A Novel Canopy Seal for the Long-EZ and Varieze Aircraft
by Art Bianconi
Long-EZ's and VariEzes are not known for being especially airtight or quiet aircraft. In recent discussions on the Canard Aviators discussion group Art Bianconi posted a novel approach to sealing the canopy on a Long-EZ, VariEze or similar aircraft. He has agreed to post his thoughts here. (ed)
Take a ¼ inch diameter ball nose router bit and cut a ¼ inch deep channel in the center of top longerons, both sides of cockpit. Create a similar channel where canopy frame seals above instrument cluster.
Do what is necessary to link all three grooves so that they form one continuous channel from the left aft, around the cockpit to the right aft portion of the cockpit.
Measure the length of the entire channel and purchase a suitable length of ¼" surgical rubber tubing. Seal one end of the tubing and, starting at one side of the the rear compartment, glue the tubing into the channel you cut using a suitable adhesive (silicone works). Do not stretch the tubing when securing with glue. Tack the tubing about every 8 to 10 inches. When you have routed the tubing along the entire length of channel, snip off the excess and plug that end of the tube. Allow the adhesive to cure.
Purchase a hand pressure bulb like those used in blood pressure manometers. Make certain yours has a valve built into it or, failing that, purchase a separate screw valve body. Install the bulb in a length of tubing and, using a "T" connector, install it at some point in the previously installed channel seal. Typically, this is somewhere near the front of the cockpit as the T connector can interfere with proper closure of the canopy. It's easier to find a loop of exposed surgical tubing for the T connector than it is to drill holes and carve relief's in the longeron for the T connector.
What you now have is essentially a tubing system that loosely resembles the letter E with the pressure bulb at the end of the center leg. Mount the bulb end of the system where you can reach it in flight. Now when you close the canopy and latch it, close the valve and squeeze the bulb as many times as it takes to get resistance. On my Long it's about 4 squeezes. You've now expanded the tubing it's entire length and thus sealed the canopy against rain and water in flight. When you land, simply unscrew the valve and the system will depressurize.
One pilot I knew, did this on his Piper Cherokee 160 which has a fiberglass door with a curved top section that's supposed to seal into the roof. It took him about 10 hours to install but he swears it's never been more quiet. He claims a 20 db reduction in cabin noise! I can't verify that claim but it will reduce the wind noise and water leaks almost completely.
Avoid substituting tubing if you can. The reason I chose surgical is because it's the softest available and will seal better than any others I've tried to date. One downside is that the oil from your hands will cause the tubing to get brittle in a few years. Since it's almost impossible to get into and out of a Long-Ez without putting your hands on the longerons, this problem appears unavoidable. Fortunately, only a short length of the tubing need be replaced. The T connectors and related plastic connectors can be purchased cheaply at most Auto Parts stores. The Pressure bulb is available for less than $8.00 from most medical supply houses and in rare cases, local drug stores. Ditto on the tubing although some enterprising hobby and hunting stores buy it in spools so kids and hunters can make sling shots!
I tried doing the same installation but with the channel in the canopy frame instead of the longeron. Didn't pursue it. Granted, the tubing wouldn't get abused getting in and out but the lip of the frame would be seriously weakened at a thin spot. There have been some questions raised about how this procedure affects the strength of the longerons. It doesn't reduce the strength of the longerons but does reduce some of the shear strength of the layup of the glass to the wood. I do not believe this to be a critical area as the majority of the loads have alternative load paths and are, for the most part conentrated up front near thje canard and aft near the engine mounts. Remember, you are only cutting on the exposed canopy portion, not the entire length and you still have glass on the other side of the foam.
If you are concerned, route the channels BEFORE glassing the top longeron. Or, if it's already built, wrap an extra ply of BID on the cut after routing.