Pitot Tube Plumbing   June 28th, 2010

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…

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Pitot Tube Screws   June 16th, 2010

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.

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Installing the Pitot Mast   April 11th, 2010

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.

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Riveting the Bottom Skins   April 10th, 2010

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…

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Aligning and Mounting the Flaps   February 2nd, 2010

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.

At this point the wing is upside down in a wooden cradle, so there is no good way to hold the flap while the hinge is drilled. I used the following method:
  • First, cut two scraps pieces of hinge, long enough to cover about 9-10 rivet holes on each end of the flap. Cleco the bottom skin to the wing and to the flap brace. Put a cleco in every skin-to-flap brace hole, except for the few holes on each end where the scrap piano hinge will sit.
  • Attach the pieces to the flap and mount on the wing using cleco clamps.
  • 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 🙂
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After mounting the ailerons, I tried to test-fit the flaps to see how well they lined up with the aileron trailing edges.
Well, they did not line up too good 🙁
The two trailing edges are supposed to be even, and as you can see, if I make the flap hinge flush with the flap brace, there is about 0.2″ mismatch between them. I could ‘push out’ the flap some more, but then the holes in the hinge that holds the flap to the wing would be very, very close to the edge.

After doing some research, I found out this is quite common. Fortunately, there is another variant of the flap hinge that is slightly wider, and would allow me to make the flap even with the aileron while maintaining an acceptable edge distance on the hinge.
So, here’s $10+shipping to Aircraft Spruce for a wider flap hinge….
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Mounting the Ailerons   January 10th, 2010

With the wings in the cradle, I can now start mounting the ailerons on the wings. First I gathered all of the hardware required, as shown in the plans. There are two spacers that need to be fabricated from aluminum tubing. for the aileron-to-wing bolts. First I cut the aluminum tube slightly longer than needed, and chucked it into the drill press. I used a block of wood and some sandpaper (probably 100 grit – whatever I had around) and applied light pressure first to square the end of the tube, and then to get it to the final length. Using this method, I could take off less than 0.001″ at a time, so it makes for very precise spacer lengths!
Getting all those washers in the tight spaces of the aileron brackets was no fun. I probably dropped ten or fifteen washers on the floor before I decided to tape them together and put them in all at one time. I could now use needle-nose pliers to put the washers precisely where I needed them without having them slip and fall on the floor.
These are two views of the inboard aileron bracket — the bracket that holds the aileron to the wing and connects to the pushrod that controls aileron movement. As you can see, I am not tightening the nuts yet, as I will probably take the ailerons off a few times before this things flies..
While I am working on this part of the wing, I am going to install the bracket for the Dynon autopilot servo. You can buy the bracket now and wait until much later to buy the servo ($$) and autopilot/EFIS ($$$!) Basically, the servo mounts next to the aileron bellcrank, and it uses a small pushrod to move the bellcrank when the autopilot is engaged. In order to attach the pushrod to the bellcrank, a single hole is drilled in the bellcrank:
The bracket simply replaces the oiginal bottom bellcrank bracket, and it also includes another support arm that bolts from the upper bracket to the servo
I repeated the whole process on the left wing. Here are a couple of pictures of the aileron mounted on the wing and the bellcrank bracket (the autopilot servo is installed on one wing only).

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Wing Cradle   November 26th, 2009

The wings are almost done, so I figured this would be a good time to build the wing cradle. I used the design shown in the plans, but added some casters. Fabiola helped me move the wings from the jigs to the cradle.
At this point, I have to install the flaps and ailerons, and rivet the bottom skins…we’ll see how long that takes!
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Leak Testing the Tanks   September 6th, 2009

The last step in building the fuel tanks is to test them for leaks. This is done by pressurizing them to about 1psi and making sure they are airtight.
The tanks have a total of four openings:
1. Fuel Cap
2. Fuel drain
3. Fuel pickup tube
4. Vent Line
I installed the fuel cap with a latex glove to make sure it was airtight. I also capped the main fuel pickup line, and installed a bicycle-style stem on the fuel drain. I left the fuel drain line open.
There are two ways to pressure test the tank. One is to hook up a balloon to the fuel vent line, and inflate it through the fuel drain. You then make sure the balloon doesn’t deflate after a few days. The problem here is that you have to compensate the expected diameter of the balloon for any temperature changes. This sounded difficult.
The other way to do this test is to connect a clear plastic hose to the fuel vent line, and pour some water in it to form a water column (making sure the water doesn’t go into the tank!). This also requires compensating for temperature changes, but I figured it’d be a lot easier to accurately measure the distance between two water levels than a balloon diameter. So, I got me some clear hose from Home Depot (they have them in the plumbing section) and used food coloring to dye some water for my test. I then mounted the tank up high on two special platforms and used my little bicycle pump to get about 27″ of water (~1psi). I installed an old thermostat nearby, and I would check the temperature two or three times a day, as well as the water level.
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Riveting Flaps   August 26th, 2009

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.

Then I put on the top skin and used the fuel tank cradle to somewhat hold things in place. There is just enough room for a small bucking bar in there, but things turned out pretty good.
The last things to do were to assemble the inboard rib. This rib holds a bracket where the flap actuator is connected. Finally, I riveted the spar to ‘close the flap’
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