Osker (oz7766)

About this Plan

Osker. Radio control sport seaplane.

Quote: "Because I live in Vancouver, Canada, with the sea only a stone's throw away and many lakes resting still between the mountain peaks, I was moved to build a seaplane. That was four years and many seaplanes ago.

Difficulties always arise when I try to fill the car with picnic and camping equipment, and then try to stuff in a six-ft seaplane wing and a five- to six-ft fuselage. Then follows the cramped drive to the flying site. Out for a flight and - sploosh! Wet servos, as usual! $e/o&*/t! Oh well, to the beer and sun-shine for the day, while everything dries out. A beer, a chair and thought. Scratch, scratch - a finger full of dan-druff and a thought: receivers sealed in plastic bags inhale water because the air in the bag contracts when the bag is immersed in cold water - thus a wet goodie.

Scratch, scratch - another thought: an upright glass will hold water, but turn it upside down and it will not. To date, all high-wing seaplanes use an upper access hatch to the radio compartment - the upright glass. An inverted glass, if used, would have to be held above the water. This would eliminate direct contact with cold water temperatures, thus reducing any water inhalation which may occur. Now, to keep the radio dry, we may as well put a lid on our inverted glass (the radio compartment) to prevent any splashing. Scratch, scratch, flick - another blob of dandruff lost in the sand. How can I put the radio together, so that there are no extension plugs and only one radio compartment? Let's see - motor on wing, ailerons on wing, elevator on - wing? Rudder on - wing? Ah! The whole radio in an inverted glass on the wing. Now what do we land on: a ski or a float? As usual, a float. Motor on a wing, wing on a glass, glass on a float, with the radio under glass—you're crazy! Let's try it.

The result of those misguided thoughts was Osker, my mid-sized seaplane. The desire was for a 35-45 size aircraft that would fit on the back seat of my car. Simplicity of construction and economy were considered, since sea birds eat a lot of green stuff.

Osker has a 56-in span with a ten-in chord. I was also after some performance, so I wanted the aircraft to be as neutrally stable as possible. This led me to the symmetrical wing with no dihedral. The angular difference is 0°-0°. However, with the high thrust line, I knew some up thrust would be required. How much was uncertain, so I made it adjustable - this was accomplished by an adjustable engine pod.

With these thoughts fabricated, I went to the seaside and gave Osker a try. What a shock! I did not bother checking the balance and I started off with 30 up thrust. Osker took off in five ft, jumped up eight ft, down five ft, up ten and down four. After two mins of this, I managed to flop her on the water. Balancing was achieved with nose weight and a few flights later, 1-1/2° was found to be the best thrust angle. Now she will do double stall turns, inside and outside loops, etc. Now, if you are interested, take a clean swipe over your workbench and let's go!

CONSTRUCTION Start construction by cutting out the sides of the hull from 1/8 x 4 x 48 in medium weight balsa. The widest bulk-heads in the hull utilize four-in, wide stock. The top keel is 1/8 x 4 inch stock. Cut the front bulkheads to size, and the top keel to length. Assemble the bulkheads and the keel on the fuselage sides upside down, checking for alignment. Put the center keel in the front. Sand the front hull to correct profile, and plank the bottom. Lift the hull from the board and install the sub-rudder; then finish the rear with cross planking. Put the one-in. sq. stock on the top front, sand flush when dry, and then cross plank the top bow. Carve and glue the nose block. This gives you the basic hull..."

by TR Thorburn, June 1974 AAM.

Update 02/06/2016: Added article, thanks to RFJ.

Update 1/3/2022: Replaced this plan with a clearer copy, thanks to JJ.

Direct submission to Outerzone.

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