Firefly (oz9347)

About this Plan

Firefly. Control line combat model.

Quote: "BEFORE THE START of the 1974 Western Associated Modellers (WAM) combat season, Englishman Edmond L. Bridant and I got together and decided to develop a new Class A combat aircraft. Edmond (a 13-year expert) gave me the rib and dimensions with which to work, and I proceeded to draw up the plans and build several prototypes, plus two display models. Prior to actual competition, tests were conducted by advanced flyer Paul Klahn and I to determine the best prop and fuel combinations.

WAM Class 'A' rules allow the use of engines from .051 to .19cu.in. displacement: the majority of flyers favour .19s, but many others use the high performance 15 engines. The Fireflys that we enter in competition use Super Tigre G15-19 motors, with one of our club members, rookie-expert Mike Spindler, using the Veco -19, and we were highly successful! A seven-year expert myself, I captured the Class 'A' combat championship in the 1974 WAM contest season, with five first places and one second out of nine contests entered. Mike Spindler ran a very close second, only two trophies down, while Edmond was an even closer third, only one point down on Mike.

What prompted the development of the Firefly was our dissatisfaction with what was available on the market for Class 'A' or FAI combat. Construction of the Firefly is such that mylar iron-on coverings work well with the structure: anyone who does any amount of combat flying knows that these coverings are the hot set-up. They save both time and money over conventional tissue, Silkspan, silk or nylon and dope. The use of a marking pen on the balsa structure before covering with a transparent film is an ideal way to affix name and number, clearly and permanently, to the aircraft.

Firefly is an outstanding flier; it has a very tight turning radius, and is capable of very high speeds with a 'strong' engine. It is very durable and yet light if you choose your wood properly - aim for a flying weight around 13 to 14 oz. At that weight you will have a real performer!

We have been running our G15-19's on 7 x 6 and 8 x 5 wooden props, and using fuel with a nitro-methane content of about 30 to 40 per cent. I recommend that anyone experiments with different combinations of engines, fuels and props, as what works well out here on the west coast may not necessarily be the best com-bination elsewhere.I have been using the Super Tigre G15 Goodyear engines in my FAI Fireflys. These motors need props. that are about 6-1/4 to 6-1/2 in diameter with 6 in pitch in order to really perform, and they seem to run best on a fuel that contains 40 to 50 per cent nitro. However, some of the fellows at the 1974 Nationals were using as much as 60 per cent nitro, with excellent results.

We use a spiral cardboard tube, 1-1/4 inch in diameter, as the bladder tank tube - an empty tube that contained piano wire is ideal for this application. You may unravel a layer or two of cardboard from the inside of this tube to reduce weight, and it must be doped several times and sanded on the inside before installation (roll up a full length of sandpaper to sand the inside). The surgical bladders are made from 3/16 by 1/32 in wall latex tubing. They are made as shown on the plans; note that a small rubber band may be substituted for the copper wire shown on the plans. The bladders are filled with a 60 cc disposable plastic syringe, as used in hospitals. Important note: The first time you fill the bladder, pinch the latex tubing 1/2 in from the eyelet and fill with air. This procedure will ensure that it fills from the inside to the outside every time.

The running of a motor on a surgical bladder can be quite tricky! The initial setting of the motor may be obtained in this manner: close the needle valve, fill the bladder and hook up, using a filter. No clamp on the fuel line is necessary yet, as the needle valve is shut. Open the valve slowly until you get fuel spraying into the venturi. At this point, clamp or pinch off the fuel line, Start the motor; only minor adjustments of the valve will be necessary to allow the motor to warm up before you decide on the final setting. Try to get the richest setting possible on the ground, then launch. A motor running off a bladder tends to unload once in the air; for this reason, the perfect setting on the ground will be too lean in the air. Experiment with your own ideas on how to best use this system.

Fly this aircraft on 52 ft 3 in lines (measured from centre line of handle to centre line of model). FAI combat lines may be of .012 in diameter, but WAM Class 'A' rules requires the use of .015 in lines..."

Firefly, Aeromodeller, May 1975.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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