I completed my first turtleback and canopy in 1999.† While it functions just fine, there are some personal preference issues that I canít live with.† So, Iím going to rebuild the canopy again.† John Slade likes to drag my name through the Chapter 18 mud, so I must redeem myself! J†† My Chapter 18 webpages are going to chronicle a mix of old and new for a while until I complete the new canopy.
If youíve sat or flown in a Cozy IV, you know that the canopy glass comes really close to the side of your head!† So I knew from the outset that I wanted a wider turtleback and canopy.† I originally purchased a prefabricated turtleback, then forcibly widened it by two inches.† (First mistake.)†† But in trying to widen it, I introduced some distortions that it was not designed to take.††† Thus, the turtleback distorted over time such that the forward and aft halves donít line up anymore at the cut line.† It would have been a cosmetic nightmare to fix since the windows are already installed.† Since Iím determined to have a wider canopy and since no one makes a T-back wider than plans, Iíll build the T-back myself.† Iíll widen the jig by 2 inches and raise the height by 1 inch.†
When mounting the canopy glass, I tried really hard to get rid of the depression at the junction of the glass and turtleback. An acceptable way of doing this is to lower the forward part of the glass by trimming more acrylic where it meets the instrument panel. (Second mistake.) Yes, lowering helped smooth out the depression, but I carried it too far. In lowering the nose, the forward point moved aft. Alot aft! It is now about 7 inches aft of where the BL0 template says it should be. While that in itself in no big deal, I had to remove some of the switch row on the top of the instrument panel for the glass to fit. The bigger problem is that the width of the canopy deck at that point is much more narrow than planned. The canopy deck now blocks my view of the airspeed indicator. So this time, Iíll pay more attention to setting the width of the canopy glass and pay less attention to the glass-to-turtleback depression. If I need an eyebrow to fill that area, so be it. I also talked with Jeff and Becky at Airplane Plastics. I now better understand how the canopies are made. Changing any of the turtleback dimensions changes the circumference of the canopy bubble. (About a 4-inch change in my case, two inches wider, one inch higher on each side.) The Mark IV bubbles match Nat's instructions, so when ordering the canopy bubble from Airplane Plastics, it helps to tell Becky and Jeff if you've changed the width or height on your turtleback. They are good folks and will do alot to help you.
Finally, the cosmetic appearance of the nose/canard cover/canopy is the most critically judged parts of the entire airplane.† You can have gorgeous wings and cowls, but if your nose and canopy donít flow together the plane looks compromised and the builder comes off looking like an amateur instead of a craftsman.† I had always promised myself that Iíd carve the entire top section of foam all at the same time -- nose, canard cover, and canopy deck.† (Uh oh, Mistake #3 coming up!)† Now this is going to sound really stupid, but I finished stacking the foam blocks against the canopy glass a day before we got struck by a hurricane.† Well, uncarved urethane foam is as tempting as a double-fudge banana split with extra nuts and whipped cream. (Should I say with two cherries on top?) †††The hurricane was a really mild one, so I ventured into the garage and started shaping the foam.† Then we lost electricity.† I foolishly carried on using the ambient daylight coming through the windows.† (It wasnít enough.)† Oh, the carve job looked great, but I carved the decking way too shallow and flat.† After carving the nose and canard cover, I couldnít live with the crooked nose effect.† So I pour-foamed the canopy deck and tried to reshape it.
So the bottom line is I have a dorky-looking canopy that weighs too much.† So Iíll rebuild.
A Note about Prefabricated Turtlebacks
If you are sticking with the plans-built dimensions, then you should really consider buying a prefabricated turtleback.† The purchase price more than offsets the work required to build the jig, form the foam strips, fair, fill, and sand.† I had purchased an approved "SB" pre-fabricated turtleback from AeroCad and was very happy with the quality.† Featherlite also makes a nice, nomex-cored T-back, but youíll need to plan ahead as there is usually a one-month turnaround.