[Courtesy of Pete Young, December 1998 - as published Pete's RCM Soaring Column]
The Mystique 2 meter sailplane kit from Major Hobbies is an extremely intriguing product in several ways. Like its "big brother" - the 118" span T-tailed Mystery Ship - the 78" Mystique features completely laser-cut ply and balsa built-up construction.
This new multi-function ship is intended for advanced sport and competition flying and is a "no compromises" contest aircraft requiring 6 servos and a computer radio for best performance. As far as I can recall, there are no other 2 meter sailplanes that have all built-up construction and are so designed for multi-function performance - so the tough question is, what exactly does the Mystique offer for the sailplane fliers who enjoy building? (And there are a few of us diehards left!)
From an aerodynamic design point of view, the Mystique uses a SD7037 airfoil on a Schuemann tapered wing planform, has detachable plug-in wing and flying stab panels, and is designed for "full-house" control with flaps and ailerons in addition to rudder and elevator. In design approach, functionality, and appearance, the most similar 2M glider design that I can recall is the aileron-modified Sagitta 600 formerly kitted by Airtronics. Although the Sagitta was quite a nice airplane to build and fly in competition and for fun-flying - and I've built and flown four of the S-600 aileron-equipped configurations - the performance of its 1970's era E-205 airfoil has since been superseded by the performance of the modern Selig family of sailplane airfoils. And the S-600's wing structure was not designed to handle both ailerons and flaps, control devices important for today's competitive flying.
By comparison, the Mystique's SD7037 wing airfoil has established itself as a superior airfoil for all-around thermal flying performance - it has high efficiency when flapped and has good high-end cruise performance. There may be airfoils which may do one or the other as well, or slightly better, but the SD7037 has good performance throughout the flight envelope. And I was very impressed by the Mystique's structural layout - with its massive spars and LE's sheet covered top and bottom, it is very strong and rigid.
With a great deal of anticipation, we started construction of our Mystique with the wing panels. Here we found that the balsa ribs, ply doublers, and ply end ribs of the Mystique are laser-cut with uncanny precision. The quality of the wood materials - sheet and spar stock as well as laser-cut - was excellent throughout, and the spar stock, leading edges, and trailing edge stock were dimensionally "spot on". As a result, the Mystique's wing is exceptionally easy to assemble if you take care in alignments during the building steps. The 32 page manual is thorough and clear, with many supplementary computer-aided drawings to highlight individual steps during construction.
The wing is a D-tube layout with 1/8" x 3/8"spruce spars, heavily shearwebbed for strength, and with extensive use of 1/16" balsa sheet for top & bottom leading and trailing edge sections. The quality of the sheet wood was excellent throughout and I did not have to replace any of the wood supplied in the kit. Pre-tapered balsa sections are used to form the wing's leading and trailing edges, as well as the leading edges for the flaps and ailerons. The ailerons and flaps are assembled as part of the wing structure during the initial building, then cut loose and shaped to final form. By the way, I found that the wing ribs are "true" SD7037 outlines by comparing them to SD7037 templates out of Soaring Stuff's "Airfoils to Go" book. I have found in many other sailplane kits that their "modified" airfoils bear scant resemblance to the cited airfoil section! In the case of the Mystique, you are even instructed to shim in a 1/32" TE "droop" during the wing layup, so the designer is really serious about providing as close to a true SD7037 airfoil as possible - every other kit that claims to use SD7037s flattens out this portion of the airfoil.
The 2 wing panels are connected by a hefty 5/16" steel wing rod that runs inside brass tubes sandwiched between the spruce spars. I could not help but compare the Mystique wing rod's 13 ´" length to the Sagitta 600 whose wing rod was probably no more than 5" long - there's no question that the Mystique is designed to take some hefty winch loads.
The Mystique's inner wing panels sections are each built "flat" on the plans, with slight root dihedral provided by the fit of brass wing rod tubes through the root ribs. Unlike other glider designs where the wing rod tubes have to be manually aligned to the proper dihedral angles, laser cut holes precisely align the tubes to the proper angles. I did note a slight omission in the instructions - after installing the tubes in step 16, don't forget to add epoxy and microballoons around the tubes to distribute the stress loads to the spar structure. The wing tip panels are built separately and incorporate approximately 3/16" washout to reduce the severity of tip stalls. Accurate joining of the tip panels to the inboard panels is a crucial step, so be sure to read the detailed instructions carefully. My personal building preference is to first construct each inboard panel, block each to the proper dihedral angles to mate to the yet-unbuilt tip panels, then build each tip panel joining them directly to the inboard panel. Use the techniques with which you are most comfortable.
The fuselage is built up of 1/8" light ply and sheet balsa with laser cut sides, formers, and canopy sections. One slight change that I made was to install an adjustable towhook manufactured by George Voss of Soaring Specialties. The weight of this all-metal towhook assembly is less than 1/2 ounce and it provides approximately 1 1/2" of adjustable travel. The one piece stabilator is actuated by an internal custom bellcrank assembly while the rudder linkage exits the fuselage side in the conventional manner. The 1/8" stabilator mounting wire is fixed to the rudder structure by nylon buttons which I would dearly like to use in my other stabilator-equipped aircraft - perhaps Major Hobbies can make the custom bellcrank and nylon buttons available as a separate accessory - I'd buy them in a heartbeat!
The Mystique's horizontal stabilators have a full symmetrical airfoil section - in marked contrast to aerodynamically inferior "flat plate" or trapezoidal stab sections found in other gliders - and are completely sheeted with light 1/16" balsa on top and bottom sides. Laser-cut saddle jigs are assembled into cradles which hold the sheet balsa to proper contours while the stab's ribs and spars are being attached.
Following the excellent instructions carefully, construction of the Mystique offered no significant surprises and it was very pleasurable to work through the building phases. I did uncover a set of dimensional discrepancies in my kit which the manufacturer has since rectified. The triangular rib "tails" on the wing and horizontal stab were slightly short of their desired chord length and required some slight patching to properly fit. This minor discrepancy was flagged to the manufacturer and has since been corrected.
Radio installation in the Mystique requires micro-sized servos in the wings and slightly larger servos can fit into the fuselage. I installed JR 341s throughout, 4 in the wing for ailerons and flaps, and 2 in the fuselage for rudder and elevator control. Final installation of the wing's servos will require fabrication and installation of extended wire harnesses - do a good job here - if you have any doubts about the proper wiring conventions, consult with more experienced modelers before powering up the servos. The servos are wood screw-mounted to laser-cut ply plates which fit into matching ply cutouts glued permanently in the wing; be sure to do a good job gluing the triangular wood pieces in the corners - they provide the mounting to hold the servos securely in the wings. I installed two more 341s into the forward fuselage for rudder and elevator control. With a 600 mah battery pack and 7 channel Airtronics receiver, everything fits into the forward fuselage, although there's not much room to spare.
As a final step, I added a plastic "sharks' tooth" landing skid from Tim McCann. Tim has quite a line of plastic skids and landing skegs, and his landing devices should help my Mystique to stop, hopefully, right on the highest scoring section of a landing zone - of course, that means I'll have to go out and practice a lot when the weather improves but that's the fun part!
Final finish film covering on our Mystique was done with Coverite's Black Baron lightweight film. The Mystique's wing structure is sufficiently robust so that the wing does not have to rely on covering tightness for rigidity. The fuselage was prepped with nitrate dope, then sprayed with Coverite primer, fine sanded, then final sprayed with Coverite's Century 21 gloss white paint. Computer-cut graphics from Don McColgan's Comp-U-Cut provided the finishing touches to this project - really adds an extra bit of eye appeal, don't you agree?
Flight tests to date have been with a fairly strong highstart more suited for larger airplanes. With the Voss towhook set at the recommended position, the plane shoots up the line as if on rails. Once released from the towring, the plane exhibits a stable and buoyant glide and is responsive to all the flight controls. Using the various mixes and adjustments of the Airtronics Stylus, I soon had the plane responding to suit my personal flying habits. The plane is not a floater and should be flown fairly briskly for best performance. I'm still making minor adjustments to aileron deflections and rudder-to-aileron mixes but can report that the plane has excellent performance in all the flight modes I've tried to date. Thermalling performance, cruise performance, and landing characteristics have been excellent and pleasurable to fly. In the landing modes, I am especially pleased how the Mystique has very stable and predictable handling with 90 deg flap deflections - almost no elevator compensation is required and the plane is comfortable to fly through final approaches and landings. I'm looking forward with great anticipation to future flying sessions and more opportunities to do the intensive "fine tuning" that produces the best performance in multi-function gliders.
Overall I was very pleased and impressed with the kitting and flying performance of this very modern and up-to-date glider design. My firm opinion is that the Mystique marks a key milestone in the application of laser-cut engineering, structural and aerodynamic design, and competitive performance for a competitive multi-function glider at extremely reasonable cost. I would recommend this as a good kit for modelers who want to fly a multi-function competition sailplane and are not ready to step up to the composite glass and foam machines more prevalent in 2 meter competition. To put it another way, the performance-to-price ratio for the Mystique is extremely attractive for modelers who enjoy building with traditional wooden materials.
Addresses for accessories mentioned:
COMPLETED MODEL Finished weight 43 oz. Wing loading 10.3 oz/ft2 Radio used Airtronics Stylus transmitter and receiver, JR 341 and 351 micro servos Covering/Finishing used Monokote and Black Baron film Special items Sailplane Specialties adjustable towhook; Tim McCann's landing skid; Comp-U-Cut vinyl graphics
CHEERS - precise laser cut parts, ultra-precise kitting and engineering, superb quality of materials, custom stab bellcrank and stab wire retainer mechanism
JEERS - wing and stab ribs cut slightly short - since corrected by manufacturer;