Summer Swappables: simple/cheap DIY floats

Every year in the middle of summer many of us have a lot of free time. Unfortunatelly, it's usually the time when unbearably high temperatures keep us indor, and those who decide to risk going outside usually face the same dilemma: swimming or flying? If only one would have a plane capable of flying off the water, he or she would easily be able to avoid making difficult choices. Problem is: not every plane can fly off the water. Some BnF/RtF planes are offered with factory-built floats, but that option usually comes with a price. The same is true when you try to buy ready-made floats for your currently own planes - they are usually quite expensive. There are some planes out there that can land on water without floats (e.g. Polaris), but not everyone can afford adding more planes to the hangar (for any reason) just to fly it a couple of weekends every year. The solution is only one: build your own floats that will fit a plane you already have.

Contrary to popular belief, floats don't have to be exactly "perfect" to let you enjoy this new experience. You just need to follow few basic rules about their shape and location, and you will be good to go. In this article I will try to present you how I've build floats that fit my own waterproof FT Simple Storch, what decisions I made during the process and why, and what I've learn about flying the plane off the water.

There were two decisions I made before I even started the research. One - and the most important - was that my floats have to be easily swappable with the wheels and other kinds of landing equipment I'm using on my planes. The other one - and this was more like "need" than "decission" - was that those have to be easily built in a very short period of time. I've managed to build them in just two days, being away from my usual working place; and I'd like to share my experience with you.

The very first real choice to make is the build material. There is a very nice article about how to build DTFB floats on the forums, but not everyone have access to this material and still there is a lot of work with making them waterproof. After doing some research on the internet, I've decided to use 2" styrofoam insulation board instead. It's not the best choice either; but it's readily available, low weight and low cost solution that does not require any fancy tools and/or techniques.

The second choice is the shape. I've found pretty old web page that cover the basics of this topic, including general guidelines about overall dimensions. Here's one of the pictures from this site:

In case of my Storch, the dimensions were as follows:

WIDTH/HEIGHT: 2"/5cm 

L: 27"/70cm

B: 14"/36cm

D: 3"/8cm

Using a knife with very sharp and long blade, I carefully cut out this shape from the styrofoam board, and... that was it. I do know all the advantages of "v-shaped" floats and it's not difficult to find detailed, step-by-step instructions about how to make them; but I decided to stay on the easy/cheap/quick side. On the plane of this size it doesn't really change much (except the look, maybe).

At this point it is neccessary to determine the position of floats relative to the fuselage; without that, you will not be able to install the mounting "hardpoints" in the right place. There are three main elements of float position: side offset, longitudinal location and inclination (an angle between floats and wing). In case of the FT Simple Storch, two of those are really simple. According to the discussions I've found on the internet, the general rule for the side offset is that the floats should be not less than 20% of the wingspan apart from each other. This does mach the distance between wheels pretty close; no modifications are required here. The inclination is also pretty easy to find: the angle between the top of cabin section and the tail section of the fuselage is almost perfect. Just make sure the top of the floats is parallel to the top of the tail (two red lines on the picture below), and you are good to go:

The only thing left is to find the longitudinal location, defined as the distance between the CoG and "the step" (the place where floats change their height). All materials I've found agree that the floats are positioned correctly when the step is 1/2" to 1" (1,2cm to 2,5cm) behind the CoG. There is one important note: since CoG is usually located pretty far from the floats, this distance needs to be measured using lines exactly perpendicular to the floats' upper surface (see green lines on the picture above). It does require some creativity to make it right; but remember that there is some flexibility for this dimension, so it can be done without overengineering it. One piece of advice: you may want to build some sort of "jig" to hold the plane and floats in place when making the measurement. It may even be "very temporary" in nature (few books under the fuselage plus some trash under the float), but don't disassemble it yet (or make sure you know how to put it back together); it may be useful later. When you find the correct position, mark the wheel axle location on the floats (one is usually enough). 

With the axle position found, it's time to make and install the front hardpoints. I've made very simple ones just by cutting 1"x3" (2,5cm x 7,5cm) strip of 1,5mm plywood. Using the sharp blade again, I cut a slot for the plywood in the middle of the top surface of the float. The slot was just slightly deeper than 1/2" (approx. 1,5cm) with the axle position roughly in the middle of it. I glued it in using 5min epoxy and drilled a hole for the axle (in this order). Then I repeated the process for the other float.

Now it's the time to join both floats together. I cut two stripes of plywood, 1" (2.5cm) wide and 14 1/2" (37cm) long. keeping both floats parallel, I glued in one of them just in front of the forward hardpoints. Then I measured the distance from the forward end of the float to the strip (turned out to be approx. 5"/12cm), and glued in the second one roughtly at the same distance from the back.Then I repeated the "hardpoint mounting process" for the rear hardpoints, mounting them in front of the rear joining strip. Note that I did not prepare rear support struts before and I did not make any precise measurements here; that's what we are going to do next.

Before proceeding to the next step, you need to figure out where and how to mount the rear struts to the fuselage. I did that at the building stage since I already knew I'll be putting it on floats. You may find the details in the related article. You can easily find many good solutions on the internet, or just choose any FT plane with "one wire landing gear" and apply it here. With the fuselage ready to accept the strut, install the floats on the wheel axles and fix them in the correct final position (I use four wheel collars - two on each axle). That's where you can reuse the jig from the "finding correct position" step (if you built one). Having the floats position fixed, use a string or wire (or anything else you have) to measure the distance between rear hardpoints on the floats and rear strut mounting point on the fuselage. Repeat the measurement on both sides to make sure both are equal; this is the last time you can easily make some adjustments. Since in my case all the LG struts are mounted into the brass tubes glued in to the fuselage, the rear struts are actually just 8"/20cm long steel wires (the same as used for the front LG struts) bent to 45 degrees at both ends. Those struts are fixed to the floats using wheel collars (just like the wheel axle) and slide into the tube in the fuselage. The only thing that holds them in place is... one piece of rubber band.

If you decided to build your own floats and followed this article up to this point, CONGRATULATIONS! Your work is over, and you are left with maybe not perfectly looking, but definitely working, brand new floats. All you need to do before the first flight is to waterproof your electronics - I can't stress it out enough how important this is. You can find a lot of tips in FlitetTest videos and all around the internet.

That's how the plane looks ready for the first flight with new landing gear:

 And here's how it flies:

(in case of any problems with the embeded player, the video can be found under this direct link)

Let me show off just few pictures made by my wonderful partner and long-time aircraft photographer; while I'll describe my experience of actually flying the plane.

The very first thing that surprised me was the difference in response to the rudder input when taxiing on the water. I knew there will be some; but without the water rudders the plane actually did not want to turn right at all, and even the slightest breeze coming from the left side made that impossible. I had to plan the path on the water very carefully, especially close to the boats / swimmers and when approaching the shore.

The next thing was the power required for take-off roll. I'm using quite light motor and prop combo (120W, 8x4) on my plane, and because of that I had to strictly follow the of-water take-off procedure. The procedure is:

1. apply the take-off power, let the plane gain some speed in "displacement phase" (when the plane floats by the displacement only, just like when it stands still);

2. apply moderate, short lasting up elevator "impulse" to make the transition into "planning phase" (the floats start to "slide" on the water surface);

3. let the plane gain more speed, try to keep the path straight and wings level;

4. apply another, much more emphasized elevator "impulse" to pull the aircraft off the water, but avoid "jumping high";

5. gain more speed (again), proceed to climb-out.

I found this phase of the flight much more difficult that anything else I experieced before. I spent a lot of time practicing it, and most of the "flip-overs" I had happened during take-off attempts.

I did not notice anything unusual during the flight. It was pretty much like flying with the skis (described in my other article, Winter Swappables). The floats are very light, adding only 100g/3,5oz to the total weight (including rear struts, wheel collars and the rubber band) - this is something even an underpowered Storch can easily deal with.

Landing the plane on the water was a whole different story. Due to the floats position and angle, I had to limit the flaps deflection significantly (compared to the one I use with wheels) to be able to use them for landings. With full flap deflection, the plane was almost always flying with the floats "pointing down". Because of that, the floats could easily hit the water "forward first" and cause the plane to flip over. I found out that the best way to land is to do that with flaps fully retracted and with a little power applied all the time. This way the plane approaches the surface in the shallow descend, making the touchdown very smooth and gentle. The plane slows down almost immediatelly after hitting the water, making it easy to land on the small area without using flaps at all.

Night flying was an experience I could never imagine before. Having no people anywhere around (and thus not having to avoid them) made it easier to fly in the tight area surrounded by tall trees. Completely still air contributed to very calm and uneventful flights; and provided amazing views with the lights reflected on the perfectly flat surface of the lake. It also made the landing much more pleasant, since it was very easy to see how high the plane is flying over the surface.

One additional note about the wind: with the light, underpowered plane, take-off and landing has to be performed directly upwind. Any other option will almost certainly end bad; and this is true especially during the take-off. On the other hand, the wind may be your biggest ally. My Storch did not need much to take-off upwind, with flaps deployed, separating from the surface even before entering the "planning phase". I've found that type of take-off much more safe and much less stressful.

I hope you enjoyed the article and the pictures. Please feel free to ask me any questions and/or share your own floats experience in the coments below; and if you don't mind, please take some time to rate the article. Thanks in advance.

Don't forget to waterproof your electronics before the first flight, and Have Fun!