After a long hiatus on the project, I'm easing my way back in with some small items. That, and the shop is still filled with my DR-107 that I'd worked on over the winter so I don't have a lot of room right now.
It seemed like a great opportunity to look at the canopy. There are no real drawings for the canopy but its operation is mentioned in a couple of the articles written when the plane was introduced. In some aspects it's quite neat. In other aspects, it's mind boggling. Rube Goldberg had nothing on Michel Dalotel.
The canopy is simply a flat sheet of plexiglass secured on either side to the fuselage and bent overhead. It's no different than a piece of paper held at opposite ends. Bringing the ends closer together causes the paper to arc upwards or downwards. With the Dalotel, the plexiglass is secured to a hinge on the RH side of the cockpit and bends overtop the cockpit to a hinge secured to a frame on the LH side of the cockpit. The frame on the LH side pivots 2/3 of the way up the canopy side. As the frame is closed, the sheet of plexiglass bends around a ledge ahead and behind the pilot's head. This ledge provides the correct curvature of the sheet of plexiglass and when the frame is closed and latched, the plexiglass is snug. To open the canopy, the frame is rotated outwards and upwards causing the plexiglass to straighten out as the frame travels. Simple and elegant just like the articles from 1969 described.
The complex part of it comes into the ability to jettison the canopy in the event of an emergency. Most hinged canopies use a hinge pin that can be quickly removed by pulling a handle in an emergency. Not on the Dalotel. The previously mentioned hinges on either side of the canopy are not bolted or riveted to the canopy frame. Rather, the hinges are secured to 6 tabs that will release the lower portion of the canopy hinge when the jettison handle is pulled. Getting more complex? Just wait...
These tabs that secure the canopy hinge are mounted to a tube that runs inside the canopy frame. The canopy frame is notched in 6 places, each notch lining up with one of the 6 tabs. There are some unique rivets on the lower half of the hinge that pass through the frame and are secured when the tube/tab assembly is rotated towards the rivets. The rivets are not rivets as we all know them. They aren't clamping anything together, rather they have two heads, like duplex nails used in house framing construction. Each tab hooks onto its respective rivet between the two heads. The tube is held in place and prevented from rotating within the canopy frame by a complex latching mechanism. The latching mechanism secures a ball bearing in place that nests into a pocket in the tube/tab assembly. When the jettison handle is pulled, the latches on either side of the cockpit are released, causing the ball bearing to come out of the pocket, allowing the tube/tab assembly to rotate away from the rivets, releasing the hinges which hold the plexiglass into place. One of the elegant features of this design is that if one side hangs up and doesn't rotate fully, the release of tension on the other end of the plexiglass will allow the hung up side to also release. Of course, the system isn't as simple as that. There's more to it.
The 6 tabs that are mounted to each of the tubes (one tube per each side of each cockpit) have a some additional work to them. To allow adjustability to each of the tabs, they are actually part of a sleeve that rotates around the outside of the tube. The sleeve is held in place and adjusted by a beautifully machined brass wheel that is mounted in line with the tube. Each brass wheel is larger diameter than the outside diameter of the tube and each wheel is protrudes from the tube on either side. The brass wheel is knurled and it has a coarse thread to it. The brass wheel is secured to an allen screw that crosses the tube from one side to the other. As you turn the allen screw, it rotates the brass wheel. As the brass wheel turns, it causes the sleeve with its tab to rotate independently of the tube. This allows infinite adjustability for each tab providing the ability to adjust the tension on the plexiglass and the security of the canopy. Finally, to add one more level of complexity, there is short section of extremely fine music wire that also crosses the tube, parallel to each allen screw. This music wire catches the knurled edges of its respective brass screw, preventing it from turning on its own...
There are holes on the inside of the canopy frame which line up with each of the allen screws. This allows one to adjust them once everything is assembled and the canopy is closed.
Complex? YES.
Make sense? Maybe not. It took a couple of hours of head scratching with the pieces in hand before I was able to figure it all out. Fortunately there's a piece of original plexiglass and hinge left. If I didn't have that piece, I wouldn't know about the duplex rivets and how they hook into the tabs. It took quite a while of cleanup and experimenting to discover that turning the allen screws turned the brass wheels, which rotated the sleeves. There were many "A-ha" moments when figuring this assembly out.
More interesting details to come. More complexities and weird assemblies.