Cathexis (oz16820)

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Cathexis. Free flight FAI power model.

Direct submission to Outerzone.

Update 16/6/2026: Added article, thanks to JeffGreen.

Quote: "The very latest in FAI designs for the seven-second engine run incorporates propellor brake and both auto-stab and auto-rudder. Cathexis, by Dave Parsons.

IF AT SOMETIME you have considered extending your AMA gas involvement to include FAI power, but for all the usual reasons you have balked at the prospect, then quite possibly what follows may be of special interest. Let's examine a few of those usual reasons for not getting involved, and see how each of the popular mythology we can dispell.

The complaint I hear most often of late, has to do with the recent reduction of the FAt engine run to seven seconds. Apparently there arc those that feel the required time. effort, and expense can't be justified by so brief an engine run, and the resultant difficulty in achieving a max. The error made here is in judging FAI power by AMA gas standards. AMA gas and FAI power are very different events, each stressing different parameters of performance, and as such there is no legitimate basis of direct comparison. The truth of the matter is, that three minutes is very possible from a seven-second engine run. Only the margin for error has been severely reduced. It pays to keep in mind also, that all power flyers have to cope with the identical set of circumstances. As a result of the reduced engine run the overall level of competitiveness in the event is heightened, and I feel this is conducive to a more interesting involvement.

Even a quick look at the present development of FAI power designs points up a few more of the usual reasons for non involvement. It might be easily concluded that expensive super-tuned engines, sophisticated sheeted construction, and complicated variable incidence devices are at the very least necessary ingredients for any hope of success. This. however, is really not the case. The stock Rossi .15 is very competitive right out of the box, and costs less than the hot domestic class C engines that now seem to he so prevelant. As for construction, conventional techniques properly applied are entirely sufficient.

The concept of variable incidence should not create the apprehension that it usually does among modelers that have yet to try it. In actuality, the auto-stab and -rudder make the high-speed power model easier to trim and to fly. The single most important reason for this, is that the auto mechanisms allow power trim and glide trim adjustments to be made totally independent of one another. I first used the auto-stab system presented here in 1961. It is a very simple and well-proven system that can be applied by anyone with a real minimum of effort. Further details of the auto systems and their applications appear on the plans and in the trimming section of this article. Also, to further simplify the prospective power Fliers initial involvement t have in-cluded the names and addresses of suppliers of the necessary accessories to put that first ship in the air.

The specific design considerations relevant to Cathexis were conceived under the 1971 rules which allowed a ten-second engine run. I felt at that time the general trend placed too much an emphasis on climb and not enough consideration was given to glide duration. I selected the moderately high aspect ratio wing (10:1) and the C(P) 5408 airfoil to personally reverse this climb-oriented trend. The C(P) 5408 section devised by Hank Cole for one on his FAI power models of the late Fifties supposedly gave an excellent glide without affecting the fast climb. As it turns out, all claims were valid. The glide of Cathexis is truly excellent and the climb appears to be nearly equal to the thin flat-bottomed air-foils of my earlier ships. With the advent of the senen-second engine run, these considerations seem to have been made at just the right time. Cathexis performs admirably indeed under the new rules..."

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