Little Owl (oz14699)
About this Plan
Little Owl. Free flight canard model for EDF.
Quote: "Low cost, high entertainment EDF free flight fighter. Little Owl, by Stephen Glass.
I'm very fortunate in having the large expanse of Wroughton airfield, home of Swindon MAC on which to chase my free flight models. It's nice though, when the wind drops during the evening, to grab the dog and a small model and head for the local playing fields. Electric powered free flight models are ideal for small field flying, careful charging of the flight batteries will shorten or extend the flight to fit the available space.
Little Owl has been well received by the fetchermites that soon appear during these outings, most of whom hadn't heard of free flight and didn't know that aeromodelling could be done on a pocket money budget.
The excellent Union ducted fan unit comes complete with a powerful electric motor, that has been known to take up to six cells. The Little Owl prototype, AUW 196gm (7oz) uses four 200mA AAA cells which, fully charged, gives a climb to about 40 ft and a duration of over one minute. If your model comes out a bit heavy, or lacks sparkle, then add another cell.
One useful modification, that is strongly recommended to improve efficiency, is to reduce the fan blade clearance to a minimum. Just cyano a 12mm strip of 0.8mm balsa, grain widthways, to the fan shroud, around the circumference of the fan. Sand the high spots until the fan moves again fairly freely and then finish by running the unit a few times. The balsa strip must be sealed against moisture or it will swell and foul the blades, dope may attack the plastic so use varnish. This is best done before the fan is fitted.
Please try to use stiff, light balsa throughout, there's not much of it, so use your best stuff.
The first job is to form the 0.4mm ply duct, cut a piece 185 mm sq and place in boiling water for 1/2 an hour, to soften the glue. When the time is up, wrap the ply around a cylindrical shaped form, roughly the same diameter as the duct; a Sodastream CO2 bottle is about right. Bind with a bandage and put aside for a day or two.
Profile Fuselage:The forward part of the fuselage is built over the plan. This consists of spruce spars, top and bottom, that carry on through to the end of the duct, 6mm balsa nose and uprights and Depron foam for infill and the cockpit. Don't forget to protect the plan with clingfilm.
Depron foam is easily shaped with sandpaper, it has a 'grain' and is stiffer along the length of the sheet, which is important when making the wing and canard. Use PVA to glue the Depron, allow extra time for drying as the moisture can only escape from the wood side of the joint.
When dry, remove from the plan and sand smooth. Add ply nose reinforcement and the canard seat to each side. Round off the balsa adjacent to the air intake.
Wing, Fin and Canard: Cut the fin and canard from 6mm Depron, remembering to have the span along the length of the foam sheet. Just round off the leading edge, trailing edge and tips.
Make the wing in three flat sections; port, starboard and centre section. Sand the panels to the profile shown on the plan and gradually thin the wings from the tip panel dihedral break to the tip. Cut off the tip panels. The wing panels are simply butt jointed together to the dihedral angles shown on the plan, sand the dihedral joint to fit as accurately as you can. Superphatic glue works well but go over the joint two or three times; it is best just to do one joint at a time. Add the ply reinforcement to the centre section trailing edge.
Duct: When dry, remove the ply duct from its former and glue the seam. Make a kit of parts F1, F2, F3, two wing seats and make a foam fairing to the same shape as F1, plus the width of the 0.8mm sheet. Carefully, with a scalpel, trim away the circular rear flange of the fan shroud, leaving the flanges intact..."
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Update 24/7/2023: Added article, thanks to RFJ.
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User commentsBuilt one of these back in the day using blue foam. It flew a treat for sport FF at the Grassy Knoll in Sepulveda Basin--Los Angeles.
I've got some 6 mm depron and may just give her another go.
Mike Myers - 25/07/2023
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