Airborne Magazine


Water Rat plans are available from: Airborne Plans Service for AU$45.00 (2 sheets) plus P&H2 (AU$2.80 within Australia).  
Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).Plan No. 645
To return to Airbornes home page

I have always had that yearning to build a float plane, but there were so many unknown factors that I just took the easy way out and built a glider or a P51 or something else instead. I didn't know anyone who could give me any clues about float planes, i.e. taking off on water or landing on water. (The two big unknowns). 1 have always done things pretty much on my own when it comes to modelling and so, when Airborne plans department offered me a float plane project, I jumped at the opportunity. As I always test fly on my own aircraft. I was going to learn to fly off water and land on water with a prototype aircraft, and if I could do this with no assistance, then that would be a great recommendation for the Water Rat. Well, I did it and it was a great feeling and a lot easier than I had imagined, but more of that later in the flying review.

The Water Rat is a very distinctive aircraft combining the looks of a pylon racer, sport aircraft and float plane all in one. I believe it to be one of the more attractive of the sport float planes available today. The long nose (if you can imagine it with exhaust stacks) even has an almost Spitfire'ish look. Even the floats have that 'full size' look about them, giving the aircraft that more 'realistic' look.

The Water Rat can easily be adapted to fly off terra firma as well,(details shown on plan) so even if you make the float version, make sure you fit the tail skid as you may be short of a plane for your local club 'fly in' one day.


Mark and cut out all the formers.

Cut out the two top float skins, remembering to leave a little overlap at the rear to blend in with the rear balsa block. Cut out the keels, as well as the plywood undercarriage support plates. You may also cut out the float side panels.

Draw a centre line the length of the float top skin and mark the position of all the formers and ply undercarriage support plates. Lay and pin the top skins to the building board and arrange and glue all formers into position.

Glue the ply undercarriage mounting blocks in place and then lay on the keels.

When the skeletons have set, temporarily lift them from the board and mark the position of the spreader bar mounting bolts. Drill the 3ram holes and recess them with a 4.5mm drill to fit the blind nut assemblies now.

Fit the BOTTOM skins, butting them together on the centre line and making sure that they are flush with the outer edges of all formers, then apply the side skins.

Carve the balsa blocks to closely fit the front and rear of your floats. Glue them on and when dry, sand the float assemblies in preparation for finishing and then add the keel strips of hard 3mm square balsa. Now liberally dope the floats to seal them. I now finished the floats by the tissue and dope method. I undercoated them with grey primer surfacer and painted them.

Make up the float spreader bars and bend the 3mm piano wire as per the plan. Sand the spreaders to shape and then bind, solder and glue them together. Mark and drill the mounting holes to suit.


Cut out all formers, ply and balsa, doublers and fuselage sides.

Mark the positions of the 3mm x 6.5mm spruce 1ongerons and glue them into place.

Glue on the 1.5mm ply doublers and the wing seat doubler. Glue F2 into place on one half of the fuselage. Continue with F3, F4 and F5 and when set fit the fuselage' sides together, making sure the four formers are square.

Join the rear of the fuselage halves together, insert F6, F7 and F8 and glue in place. Next insert the ply tail plane seat. Now fit the wing seat and all the 9.5mm tri stock balsa along the bottom of the rear fuselage.

Do not drill the holes for the wing bolts until fitment of the wing is being undertaken. UI and U2 can now be positioned and glued in place. Add a bit of tri stock around U2 to reinforce the area.

Install the servo rails and install your choice of push or nyrods.

Now fit Fi in position with 2 degrees RH thrust. Sit the motor and mount assembly in place and mark the position of the mounting bolts, fuel line access holes and the throttle cable. Drill all the required holes.

Fit the engine mount blind nuts in place. Now cover the rear, top of the fuse with 3mm balsa and the top balsa block. Sand to shape.

Next I fitted the fuel tank and plumbing, and the throttle cable and epoxied the ply nose ring in position.

Now build up the rest of the cowl to the nose ring, leaving access holes where required.

Complete the top front half of the fuselage and cockpit area. Glue balsa blocks together to make up the lower front fuselage and engine cowl. Epoxy in place and finally trim to rough shape. Have the motor in place.


Cut all parts and build as per plan and sand to the finished shape. You may wish to cover the assemblies with film and fit the hinges, before affixing them to the fuselage. Fit the ply tail skid plate to the rudder and bind and epoxy the piano wire skid.

Glue the vertical fin squarely to the stabiliser. Now glue the assembly to the fuselage ensuring it is square. Fill in the gaps on the top of the tailplane with scrap 12mm balsa and sand to shape.

Fit your servos temporarily and make up the pushrods. Once the rods have been fitted, the bottom of the fuselage may be sheeted over.


Cut out all the ribs and ply wing braces. Assemble the wing either side of spars. Make two tapered packing strips, 810mm long and tapering from 6.5mm. These are used as packing under the main spar when you fix it to the building board over the plan. Secure the spar assembly to the board with pins. Now fit in place wing ribs W5 through to W12, but don't glue them yet. Cut two trailing edge pieces (aileron spars) from 6.5mm balsa, 815mm in length and 12mm deep at one end, tapering to 11mm at the wing tip end. Insert some 10mm packing under the rear of W12 and some more 10mm packing under the rear of W5. Pin and glue the aileron spars to ribs W5 and W12 and glue these ribs in their respective positions over the plan. Do not glue ribs W6 to WI 1 yet, nor ribs WI to W4. Cut the false leading edges from the 3mm sheet. These are 815mm long and taper from 17.5mm to 14mm. Now glue the false leading edges to ribs W12 and W5 and butt joint them together in the centre of the wing.

When secure, glue ribs W6 to W11 in place. Now install the ribs W1, W2, W3 and W4. I used cyano to tack the ribs and added P.V.A. later. While the assembly is still pinned to the board glue in the triangular gussets and then add the trailing edge top sheeting and the webs between W5 and W12. Apply the leading edge sheeting and when dry lift the whole assembly from the board and turn it over. Fit the balsa block wing mount supports inside the trailing edge spars, and then pin each trailing edge, in turn, flat to the building board, and add the lower trailing edge sheeting.

Finish all the sheeting and cap stripping on the bottom and then turn the wing over to finish the centre sheeting. Cut your servo mount plate from 1.5mm ply and glue it in position. Fit the stock leading edge and add the wing tip blocks and the wing tip trailing edge. Add the centre trailing edge pieces and slot them to accommodate the aileron torsion rods, which of course must be fitted at the same time. Finally cut your ailerons to length. Slot and hinge the ailerons for a prefit. Temporarily fit the servo so that you can measure and make up the aileron pushrods.

Sit the wing in position on the fuselage and check fitment. Sand the leading edge flat where it butts against the F2 former. mark the position of .the wing locating dowels and drill the leading edge to suit. Put a little epoxy into the holes in the leading edge and then push in the dowels. Sit the wing into position on the fuselage.

Mark the position of the wing hold down bolts and then drill carefully straight through the wing and the anchor plate in the fuselage with a drill and tap to suit your wing bolts.

Finish the underside fuselage sheeting under the wing. Sand and shape the blend into the fuselage and finish by adding 1.5mm ply plates for wing bolts.


The cockpit area was kept simple. I made a very simple instrument panel on my computer and painted the area matt black. The pilot was a survivor of a piloting blunder in a P51 Mustang, and was not too impressed about having to test fly a float plane when he had never had any experience with such a beast before. However, 1 assured him that this was an Airborne design and he was quite OK after that and settled into his glue nicely. 1 then applied the canopy quickly with Super Glue before he could change his mind.

Ailerons are fixed into place after they have been covered with film.

Now you can sand and finish. I chose to tissue and dope the fuselage, finishing with grey primer/surfacer and quick dry Dulux enamel. The wings and tailplane were covered with film. Finally I fitted the radio gear and made and exit hole for the antenna just behind the cockpit to keep the antenna as high as possible. The Water Rat weighed in at 8.51bs or 3.78kgs.


I carried out initial motor run and pre flight checks at home so that I would hopefully solve any unforeseen problems before a journey to the water. Everything worked fine. I use a Perry pump on the motor and do not use fuel pressure. The thing that startled me was that I could taxi the Water Rat with floats around on the lawn just like a wheeled aircraft, and steer it accurately just with the rudder. I had been concerned that it may be a little hard to steer in the water without a water rudder. In actual fact is steered better on the lawn than in the water.

We had planned a day at a beautiful spot near Warwick in Queensland with our daughter and family. They have a boat (need 1 say more). Leslie Dam is perfect for model float planes as it has very shallow edges and a very gentle slopes all around its perimeter. You can wade out for 10 or 20 metres and only get your shorts wet. It is very popular with water skiers and personal water craft. and has excellent fishing as well There are plenty of places to launch a model from, keeping in mind ski boats and the safety of other people. Even so there was no-one within cooee of US.

In the initial flights the C of G was 25mm forward of the plan position with no fuel in the tank however I elected fly it like this as I prefer a nose heavy aircraft. Once the wing is in place a radio check was carried out. Next I took the plunge and lowered the Water Rat into the water. Wow! (I get excited over a piece of string). Even though the water at that stage was quite choppy the plane felt extremely buoyant and bobbed about quite happily

I pushed it quite hard into the waves and it handled them beautifully. Now was the time to fuel up and recheck the floats with 10oz. of fuel in the tank No problem at all. in fact the extra weight seemed to make no difference at all. 1 was determined to find some fauh with this floating beast and so I picked it up and dropped it into the water. No problem. Next 1 tried rocking the thing from side to side and diving it into the water at a steep angle. All it did was bounce up happily and taunt me some more. I gave up the float test more than happy with the result.

Next came the taxi tests. Once the motor was going I had a quick taxi and even though it was quite choppy and there were some rather large waves, decided to open her up. The wind was blowing directly into my face so I knew that if the motor cut the plane would soon blow back to me. 1 will never forget that moment, watching the plane attacking the waves and when a larger wave came the floats would just go through it. This proved the plane to be very stable and prop clearance adequate. The other little thing that niggled at me was the fact that the carby was pointed down and into the waves. This was not a problem as even with all the splashing and spray the motor did not hesitate. I eased back the stick a tiny bit and she started skimming the tops of the waves. As it climbed away 1 adjusted in a little bit of right trim and a touch of up elevator. The Water Rat felt good right from the start.

After a circuit to recheck trims, I went straight into some rolls. I expected that the rolls would be a bit barrelly, but I have never ever managed such perfect rolls!

There was no inclination to barrel at all. Next a loop. Slight roll off at the top. Adjust rudder trim and try again. Perfect. Talk about a plane on rails, this is it. On descending turns, the Water Rat had a tendency to tighten in, but I believe that this was due solely to the extremely forward centre of gravity that I had chosen to initial flights with. While everything was going good I thought that 1 should set up for a landing. Throttle down and complete a full low circuit. The water was still very choppy, but this is what these test flights are for isn't it? Flying in from out over the water to circle terra firma out behind me and then touch down into wind the motor cut as I circled behind me. Now this doesn't normally worry me in the least, but Anyway there was no problem with the Water Rat she just carried on greasin'. In whistled in past me and the touch down was so beautiful to watch I wish you there. I decided to have a spell until wind died down in the evening. This me time to make adjustments to the push rods so that trims could be returned to neutral.

The wind did not drop until about hour before dark and so my flying was at a premium. All checked out and taxiing out with only a slight breeze. I noticed that the steering did not respond as well in the water as it did on the at home. The turning circle was large, but manageable. If there was any breeze, it made directional control on water more difficult, however, with a bit of throttle manipulation I coped quite well. If you had limited manoeuvring area, I would suggest a water rudder.

Back to flying. Throttle up and off we go. This is so easy. I believe it is easier than flying off grass which really surprised me. The Water Rat does not have to be dragged off the water, but flies itself off and looks good doing it. Landings are a joy to watch, not only for the pilot, but also for the many observers that seem to materialise from who knows where. As it was getting late I concentrated on circuits to get as many take offs and landings as I could. Apart from one landing they were all greasers. The other one? I was a little high and tried to dive in a bit quick. If it had been on ground then 1 probably would have cartwheeled. However, there was just a bigger splash than normal as the wing and floats hit the water and it righted itself instantly, so I carried on flying circuits. With all the excitement I forgot to try inverted but the way the Water Rat rolls I have no doubt that it is more than capable of this as well. My personal joy comes from the takeoffs and landings on the water and I am looking forward to many more.

Airborne deserves full credit this amazing aircraft on floats.


The Water Rat performs very much like a pattern ship. It also flies very fast with a .60 motor and is not a beginners model. It must have plenty of room to slow down as it is a very clean aircraft. Nice wide final circuits are recommended. I had never flown off the water nor had I even seen a float - plane flown before, but I found the Water Rat so easy on the take offs and landings that I will probably worry myself sick next time I have to take off on solid ground.

The .61 motor had enough power that I believe with floats it could take off from solid ground. In fact, on the last flight I taxied the plane to the beach and then up the beach to my flight box which was twenty feet away from the water. I might add that I had applied a 3mm strip of carbon fibre to each keel just to add a bit of protection from abrasion. As for the exP51 Mustang pilot ... I can't get him out of the Water Rat. He looks so happy.


Type: R/C Sports Float Plane
Wingspan: 1.6 metre
Length: 1.25 metre
.60 - .90
Weight: 3.78 kg
Radio: 4 function R/C required

Water Rat plans are available from:
Airborne Plans Service
AU$45 (2 sheets) plus AU$2.80 P&H1

Plan No. 645

Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).

Click here to order this plan

To return to Airbornes home page

or you can contact our Credit Card Orders Centre
Phone: 61 3 9333 5100
Fax: 61 3 9333 5099
Or E-mail us

This page was last modified on the 21-May-02