Several factors went into the decision to buy a Model Tech Cap 21. On the construction side, there was the need for a plane that could be built quickly before the end of the summer. An Almost-Ready-to-Cover (ARC) plane is an excellent compromise between a kit and an ARF. Previous experience in assembly of a Model Tech Dragon Lady 40 ARC helped to lead to the choice. The idea of adding the covering scheme and the accessibility to the frame for modifications is appealing. On the flying side, there was the desire for a plane that could do any maneuver in the book and offered a challenge to fly. A post to the R/C newsgroup resulted in several replies, which led to the decision to get the Cap 21.
The kit arrived with no damage thanks to Model Tech's nice packaging of the materials. The balsa sheeted foam core wing was cradled in styrofoam forms and the fuselage was protected by cardboard. The overall quality of the construction was very good. The fuselage was straight and true and all major parts seem to fit together nicely. The stabilizer, split elevator, fin, and rudder are solid balsa. The rudder has large cutouts for weight savings. In addition, there is a pattern for cutting out the stabilizer if tail weight reduction is warranted. The supplied canopy is a bit thin, but it has not been a problem. The only odd part of the kit, was the wooden cowl. This was known in advance so a fiberglass replacement was ordered from Fiberglass Specialties. Of the five owners of the Cap 21 with whom correspondence was held, none of the others had decided to replace the cowl. Apparently, the wood cowl works just fine but the fiberglass cowl was used for durability peace of mind.
The kit comes complete with a nylon engine mount, a nice but heavy tail wheel assembly, strange hardware for the wing bolts and other standard hardware. As a matter of personal preference, none of the supplied hardware except the aileron torque rods was used in the construction. There is no servo tray supplied; though there is ample room in the fuselage for many different applications. The instruction manuals are pretty pathetic. They consist of two booklets that are typical of those produced in the late 70's or early 80's. One is a generic construction booklet that is useless. The other is a four page booklet with two pages containing the instructions in list form with no pictures and two pages contain drawings with throws, dihedral, CG, radio placement tips, and so on. Despite this, the construction is straightforward and all but those new to the hobby will not have any problems.
The construction time, excluding covering, was about three weeks working on the plane several hours each day. The wing assembly is straightforward although plywood reinforcement is definitely needed near the wing bolts on the trailing edge. In addition, a frame for the single aileron servo is not supplied and must be constructed. Dual aileron servos could be installed, although the foam makes it a little more difficult. Cloth to fiberglass the wing center is supplied. The hardware for the main wing attachment was not used. There are two plastic hold-downs that are to be screwed to the side of the fuselage to receive nylon bolts. This hardware does not seem strong enough. Instead, a 1/4" plywood brace spanning the width of the fuselage was epoxied at the rear of the wing cradle. Blind nuts were installed to receive 10-32 metal bolts. In addition, the plate which receives the two wing dowels was doubled in thickness since it seemed a little thin.
The main landing gear is a two piece aluminum set that is attached to blocks already built into the wing near the leading edge. Although there was some apprehension about the wing mounted landing gear, especially with it being a two piece gear, the decision was made to build it as given in the instructions except that the supplied wood screws were not used. Instead, 6-32 threaded inserts were installed into the wooden blocks and were capped with 1/8" plywood to ensure that the inserts would not pull out. In addition, fiberglass was added around both of the landing gear areas. The ABS wheel pants were not installed since the plane would be flown off grass.
The supplied 1/4" plywood firewall was increased to 3/8" to take a SuperTiger G-90 powerplant with Slimline muffler mounted on a JR aluminum mount. This combination was suggested by several modelers in response to a newsgroup request for information. Pushrod guides and metal pushrod installation was uneventful, although the fuselage bottom was opened up to facilitate installation of pushrod guide brackets on several of the formers. It was decided that the split elevator would be joined with 1/8" music wire instead of using two pushrod linkages. The battery pack, receiver, and servo tray were arranged close to the trailing edge, which worked out well requiring only 2 oz. of tail weight in order to balance at the suggested CG. Low and high rates on the control throws were set as instructed in the manual. Final weight for the plane was around 6.6 lbs., much less than what was expected.
After many tanks of fuel, the ST90 was broken in and ready to go. The day of the maiden flight, the sky was cloudy and there was a 10-15 MPH crosswind. The flight was put off while flying a Great Planes Extra 300S but fellow club members were pressuring for the flight of the Cap 21. During taxi tests, the Cap seemed to nose over too easily. This was due to the landing gear being installed backwards. After this was corrected, it taxied perfectly with no bad habits. It was then taxied to the runway and lined up for the take-off. The throttle was slowly advanced and a little right rudder was applied. The elevator stick was pulled back slowly and the Cap lifted off. After a couple minutes flying to set the trim, it was taken to a higher altitude to determine the stall characteristics. It was pretty surprising how slowly this Cap would fly. Most stalls were straight ahead. They could, however, be quite violent, dropping a wing suddenly. Stalls become unpredictable if this plane is flown too slowly. The low rate throws suggested in the manual are way too much for normal flight. Care must be taken with any high-G maneuvers, as it will snap out in an instant. The plane tracks very well and qualifies for the "it flies like it's on rails" tag line. The first landing was rather anti-climatic as much more of a challenge was expected. It landed very much like the Extra. It requires a steep glide path and proper throttle management during the approach.
After some confidence was gained, it was time to ring out this plane. On the second flight, it was pulled straight into vertical and it climbed, rolling all the way. There is no problem with power with the ST90 and the Cap has unlimited vertical. This plane will knife-edge as long as it is held in position with just minimal elevator input. It can easily perform a knife edge loop. Snaps are extremely violent and it does tumbling maneuvers with authority. Inverted flight requires minimal elevator input. Recovery from a spin is easy but it seems to over rotate on many maneuvers. The second landing was better than the first.
The flight envelope of the Cap 21 is well defined and it is not difficult to become comfortable with it, but requires the pilot's constant attention. Controls get mushy if it is allowed to get too slow. Care must be taken during assembly in order to keep the weight down, as it is obvious that more weight would make this plane unpleasant. The landing gear has proven soft for most people but no problems have been experienced yet although the stock landing gear has been replaced with a better grade aluminum gear to avoid problems in the future. The low rate control throws have been reduced to about 1/2 of the recommended throws. When flying the Great Planes Extra 300 and the Model Tech Cap 21 back to back, it is easy to "feel" the difference. The Extra offers very precise stable aerobatics and is always a joy to fly. The Cap 21 gets the adrenaline pumping and can do sorts of amazing maneuvers. It is capable of doing very graceful, precise aerobatics, but it is more of a challenge since it is ultra sensitive to control input. Exponential control would probably help this condition but it is plenty of fun as it is now.
The Model Tech Cap 21 is exactly what was wanted, a very challenging and unlimited aerobatic plane. It is definitely not a second or even third plane. For those who want an "on-the-edge" thrill, the Cap 21 is definitely the ticket.