A heated pitot probe with mounting hardware is available from Gretz Aero (Photo 1). The kit is complete and includes installation instructions. The parts shown in the photo have already been fitted to the wing and have been dimpled and primed (i.e. don't expect them to arrive exactly as shown!).
Since the heated pitot is large, it cannot be installed in exactly the same location as the "stock" bent tube unit shown in Vans' plans (RV-6/6A). The Gretz instructions appropriately recommend that the pitot be installed adjacent to the rib just outboard of the stock location. This places the pitot immediately outboard of the aileron bellcrank access/inspection panel (i.e. easy access), but also in the vicinity of the wing tie-down point. If the wing tie-down bracket were yet to be installed it would be wise to move the tie-down outwards by one bay to eliminate interference between the tie-down rope and the pitot. If the bracket is already installed and relocating it is not practical, then the pitot could still be positioned as Gretz recommends (however one would forever need to be careful when tying down the plane). Alternatively, the pitot could be installed elsewhere on the wing.
The bottom line with regards to pitot locations is that maintenance access to the pitot should be available once the aircraft is complete. Assuming a dedicated access plate isn't desired, this leaves two options: (1) vicinity of the aileron bellcrank inspection cover or (2) vicinity of the wing tip. To avoid conflict with the tie down, the location just outboard of the inspection cover was avoided. What about installation just inboard of the inspection cover? It is possible for pitot plumbing & wiring to interfere with the aileron pushrod, not to mention that this may be close to the prop wash. Additionally, the fuel tank could be accidentally lowered onto the pitot during fuel tank removal. The remainder of this write-up describes some of the implications and methods of installing the pitot near the wingtip.
Are there drawbacks to mounting the pitot near the wingtip? The possibility of dragging the probe or snagging it on something is higher, service access requires removal of the entire wing tip instead of a relatively small cover, longer tubing lengths are required, and the probe may not be as accurate due to spanwise flow (especially at low speed / high angle-of-attack). Regarding the possibility of reduced accuracy, all airspeed installations ultimately need to be calibrated, so this may be a non-issue, even if it is detectable.
It made sense to route the pitot tubing along the forward face of the spar. Pairs of holes were drilled in the ribs with a unibit and snap bushings installed (Photo 2). The photo is looking outward at the left wing D-section. If the holes are drilled in the rib as close as possible to the rib reinforcement angles, the tubing will just barely clear the fuel tank baffle. Note that many builders simply drill through the rib and the middle of the rib reinforcement angles. Plastic clips (hardware or electrical store) were pop riveted to the spar web in the fuel tank area to hold the pitot tubing. The smaller tubes near the lower spar strips are for the angle-of-attack ports and are discussed in another write-up.
The conversion from aluminum tubing to the tygon tubing was performed with modified bulkhead fittings. The AN bulkhead elbow fitting (see Photo 3) was re-threaded to 1/8 NPT, instead of using an AN to pipe thread (NPT) adapter fitting. It is the same elbow fitting used at the fuel tank inboard rib for the fuel vent (prior to the NPT modification, that is). The Nylo-Seal fitting simply threads to the modified AN fitting. A small amount of Permatex Form-A-Gasket was applied (pipe sealant,teflon tape, or Pro-Seal should also work fine). Just as for the fuel tank vent fitting, a washer or spacer is required between the bulkhead nut and the mounting surface. The fittings required for the installation were as follows:
Bent aluminum tubing was used between the bulkhead fittings and the pitot probe (Photo 4). In addition to the small angle installed between the rib and the pitot mount plate (per Gretz instructions), another angle spanning the wing bay was installed. This stiffened the bottom skin and significantly reduced the fore/aft motion of the pitot.
Once the wing is skinned, pitot installation is likely to be a two-person job. The aluminum tubes must first be fed through the pitot mount (Gretz bracket) from inside the wing and then connected to the pitot fittings (while holding the pitot outside of the wing). The pitot probe can then be inserted into the pitot mount from outside the wing. The tubes attached to the pitot will then line up with the bulkhead fittings on the spar web. Photo 5 shows the installed pitot probe.
Photo 6 shows an alternate pitot installation by Mike Nellis. The conversion from aluminum to nylon tubing occurs almost immediately and uses the AN-816 flared tube to pipe thread fitting. The Nylo-Seal fittings are the same as described above. Routing of the plastic tubing to the front face of the spar can be performed without a bulkhead fitting. Visit Mike's website for more information.
