Praying Mantis (oz7703)

About this Plan

Praying Mantis. Radio control sport model. Canard pusher design.

Quote: "if you think today's designs are in a rut, you won't be able to resist this XB-70 type design. And you won't believe it even after you fly it! Praying Mantis by Whitey Pritchard.

WOULD you believe a supersonic transport? A Graf Zeppelin? Would you believe a single-channel type canard? The latter is what we've got.

This little fellow is not so little, being six feet long, yet it performs on single channel servos just like the big boys. The stability is phenomenal and the take-offs put you in the Jet Set. The flying platforms (wing and tail) are all sheet-wood with the only built-up construction utilized being in the fuselage. It is a simple straightforward design that is easily constructed and which lends it-self to the Sunday Flyer.

Due to the canard configuration the Praying Mantis is very forgiving in stalls and will not slip off into a spiral dive in the turns, As a matter of fact the first prototype might have been considered too stable, inasmuch as the only way to get it down was to reduce power. We have increased the rudder area on subsequent versions and it is now capable of a gentle spiral, this area change incorporated into the plans presented with this article.

The original Mantis is equipped with F&M receiver and Royal Products single channel servos driving throttle and rudder. Galloping Ghost equipment can be used, and even though it has an all-sheet wing, it has the weight carrying ability to accommodate the receiver, battery pack, and two servos of the larger proportional systems. The installation of the latter would require a wider fuselage to accommodate the receiver and servos, but other than that. the ship would remain the same with no CG change. If you decide on the latter course, widen the bulkheads accordingly.

The prototype made its maiden flight with a .15 engine, but once airborne, it would not sustain this design. As the nose angle increased, the mass area of the rear wing acted like an air brake and she settled back to earth. It was decided that a .23 would be a better choice. A visit to the local hobby shop didn't produce a .23, and inasmuch as Sunday was drawing near, I decided to use an OS .35 which I had on the shelf. There was also an ulterior motive in this decision, for if I could control the beast with a .35, then I could go to a reverse crank K&B .35 and forget the pusher prop, which can be a problem if your local hobby dealer doesn't stock them.

On a cold, wet, foggy Sunday morning, the OS .35 was fired up. Small children were gathered up, and with their mothers, took shelter in the cars. A few dedicated modelers remained exposed - taking faith in being behind the Mantis as the canard was aligned with the runway. The group quieted as the control functions were given the final check. Someone piped up - 'You've got your ship on backwards' - and with that, the Mantis leaped down the runway. At seventy-five feet the nose broke ground and the ship arched up in one sweep to a near vertical ascent with a gentle rotation to the right. At 200 feet medium speed was programmed and the nose dropped to a more normal attitude. A couple of circuits of the field and the model was in the cloud bottoms!

Full right rudder was held for a descent, but she con-tinued to climb. Left rudder produced the same results. It was now flashing in and out of the fog. Low engine was blipped, and on the second try, the engine was heard to throttle down and it reappeared out of the fog like some demon from the deep! Further flight tests showed that full throttle produces better than a 45 degree climb; medium speed, a normal flight attitude; and low speed, a very slow power descent. With power off, the glide is flat and fast, but the overall descent is quite mild. Contrary to what might be expected, the sheet wing does not fall out of the sky, but it does require keeping up air speed.

The main wing (rear) has two features which increase the lifting ability of the all-sheet wing. Fifteen inches of the leading edge has been turned down much like the leading edge slots on swept wing jet aircraft. The 'down-droop' of the outer wing panels func-tion similar to tip plates inasmuch as they work in conjunction with the sim-ulated fences on top. This anhedral the-oretically decreases stability, but this ship has so much inherent stability that..."

Supplementary file notes

Article pages, text and pics, thanks to hlsat.

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