Luis & Fab's RV-7A Construction Log

The pitot tube comes with very long aluminum tubing.  You can’t really bend it and be able to take it in and out of the mount.  So, I cut it down to a more reasonable length, added some clear platic hose (from Home Depot) to protect against the two tubes rubbing against each other, and installed the required connectors to go from aluminum tubing to the clear plastic tubing provided by Safeair (http://www.safeair1.com)

With the pitot inside the mount, I tried to route the two plastic hoses from the grommet in the rib to the pitot.  The problem is that these hoses have a minimum turning radius of 2″, so there was no way I was getting the tube to do what I wanted without putting kinks in it.

I figured I could use two 90″ connectors on each line (only one of them is shown below).  These are over $5 if you buy them at the usual aviation places.  However, if you go to AutomationDirect and search for Union Elbow under Pneumatic Components, you can find them for $5.50 for a 5-pack :-).  I bet they also have the plastic tubing for them at a much lower price.

Once the tubing is pushed fully into the fittings, they will look a lot more straight than they do below.

Finally, this is what it will look like from the outside…

Before mounting the pitot mast to the wing, we need to drill and tap four holes for screws that hold the pitot tube to the pitot mast.  Drilling the holes was a bit tricky, since the pitot mast is a curved surface.  I used a leather glove to sort of hold the pitot mast in place, and did my best to drill a hole perpendicular to the pitot mast.  Dynon recoments using 6-32 screws, so I drilled the holes with a #36 bit.

I then match-drilled the pitot tube through the mast, and used a 6-32 tap to cut the screw threads on all four holes.

I was not sure which kind of 6-32 screw to use, so I ordered three different kinds from Aircraft Spruce (They are something like $0.05 each, so I figured it was worth the investment…)  The one on the right was the ‘safe’ choice, but it kind of looks like crap.  I ended up using countersunk screws like the one shown on the left.  I was not sure if the mast would be thick enough to countersink, but I decided to try it out anyway.  The hole did end up slightly enlarged, but there is plenty of material in the pitot tube for the screw to grab on and hold on to the pitot mast.

The pitot tube included in the RV kit is just a bent piece of aluminum tubing.  Nothing wrong with that, but I wanted a “real” pitot tube like any other grown-up plane.  In addition, I am still leaning towards using Dynon for my instrument panel.  They have a pitot tube with an Angle-of-Attack, which I would like to use instead of a stall warning horn.

So, I ordered a pitot mast from SafeAir.  It gets riveted to the main spar and to the bottom skin.  It comes with a paper template, which you simply tape up to the bottom skin and then cut out.  One important thing to point out is that the template was originally drawn for an RV-6.  For an RV-7, the template needs to be slightly offset outboard.  This allows the pitot mast’s plate to clear the rib that sits next to it.

The bottom of the template is aligned with the edge of the bottom skin and then you just got at it to make the hole for the mast.  I used a unibit to remove as much material as possible.

After I couldn’t take any more material out with the unitbit, I used a dremel tool with a little sanding drum to finish shaping the hole to match the template.

It took a bit of trial and error, but finally the hole was just the right shape for the pitot mast to slip through.

The template is supposed to be held by three rivets through the main spar and two other rivets at the opposite corners.  This wasn’t as solid I would have liked, so I added a little piece angle.  This angles has three rivets going through the pitot mast plate and the bottom skin, and three blind rivets to the adjacent rib.  This makes things a lot more solid.

I ordered a pitot-static-AOA plumbing kit from SafeAir.  After drilling one extra hole in the ribs for the AOA line, I figured I was ready to rivet the bottom skins on.

After helping another builder rivet his bottom skins on, I decided to not put in the wire conduit in the ribs until after riveting the skins.  Sure, it was going to be a pain to do it afterwards, but it would have been more of a pain to try to rivet 1-2 rivets per rib with the conduit in the way.  In the end, I ended up pushing in the conduit one rib at a time.  After completely riveting one rib, I would push in the conduit and then move on the next rib.

I found I could reach all but 3 of the inboard skin rivets (on the bottom spar, between two of the wing-walk ribs).  I used pop rivets here.  Better that than a banged-up bottom spar and half-assed solid rivets.   I did the entire inboard skins without having to bend it back.  I guess having skinny arms has some advantages.  Also, I found it easier to do it all myself.  Since I had my arm inside the wing holding the bucking bar, and I could not see while riveting.  I had perfect control on when to stop the rivet gun if the bucking bar slipped, etc.  After setting a few rivets, I would use a flashlight and an inspection mirror to make sure the shop heads turned out OK.  I was pleasantly surprised at how few rivets I had to drill out for the entire bottom skins!

For the outboard skin, there is just no way to rivet it without folding the skin back.  This is not as scary after you’ve done it.  For a given ‘bay’, I would first do all the rivets along the bottom spar.  Then I would rivet the rib, but only halfway down.  I would then move to the rear spar on the next bay, and halfway down on the rib (since the wing is upside down, ‘down’ actually means ‘forward, towards the leading edge’).  I would then move back to the previous bay and finish the rib.  After the rear spar and both ribs were riveted in a bay, I would then do the line of rivets along the main spar.  Overall, this was not as bad as I was expecting…

Here are a couple of shots of my gorilla-arm abilities.  Note how the skin is folded back.  Van’s suggests laying the wing on a table while riveting the bottom skins, but I found it much easier to just do it on the wing cradle.  By keeping the wing in the cradle, I was able to squeeze between the skin and the skeleton and stick my hand through the rib holes to buck the rivets.  Being skinny as a weasel helps, too.

These were probably the hardest on the outboard skin – not a whole lot of room to squeeze my body between the skin and skeleton, but still too far away to just stick my hand in through the outboard rib.  But again, not too bad compared to trying to reach the rear spar rivets on the inboard skin without folding back the skin…

After ordering a wider piano hinge from Aircraft Spruce, I was able to ‘pull out’ the flap enough to make it match the aileron trailing edge.

• To check the alignment with the aileron trailing edge, first make sure the aileron is set to its neutral position, and then lightly clamp the flap and aileron together.

• Before drilling, use a long straightedge (like the red level in the picture below) to make sure the flap and aileron’s trailing edges are aligned. I went one step further and used a digital level to make sure the angle of the aileron trailing edge was the same as the flap trailing edge (don’t expect this angle to be 0 degrees, as the wing will probably not be level with the ground while in the cradle.

• After I was 100% positive the two trailing edges matched, I very carefully drilled each hole of the two scrap hinges, putting a cleco in every hole as I went.
• Remove the flap, separate the scrap hinge pieces, and use a dremel tool cutoff disk to remove the loops on the scrap hinge.

• Now lay the scrap on top of the full-length hinge to be drilled. Match drill the holes from the scrap to the full-length hinge. I used the loop tabs to line up the two pieces, and then clamped them together before drilling.

• After both ends of the hinge are match-drilled, simply cleco the full-length hinge back on the wing and match-drill the rest of the holes.

The other flap was mounted with the same method, and I was very happy with the resulting alignment on both flaps.

And by the way, I didn’t come up with this method of mounting the flaps — I read it at www.vansairforce.net 🙂

I started riveting the flaps by attaching the ribs to the bottom skin. Some of these I could do with a squeezer, and some with the rivet gun.