Fifteen (oz6448)

About this Plan

Fifteen. Free flight contest power model.

Quote: "In my opinion - says Alec Burns - it is the gadget-free model which is the consistent contest winner. And in this viewpoint he has the support of most competition fliers. 'Fifteen' (the 2.5 cc class is .15 cu ins in the USA and Canada, hence the name) certainly reflects this opinion, for a simpler or more straightforward contest job would be hard to find. The Hogan (oz5350) influence is apparent, and the only gadgets employed are the gravity tab, the timer, and the metal engine mount, which offers advantages for simple thrust adjustments. In flight, the model has a vertical climb to the right and left glide circles, and has proved particularly safe in windy weather, flicking out at the top of the climb without loss of height. With a motor of up to 2 cc it would be a trouble-free introduction to contest-style flying, and, with a good 2.5 in experienced hands, a threat at any contest.

Building procedure is normal, the box fuselage being built in the usual way. Side sheeting (except in tank bay) should be fitted in before removal from plan and the pylon added after being constructed separately. The front former is laminated and the dural motor mount bolted in place, together with the undercarriage, before cementing the former to the fuselage. After installation of tank and timer the front former should be reinforced with liberally-cemented strips of silk. Wing and tail mounts are self explanatory. The pylon and entire fuselage are silk-covered and given seven or eight coats of thin clear dope.

Construction of the flying surfaces is also perfectly conventional, but the positive rudder tab is worthy of mention. After attaching the tab to the rudder (left flat at the appropriate place) with a silk hinge, a 10 BA bolt is passed through both tab and rudder ; packing placed between the two is varied for the right trim, the bolt being tightened to retain the packing. Use Modelspan for covering the wing and tail.

After assembly and alignment check, balance the model as indicated, using ballast if necessary. Up to 1/16 in packing may be used under the LE or TE of wing and tailplane to obtain a slightly stalling left-hand glide. Use a 9-1/2 x 6 prop for windy weather and a 10 x 3-1/2 in flat calm, and make initial power flights with reduced revs. A right-hand climb is required, and sidethrust should not be necessary. If a left turn is evident, fit washers behind the port engine mount. Increase power and aim for a 100 ft power turn. Slight left rudder may be needed for the glide, but clay added to the gravity tab should remove stalliness. Excess left rudder will call for additional right thrust. The built-in downthrust should take care of any looping tendencies; increase if necessary. "

Quote: "Hi Steve: I've been looking for a plan for this power model for awhile and found it on the RC Groups site yesterday. It is designed by Alec Burns from right here in Toronto who was still active in model airplanes until he died a few years ago. It's a nice easy to build FAI model from the early 50s and would be great for the nostalgia gas and vintage FAI events we have here in North America ...All the best,"

Direct submission to Outerzone.

Update 19/05/2015: Replaced this plan with a clearer copy (patterned background removed) thanks to TonyP.

Update 22/08/2017: Added PDFvector plan tracing, thanks to hogal.

Supplementary file notes

Article page, text and pics.
Previous scan version.
PDFvector plan tracing.

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