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Thursday 28 de October de 2010 12:56

"como armar una replica del avion de sarabia"

  RCU Review: Great Planes Gee Bee ARF

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  •     Contributed by: Henry Korczak | Published: July 2004 | Views: 91015 | email icon Email this Article | PDFpdf icon


    Posing Time
    Manufacturer Info

    Great Planes
    P.O. Box 9021
    Champaign, IL 61826

    Phone: 217-398-3630
    Fax: 217-398-0008

    Watch video of the
    Great Planes Gee Bee

    Ease of assembly:
    Basic aerobatics:
    Advanced aerobatics:

    • Fast assembly
    • Well constructed
    • Beautifully painted fiberglass fuselage, cowl and wheel pants
    • Excellent manual
    • High cool factor
    • Flies great!

    • Some assembly steps out of sequence
    • Belly pan difficult to fit

    • Outstanding painted fiberglass fuselage, cowl, wheel pants and rudder.
    • Built up and MonoKote covered wing and stabilizer.
    • Trim scheme expertly applied.
    • Complete hardware package includes: fuel tank, wheels, tailwheel assembly, pushrods, control horns, clevises and misc. nuts, bolts, screws etc.
    • Pre-painted canopy.
    • Painted pilot figure.
    • Dummy engine assembly.
    • Detailed decal sheet.
    • Excellent assembly manual.
    • Foam building/storage cradle.
    The Gee Bee Story

    Established in 1929, Granville Brothers Aircraft of Springfield, Massachusetts started a business of building small private planes. In the beginning they sold well, but the depression pretty much killed the aviation market and almost killed the Granville's company. In the prevailing years, the Granville brothers designed several radical planes with high performance. The most notable of these was the Gee Bee Model "Z" racer. Tragically though on December 5th, 1931 during a record speed attempt, the "Z" racer abruptly pitched its nose upward, shed its right wing and rolled into the ground instantly killing its pilot, Lowell E. Bayles. Undoubtedly you've seen this spectacular crash in old newsreel footage. In 1932, famed distance pilot, Russell Boardman had purchased 51 percent of the Springfield Air Racing Association (SARA) and placed an order for two racing planes with the Granville's. The new racers were to be designated the R-1 and R-2. The two aircraft were identical except the R-2 had a different cowl shape to accommodate the smaller Pratt & Whitney Wasp Jr. engine and a slightly longer wingspan. It was hoped that the R-1 with a Pratt & Whitney 1340 Wasp T3D1 engine rated at 550hp (jazzed up to 740hp) would be fast enough to win the 1932 Shell Speed Dash as well as the Thompson Trophy Race. While the R-2 with its smaller engine and greater fuel capacity and range, was used to hopefully win the Bendix Cross Country Race.
    How did the Gee Bee racers obtain their distinctive barrel shape? Racing plane design wisdom in the early '30s dictated that the fuselage should be as narrow as possible. Zantford "Granny" Granville and design engineer Howell W. "Pete" Miller reasoned that a teardrop-shaped fuselage would be the best way to streamline the big radial engine and applied the following aerodynamics. By conducting drag tests on fuselages of varying fineness ratios (length: diameter), tests showed that minimum drag was attained at a fineness ratio of 3.00 to 3.50. The Wasp engine was 54 inches in diameter and the fuselage diameter was 61 inches at its widest point. With a fuselage length of 17 feet 9 inches, a fineness ratio of 3.50 was obtained. This showed that large frontal area would create less drag than a smaller frontal area. Using wind tunnel test data, Miller predicted that the Gee Bee would have a top speed of 298mph. This turned out to be very close indeed, as the Gee Bee had an actual top speed of 296.2mph.

    In 1932, the legendary Jimmy Doolittle flew a Gee Bee to win the Thomson Trophy race and on September 3, 1932 he set a world landplane speed record of 296.287mph in the R-1. Within a year though, both the R-1 and R-2 had crashed, and in 1934 the eldest of the five brothers, "Granny" was killed in another accident, and with the driving force missing, Granville Brothers slipped into bankruptcy and history.

    Full-Scale Gee Bee Data
    Wingspan: 25 ft.
    Wing Chord: 4 ft 5 in.
    Wing Area: 100 sq. ft.
    Length: 17 ft 9 in.
    Fuel Capacity: 160 gal.
    Weight Empty: 1,840 lb.
    Weight Fully Loaded: 3,075 lb.

    Kit Name: Gee Bee ARF
    Manufacturer: Great Planes
    Price: $279.99
    Wingspan: 68 in.
    Wing Area: 743 sq. in.
    Length: 45 in.
    Ready to fly weight: 12.5 lb. (less fuel)
    Wing Loading: oz./sq. ft.
    Engine Used: O.S. FS-1.20 Surpass 4-stroke
    Fuel Used: Cool Power 15%
    Prop Used: APC 15x6
    Radio System: Futaba 9C transmitter

    (6) Futaba S3004 Standard BB Servos;
    (2) ailerons,
    (1) elevator,
    (1) rudder,
    (1) throttle

    Channels Used: 4 total: aileron, elevator, rudder and throttle

    Required Items:

    4-channel radio with 6 servos (minimum 40 oz-in torque)
    2-stroke .91 - 1.08 2-stroke or 4-stroke 1.20 engine
    Fuel tubing
    2 - 12" servo extensions
    Servo reverser for elevator servos
    Thin and medium CA, 30-minute epoxy
    Assorted drill bits
    Dremel Moto-Tool
    Standard building tools


    The Gee Bee doesn't have a lot of parts and assembly goes fairly quickly. A unique feature of the kit is included fuselage cradle. When you unpack the box, you'll notice that the fuselage is held in place with foam cradles. Don't throw these parts away! They are actually part of a foam cradle that you assemble to hold the barrel fuselage during construction. There's a total of 8 pieces, 4 cradles for upright and inverted building/storage, 2 extensions that lift the fuselage higher off your workbench and 2 heavy-duty plastic pipes that slide into holes in the cradles. I thought this was very cool of Great Planes to include such a handy accessory.
    Before getting started it's always a good idea to study the instruction manual. You'll gain an insight on how the model is built and what tools and supplies you'll need. In the Gee Bee's case there are a few steps that I felt were out of order. I'll touch on them as I go along.

    As with most ARF's, the first thing to do is to heat up the covering and trim iron. My Gee Bee had a few wrinkles and a couple of seams needed to be touched up. Nothing out of the ordinary here. I also took the time to cut up the sheet of CA hinge material into individual hinges. While I have the iron out, I check the manual and remove the covering from any openings (like servo pockets), this makes assembly go quicker. For small openings like the slots for the landing gear, I used a pencil soldering iron to melt the covering away. This method is a lot easier than using a knife and a no. 11 blade.
    Wing Assembly

    There's not too much to do to assemble the wing and is typical for an ARF model. The first step is to hinge the ailerons to the wing panels. The precut hinge slots were deep enough and only required the weep holes to be drilled. Next the manual has you install the aileron servos. Remember I said that a few steps were out of sequence? Well here's the first one. If you went ahead and install the servos and landing gear assembly, especially the aileron left servo, when it came time to apply the rather large decal on the bottom of the left panel, you'd have to remove the servo, linkage and the landing gear assembly to apply the decal. It's much easier to apply the decal now and then proceed with the wing assembly. After I applied the decal, I installed the servos and made the linkages from the supplied materials. Just make sure that when you install the aileron horns, you mount them on the plywood pads.
    The instructions now have you join the wing panels together and then install the landing gear. I decided to install the gear first as it's a lot easier to work on the individual panels; there's less chance of hangar rash this way. Each wire landing gear is installed into two hardwood blocks and the main leg is braced with joiner wire that has a "U" bend in it to absorb shock loads. After the gear in inserted into the blocks, make sure that it has a forward rake to it. Eight nylon straps secure the gear in place and it's very important that the straps are place where instructed. If not, they will interfere with the wheel pants. The painted fiberglass wheel pants add all the charm and personality and cannot be omitted from the construction of the model. Great Planes has done a good job here, as their installation is fairly easy and so far, the pants have held up well on my grass field and less than perfect landings. Before mounting the pants, determine which pant goes on the right wing panel (to match the manual's sequence) as the base of the pants is angled to accommodate the wing's dihedral.

    Placing the pant over the installed gear leg and temporarily installing the wheel and its axle determine its location on the wing. Center the wheel in the pant opening and make four marks on the base of the pant for the mounting screws. Make sure that the marks are over the hardwood rails that the nylon straps are screwed into.

    When I made the marks, I used a couple pieces of masking tape to hold the pant still and made reference marks on the wing so I could place the pant back in exactly the same position. Now remove the pant use a 1/8-inch drill bit and drill the holes at an inward angle. Don't drill the holes near the lip of the pants, you'll crack and chip the fiberglass. Remount the pant and transfer drill the screw holes into the wing and then use the supplied #4 screws to secure the pant. It's a good idea to remove the screws and harden the screw holes with a few drops of thin CA.

    The pants are reinforced inside on both sides of the wheels with plywood pads. Make sure you use course sandpaper to thoroughly roughen the fiberglass and then clean the area with rubbing alcohol. The instructions state to use 6-minute epoxy mixed with microballoons for a stronger bond when gluing in the plywood pads. I agree with the microballoons but not the 6-minute epoxy as it doesn't give you nearly enough working time before it starts to setup. Thirty-minute epoxy is a better choice. Repeat the process for the other wheel pant.
    The wing joiner is laminated from 3 pieces of plywood and to make gluing them together easier, I drill a guide hole on each end and insert a 1/16-inch diameter dowel into the holes. This keeps the parts from sliding around when the epoxy and clamps are applied. To securely hold the wing panels together while the epoxy cures, I wrap rubber bands around the wing hold down bolts and the dowels in the leading edge of the wing. Now join the wing panels as instructed to complete the wing.

    I'd like to be able to say that the belly pan (BP) fit perfectly but that wasn't the case on my model. After reading different threads on RCU, I could see that some belly pans fit well and others didn't.

    The first task is to cut a notch in the center of the front face of the BP so it'll fit over the leading edge of the wing. Next install the wing onto the fuselage and position the BP on the wing. It was immediately obvious that the BP was a little too long. If forced to fit in the fuselage opening it would slightly buckle and wouldn't seat on the wing. If the BP were fitted flush at the front or rear, it would seat very nicely on the wing but the opposite end wouldn't be flush with the fuselage. After pondering the problem for a while, I decided to sand the rear of the BP and the rear of the fuselage opening. It took a fair amount of sanding to make it fit half way decently.
    I next drilled the holes for the wing hold down bolts and used a Dremel tool with a stone bit to enlarge it to the proper size. If you use a large drill bit, you'll surely crack and chip the fiberglass. Using a black marker, I traced the outline of the BP on the wing. Following the "Expert Tip" in the manual, I used a soldering iron to remove the MonoKote from the gluing areas where the BP was to be attached to the wing. Instead of using 6-minute epoxy, I again used 30-minute epoxy and taped the BP in place until the glue cured.

    Because the fuselage is so large in diameter, it presents some unique problems that Great Planes solved rather nicely. Items like routing the engine's exhaust out of the cowl, mounting the cowl cleanly and throttle pushrod hook up are all well thought out and easy to implement.

    First is the exhaust. To make room for the muffler, a tunnel in molded into the bottom of the fuselage that the muffler nestles into. Your choice of engine will determine if any cutting of the cowl or fuselage is needed to accommodate your installation. One thing that Great Planes neglects is to mention that you need to use some type of exhaust diverter. If you don't, the hot exhaust gases will hit the front of the belly pan and burn a hole in it. Exhaust fumes will also fill the inside of the fuselage. To compensate for the really short nose moment, the throttle servo is mounted on the firewall near the engine to move as much weight forward.
    Actual assembly starts by mounting the engine. I used the included engine mount as the O.S. 1.20 4-stroker I was going to use fit the mount perfectly after I ground away the supports for the nose gear leg. Thrust line reference marks are molded into the firewall and use need only to use the proper engine mount template to locate the engine and its mount. Next I built the plywood throttle servo tray and fuel proofed it with a coat of alcohol-thinned epoxy. I installed the tray on the firewall where suggested and this worked out well. If you chose, you can install the throttle servo inside the fuselage; it's up to you. Given that the engine is mounted more inverted than sideways, I decided to install an ElectroDynamics EDR-103 on-board glow system to ensure the engine wouldn't quit at low throttle settings.
    The included fuel tank and setting it up is pretty standard stuff and I included a third line in it to make fueling the model easier. The tank is then installed with the neck protruding through a hole in the firewall and secured at the rear to a bulkhead with a #64 rubber band. Before installing the tank, I applied a generous bead of PFM adhesive around its neck, it would help keep the tank in place and provide some vibration damping.

    The cowl on the Gee Bee is a focal point of attention and Great Planes has paid a lot of attention to this area of the model. Instead of simply gluing hardwood blocks around the perimeter of the firewall of the fuselage and then screwing the cowl to the blocks, Great Planes has designed a simple and effective method of hiding the cowl's attachment screws and preserving the clean looks of the model. Great Planes also includes a dummy radial engine that looks great and completes the scale look of the model.
    While the cowl installation isn't difficult, it does take a little patience to line things up properly. Four 1/8-inch plywood mounting tab are glued and screwed to the firewall at approximately 90 degrees intervals. You can juggle them a little for the best clearance, but they must still line up with the cowl ring that is glued to the inside of the cowl. When placing the cowl ring on the fuselage, make sure that it's spaced equally around the sides of the fuselage. After the mounting tabs are glued into place, use some small clamps to hold the cowl ring in position on the tabs. When all looks right, number the tabs and the cowl ring so you can match them up later. Next drill holes through the ring and the tabs and then insert the 4-40 blind nuts into the ring. The dummy engine is trimmed, fitted and painted next but not glued into the cowl until later.
    While the cowl-mounting ring is still attached to the fuselage, the cowl is fitted and glued to it. First thoroughly sand and clean the inside of the cowl where the mounting ring is going to be glued. Next I made a reference line on the inside of the cowl 2 inches in from its back edge by taping a marker on a box of the appropriate height. The cowl is then placed onto the mounting ring and is centered using the engine's crankshaft and the reference line on the inside of the cowl. When it looks just right, tack glue the cowl to the ring with CA. Don't try to remove the cowl before the glue is fully cured.
    Mounting the Cowl and the dummy engine
    Remove the cowl and mix up a batch of 30-minute epoxy and microballoons and apply a generous fillet to the ring and cowl. When fully cured, place the dummy engine over the engine and then attach the cowl to the fuselage. Take a couple of long balsa sticks and rubber bands and loop a rubber band through a couple of the aluminum tubes on one side of the dummy engine. Slide one of the balsa sticks through the rubber band and center it onto the front of the cowl and repeat for the other side of the cowl. This will pull the dummy engine into the front of the cowl and hold it in place. Center the dummy engine over the engine thrust washer and the cutout in the dummy over the cylinder head. Now carefully remove the cowl without disturbing the dummy engine. If it moves you'll have to start over. Tack glue the dummy to the cowl and reinstall it on the fuselage to verify that the dummy is properly placed. When satisfied, permanently glue the dummy to the cowl; I used PFM adhesive instead of epoxy and microballoons as recommended.

    The vertical fin is part of the molded fuselage so only the stabilizer needs to be glued into the fuselage. There's nothing tricky here, just make sure to remove the MonoKote from the gluing area and square it up with the wing before gluing it into place. Because the fuselage is so short and large, you can easily apply glue to the stab/fuselage joint from the inside. Another task that I felt was out of sequence is cutting the pushrod exits into the rear of the fuselage. Having the stab glued in place before cutting them out limits your working room so I made the pushrod exits before I glued the stab in place.

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