September 2009 Archives

I finished fabricating the shims to make the outboard leading edge flush with the tank on the right wing.  It's hard to tell from this picture, but these shims vary in thickness along their lengths anywhere from <0.010" to around 0.040".  Unfortunately, it's really hard to tell for sure if these are exactly the right thickness because clecos can't exert enough clamping force to pull everything together as tightly as rivets will.  I'm just going to have to rivet it together and trust that my measurements were accurate.



Wing Skin Prep

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Working on shims is slow tedious work, so I took a break tonight and started working on the main wing skins.  Here are the two wing walk doubler skins, deburred and dimpled.  These will be primed before installation since any water that seeps between the skins could be trapped there for a while before it dries out and I want to do everything I can to avoid corrosion.



I also started on one of the larger wing skins by removing the plastic along the rivet holes.  A 50 watt soldering iron makes extremely quick work of this.



More Wing Skin Prep

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I finished deburring and dimpling the left inboard top main wing skin.  You can see the four closely spaced rows of rivets near the top of this picture.  These are for the ribs in the wing walk area.  It's taking me about 90 minutes per wing skin to remove the plastic, prep the edges, debur both sides of every hole, and dimple.  Since there are eight main wing skins total (two each on the top and bottom of each wing), I figure it will be about 12 hours total of this kind of work to get all of the wing skins prepped.  I really understand why people say the wings are boring.



I prepped the other three top main wing skins today.  Since the top skins are the only ones that will be attached soon, that's all I'm going to do for right now.  It will be good to take a break on these and work on something else for a bit.



After reevaluating the shims I had made, I decided that using shims that varied in thickness was the wrong approach.  The ribs already define the correct wing curvature, so shims that vary in thickness would just create ripples in the skin.  The problem is really that the splice plate is too low and the variation I measured was due to the tank skin getting pulled tighter where the screws attach and pillowing out between them.  Instead, the entire splice plate needed to be shimmed out a small amount.  Looking at the measurements I made previously, I determined that shimming the splice plates out 0.016" and shimming the skins out a further 0.008" would be about right.

I fabricated the new set of shims using some 0.008" aluminum flashing purchased from the aviation isle at Home Depot.  Two will fit between the inboard rib and the splice plate and one will fit between the the splice plate and the skin (the outboard skin is 0.024" and the tank skin is 0.032", so this should bring the skins flush).



My wife Jenn helped me rivet on the rib (it was only her second time riveting, and she did a fantastic job).  The fit was nearly perfect right after installation.  I did a little adjustment, and now the tanks and outboard skins are flush to within a few thousandths pretty much the whole length of the joint.



Ordered Fuselage Kit

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I ordered the fuselage kit today.  As I've mentioned before, I'm going with the tailwheel configuration with tip-up canopy.  I recently had a chance to fly in Kevin Hester's RV-7A (thanks Kevin!).  He has an A model (nosewheel) and a slider canopy, so pretty much exactly the opposite configuration as I'm going with.  The slider has a roll-bar in front of you which blocks part of your view.  Although I didn't find this objectionable, I was so blown away with the unobstructed visibility in the factory RV-7 that I really wouldn't even consider building a slider.

I also added the electric aileron trim option since I like gadgetry.
My wife is leaving town for a few days, so I wanted to get the leading edge riveted back together before she left.  In preparation, I went out this morning before work and drilled, dimpled and primed the shims.



I clecoed everything together, but it's too late to rivet this tonight.  We'll knock this out tomorrow morning before she leaves.



Since I couldn't move forward on the leading edges, I went ahead and drilled and dimpled the wing access plates.  The holes along the straight edge are drilled and dimpled for #6 screws and the rest are drilled and dimpled for #8 screws.



Miscellaneous Wing Tasks

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Before leaving town, Jenn helped me rivet the splice plate back onto the left wing.  This side looked even better than the other.  Right after initial fitting, the joint in basically perfectly flush along almost the entire length.  I have to do a little adjustment in a couple of spots, but it should be relatively minor.  This blurry picture really doesn't capture how nice this looks.



I'm ready to rivet the leading edges on, but since I don't have a riveting partner right now, I got started on a few other tasks that need to happen on the wings.  I got started fabricating the aileron bellcrank bushings.  These are brass tubes that have to be reamed out to 1/4" for an AN4 bolt and trimmed to a very precise length (basically about 0.015" to 0.030" longer than the bellcrank).  I did this by chucking them into my drill press and pressing them down onto a file.  This slowly filed off the ends until they were the correct length.  I also polished the outside with a scotchbrite pad while I had them running on the drill press.



Here is how the bushing fits in the bellcrank.  The bushing is clamped between two brackets mounted to the spar and doesn't rotate.  The bearing surface is between the outside of the bushing and the inside of the tube on the bellcrank.  A layer of grease keeps everything moving smoothly.  The bushing has to be slightly longer than the bellcrank tube to prevent the brackets from causing the bellcrank to bind.



Here are two of the brackets loosely bolted to the bellcranks.  These can't be permanently installed yet because I don't have the appropriate grease to install these with.  The other brackets are already installed on the wing and torqued.



I also fabricated the pushrod that the autopilot roll servo will use to drive the aileron bellcrank.



Here is how the pushrod attaches to the bellcrank.  When I get the roll servo, all of this can be installed in the wing permanently.



I picked up some Aeroshell 7 grease today and installed the aileron bellcranks permanently.  When torqued to the wing, I found I had a little bit of binding.  I traced this to making the brass bushings about 0.030" too short.  The plans say to make them 1/64" to 1/32" longer than the steel bellcrank tube, but you really want to make them whatever length will just fit between the brackets.  I ended up elongating the holes in the upper brackets to allow them to be installed without bending towards the bushing.  Here is the right bellcrank with autopilot servo pushrod (currently just hanging down) installed.  This side also has a longer bracket on the bottom side of the wing where the servo will mount and a brace that is installed diagonally from the top bracket to the servo (you'll see when I install the servo).



Here is the bracket installed in the left wing.



To install the leading edges, you need to grind away part of a double offset rivet set because the manufactured heads are right up against the main wing ribs.  This allows you to get the rivet set square to the rivet.



Really jumping around now, I pulled down the rough stock for the ailerson stiffeners and cut them down to size and began cutting the tapers.



Aileron Stiffeners

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I finished trimming and deburring the aileron stiffeners.



I use a cheap $3 punch set from Harbor Freight to mark all parts before priming.  I don't bother marking the actual part number, just something that helps me get all the parts back into the same position.  Here for example is the stiffener that goes on the right aileron, bottom side, 3rd out from the inboard stiffener.



All the stiffeners have been drilled to the skins...



...deburred, dimpled and primed.



Here's a cool artistic shot of all of the rivets in the holes (held in place with rivet tape since I'll be back-riveting these).  It's too late to rivet these on tonight, so I'll do that before work tomorrow.



Aileron Skins and Spars

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I went out before work this morning and backriveted all of the stiffeners on both of the aileron skins.



Using the bending brake I made for the empennage skins, I bent the aileron skins.  I ended up having to fine tune the bends with the hand seamer.  Just like on the elevators, you want the skin to stay perfectly straight from the spar back to the trailing edge radius.



The ends of the aileron spars need reinforcing plates where the hinge brackets attach.  These are made from 0.040" aluminum and match drilled to the spars.



After match drilling, the hinge brackets are clecoed on...



...and drilled out with a #12 drill for AN3 bolts.



Before calling it a night, I also clecoed the leading edge ribs in place and match drilled them to the skin.



Drilled Left Aileron

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I clecoed the left aileron completely together in preparation for match drilling.



The aileron counterweight is a galvanized iron pipe that runs the whole length of the aileron.  This has to be drilled to #30 for countersunk blind rivets.



The entire bottom of the spar (with the exception of the outboard two rivets) also has to be drilled to #30 for blind rivets because there is no way to reach inside and buck these.



There is also a hole that attaches the counterweight pipe to the nose ribs so that the pipe can't rotate.  This can be reached through one of the #30 holes in the spar after the trailing edge skin has been removed.



Drilled Right Aileron

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No pictures tonight as they would be indistinguishable from yesterday's.  Basically, I repeated all of yesterday's steps on the right aileron, but I did it quite a bit quicker tonight since I didn't need to refer to the instructions.  Afterward, I got started deburring some of the components.  Van's instructions have you prime at several points along the construction.  Instead, other than the stiffeners, I'm waiting until all of the aileron components are ready to prime at the same time.

Worked on Ailerons

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My Dynon autopilot roll servo showed up today.  I'm not going to install it just yet because I'm waiting on an order from B&C for some d-sub 9 connectors so I can fabricate a connector for this at the servo.



I countersunk the galvanized pipe used as the aileron counterweight.



To form the dimples in the skin, I mounted the 1/8" male die on a special bucking bar I bought.  Using the galvanized pipe as the female die, I hammered this into the holes in the skin.



...resulting in dimples in the leading edge for the CS4-4 blind rivets.



I put together a punch list of things to do before riveting the wing leading edges and top skins.  I made it through most of the list today before running out of steam.  My buddy Andre is coming over tomorrow morning to help with the riveting, so I want to be ready to hit the ground running.  Unfortunately, the 4x4 posts on my wing jig twisted and pulled the brackets out of alignment.  I had to take both wing skeletons down, redo the brackets, and re-level and straighten the spar.  That took most of the time today.



Here are the outboard leading edges clecoed on for the last time.



I got started this morning by forming the scarf joint where the inboard and outboard top wing skins meet just behind the tank skin.  This keeps the skins from sticking up where they are doubled up.



Andre stopped by and we got started by riveting the leading edges onto the spars.  This required the double offset rivet set I modified the other day.  Bucking these was tricky since it required reaching way into the leading edges through the lightening holes and bucking blind.  We managed to get all solid rivets into these holes.



Here's a shot inside the leading edge showing the shop heads for some of these rivets.



Afterward, we squeezed the rivets along the spar.



We then clecoed the wing skins on (remembering the wing-walk doublers of course).



We back-riveted all of the skins on using a 5 lb back-rivet bucking bar.  This was held against the outside of the skins while...



...the rivets were driven from the inside using an extended reach double-offset back-rivet set.  This worked beautifully.  The outside of the skins look perfect and we didn't have to reach between the ribs to hold the bucking bar as we would for normal shooting/bucking (which is painful between the wing walk ribs.



After squeezing the rivets on the rear spar, the left wing is ready to come off the wing jig.



Here is the top of the wing from the outboard end.



Here is the bottom of the wing.  The bottom main skins (inboard and outboard) are riveted after everything else in the wings are complete (ailerons, flaps, control linkage, pitot tube, autopilot servo, etc.).



My order from B&C Specialty arrived yesterday with the wiring components I need to fabricate the connection between the autopilot roll servo and the wiring harness.  First up is to crimp the sockets onto the wires on the wiring harness.  It's hard to tell from this picture, but these wires are small.  The wires are a mix of 20 and 22 gauge, and these sockets are about 1/16" in diameter.



Next up is to crimp the corresponding pins onto the wires on the roll servo.  Afterward, I put these wires in some heat shrink tubing to keep them tidy.



Here are the wires from the servo inserted into the D-Sub 9 pin male connector body.  The goopy stuff on the wires in E6000 adhesive.  Basically, this forms a strain relief that prevents individual wires from flexing at the connector.



Here is the corresponding female connector on the wiring harness.



Pitot Mount Fitting

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I didn't have much time to work on the plane tonight, but I decided to start modifying the left bottom wing skin for the pitot mount.  I'm using the pitot mount from SafeAir.  The mounting instructions call for mounting the pitot tube in the bay just outboard from the last access hole.  The problem with that is that it also puts the pitot tube just outboard of the tie-down bracket.  Since RVs have relatively narrow wing spans compared to typical GA aircraft, it means that tie-down ropes typically splay outward from the tie-down brackets.  This means they could easily get caught up in the pitot tube and damage it.  Instead, I'm mounting the pitot tube in the bay just inboard of the last access hole.  This is only about 1' inboard from the recommended mounting location, and only about 3" inboard from Van's stock location, so it shouldn't have any impact on pitot measurement (others who have mounted it here confirm that it works great).

Since I'm mounting the pitot tube just behind the tank, the tank attach platenuts prevent the mounting bracket from sitting as far forward as the installation instructions call for (I have to mount it about 1/4" aft of the recommended location).  Since I'm deviating from the instructions so significantly, I decided to just scrap them and improvise.

I took some measurements off of the leading edge and the adjacent rib holes.  While ensuring the tube will be aligned with the airflow, I marked where the cutout goes.  It's late, so I'll cut this later.



Pitot Tube and Mount

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I got started tonight by cutting out the hole for the pitot mount that I laid out a couple of days ago.  I used a unibit to drill out the bulk of the material, then used a nibbler and files to finish off the hole.  Next, I laid out some holes to rivet the mount to the skin (in addition to the holes along the right edge where it will rivet to the spar).



I installed the skin on the wing and match drilled the mount to the spar.



I test fit the pitot tube.  The 3/16" aluminum tubes coming out the other end needed to be trimmed somewhat to allow the pitot tube to fit fully into the mount.



I laid out holes to attach the tube to the mount and used some aluminum tape as a clamp to hold the tube in place.



After drilling through the mount and the wall of the pitot tube, I countersunk the mount for #6 screws.  This was tricky since this is a curved surface.  Instead of using my microstop countersink, I basically just did these freehand.



I also tapped the pitot tube for 6-32 threads.  The stuff with the red lettering on it is aluminum tape.  I wrapped this around the pitot tube because there was a little slop between it and the mount.



Here's the finished pitot tube installed in the mount.  This really turned out well, the pitot tube is tight in the mount and the screws are nice and flush.



Here is the business end of the pitot tube.  The hole at the top is for measuring pitot pressure and the hole at the bottom is for measuring angle of attach.  Basically, as the wing's angle of attach increases, this hole becomes more directly aligned into the wind.  This increases the pressure of air inside this tube which the instrument indicates as an increase in angle of attach.



I disassembled everything and countersink the pitot mount for the dimples in the skin since this will be flush mounted.



I cut the 3/16" aluminum lines on the pitot tube shorter so that they just stick out of the mount in the wing, then installed fittings and flared the ends.



The male end of the fitting is installed and torqued.



Using some EZ-Turn, I then installed the quick disconnects on the ends.  The tubing I'm using will just push into place on these fittings.



Finally, I installed the AOA tubing in the wing.  I didn't have enough 437-4 snap bushings to install the pitot tubing, so that will wait until I order some.



Miscellaneous Wing Tasks

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I started pulling the conduit through the wing ribs on the left wing, but it turns out that this makes a hell of a racket.  Since the kids were asleep, I put this off and moved on to something else.



I went ahead and squeezed the rivets on the right wing outboard leading edge.  I still have to rivet the ribs to the spar, but that has to wait until I have a riveting partner.



I deburred the edges of the flap brace and trimmed it to clear the rear spar doubler.jk



I clecoed on the flap brace (on the left) and the inboard aileron hinge bracket (center) and match drilled them.



I also clecoed and match drilled the outboard aileron hinge bracket.



After deburring and priming the mating surfaces, I riveted the aileron hinge brackets on (though only the rivets I could reach with a squeezer since it was late).



Here is the rear part of the outboard aileron bracket. Notice that the lower hole (right in this picture) needs a countersunk rivet. This is to clear the leading edge of the aileron since it comes very close to the bracket here.



Fuselage Ship Date

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I received my letter from Van's today with the fuselage ship date.  It will ship during the week of 11/2, giving me about 5 weeks to finish up the wings.  The second wing will come off the jig this weekend, so the remaining tasks are to finish up the ailerons, build the flaps and control push rods, install the autopilot servo, pitot tube, bottom skins, and wing tips.



Flap and Aileron Braces

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I noticed last night that the bearing in my right outboard aileron hinge bracket was binding.  I called Van's about it today, and they happily sent out a replacement at no charge.  I went ahead and drilled out the rivets holding this together, which was a real pain in the ass since those top rivets are AN470AD4-9's.  Even once you drill the head off, they're nearly impossible to drive out.  I ended up having to drill nearly all the way through them before I could drive the rest out.  Fortunately, I didn't elongate any holes.

Oddly, after removing the bearing, it was no longer binding.  After resqueezing the two lower AN426AD4-7 rivets (the flush ones near the bearing), it bound up again.  Argh!  After drilling them out a second time, I determined what was going on.  Basically, the holes for those two rivets were not perfectly normal to the surface, so squeezing the rivets caused the two surfaces to shift slightly which applied a sideways load to the bearing (squeezing it out of round).  I ran a drill bit back through those holes and resqueezed the rivets and the bearing now moves as smooth as silk.



I also clecoed on the bottom skins on the left wing so that I could match drill the flap brace to the skin.  The flap hinge will also rivet along here, but I can't do that until after I build the flaps.



While I was at it, I went ahead and clecoed on the aileron brace, and match drilled it to the skin.  I still have to match drill it to the rear spar, but I'll wait until the bottom skins come back off so I have easy access.



I finished installing the conduit in the left wing.  I still need to put a little bit of sealant around the conduit where it crosses each rib to prevent vibration from cutting through the conduit.



I also got started on one of the bottom skins.  I removed the plastic along the rivet lines, deburred, and installed the nutplates along the perimeter of the access holes.



Andre will be stopping by later today to help me finish up the right wing, so I got started this morning by making the wing cradle that will hole the wings after they come off the jig.  This is basically built according to plans with the exception of the casters so that it can be easily moved.



I didn't get any pictures during the process, but in about three hours, Andre and I knocked out the leading edge and top skins of the right wing.  I still need to squeeze the rivets along the rear spar and inboard rib, but other than that it is ready to come off the wing jig.



I went ahead and installed the autopilot roll servo and torqued the mounting bolts.  The wire still needs to be secured to keep from interfering with the aileron bellcrank, but that will have to wait until I get some adel clamps.



My 437-4 snap bushings showed up from Aircraft Spruce today, so I was able to install them and run the green pitot tubing through the right wing.



I also neglected to install any of the bolts holding the right fuel tank z-brackets to the spar, so I put a couple of bolts in each of the z-brackets and torqued them down.



Miscellaneous Wing Tasks

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I have my second tech counselor visit this Saturday afternoon, so I'm trying to knock out as many tasks as I can before then.

Since installing the wing conduit is so loud, I came out to the garage this morning after Jenn was at work at the kids were at school/daycare and installed it in the right wing.



After work, I squeezed the remaining rivets along the rear spar and inboard rib.  The top of the right wing is totally done now.



I also deburred the edges and clecoed on the right wing flap brace and aileron gap seal.  It's late, so I'll drill these tomorrow.



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