Cutlass (oz12836)

About this Plan

Cutlass. Radio control pattern plane, for .60 power.

Quote: "The Cutlass is the result of an attempt to produce an airplane more nearly suited to large, graceful, and smooth maneuvers of the FAI pattern. After altering throws and CG locations of relatively successful AMA pattern type designs on hand, it was determined that this still left a little to be desired. With existing competition here in the South, I needed to gain every edge possible. Today top competitors are all excellent flyers, good 'engine men,' unequalled builders and very contest orientated individuals. Today's radios are reliable and follow transmitter commands perfectly (in my case, many times too perfectly). With these facts in mind, it became apparent that the only area available in which to gain an advantage was in airplane design.

Through sheer luck or stupidity or both, Cutlass is not the last modification of several years of testing, making minor design changes and retesting. Prototype was test flown in November 1969 and had its first competition trial at the Tangerine Internationals in Winter Park (Fla.) in December '69. Considering the competition present and lack of practice opportunities prior to .contest, its performance was commendable. Only modifications anticipated are minor ones to permit installation of retractable gear.

Although Cutlass was designed primarily for FAI competition, it is an easy airplane to fly and exhibits no bad characteristics other than moving quite rapidly (if this can be considered bad). It is very honest in its response, while being exertmely smooth. In spite of its full bore speed (which I suspect will be noticeably reduced with advent of sum-mertime heat and humidity) it may be slowed down to a walk for landing. With my frequent misjudgment necessitating application of the final approach "stretcher," I have made many "nose very high, full-up elevator" landings with no wing dropping tendencies. Even with its seven lb. weight and 22 oz. wing loading, sink rate is not too fast. I might add here that it is now being flown with a Silencaire muffler. At our present 40-70 degree temperature range, the power has not been reduced measurably.

Design Characteristics: Unless a new design were to be a canard, a pusher, a flying wing, or some other obviously radical departure, it would be difficult to produce a new competitive machine without borrowing measurements and ideas from previous designs; Cutlass is no exception.

In order to discuss design evolution, let's turn the calendar back to September '69 when I cut off a long piece of paper from the local friendly butcher's roll. After drawing a long relatively straight line to represent thrust, the first step was to determine moments. Several years experience with the Citron (oz9711), interspersed with Quik-Fli, Now Orleanian, Triton, etc, determined that the good old standby Citron nose moment seemed to offer the best compromise between handling characteristics and internal installations. Contrary to some, I found that very long tail moments required a lot of elevator jockeying to make nice round loops. The two airplanes I flew in 1968 and 1969 had tail moments 1-1/2 in shorter than Citron and they handled very nicely on the pitch axis and were quite capable of competing with more violent maneuvers of the AMA pattern. However, since I was striving for more smoothness, tail moment is a compromise between last years' P-51 and the good old Citron.

Next consideration was flying surface placement in relation to the thrust line. My previous airplanes had the center-line of wing and stab separated quite far from the thrust line. Supposedly, this prohibited any blanking effect on stab. New designs, such as the very fine 'Eyeball' and others, disproved this effect so now there was no reason not to bring these surfaces closer to the thrust-line. Here again Cutlass is a compromise. Common sense dictates the rolls can be more axial if the wing and stab are close to the thrust line. However, everything centered on the thrust line seemed to produce hatch problems, wing saddle and wing removal problems, long main gear problems, internal installation problems, etc. Hence, the Cutlass wing center line is one inch below thrust line and stab center line one inch above thrust line. This produced rolling maneuvers far superior to any other airplane I have flown. (Needless to say, I have not flown every design. This roll axis result was of my own personal experience.)

Now let's consider fuselage profile. Compared again to the trusty old Citron, experience and observation dictated more lateral area. Pure old bunch and stubborn conviction made me think that a great deal of this increased lateral area should be forward of the CG; hence the Cutlass fuselage profile and subsequent appearance was the result of trying to make these ideas look like an airplane. (Many think I didn't succeed, but after all, the primary purpose was a better flying FAI type competitive machine. Note my introductory sentence.) Side mounted engine allows muffler to nestle in close to the body and throw most of the 'junk' below the airplane. Large open ring nose was borrowed from a former Triton which is pleasing to the eye and certainly allows easy linkage and engine adjustments. Also, viewed from the port side, engine is completely hidden. Rest of fuselage side view evolved from a series of erased lines, different canopy placements, and an attempt to sculpture lines ala Detroit. Hopefully, these helped to disguise vertical height. (By now that piece of butcher paper was getting pretty well mangled.)

The large rudder with as much area as possible below thrust line, and placed well behind elevator hinge line, was a result of experience with last year's P-51 and P-51-1/2. This feature makes the double stall turn on figure M a breeze. It also help spin characteristics since elevator throw is considerably reduced. Area of fixed portion of vertical stab is small, and so shaped because the movable portion is so large. After all, if you're not moving it, the movable portion acts as a fixed portion. Stab used was identical to ones on last year's P-51 and 5-51-1/2. I couldn't find anything particularly wrong with them. Elevator area was reduced since the FAI pattern requires more smooth-ness and grace.

The wing chosen was a slightly modified Triton wing. I really liked its characteristics. My experience with Jim Kirkland's design was very pleasant. You can see from all this design discussion that Cutlass is a result of mass plagarism. I'm guilty and admit it, but am still quite proud of the result. I hope you will be, too.

Construction Hints: Construction is very basic, so I will point out only possible pitfalls. Firewall location may have to be altered to suit your choice of engines and mounts. Bottom corners of the firewall can best be contoured after all filler blocks are glued in place. Choice of fuel tank and position is optional. I have found, however, contrary to experience with upright and canted engines, that side mounted engines require center of tank to be even with thrust line. I don't know why, but if center of tank is a little below thrustline, it will go rich when inverted..."

Cutlass, MAN, October 1970.

Direct submission to Outerzone.

Note this plan shows a foam-core wing. For a version showing built up balsa construction, see the Joy Products Cutlass Supreme (oz14741).

Supplementary file notes

Article pages, thanks to RFJ.

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