Blowing Your Own Canopy

Nuts & Bolts Craft & Technique You CAN MAKE A CANOPY FOR tion window in one side of the your project two ways. You oven, and I put a lamp inside can pneumatically form the so I could inspect the blowing plastic sheet in a mold or process. form (commonly called Almost any readily available "blowing" a canopy), or you Making an aircraft canopy heat source will work with the can draw a sheet of plastic oven, and I used a 200 KBTU over a form. propane torch heater. I located PAUL MOFFAT, EAA 602025 Both methods have advan- it at the center bottom of the tages and disadvantages. A oven and used an air recirculat- blown canopy is generally free of de- ing blower to keep the air moving. fects that cause visual distortions, Just above the plane where the plas- and usually one person can perform Before heating the tic sheet would go I located a tem- the task. But, the canopy's shape is perature gauge. For the acrylic to difficult to control, the thickness of plastic, prepare a blow freely the oven needs to reach the plastic varies, and you shouldn't 325°F. glue the formed plastic because of female mold that The plastic sheet is attached to a crazing. flat sheet of plywood with !he pat- A drawn canopy does not alter matches the air- tern retainers, which are pieces of the plastic's thickness, you can use a wood screwed in place that outline smaller sheet of plastic than you craft structure the the shape of the canopy's base (and would if you were blowing the same also determine its vertical dimen- canopy, and you don't need as large canopy must fit so sions and shape). In the bottom of of an oven to warm the plastic be- the plywood base is a 1/4-inch steel fore drawing (or blowing) it But, you can bring the tube that introduces that air that • @ • ' when drawing a canopy the plastic s blows the canopy. temperature must be just right to outline shape in When attaching the plastic to the avoid the possibility of rips and dis- plywood base, creating an airtight tortion-causing ripples, and the task line with the seal with the retainers is important can require up to four people. because a leak will require more finished surface. pressure to blow the canopy. A leak Blowing a Canopy will also create a cold spot that To blow a canopy the causes distortion. When first thing you need is blowing the canopy the an oven in which to air pressure only needs heat the plastic sheet. to be about 10 psi, and I Your oven must be large control it with a needle enough to hold your fin- valve and measure it ished canopy, with room with a low pressure to spare. My oven meas- gauge. ured 4-foot square by 10 Before heating the feet long and could han- plastic start a 1 or 2 psi dle a 38-by-96-inch flow of air under the sheet of plastic. Before blowing the final version of the canopy we created plastic to lift it off the Making the oven of this test version (and used a plastic sheet too small for the plywood, which keeps ordinary plywood, I airplane) la you from having a ply- lined the interior with wood-grained canopy. Fiberglas batting, held in place with net. Using the heat-resistant glass The plastic sheet should be about chicken wire, to insulate the cabi- from an old lamp, I put an inspec- 1.5 times thicker than the target, but 94. JANUARY 2002 We formed this canopy by pulling a sheet of plastic over a mold. screw points. Before heating the plastic, prepare a female mold that matches the aircraft structure the canopy two times may be more practical, must fit so you can bring the outline IK2000 TM shape in line with the finished sur- FLIGHT & ENGINE MONITOR Bl0wing a Shape face. This mold should have all sur- Combines 12 Instruments In When blown, the plastic wants to faces that may contact the plastic. 2 Independent, Redundant Displays! follow a spherical shape, which may * See if all at once - no scrolling be far from the shape you desire. To * Digital and graphic displays get the shape you want, use this * Tri-color bar graphs give instant alerts concept: The desired height equals * Use with all 4 & 6 cylinder engines the radius on the plywood. If you at- * Affordable! 10% of typical airframe cost tempt to shape the plastic according to the outline o! the retaining frame, Just add a GPS/COM & transponder and vou're readv to flv! the plastic will become grossly overblown. I-K Technologies As shown in Figure 1, the desired 310.745.1130 www.i-ktechnologies.com portion is a small part of the whole patent pending sheet. To preserve the desired shape Your oven must be large enough to the excess room would be best used hold your finished canopy, with for a second canopy. The retaining room to spare. My oven measured clamp follows the outline and is se- 4-foot square by 10 feet long. curly screwed to the sheet below. To keep the form airtight and to pre- To prevent scratching, cover the fe vent blowouts, you'll need a lot of male mold in soft felt that is liber- screws. A screw every 2 inches is ad- ally covered in grease. (Bacon fat equate, works well and is easily removed.) NOTE: After you blow the canopy Without this female mold and fi- remove the screws as soon as the nal step, the finished canopy may plastic is firm. Depending on the split as you draw it to the frame. The grade of plastic, the sheet will shrink forming is made easier if the mold is almost 2 inches over an 8-foot hinged on the top and closes over length. If the plastic is still screwed the bubble like a clamshell. That will in place, it will split at one or more avoid scrapes if the frame is pulled Excess, or second canopy, Desired shape for symmetry / Figure 1 ~,,_ Radius here = desired height curve For more information, visit SPORT AVIATION Sport Aviation 95 on the Web at www.eaa.org Automated Engine Monitoring... Craft & Technique ..m one instrument! From RPM to peak-detection leaning, the EIS does it all. Includes graphical and digital displays, customizable screens, and alarms with Actual Size 6"W x 2.75"H x 2.5"D external warning light. Models for all engmes...find out why the EIS is the chome of thousands of pilots. S473 S553 $995 2-stroke 2-cyl 4-stroke 4-cylinder Prices include probes. ml- propPiipr. The Wz ner PropelEer/ This is my first successful canopy If you are looking for performance, we sell it! (on my second overall attempt) from FAA certified Hydraulic or Electric Constant Speed Propellers for all high performance aircrat~, like LANCAIR., GLASAIR, CIRRUS, EXPRESS, QUESTAIR, VAN's, VELOCITY, the oven. Just visible in the top is a etc. 2-, 3-, 4-, 5- and 6-blade designs available up to 2000 hp. National, European and cold spot. This is the same canopy World Aerobatic Champions win with our specially designed, light weight, low noise and high performance propellers. pictured at the start of the article. FAA STC for Pitts S2A and S2B, Cessna 172, 182, TIP210, Piper PA 46-310P/350P, PA60-601,602 and more. down over the plastic. H~ Serwce Center" MT-Propeller Entwicklung GmbH MT-Propeller USA, Inc. Blown Plexiglas is more prone to Flugplatz Straubing-Wallmtihle 1180 Airport Terminal Drive D-94348 Atting, Germany De Land, FL 32724 cracking from added stress lines, so Tel: 011-49-9429-94090, Fax: 011-49-9429-8432 Tel: (386) 736-7762, Fax: (386) 736-7696 do not glue it with any solvent- e-mail: [email protected] e-mail: [email protected] Internet: www.mt-propeller.com based cement because the adhesive will craze the plastic. Silicone or other glues such as Goop work well. Goop is especially adhesive, and the plastic may never be separated on curing. Trade Show • Safety Seminar Sport Seminars • 99s Flying Companion Seminar This is a blowout, which was Speakers & Seminars caused by using too thin a sheet of plastic and the existence of a hot spot at the far end of the canopy. Chas Harrel • AOPA Pres. Phil Boyer Transport Canada • Catherine Fish Bythe Numbers s Once you have all the forms and EAA-Oshkosh • Catherine Fish oDoug Ritter patterns ready, check the plastic's airtight seal by applying around 8 Hall of Fame Banquet psi of air pressure and closing the Saturday Night - Tickets $30 valve. If the pressure remains constant, you've got an airtight seal. If it More information: doesn't hold, find and fix the leak. 1-866-WAA-SHOW To mark the canopy's target www.wash i ngton-avi at ion.o rg height I used a small wire hanger FREE PARKING • FREE R DE FOR FLY-INS from the oven's ceiling. When the For more information, visit SPORT AVIATION on the Web at www.eaa.org g6 JANUARY2002 plastic just reaches the marker I turn off the air pressure and open the oven to start the cooling process. Start with a 1/4-inch acrylic sheet. The medium thickness at the peak will reduce the thickness to about 0.100 inch. You can use tinted plastic, but the tint will lighten because blowing thins the plastic.

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