Monday, December 23, 2013

How to build one of scotty's surething wings

I've provided dxf drawings and parts list and airfoil template images for some of my wing designs as can be seen for example the S3 wing set seen here but some people have been asking me questions on how to build them. So I plan to collected some links and other material that I found that use the same or similar methods that I use in the construction of my wings. To start this is how I cut my wings out of a block of a 2 inch by 2 feet by 4 feet block of epp foam with a hot wire. With a hot wire guided with a positive template I cut out each wing side panel to give you an idea here's a simulation of what I do: I first make a template from the airfoil that is in my list of drawings for example the tl54_15.jpg file that I print out on a printer to the scale desired for the template and I stick it onto a 4mm sheet of fiber board that I then cut out with a jig saw or hand coping saw and sand edges smooth. Here's a video of a guy that makes templates similar as I do to give you more details on template making: The other side of the hot wire is tied to a fixed point. I use a door jam to tie my hotwire end to. I use a bamboo pole in a door jam to distribute the load and I hang the bamboo pool on the door nob to hold the altitude where I want it that is level with the table that I'm cutting on. see bellow video example of a cut: After the wing is cut you will have to sand it and cut off the trailing edge and wing tip and cord to the specifications shown in the dwg drawings. After wings are fully cut to shape it's time to sheet them with tape. I first spray the foam wings with 3m77 spray glue to help the tape stick better. I couldn't find a video with someone sheeting a cut wing but this video does have information you can use on how to sheet wings. note the overlap of the tape you should start taping from the rear of the wing to the leading edge. see example video bellow: After the wing is sheeted with tape you can cut out some elivons from the 5mm thick balsa to the shape that is provided in the drawings. you should sand the trailing edge a bit sharp to about 2mm and sand the front side that will connect to the wing at a 45 degree angle to provide a piviot on the top side of the wing. Make sure you make a right and lift hand elivon as they are mirror images not identical. Then attach the elivons with tape hinges as seen in the example video bellow: with the method above he makes both sides of the hinge 45 degrees I normaly only put the 45 degree cut on the elivon side only. I also sand instead of cut the 45 degree angle into the elivon as in our case we are using balsa not foam. I also use wider tape the same as I used to sheet that is 2 inches wide not the filiment tape that he uses, not that it's better or worse, it's just what I happen to have already and it works too. Now that the wings are sheeted and have elivons installed you can go ahead and connect the two wing halves together. You could have hooked the wing halves together before the elivon hinging if you prefer. for this we cut slots with a razor the depth of the bamboo spars in the locations shown in the drawings. If you have carbon fiber tubes instead of bamboo then what I do is mark my wing with a pen with the location of the spars and then I melt a slot with my soldering iron. The melted foam makes for a stronger surface to glue carbon fiber spars with slow dry 30 minit two part expoxy. then glue them in with the two wing halves flush together on a flat table (no dihedrel). in the case of bamboo I didn't even bother to glue them in. Just the tape I add after the spar is installed to hold it in place as the bamboo is a tight fit into the foam already. But I'm sure epoxy glue in the case of bamboo would probly be even better. But if your poor like me you can do without it. tape cross wise across the joint of the two wings with filiment tape if you have it and add some cross tape on the bottom with filiment if you want to beef up the wing for more load baring. Also if carbon fiber tubes are used instead of bamboo as shown in the drawings then use 3mm tubes on the leading edge tubes and 6mm tubes for the two cross wing joint spars. I normally put both the tubes on the bottom of the wing but it might be better to put the leading edge spars on the top of the wing as I did with the bamboo spars. This I think is better since the top will be in compresion in a high G turn and the bottom will need more stencel strength that we can get from the tape (filiment tape if you want a stronger wing). But it will work on ether side not criticle choice. after glued in place put tape over the top of each of the spars. Then it's time to cut out the wing tips and battery mount board out of the 2mm coroplast as seen on the drawings. cut the holes and slots in the coroplast with a hot soldering iron. add the velcro straps into the slots to hold the batteries in place and mount the motor with it's 90 mount and base screewed together. the motor mount is then straped onto the coroplast sheet with 3 nylon tie straps. The wing tips are installed by melting holes in the coroplast triangular wingtips and at the wing tip about 1 cm in from the tip of the wing. line up the holes at about 30% in on the wing on the front and back. Install the servo's and control rods as located on the drawings. you can melt the hole for the servo or cut it out with a razor. I just tape the servo's in place but you can add glue expoxy or hotmelt to better hold them in place. to setup corse trim I set the elivons to be flush with the bottom of the wing. When motor and batteries are installed make sure that the CG is within 1cm from the rear cross spar. there are some other methods of embeding the batteres and motor that I will show you at a later date. A very good example of how I make my wings can be seen at the geek show as seen here: and it continues here: I didn't have the problem they had with glueing the two foam sheet parts together as I use a thicker block of 2" foam to start that is thick enuf for my wing templet. also I don't use nicrome wire I just use thin 22 gage steel wire and I just put an aligator clip to put the power across the wire as close to were the wing foam starts as posible. Also for my power supply I use just a 12vdc 5amp battery charger transformer. But one thing I did learn from the geek method above is that we could make even bigger wings of say 3" or 4" thick airfoils by using two blocks to start. As the 2" foam is the thickest I can find here in Pattaya. The last part of the geek series to a successful flight can be seen here: As I get more feed back and questions I'll add to my instruction details above. I would like to thank the people who created the videos in this collection as you may have noted they aren't me. It's just a collection that I found on the Internet. Thanks for reading it and enjoy. By Scott Carlson

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