August 2010 Archives

Back from Oshkosh

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I got back from Oshkosh today.  I had a few goals for the trip:

Audio Panel: I had been trying to decide between the Garmin GMA 240 and PS Engineering PMA5000EX.  They're both really nice units and each have their strengths and weaknesses.  The PMA5000EX unit has the IntelliVox (auto-squelch) feature while the GMA 240 has the old style manual squelch control.  However, the front panel controls on the GMA 240 are substantially more user friendly and intuitive.  I had been leaning pretty heavily towards the PMA5000EX, but after the show I'm more split.  I still need to do some more research on this.

Canopy Attach:  I have been trying to decide between screwing the canopy to the frame and gluing it on with sikaflex.  The sikaflex solution results in no holes in the canopy which dramatically reduces the chance of cracks, but it's still a relatively new solution, so the long-term success of this solution is not proven.  The plans specify that the canopy is held on with screws all around, but the difference in the coefficients of expansion between aluminum and plexiglass is substantial, and a rigid fastener like a screw can put highly localized pressure on the canopy.  After looking at a bunch of RVs parked in the parking area, I've decided that I'm going to use screws along the side skirts and around the aft edge of the rear window, but adhesive across the canopy and cabin frames.  I saw one plane done like this and the results were outstanding.

Electrical System: I've been planning on following the AeroElectric Connection wiring diagrams (Z-13), but recently Vertical Power announced the VP-X.  This provides a solid state electrical system that is controlled through your EFIS.  The only issue is that Dynon has not announced support for this since they're still trying to finish the SkyView system.  I think there is a high likelihood that they will provide support for it at some point though, so the question is whether it will happen by the time I need it.  The VP-X provides some really nice features though such as start button disabling, landing/taxi light auto wig-wag, flap overspeed warning, flap positioning, flap extend disable above Vfe, auto trim speed adjustment based on airspeed, better fault detection and alerting, etc.  If Dynon supported it with the SkyView, there is no question that I would go with it.  I could gamble that it will be done by the time I need it, but then I could be grounded if it wasn't.  I also need to do some more research on this and see if I can put the decision off as long as possible.

Started Canopy Latch

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I started working on the canopy latch.  Instead of the latch included with the kit, I'm using the canopy latch from fairings-etc.com.  This will be perfectly flush on the outside of the plane instead of the protruding fingers of the stock latch.  The only disadvantage is the weight.  These are cut from 5/8" thick aluminum stock instead of the 1/8" thick stock used in the kit latch, so they're quite a bit heavier.  I laid out a few lightening holes, but I may just drill holes part way through from the bottom side to remove weight without changing the appearance.

The quality of these as received is pretty marginal.  The cut edges are all very rough and will require quite a bit of hand work to smooth out.  Also, the predrilled holes are too large which makes for a sloppy fit around the pivot bolts.  I'm going to have to ream these holes out larger and fabricate some bushings to eliminate the slop.

The other problem with these latches is that the outer skin of the aircraft is used as the spring to keep the aft piece (on the left in the picture) engaged with the forward piece.  This seems like a pretty poor design as it will repeatedly flex the outer skin and could fatigue it over time. Fortunately, I knew this prior to purchasing the latch and ran across a good way to solve the problem on Roee Kalinsky's site.



I stopped by the hardware store this morning and picked up some 7/32" and 9/32" brass tubing.  I then drill out the latch pieces so that these are a press fit into the holes.  This will allow the brass tubing to rotate around the bolt.  This totally fixed the sloppy fit and the bolts are a slip fit through the holes now.  I'm not going to install these permanently in the holes yet since I'm planning on having the latch components hard anodized.



I also drilled the latch attach angles to the latch components.  Here is the latch temporarily assembled so that I can check the clearances and movement.



On the other side, you can see how the latch sits proud of the attach angles.  This is because the attach angles will sit flush with the inside of the skin, but the latch components should be flush with the outside of the skin.  The skin is 0.032", but I positioned these currently 0.036" proud of the angles.  After I get them back from the anodizers, I'll file the outside faces flush with the side of the plane since they'll be painted the same color as the exterior.



I've temporarily clamped a piece of scrap material across the outside face to simulate the skin since the skin acts as a stop for the forward catch.



To open the latch, you push forward on the forward knob until the aft part is released.



Once the latch is released, the aft part pops back.



It can then be pulled aft to release the canopy.



Finally, I laid out the cutout for the side skin.  It's late, and I want to do this when I'm fresh, so I'll start this tomorrow.



I wasn't completely tired, so I wanted to figure out how the engine start switch will be wired.  I don't think I've mentioned it before, but I'm using the engine start switch from a Honda S2000.  It has an integral light, but it's really dim and can't be controlled separately from power to the switch.



To solve this, I disassembled the switch, cut the traces to the light and wired them to the two unused pins on the connector.  If I end up using the Vertical Power VP-X, it can turn on the light when the start button is enabled.  I think I'm going to have to use a relay between this switch and the starter relay since I've heard the starter relay pulls about 4 amps and I don't think this switch can handle that kind of current.  I need to confirm this though.



Cut Canopy Latch Slot

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I double checked the measurements I made last night and found them spot on, so I got started cutting out the slots.  I used a unibit to remove most of the material.



I then spent a few minutes with the hand nibbler removing most of the rest of the material to just inside the lines I'd marked.



I then clamped a steel straight edge along the line I drew and filed down to the line.  The steel straight edge serves two purposes, it helps ensure that the filed edge is perfectly straight and it prevents filing past the line since the file basically stops cutting when it hits the straight edge.



After about 30 minutes of filing, the latch fits pretty well in the slots.  I had to round the corners of the latch pieces slightly since I didn't want a sharp inside corner on the skins because that could lead to cracking.  At this point, the latch operates pretty well; good enough that I can go ahead and drill the attach angles to the skin.  Once the final position of the latch is defined, I'll finish filing the edges to provide even clearance all around the latch.



I took a break from the canopy latch handle and went back to the latch itself.  I trimmed the lower ear as specified in the plans for weight savings.  After taking this picture, I used the touch-up paint that matches the powder coat to cover the bare metal.



Next, I drilled the bushing blocks out to full size and temporarily bolted the latch into place.



Finally for this evening, I fabricated the idler and linkage.  The upper hole in the idler will connect to a pushrod whose other end is attached to the canopy latch handle.  Here's the mechanism in the latched position.



And here's the mechanism in the unlatched position.



I laid out and drilled the holes on the attach angles.  I also put four layers of blue painters tape between the angles and the latch pieces.  These add about 0.018" of clearance between the pieces to make room for the 0.016" thick UHMW tape that will be installed in the completed assembly.



I then clamped the latch in place.



And backdrilled through the skins.  This is the opposite of the way the Van's plans specify, but it ensures that the latch is perfectly centered in the slots and the holes are centered in the attach angles.



Finally, I fabricated the connecting rod that ties the latch handle to the idler.  I ended up needing to make mine about 1/8" longer than the plans specify.  The tube has to be cut to length and then the ends tapped out to 1/4-28 for the rod-end hardware.



Here's a closeup of the handle end.  You can see how I had to notch the upper attach angle for the rod-end.



With the handle in the closed position, you can see how the idler is pulled forward which pushes the latch finger into the slot on the bulkhead.



Here is the latch handle pulled back all the way.



With the latch handle pulled back, you can see how the idler is pushed back which pulls the latch finger forward.



Received Van's Order

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No work on the plane tonight, but I received an order from Van's that included the baffle kit and induction kit.  I spent a couple of hours inventorying the kits and reading through the plans to see what is involved.
I received some UHMW tape from Van's yesterday, so I disassembled the latch and put pieces of tape between the attach angles and the latch handle pieces.  I then filed out the openings so that the handle has about 1/64" clearance all around.  This required removing and installing the latch handle countless times to get the fit just right.  I still have a little work to do to get this where I want it, but it's operating smoothly now.



Started Canopy Frame

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I reassembled the subpanel along with the hinge blocks and clecoed on the top skin.



I drew a centerline down the aft tube on the canopy frame.  This will be used to ensure the holes drilled through the top skin will go into the center of the tube.



Several other builders have commented that some of the welds prevent the skins from laying down properly.  The instructions mention this, but a picture is much more clear.  Here you can see that the weld would push the skin up about 1/32" or so.



30 seconds with the vixen file and the weld is nice and flush with the angle.



The instructions also mention that the flange needs to be filed square with the face of the forward channel through the center.  A few minutes with the vixen file also took care of this.  Sorry for the blurry picture.



I clecoed the skin to the forward channel of the canopy frame and drilled most of the aft tube (the one I drew the centerline on).  I've seen a number of other builders have a problem with these holes not lining up with the centerline, but mine was almost perfect.



I fit the canopy frame for the first time, but almost immediately I had an interference problem.  I couldn't get the canopy frame far enough forward.  I had anticipated interference from the hinge spacers, and a quick check with a mirror confirmed that was the problem.



I pulled the spacers (which involved climbing under the subpanel and removing the hinge blocks which was a pain in the ass).  I trimmed 3/16" off the back edge.



I reinstalled the hinge blocks and spacers and then reinstalled the canopy frame.  Another builder commented that using a strap helps pull the skin down tight.



That resolved the issue.  I now have almost 1/8" clearance between the hinge arm and the spacer.  Do yourself a favor and cut at least 1/8" off the back of these spacers from the dimension Van's specifies.  It will save you a lot of headache.



With the hinge spacer interference resolved, I could get the canopy skin almost all the way forward.  I'm still getting some interference somewhere because I can't seem to get these skins any closer.  I have almost 1/32" on the left side.



On the right though, I have almost 1/16" gap.  I need to determine where the interference is so I can pull these skins tight.



Fit Canopy Frame

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I couldn't find anything obviously preventing the canopy frame from moving farther forward, but I suspected the seal support flange.  I unclecoed the outboard portion of the canopy frame skin and sure enough the forward channel of the canopy frame was pressed firmly against the seal support flange.



A few minutes with the vixen file removed the interference and now the canopy frame could be moved far enough forward that the skins butt together.  The plans want you to put a 0.020" spacer between the skins, but the fit isn't perfectly tight along the whole joint.  Instead, I'm going to butt the skins tightly together and then file the canopy skin to create a uniform gap along the whole joint.



I put a couple of ratching straps on.  One is pulling the sides of the frame inward to ensure the frame is the correct width.  The other is pulling the frame down to ensure it's tight against the fuselage.



I also use a couple of clamps to make sure the canopy frame wall pulled down tight.



I drilled the channel to the flanges on the hinge bracket.  I then disassembled the frame and deburred everything and countersunk all of the holes on the forward face of the channel.  You can also see the little target I drew on the hinge arms.  Once I get the canopy frame in position, I can look through the holes in the hinge blocks.  As long as I don't see any of the red line, I will have plenty of edge clearance on the pivot hole.



After spot priming all of the mating surfaces, I clamped the frame to pull the sides in as far as possible since the clecoes allow some flex.  I then squeezed all of the rivets in the splice plate.



I also squeezed all of the rivets holding the hinge bracket to the channel.  I ended up needing to make some spacers that fit between these two pieces since the hole spacing on the skin pulled the bracket back slightly.



I then reinstalled the canopy frame on the fuselage and got it back into position.  I crawled in the fuselage to confirm the holes would land in the right spot and they were great.  Plenty of edge clearance all around.  I tried using my right angle drill, but I couldn't get squarely on the hole.  Instead, I decided to peel up the outboard portions of the forward skin and use a straight drill.  If you click on the picture to zoom in, you can see that the hole is nearly centered on my target.



I used my straight drill with a 6" long, 1/4" bit to mark the holes.



Then a fabbed up a little drilling block to ensure the hole would be square and drilled all the way through the brackets with the 1/4" bit.



I then opened the hole up to 23/64" and then used my 3/8" unibit to open the holes up to 3/8".  Here you can see the bushing block in the right hinge arm.



And here's the bushing block in the left hinge arm.



Finally, I put the canopy frame back on using some temporary pins and checked the motion.  As the instructions specify, the seal support angle interferes with opening the canopy frame.  I filed back the seal support angle a little bit and retried the frame.  After a few iteration, I have the canopy frame swinging smoothly.



I finished the fit of the forward canopy frame to the forward skin.



I ended up with about 0.032" along the entire joint.  I did end up having to put a 0.016" spacer under the forward channel of the canopy frame to lift the skin up a little bit.  Otherwise, the front edge of the canopy frame skin was pushed up by the subpanel a bit and the front edge of the canopy skin would catch on the aft edge of the forward skin when I tried to raise the canopy.  You can also see here that I installed a bunch of clecos from the inside to give me a little more room to open the frame.  These still stick up too much to allow the frame to open fully though.



This is about all I can raise the canopy before it interferes with the clecos, but it's enough to ensure everything moves smoothly.  Beyond this point there would not be any interference anyway.



Fabricated ADAHRS Mount

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I decided to take a break from the canopy and fabricate the ADAHRS mount for the Dynon SkyView ADAHRS box.  I looked at several builder's sites about how other people have done this and settled on a U shaped piece hanging between the center rib and left stringer.  I decided to add some bends along the edges though to stiffen the structure.  It's approximately level in both axes right now, but I need to fine tune it slightly before drilling the holes though the rib and stringer.

I made the box deep enough that I could put two ADAHRS boxes (stacked vertically) in here if I decide to do that.



Worked on Canopy Frame

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I finally got a long day on the project for the first time in a while.  I got started by making some 7/8" and 1/8" spacers.  I used some blue tape to make the wood spacers exactly 0.875" thick.  The aluminum bar was already 0.125" thick.



The flanges of the canopy channel need to be bend to 92.5º (they come from the factory at about 88º).



Bending the flanges of the channels severely warps them.  I had to flute them to get them flat again.



Here's a closeup of some of the flutes.  Fluting this 0.063" thick channel is tough.  My hand is aching from this.



I laid out the holes for the splice plate that will join the two canopy channels.  I should have read a few of the builder's logs a little closer.  The outer holes on the center row end up too close to the tooling holes in the channels.  If you haven't already drilled the splice place, you probably want to move those holes 1/4" up.



I drilled the splice plate to one of the two channels.



There is a sharp bend in the canopy weldment.  A few squeezes with the hand squeezer smoothes out the curve.



Next up, I laid out and drilled the holes in the two forward splice plates.  These join the canopy frame sides to the forward weldment.



The splice plate sits immediately  on the other side of this joint.



Here are the side channels clamped down to the 1/8" spacers.  You can also see the splice plate clamped to the side channel and forward weldment.



The aft end of the side channels are also clamped down on top of the 1/8" spacer with the rear angle flush against the channel.



The side channels need to be positioned so that the 0.032" thick canopy skirt will be flush with the side skins.  Here I'm using a piece of scrap to make sure the side frames are positioned correctly.



After everything was finally positioned, the aft end of the side frame can be drilled to the canopy channels.



The forward splice plates were then drilled to the side channels and forward weldment.  After drilling these, I removed all of the clecoes and disassembled all of the canopy frame components.



Because of the angle the side frames meet the forward canopy weldment, there is a gap between the bottom flange and the splice plate flange.  To fill this, you have to fabricate a wedge out of aluminum.  This took probably one hour to make two of these, but it wasn't as bad as other builders made it out to be.  The plans specify that it should be 5/32" thick at the forward end, but fortunately my gap was only 1/8", so I could use some scrap I already had on hand.  The scrap already had a radius on one edge that tucked nicely into the radius on the bottom flange of the forward weldment.



After fitting the wedges, I laid out and drilled four holes along the bottom flange.



Finally, I deburred all of the canopy frame components.  Next up is to countersink a bunch of the rivet holes and then start riveting this puppy together.  After that, it's time to start on the canopy itself.  I was really hoping to get the canopy cutting done during August while it's still pretty warm, but it looks like it's going to stretch into September.



I primed all of the mating surfaces and then clecoed the canopy frame back together.  I then clamped the frame back on the fuselage to ensure everything was aligned properly since clecoed joints have a little bit of flex.



I had to use my stubby clecoes to cleco the wedges in place.



I then riveted the splice plates in place.  I had to pull the frame off to reach the rivets on the bottom flange.



Here's the inside of the joint.



Started Cutting Canopy

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Another RV-7 builder from Paris stopped by tonight and we chatted RV's for awhile.  It was good to finally meet him as we've only exchanged emails up to this point (hi Frédéric!).  After he left, I rearranged the workbenches and pulled down the canopy.  I forgot to take a picture of it, but I then drew a centerline down the canopy to use as a reference point.



First up is to trim off all of the clamping marks on the edges.  I started with the front edge by cutting back the plastic and taping a cut line with some masking tape.



Here's a closeup of the clamping flange and taped cut line.



It probably took five minutes to cut off the flange.  I'm using the cutoff wheel that Van's ships with the finish kit.  I've installed it on my 90º angle die grinder which helps keep it aligned with the cut line.



I'm covered in fine plastic snow.  I'm not looking forward to all of the cutting that I'll need to do on this canopy.



I started prepping the fuselage to receive the canopy.  First up was to cleco all of the skins back on.  Next, I put some masking tape over all of the places the canopy could touch to prevent scratching it.  Next, I marked a centerline down the cabin frame.  This will be the eventual split point between the forward canopy and the rear window.



 I also taped up the the ears on the canopy frame skin to prevent them from scratching up the inside of the canopy.



Finally, I finished cutting all four sides of the canopy, smoothed out the edges, and then placed the canopy on the fuselage.  This looks so fucking cool!  The edge finishing technique I'm using is to clean up the rough cut marks with the vixen file and then sand with 80 grit sandpaper to smooth things out.  I tried breaking a piece of the scrap without edge finishing, and it takes a surprising amount of force, so I'm confident that edge finishing to this degree is more than sufficient.  The shop was between 75º and 80º though, so that definitely helps keep the plexiglas soft.



Started Baffling

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My buddy John Soward from KY was in town over the weekend, so we spent a little time working on the plane.  The canopy wasn't a very good project for two people to work on, so instead we started on the engine baffling.  These are a few of the many pieces that form the baffles that fit on the engine to direct cooling air down through the cylinders.  We basically only made it through the first couple of pages of plans.  It's easy to see that the baffles will be quite time consuming.  There are lots of pieces to fit together and tons of nooks and crannies to debur.



I only had a few minutes to work on the plane tonight, but I cleaned up the baffle parts and moved the canopy back to the workbench.  I wanted to cut the bulk of the material off of the front of the canopy, but I haven't seen anyone come up with a good way to ensure the left and right sides are approximately uniformly cut.  What I ended up doing was taping a piece of string to the top of the canopy along the centerline near the rear.



With some tape in the center at the bottom of the apex of the curve, I used the string to determine how far that was from the taped point.



I then swept that string along the canopy to define the position of the tape.  Here's approximately the midpoint of one side.



And here's where the curve intersects the side.  Using this technique, it's easy to get each side within 1/8" or so which is more than symmetrical enough.



After using narrow tape to follow the curve, I used wide tape to seal up the gaps in the plastic covering.  It's too late to cut this tonight, so I'll do this cut next time.  This will remove the bulk of the flattened flange on the front of the canopy.  There will still be a small radius along this cut line that will need to be removed, but I want to sneak up on the proper fit instead of risking cutting too much.



Cut Front of Canopy

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I got out in the garage before work this morning because it's the only time that I can work on the canopy during the week.  The cutting process is really loud, so I can't do it in the evenings after the kids go to bed.

Anyway, I cut along the line I laid out yesterday and put the canopy back on the fuselage.  The fit was pretty good right off the bat.  The sides also pulled in quite a bit closer just due to this cut.



The center still has about a 1/8" gap.



And there's about a 1/16" gap on each side.



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