My Priority Mail order from Van's that I ordered on Tuesday came today. It had one of the UHMW plastic bushings that I was missing, plus a few other thin UHMW blocks (which I might use if I experiment with making my own throttle quadrant), some single-leg nutplates, and various different sizes of snap bushings.
The construction manual contradicts itself in certain areas...this is one of them. The instructions said to rivet the small F-644 ribs onto the center sub-panel, but now they say that those ribs should not have been riveted. Whatever, it's easy to work around it. The point was that it's a bit easier to drill things with the short ribs removed. I just went ahead and removed the center sub-panel...problem solved.
Basically you clamp the bushing blocks to the forward fuselage ribs and drill some pilot "dents" through the two bolt holes that are already drilled in the ribs and into the blocks...remove the blocks, final drill 'em in a drill press. Then the blocks are placed back against the ribs and the 1/4" pin holes are drilled. This is what you get when that's all done...the bolt holes and pin hole are drilled.
Then you drill the 2nd hole in the aluminum spacer, which gets sandwiched between the UHMW blocks.
Next the short ribs go back on (the center sub-panel, actually), and stuff gets put into position in preparation for drilling the bolt and pin holes through the short ribs, which don't come pre-drilled. Here you can see the bolts are pushed in up against the short rib. It's not as easy as just drilling through those holes with stuff in this condition, though. The ribs need to be in their exact final positions, which is dictated by the skin.
Here the top skin has been clecoed on, and you can see the slot where one of the canopy "gooseneck" hinges goes.
To gain access to drill the holes, you just peel the outboard sides of the top skin up.
Here's a view through the firewall recess hole after the 3/16" holes in the left rib have been drilled and the bolts have been pushed into place.
I spent about an hour really considering which approach I wanted to take with the canopy release mechanism. Not that an hour is all the consideration I put into this...I've been deliberating for months now. Here's the deal... The standard canopy release design uses that T-handle thing I drilled the other day, which passes through the panel and sub-panel and attaches to a weldment arm. When you pull on the T-handle, it rotates the weldment and pulls the pins out of the canopy's forward hinges. Just so we're all on the same page, the forward hinges aren't the only attach points for the canopy. You've got three aft latches...two at the base of the frame and one up at the top of the arch. You've also got the gas struts which help keep the canopy propped open when it's tipped up.
Ok, all that said...the idea behind the T-handle release system is twofold. First of all, if you need to remove the canopy from the aircraft on the ground, i.e. to provide better overhead access to the instruments and what not, you can simply and quickly release those forward pins and lift the canopy right off. Sort of...you still obviously have to unlatch the rear points and remove the gas struts. But you don't have to crawl under the panel to undo bolts/nuts. It's very convenient.
The second advantage to the T-handle release system is that you can theoretically jettison the canopy in flight if the need arises. Let's say you wanged through a split-S but got complacent and you went blazing past Vne and exceeded 9 Gs in the pullout (yeah, right). You busted the wing or the tail or something...unrecoverable. Just pull the handle to jettison the canopy and jump out (you're wearing a parachute, right?). Not quite! First of all, the only way the canopy is just gonna "fly off" is if you made provisions for the forward hinge brackets to slip vertically through the top skin...which means you have to cut slots in the skin...which is a potential source of leaks. And we're talking moisture coming in directly over your expensive stack of electronic toys. And what about the gas struts? I guess they might rip off, or maybe you're unlucky chumpy and they don't. And what about the possibility of the canopy taking off your head as you jettison it? It's a realistic possibility. So in order to take advantage of the jettison feature, you need to cut slots in your top skin, inviting leaks, and take the risk that you might not live through the canopy exiting the aircraft. Nobody has ever jettisoned an RV-6 or RV-7 tip-up canopy in flight. It hasn't been done. Can it? We don't know.
I'm happy to assume that it can't be done. I'm not cutting slots in the skin, and I will fly with the assumption that if I need to get out, I'm either going to have to push the canopy open enough to clammer out in an adrenaline-induced fury, or I will take the passenger stick (a friction fit) and shatter the canopy. That's my exit strategy, so to speak.
Ok, and let's talk about the need to remove the canopy on the ground for maintenance. Everybody I've spoken to says stuff like, "I haven't removed the canopy once in 600 hours, nor do I ever anticipate needing to." One of the beautiful things about the tip-up is that you have excellent access down into the instruments from above without having to remove it. Unlike the slider, which has a fixed windscreen covering everything, forcing you to crawl underneath on your back (unpleasant), the tip-up affords great access by default. So I don't believe I will be removing the canopy on the ground on a regular basis, if at all!
Now let's talk about one more factor, before I spell out my obvious decision. It has to do with "lost panel space." There's about 8" between the instrument panel and the sub-panel. My GPS/Comm and Nav/Comm radios are about 11" deep, not including wire harnesses. There's going to be a radio tray into which the avionics can simply slide. The deal is that the tray will have to pass through the sub-panel. Not to worry, this is common. But the implication is that if you use the standard T-handle pin release system, you give up a few inches of vertical space at the top of the panel, at least you've given up having the radio tray at the top of the panel. The pin release linkage, if installed, is back there along the top.
Now to state the obvious. I will not jettison the canopy in flight. I will forego the ability to quickly release the canopy on the ground. I will install bolts instead of pins and call it a day! I will regain vertical panel space where the avionics stack needs to go. I will shed a pound of steel linkages, pins, bolts, bushings. Sound like a plan?
Here's the only catch, and it's very minor. The outline shows where the avionics tray will pass through the sub-panel...it will actually come back about 3" toward you. I left that AN4 bolt sticking way out to show that when installing that hinge bolt over the avionics stack, I will have to fish my fingers up in there when first feeding the bolt through. Getting a wrench on the bolt head will be easy, it's just fishing the bolt in the first time that will be a bit tough. Oh, well, right? It's doable.
Anyway, it feels great to have made yet another decision that affords me excellent ergonomics in flight at the small cost of convenience in an activity that happens once in a really, really blue moon. Another big check mark over a big question mark. Oh yeah...and weight and complexity saved, too. The pin release linkage is all 4130 steel! Ballast that I can leave behind now. Of course I've already fabricated half that crap in case I change my mind later.
Ok, back to working on the canopy side latch. I deburred the edges of the latch levers.
The long lever had a slight bow to it (as do most 1/8" thick stamped Alclad parts it seems). Using the vise and a rubber mallet, I straightened it by strategically tapping, reclamping, tapping...
I cut the required semi-circular notches in the latch mounting angles.
The instructions and plans lead you astray a bit here. I followed the drawings to the letter and had a slight issue. It's more aesthetic than anything, but c'mon, we all want perfection. The issue is that when the lever is bolted to the angles, the straightaway that the arrow points to is supposed to be flush with the angle face, and the bit to the right is supposed to protrude .032 through the skin to be flush with the skin. Well...where the plans have you drill the bolt hole, the lever ends up being slightly tucked in, and it doesn't fully penetrate the skin. It looks recessed. No good.
So I fabricated two brand new attach angles but I did NOT drill the holes where the plans say to. I marked the lengthwise positions, but I determined the in/out position by clamping the lever in place and ensuring that the supposed-to-be-flush part was actually flush. Save yourself some time and do it this way from the get-go. You can kind of see the as-per-plans mark through the bolt hole, but it's off by about 1/32" (.032). So I drilled my hole .032 lower (left, technically) than the plans call it out.
Next I drilled the whole contraption to the side skins. Before doing so I bolted it together and put .016 shims both above and below the levers, as spacing between them and the angles. There will be UHMW tape in there to "lube" the works, and the .016 shims simulate that thickness so things don't bind up.
Here's the view from the inside.
Next I deburred and machine countersunk the angles, and I cut the semi-circular notches out (again).
Here's the yellow knob that comes with the kit. You have to position it, drill through the lever, and then thread a screw in there. The knob is an extremely tight fit. If you're building one of these you'll see what I mean.
Next I installed the return spring on the latch lever. There's a stiff steel wire that S's into the latch and passes forward through a hole in the F-704 center section, and the spring helps the lever return to latch the other lever into place.
Here's a top-down view that shows the interlocking profile. To unlatch the canopy from inside the cabin, you flick the forward lever forward and pull back on the yellow knob. When you latch it, you get a nice positive snap.
To get into the aircraft from the outside, here's what you see when you walk up to a closed canopy (minus the clecos, of course).
Squeeze the levers together and push the aft tab in.
The long lever pops out the back, and just pull it to unlatch the canopy. Very simple, elegant, low-drag system. Way to go Van.
