Conduit Holes Drilled for Left Wing Ribs

Friday night I managed to drill the Conduit  holes for the left wing ribs. I messed one up so it is at least1/8 inch off center from the others, but I should be able to make that work OK since the conduit I am using is flexible. I will drill the right wing rib holes today. The unibit makes quick work of this. My only concern is that many builders seem to enlargen the holes just a bit more to get them to fit easier, but we'll see how it goes.

In retrospect, there is one thing I should have done differenty before applying my template to mark the holes for the conduit. I should have drawn a difinitive line a specific distance perpendicular to the rib web to more clearly mark the location for the edge of my template, instead of relying on the "edge" of the stiffener depression, which is much less clearly defined. This has resulted in slight varances of the hole alignment from one rib to the next. As I said at the beginning of this process, I was not out for precision, and only time will tell if I really should have applied a bit more attention to detail than I have. I think that either way I slice it, pulling this corrugated conduit through these holes is a major pain in the ass, regardless of what you do. I will be glad when that work is all done.

I spent some time researching VAF, Vans, and Steve Riffe's builders log last night to get some more info about the size of the holes and bushings needed for the RG400 antenna coax that I will use for my Bob Archer wing tip nav antenna, and the pitot lines that will run from the pitot tube back to the fuselage to the necessary avionics locations. I needed to get some specifications for the coax so I know what size hole to drill in the rear tooling holes of each rib. I have to be careful though, because I need to leave the tooling holes in tact to assist with determining the "level" attitude of the ailerons and possibly the flaps against the chord line of the wing, so I need to leave those "as is" until I reach that point in the build.

Steve's site has some really good pics and info about a borrowed solution from other builders to fabricate a bracket that utilizes the attach brackets and harware for the aileron belcrank asembly. This bracket provides a guide that will keep the pitot air lines very close to the web of the main wing spar and away from the actuating arms of the belcrank, and the push rods connecting the joy stick and the aileron. This ensures that the air lines will never come into contact with the moving parts for the aileron or auto pilot servo by routing them underneath that entire assembly. This is a great tip and an easy one at that.

Specs for hole requirements that I was able to find:

Diameter of RG400 coax antenna cable: 3/16 inch (4.9530 mm) (requires at least a 3/16 inch hole and will probably go up to 1/4 inch for ease of pulling it through, so may need 3/8 inch hole for SB375-4 snap bushing

Diameter of SafeAir Pitot/AOA lines: 1/4 inch ( requires 3/8 inch hole for SB375-4 snap bushing - supplied with line kit)

Max diameter Vans says tooling holes can be enlargened to in each rib: 5/8 inch.

My plan:
I am still hedging more toward a grand rapids ADHRS avionics package, and as such I do not plan to use the Dynon AOA solution which requires a separate air line coming from the pitot tube. Grand Rapids calculates the AOA from other information that is evaluated by the ADHRS unit, while Dynon apparently evaluates pressure differential between the aoa and pitot air lines to determine AOA. I am, however, more than likely going to purchase a new Dynon Heated Pitot tube for value and cost reasons, and this unit has both air lines already built into it. I will call Grand Rapids to discuss this application with them.

As for the holes on the leading edge of the Wing rib webs, It looks like the W711 ribs all come with 3 holes already drilled. One of them is for the supplied aluminum tubing pitot air line that comes stock with the Vans Wing kit. They do not supply a heated pitot tube solution, and lots of folks stick with the stock method for reasons of cost and simplicity. My plan for these holes is to use the bottom 2 holes for the pitot and potential AOA air line, so those will be drilled to 3/8 inches most likely to accept the correct size bushing for 1/4 inch air lines. The top hole will be drilled to the max 5/8 inch hole to accept the larget bushing (SB625-7) I can put in there for additional wire runs above and beyond whatever I can imagine will fit inside the 3/4 inch conduit holes I am drilling now. Probably a lot of overkill, but better to build the capability in now instead of fretting later over why you did not do it when you had the opportunity.

After doing some research, I found that I could shop for used heated pitot tubes online, and the cheapest one I could find would be about 200 to $250.00. The Dynon Pitot tube sells new for about $450.00. I am a little leary about purchasing a used Pitot tube and find out the heating element does not work, or the wiring is decayed beyond usefulness, or it is corroded to the point if restricting airflow through the tube, etc. New pitot tubes, on the other hand, run in the 1500.00 to 2000.00 range and up from there - absolutely rediculous, as are most prices involved with anything in aviation. So the Dynon Pitot tube by far seems to be the better value any way you slice it.

SO the question them becomes, what will I do with the additional AOA airline in the Dyon pitot tube? My original plan was to go ahead and run the additional line from the pitot back to the root of the wing and then plug it there. Then I read a post the other night that hinted that the est thing to do was to cap the line as close to the pitot tube as possible, or in other words, do not run any additional line from the pitot and cap it right at the end of the supplied tubing on the pitot tube. Perhaps there is some element of trapped air in that line that may affect the air pressure coming from the pitot line, and therefore introduces some sort of error into the pitot line, which would not be good.

Anyway, I will have to think about this a bit more and ask some questions before I decide what to do. Plenty of time to come to a solution for this. With a nice bonus from work, and hopefully a somewhat decent tax return coming soon, and a birthday on the horizon, I have plans for several wing-related purchases in the not-too-distant-future. Now, what to do about the landing, strobe, and position lights? Hmmm. :)