LIGHT WEIGHT FLOATS
FILM COVERED FOR ELECTRICS
By - Brandon Ulmer
Construction Manual for light weight floats design to fit the E-flight Apprentice
Written by: Brandon Ulmer, PE
Once you receive your 27” floats from Seaplane Supply, unpack them and label all parts to help with following this manual. The photo above shows all parts as they come from Seaplane Supply. The parts labeled (L, R, and T) are not required for this manual and can be discarded. The part labeled F is the main section of the float and the part labeled C is the cradle and is used in the construction of the floats. Some care is required so as not to damage the edges of the floats since they are raw foam at this point. The floats are always kept in their cradle during and after construction to protect them from any damage. The floats (part f) are stored with the cradles (part c) on at all times and secured with rubber bands to keep them protected. The only time the cradles are removed is when the model is on the water.
Tip: The extra foam parts that are to be discarded can be saved for testing of glues and iron temperatures in the covering section.
Since the floats (part f) come pre-cut, there is not that much work required to finish the floats. ¼” x ¾” balsa (not supplied) is used as a stringer running the full length of the floats. (or use plywood & foam filler supplied)The balsa is trial fitted and adjusted as required to get a good, snug fit in the pre-cut slot on the top of the floats. The balsa stringers can be glued in at this point. A waterproof glue, such as Gorliia glue or epoxy is recommended. You can use an epoxy brush to coat the foam with a thin layer of glue (see photo above). Once the stringers are glued in place, make sure the holes for the carbon rods are free of glue. You can now set the floats upside down (so no glue falls in the carbon rod holes) and let dry.
Once the glue is dry, you can begin to prepare the floats for covering. As you can see in photo to the right, there is a little edge between the balsa stringer and foam floats. This edge must be removed in order for the covering to go on evenly. During this process, you can carefully cut the balsa stringers even with the front and back of the floats. (Cut them close. Then use a sanding block to make them even with the front and back of the float (part f). At this point, you should have a set of floats that are ready for covering as seen in the photo above.
Tip: I removed a section of the cradles as seen in the photo above. This will help you get the cradle on and off. The cradles protect the floats and also keep the model level when it’s on the ground.
To finish the floats, use a low temperature covering, such as Econokote. This covering is applied directly on the foam. The floats are covered starting with the back of the floats. The next step is to cover the bottom with an overlap on the sides of about ¼” (see photo below). In the next few photos, you can see the bottom being covered, as well as the required overlap on the sides. Once the bottoms of both floats are finished, it is time to cover the top. The top is a little challenging since I use one piece of covering which covers the top and sides. If this is too difficult, the top and sides can be covered in two pieces overlapping on the balsa stringer. Whichever way you choose to cover the top and side, make sure you seal all the seams well. If you use CA make sure it is foam safe!!
Tip: The iron I used to cover the floats was on about ¾ heat. You should test your iron temperature on a scrap piece of foam prior to covering the floats. As long as it does not melt the foam, the temperature is ok.
The above photo shows the completed floats ready to be mounted to the model.
Installing Carbon spreaders
It is now time to make a left and a right float. If you are planning on installing a water rudder, it would be a good idea to weight the floats and install the rudder on the lightest float. I have done some experimenting and found that the water rudder is not worth the hassle for this model.
The holes for the carbon rods will have to be opened to accept the rods. I use a sharp E-xacto knife. It will make a very clean hole in the covering (Make sure you only open the holes on the inside of the floats, you will then have a left and right float).
The floats (part f) should be approximately 14” from center to center (see photo above). The carbon fiber rod needs to be cut to a length of approximately 15.5” to get a final center to center distance of 14”. Once the carbon rod is cut, trial fit the two 15.5” spreader rods in the floats (part f). Make sure they don’t push on the outside covering. Now that the fit is satisfactory, you must scuff up the portion of the carbon rods that protrudes into the floats (part f). This can be accomplished with a sanding block or file.
It is very important that the carbon rods are glued in straight and that the floats are parallel to each other. The best way to accomplish this is to first put the floats (part f) in their cradles (part c) then line them up against a straight edge (in this case, a wall). Now, trial fit the assembly together and make sure you have 14” from center to center as stated above.
A very slow set epoxy (overnight) is recommended to glue the carbon rods. This will give you the strongest bond and maximum working time. You can use half of a popsicle stick to work the epoxy into the holes for the carbon rods. Glue the rods in and make sure you have the floats (part f) parallel to each other. Let dry overnight. (Gorilla Glue works well for this also.)
Tip: You can push some foam in the ends of the carbon rods so that the excess glue will not go in the rods, but rather will be squeezed out. The epoxy can be cleaned up with Denatured Alcohol (this can be purchased at a hardware store). This will not harm the covering or melt the foam.
Mounting Floats to Apprentice
First the wheels must be removed from the original gear. Now, mount the main gear support over the rear carbon spreader with Dubro 1/8” nylon straps (#239). Use two on each side as see in the photo. Some foam safe CA can be used to strengthen the screw holes. The nose of the model is attached to the front carbon support with a piece of 1/8” spring steel.
(The original wire nose strut is not long enough). The spring steel fits very tight in the nose steering bracket. You might have to sand slightly to make fit. The wire should be about 5.25” long with a 90 degree bend as seen in the photo to the left. The new front nose strut is then mounted to the front carbon spreader rod with tie-straps. Make sure that the incidence of the wing is approximately ¾” from leading to trailing edge. This can be measured on a flat surface with the cradles on the floats. Once satisfied with the incidence of the model, tighten the screw in the nose steering arm. The push rod for the nose steering must be removed from the rudder servo. Tip: When mounting the main gear support, make sure it is in a relaxed state. Do not squeeze as it will raise the back of the model and adversely affect the wing incidence. Although the model is very predictable and forgiving, it is recommended that you have an experienced pilot fly the model and trim it out for the first flight on the water.
The Secrets to Success on the Water:
#1 Balance- As with all types of model aircraft, balance in the air and on the water is very important. Make sure that your model sits in the water similar to a boat (with the front slightly higher that the back of the floats). Also, make sure the center of gravity on the model is close to what the manual recommends. For best results, the model should be laterally balanced to make sure one float is not considerably heavier than the other.
#2 Weight- The reason this model flies so well with these floats is because the weight of the finished floats is very close to 5 ounces. This equates to an overall weight of approximately 38 ounces (model with floats, less the battery), which is less than 15% additional weight. Compared to most popular brand of fiberglass floats, this is almost unheard of. EXAMPLE: Take the 25 size floats made by E-flight. They weigh approximately 28 ounces, and the model they go on weights approximately 68 ounces with the battery. That is an incredible 40% weight increase. I have not found a model aircraft that will perform very well with this kind of weight increase.
#3 Experience- Make sure you do some research on the model you are trying to fly on floats. If you are not experienced with float flying, it is a good idea to try and find someone in your area to help you the first few times. Flying off floats is a whole different world and much more exciting that on the pavement.
I want to thank Brandon for sharing this information with the float flying community.