March 2009 Archives

While Madeline was taking her morning nap, I snuck out to the garage and finished riveting the vertical stabilizer.  I thought that all of the remaining rivets could be done with a squeezer.  They can certainly be reached with a squeezer, but the placement of some of the rivets and hinge brackets in the rear spar prevented getting proper alignment.  I ended up shooting and bucking probably a dozen rivets along the sides of the rear spar.



Here is an example of the bad access.  The shop head of the lower rivet which is holding the skin to the rear spar actually extends behind the plane of the face of the shop head of the upper rivet which is holding the middle rudder hinge bracket to the rear spar.  Fortunately, I have a small tungsten bucking bar with a tapered end which could tuck nicely back in this area.



I got started on the rudder stiffeners tonight.  To save a little time, I marked them to length and ganged them up to rough cut them to size.  The bandsaw is pretty loud, so that's all I can do on these tonight.



Ordered Wing Kit

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I ordered the wing kit today.  Van's says the lead time is 8-10 weeks typically, so I should get it sometime in early May.  I only have the rudder and elevators left to do from the empennage, so I'll likely be done with that before the wing kit gets here.  Since I now have all of the materials to do the fiberglass tips on the empennage components, I'll probably get started on that while waiting for the wing kit to get here.
I finished deburring the rudder stiffeners and drilled them to the skins.



The rudder stiffeners have a slight bow to them as they come from vans.  This would create a slight concavity in the rudder skin, so I slightly fluted the stiffeners to make them lay flat.  They had to be fluted on both faces since the flutes to pull the stiffeners flat also pulled the holes out of line.  Fluting between the holes pulled them back in line, but typically bows the stiffener slightly so it doesn't lay flat anymore.  Definitely an iterative process, but by the end they were only taking me a couple of minutes per stiffener.



Rudder Skeleton

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I began assembling the rudder skeleton tonight.  First up is to drill out the 3/8" hole through the lower part of the spar where the lower hinge bracket will attach.



Next is to fit the rudder horn in place and match drill it to the spar.  This view is looking aft from the bottom of the rudder.  The outer holes at the top of the horn will eventually attach to rudder cables coming out the side of the rear part of the fuselage.  The lower holes are for chains that will connect to the tailwheel assembly (though I'll almost certainly use the rocket steering link).



I started to flute the tip rib when I noticed that the rib is apparently bent incorrectly.  The flange (and therefore hole) on the right side are almost 1/8" higher than the flange and hole on the left side.  I clecoed on the skin, and this definitely causes alignment problems.  I'll shoot Van's an email tomorrow and see if they can send me a new rib.



I still haven't received an email back from Van's about the top rib, so I gave them a call.  They're going to take a closer look at my pictures and get back to me, but they did say that the top rib often requires a bit of massaging by the builder to get everything to line up.  Since I may end up using this rib anyway, I spent some time tonight getting it bent such that all of the holes lined up and the skin laid flat against its flanges.  Here is the rudder fully assembled to see how things lined up.



Here is the tip of that rib after I adjusted it a bit.  The holes line up well enough now that the clecos interfere with each other (causing the top one to lay over a bit).  I still have to adjust the fluting a bit more (you can see a slight gap between the skin and rib where the second cleco in on the top is located).



I went ahead and trimmed the rudder brace and fitted it to the rudder horn. 



This looks a lot like the picture from yesterday, but now the rudder has been fully drilled and is ready for disassembly and prep for riveting.



After disassembling, I drilled the rudder counterweight to the R-912 counterbalance rib, dimpled the rib and countersunk the lead weight to accommodate the dimples.



You have to make the rudder bottom attach strips from a piece of 0.032" alclad.  Basically, you just cut these to 18" and trim the corner as specified.



Here are the strips, temporarily clamped to the R-904 bottom rib to match drill with the existing holes.  Holes in the lower half of this strip will be drilled in conjunction with the fiberglass rudder bottom.



The R-913 counterbalance skin in 0.032", and because the rudder skin is 0.016", the overlap can cause a visible joggle in the rudder skin.  Beveling the two points on each side of the counterbalance skin where these two skins overlap with the underlying structure smoothes out this transition.



In order to dimple the rearmost holes on R-903 and R-904 (top and bottom ribs respectively), I broke out a tool I made while building the practice control surface from Van's.  It's basically just a small piece of steel thats been drilled and countersunk for #30 and #40 drills.



Here you can see how it's used.  The rib is slipped over it and the rivet gun is set up with a special rivet set that holds any type of squeezer set.  Here it's holding the #40 male dimple set.  A few hits with the rivet gun and this creates a nice dimple.



Next up was to countersink the trailing edge wedge.  Unlike the other control surfaces on the RV-7 which use a folded trailing edge, the rudder uses two separate skins that are joined at the trailing edge with this wedge.  This is countersunk from both sides to receive the dimples from the skins.  A rivet is then set against a back rivet set such that it fills the dimples on both sides of the rudder.



One skin fully deburred on both sides.  The RV-7 rudder uses very thin 0.016" skins, so you have to be very careful when deburring to avoid removing so much material that the inside of the hole has a knife edge.



Here's the same skin fully dimpled.  I only need to prep the other skin, prep and prime the internal components, and the rudder will be ready to assemble.



I received confirmation from Van's today that my wing kit will ship on April 20th, so I should have it within a few days after that.  That gives me 4-5 weeks to finish up the empennage which should be no problem.



I deburred and dimpled the other rudder skin tonight.  I highly recommend the DRDT-2 dimpler.  Not only is it quiet and very low impact, there's basically no chance of damaging the skin.  I can't tell you how many builder's websites I've run across where they accidentally put an extra hole in their skin while dimpling using the standard c-frame dimpling tool.  Unless you're completely not paying attention, I simply can't see how that could happen with this tool.  If you lower the handle gently into the hole and only press firmly after the dies are engaged, you'll never make a mistake.



The aft three holes at the top on each skin need to be drilled to #30 and dimpled for the rudder top fairing.  The rudder is very narrow here, so there would basically be no access to dimple these after the rudder is assembled.



Began Riveting Rudder

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I prepped and primed all of the rudder components.



After the primer dried, I clecoed together the rear spar with reinforcing plates and nutplates for the rudder hinges.



Here's a closeup of the rudder horn showing the nutplate that will receive the rudder hinge.



Here are the reinforcing plates all riveted on.  The plans don't include the rudder callout of the nutplate rivets, but you should be able to figure it out by this point.



I couldn't reach the outer two holes in the rudder horn with any of my squeezer yokes, so I'll have to shoot and buck those.  It's too late tonight to make that much noise though.



I could squeeze the counterbalance rib and skin rivets, so I did those.



I also mounted the counterbalance weight.  This required considerable trimming of the lead weight in order to fit between the rivets.  A vixen file cuts through lead like butter though.  This is all torqued and ready to be closed up.



Jenn helped me shoot the last two rivets (seen here at the far left and right edged inside the rudder brace hole).  Jenn had never riveted before, but she picked it up quick and did a great job.



Here are the rest of the rivets that hold the rudder brace on.  I managed to get all solid rivets in here without too much trouble.  This would have been nearly impossible without the longeron yoke.  A lot of people wait until the fuselage to order the longeron yoke, but it's been invaluable on the empennage.  There have already been a number of spots that couldn't be squeezed any other way.



I riveted all of the rudder stiffeners on this morning before work since I've been getting home too late to do it before the kids go to bed.



These rivets are back-riveted which means the rivet gun forms the shop head while the manufactured head rests against a back-rivet place (in this case a large piece of cold rolled steel that I picked up at a local metal supply shop.  Below, you can see the rivet tape that is used to hold the rivets in place until they're driven.  As everyone says, back-riveting rocks.  The skin is amazingly smooth.



Here is the structure all clecoed together.  Most if not all of the remaining rivets except the trailing edge can be squeezed.  I'll knock that out tomorrow and then get started on the trailing edge.



Here are a couple of pictures of the back of the rudder hinge reinforcement plates, mostly for the DAR to see that these are set correctly since there is no way to see inside the rudder once the skins are riveted on.  Here's the middle hinge reinforcement plate.



And here's the upper hinge reinforcement plate.



I got both skins fully riveted on (except for the trailing edge).  Here are the counterbalance skin to main skin rivets.  You can sorta see here how the tapering I did on the counterbalance skin allows the main skin to flow smoothly down on to the spar.  When you feel it, you can barely detect the joint.  This will all get covered in filler most likely when I do the fiberglass work for the rudder top fairing.



Here's the top rib riveted on.  The top rib is riveted to the spar with pop rivets since the other side of this joint is inaccessible (or nearly so).  The only thing to remember here is to switch from AN426AD3-3.5 to AN426AD3-4 rivets where the skins overlap since there's a little more material the rivet is going through.



Here's the completed rudder structure (again excluding the trailing edge.  I've already drilled two aluminum angles that I picked up at Home Depot, so all I need to do is clean this, apply the sealant and cleco it together.



I managed to get all solid rivets where the skins and bottom rib join the horn brace.  The longeron yoke got the rear three, but the hinge nutplate interfered with the yoke when I tried to do the front rivet.  The three inch yoke with a 1/2" flush set cleared fine.  I hand squeezed all of these so that I could easily back off if I felt interference.  The pneumatic squeezer has so much power that it would easily bend any interfering parts before you could stop it.



I didn't get any pictures of the actual process since the sealant is sticky as hell.  Literally everything that it touches will stick and you can't get it off without a fairly aggressive solvent like MEK.  Anyway, I used one of the tubes of sealant available from Van's that is ready to be mixed.  It was kind of a waste since you only use maybe an ounce on the trailing edge wedge.  After mixing it, I used the semco sealant gun I picked up on eBay to put a thin bead down both sides of the wedge then spread it smooth with a popsicle stick.  It was then just a matter of clecoing on the angles that I already made.  I put clecos every hole to provide even clamping pressure (you can see just a bit of sealant oozing out of a couple of spots along the edge).



Here's a closeup showing the sealant that has squeezed out.  Now I just have to let this sit for 2-3 days to firm up and I can rivet the trailing edge. 



Began Elevators

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Since I'm waiting for the sealant on the trailing edge of the rudder to cure, I went ahead and started on the elevators.  Here's the left skin drilled.  The missing section of the trailing edge on the left is for the elevator trim tab.



Here's the trim access reinforcement plate drilled to the skin.



Nutplates mount around the inside edge of the access plate to provide a place for the screws that hold the access cover to attach.  Van's doesn't provide any guidance about how to attach these, but you're expected to know enough by this point to do it.  The nutplates are held on with AN426AD3-3.5 rivets and the access plate is 0.032".  AD3 rivets are 3/32", and AC 43.13 (google it if you're really interested) specifies that you must dimple material thinner than 0.032" and countersink material thicker than 0.040".  For 0.032" material, you can do either.  If I had dimpled the access plate, it would require either dimpling the nutplate mounting ears (which would have necessitated grinding down the edge of my female #40 dimple die).  Countersinking eliminates the need to do that.  It's a little tricky countersinking 0.032" material for a AD3 rivet since just as you countersink deep enough, the countersink penetrates the back side of the material and the countersink cutter loses its center reference.  To avoid this, I clamped a piece of scrap to the back of this plate and match drilled through it and then countersunk through the pair.  This provided an extended center reference for the countersink cutter.



I also dimpled the plate for #6 screw to receive the dimples from the cover plate.  Here, you can see a closeup of one of the dimples and the countersinks on either side to attach the nutplate.




I deburred, dimpled, prepped and primed all of the elevator stiffeners along with the spar reinforcement plates and trim access reinforcement plate (both in the foreground).



After the primer dried (15 minutes or so), I installed the platenuts on the trim access reinforcement plate.  Countersinking the reinforcement plate was definitely the right way to go.  The mounting surface for the trim access cover is totally flush.



Here is the backside showing the platenuts and rivet shopheads. 



I back-riveted the trim access reinforcement plate to the left elevator skin.



I also prepped the trim cover plate and attached it with AN507-6R6 screws.



Finally, I deburred, dimpled and put rivets in all of the skin holes where they are riveted to the stiffeners.  It's too late to rivet these tonight, but I can knock these out quickly tomorrow morning.



Here's the left elevator skin ready for back riveting the stiffeners.



Since I couldn't rivet last night because of the noise, I got up early and riveted the elevator stiffeners on before work this morning.  Here's the left elevator.



And here's the right.  Near the trailing edge, it was difficult to get the skin bent out of the way enough and still keep everything flat on the back rivet plate.  I ended up having to drill out a couple of rivets that didn't end up flush with the skin.



Finished Rudder

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My buddy Andre stopped by tonight to help me rivet the trailing edge.  It turned out great.



Here you can see that it's completely straight.  One of the things Van's really cautions you about is that setting these rivets can cause a hook in the trailing edge.  Using the sealant helps ensure this won't happen.  I did get some very slight puckering between the rivets, probably due to slightly overdriving them.



We also got the leading edge rolled and riveted.  This was probably by far the hardest part of the rudder.  Despite how thin the skins are, these things are a bitch to roll.



I also got the rudder hinges installed.  Van's uses rod end bearings for hinges on the elevator and rudders.  These are just screwed in to a specified distance from the spar web (or reinforcing plate in this photo).



I fabricated a simple bending brake out of a 2x8 and a bunch of hinges.  I've heard other builders complain that they didn't get a crisp bend between hinges, so I went a little overboard on the hinges.  They were on sale for 96ยข, so it didn't cost much.



After reading the experiences of others on vansairforce.net, I put the trailing edge up against the hinges and bent the skins basically flat (until the stiffeners were touching the opposite skins).  They spring back to roughly where they will sit once the spar is attached.  You have to put a surprising amount of force on this.  I basically climbed up on top of it and bounced (and I weigh 230lbs).  The whole process for both skins only took about 5 minutes.



Here's what you're looking for.  The skin stays flat right up until the trailing edge radius.



I clecoed the counterbalance rib to the end rib and attached both to the spar.  Getting the last holes in the spar flange to line up with the holes in the counterbalance rib was a real pain and required several iterations of adjusting the bend of the counterbalance rib flange for that last hole.



Here is the counterbalance skin clecoed on with the counterweight in place.  I drilled through the holes in the end for the counterbalance weight attach bolts.



Here is the elevator skin clecoed on.  This is the left elevator.



And this is the right elevator.



While I was at it, I clecoed the elevator horns on so that they could be drilled at the same time.



Drilled Elevator Skins

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These pictures look the same as yesterday, but all of the holes have been drilled.  Here's the left elevator.



And the right...



For a little diversion, I fit and drilled the elevator trim mounts to the trim cover plate.  Ignore the left/right measurements in the plans, just visually center the trim servo arm over the cutout and clamp it in place.



Misc Elevator Work

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A few of the holes in the elevator spars have to be countersunk, but the spar flange is too close.  I took one of my extra countersink cages that I picked up on eBay and ground off part of the foot to allow it to get up close to the flange.



I didn't like the idea of routing the trim servo wires through the hole on the left since the servo shaft (which is threaded) extends through this hole in the full nose-up trim condition.  I'd much rather avoid the potential for chafing and drill another hole.  Since there was already a lightening hole in the elevator horn, I just drilled a 3/8" hole in the center of that.  I'll put a snap bushing in that hole later.



I haven't had much time to work on the plane the last few days because work's heating up.  We're working 7 days a week to get the new iPhone 3.0 software out the door.  I need a little break though, so I managed to get a few of the elevator parts ready for priming.  Here's the counterweight skin.  I beveled the side and back edges where the main skin overlaps to prevent a bulge in the skin at this spot.



There's not enough room between the trim spar flanges (partly visible in the upper left) to get a normal squeezer to dimple the rivet holes, so I tried the pop rivet dimple dies.  I only got one done before the nail broke (expected at some point).  The female portion of the die shot off with blinding speed and it took me about 5 minutes of searching the garage to find it.  I think I'll look for another way to dimple these holes.



The right elevator counterweight (shown here on the left) has to get trimmed because the right elevator is lighter (the left elevator contains the trim system, so the counterweight needs to be heaver to balance the left elevator.  Trimming this was a pain.  I tried the bandsaw, but the counterweight jammed in the blade (and bent the blade).  I also tried a hacksaw, grinder, chisel, and file.  Nothing worked great, but I eventually got all the metal removed.



Here are all of the parts cleaned and primed, ready to be assembled.  I have no idea why Van's has you build the elevators separately.  It's going so much faster to just build them at the same time.



Riveted Right Elevator

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I started by riveting the hinge reinforcement plates and platenuts to the elevator spars.  I'm still working on both elevators to save time.



Here is the trim servo supports, back-riveted to the trim cover plate.



And here is the servo, mounted to the supports.



I riveted the root ribs onto the spars.  This is the root rib for the left elevator.  You can see it has a blunt end where the trim spar attaches. 



The instructions are definitely not in the best order here.  They have you rivet E-703 (end rib) to E-704 (counterbalance rib) before riveting them both to the spar.  The problem with that is that these rivets can't be squeezed if you do that and must be shot/bucked (probably with a double offset set).  Instead, I squeezed these now while they're easy to reach.



And then squeezed the rivets holding E-703 to E-704.



The elevator horns can now be riveted on.



I added a dab of RTV to the back end of each stiffener pair to tie them together.  This helps prevent cracking here according to Van's.



And the right elevator is complete except for the leading edge rolling.



After researching this issue on vansairforce.net, I decided not to follow the plans again when it comes to the trim tab.  The trim tab and left elevator skins come with little ears that are supposed to be folded together to close in the end of the surfaces.  The problem is that many (most?) people end up not happy with these bends and either redo them (which would be expensive with the elevator skin) or live with it.  The consensus seems to be to just cut off the ears and fabricate little riblets to fit in there.  If you're not happy with how these come out, you're only wasting a few cents worth of scrap aluminum.

Here, I've cut off the ears on the trim tab and I'm ensuring that the cut line is perpendicular to the trailing edge.


I clecoed the top of the trim tab to the bottom of the elevator to mark where the cut line should be on the elevator skin.



Then moved 3/32" away (the minimum gap between the trim tab and elevator), and marked the elevator skin.  You can see that I stuck a couple of extra rivets loosely in the holes for the trim spar to ensure these lines stayed perpendicular to it.



I took a little break from the trim tab to try my hand at some fiberglass work.  Here, I've fit the vertical stabilizer tip into place and drilled the holes to full size.  The tip was too long, so I had to cut off about 1/4" (you can just see the blue line near the bottom edge) to line up with the vertical stabilizer joggle.



I also cut a piece of 1/4" last-a-foam to fill the gap.  This stuff is really light, but it's a bit brittle.  This piece snapped while I was trying to fill it.  It will epoxy back together though.



Here is the foam epoxied into place in the tip.  I left a slight reveal (less than 1/8") to allow for some filler here since this area needs to be slightly concave to allow for the swing of the rudder. 



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