Steve Fredericks’ Maule Rocket uses Balsa USA
EDO floats that are available in 1/3 and 1/4 scale.
Ernst Manufacturing retractable rudders are available in different
sizes and work well.
The placement of the floats and the design of their bottoms can make a significant
difference in how they handle on the water.
Photos by Darrell Watts and Jay Smith
The Right Float Size
The rule of thumb is that the float length should be 75-80%
of the length of your fuselage, from the propeller disk to the
rudder hinge. If in doubt, go to the larger float size, particularly
if your model has a higher-than-average wing loading. You may
think that smaller floats look correct, but undersized floats
create multiple takeoff and landing problems.
The design of the bottom of the float can make
a significant difference in your model’s water
handing! On model aircraft, flat-bottom floats
generally work fine on sport models up to a .40
size. For larger models or Scale models, a shallow
V-bottom works best. Deep “V” or Cathedral
bottoms can be challenging to use and should be
left to advanced pilots. They have a tendency to
groove in the water, which can result in sudden
Most commercially available floats are of the
correct proportions and have shallow V-bottoms.
ARF floats are available from Horizon Hobby,
Tower Hobbies, and other major suppliers. Plane
Fun Floats has sheeted foam core floats, while
SeaPlane Supply provides foam cores in many
sizes and designs or will custom cut cores to your
I will not attempt to cover designing your own
floats here because it is an extensive subject.
For most models you can use the existing main landing gear
as the principle
Simply add a
matching, or similar,
landing gear at the
rear of the fuselage.
You will need to
add a plywood plate
on the inside of the
fuselage where the
second set of gear is
mounted for reinforcement.
Because most commercially available floats have a hardwood
spine down the top of the float, I use nose gear-mounting blocks
to attach the axle to the float. The recommended distance
between the floats, center to center, is 30% of the wingspan. The
existing gear is not that wide, but it works for my models up to
and including a 1. 80 cu.in. model—except in significant wind.
Your entire float system should be rigid. This requires a
crossbrace slightly ahead of the front mounting point. On
larger models, another crossbrace behind the rear mounting
point is a good idea. I use aluminum straps from a local
hardware store. On larger models I also use an N-strut from
the bottom of the rear landing gear to the top of the front
Positioning the Floats
Block up your floats on the workbench so that the tops are
level and they are the appropriate distance apart, allowing you
to set your model on its landing gear on the top of the floats.
Typical floats have a step roughly 50% back from the tip of the
float. When the model is setting on the top of the floats, the
step should be 1/2 to 1 inch behind the CG. Think of the step as
the axle location on a tricycle-gear model. You want the nose
to gently come down when the model lands on the step.
40 Model Aviation APRIL 2014