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 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 fe- male 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 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 ~,,_

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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 con- stant, 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 thick- ness 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. By the numbers: 1. Heat the oven to 325°F and let the plastic soak for 20 to 30 minutes (20 minutes seems right for 1/4-inch plastic). The sheet should have only 1 psi on it to lift it off the plywood. 2. Turn off the heat and let the plastic "relax" for about five minutes. 3. Now start slowly blowing the canopy to the desired height. Slow down the pressure rate as the sheet nears the marker. The oven will heat the air in the form, caus- ing it to expand and add to the blowing process. 4. Once the canopy reaches the desired height, wait a minute or so and then open the oven to start the cool- ing process. 5. Pull the sheet out of the oven and slip the frame form over the plastic to shape the peripheral edges. You will have to keep the air pressure up to keep the plastic from collapsing. When pressing your fingers on the plas- tic no longer deforms it, cooling has progressed to the stage where you can remove the canopy from the form. Remove all the screws and separate the plas- tic from the form; hot air will be trapped in the canopy, so take v care when lifting Mark III Xtra if off. This is the inside of my form, with Drawn Canopy its bulkheads and stringers. The at- Making a drawn tached fabric was a failed attempt Our safe, high quality canopy requires at a release surface for the plastic. ultralight and experi- you to create a I used felt, and it left ridges in the mental kit-build aircraft Sport 600 and powered parachute male mold that plastic when we drew the sheet offers the broadest duplicates the over it. product line ~n the light plane industry! ~jae desired canopy exactly, and you need a way to heat the sheet for form- ing. The mold must be precise, and every imperfection in its finish will be painfully visible in the final product. You can build your mold using plywood and wood

= k stringers to create the desired curves. Strive for a mir- Kolbra We also manufacture ror finish on your mold because every defect you see the Firefly, FireStar, or feel will be magnified 10 times in the finished Mark III Classic, Flyer, and Slingshot drawn canopy. Over this mirror finish stretch a release surface. If you London, KY 606 • 862 • 9692 don't, the drawn plastic glues itself to the mold. I used www.tnkolbaircraft.com felt on my first attempt, and it left ridges in the plastic. AIRCRAFT, CO. email." customersu [email protected] For more information, visit SPORT AVIATION on the Web at www.eaa.org Sport Aviation 97 Craft & Technique

After numerous experiments I found in a metal garbage can. Next to it that a plain cotton bed sheet works was a tray that was 3 inches deep best. The higher the thread count and several inches bigger than the the better, but go no lower than 180 sheet of plastic. to 200 threads per inch. After heating the oil to 380°F we To heat the plastic I used hot oil. poured it into the tray to preheat it. Using an outdoor cooker (turkey We poured the oil back in the can to fryer), I heated 10 gallons of inex- reheat the oil, and then poured the pensive deep-fry oil from Sam's Club oil back into the tray and put the Cut the finished canopy with a hot knife or a Dremel tool with a cutoff ,t ~ j',a~ - - • , iE,r i Tools, Videos, Trainings disk. NEW Video: Those Doggonned Reverses ~.~1, This 2+hr. video covers the development and construction of a variety of plastic sheet in the oil. The sheet aircraft falnngs, using both hand tools and the Air Hammer. $40 tends to float on the oil so you have ~_~; Aircraft Aluminum Gas Welding System to use some daubers to keep the i., Ratedas the finest system ever available--Video, Booklet, Torch, Special sheet submerged. Use care with the ~.~ Eyewear,Flux and Methods. Items sold seperately or as a kit. ($285) 4130 Chromemoly Airframe Construction Video daubers because the plastic will "re- 4+ hours. Shows you how to build complete from plans. Table-jig con- member" this prodding and will re- struction, bending, fishmouthlng, welding and stress relief. See tain a mark. ~pedals and rudder built from scratch. After about five minutes the plas- ~1~ 1 1 1 most-asked questions at ---..- ,, • ~~` Oshkosh weld,ng workshops. tic should be ready for drawing. Just ~T-.. ~ ~. 2-tape set. Sale: $70 O' k before you and your team of helpers ~~i ,~ Tools and Methods for Better Metalwor pull the sheet over the mold, pour some hot oil on the mold to preheat its surface. To give us a good grip we added handling rails to the plastic, short stubs of 2-by-2s with bolts that entered holes in the stretching frame. Hot oil dripping on your hands is not nice! Pulling the sheet over the form The four-seat STOL OH 801 is a true sport utility kit aircraft, offering a takes a lot of force, and this is h'~lf.÷nn =,e,',f,,I Inch ~nt'l eimnlw ,~m~7,nn ~hnrf f,-~L-,~.nff ~n¢t I,~nrtlnn where your friends come in. Put one on each corner. And you need to work quickly. Because the plastic begins to cool immediately, you've got a minute or two to complete the job. After you've drawn the canopy, remove it from the mold and clean off the oil. If you don't clean the oil off right away, it will leave a "sheen" that's difficult to remove later. Whether you've blown or drawn your canopy, trimming it is your fi- nal step, and you can do this with a hot knife or a Dremel tool and a cut- off disk. A band saw also works. Don't use a jigsaw because the blade can snag the plastic and cause a split. When you mount the canopy, to prevent thermal cracking remem- ber to leave some expansion room around any screws or bolts. For more information, visit SPORT AVIATION on the Web at www.eaa.org

98 JANUARY 2002