Pond Baby (oz2233)

About this Plan

Pond Baby. Micro RC seaplane, 3 channels and an electric motor.

Direct submission to Outerzone.

Note for the original 2-page Pond Baby article online (RC MicroFlight site is now defunct) see waybackmachine at: http://web.archive.org/web/20050403154452...

Quote: "I am completely inexperienced in the design of seaplanes. I lived near the ocean for many years, but salt water is very unfriendly to electronic gear, so I avoided operating models in it and was very satisfied as a landlubber. We now live on a farm with a pond. Considering how much fun I have had with land-based micro electric RC models, I decided to give a seaplane a try.

My inexperience probably worked in my favor because I had to check back issues of model magazines and study successful designs. In particular, I give credit to the late Don McGovern, who wrote much about seaplanes in Flying Models. Woody Blanchard also gave me many useful concepts.

Armed with this information, I pulled out a fresh sheet of paper and began to lay out the features I wanted in Pond Baby. I faced issues I had never dealt with: how deeply would it float? What about the very high thrust line? Would the hull behave normally at this small size? Out came the handbooks to calculate how much water Pond Baby would displace; this led to the hull width I selected. Thrust line? Mount the motor with some upthrust and give it a try. Hull effects? Table this one, and assume the model will work well! The rest of the design process followed Blanchard/McGovern thinking with some of my micro RC experience mixed in.

I avoided having to build a new wing by pulling the wing off my Pixie prototype. This also helped to determine the size of the rest of the airframe. The construction of the hull/fuselage (called a "hull" from now on) went quickly. I cut the tail out of 1/16-inch-thick sheet balsa and mounted it. I made the motor mount out of a sandwich of balsa and plywood and glued it to the wing, then I carved a set of tip floats out of soft balsa.

Because I’d be tossing this little bird into the water, I decided to paint the wooden parts and then wax them. I mounted the DC5-2.4 motor with a 4.2:1 gear set driving a 5.25-inch prop cut from a 6-inch Peck Polymers plastic prop. For good measure - and to cause a little confusion - I mounted a balsa replica of a glow-plug engine on top of the motor. The battery is a 7-cell 50mAh Ni-Cd positioned in the hull bottom to provide the correct CG. I used one WES-Technik servo and one cut-down Hitec HS-50 servo, and my speed control is an FMA Mini 5. A trusty Sky Hooks & Rigging receiver passes on the control wiggles, and the servos drive the controls with 0.015-inch-diameter wire pushrods run through a few bushings.

After strapping the tip floats into the predicted locations and clamping the wing assembly onto the cabin top, I fastened the long receiver antenna to several corners of the airframe - ending on the fin, to avoid its dragging in the water.

A braver person would probably have headed straight for the pond, but I still had a few concerns about flotation. When the family was elsewhere, I headed for the bathtub. Hallelujah! It floats - and at about the right level as well.

Bearing in mind all the unknowns, I headed for the pasture and a hand-launched flight. Right from the start, Pond Baby behaved like a dreamboat (sorry!). Power affects pitch trim slightly: full power holds the nose fairly level and fast, while power-off, trim is a little nose-up. Ready for sea trials!

At the pond: With a fresh battery charge, I switched the radio on and slipped Pond Baby into the water. Would the rudder have any effect while taxiing on water? Sure; I taxied out from shore and turned the bird into the slight breeze. Full throttle brought Pond Baby up on step very quickly, and things looked great; then, while I held full throttle, it suddenly cut back and started to surge up and down. The solution was a 'buggy whip' antenna for water operation.

Having solved the signal problem, I went back to the pond. Now, when Pond Baby started to pick up speed on the step, it would suddenly whip around in a 'water loop.' I had overdone the tip floats streamlining by bringing their rears to a point, and when one touched the water at speed, the drag was excessive. The solution? I cut out two patches of very thin soda-can aluminum and fastened one to each float to create a planing surface.

Recharge, and back to the pond. At last, Pond Baby whizzed across the surface and lifted off with just a touch of up-elevator. Neato! After a couple of laps, I realized that I had never made a water landing; perhaps I should try it. Power back and trim for a nose-high touchdown; looking good until it touched the water! I was reminded of a Disney film about poor birds making awful landings. Pond Baby was not broken, but I hadn’t sufficiently sealed the cabin around the wing, so water sloshed around inside.

Dried out and with a better cabin seal, things were coming together: smooth liftoff and cruise and then set up a landing with more speed so that the touchdown would be in the planing attitude similar to a takeoff (just like a tail-high landing with a tail-dragger). This was the fix! I explored the flight envelope: Pond Baby looped, rolled and did a nifty stall turn, but its real charm lies in the water operations.

Construction: In micro RC models, wood selection is vital to control weight. I used mostly 1/16 and 1/32 balsa sheet; one sheet of 1/16 x 3 x 36 balsa should weigh no more than 15 grams (½ ounce), and the 1/32 stock should weigh half of that. The same applies to nose blocks: the lighter the better. I strip my stock from the lighter sheet wood, and I use Goldberg medium CA and Hobby Lobby’s Oracover Light for the wing. You’ll also need 1/64 plywood and 0.015-inch-diameter music wire.

Wing: Lay the plan flat and cover it with wax paper. The trailing edge (TE) must be shimmed up to match the airfoil angle. Clamp the edges into place and then glue in the ribs, tilting the two center ones for the dihedral. Add the top spars and center sheeting; when the glue is dry, flip the assembly over and glue in the bottom spar. Use a sanding block to trim the angle at the wing center, then glue the panels together..."

Update 17/4/2023: Added article, thanks to theshadow.

Supplementary file notes

Article.

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