USA # 2-1999
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RC MODELER ( FEBRUARY 1999 ) |
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RC MODELER [PAGE 1] |
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While we were adding more of Prather's stick-on
weights to the firewall, we received a call from the 3 Sea Bees who
told us that their recent flight tests indicate that the C.G. should
be forward of the location indicated in our prototype assembly
instructions. We mentioned that we had just discovered the same thing;
with a "normal" .60 on the firewall, weight must be added.
(A procedure for modifying the firewall for a 4-stroke engine is now
included in the revised assembly instructions. That seems like a great
idea since the plane needs the additional weight and a 4-stroke will
swing a larger, more scale prop.) The total weight of the plane on our
first test flight was 8 pounds 2 ounces, with the C.G. 8.5cm behind
the leading edge of the top wing. With the addition of the nose
weight, the total weight increased by 14 ounces, to bring the plane to
a total of 9 Ibs. The C. G. was now located at 6.5cm behind the
leading edge of the top wing. Out at the flying field, again, we
taxied to the runway and gradually opened the throttle. The tail
lifted in a few feet as it picked up speed for a more
"normal" lift-off. Up at altitude, some minor elevator and
aileron trimming was done and we were ready to relax and enjoy the
plane. Thanks to the undercambered airfoil, there was no indication
whatsoever that it was carrying additional weight, other than it was
flying as we hoped it would. Response to the controls was fine
although we usually have them set up for maximum throw and go easy.
After flying a loop or two, some gentle axials, a wing-over, Immelmann
turns, and such, we decided that the aileron throw should be reduced a
bit. Still somewhat cautious about the location of the C.G., we got
the Tummy quite high, gradually throttled down while dragging up
elevator, then hit full left rudder just before the stall and over it
went into a spin. After a turn or two, we flew out of the maneuver
-just to play it safe until we were absolutely sure the C.G. was where
it should be. After more flying to check control throws and slow
flight handling, we felt it was time to set up for the touchdown. As
we had come to expect, the landing was super smooth and uneventful,
but with the exception that when we made a hard turn to the taxiway,
one of the tires came off the hub. A shot of thick Hot Stuff assures
that this won't happen again. I should have done that before our first
flight!
Conclusion There's no doubt that there are many modelers very involved in R/C who really enjoy exercising their craftsmanship in order to build a scale or stand-off scale airplane. Unfortunately, however, there are also many of us who would like to show up at the field with a neat stand-off scale R/C plane, but just can't find the hours of building time needed to create one of those beautiful models. If you don't have the time to build, but prefer to cover and do the detailing, the Tummy is available in a framed-up version. On the other hand, if your time is limited or you just don't feel up to the detailing task, you can get the Tummy (or others from the 3 Sea Bees) as what we prefer to call Custom Built rather than ARF. (Most ARFs require some airframe assembly such as gluing the wing panels together, gluing the tail feathers in place, and so on, but the Tummy doesn't require any such work!) Completely built and assembled at the factory, their planes are then disassembled and carefully packaged for shipping. (We found no shipping rash anywhere on our plane.) Install your R/C system and engine, check the C.G. and control operations, and you're ready to go. (We've even heard rumors that the 3 Sea Bees are thinking about marketing some planes with radio and engine installed!) The Tummy is a good-looking standoff scale model. It is very well built using lots of hardwood and balsa with aluminum trim and is covered with Solartex and painted to scale. If you glance down inside the fuselage, for example, you'll find that all of the bamboo diagonal bracing is gusseted. With its undercambered airfoil and a .60 up front, it's a very gentle flier -as was the full-size aircraft -and it looks great in the air. Since it's not a plane you'll find allover, it's also a real attention-getter. And there's one other thing we also want to mention: In our view, the 3 Sea Bees is a very responsible company. If they discover a mod that will make their planes look or fly better, they immediately fax or mail a bulletin to those who have purchased a plane to let them know. We're convinced that when they say they want to market a fine product, they mean it. And it is! |
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To make room for the receiver battery on the
shelf, we moved the factory servo cut-out in the ply tray about
1/4" toward the receiver box. We also moved the rudder servo
cut-out in the floor of the fuselage toward the fuselage side so the
rudder cable idler arm wouldn't hit the side of the servo. While all
of the pull-pull cables are factory set up for you, be sure to check
all of the wedges to assure they are snug. Not all of ours were
-although they were probably left that way so we could make final
adjustments without undoing their work. The factory installed rudder,
elevator, and aileron servo linkage all work fine. For the throttle
linkage, which must pass under the fuel tank to the other side of the
firewall, we mounted an idler arm to which the throttle linkage and
servo linkage were both attached.
To lock the hatch in place, we put a screw through the firewall into the forward hatch bulkhead at both sides. The plane is designed so that tail feathers can be removed for transport by unscrewing four screws. While the elevator halves are attached with what appears to be a 1/4" wood dowel, it isn't really wood, it's a flexible bamboo-type material. We mention that because you will need to adjust the pull-pull cables on each elevator half carefully to assure the elevator halves are aligned. One advantage of using bamboo is that the elevator halves can be independently adjusted, if needed, for optimum flight performance. The instructions point out that it may be necessary to push quite hard to get the bottom wing to fit to the wing saddle. We pushed so hard, we were concerned that we might crush the fuselage, but it still didn't drop in place. To avoid the hassle, we filed and sanded the block at the back of the wing saddle and the back edge of the wing cut-out. With this mod, the bottom wing goes in place more easily. The sanded areas were then sealed with thin Hot Stuff CA, as was the firewall, to fuelproof them. The full-size aircraft flew with a tail skid, which is what you'll find on the model. If you fly off of a grass field, that's no problem. It can be a real problem though, if you fly off of blacktop. Because the fields of the four clubs to which we belong are blacktop, we designed an easy-to-switch-to tail wheel assembly (takes only a removing and reinstalling of four screws), and the tail skid can easily be reinstalled for show. Or, you can forget the tail wheel, if you prefer to keep the plane true to plan. When we first assembled the complete plane, we discovered that the wheel axle goes above the bottom of the strut and is held down to the strut with a couple of elastic bands on each side. The advantage of that installation is that, depending on how much you have stretched the elastic bands, you have some shock absorbing in the axle. And, you will need to custom-fit the dummy engine provided to your engine. |
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First Flights Just about ready to go when we unpacked it, the engine and R/C installation work was done and the minor mods we did were completed. The C.G. was set up 8.5cm aft of the leading edge of the upper wing, as recommended in the prototype assembly instructions. Everything was ready to go with the exception that the dummy engine was not installed to permit easier engine adjustments, if needed. It took us about 15 minutes at the field to put the wings in place and connect all of the flying wires. That process alone began to draw some onlookers and question-askers. When we commented that the plane was an ARF, they couldn't believe it. Our Clarence Lee K&B blueprinted and fine running Veco .61 with the 12 x 6 prop started easily and we taxied out to the flight line -looking good. After the run-up to clear the engine, we pulled onto the center of the runway and eased the throttle open. We blinked and it was airborne and was heading for the clouds. Oops. Holding down elevator to keep the plane from going straight up, we easily climbed to a safe altitude. At that point, we throttled down and put in all the elevator down trim we had -which wasn't enough. It still wanted to climb. In order to get the nose level, we had to hold about 25% down elevator. Because it flew like it was tail heavy (rather than a thrust problem), our decision was to get it down before we'd use up more fuel and have even more of a handful. Holding down elevator, we throttled down and headed back for the runway. Despite the fact that our knees, thumbs, and just about everything else we had was shaking real good, the touchdown was' uneventfully slow, smooth, and gentle -no bounce to the ounce. In the pit area, we pulled the prop nut and added a prop shaft weight and a 2 oz. "heavy nut." About 4 oz. of Prather stick-on weights were also stuck onto the firewall where there's plenty of room. On the next take-off, the plane stayed on the runway longer, although once airborne, we had to put in full down elevator trim again. Apparently, the C.G. should be at least 1/2" forward of the location indicated. Since we had used up all of the stick-on weights in our flight box, we elected to pack it in for the day and finish the job back at our workbench.
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RC MODELER [PAGE 1] |
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RC MODELER ( FEBRUARY 1999 ) |
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