A-B Okie Bird (oz3189)

About this Plan

A-B Okie Bird. Free flight power model, for .15 to .25 engines.

Quote: "basically an enlarged version of the 1/2A Okie Bird designed in 1970" (see text). This plan shows 2 variants of the same model, differing only in the tail layout. From Model Builder magazine issue 04-75.

Direct submission to Outerzone.

Update 27/10/2021: Added complete article, thanks to RFJ.

Quote: "Here's your Class A or B competition free flight ship for the coming season. Both the design and the designer come well recommended. Aft and sub fin models are shown on the plans.

The A-B size Okie Bird for engines .15 to .25, is basically an enlarged version of the 1/2A Okie Bird which was designed in 1970. Without much fanfare, the latter has compiled an impressive contest record, including two first place Nats wins; one in 1/2A Open, the other in A Open. Its contest record is especially good considering that only a limited number of 1/2A kits have been made available since 1971.

Inspiration for the A-B size stems from the success of the 1/2A, and the desire of several modelers to fly an intermediate size. Dick Smith, of the Central Ohio Free Flight Club, has been an advocate of this design and has assisted in its development by his flight test reports. Dick has been concentrating on the aft rudder version, which is included as an option on the plan.

Let's take a close look at the A-B machine and briefly discuss philosophy of design. It's small enough (wing area 486 sq. inches) to be very fast in the climb with a good .15, .19, .23, or .25, and its large and light enough to stay upstairs a respectable length of time after the engine quits. It could be referred to as a 'compromise' ship; not too small to glide well, not too large to climb fast.

If you examine the plans closely, you will notice the thrust line is above the rudder, even on the aft rudder version. This puts the rudder in the right side of the prop blast, which produces a natural right power turn. Some pylon ships of similar design have a tendency to dip to the right immediately after launch, before assuming their intended upward flight path. This undesirable trait is eliminated by the use of left engine thrust.

The Okie Bird has a left glide turn which comes about naturally. Most modelers like to use wash-in in the right wing panel of a ship that climbs to the right under power. This keeps the right wing up going into the turn. When the engine stops, the plane naturally wants to go into a left glide because of the wash-in in the right panel and the left rudder tab.

If you're looking for an easy contest machine to build, give the A-B Okie Bird a try. If aft rudder is your thing, this option is shown on the plan. It should be pointed out, however, that the sub rudder will handle the power just as well. As far as performance is concerned, there has been no discernible difference between the two machines. The weight of the A-B Okie Bird will vary from 19 to 21 ounces..."

Supplementary file notes

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