Experience Flying Off Water
By Rick Haney
If you take off and land on a grass runway you shouldn’t have trouble flying off water.
First you have to determine the proper airplane. You need a plane that you are
comfortable with and has a very reliable engine. A sport plane can be used but for the
newbie you should use a high wing trainer. It will be more forgiving. If the plane can take
off from a grass runway at ¾ throttle, it will take off from water just fine. Water has a
great amount of drag on the floats so if your plane happens to have a 40 size engine
you will need a 50 size engine. Avoid using wooden props as they can splinter if they hit
the water.
Second on the list is deciding what kind of floats you want to use. There are a number
of floats are on the market. Plastic floats and balsa-plywood built up floats will work
unless you punch a hole in them. In this type of construction, water can run forward and
to the rear which will affect the plane’s CG possibly causing the plane to crash. Foam
core floats do not have this problem. They can be sheeted with balsa wood, covered
with packing tape, plastic covering, fiberglass cloth, painted with polyurethane or not
covered with anything at all.
Next you need the correct size of floats. The rule of thumb is 75 to 80% of the length of
the fuselage measured from the prop back to the hinge line of the rudder or elevator,
whichever is furthest back. No matter what floats you use, always go bigger not smaller
than the 75% figure.
If you cut your floats from foam the easiest is to make a flat bottom configuration. If you
want V bottom floats it gets more involved than I want to discuss at this time.
Listed are some of the critical things to keep in mind while mounting
your pontoons.
Center of gravity: When adding floats to a plane it will probably change the CG. Do not
add weight to the plane. Adding weight to the floats will allow you to switch from wheels
to floats without the CG changing. When adding weight to the floats, divide the weight
between the two floats to keep the side to side balance correct.
Angle of attack: Rule of thumb is to have the top of the float parallel to the horizontal
stabilizer. If you have a semi symmetrical wing design you can use the datum line of the
fuselage and drop the front of the float 2 to 3%.
Float distance in front of the prop line: The float needs to be 10 to 12% of the float
length in front of the prop line. This keeps the plane from nosing down when you
accelerate causing them to dig into the water.
Step placement: The step always will be ½ to 1” behind the CG. For larger planes this
measurement will be larger.
Taxiing: If there is any kind of breeze, it could be almost impossible to make a turn
away from the wind. The plane turns into a weather vane and will try to keep its’ nose
pointed into the wind. Water rudders will aid in maneuvering the plane when taxiing.
One rudder is OK, but two will be much better. You can buy or make water rudders.
There are several ways to operate the rudders. You can use nyrod to connect the
rudder horn to the water rudder’s arm, but make sure both the water rudder and the
plane’s rudder move in the same direction. You can mount a servo on the pontoon
attached directly to the rudder and use a Y harness on the rudder channel of the
receiver.
Landing: Never try for a cross wind landing and don’t side slip a landing. Both will lead
to a wet and probably broken airplane. The first landings need to be made coming in a
little faster than you would on wheels just to get the feel of it. Make your landings nice
and easy. You have a long flat runway to land on so don’t hurry it. Hold the nose up a
hair and the wings level, let the speed bleed off and let the plane settle onto the water.
This is the same landing procedure that you should be using at the flying field.
Water proofing the plane: It can’t be done 100%. No matter how hard you try to keep
water from finding its way to the inside of the plane, water will get in. however there are
some things that will help. Wrap your receiver in a plastic bag using a tie wrap and
lithium grease to seal the bag. I also use some lithium grease around the servo shaft of
the servos and also where the wires come out of the case. Some clear tape at the wing
saddle and over the charging jack will help. Internal switches are preferred but you can
cover external switches and external jacks with clear tape.
If you have the misfortune of making a not so great landing and the plane gets wet, you
don’t want to get the plane wetter than it already is. Pick it up and hold it in the same
attitude that it was in when you retrieved it. If you turn it right side up you could get more
of the inside wet. Carry it back and try to empty the water by whatever means
necessary. You might have to cut some covering to let the water out of the wing. As
soon as you can, pull out the glow plug and turn the engine over by hand several times
and then use the starter to spin it to get all the moisture out. Be careful not to get a face
full of spray from the plug hole. Reinstall the plug and start the engine and let it warm up
to normal operating temperature. Don’t worry about getting water in the fuel tank unless
the plane is in the water for a long time. If the receiver gets wet take the case apart and
make sure it is completely dry before trying to fly again. The battery should not be
wrapped in plastic. Batteries need to breath. If it gets wet, you should cut the shrink
wrap and make sure it is dried so they won’t corrode.
Building Foam Pontoons (Floats)
You will need to know what size floats you will be building. I will use the dimensions for
my Kadet Sr. the Sr. is 60 inches long, measured from the elevator hinge line to the
prop hub, weighs 8 pounds 5 ounces, has a 78” wingspan and has an OS 95 AX for
power.
Using the diagram you will see how the percentages come into play. A picture is worth a
million words. The percentages will stay constant only the measurements will be
different.
The fuselage being 60 inches long, the floats need to be at least 45 inches in length. My
floats are made using white foam, sheeted with 1/16th inch balsa, are 45inches long and
4 inches wide. The step is 1 inch behind the CG. The float tip is 4 inches ahead of the
prop line. The top of the float is parallel to the bottom of the wing and/or the horizontal
stabilizer. I didn’t install water rudders and this has been a problem at times.
I think you can purchase 4 inch thick white foam from Home Depot. You can contact a
commercial insulation contractor to get thicker foam blocks. A hot wire cutter is used to
cut the foam to shape unless you glue several pieces of foam together in which case
you will need to use a band saw to cut the foam to shape. You can use a hand saw to
cut the foam to shape if you don’t have a hot wire cutter.
Using the diagram as a guide, draw a full size float onto cardboard and hold it to your
plane to see where the front of the float and the step needs to be and where the mounts
need to be placed. You might have to move the step to place it correctly with the plane’s
CG. (The step will be very close to where the main gear axels are on a tricycle landing
gear setup.) Do what it takes to get the step in the correct place. The rear of the step is
what the plane rotates from on takeoff.
Once you have the shape you are happy with, you will make two templates to guide the
hot wire cutter. I made my templates from tempered masonite. The area that the hot
wire will be sliding on will have to be as smooth as you can get it. You don’t want the
wire to snag on a ruff spot while you are cutting. Drill holes near the front and rear of the
templates so you can insert nails to hold them to the foam. I used a table saw to give
the top of the float some shape and to remove some weight that isn’t doing anything for
you. Cutting foam with a table saw is kind of messy!
The “back bone”, as I call it, is made from plywood and can be laid flat on top of the float
or inserted into a slot, cut in the top. Both work. If laid flat you will need to drill ¼ inch
holes for the insertion of dowel rods through the plywood and into the foam to keep the
plywood from popping off. I use epoxy or gorilla glue to attach the plywood. All plywood
needs to be 5 ply aircraft grade.
Whatever means you use to attach the gear to the float it has to be extremely strong.
Hitting the water at speed can be quite a shock. The more ridged the floats are attached
to the plane the better they will perform.
For some good information on float flying basics look up on the net “The basics of float
flying” by Ironsides
On the last page you will find some drawings which shows the percentages needed to
make floats. You will see two methods of attachment. I generally cut a slot down the
center of the top of the float, with the table saw, and use a piece of 1/8 th inch aviation
ply (never use light ply) as the back bone. When using this method you should use a
piece of ¼” ply on each side of a 1/8” piece as shown. If you use pine or spruce, they
can and will split with the grain and dunk the plane. Trust me on this one because I’ve
been there and done it.
Engine Size
10 – 20
30 – 40
50 - 60
70 - 120
120 – ¼ Scale
Float Width
2”
3”
4”
5”
6”
Step Height
3/16”
1/2"
3/4”
1”
1 1/8”