DESIGNING FOR WATER FLYING SUCCESS

By BRUCE K. STENULSON

Flying RC aircraft on floats from water opens a whole new world of possible flying sites. In July of 1991, I first flew my modified TELEMASTER 40 on custom built floats from a lake at 12,000 feet. The ground was a carpet of wildflowers, and the sky was dominated by four of Colorado's 14,000 foot peaks which circle the north end of Kite Lake. What a beautiful place to fly!

In July of 1992, the South Park Area Radio Control Society sponsored their first annual Float-Fly-In at Kite lake. I expect that at that time, this may have been the highest AMA Sanctioned Fly-In for powerwed planes ever held. 16 pilots registered to fly, with over 200 spectators present over the course of the day.

On September 30th, 1992, I drove up Mount Evans to Summit Lake, at an elevation of about 12,800 feet. It was another incredibly beautiful day, with only a light breeze, and a dusting of fresh snow on the north face of Mount Evans, which reached from the shore of the lake to over 14,000 feet above. A thin film of ice covered the surface in the quiet water at the outlet of the lake, and there was a definite feel of Fall in the crisp morning air. I set up my TELEMASTER, started and adjusted the ASP .61 engine, then set it into the water and taxied out along the south edge of the lake, walking along the shoreline to follow.

There's always a certain amount of anticipation when you're poised to try an entirely new aspect of RC flying; was I really ready for this? There was, in the end, only one way to find out.

I dropped the throttle to a low idle, and let the airplane weather- vane into the gentle breeze. I pulled in full flaps, close to 60 degrees, then smoothly advanced the throttle to full. The engine sounded strong and solid, and the float plane came up on step quickly and easily, as I had come to expect. As the speed built, the plane ran lighter and lighter on the floats, until it lifted from the water's surface into the nose-up attitude typical of the modified Telemaster's full flaps takeoff. I immediately took out about half of the flap deflection, working out the rest over the next 10 seconds as the plane built airspeed and climbed out above the lake: it was flying beautifully!

The most noticeable difference I've found in flying at very high altitudes is that the plane just never seems to slow down to land! Even with 60 degrees of flaps, the plane's airspeed on landing approaches is obviously higher. (This is not necessarily a problem, just an unsettling observation.)

After all of my nervous anticipation, actually flying at 12,800 feet was almost anti-climatic; the plane had adequate power when flown on the wing, and would do loops and rolls about as well as it would at the lower elevations. After several minutes of flying, testing low speed handling as well as the high speed, and checking low speed stall characteristics, I dropped the throttle to about and began a landing approach.

As the airspeed decreased, I slowly increased the flap deflection to the full 60 degrees of down, and turned smoothly onto the final leg, but the plane was moving faster than I had anticipated, and was going to overshoot my selected touchdown point. I decided to go around again, and increased throttle to just above half, decreasing the flap deflection to about 20 degrees. Again I set up, and this time made a lower approach, and with full flaps and low throttle, the TELEMASTER settled smoothly on the water surface. Success! I taxied back into position, turned into the light breeze, and advanced the throttle to full again, with predictable results: it again came up on step and lifted off the water's surface in about 75 feet.

I was flying against a breathtaking backdrop, with Mount Evans towering another 2200+ feet above on one side, and the sky dropping away to the eastern plains of Colorado on the other! I was developing a satisfied grin that wouldn't quit for a while! After a couple more successful takeoffs and landings, it was time to taxi back to my launch point near Summit Lake's outlet.

Competition holds different meanings for different people; for me, the challenge is to design and optimize an aircraft system which does a particular task well. Flying from the surface of Summit Lake had taken flight testing of my float system to a new level, proving the extended stability of the design.

In mid-July of 1991, after a couple of months of float flying, I had flown the same plane for the first time at Kite Lake, which sits at 12,000 feet elevation at the head of Buckskin Gulch above Alma, Colorado. Several successful takeoffs and landings were made at that time.

In mid-July of 1992, the South Park Area RC Society sanctioned their first HIGH ALTITUDE FLOAT FLY CHALLENGE; I was the CD. The event was a Float Fly-In with no competitive events; the competition existed between the pilots and Mother Nature, dealing with the effects of lower air density, and the resulting reduced power output of their engines. Without the extra power which many fliers rely on to get their planes into the air at lower altitudes, it became obvious that, in addition to effective airfoils and airframe design, efficient float design and proper setup relationships were extremely important in contributing to the sucess of an aircraft's operations in this rarefied environment.

The results were educational, to say the least! Of the 16 registered pilots and over 20 planes which came to fly, between 50 % and 60% actually made it off the water. Kite Lake is 500 feet wide and 800 feet long at it's maximum dimensions, certainly enough formany aircraft for float flying. Some of the floatplanes brought to fly there could only get off when the water surface was choppy; when it became mirror-smooth later in the day, they failed to achieve separation from the water's surface, even with repeated attempts. Some were capable only of high speed water taxiing, and never made it up at all, no matter what their pilots tried. A few, after being fourced into the air, were unable to fly stably, and left the airspace ungracefully....

Lack of power is blamed by some for the inability to get off the water. After observing many successful and unsucessful float planes over the past few years, however, I've come to believe that most of the problems can be attributed to two possible areas; 1) poor airfoil/ wing design performance, or 2) inadequate float bottom design and improper setup in the areas of step location, and float planeing surface to wing incidence angles.

At 9# dry, my TELEMASTER 40 is certainly not over-powered; it flies on floats at a wing loading of over 23 ounces per square foot. What it does have going for it are optimized floats, set up correctly for that particular aircraft.

Late in the day at that first Kite Lake Float Fly, with the surface of the lake perfectly smooth, I made 8 to 10 consecutive takeoffs and landings with no problems at all. OPTIMIZED float hull design and optimized setup incidences had a lot to do with this consistant success.

I had previously flown the same plane with floats powered with an ASP .46 engine from a 2 acre pond at 10,500 feet elevation, again with no problems. The aircraft definitely flies on the wing, not on the prop, but when set up properly on a well designed set of floats, it performs well.

Before building these floats, I had done a lot of research on float design. Andy Lennon's series of articles in RC Modeler magazine early in 1991 gave much more insight into the hydrodynamic design considerations, and gave me a lot of information and references that I had been unable to find elswhere; information many seemed to have been unaware of in designing many of the floats in use at that time. Working from all of this gathered information, I set out to design a set of lightweight yet durable floats which would perform well in a wide range of water conditions. The results have exceeded all of my expectations. All of the combined design aspects and recommended setup guidelines incorporated into APPLIED TECHNOLOGY FLOAT SYSTEMS contribute to their consistent performance as very possibly the best floats we have seen working here at high altitudes. When properly sized to match the plane on which they are mounted, and set up correctly according to the provided instructions, they perform beautifully!

Part 1 posted 2-23-97.


Part 2 will go into some of the optimizable details of float design, construction, and installation / setup; many of these items shouldn't be left to " Aw, that looks close enough!?!"

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