Puff - The Magic Dragon
While searching for interesting aircraft to build, I came across Puff, the Magic Dragon. Perfect for EPP to give the skin some texture and to absorb the inevitable mishaps. Puff flies reasonably well and I fly mine quite a bit. It's smooth and stable in calm weather and can be flown in brisk winds because it is fairly streamlined. It only turns on rudder so this is easiest if mixed with ailerons on the TX. It can roll but if you keep rudder mixed it gets a bit 'interesting'. Loops are great if entered level. Inverted flight is not really part of its repertoire.
The wingspan is 36" and area 220 sq in. It weighs 9oz (255g) with a CD-Rom motor and three 540mAh lithium cells (now placed between the eyes). Four 6g servos are needed, two for the ailerons and another two for the V tail. The plane has been built from 3 and 6mm flat sheet EPP from Flying Foam in the US. 3mm sheets are also available from FlyingWings in the UK. Other potential sources of EPP are on my Links page. The tail can be a bit floppy so do what you can to stiffen this.
Construction is very similar to Bounce with 3mm EPP fuz sides and doublers, 2mm carbon stiffeners and a 6mm EPP spine. Almost everything is glued with Uhu POR although any contact adhesive could be used. The sides are pulled together into a diamond shape at the back using a bead of POR to hold them. The front has some flat sections glued between the sides.
The wing's spar comprises four lengths of 3mm hollow carbon tube, joined with three 2x50mm steel dihedral braces. These are bound to the carbon and saturated with cyano. The wing's skin comprises four sheets of 3mm EPP. These have to bend into compound curves due to the dihedral angles and curvature of the airfoil so it is normal for the wing to distort. In particular, the angle of attack becomes greater near the centre (rib 2) which is good for stability but does change high and low speed flying characteristics. The four ribs are glued to each of the bottom skins with POR and allowed to dry. The spar is threaded through the fuz and the holes in the ribs. You will notice how the 2mm spars and 6mm EPP spine in the fuz prevent the entire wing skin from entering the fuz so the skins are trimmed to allow the rest of the skin to do so.
Once both bottom wing skins have been glued in place, thread aileron extension leads through. The top skins are then also trimmed at the centre and positioned accurately above the bottom skin. Now apply a generous bead of POR along the leading edges and on top of the ribs (but not the trailing edge). Tape the top skin to the bottom and press the top skin onto the ribs to transfer some POR onto the top skin. After 10 minutes this will act as contact adhesive and the top skin will stick to the ribs when pressed into contact. Glue five mylar or thin plastic strips into the ailerons as hinges. Now apply another bead of POR inside the trailing edges of the wing while gluing the ailerons in place. Cut holes in the bottom of the wing for servos. Aileron movements should be about 15mm each way; more for brisk rolls.
The V tail is reinforced with a thin steel dihedral brace glued into a slit cut in the bottom surface. I mounted the servos under the tail to make them more discrete, more rigid and to help with CG (the nose is very long). Elevator and rudder throws should be over 25mm each, each way. The right-hand control surface should go down for a right rudder command. Glue a 3/32" (2.5mm) firewall in place with epoxy and add 'nostils'. Install LEDs to make them glow firey red! A plastic tea spoon makes a good 'eye' (or vacuum form (ie: stretch) a plastic food container over a metal spoon with a hot air gun). Use velcro to 'zip' the bottom of the fuz closed over the length of the fuz doubler. Add the spikey bits and paint the model with permanent water-based acrylic.
Hopefully the pictures will fill in most of the gaps in my brief descriptions but send me an email if something is not clear. * As usual you may build the model but may not profit from the design. Plans in various formats follow. On the PDF's you probably don't want to 'fit to paper' as this may distort the size. Page 1 should print a reference line to check. The DXF file may need changing from imperial to metric.
|'PDF' A4 paper
|'PDF' Letter paper
|CAD 'DXF' version
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