by Jim Feldmann

Extra 300S ARF

Aircraft Type 1/4 Scale Aerobatic
Mfg. By Great Planes Model Mfg. P.O. Box 9021 Champaign, Illinois 61826 (800) 682-8948
Mfg. Sug. Retail Price $599.95
Available From Retail Outlets
Wingspan 78.5 Inches
Wing Chord 15 Inches (Avg.)
Total Wing Area 1180 Sq. In.
Fuselage Length 70 Inches
Stabilizer Span 35 Inches
Total Stab Area 315 Sq. In.
Mfg. Rec. Engine 2.5-3.8 Gas 1.60-2.10 2-stroke; .2.00-3.00 4-stroke
Rec. Fuel Tank Size 27 Oz. (Included)
Rec. No. of Channels 4
Rec. Control Functions Rud., Elev., Throt., Ail.
Basic Materials Used In Construction Fuselage Balsa & Ply; Wing Balsa, Ply & Hardwood Spars
Tail Surfaces Balsa
Building Instructions on Plan Sheets NA
Instruction Manual Yes (40 pages)
Construction Photos Yes

Radio Used Futaba 8UAPS, 1 Hitec HS-425BB Servo 6 Hitec HS-5625MG Servos
Engine Used Moki 2.10, Bisson Muffler
Fuel Tank Used 27 Oz. (Included)
Weight, Ready to Fly 248 Oz. (15 Lbs. 8 Oz.)
Wing Loading 30.3 Oz./Sq. Ft.

WE LIKED THE: Overall appearance, flight performance, and "WOW" factor.
WE DIDN'T LIKE THE: Parts fit and build quality not up to Great Planes standard, wing tube would not go into wings or fuselage [Tech Notice: Wing tubes have since been replaced with fiberglass by Great Planes to resolve the problem of the wing tube not fitting in the fuselage or wings.]

Extra 300S ARF

Surely everyone who loves airplanes knows that Patty Wagstaff is a brilliant, dramatic, and highly successful airshow performer. Before her retirement from competition a few years ago, she was a three-time U.S. National Aerobatic Champion. She has used a number of Extra models during her career, and her current mount is a very colorful red, white, and dark blue Extra 300S. Patty and the Extra are so awe-inspiring in the air that she has driven her airshow competitors to devise more and more hair-raising stunts, just to stay on the program.

Great Planes recently released a 1/4 scale ARF version of Patty's Extra, complete with her beautiful airshow color scheme. Even the sponsor stickers that make competition and demonstration airplanes so distinctive are included with this ARF. Clearly, Great Planes' design goals for this model were: 1) to duplicate the awesome aerobatic capabilities of Patty's full scale Extra, and 2) using the lower wing loading and higher power to weight ratio that a model can achieve, to make the model capable of 3D and high alpha maneuvers that even Patty's full scale Extra couldn't duplicate.

The Great Planes Extra 300S ARF (as it is officially called) is a big airplane, with big airplane features like plug-in wings and horizontal stabilizers, airfoiled and double beveled tail surfaces, tail mounted servos, and a heavy-duty structure tailored to allow the use of a gasoline burning engine. It also comes in a big box (56" long x 22" wide x 12" high). The packaging includes the usual plastic-bagged components with corrugated dividers and the heavier items are taped to the inside of the box. My kit arrived without major damage, although the hardware and accessory items packed inside it had managed to add a couple of star-shaped cracks to that beautiful painted fiberglass cowl. Fortunately, the cracks are not in highly visible areas so I just rubbed some clear polyurethane over them to keep them from spreading.

Extra 300S ARF

The first thing I do with any ARF is dry-assemble it on the living room floor so that I can "ooh" and "aah" over it. That proved to be a problem for the Extra since the aluminum wing tube would not go into the cardboard tube guides in the fuselage and the wings. Apparently this was a problem with a number of the kits in the first shipment. I am told that the second and later shipments will have fiberglass tube guides so this problem should be eliminated. If you do get one of the first kits, you will need to make a tool and hone out the inside of the guides. Great Planes Customer Service will give you directions on how to do it. (Carry the tool with you when you take the Extra out to fly, because the cardboard guides will shrink and swell as the weather changes.)

The covering and trim was expertly applied, but the usual bubbles began to appear as soon as I took the parts out of the plastic bags. A couple of hours with the covering iron had it tight again. Top Flite's "Hot Sock" iron cover and MonoKote's "Hot Glove" soft mitten helped ease this job and kept the MonoKote scratch-free.

While examining the factory-built subassemblies I was a little disappointed with the build quality of my kit. There were quite a few dings, cracks, and glue blobs under the covering, and several shims and scabs had been used to make the fuselage formers fit properly. This is not what I usually see in Great Planes ARFs so I'm hoping mine was not the norm.

The hardware supplied with the Extra is heavy-duty and should be adequate for normal usage except for three items: 1) CA hinge material is provided and the instructions tell you to cut 3/4" x 1" hinges for all of the flight controls; that's the size generally used in 40 and 60 size airplanes, 2) the aluminum tubes, fuel line and clunk supplied with the fuel tank have a "small" inside diameter, and 3) the tailwheel assembly is the same unit supplied with the Great Planes Giles 202 ARF and we found its strength and small, shielded wheel inadequate for that airplane. For insurance, I bought some additional hinge material and made the hinges 1" square (33% wider); and to better feed a thirsty engine, I drilled out the clunk, replaced the clunk line with "large" fuel line, replaced the aluminum tube for the clunk line with 1/8" I.D. brass tubing, and ran "large" fuel tubing to the engine. I replaced the tail wheel assembly with the excellent Sullivan #S861 bracket and a 1" Klett tail wheel.

Extra 300S ARF


The wings are assembled first and there isn't much to it. Be sure to install the ailerons with the hard points for the control horns on the bottom side. The servos are installed upright in the wing and covered with a pre-cut ABS cover. The pushrods are 4-40 and use a threaded metal clevis on one end and a solder clevis on the other. The instruction manual thoughtfully provides details on how to solder for those who don't already have that skill. I used matching red and white MonoKote to seal the hinge gaps on all control surfaces. This is a step I consider very important for increasing control effectiveness and preventing flutter on any large model.

Speaking of clevises, I felt that the angle between the aileron and elevator pushrods and their servo arms was too great for the clevises to be secure, so I changed to Hangar 9 ball links on those four arms.

Fitting the wings to the fuselage was a little harder than I felt it should have been. The predrilled anti-rotation pin holes in the fuselage sides were undersized and did not line up properly with the wing tube. By the time I had enlarged them enough to get the wings on, I found that the incidence was off 1/2 degree between the two wings. I left it that way, but it did show up later as a couple of clicks of required aileron trim. [Tech Notice: Wing tubes have since been replaced with fiberglass by Great Planes to resolve the problem of the wing tube not fitting in the fuselage or wings.]

Before mounting the engine you are instructed to pin the firewall through all four sides of the engine box with the supplied 1/8" dowel. I also added 1/2" balsa triangle to the front of the firewall where the sides of the engine box extend past it, and covered the lightening holes in the engine box with scrap 3/32" sheet balsa to keep fuel residue out of the fuselage. For some reason, the instructions for mounting a glow engine have you install the throttle servo in front of the firewall. That's not a very healthy environment for a servo, so I installed it in the servo tray under the canopy, in accordance with the gas engine instructions.

The fuel tank is intended to go just behind the firewall, but I chose to build a custom tank tray and mount the tank above the wing tube socket, centered on the airplane's horizontal C.G. (see sidebar). Fitting and mounting the cowl can sometimes be a nasty job, but the instructions lead the builder through the process with a minimum of grief (including installing and pinning the cowl mounting blocks to the front former).

Installing the horizontal stabilizer is also straightforward if you follow the instructions, but do yourself a big favor and enlarge the wire feed hole in the bottom of the center section to about 2" long. You won't lose any strength and feeding the servo wires through after installing the stab will be much easier. Be very careful not to get epoxy in the joints where the stabs separate from the center section while you are gluing it into the fuselage because you will have to take them off to feed the servo wires through. As with the ailerons, be sure to install the elevators with the hard points on the bottom.

When tail mounted servos are used, I have found it very helpful to finish the airplane as far as possible without installing the rudder servo(s) and then do a pre-balance to see where the servo weight will be most helpful. This step showed that my Extra would be tail heavy if I installed the specified two rudder servos in the tail. To eliminate balancing weight and simplify the control set-up, I used one high-torque rudder servo mounted in the center of the tray under the canopy with a Du-Bro 4-40 pull-pull control system.

One final assembly caution: the tabs that retain the canopy/hatch don't contact the fuselage sides and tightening the retaining screws tends to break off the tabs. It is a good idea to glue a balsa filler to the fuselage sides so that the tabs have something to tighten up to. While you're at it, reglue the dowel that holds the front of the hatch in place as well. Mine fell out after a few flights. Fortunately, the Extra was on the ground at the time.

Although the box says that the Extra 300S ARF is IMAC legal, it does not include a dash panel. (Technically, the IMAC rules don't say that you have to have a dash panel, only that you will suffer a scoring penalty if you don't.) I built a simple dash panel from scrap balsa and added a low cost stick-on panel graphic from HorizonsNZ Model Graphics. The total weight of my dash panel is under 1/2 oz. As of this writing, there is no 1/4 scale blond Patty Wagstaff pilot figure available (yes, she is blond now) so I settled for a cute blond doll that my wife found at the 99 cent store. The raw wood of the canopy/hatch framing shows through the canopy on a sunny day too, so I painted it flat black.

Extra 300S ARF
The Moki 2.10, Bisson high volume Pitts muffler and Perry regulator pump add up to a reliable and very powerful power package. Note the triangle stock added to the front of the firewall and balsa sheeting covering the access holes in the engine box.


I used my trusted Moki 2.10 to power the Extra. I was able to use the supplied Great Planes engine mount and my Bisson large volume Pitts muffler fit completely inside the cowl. A Perry VP30 regulating pump was installed to assure a constant fuel flow from the remotely mounted tank. This engine/pump/muffler combination has been 100% reliable in all of the airplanes I've used it in. I have been using an APC 20 x 8W prop on the Extra and am very happy with its performance.

Extra 300S ARF


A 15-1/2 pound airplane with 5 horsepower requires a more sophisti-cated radio set-up than a smaller model would (see sidebar). I used a Futaba 8UAPS with an 8-channel PCM receiver, five Hitec HS 5625 digital high-speed servos and an HS 425BB standard servo for the throttle. Two 1650 mAh 5-cell NiMH battery packs were mounted under the wing tube on the left side of the airplane to help balance the weight of the horizontally mounted engine. I used Hitec's new digital servo tester and programmer to minimize the dead band and set the end points of the digital servos. The programmer would have been invaluable in matching the performance of the two servos in the recommended rudder hookup if I had not changed to the single servo for balancing reasons.


My Extra required no added weight to balance just behind my calculated C.G.. I set the control travels at the recommended high and low rates with no exponential and switched everything to low rates for the first flight.

While adjusting the needle valve before the first flight, the right aileron started flapping. The servo arm screw had fallen out. The left one was loose also, and ready to fall out. WOW! What if that had happened five minutes later? One of the heli fliers at the field had some of Pacer's Z-42 thread locking compound, which we applied to all of the metal to metal servo arm screws. After a little setting-up time, I was able to proceed with the first flight with no more screws falling out, but what a scary thing that was!

Extra 300S ARF

Note the filler blocks added to prevent the canopy hold-down tabs from breaking off when tightening the retaining screws.

This was my first experience with "metal gear" servos and when I called Hitec the next day I was told, "Oh yes, you have to use a thread locking compound on those screws or they will loosen up from vibration," and "No, it isn't mentioned in the servo instructions." Hmmm... This is not meant to single out Hitec. It isn't mentioned in Futaba or JR's instructions either.

Extra 300S ARF
The author built this lightweight dashboard from scrap balsa and added an inexpensive color printed instrument panel from Horizons Model Graphics.

Well, come on Jim, how does she fly? Superbly! The Extra 300S ARF powered by the Moki 2.10 is the most capable and, at the same time, the most forgiving mid-size aerobatic airplane we have ever flown. And we've flown most of them. On take-off it runs straight down the centerline, with the tail up, until you pull it off with a touch of elevator. Point the nose straight up and it will fly out of sight, seemingly at full speed and its aerobatic ability is as unlimited as its vertical. Slow flight is as stable as a rock and can be very, very slow. The recommended low rates were a bit too gentle for us. High rates gave about two rolls per second, beautiful square corners and the sweetest 45 degree nose-high slow knife-edge you will ever see. All at half throttle. Speaking of knife-edge, the Extra does it with just a tiny touch of proverse aileron and up elevator (easily mixed in at the transmitter). I was able to do nice torque rolls on high rates on a calm day. Still, the high rates felt just a little too quick for precision maneuvers. Halfway between high and low rates gave a nice smooth rate for sport and precision aerobatic flying, so for subsequent flights we used that travel as our low rate and the recommended 3D rates as our high rate. The 3D rates open the door to every known high alpha maneuver and the Extra does them all. Maybe not quite as well as a 40% aerobat can, but darn close.

And if you make a mistake, the Extra will give you time to make a couple of corrections before it bites you.

Extra 300S ARF
A Sullivan tail wheel bracket, Hangar 9 ball-links and a Du-Bro pull-pull system were used along with the supplied Great Planes control horns, 4-40 pushrods and solder clevises to provide a clean, functional control system for the tail section.

The only negative comment I could make about the way the Extra flies has to do with the way it lands. The curved main gear struts are a copy of those on the full-scale Extra, and they seem to be stiffer than the usual straight/angled struts. As a result, they tend to make the airplane bounce on 3-point landings. This may not be a problem on grass, but on our hard-surface runway, the Extra doesn't want to stay down as well as similar models do. I may try some curved composite gear to see if this tendency will go away. In the meantime, every landing has to be on the mains. Fortunately, I fly from a pretty long runway.


The Great Planes Extra 300S ARF is not a beginner's airplane in assembly, set-up, or flying. But with its outstanding and very comprehensive instruction manual and forgiving flight characteristics, it would be an excellent choice for the experienced ARF modeler who wants to move up to large scale aerobatics. Experienced Giant Scale fliers will love it too, because it flies like a bigger airplane than it is and we truly couldn't find anything that it wouldn't do in the air, and do well.

If you enjoy IMAC or freestyle aerobatics, you will love this airplane. But don't try to buy mine, because I'm not selling.

A Center Mounted Fuel Tank and the C.G.

Extra 300S ARF
A light ply tray was built to support the fuel tank above the wing tube socket (at the airplane's horizontal C.G.). A 1/4" foam pad was added and then the tank was rubber banded in place.

When we finish a model, ARF or kit, we carefully balance it at the recommended C.G. Maybe sometimes a little forward for a safe first flight or maybe a little aft because experience has told us that we like them that way. Then we fill the fuel tank and completely change that carefully selected balance point. When the tank is in the usual position right behind the firewall, filling it moves the C.G. forward. Sometimes a little, sometimes a lot. On the review airplane, filling the tank moved the C.G. forward 5/8".

The recommended C.G. on the Great Planes Extra 300S ARF is 3-13/16" behind the leading edge, measured at the wingtip, with the tank empty. In technical terms, that's 34.4% of the Mean Aerodynamic Chord. Then with the tank full, the airplane balances at 3-3/16" (30.5% MAC). So in effect you take off with the C.G. at 30-1/2% and then during the flight, as you burn off fuel, the C.G. moves to the rear. (Have you ever had a model that wouldn't snap roll until halfway through a flight? I have.) But unless you run out of fuel, the C.G. will never get back as far as the recommended 34-1/2%.

Moving the tank to the center of the fuselage (over or under the wing spar) is a good thing. Burning off fuel does not change the C.G. and the flight characteristics of the airplane. Of course with the tank that far from the engine, you will need a fuel pump, but fuel pumps have advantages of their own (consistent running at all attitudes and the ability to safely use a leaner needle setting for more power) and if you are using a gasoline engine it already has a pump built into the carburetor.

But what about the C.G.? With the tank moved to the center, do you still want to set the balance point at the factory recommended C.G.? NO! Remember, when the tank is at the C.G., filling it does not move the C.G. forward, as the factory expected. After considering the filling and draining of the tank, the factory recommended C.G. for the review airplane really amounts to 3-3/16" at take-off and somewhere around 3-5/8" at landing.

I felt that the factory's effective take-off (full tank) setting of approximately 30% of the MAC would be a safe place to start, so I balanced the airplane at 3-3/16" (5/8" in front of the recommended setting, but still within the recommended range). That turned out to be an excellent choice for the trim flights. My airplane flies inverted with just a hair of forward stick and landing approaches require only a light touch of back stick. Elevator sensitivity at the recommended throws is normal. I moved the C.G. back to about 3-5/16" after I got thoroughly comfortable with the airplane, and at that point it will fly hands-off inverted. It is clear that with a center mounted tank, setting the C.G. at the recommended point would result in a severely tail-heavy airplane.

NOTE: This analysis applies only to airplanes with the fuel tank mounted at the center of the fuselage. If you install the tank in its planned position behind the firewall, you should stick with the factory's recommended C.G. position.

Extra 300S ARF
Hitec's HS 5625 digital servos and Servo Programmer/Tester, combined with redundant 6 volt NiMH batteries, redundant heavy duty switches and heavy duty extensions make a safe, powerful, and up-to-date onboard radio system.

On-board Radio Equipment for Large Scale Models

That big, high performance airplane probably represents a large proportion of your hobby budget, and it has the potential to cause serious damage should it go out of control. Both very good reasons to use the best and safest radio equipment you can.

For the Extra 300S, I decided to use Hitec's HS5625 digital servos (130 in./oz. at 6v.) for their great power and precision, and these proved to be an excellent choice. But nothing comes for free, and digital servos use a lot more battery power than standard servos would. This creates two potential problems. First, a larger capacity onboard pack is required. (Great Planes recommends at least 2800 mAh if you are using digital servos.) Second, the five or six digital servos in the Extra, all working at once, could pull so much power out of a 4.8 volt system that the receiver would lose the signal.

To keep the battery weight from getting out of hand, an NiMH battery would be a good idea, and to keep the voltage well above the receiver's drop out point, it should be a 5-cell pack.

Now let's talk about redundancy. The first and second most common causes of in-flight radio failure are the battery and the switch. The cost of two smaller batteries and two switches is only slightly higher than one of each and the security gained is well worth it. I used two 1650 mAh, 6 volt, NiMH battery packs and two heavy duty switches from Cermark. Speaking of heavy duty, all of my servo extensions used the larger heavy duty wire as well.

George Steiner, who writes many of RCM's radio articles, feels that no isolator is needed between the batteries if they are the same type and capacity, and Hitec does not require a regulator when running their servos on 6 volts, so neither was used. I did add a 6 volt LED battery monitor plugged into the receiver so that I can check each battery and switch separately before each flight.

The accompanying photo shows the complete on-board radio system before I decided to use the single servo pull-pull rudder system.

Photos by Jim Feldmann and Jim Pearson. Reprinted with permission.
June, 2003 R/C Modeler Magazine
Editor: Patricia Crews