Making a Float Plane (1 of 2)

Float Fly Plane Part 1

Let me start out by saying that I have very limited experience with float planes. This by no means makes me an expert in the subject of float planes and flying. In anticipation of writing this article, I have spent a great deal of time researching the subject. The majority of information I will providing was compiled from multiple sources and a little bit of conjecture. I cannot speak of certain subjects with firsthand experience, so I will do my best to provide information that seems logical or well thought out. Opinions will vary when it comes to equipment and methods. It is impossible to write about every nuance of float flying, but I will do my best to provide the information I have concluded to be relevant. This will be the first of a two part article. The first part will cover the plane itself and how to setup your plane. The second part will have to do with float installation and placement. You can read part 2 here.

Flying

Float flying is a little different than conventional flying, but is simple enough once you understand the physics involved. There is something beautiful and relaxing about standing at the beach of a lake and flying a plane. As an added bonus, the runway will always be very long, wide, and generally flat.

Starting off with a good plane will ensure you’ll have a good experience. It would appear that the best types of planes that can be converted to a float plane are planes with a long nose, long tail moment, and a light wing loading. Most high wing planes or trainers make good conversion planes. If you start off with a flying brick, when you put floats on it, you’ll have a flying brick with floats on it. Generally speaking, larger planes handle better than smaller planes. Small planes can get tossed around in gentle waves pretty easily.

There are two basic types of planes that can fly off of water. The first is a standard airplane frame that has had its wheels removed and replaced with a set of floats. The second type is referred to as “flying boats” or an airplane frame that has a boat-like hull. If you can afford a dedicated float plane, a flying boat design is believed to be much easier to handle. It doesn’t require any additional increase of engine power to overcome the additional drag that floats can create. Flying boats are significantly more aerobatic and can also handle higher winds on the water.

When it comes to picking a plane, don’t go for what looks the prettiest. Talk to people who have had some experience with different types of float planes and get their opinions on what type of plane(s) to buy. A good example would be the 60 sized Seawind ARF from Great Planes. I personally think it’s a beautiful flying boat type plane, but from what I’ve heard and read, it’s a handful to fly. It has a high wing loading and isn’t meant for the beginner.

From a beginner’s point of view, the consensus is that a flying boat is easier to fly. However, most people don’t want to spend the money on a dedicated float plane. I would recommend converting an existing wheeled plane and see if you enjoy the experience. For the purposes of this article, I will be discussing items that are specific to a wheeled converted plane.

Floats

The most important items that you’ll need are the floats themselves. You can buy pre-built floats. Hanger 9 makes a great set of floats that are designed to bolt on to their Piper Cub with no real modifications being required. You can also buy kits to create built up floats (hollow) out of balsa and/or light ply. However, hollow floats are a great place to store water, and it seems that all hollow floats take on water at some point in their life. Another type of float is a foam core that is balsa sheeted and then finished with fiberglass or a plastic film covering. These floats can be used on any plane, although it’ll be up to the builder to make sure the floats are positioned correctly. Floats need to provide enough buoyancy for the weight of your plane. There are formulas on the internet that explain how to calculate how much buoyancy you’ll need for your plane.

There are also hollow molded plastic floats. I have read on numerous websites about these types of floats. The bottom line is I couldn’t find anyone who thinks they are worth anything. They are prone to cracking and will expand after sitting on a hot beach which causes them to blow out along the seams. This type of floats is recommended to be avoided.

Engines

I am not going to advocate for one type of an engine over any other type. Whether it’s glow, gas, or electric, the bottom line is you need to have some power to break the surface tension when taking off from water. A quick and easy way to tell if you have enough power is if your plane can take off from a traditional runway with 3/4 throttle or less, then you’ll be fine with your existing power system. If your plane needs full throttle, then you’re going to need a bigger motor.

Propeller

As a general rule, never use wooden propellers when flying off of water as they tend to shred almost instantly when striking the water. A little bit of water spray is going to hit the propeller and wood propellers can warp or become weak from the moisture if not sealed correctly. For most applications, a plastic or composite type propeller (such as APC) will work the best.

As a rule of thumb, the propeller should clear the top of the floats by two inches or more. You don’t want water to get sucked up into the propeller. This robs the plane of power that you’ll need for takeoff and taxiing. If you find that you have a clearance problem, you can always change to a smaller diameter three blade propeller.

Waterproofing

Most engines (including electric) will be fine if they become submerged from a bad landing or takeoff. When a plane tips over in the water, it will generally come to a rest with the engine submerged and the fuselage pointing upwards at a 60+ degree angle. Water will creep into every crack and crevice including the wing saddle and the canopy.

If your glow/gas motor has become submerged, do not attempt to start it immediately after removing it from the water. Water may have leaked into the cylinder and the piston will probably be in hydraulic lock. If you try to start a motor that is in hydraulic lock, you can damage the connecting rods because water does not compress. Before you attempt to start the motor, remove the glow plug and turn the engine upside down to drain out all the water. Pour a little bit of fuel into the crankcase to act as a lubricant, and hand crank the engine a couple of times. Reinstall the glow plug and you are ready to go. If you fly electric, the motor will be fine if wet. A typical R/C electric motor runs off of DC current and can even be run underwater although this isn’t recommended. The Electronic Speed Controller on the other hand, cannot operate with any moisture being present. If the ESC has gotten wet, you will need to let the part air dry before attempting to start the plane again.

Make sure any exposed balsa has been waterproofed. You can use water based polyurethane to water proof wood without adding a lot of weight. You need to wrap the receiver in plastic to prevent water damage. One method I came across that seems like a good idea is to use a rubber surgical glove. You can cut holes into the fingers to pass the servo leads and antenna through these openings. Seal up the small holes with waterproof glue and place the receiver in the palm part of the glove. Wrap a rubber band around the wrist part and encase the package in foam to protect it from vibration. DO NOT use silicone sealant as it contains chemicals that attack electronics.

The item you SHOULD NOT wrap in plastic is your NiCad or NiMH battery with any impervious material. First of all, any watertight wrapping will cause the battery to overheat. Secondly, there is a small vent hole in a NiCad cell that allows gas to escape. A vapor barrier will trap these gasses and lead to cell deterioration. The normal methods of wrapping a battery will be waterproof enough for our needs.

The wing saddle is usually the easiest way for water to infiltrate the innards of your plane. Using wing saddle foam which is available at all hobby stores is the quickest way of sealing the gap that most ARF’s will have. A better way of sealing the gap is to lay down a bead of silicone sealant on the saddle and drop the wing (cover the wing with plastic wrap) into the saddle and tighten down the wing. Let the bead dry (it can take up to three days) and remove any excess with a straight edge razor blade.

Water Rudder(s)

One water rudder is adequate most of the time. Two seem to be the preference on large aircraft or when you have windy conditions. Like a tail dragger wheeled plane, you should taxi with full up elevator. This forces the heel of the float into the water which increases the rudder’s effectiveness. Water rudders should be retractable or built to kick up as the speed increases. This minimizes water looping. Use the rudder sparingly at high speeds. I read where someone noted that when one water rudder is used on a full scale plane, it’s always on the right float. So if it’s good enough for full scale, it’s probably a good idea for our planes.

The water rudder has to work in conjunction with the air rudder. There are many different ways of achieving this. The first way is to install a servo in the float that will drive the water rudder. The servo lead will plug into a Y-Harness on the rudder channel. Another way is to use a system of cables or flexible pushrods. Secure one end to a control horn on the rudder and then run the other end in a big loop (assuming you’re using a flexible pushrod) to the control arm on the water rudder. Dual rudders can be linked with a cross rod. There are many ways of controlling a water rudder and each way will be specific to the floats and the type of plane. Some creative engineering might be needed by the builder to figure out the easiest way to have a functional water rudder.

With anything more than a light breeze, it is nearly impossible to control the taxiing of a float plane on water if it doesn’t have a water rudder.

Ventral Fin

A plane with a long tail moment and large enough tail feathers can get away with a ventral or sub-fin. A quick way of determining if your plane has inadequate tail moment is to taxi downwind and reduce the engine to idle. If the plane doesn’t turn its nose into the wind, (referred to as weathervane) the vertical fin area isn’t big enough and a ventral fin needs to be added.

Floats add a huge surface slab of hull that reacts against cross winds. The effect can be so bad that it forgets which way is forward and starts to weathervane into the side wind. By adding a removable ventral fin or sub-fin on the bottom of the fuselage will solve this problem.

Flying Techniques

As with all planes, the first thing you must do is take off into the wind. Before taking off you must verify the direction of the wind. If you’re not sure of the wind direction, attach a bit of string to the end of your antennae. Or let you plane idle for a little bit in the water so the plane will weathervane into the wind. Taking off in a cross wind situation isn’t advised. The floats create a lot of drag and weight making cross takeoffs difficult. It can be done, but the plane will have a tendency to lift off and immediately cartwheel into the water. The reason for this is the downwind side float will still be in the water creating drag when the upwind float becomes airborne.

When getting ready to takeoff, taxi into position. When lined up, apply full up elevator and advance the throttle steadily. The point of doing this is to get the floats to lift up onto the “step”. The “step” is generally the mid section of the floats where there is a difference in hull shape and size. As soon as you see the plane “step up” and is increasing in speed, relax the elevator to neutral. As you approach full speed, try not to use the rudder unless you absolutely have to. Too much rudder can cause the float tip to dig into the water and will slow you down or even flip the plane. As you reach takeoff speed, gently apply up elevator until the floats leave the water. Then level out to gain even more airspeed before completing the climb out.

One of the difficult aspects of taking off from water is dealing with waves. When you are racing down the water runway at full throttle attempting to gain liftoff speed, a wave can launch the plane into the air before it’s ready to fly. This can cause the plane to stall and crash back into the water. This is the main reason not to hold any up elevator until the plane is at takeoff speed. Try to takeoff parallel to the waves if the situation allows.

I have found that landing a float plane is pretty easy compared to a wheeled plane. You have a huge runway and don’t need to worry if you aren’t 100 percent straight down the runway. When coming in for a landing, the main thing to remember is the flare at the last second. While you shouldn’t be attempting a full 3-point style landing, you want to make sure the tips of the floats are the very last thing to touch the water. Another tip to ensure a perfect landing is to keep a little bit of throttle input. Putting floats on a wheeled plane creates a lot of extra drag and weight. Your plane might require a little more power upon landing to make sure it doesn’t stall out.

Rough landings are far more forgiving on water than on land. You can hit the water pretty hard and still have a reasonably good chance of it walking away with no damage.

Conclusion

That should cover the basics of what you’ll need to know if you want to convert your wheeled plane into a float plane. Float flying is a great way to spend a day and you would be hard pressed to find someone who didn’t enjoy themselves when flying around a lake. Refer to our event calendar to see when the next float fly is scheduled.