by Obi Mapua
After the success of “The Bipe”—the 40-46 (and up) engine sized corroplas biplane, the modelers flying at Baradas wanted a bigger one. How big? Well, something for their gas engines, but reasonably sized so they don’t have to hire a cargo van to bring it to the flying field. They also wanted a gasoline (petrol) engine to power it. The smallest common gas engine was a 23 to 26 cc Zenoah. Now there are the same sized gas engines coming from China, of lower cost. This gave me an idea of how big the BIG BIPE should be. After the pencil, calculator, and CAD pushing, we came up with the following size:
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Wingspan (top wing)
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64”
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Chord (top wing)
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12”
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Wingspan (bottom wing)
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52”
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Chord (bottom wing)
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9”
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Total wing area, 2 wings
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1220 sq. in.
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Overall fuselage length
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56.5” (approx.)
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Height from ground to top wing
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23” (approx)
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It does not look like a big plane, but when you see it on the ground, it’s chunky.
Making a corroplas plane may be quick, but it’s not easy. BIG BIPE was completed in 10 to 14 days. Excited, we rushed to finish it. My Zenoah G-23 was bolted on the firewall, with a 17 x 6 wood prop. The landing gear was “borrowed” from my Ugly Stick, and we put on a pair of 3-1/2” wheels on it. The landing gear was a bit too tall, and the wheels too small. Now to go flying.
Flying: The first take-off was very graceful. A few minutes into the flight, however, we experienced aileron flutter. We landed immediately—a smooth landing, but with the small wheels, and the tall grass on the runway (still not yet cut), BIG BIPE flipped over. No damage—except to the prop, which broke. That’s the end of the flying for that plane for the day. Back to the building board.
The “culprit” was that the aileron was 3 inches wide, and only 1 thickness of 4 mm corroplas. The construction was like the 40-sized bipe, except that the BIG BIPE’s aileron is one inch wider. This was too flexible, even with the bamboo rod stiffener.
At the building board, the aileron design was revised. A folded sheet of 2 mm corroplas was attached to the 4 mm corroplas “hinge”. See the illustration.
The total aileron thickness is now 8 mm. Back to the flying field.
Test Flight 2:
The Zenoah G-23 is humming with the 16 x 10 APC. Another beautiful takeoff. The ailerons don’t flutter this time—the stab does. A quick landing, nice and easy. We don’t flip over on landing this time. Back again to the building board.
The stab/elevator setup was just a simple 4mm plate of corroplas, with just bamboo rods to stiffen it. It was not enough for a big plane like this. It would have to be a lot beefier, and stiffer.
The stab/elevator (horizontal tailplane) is now 8 mm thick; this is made up of two (yes, 2) plates of 4 mm corroplas AND braced with an aluminum strut underneath, AND cable-braced to the fin/rudder (vertical tailplane) on top. It is rigid. This is looking very scale, almost like a Fokker-D7!!
We were able to get 6” wheels, a bit semi-scale, from a second-hand pram (baby carriage)—no, I did not steal this from my grandchildren! This was then attached to the gear. These wheels are nice and light, but the tires are not soft.
Test Flight 3:
Again the Zenoah hums, the 16 x 10 APC a blur. Another smooth and beautiful takeoff. The wings and tail seem to be holding…turn, trim, low pass…nice. Up to altitude, now for the real tests…
Loop: You need to dive to get it “over the top”, then cut power. Really scale. If you try a loop from level flight, it makes an egg-shaped maneuver, dropping down as it goes over the top. Dive for beauty.
Roll: Nice and slow, maybe it will roll faster if I increase aileron travel, but then it will get too “nasty”. Keep the ailerons on the smooth side.
Stall turn: This plane, with this engine, is not a lunar rocket like a pattern ship. It has some vertical, and then you can lessen power and apply rudder. Watch it! That rudder is really powerful.
Inverted: Yes, it does. You have to be careful on this one, as you have to apply a bit of down elevator as the gas engine is on the heavy side. Inverted needs to be executed at full power on the G-23. Do this a bit high, as the roll-in and roll-out are a bit on the slow side.
Spin: Do this also quite high. BIG BIPE spins readily, and in a 3-turn spin, will spin ½ turn extra. This may be due to the momentum from a slightly nose heavy condition.
Stall: Nice and gentle, a forward mushy drop.
Landing: This is the best part. Align to the runway, reduce power, leaving a slight bit just in case it’s windy, and reduce to idle just before final. The glide angle is very steep, but controllable. Easy on the rudder…Lineup is so easy. You can do a mains or a 3-point, it’s up to you.
How is it to fly? Erwin Guinto, one of the test pilots, remarked how much like a real airplane it is to fly—you have to think ahead of what to do; before you move the controls, you apply a little power. Flying BIG BIPE is not a full-throttle experience—you take off with power, then you cruise at half power, pretty much like the real thing. (Erwin flies “full size” ultralights)
Albert Roa, a dedicated pattern flier, remarked at how easy, and sweet, BIG BIPE is to fly. In Filipino, the word is “mabait”, meaning, “well behaved”. Smooth, co-ordinated turns, (ailerons with rudder), and the ease of landing is what he liked very much.
BIG BIPE is not to be handled as “aggressively” as the smaller, 40-46 “Bipe”. It is slower, reacts slower, and has a “heavier” feel to it. Maybe this is due to the G-23—the G-26, I’ve heard, has a bit more power, and this might make a difference in performance and handling. We will test the 26cc engine made in China, and see how this performs. If the engine performs up to expectations, we would like to put it into a BIG BIPE.
The BIG BIPE is still a prototype, and is being refined. We should have more information as to cost and availability by the end of 2007. Keep in touch!
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