Great Planes: Extra 300S 1.60 ARF

Model Airplane News, May 2004 by Smith, Jerry

A ¼-Scale showstopper!

The last seven U.S. Unlimited national acrobatic champions have competed with an Extra 300; that's quite a record! Produced by the Walter Extra Flezgeugbau in Germany, the Extra 300 bears impressive credentials that include a roll rate of 400 degrees per second and the ability to withstand plus or minus 15G. Put yourself in the cockpit of one of these beauties, and you can produce violent maneuvers that are the equivalent of riding a Brahma bull.

The Great Planes ¼-Scale Extra 300S 1.60 ARF is a good representation of the Avemco-sponsored Extra 300S flown by Gene Soucy in competition and in his airshow. Looking it over closely, you will notice its increased tail surface and slightly larger ailerons; those characteristics certainly contribute to its outstanding 3D performance.

Assembling the Extra is very straightforward, and the dearly written, 27-page manual provides many photos and offers extensive information on flying and flight trimming.

When I spread the parts out on the floor to thoroughly inspect them, I could immediately see that this was going to be an impressive model! The Extra features excellent built-up construction, expertly applied MonoKote covering and trim and a painted fiberglass cowl and wheel pants. It also comes with a polished aluminum spinner, landing gear, clear canopy, wheels, all necessary hardware and scale wingtip aerobatic sighting reference guides.

WING ASSEMBLY

The wing comes in two, 37-inch panels. I like this because it's easier to work on a panel than a whole wing. After installing the aileron with the provided CA hinges, I removed the covering over the servo well with a micro-tip soldering iron. Running a heated iron tip around the edges of the opening removes the excess material and seals the covering to the edge at the same time.

Before you can mount the servos, you'll need to attach two 12-inch extension leads to the servo connectors. To keep the connector pairs together, 1 looped a small plastic zip-tie around them and pulled it tight. With the servos mounted and the lead pulled through the wing, the aileron control horns were next. The hardware included in the kit was fine, but I really wanted to try out some new Du-Bro heavy-duty control horns that I already had. These horns feature a ½-inch offset in the horn connector, and you only need to drill a single hole to mount them.

I used FMA PS705MBB servos for all of the control surfaces. These metal-gear servos produce 106 oz.-in. of storque-more than I needed, but they provide good response. I also like the connectors and the heavier lead wire on them.

The 4-40 pushrod between the servo arm and the control horn is very short. On one end, you must solder the clevis into place. After you've finished working on the wing panels, slide them together onto an anodized-aluminum tube spar. A pin near the trailing edge will keep the panels aligned. My wing halves mated perfectly! The wing also aligned with the same precision when mounted on the fuselage. 1 was amazed at the degree of accuracy built into this almostready-to-fly (ARF). There are several benefits to a wing assembled on an aluminum spar: you can leave it in one piece, carry it in two pieces in a wing bag for protection and work with one panel at a time on the bench when setting up control-surface deflection.

TAIL INSTALLATION

With the wing assembled, I turned my attention to the airfoil-shaped tail. I always worry about getting the tail on straight, but this time, all went well. The supplied elevator control horn is sturdy and has a large footprint; it's held in place on the plywood hard point with four screws. This keeps the top of the elevator clean. The elevators are split; each is powered by a servo in the tail with the output arms in an opposite configuration to avoid reversing one servo. The 4-40 pushrods (the same as the aileron pushrods) are short and adequately stiff. With this setup, you'll need to install a Y-harness and a 12-inch servo connector extension to reach the receiver.

Because I used slightly heavier servos, I thought the plane might be tail-heavy if the rudder servo was also mounted there. I decided to go with a pull-pull system on the rudder and mounted that servo on the servo-mounting board, close to the airplane's CG. This turned out to be the right decision; I had no problems obtaining the CG stated in the manual.

To hook up the rudder, I used Du-Bro heavy-duty control horns with a piece of 6-32 threaded rod and a Du-Bro 4-40 pull-pull system. For the pull-pull lines to clear the bulkheads in the fuselage and the wing hold-down support, I had to raise the aileron servo % inch off the fuselage servo mount. I installed a large Du-Bro Super Strength servo arm on the rudder servo. It perfectly matched the control-horn width on the rudder, and the hookup was complete.

When I installed the tailwheel, I thought the linkage and hardware required to hook it up could have been simplified. If you later decide that you want to set your Extra up for 3D maneuvers, you'll need to rework the tiller arm for more throw. Although it doesn't look as scale, I substituted a simple Sullivan no. S861 tailwheel.