tip. Just outside of the aileron bellcrank is a good location in RV?s. This places the tube solidly in the flow field under the wing.

Cheers,

Vac
FlyONSPEED.org
 
Hey, just wanted to thank everyone for the feedback. After some more consideration and experimentation - including bending up a piece of Romex as a stand-in for the hard pitot lines - I've concluded that whatever accessibility benefits there might be to the wingtip location are outweighed by additional packaging complexity. So I'm sticking with the more usual mid-span location.
 
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