Flying of Water

While some R/C pilots build floats for their planes from commercial kits, there are others who like to make their floats. A purpose of this article is to show how to make good light weight floats and attach them to your plane. All planes pictured fly well off water.

Starting in 1999, about 5 to 7 morning float flys have been held each summer at Standing Bear Lake in Omaha, Nebraska. This 310 acre lake was created by a dam constructed by the U S Corps of Engineers, with the city of Omaha being the local project sponsor. The city maintains a park around the lake. These flys have been sponsored by the Omahawks R/C club. They always include a retrieval boat, coffee and donuts or krispy kremes. They usually go from 8:30 to 11:30 am. By then the winds have usually picked up, making it more of a challenge to fly, and many are ready to go home and take a nap.  This article includes photos taken at the July 22, 2006 float fly. A popular homemade float seen at these events has been patterned after the design of Chuck Cunningham that was published in model magazines about 15 to 20 years ago.  A description of these floats follows.

Float Material. The Cunningham homemade floats are made of Styrofoam. Boat dock weight Styrofoam or strong insulation foam is the preferred material. The bottom of the float is flat and usually covered with thin plywood or epoxy/fiberglass or painted or a combination of these. A small piece of hardwood is epoxyed to the top of the float. The author used a piece of 3/16 by ¾ spruce for 4 inch wide and 40 inch long floats. On 3 inch wide and 36 inch floats, he used 3/16 by ½ spruce. This piece is also anchored into the foam with wood dowels (see illustration). This gives necessary strength to the floats. Some use polyurethane to paint the entire float. Having a thin coating of paint or epoxy on the floats protect them from exhaust fuel and makes them easier to cleanup. The flat bottom gets the plane up on step quickly when taking off. Some also install thin plastic splash guards on the front inside of the floats.

Dimensions and Layout. Refer to illustrations.  This shows the setup for planes with a tricycle landing gear. For this type, the rear landing gear can be kept in place and the nose wheel mount can be used to attach the front of the floats.  For tail draggers, a new rear landing gear needs to be installed. The step is located under the CG of the plane for both types of landing gear. To steer the plane on water most use a water rudder attached via cable to the nose wheel servo or install a separate servo.

The float spread or distance between them is recommended as 25% of the wing span or 50% of the float length. See photo for a way to get this desired spread. The spread helps keep the plane from tipping over in windy conditions. However, as seen in other photos, some just use the normal wheel landing gear spread. The spread should also be stabilized at the rear landing gear with wire or hardwood, connecting the floats. Some also provide diagonal wire bracing to stabilize forward/backward movement of the floats…The front of the floats should be a few inches ahead of the propeller. The bigger the plane or prop the more distance. For example, with a 10 inch prop on a .32 engine, with 36 inch long floats, the author had a distance of 4 inches. With an 11 inch prop on a .46 engine, with a 40 inch long floats, there is about 5.5inches.  Using 75-80% of the fuselage length for the float length should achieve the desired distance. The bottom of the prop should be about 2 inches above the top of the floats.

Positive angle of attack attachment. Chuck Cunningham said, “The most important item in attaching the floats to the aircraft is to make sure that the wing of the model will be located at a positive angle of attack. You want the wing to lift the aircraft out of the water, not glue it down. An easy way to decide how much to lift the wing is to remember that 1 degree of incidence is equal to 1/16 inch at 3 inches. If your wing has a 12 inch chord, then 1 degree will be equal to ¼ inch.” He started using plus 2 degrees. If lift off is still a bit sluggish, then he said to add another degree to the float. Some builders eyeball to attain a small positive angle between the top of the floats and flat bottom wing or centerline of symmetrical shape wing ribs. The following table can be helpful.

WING CHORD                    1 DEGREE                                2 DEGREE               

      9 INCHES                       3/16 INCH                      3/8 INCH

      12 INCHES                     ¼ INCH                 ½ INCH

      16 INCHES                     5/16 INCH                      5/8 INCH

Engine. Flying off water usually requires a slightly bigger engine than flying off land. A plane with a 73 inch wing span, like the SIG LT 40 or Telemaster, fly very well off water using a .46 two cycle or .52 four cycle engine, using these home made flat bottom floats. See the photo captions for other engines used on float planes. On taking off, if the engine has marginal power, care is taken to not pull up too soon after the floats break with the water… A plastic prop should be used as a wood prop may break when it gets wet.

Click here for Flying off water photos

Richard F Behrens

8521 North Ridge Drive

Omaha, NE.

68112