Great Planes PBY Catalina ARF

Great Planes

PBY Catalina ARF

By: Frank Granelli

The Consolidated PBY Catalina first took to the air on March 28, 1935. It left US Navy service in January 3, 1957. The PBY’s 22-year service life is even more amazing considering the tremendous technological changes that occurred during this period of aviation. Most aircraft of its time didn’t last even 10 years in service.

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Photo courtesy of Wikipedia

During its long service life, the Catalina flew patrol missions, night bombing attacks, emergency supply runs and hundreds of other vital war missions it was never intended to accomplish. And it did them all well; although a mite on the slow side considering its cruise speed was just around 120 mph.

In fact, the PBY Catalina still holds the record for the longest (in terms of airtime) regularly scheduled commercial route. That was a 3,592 mile long weekly Quantas flight from Perth Australia, across the Indian Ocean to Colombo, Ceylon (today’s Sri Lanka). Flown from 1943 to 1945, this was the flight of the “Double Sunrise” and required about 32 hour’s airtime.

The PBY was the airplane that spotted the Japanese fleet on its way to attack Midway and spread the warning. Four of these massive, slow Patrol aircraft even tried a night torpedo attack on this fleet. Poorly armed for self-defense but with a gigantic range, the PBY Catalina was one of the major factors in winning the Battle of the Atlantic against the German U-Boats.

In short, the PBY’s story is one of resounding success against difficult odds. Plus, it was an attractive looking airplane in a pudgy sort of way. It was also easy to takeoff, fly and to land. The first four major variants had retractable tip floats but no wheels. But the PBY-5 series and later models were amphibian; able to operate from any surface.

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The Great Planes PBY version however, is a seaplane only. That is only natural as the PBY-5’s retracting mechanism is extremely complex and very heavy. Even though I have heard stories about pilots flying the Great Planes Catalina from snow and short grass (with a hand launch and no tip floats and water rudder removed), this is primarily a water aircraft.

The Great Planes PBY Catalina Almost-Ready-to-Fly (ARF) airplane is not a Park Pilot airplane despite having two electric motors. It weighs 3.2 pounds, well over the two-pound limit. While it is easy to fly, its takeoff and landing speeds are faster than those of the average Park Pilot aircraft.

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This “kit” is more complete than most ARF’s and a little easier to build. For a twin-engine airplane, it is extremely easy to build and very rugged. The fuselage is made from a light, but very, very rugged fiberglass. The wings are standard wood construction employing an aluminum spar for added strength.

The electric motor mounts are factory assembled as are all control surfaces and the tip floats. In addition to 12-minute epoxy, you will need some silicone adhesive to attach the rear blisters to the fuselage. The silver aluminum tube is the main wing spar. Both wing halves just slide over the spar; no gluing necessary.

For the most part, building the Great Planes Catalina is exactly the same as building any ARF airplane. For complete details on building an ARF, see the three-part Sport Aviator article series on “How to Build an ARF Trainer”, Parts One, Two and Three.

Building the Wing

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Photo 5 is all the hardware and parts needed to complete the wing. Note: the red double motor / single battery connector has been added as it arrived after this photo was taken. But it is needed for proper operation. It is called a Great Planes Parallel ESC Deans Ultra Adaptor (L5PTT603).

The Rimfire® 950kV Outrunner motors (GPMG 4560) produce more than enough power to maneuver the Catalina far beyond the full-size aircraft’s abilities (beyond even its wildest performance dreams). The two ElectriFly 25-Amp Electronic Speed Controlers (ESC), one for each motor, (GPMM1820) feature a 2-Amp, 5-Volt Battery Eliminator Circuit (BEC). The ESC’s power the Catalina’s on-board radio system from the single ElectriFly 3200 mAh, 3-cell, Lithium Polymer battery (GPMP0623).

Two Futaba S3107 micro servos power the Catalina’s ailerons. The S3107 Futaba servos produce 17 in. oz. of torque, more than enough for the Catalina’s smaller ailerons, and are very fast at .12 seconds for 60-degrees of rotation. They weigh just 9 grams each. Although the two heavier duty, S3114 Futaba servos are also pictured here, they are used to power the elevator and rudder.

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There is a lot more hardware included in the Catalina “kit”. Even the two propellers are included as are battery hold-down strips (hook and loop fasteners) and the now standard Mylar® hinges; precut for convenience. The motor extension wires are factory installed into each wing panel as are the aileron extension wires. I am not sure I have ever seen an ARF that had universal aileron extension wires pre-installed before. Good move, Great Planes.

Installing the control surfaces using these hinges is a good first step. For complete details concerning this installation, read the Sport Aviator article “Installing Mylar hinges in ARF Trainers” in the Flight-Tech section. Make sure to use thin CAA and never use an accelerant during hinge installation. The so-called “Kicker” prevents the thin CAA from wicking all the way into the hinge material. Also ensure that the thin slit is perpendicular to the wing’s trailing and the control surface’s leading edges. The slit is the CAA highway allowing the adhesive to wick into the deepest reaches for the strongest bond possible.

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Install the aileron servo in the under-wing pocket. Then attach a control arm clevis to a control horn. Position the control arm over the servo arm hole as shown and mark the two control horn screw holes. Check photo 9 carefully, click on it to expand the picture, and make sure that the control horn is parallel to the aileron leading edge and that the control horn holes are exactly centered over the hinge line. Then mark and mount the control horns.

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Locate the preassembled motor mounts in the correct position on the wing. Mark the attachment points. Then make the wing cuts as outlined in the manual. Mount the motor using the supplied hardware. Run the motor control wires from the ESC out the wing hole as shown.

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Make sure to use thread locking compound on all the motor mount bolts as shown. Put the locking compound on the bolt and a little more in the threaded socket.

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Note in Photo 14 that I have installed a short length of heat shrink tubing on the motor control connections. This not only secures the connections but also makes them water-resistant (never say “water-proof” when discussing a seaplane). Check that the motor rotates in the correct direction. Then shrink the tubing in place before installing the connections onto the wing.

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Check the motor mount position on the wing and measure to make sure it is straight. The notches and wire holes in the wing sheeting were factory installed. Remove a slight bit of wing covering material from around the slot openings and along where the mount touches the wing. Epoxy the mounts in place using 5-minute epoxy.

Once the epoxy cures, slip the flexible outer nacelles over the mounts. They do need to be removable for motor servicing. These can be either taped down or, as was done on this airplane, just pressed into place. The nacelles need to be easily removable.

Connect the motor wires to the factory installed motor wire extensions. Check each motor by running it without a propeller. Make sure it turns correctly and responds to the throttle. Then remove the battery connection from the ESC. Install the propeller. Make sure both propeller adaptors are an equal distance onto the motors.

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Locate the factory installed tip float slots in the wing underside and cut them out as in photo 17. Draw a line connecting the slots and remove the covering material inside those lines. Epoxy the tip floats in place. Make sure they are perpendicular to the wing and that the epoxy is applied to all the wood surfaces contacting the wing. The tip floats suffer a great deal of strain and need to be firmly mounted.

Slide the wing halves together over the aluminum spar. The anti rotation pin should slide easily into the matching hole in the other wing panel. Once mounted on the fuselage, the four wing hold-down bolts hold the wing halves firmly together. There is no need to glue the wing halves together.

Getting the Fuselage Assembled.

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Assembling the Catalina’s fuselage is a little different from that of the standard ARF aircraft. The fuselage is made from a very tough, and I do mean very tough, fiberglass. Yet it is light weight. But then things begin to get very different from the standard ARF.

The wing mounts to a pylon using four 4-40 bolts, not into the usual wing saddle. The rudder and elevator servos are mounted in the fuselage’s rear mid-section right under the clear blisters; not under the main wing. The horizontal stabilizer is mounted half way up the vertical fin. Instead of a tail wheel, there is a steerable water rudder in the rear.

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Starting at the rear fuselage, assembling the horizontal stabilizer come first. As usual, remove the covering from the stabilizer where it will glue to the under side of the vertical fin. This is best dome with a hot knife to prevent accidentally scoring the wood. Sand away the paint in the fin area where it will contact the horizontal stabilizer.

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Temporarily bolt the wing in place. Test install the stabilizer in place and make sure it aligns parallel to the wing. Once it is aligned, use some 12-minute epoxy and install the stabilizer. Clamping it in place as shown works well; just make sure it is parallel to the wing (note: the level insuring that it is).

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While the stabilizer is curing in place, assemble the elevator. Before installing the metal coupler shown in photo 22, be sure to remove a small amount of wood from just the inside edge on the hole in the elevator. Relieving this area to fit the bend in the wire allows the metal joiner to lie completely inside the elevator halves. Align the halves against a straight edge as shown (photo 24) and install the joiner using 5-minute epoxy. Make sure that both halves are parallel with each other by using weights as shown. Once everything is cured, install the elevator onto the horizontal stabilizer as was done with the ailerons.

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Tie the servo extension wires needed for the elevator and rudder servo wires to reach to the receiver. This connection should never come loose. The Catalina is not the world’s best no-elevator airplane (most ARFs are not). Make sure this connection is tight and firm. If you wish, use some 1/2 inch shrink tubing over this connection to increase water resistance.

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Mount the elevator servo, here a Futaba S3114, in the tray under the blister as shown in photo 25. Use a hand drill to make the servo mounting screw holes. Using a power drill, such as a high-speed rotary drill, might mean a hole in the otherwise water proof (resistant?) hull. Note the tubing just to the right of the servo. This tubing guides the flexible elevator pushrod back and up to the elevator control horn.

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Cut off three ends of a servo arm and attach it to the elevator servo. Use the adjustable connector provided and slide the control rod through it and into the guide tube. Install another adjustable connector onto a control horn. Then slide the pushrod wire into the connector as shown in photo 27 and hold it in place against the elevator. Mark the horn mounting holes.

Push a large modeling pin through the marked holes. Install the control horn as shown.

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Install the rudder servo in the same manner. The rudder mounts using a combination of two standard Mylar hinges in the upper part of the vertical fin and a metal rod through a bearing in the lower section. The metal rod is actually the tiller for the steerable water rudder. Make sure the lower rod is in place while gluing in the upper hinges.

Install the rudder control horn as was the elevator horn. Check and center both the elevator and the rudder NOW. Once centered, remove each of the lock bolts in each servo’s adjustable connector. Apply plenty of thread locking compound to each locking bolt and re-install. Once the blisters are glued in place, you will not be able to re-tighten these set bolts.

Great Planes does include extra blisters in case servo maintenance should become necessary. But a little forethought here goes a long way later. I would imagine that removing a blister would be a no-fun project while installing a new one and getting it water tight would be more difficult than I would enjoy doing.

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Moving forward, this would be a good time to install the drain plug. You do not want to test float your new Catalina without this plug in place. No, I didn’t do that, but make sure you don’t do it either.

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The twin ESC’s mount one to each side of the internal wood structure bracing the battery tray. Position the ESC’s so that their motor wires are long enough to reach up in the pylon to connect with the motor wires coming from the wing. The battery installs just in front of the speed controllers. Note the adaptor that connects both ESC’s to the single ElectriFly 3200 mAh, 3-cell, Lithium Polymer battery.

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The FASST 2.4 GHz R606FS 6-channel receiver mounts just under the pylon using hook and loop tape. The FASST system uses frequency hopping technology to rapidly switch between the 80-available frequencies to prevent interference. The computer transmitter allows setting up the flaperon, differential, dual rates and exponential options that help the Catalina be so easy to fly.

Note that the twin receiver antennae, the light gray wires in the photo, branch off to form a right angle to each other. No matter which 2.4 GHz system you are using, always remember to ensure that the multiple antennae are always 90-degrees to each other.

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A lot of wires exit the pylon. I put the six motor wires, each clearly marked, up through the narrow part of the pylon so that they would stay in place and be accessible when the wing was removed. The wires were just long enough to reach the pylon’s top and I didn’t want to have to fish them out of the fuselage before each flying session.

The aileron wires exited through the larger “hatch” as they were more than long enough to remain outside the fuselage once the airplane was disassembled.

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A dimple marks the spot where each of the non-functional plastic wing struts attach to the fuselage. Drill the small hole and attach each strut using the small screws provided. Remove the screw and strut. Then use some thin CAA to reinforce the threads inside the holes.

The last construction step is to install the two rear blisters. Save this task for the end. Put everything together first, make sure everything works as planned, especially the rudder, water rudder and elevator.

Test the motors, without propellers installed, and check that they respond properly and rotate in the correct direction. Center the ailerons and check their movements. Set up the elevator and rudder movements as directed. Only after everything works does it become time to install the blisters.

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Use low-tack masking tape for the blister installation. I used the so-called “canopy” glue for this installation as the first adhesive. The glue dries clear and is water soluble before it cures so any excess adhesive can be easily removed. Once cured however, the adhesive molecules “cross-link” to form a very strong and water resistant bond.

However, this part of the Catalina is frequently under water while taxiing. I took the second step of masking off the fuselage area just outside each blister and the blister itself. I applied clear bathroom silicone adhesive to form a fillet around the blister where it contacts the fuselage. The silicone not only fills in any areas that the first adhesive might have missed but also adds another layer of water resistant sealer to protect the canopy glue.

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Finally, install the twin 8 x 6 in. propellers (GPMQ6610) that were included in the kit. The propeller adaptors are also included.

Photo 41 Photo courtesy of Great Planes

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Going from the box contents on the left to the completed airplane on the right required about 11 hours. There were many “new” techniques to learn but learning them made me a better builder. And, they were not that hard to learn anyway. My own thought is that 11 hours is not much of an investment to own and fly such a unique aircraft as the one on the right. What do you think?

Flying the PBY Catalina

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Sport Aviator does not review many twin engined airplanes. The usual twin airplane is more complex and difficult to fly than Sport Aviator’s review guidelines. Most readers know that if an airplane is reviewed in Sport Aviator, it will be either a Basic or Advanced trainer or a sport airplane that most newer pilots will have no difficulty in flying. Some of the airplanes selected, like this twin, are surprising.

The big Great Planes Curtis P-6E Hawk was one such surprise. Although big and powerful, the Hawk’s flat bottom wings and low wing loading made this a fun, and easy, airplane to fly. Like its brother, the Great Planes Tiger Moth, The Hawk is a true kiddy car once airborne. It has no vices, will fly extremely slowly if asked, looks great and glides absolutely forever given half a chance.

The Catalina is another such surprise. It also has a flat bottom wing with a very low loading of 18.7 oz per square foot. This wing loading is well in the Basic Trainer range. The Catalina’s slow flight, gentle handling and superb glide performances reflect this low wing loading. If it had only one power source and a more conventional construction, the Catalina would qualify as a basic trainer instead of a sport airplane.

Its twin motor configuration does not take it out of the newer pilot’s flying abilities as its motors are electric powered. An engine-out scenario is unlikely, although one was experienced during the initial flight testing. This is an excellent sport flyers airplane yet its flight performance is far from boring or limited.

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Once afloat, the Catalina is level but low in the water. Full “up” elevator must be held during taxiing to keep the nose level above the waterline. Slow speed taxiing looks much like photo 45. But once some power is applied, the airplane immediately picks up its nose and rises out of the water as shown in photo 46. The water rudder is very effective at maintaining directional control even in moderate crosswinds.

As photo 46 shows, the rear blisters are in the water much of the time while taxiing. You can see why the extra silicone sealer was added. Once full power is applied however, the Catalina rises out of the water nearly instantly even without “up” elevator (photo 46).

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The takeoff run into the wind is easy to manage as long as the floats are kept out of the water. The Catalina has not tendency to “dig in” a tip float unless the pilot commands it to do so. Keep the wings level during the “water” run. Even in a crosswind (one of water flying’s advantages is that most takeoffs and landings can be flown directly into the wind), the Catalina handles well and does not tax a pilot’s skill. Part of that is because the time on the water is extremely short. Takeoff requires about 40 feet. This airplane has a lot of lift and a lot of power.

Do not ever “yank” or “horse” the Catalina into the air before it is ready to fly. Even if you are quick on the rudder during the resultant snap roll, this airplane will not recover level flight in its own length and so will hit the water. Fortunately the water is softer than the ground at takeoff speeds so no damage will be done but you will be out “boating” for a while. Besides, with so much power and only a 40-foot run, there is no reason to make this airplane fly too soon (except for flight testing of course which you now do not have to do as we already have).

Once airborne, the Catalina climbs at a good rate. My guess would be around 750 ft. per minute. Most model seaplane flying sites are “tight” and have trees close around the “runway”. This site was no exception but the Catalina would clear all obstacles with a hundred feet to spare; maybe more.

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Fly-bys with the twin-motored Catalina are impressive. The matched propellers make just enough noise to impress but not too much to annoy. The Catalina looks great in the air and attracts a lot of attention.

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While straight flight is impressive, we all know that even sport scale models should perform far above their full-size counterparts. The Catalina is no exception to this rule. Single slow rolls require elevator input while inverted to keep the nose level and in knife-edge to prevent the airplane’s “walking”. There is not sufficient rudder control for extended knife edge flight but point rolls are no problem. Using all the controls at the proper time can result in a level slow roll more than 300 feet long. Watching this twin fly like that is the reward you get from making sure all those surfaces were properly aligned during construction.

Flying dual fast rolls are not a problem but use a lot of “down” elevator while inverted if you try for that elusive third consecutive roll. When flying point rolls, don’t spend a lot of time at the points, especially at the knife edge ones. 8-point rolls are easier to fly with the Catalina than are the 4-point rolls as the airplane has no pulling tendencies at the 45 degree points.

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Inverted flight is extraordinary for a flat bottom airfoil. Little “down” elevator is needed while inverted to hold up the nose. The Catalina’s outside loops from the bottom are about 75 ft. in diameter and round. About half the available rudder is required over the top to maintain heading. But the extra motor power is sure there when you need it.

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Inside loops are easier and larger. The Catalina will fly inside loops at least 100 ft. in diameter since no rudder is required to stay on course. When upright, the Catalina will track as well as any sport airplane, maybe better. There is a lot of roll coupling; rudder input also rolls the airplane. But it is manageable and does not detract from the airplane’s aerobatic abilities

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However, the roll coupling does manifest itself in the stall turns. Almost full aileron is required at the stall point to stay wings-straight during the 180-degree rotation. But the rudder does rotate the airplane quickly and is powerful. Photo 55 was actually taken during a figure “M” maneuver.

A figure “M” is performed by first going full vertical from level flight, rolling 270 degrees and then doing a stall turn. The airplane then rolls another 270 degrees in the downline. Now inverted, the Catalina pushes into a half outside loop back to vertical on the other side, 270 degree rolls on the way up again, stall turns and rolls another 270 degrees down to upright flight.

And yes, the Catalina has more than enough power to fly this maneuver but the pilot must manage the airplane’s energy well; keeping the uplines short. The Catalina’s high roll rate makes this possible.

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After flying its decidedly non-scale maneuvers, even the Catalina has to land. After all, the “beach” is where the food is! The Catalina will fly short approaches without difficulty. The twin propellers at idle and its wide body plus the tip floats create extra drag that makes managing the approach speed child’s play. Back off a little on the throttle and the Catalina immediately starts to sink. Bring back the throttle just a touch and the airplane settles into a semi-flaired attitude ready for a gentle touchdown (photo 57).

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Carry about 15% power into the touchdown to maintain elevator control once the water’s drag starts to slow the airplane. Start adding “up” elevator slowly as the airplane settles into the water. Even without the final “up” elevator, the Catalina never showed a tendency to dip its nose during landings or takeoffs.

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Electric-powered twins do not usually have to fly around on one motor so single-engine performance was not a test criterion for this airplane. However, the Catalina must have felt slighted that the full twin testing procedure was not being done. Its very first flight was from “Lake Shawnee” (see video 1, “Field Tour” in the Baggage Compartment article on the Fly Cam One review). Lake Shawnee is a large puddle that forms after the Delaware River floods the field.

Immediately after photo 60 was taken, while the airplane was at stall speed and only about 15 ft. above the ground, full power was applied. The airplane immediately threw its left propeller. Well below its single-engine control speed (Vmc) the Catalina immediately rolled hard left and pointed straight down. I am happy to say that even in such a bad situation, the Catalina was able to regain level flight in time to avoid an unplanned aircraft-ground interface. Rather than risk further single engine flight on its first airborne trial, the Catalina was hard landed in the “rough” with no damage. This is why I know this is one rugged fuselage and airplane.

Summary

Because of its twin-engine configuration, we tested this airplane far beyond our usual procedures. After about 35 flights, I am happy to report that any new RC pilot just out of Basic Trainers will have no problem flying this attractive and special airplane. While gentle and easy to fly, this airplane can fly with the better performing sport airplanes with pride.

Just make sure to properly install the propellers (the left propeller adaptor was factory drilled 1/16 in. too shallow which Great Planes immediately replaced) and check that both seat equally. After that, this is one airplane that is unique, easy to manage and extremely rugged.

For more information on this special, $130 airplane, click here.

Additional Aircraft Specifications Manufacturer: Great Planes               Length:           34.25 in.          Cost: $130.00                                     Wingspan:       53.5 in. Radio: Futaba 6-ch FASST                  Wing Area:     395 sq. in. Servos: 2Futaba S3114+2 S3107       Wing Loading: 18.7 oz./sq. ft. Engine: 2- Rimfire 28-30-950kv         Weight:           3.2 lb. Airfoil: Flat bottom Special Airframe Features: Strong fiberglass fuselage, Twin engined, Pylon mounted wing and semi- “T” mounted stabilizer.

Notable Positives Excellent aerobatic abilities Extremely fast assembly Installed motor and aileron wires Light flying weight Twin engine performance Good single-engine abilities Notable Negatives Weak Knife-Edge Performance Blisters must be well sealed

Setup Information Center of Gravity: 2 1/8 in. back from leading edge Control Movements: Elevator = 9/16 in.  Rudder = 7/8 in.    Ailerons = 1/2 in. with 15% differential Exponential: Elevator = 40%     Rudder = 60%   Ailerons = 35% Flaperons: Active but had little effect

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