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Old 08-06-2013, 06:24 PM
maxflyer's Avatar
Join Date: Sep 2012
Location: Santa Fe, NM
Posts: 362

My latest. Have been playing around, unsuccessfully, with flat-plate 3D EPP foamies recently, largely due to their inability to handle wind, and unresolved setup issues. Wanted to build a mild sport plane that would enable me to fly in winds of 10 MPH or so, and also give me some stick time with ailerons, without the twitchiness of the 3D models. This plane uses a EPS KF3 wing originally built for a trainer designed by Russ40 and shown on RC Groups. The design had some construction weaknesses and never flew. I salvaged the wing and reduced the dihedral of the two tip sections down almost flat. It has two CF spars for rigidity. The tail section generally replicates Russ40's shapes and areas. Wingspan - 48.5." Chord - 9.5." Wing area - 460.7 sq. inches. Fuselage, length - 37.5" is a 2 x2 inch block of blue builder's foam with a CF arrow shaft embedded in the top center. Foam was then given a slight aerodynamic shaping. Weight was relieved aft of the wing area through use of a Forstner bit, drilling from opposite sides and leaving a thin web at the center. As much as practical, the components are buried in cavities in the blue foam. Colored tape is mostly to add a bit of durability at the edges and for visual orientation cues, NOT for looks. This is a modified version of the original, which I equipped with a Keda KA20-50 29G 1088KV motor. Much to my surprise, with an AUW of only 17 oz. the beast wouldn't even leave the planet! I then re-fitted with a Firepower 400 2830 motor, 20A ESC, Hitec 7CH RX and an APC 8x4E prop, drawing 9.5A, which proved to be a perfect match, and gives me sprightly performance if requested, and also a leisurely 10 minutes on a 3S 1000MAH battery, with over 500 MAH remaining after flight. With the larger motor the AUW is now 18.3 OZ without battery. After a couple of test flights, I have what amounts to a great aileron trainer or mild sport flyer. It floats well, power off, flies nicely on maybe 1/3 throttle, will pull nice loops and barrell rolls. Won't do anything even faintly close to advanced maneuvers like a KE. So far it totally refuses to even fly inverted. When rolled on it's back, it heads for the ground - full elevator be damned! T&G's are great fun, even with a bamboo stick "tailwheel." Most of all, it seems to handle very reasonably in wind of 10 MPH or so, which was really my goal from the outset. How much the KF3 airfoil has to do with performance parameters I don't know. This is my first use of one. Simple curved sheet airfoils have worked very nicely for me on 3 CH models under 9 OZ, but they would not survive at this scale. Future attempts may involve use of actual airfoiled constructs. Perhaps at some point I will gain more skill and have better results with the flat-plate 3D models, but at this point I must say...nothin' beats a real airfoil!
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