PAA Ray (oz3506)

About this Plan

PAA Ray. Free flight contest model.

Quote: "The square simplicity of this model is deceiving, however a look at the contest record will clarify the performance question. The 'Paa-Ray' is an outstanding 1/4A free flight competition model with or without the PAA dummy. This model is a balance between Jet PAA-load and free-flight gas design experience. Basic requirements of such a model are to climb as high as possible with the power available, stay with a thermal, and descend slowly. The main climb controlling factor (the weight) is fixed by the rules. Maximum climb is obtained by getting the most out of the engine and propeller combination, a clean airplane, and trimming for maximum altitude.
The thermal sensitivity is a result of very light wing loading which gives
a sort of 'parachute effect'. The model does have an excellent glide but if we are realistic we will try to design for thermal stability and sensitivity.
The main points of interest of this configuration are the airfoils, wing placement and offset rudder. The main airfoil is very similar to Taibi's Starduster (oz2098) section with an upswept leading edge, which has low drag and good penetration. This allows large surfaces with minimum drag consistent with good structure. The stabilizer airfoil is similar but thinner. The wing location has structural advantages and I believe all models would use shoulder wing mounts if power handling were not a problem. In this case the off-center mounting of the rudder was employed to eliminate the power-turning tendency, due to helical flow from the propeller wash. I believe this same set-up can be used in free-flight power design. The engine is side mounted to allow most of the exhaust to flow away from the model...
Construction requires very little explanation. Built similar to an old rule 1/2A, with identical wood considerations, the model will automatically come out to weight. As with any other model, take care to keep the tail surfaces and wing tips as light as possible. Note the 1/16in diameter holes in the ribs. This allows the wing to 'breathe' with temperature changes. Build the surfaces as warp-free as possible except for wash-out in wing and stab tips, to reduce drag at these points. The landing gear location is optimum for take off. Retain the wheels with nylon keepers or spring 'dohickeys' to allow removal for cleaning..."

Quote: "...a plain, straight chord flying surfaces, box fuselage for the Cox 020. It is functional, it may be practical - pretty it aint!" This plan was printed in Flying Models Decade of Designs (1), published 1960.

Direct submission to Outerzone.

Update 25/01/2017: added article, thanks to RFJ.

Supplementary file notes

Article.

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