How To Build SEA-SKY FLYER at Home

It handles very well both on the water and in the air. Takeoffs & landings are easy & fun. The wider stance contributes to the water flying stability, while the slightly lower dihedral angle on the shorter wing tip panels contribute to it's being less succeptible to being flipped by a gust of wind from the side.
Rudder authority & response is good, and the roll rate is quite fast. The T-tail elevator works well, and this approach gets it up out of the water, while the trailing edge runs on the water cleanly. By having the rudder extended beyond the wing's trailing edge, it acts as a very effective water rudder while on the water.
It's flying off water at about 14-1/2 ounces; it has a CF2822 motor with a GWS 8043 SF prop, Turnigy Plush 18A ESC, and a 3S 1050 30C Rhino battery pack. Servos are HXT900s; the receiver is a Corona 6 channel with a base-loaded antenna modification. Control rods are 1.5mm CF rods; these are also used in opposing pairs, inset into the surface of the Bluecor foam, for stiffening structures in the airframe.
I'll be adding the LED lighting system for night flying before I do the 'beauty work"- adding some color & trim. But the test flights are completed, and it's definitely "two thumbs up" for this one!
It's basic airframe is a Disc wing with dihedral outer wingtip panels, similar to the Nutball and Lee's SEA-SKY FLYER that are discussed on RCGroups in the 'Foamies-Scratchbuilt' discussion forum. Variations and modifications were made in the layout and construction of this design to optimize it for water flying. Russ40 first offered a photo showing how he implemented the T-tail and the extended rudder, which inspired my going to using a T-tail elevator and extending the rudder beyond the rear edge of the disc wing, where it can also be effective as a water rudder when on the water.
The balance point is at 6" back from the wing center leading edge; I installed a pair of 1.5mm diameter CF rod stiffeners, top & bottom, at this line.

Front view, showing the wide stance. It also gives a front view of the motor installation. The EPP block on which the motor is mounted is 3" tall, 6" long, 1-3/4" wide. It has the front cut for 5 degrees of positive thrust line relative to the wing. The motor mount plate is 1/16" birch plywood; it is 1-1/4" wide and 3-7/16" high. This plate is epoxied to the EPP block. Then 4 pieces of scrap 1/16" (1.mmm) CF rod are installed through 1/16" holes, extending back ~1.5" into the EPP foam. glued in place with thin CyA glue. The FC2822 motor is mounted to the ply plate with the mount flush with the top edge, using 4 small screws. The extra EPP foam was carved away & edges rounded before the motor mount pylon was covered with 3 mil Doculam laminating film to prevent water penetration.
The servos were installed & linkages completed, and the radio receiver installed, then the ESC had it's ends sealed with hot melt glue and was connected, tested for motor rotation direction, and was mounted to the side of the motor mount pylon before the position of the battery could be identified to establish the balance at 6" back from the leading edge. I then cut out a space for the battery so be snugly held under the EPP motor mount pylon; battery slides in from the right side, and stops against about 1/4" of EPP foam that is left in place on the left side. The battery carrying cutout is then also sealed with more of the Doculam film. The surface of the Bluecor in the areas where the Motor mount pylon is to be glued down is 'woodpeckered' usint a thicker T-pin to poke shallow holes through the surface plastic film to allow the epoxy which use here to penetrate well into the foam core of the bluecor. Once the mottor mount pylon is epoxied in place, I add two more 1.5mm CF rod pins through the lower corners of the motor mount plate back into the Blucor foam wing.

Build started: Above: EPP floats with 8 degree side cut, 3 mil Doculam covering with an extra layer sealing the bottom, ready to mount on my SEA-SKY FLYER; 1-3/8 ounces for the set after covering
Sharp edges on the float bottoms are critical for water flying. Adding side cut, as shown in the photo below, may also improve the ability of any float plane to get up on step & off the water more easily with a modest amount of power. (Mitch Poling used even more sidecut on his Aqua Sport electric float plane back in the mid-1980s, and I've been using the technique since then.)
So when cutting out floats for my SEA-SKY FLYER, I set the bandsaw to end up with an 8 degree side cut. The idea is that it allows the float to break the suction / grip of the water more easily, and it's worked well on a lot of float planes I've built previously. It also reduces the weight a bit, and trims down the frontal profile a bit. (And it looks sorta cool, too...)
From Russ's recently posted video, it's obvious that it's not necessary to do this to fly Lee's fine design from water, but if you happen to have a bandsaw & a block of EPP & are cutting out your own floats anyway, as I was last evening, then why not?
The 3 mil 'Docolam' laminating film is very tough material; Lee has been posting about using it to cover the Assasin flying wing recently. The Colorado Slope Combat guys starteded writing about it's great qualities for covering combat slope soarers within the last couple of years, too. I've had a roll around for about 10 years, and used it to seal these EPP floats. It is great material to work with. Yes, it's a bit time consuming to iron on the laminating film, but since I needed to seal the EPP so it wouldn't absorb any water, and water flying was my primary purpose for building this SEA-SKY FLYER, it's all good. I added an additional layer on the bottoms after the main covering layer was completed to make the hull surface even tougher; there's three layers on the majority of the bottoms of these floats where all of the covering overlaps.
Weight as shown, ready to mount to the 24" Bluecor KF'ed Wing is only 1-3/8 ounces for the pair. I left the gluing surface bare of covering material so that the glue can bond well to the foam. I'll also run some CF pins through the wing into the floats, tieing the floats to the spar structure, etc.
Float height at the step is 3"
There is 1-3/8" of foam behind the step- the part that is curved up & back to extend the mounting / glue surface area. This is not strictly needed- it looked good on Ross40's floats, so I used that to make the lines flow more, & add the extra glue area.
From the step forward to the tips of my floats is 10-7/8"; that gives an overall length of the foam block I started with at 11-15/16"
Width of the bottom of the hull at the step is 2"
Width at the top of each float, with the 8 degree side cut, is 1-1/4".
The hull / running surface is flat from the step forward for 4-3/4"; my floats are actually 2.9" deep at this point at the front of the flat planing / running surface area. I used a French Curve to lay out the curvature of the float bottom going forward from there to the front tips of the floats.
If you look at the photos while going over these numbers, you should be able to duplicate them .
I started with a block of scrap EPP that was ~2-3/8" thick. I cut the hull bottom shape & the tail end first in a rectangular block of foam on my band saw; I traced the first one onto my second block & cut it out.
I laid out the 2" width of my float's hull exactly in the center of the thicker EPP block so that I would be cutting an identical amount of foam off each side. Then I mounted a rip fence - a board clamped in place with C-clamps- on my band saw's table & tilted the table the 8 degrees. I then adjusted the position of the rip fence on the band saw. When I had it all set properly, I then just ran each block through the band saw twice, flipping sides between passes, thereby doing the two side cuts.
NOTE: The step on my float installation is actually intentionally set ~1/4" BEHIND the balance point / CG, which is 6" back from the center L.E. on the 24" disc. (Andy Lennon made me do it...) There's little loading on the tail edge of the disk, and the handling is ideal, from my viewpoint. The video of four takeoffs & landings within 88 seconds during the maiden flight session speaks for itself!
For water flying I wanted to work in Bluecor PP because it does not need extra sealing to keep it from absorbing water. I decided to use a second layer of the bluecor on top, doubling out the front back to a KF type strep at 40% (9-5/8") to give the added stiffness where the motor & floats are mounted, and to reduce the pitch sensitivity which a thin flat plate wing can have. The photos show my progress so far.
I decided to do a build-out of a T-tail using a single layer of the Bluecor PP (with the plastic film on both surfaces) with an added CF rod pair as stiffeners, connecting between the pair of CF rods in the wing below, up into the horizontal stabilizer's set of CF rod stiffeners. With one of these 1mm CF rods on each surface, (glued into shallow slots that were melted in with an adjustable temperature soldering iron) there is very minimal flex, since neither rod can either stretch or compress.
I've been using this technique for several years with excellent results on many different designs; you can think of the foam between these CF rod 'spar caps' as being similar to the web between the top & bottom parts of an I-beam. As long as your glue penetrates & bonds adequately, you have a very stiff & strong structure with minimal added weight. (A 1 meter long 1mm diameter solid CF rod weighs only .02 ounce & costs under a buck... a fair value in my book!)
The center area of the elevator, where the cutaway allows the rudder to travel through it's arc, has two pairs of the 1mm CF rods- a pair that are close to full span close to the hinge line, and then another shorter pair close to the cutaway. After these were glued in place, I wrapped some 3 mil doculam around the center joiner area of the elevator; I made about three fullwraps, ironing it down as I progressively wrapped it in place. This completed the stiffening of the center area of the elevator. It was then tape-hinged to the horizontal stabilizer, top & bottom, with Scotch transparent tape.
The photos below tell a lot of the story. The floats are epoxied in place with hot melt glue sealing the joint around the edges where each float joins the wing. I still need to drill & add in the CF rod pins that will further anchor the floats to the wing; that's the next step.
I saved the motor installation for last, as the battery location has to be determined close to the last stage in order to get the aircraft to balance at the desired point.
Bluecor PP build with T-tail for water flying. Front top doubler layer extends back to a KF type step at 40%
Closer look at the tailgroup assembly, which uses opposed piars of 1mm CF rods for strength & stiffening in key locations
This is a look at the basic airframe before the motor mount pylon was mounted on the front. The main wing is simply a 24" circle cut from Bluecor. I also cut out the second top front doubler layer, which extends back 9.6" to 40% of chord, where there is a clean 90 degree KF type step.
This is the vertical stabilizer and rudder as cut out, laid over a 1" grid cutting mat.
This is the horizontal stabilizer and elevator as cut out, laying on the 1" grid cutting mat.
This is the completed assembly after the 1.5mm CF rods were installed. I use a variable temperature soldering iron with the temperature set to just melt the channels nicely in the foam without melting too much. I install a wheel colar on the soldering iron tip to control the depth and lay a metal straightedge on top of the foam as a cutting guide. The wheel colar then rides on top of the metal straightedge while the tip is drawn along the edge, forming a shallow slot where the CF rod stiffeners will be glued in place.
I use a modest amount of hot melt glue to bond the CF rods into the shallow slots, sealing them in the process so that no water can penetrate in these areas. The same process was used to place the CF rod stiffeners into the vertical stabilizer after the horizontal stabilizer / elevator assembly was epoxied in a slot cut into the horizontal stabilizer; the horizontal stabilizer is parralel to the main wing panel, located 3-7/8" above the wing.
Hinging of the beveled hingre line is done with Scotch transparent tape; a slight 1/32" gap is left between the two surfaces that are being hinged. Tape is applied to the first side, then the movable control surface is folded back so that the hinge tape can be applied from the second side. The two layers of tape touch each other at the hinge line.
The cutout in the rudder which clears the elevator was cut after the H. stabilizer & rudder were installed; it just needs enough clearance to not touch when both movable control surfaces are at the limits of their travel.
October 6th, 2009: This SEA-SKY FLYER T-tail variant is ready to Fly!! Flying weight while carrying the 3S 1050 mAH 30C Rhino battery pack is at 14-1/4 ounces. The photos tell a lot of the story. I'm happy with how the build came out.
SEA-SKY FLYER T-tail ready to fly at 14-1/4 ounces, carrying a 3S 1050 30C Rhino pack. Motor pylon's EPP is also sealed with a layer of 3 mil laminating film to eliminate any water absorption.

A closer look at gear installation. The receiver antenna is modified into a base loaded configuration; sealed within the wing under clear tape. ESC case is sealed with hot melt glue.
Extended rudder clears ground, but will be effective as a water rudder.
CF2822 motor is mounted at 5 degrees positive for easy ROW takeoffs. 1.5mm CF rod pins are glued through the motor mount bulkhead into the EPP foam to anchor the motor mount solidly.
I have everything fairly well waterproofed. For the servos, I simply add a small drop of oil on the servo output shaft area- this keeps water from wicking in if some spray / moisture gets there; this works well for snow flying, too. The receiver is nicely protected under it's tape cover, & filling both ends fo the ESC's heat shrink cover with hot melt glue has worked fine in the past.... so this SEA-SKY FLYER T is ready to head to the water (or snow!)
October 10th, 2009: Above: SEA-SKY FLYER T-tail sitting on the fringe of skim ice, ready for it's first water flight. SUCCESS! - it's handling very well flying from & landing on the water!
The floats are working superbly! Handling is great, spray is minimal, and it gets up off the water effortlessly, & lands again with ease!
I had flown float planes in the past with higher dihedral ... they did fine in calm wind conditions, but when subjected to a cross-wind, we'd see the upwind wing lifted & the aircraft flipped over. So when building this SEA-SKY FLYER T-tail, I had this in mind.
My FLIRT (a 17" diameter Nutball variant) has 24 degrees of dihedral on the tip panels... more than I wanted for water flying. (On the Nutball thread recently, some builders have commented that 18 degrees still responds well to rudder control.)
So when laying out this variant of the SEA-SKY FLYER, I started with a 24" circle of Bluecor, and made 5" wide wingtip panels instead on the stock 6" wide tip panels. I set them at 20 degrees of dihedral rise. Then I made the front 40% doubler panel (with KF step at 40%) .
This gave me a 14" wide center panel on which to mount the floats on the outer edges.... and that is working as well as I had hoped it would work! The wider stance offers a bit more stability on the water, while the narrower wing tip panels at a slightly reduced angle catch less pressure from cross winds.
While playing around and 'teasing the weasel' this morning, I still managed to have a couple of gusts flip it over on two occasions.... but it was no big deal. I'd brought along a light spinning rod with a lure to use in such cases, so it was back to shore, the excess water shaken off, and back in the air flying again very quickly.
Friends, I finally had a chance to do some more water flying this morning. I continue to be impressed with how well this aircraft handles both off the water, and in the air. It does outside loops as easily as inside loops, and can be held in inverted flight for extended periods if desired. The roll rate is very quick, and it can be flown through a quick series of consecutive rolls very nicely if you simply add in some down elevator during the inverted portion of each roll. It also does decent flat spins, and can turn quite tightly when desired. Control authority is fine- all I would ever ask for. With the double layer leading edge, it is not pitch sensitive, and it handles full throttle high speed flight smoothly. This may just be the best RET controlled aircraft that I've ever built!

I did manage to have water get into my Flysky receiver after flying for a while... in the middle of flying some acrobatics, the aircraft abruptly stopped responding and dove straight down for the water from ~40 feet up. The only damage was a crack in the Bluecor wing panel which can be quickly repaired with some foam-safe CyA. The receiver needed to be opened up & dried out, which I did; it's now perfectly happy once more, ready for more flying.

I've always enjoyed water flying, so I'm having a great time with this float plane! It doesn't need much room to fly comfortably. The pond I fly from, which is within 1/2 mile of our home is modest sized, yet it's plenty large for flying a float plane that is capable of maneuvering in such a modest amount of space, and which slows down to land so nicely.
Russ mentioned his SEA-SKY FLYER bogging down in deep soft snow... it brought to mind a couple guys who used to come to fly at our winter fly-ins who had a matching pair of well-powered lightweight aerobatic aircraft with deep chord symmetrical wings; underneath, where the gear would mount a pair of wheels in the summer (taildragger setup), they had mounted a single WIDE ski- maybe 12" wide and 12" to 14" long. It was made from thin birch aircraft plywood. They could takeoff, land, & generally do very irreverent things on the deep soft powder snow with this single wide ski underneath- much better than most twin ski setups were doing on the un-groomed snow surface.

Maybe it's time to design a foamie 'BIGFOOT' soft snow flyer.

Bigfoot Overshoes?

In keeping with the K.I.S.S. principle...

It may be far simpler to simply add a wider 'ski' running surface to the existing foam ski / floats on a SEA-SKY FLYER. Instead of having 2" wide bottoms, why not add on a plastic overlay that serves as a ski surface that's ~3-1/2" wide? That should handle really soft powder snow.

I'm thinking of either sheet polycarbonate material, or simply the plastic from a 2 litre soda bottle. Attachment can be done with the wide double stick 'Carpet Tape', with a bit of nylon filament tape where appropriate on the front edge, etc.

This would be a removable modification, so that you can go back to the standard condition for most flying; when the deep powder snow comes along, you can again quickly put the "Bigfoot Overshoes" back on!

Works for me... I have ~9" of fresh snow... this may be a good day to test out this brainstorm !
The "BIGFOOT OVERSHOES" are handling GREAT on the snow!


I pulled out a sheet of clear polycarbonate (lexan) which I had bought from Balsa-Bangalore a while back, and cut out a pair of "BIGFOOT OVERSHOES" for my T-Tail SEA-SKY FLYER. I made them 3/4" wider on each side of the 2" wide skis = 3-1/2" wide. They taper down to the width of the noses of my skis in front. This polycarbonate material is tough and very resilient- it cuts well, but will not crack in the cold conditions... ideal for this purpose.

I then peeled off the protective film that came on the Polycarbonate, and used Scotch Extreme cross-filament tape to mount these to the skis. This tape has the most agressive adhesive I have worked with; it grabs onto stuff and just doesn't let go!

The results are in the photos below; the T-Tail SEA-SKY FLYER is now flying with 3-3/4" wide skis! (This material is totally clear- invisible in the air, & not easy to photograph, but I think that these photos give you an idea- it's a fairly simple process.

So how do they work? GREAT!! I just took out the SEA-SKY FLYER across the road from the end of my driveway to a part of a lot that's vacant and unimproved... there is some tall grass and some potentilla bushes sticking out of ~14" of snow. No problem!! I was playing around doing takeoffs & landings, abusing the vegetation, and just generally having a lot of fun. Beating up on small bushes certainly doesn't phase the polycarbonate material- it'll hold up to a lot of irreverent flying. And the SEA-SKY FLYER is sitting high, not sinking in much at all in this new softer snow.

Each 3-3/4" x 12" 'overshoe' weighs 16.4 grams; so that's roughly an added 34 grams added to the floats. Yet in flight, I did find myself adding two clicks of down-trim, so there is a slight climb influence on the aircraft, despite the added weight.

Roll rate is still fast- about 1 roll per second, either right or left, on low rates; I didn't kick it into high rates for this test flight.

So here's one simple solution for flying from deep soft snow - simply add a pair of "BIGFOOT OVERSHOES" to your SEA-SKY FLYER's float bottoms!
These are the "BIGFOOT OVERSHOES" which I added to my SEA-SKY FLYER's floats, made from Lexan Polycarbonate, 3-1/2" wide, tapered narrower at the front.

This polycarbonate sheet came from Balsa USA, and it's clear, very slick, and very resilient. 16.4g per 'overshoe'. Taped in place with Scotch Extreme tape which has a VERY agressive hold.
I had been flying a GWS 8043 prop on the EMAX CF 2822 motor since building this aircraft in early October... but the GWS slowfly props are a bit more flexible than I like on some motors. So today I took a GWS DD 9x5 prop which I had trimmed down to 8-1/8", and installed it. I'm liking how this stiffer DD prop is flying the SEA-SKY FLYER, so it'll be staying on it.

***Note***This method is done by Mr. Bruce Stenulson's and pictures has been taken himself personally. Click here to visit his personal page for more information.