Aerotech Intl. F8F Bearcat

Model Airplane News, Nov 1997 by Benjamin, Bob

A warbird converted to electric power

This Bearcat is really something different! Produced in England by Aerotech Intl. and imported to the U.S. by Dare Hobby Distributors*, the 1/8-scale F8F includes foam-cores for the wings, tail surfaces and fuselage fairing sections. All foam parts are presheeted with obechi veneer. The kit features a simple, built-up, sheet-balsa fuselage box that's rounded with sheeted-foam fairings to produce an attractively contoured structure. Aerotech's innovative kit design simplifies building by eliminating multiple formers and stringers, planking and compound-curve sheeting.

NOT FOR BEGINNERS

This airplane is by no stretch of the imagination a trainer. If you're comfortable with the challenge of flying this model as the heavily loaded scale fighter that it is, you'll have a great time with it!

The kit also requires you to be experienced enough to make decisions regarding hardware and equipment installation. For instance, the plans don't show control horn or other control-linkage detail-not a problem for a truly experienced builder, but real trouble for a newcomer! I found the Bearcat to be a real change of pace and an exciting project, both on the bench and at the field. Too often we get into a "sameold" rut; the Aerotech Bearcat will lift you out of that rut in a hurry!

EVALUATION AND ELECTRIC CONVERSION

This article is a departure from the usual product review in that I will not only evaluate the kit, but will also present the details of a conversion to electric power using the Model Electronics Corp.* (MEC) Turbo 10/20 brushless motor system.

Many modelers consider an electricpowered scale fighter to be a project that has little chance of success. To make the point as strongly as possible that such a model can be built and flown successfully, I chose the Bearcat as perhaps the "hottest" fighter design in Aerotech's kit line.

WING CONSTRUCTION

The sheeted-foam wing and tail surfaces require that balsa leading-edge (LE) and trailing-edge (TE) strips and surface tips be added. I used aliphatic-resin wood glue for all primary structural assembly. Although epoxies and selected CAs will work well on white foam, they leave a hard joint line that makes it difficult to sand the skins to a smooth surface. All the control surfaces are preformed balsa and require minor shaping to fit well. Openings in the wing for center-section spar joiners, aileron servos and landing-gear (LG) mounts are not precut and must be made by the builder. The plans indicate individual microservos for the ailerons, so servo bays and aileron cable tunnels must be cut into the foam, and servo-bay covers must be made.

There is a discrepancy between the wing airfoil shown on the plan and the structure that's provided. The section shown is fully symmetric with a convex surface. When the sheetedfoam wing-cores and precut TE stock are joined, the result is actually a reflexed airfoil; that is, a symmetric section with a concave area just ahead of the TE. In fact, this works quite well and causes no problem when fitting the wing to the fuselage, Hardwood mounting blocks for a fixed main LG are provided, and their location is shown on the plan. Although a retract system is mentioned as an option, no installation details are provided.

RETRACTS

The full-scale Bearcat has an LG arrangement that is demanding to replicate accurately in model form. The main wheels retract so far inward that they actually lie within the fuselage, and the struts, which are long to provide ground clearance for the large diameter prop, include a section that folds in on itself during retraction to shorten the length of the retracted assembly! Reproducing this is not practical for a sport-scale model. The suggested main gear strut length is sufficient to clear any prop likely to be used on a glow engine and would retract properly into the wing. Since, however, this airplane was to have a geared electric power system that uses a 13-inch prop, I used the longest strut possible. I positioned the retract units so the struts were centered 10 3/8 inch from the centerline of the aircraft, and I moved the spanwise centerline an additional 2 inch back from the LE. With the no. 653 shockabsorbing Robart* Robostruts trimmed to fit this layout and the Robart 605HD retract assemblies mounted flush with the lower surface of the wing, the main gear axles are then located properly for good ground handling without "groundloop" or "noseover" problems. Aside from the effort necessary to work out the conversion, the only problem I encountered was that a scale-size wheel would not retract to fit flush into the wing. Remember that on the full-scale F8F, the wheels actually retracted into the center-section fairing portion of the fuselage! It turns out that the airplane doesn't seem to mind this, and it's really tough to see the difference in flight.

Whether you opt for fixed or retractable gear, the mounting blocks or rails are glued directly to the foam-cores in whatever cutouts are made in the wing. Although the gear mounting blocks are solid, the foam they are glued to isn't! This concern was borne out during flight testing when I landed a few feet short on a grass strip with a sloping approach end, and one gear assemblymounting rails and all-peeled right out of the wing. Although it turned out to be an easy repair, it reinforced my decision to restrict this hot little fighter to paved strips in the future. If I were to build this airplane again, I would include a full-depth centersection spar joiner of 1/8-inch aircraft ply extending out an inch or so beyond the ends of the fixed gear blocks or the rear mounting rails of the retract units. The LG mounting blocks would be glued directly onto the plywood. Though the fixed tailwheel installation is easier to build, I wasn't happy with the idea of a scale fighter with retracts that would seriously restrict ground handling. I made up a simple, steerable tailwheel using a .40-size tailwheel bracket mounted to a ply plate as shown on the plan, with a separate pushrod running back to the rudder servo.