Sky Bird (oz15306)

About this Plan

Skybird. Free flight competition power model, for .049 to .051 engines.

Quote: "An easily built, not excessively complicated 1/2A competition Free Flight that shows good promise. Lots of hard thought in the layout. Pick your wood and build with care. Sky Bird, by Larry Kruse.

Sometimes you're not just sure where things start. I remember reading a piece by Bob Sifleet, I think it was, in an old issue of Model Airplane News in which he discussed the power rudder/glide rudder configuration of Larry Conover's Lucky Lindy (oz10910). Later, I seem to recall glancing at the construction drawings of the Lucky Lindy, but I guess I never really thought too much about it. Then again, about 10 years ago, Dick Mathis had a design in Flying Models that used the same layout. About the same thing took place again, as far as I know. I filed all that stuff away in a mental drawer marked 'I' for interesting, and never got fired up enough to start cutting balsa and making sanding dust.

Seeing Lars Oloffson's FAI job at the Dayton Nats must have unlocked that file drawer, though, because immediately after returning from Ohio, I started sketching shapes and fooling around with tail moments for a V2A ship until things started to click using the power rudder layout. I wanted a design that was consistent in the, power pattern, easy to trim and would not embarrass me excessively by falling out of the air like a bowling ball.

The first version of the Sky Bird was constructed with minimal rudder and stab area, since I was concerned with avoiding a tail heavy condition in using such a long tail moment. It lacked consistency in both the power pattern and transition. It finally met its demise when my dog mercifully ran the length of the wing panel as he pursued a bouncing rubber ball through our living room.

I put a bigger stabilizer surface on the next edition of the plane which resolved most of the transition problems that showed up on the number one ship. The power pattern was perfect as long as it was flown in minimal wind conditions. However, when it was subjected to moderate to gusty winds, it developed an unnerving tendency to dutch roll. Its built-in deathwish was fulfilled one evening about twilight when it splattered full-bore into a concrete runway, taking with it a new TD .049 and a new Tatone timer.

The number three Sky Bird presented here has both enlarged rudder and stab surfaces compared to the original ship, and shows none of the errant tendencies of its forebears. Its power pattern is a consistently smooth arc to the right at about 80° vertical, avoiding an altitude-wasting spiral climb. It then flops cleanly into its glide path without any dipsy-doodle stalling and proceeds to 'hunt' very nicely with a bouncy, nose-up glide..."

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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