KR-2S :: Canopy

The KR2S Project

Canopy

It has taken some time for me to settle on a canopy style that I was happy with. My criteria was that it had to provide sufficient headroom to the sides which meant it had to be large enough to stretch across the flattish turtle deck top and down the sides which are pretty vertical. This KR is about 42" at its widest external measurement so needs a big canopy but what I wanted to avoid was a "bubble" look like a 4077th M*A*S*H helicopter. It had to enhance the streamlined appearance I was striving for and it also had to be tinted.
I received a tip on a tinted Todd's Zodiac canopy for sale which I knew would be more than large enough. So I transposed the shape of it onto a picture of my KR using my PC and figured it would be perfect.

	The round trip to pick up the canopy took 21 hours and was 1,000 miles long. This called for occasional breaks from the monotony every now and then.
	My son and I arrived in Canberra and met Jeff who sold us the canopy and many big sheets of 6061-T6 and other bits and pieces from his unfinished project including a completed horizontal stabilizer and elevators. I find I am collecting enough materials that I will probably be able to build another aircraft when I finish this one. Jeff and his sons used their rope tying skills and secured the crate that well that it needed no re-tensioning on the return trip. Thanks guys.
	I felt like Indiana Jones opening the crate that contained The Lost Ark.
	Jeff had even screwed in a cross beam and added foam for the road trip This canopy is huge!
	I measured from the top of the longerons to where I saw the top of the canopy being and then added 2" per side just to be sure. The angle grinder with a 1mm cutting disk made short work of the cutting right the way around the bottom and left me with an offcut 5" wide.
	A texta taped to the end of a stick marks the beginnings of the cutout needed to shape the canopy over the front deck.
	The back of the canopy was then fed under the turtle deck and marked for cutting. There is no turning back from here.
	When the canopy was held in place and I stood back, I could see that I had just a very slight "Bell 47" look happening. The only way to flatten the top of the canopy was to lower the front which meant cutting strips off it gradually until everything lined up from the tail to the canopy zenith. (Pardon the pun). I have used an ally sheet of Jeff's, screwed into the turtle deck as a guide between it and the canopy. The unplanned need to tilt down the front and the fact that I had taken 5" off of the bottom has left a sloping triangular gap from half way along the longeron to the back. I have come up with a pretty cool idea for this area which I will keep to myself at the moment.
	It is very hard in a crowed garage to imagine the final result. But I like what I am seeing so far.
	I begin the canopy frame by duct taping the longerons and then using expanding foam to stick a block of urethane foam in place.
	Using the surform and large sanding block I have shaped the outside of the frame to the contour of the fuselage and the curvature of the aft deck.
	A single layer of carbon fibre over the outside and the white marker line shows where the Todds canopy edge will sit in the frame. More duct tape is used in areas to stop anything sticking as the frame needs to be lifted out at some stage.
	I have used a razor blade to cut out a strip of carbon fibre and then wrapped a piece of perspex in sand paper to use as my sanding block and thickness guide.
	The bottom of the channel has a bed of flox pushed into it and then the wetted out CF and peel ply is held taught with stapled popsicle sticks.
	After sanding off the edges, the canopy sill should be the correct size to house the perspex and some flox. The outer edge of the canopy should end up sitting flush with the canopy frame.
	I have laid some plastic across the deck with some CF and peel ply set to dry. This is the beginnings of the forward part of the canopy frame.
	The canopy is held in position with rope and a small bead of flox is run around the forward edge only. At this stage the forward carbon fibre strip is not stuck to the side frame rails, only to the canopy.
	3/32" holes have been drilled along the canopy edges and then enlarged a little using a Dremel and a grinding bit. Long screws with timber caps go through the foam and meet timber pads on the other side which act to clamp everything together. I have sanded the inside 1" along the canopy perspex and added flox being careful to not get close to the screws. Then the screws are nipped up.
	While the side frames were drying I sanded a large piece of foam to the shape of the turtle deck and then used it to begin forming the shape of the aft canopy frame. I trimmed the perspex and then scribed the foam where canopy ends.
	Micro was added to the area that I wanted the carbon fibre to stick to.
	And here is the result after the CF has been cit away in the channel area.
	As with the side frames, flox was added to the right angle corner before micro and a long CF strip laid down and allowed to cure.
	I used the same clamping method for the aft frame but carved holes in the foam through which I passed the pre-drilled timber. The holes do not matter as most of that foam will be removed shortly anyway. Using the big piece of foam ensures the canopy keeps its shape whilst the flox dries. There is no chance of flexing
	After curing I have carved out the foam leaving the arch to be sanded to the correct form.
	This shot shows the beginning of the inner side rails which have been shaped to the canopy line and rounded slightly.
	With the inside of the rear canopy frame all carbon fibered up, the junction between it and the side rails met at abrupt angles. I am after a smoother transition so stuck some urethane foam down and sanded away until I was left with a nice curve. This was then covered with CF.
	In this shot the canopy is sitting vertically on its nose. I made up a wet flox and dribbled it all the way along the inside where the canopy meets the strip of carbon fiber. After going off I use cling wrap as a mold release and line the same area. Two part expanding foam is then poured in along with some very thin lengths of CF offcuts to provide some rigidity. Without this, the foam will easily break when removed as one piece. How do I know? This is my second attempt.
	And here it is popped out some 30 minutes later. The cling wrap leave the foam smooth and shiny which micro will not stick to. So a quick "de-glaze" with sandpaper will get it ready.
	Covered in micro and a layer of carbon fiber and the foam rail is pushed back into the forward ledge and allowed to cure. This time I used duct tape as a mold release.
	Popped out again, and this forward frame is beginning to take shape.
	I am roughing up the perspex, previous wet flox run and the carbon fiber strip in readiness for permanently floxing in the forward rail. Duct tape protects from flox squeezing out and onto the perspex when the frame is pushed in and clamped.
	With the first layer on the inside frame pretty much finished it's time to do the outside. Duct tape marks the edge of the completed flox and CF strip. This overlaps the perspex about 1" and matches the inner frame line. Rounded corners and angles will show a smoother look.
	After a light sand the remaining gaps and drill holes are filled with flox and the squeegee is used to taper a thin layer of flox from the frame edge to the point right the way along the duct tape. This is allowed to set for about 1 hour to harden a little and then the CF strip is laid over the top
	Here is the finished "look" and I am thrilled with it!
	I have clamped the forward deck to the canopy and fashioned some trial hinges from plywood to check for correct clearance.
	This is the canopy flipped up side down. The hinge mount point begins by removing all the foam down to carbon fiber on the other side. A good bed of flox is laid in the bottom and a foam block placed on top like laying a brick.
	More flox, then the 2" x 2" 6061-T6 extrusion on top and then some more flox before the flap is pushed back over and the whole lot is allowed to cure. The part of the extrusions now setting in the flox each have two holes drilled through to aid flox adhesion.
	I have to keep the mount points straight and square whilst the flox cures.
	Plywood mounting points are floxed together and then floxed to the underside of the the forward deck in areas which have been reinforced with an additional layer of carbon fibre to form "pads".
	AN3 bolts hold the fabricated hinges to the plywood. The holes cut in the deck allow the hinge arms to move freely and to their full extent.
	Whilst sitting inside the cockpit and the canopy closed, I am able to mark the exact drill hole locations on the hinges. There are 3 holes in each.
	The canopy raises and lowers smoothly without binding.
	These are the mounts for the Stabilus gas struts which are the same size and pressure as Mark Langford's. 585mm long, 100N pressure. Fortunately for me, the Stabilus factory is just around the corner from where I work. The steel sleeves were turned on the lathe and tapped with M8 threads to suite. The sleeves will be floxed into timber hard points in the canopy frame and the strut mounts screwed in.
	The canopy is inverted in this shot. What I have chosen to do is scallop out channels for the gas struts to recess into when the canopy is closed. The timber mount point shown is to be floxed between the inner and outer skin of the canopy frame.
	The recess is then skinned with carbon fibre and the sleeves floxed into the hardpoints. The gas mounts then just screw straight in.
	Nicely recessed out of harm's way.
	The canopy raises smoothly when pushed up and is easily lowered with both hands. It remains up on one strut which is handy when removing the piano hinge pins and maneuvering to remove the deck and canopy as one. It is high enough that entering and exiting the aircraft is not hindered in any way. The cowling is just one I have acquired along the way and will not be the final. We added it to help show off the beautiful KR lines.
	I have begun working on a lock design which had to meet certain goals. It would have to be impossible to accidentally knock or catch a sleeve on in flight and frighten the hell out of you. Has to be easily opened from the outside by a non aviator in case of an emergency. Has to be completely flush with the outer skin. I bought a couple of Hartwell latches which are strong and easy to operate. Here I am machining some 6061-T6 plate which is the perfect thickness to house the 2 buttons.
	The I countersunk some holes and tapped them for 6-32 thread as well as the 4 holes in the latch. This is the latch in the locked position. The triangular cutouts in the canopy frame will house the latches.
	Push the big round button to unlock. Simple enough.
	The lightened supports for the latch body have been tapped as well and will be floxed to the carbon fiber inside the hollowed out canopy frame.
	Quite a bit of cutting and grinding was needed on the supports so the mechanisms of the Hartwell latch could move freely.
	Floxing the full latch in place had to be done carefully to avoid the flox touching any moving parts. The hollowing out has allowed the flox to get a really good "bite" on the supports.
	The finished latches, which I decided to flip around, work a treat. They will lock on to a square 4130 tube striker plates which will attach to the longerons. Being recessed inside a cavity and flush with the surface makes the latch impossible to accidentally unlock. A clear thin film like the "tear offs" F1 drivers use on their helmet visors will be screwed to the outside frame to give a flush finish. This will be easy enough to tear/break in an emergency An "EMERGENCY PUSH" decal with an arrow pointing to a big red button should be easy to understand by everyone.