• Wing Span: 64 in (1625 cm)
• Wing Area: 744 sq in (4800 cm²)
• Length: 54.25 in (138 cm)
• Weight: 7.5 lbs (3.4 kg)
• Engine: .61 - .91 2 - cycle
  (10.0 - 20.0cc 2 - cycle)
  .91 - 1.20 4 - cycle
  (15.0 - 20.0 cc 4 - cycle)
• 4 Servos required

During construction of this kit, I had the pleasure of corresponding extensively with Gary Sandsted, who also built the GP 60 size Extra. Several of his observations and suggestions were incorporated and have been noted here.

Released in late 1998, the .60 size Great Planes Extra 300S generated a lot of interest in the modeling community because it is the only built-up version of this plane in the popular 90 four- stroke engine size.

This is an all-wood kit that incorporates some innovative engineering techniques, but that requires a lot of building. It is definitely not a kit that can be framed up over a few evenings. The supplied cowl is a two-piece ABS plastic unit of acceptable quality, as are the wheel pants. Modelers not wishing to spend time building these items or those wishing to save weight up front may opt for after market fiberglass parts available from Fiberglass Specialties. The supplied canopy was damaged upon arrival but a call to Tower Hobbies from whom the kit was purchased resulted in a replacement part arriving within a week.

Wood quality is generally good, but below that of Sig or Midwest kits. There is a noticeable lack of consistency in the weight and hardness particularly in the 1/16" wing sheeting stock. Some of the 1/8" plywood die cut sheets containing the wing bellypan formers were noticeably warped.

The hardware pack contains the usual assortment of high quality GP parts, including a well made 60-120 size adjustable engine mount, a tail wheel bracket, wire pushrods, nylon links and assorted bits and pieces. The only hardware item found to be inadequate were the self tapping screws intended for mounting the landing gear to the plywood beam mounts. The manual instructs the builder to install the screws directly into the beams, the only reinforcement being the application of thin CA glue to harden the threads. However, several modelers have reported problems with the gear ripping out with the suggested installation method, so 6/32 machine screws backed by blind nuts were used instead.

The tail feathers are stick built over the plans and present no major challenges. The fin and stabilizer are sheeted with 1/16" balsa, while the elevators and rudder are open-framework. As a matter of personal preference, the rudder was built with three ribs instead of two, thereby bringing the rib spacing close to that of the elevators. One interesting feature of the stabilizer is the inclusion of a basswood spar, which contributes to its strength and guarantees that it is up to the stresses imposed by violent snap-type maneuvers. The directions regarding cutting the supplied 1/16" balsa sheets for sheeting the stab are somewhat confusing, but a quick check with the plans revealed the correct measurements for the cuts.

The fuselage, except for the balsa turtle deck sheeting, is entirely composed of lite-ply. Construction is of the interlocking "tab and grove" variety and the parts fit and die cutting were good. A real problem was encountered, however, when trying to make the lite-ply fuse sides conform to the curvature of bulkheads 6 and 7. The problem was partially solved by soaking the fuse sides in water, rubber banding them to a quart-size paint can and leaving them dry overnight. This helped considerably, but several Easy Grip brand pistol style clamps were still required to achieve a good bond of the fuse sides to the formers. It is also recommended that 15 or 30 min. epoxy be used for this step instead of the recommended CA.

The firewall is composed of three pieces of plywood laminated together; be sure to glue them in the correct order, because the back piece is notched for the tank mounting platform and the landing gear mounting rails. To facilitate installation, Great Planes has made dimples in the firewall to mark the location for the engine mounting holes. Former 7 was doubled with scrap 1/8" lite-ply. Its reinforcement was deemed necessary because of the dual loads, from the landing gear rails and wing dowels, borne by this member. The engine mounting box was easy to construct from the die cut lite-ply. 1 oz. fiberglass cloth, applied with thin CA, was used to reinforce its joints. Since it is easy to forget that the fuselage is being built upside down over the plans, be sure to build in right thrust and not left thrust when installing the engine box. The turtle decks are not difficult to install, if directions are followed closely. It is a good idea to run the turtle deck top stringers between the cockpit backrest and former 30 before installing former 29. By bringing former 29 up to meet the stringers, a strait and true line over the formers can be assured. Once built, a liberal application of balsa filler along the stab and fin joints and some sanding produced good results and a pleasing contour.

The wing construction is of the classic "D tube" type, with sheeted leading and trailing edges. The ailerons are built-up to save weight, but wishing to save time instead, I replaced them with soft balsa solid units. The main spars are built by laminating two 3/8" x 3/16" spruce sticks which then taper to a single spar at a safe point midway down the wing. The center section reinforcement consists of two 1/16" plywood dihedral braces glued to either side of the main spars creating a "box spar" strong enough to dispense with fiberglass reinforcement. As per current practice, the ribs feature tabs allowing the wing to be built flat on the board. The wing also features an unusual lite-ply subframe for supporting the wing mounting dowels, which removes any doubt regarding the structural integrity of the installation.

Care must be taken when handling the partially assembled wing due to the relative fragility of the 1/16" balsa used for the sheeting. Despite my attempts to handle it with care, I twice fractured the sheeting while turning the wing over on the building board. This occurred a third time after the model was covered while establishing the center of gravity. Otherwise, the construction of the wing presented no major challenges and the overall parts fit was excellent.

The wing was covered with white Ulltracote, while the fuselage was first covered with Super Coverite, doped, sealed and painted with white Lustrekote. The yellow and blue trim was cut from Monokote trim sheets and Carl Goldberg 1/4" trim tape. Three inch Sullivan wheels were installed, but the wheel pants were omitted as the model will be flown from less-than-perfect grass fields.

An MK brand "fuel dot" was installed on the side of the cowl and connected to a 12-ounce. tank. The model was test flown with an APC 13X8 prop and the center of gravity at the forward end of the recommended range. To achieve proper balance, 6.5 oz. of lead was bolted to the engine mount, although, this might have been more due to the chosen finishing method, than to a design fault.

Test flights took place in August, 1999, at the CMAC filed in Stratford, CT. Although the temperature was in the mid eighties and humidity was high, the OS .91 performed flawlessly, with no sign of overheating. The stock cowl has an air exit hole scribed into the bottom. Be sure to open this hole as recommended, because, otherwise, the engine will likely overheat from insufficient airflow.

The first flight was uneventful, the Extra tracked straight down the runway needing little right rudder correction, and, as half up elevator was being held, virtually lifted off on its own. After climbing strait out to a comfortable altitude, controls were released to verify the trim. Three clicks of right aileron was all that was required to produce strait and level flight. The recommended low rates used for the first flight are adequate for cruising around. The high rates produced an excellent roll rate and crisp snap rolls. The model performs perfectly axial rolls and exhibits no roll coupling while on knife-edge. Vertical performance is good with the OS .91 four-stroke, but not unlimited. There is enough thrust for large square loops, sustained knife edge and all standard maneuvers, but those wanting to perform torque rolls and other such maneuvers should opt for a more powerful power plant.

Being concerned with stalling, the Extra was brought-in a little "hot" on its first landing, with the predictable multiple bounce landing as a result. The modified landing gear installation got an unintended opportunity to prove its strength and survived unscathed. Low speed flight was tested on subsequent flights with the Extra showing no signs of tip stalling. The Extra can be brought in quite slowly for a smooth three-point landing.

The flight characteristics of the Great Planes Extra 300S are outstanding. It is capable of all-out aerobatics, yet can also be flown around like a sport plane. Takeoffs and landings are not demanding of the pilot, being well within the range of any experienced sport flyer. This is an airplane that makes you look good and is well worth the effort of any modeler wishing to fly a scale model of this famous aerobat.