View Full Version : Conversion for seaplane

01-14-2007, 12:49 PM
Am considering my first seaplane - Katarina, a design by Ross Giddy, plans published by Model Activity Press some years ago.
I quote author "Original choice was an OS15FP and this was adequate from hand launch but not enough thrust to lift off water. Repowered with an ASP21 - the takeoff from water was fine. Later an OS25FX was tried and this arrangement is magic and has power to spare".

Rough estimates of AUW of glo plant (motor, muffler, mounts, full tank, servo, linkage etc....) is 17ozs / 500grams.

Given the good advice from the forum I would be looking for an electric in the class 400W with an AUW (motor, mount, 1/2 of total battery weight etc.....) less than the above.

Advice please on best plant, any special hints about flying electric off water would be much appreciated. :)

01-16-2007, 09:34 PM
Hi George
Flying off water by electricity is great - no deadsticks, as long as you set and obey your motor run timer!

Don't know that particular model, but the best all round electric flying boat is the Hobby Hangar "Pondside" - this is a 48" span ultralight three channel that I've had three of! Flown on variously, from a Graupner S600 on six 1200mA nicads (a long while ago!) to a seven cell / Astro 035 cobalt.

Judging from the notes you include on the glow engines, you'll need something like 3S in Lipo batteries - 10 x 2200 NiMh would work, but you have to watch the weight on a flying boat. Too heavy and it'll sit too low in the water to ever take off, even though it might be well able to fly.

You also have to watch your prop size - outrunners like the AXI series may demand a larger prop diameter than the model will take, and raising an already high thrustline may cause more problems at take-off.

Perhaps something like the Mega 22 series - perhaps the /30 model in 3 turn? That's a conventional / inrunner motor with enough torque to enable it to turn a decent sized prop in direct drive model. I can't see a cheap solution - that OS25FX is a very powerful engine for its size indeed.

You should be able to lose some weight around the model - for one, you don't need as strong a motor mounting pylon for an electric model as for a glow engine, which must also have its fuel tank right up there behind it.

The Pondside, for example, did fine with my 200W Astro mounted on top of two 1/4" x 1/2" ( 6 x 12 mm) spruce struts with a 3mm Birch ply mount plate between them! It had the battery and ESC down in the fuselage, of course.

Hope that helps


04-06-2007, 03:19 PM
Dereck, all great advice, many thanks. What the hell is lipo and the figures that follow. I know NiMh, NICAD.....Is is it Lithium Oxide cells and what is the designation please? :confused:

04-06-2007, 04:08 PM
Sorry George - figured if I'd gotten to understand LiPo terminology, everyone else had already! Am one of the worst around for rushing out and buying new stuff just because I've been told to :)

If you're happy with NiMh/Nicad - stick with them, they have a lot of mileage left in them, despite what marketing says about the new stuff. LiPo batteries need all sorts of care and attention lest you burn up/down your model / car / garage / house.

Bearing in mind that a flying boat battery is basically bolted and sealed well in under either the wing or a hatch, I'd prefer to fly something your size on around 8 300-ish nimh - maybe 10 at around 2000-ish. A lipo - lithium polymer - will get hot and sweaty in there - cooling airflow does not work in floatyboats, I met someone who tried it once - and while your clubmates may appreciate a fifteen minute flight that ends in a smoke trail to a fiery water landing, you probably won't don't want to chance it.

If you want to contemplate messing with lipos - go read the forums up top dedicated to the things. Might even put you off the idea ...

Another idle thought. As I eventually proved, sinking your flying boat up to its armpits in water is on your horizon - not 'if', more 'when'. FWIW - I landed on the neighbourhood turtle, outside a buddy's family lakeside place! A brushed motor and ESC is not only cheaper in this scenario, but more likely to survive to fly on a drier day!

My Pondside ended up with the entire radio fit submerged - the radio was quietly written off, but I recall that the Astro motor and Kontronics ESC actually made it to fly another day. OTOH, have heard odd tales of brushless stuff dying after submersion. However, it might be more a case of how bad your luck really is on the day.

Hope that helps


04-06-2007, 04:49 PM
Dereck, all very good advice thank you. As it happens I have just spent the last hour reading up on LiPo's. If cost is an issue (cells and chargers etc), scrapping old, very servicable but (kiss) gear does bother me.

I had intended sealing all radio gear in plastic bags to keep out the damp. The servos operate quite comfortably with loose plastic attached to the pushrods. So I at least can limit sink salvage to motors, cells and ESC. Who knows? the NiMH might survive.

Thanks again for the v.good pointers.

04-06-2007, 06:26 PM
Hi George
All my RC gear was in a sealed forward compartment - I didn't bother to bag it up, though I've heard of others doing it. My concern was condensation forming inside the plastic bags. As my servos were well ahead of the rear bulkhead, there was no problem with pushrod movement - I used Sullivan Goldenrods, as usual for the rudder / ele pushrods. The ESC was in the same compartment with the servos and RX, all wires through the bulkhead / former under the wing LE were silicone goop sealed after thorough testing.

Of course, when I landed atop that b!@@&y turtle, the forward compartment was the first thing to be breached ....

The next floatyboat gets a thinner balsa underside skinned with 1/64" ply! The PS only has a 3/32" balsa underside, which is fine until you hit something hard.


04-20-2007, 12:35 AM
Dereck, seems to be a dearth of floatyboat interest out there, but I have always loved the things and now intend to make my interest real.
I have a few (perhaps radical) ideas which should be worth a try. Semi scale, high wing, completely sealed (perhaps moulded carbon or PVC) fuselage, motor and power source located in the high wing (might cause too high a CG point on the fuselage cross section) so would need a good water level beam and stability.
Forced airflow from the prop accross the top of the wing through slots on the top of the wing through to the rear (behind the main beam) where the batteries would be located. The heated forced air ejected from the centre section trailing edge (might give a thrust advantage to offset the drag caused by the slots).

This way I only lose the motor and batteries but I keep all floating.

let me know what you think glf

04-20-2007, 01:40 AM
Hi George
I once came across a Puddlemaster that had been fitted with cooling air in and out ducts. The builder was an incredibly clever engineer - he told me that - who had done all sorts of clever calculations to figure out where to put the airscoops so that no water would get in.

Ecept that the first time he put her in the water and opened up the power, she nearly sank.

Seems that nature didn't know how clever he was, and the water just rushed in anyway.

I'm going to stick with a completely sealed model on the next one I build - just like the other three! Though I might just design my own, using the well-known parameters for combining floating with flying. Either I've got them written down someplace, or I still have a Pondmaster plan someplace.

The easiest route is my old one though - get another Pondmaster kit from Hobby Hangar down in Florida!

Your idea of a plastic or CF fuselage is good though - it would be hard to breach. There was a flying boat plan published in England in the last couple of years with the battery up in the wing - spanwise of course - but it looks to put a lot of weight up high. It worked well enough, but it does put a constraint on the wing, which now not only has to be the right shape to fly the model, it also has to contain a battery. But it could well work.

Based on my one sinking session, it could well have kept the battery out of the water, though my NiMh pack survived the immersion.

Mostly though, we need experimenters more than ever now, so go for it and good luck



04-20-2007, 01:20 PM
Dereck, my thoughts are turning toward a modified Grumman G44 Widgeon for single motor initially. Completely sealed hull/fuselage, completely sealed wing except for the motor nacelle and a moisture proofed space behind the main spar of the wing centre section where the batteries would sit.

Starting point for the design would be the size of the batteries which would be dictated by the centre section rib. The compartment would have slot forced air inflow end would exit out of a split centre section rear spar - much like the B2 technique.

Question, how much water and spray is thrown up over the wing while taxiing and during take off/landing?

Should this prove successful, I can replace the wing with the twin motors to make the model semi-scale.


04-23-2007, 01:13 AM
George and Dereck,

I have a Puddlemaster from the Ace kit. Instead of the speed 500/600 up top I installed two speed 400 6.0V motors on the wing to create a nice looking twin.

Came in at about 38 ounces all up with the original 7x1250 SCRs. It is now down to about 36 ounces with 7xGP2000 cells. The ESC is an Astro 215D driving two HS-60 servos.

I have her all sealed up and access is through the wing opening; I did not implement the forward hatch. The wing is secured with rubber bands and sets on a bead of silicone seal (created by banding the wing on with a wax paper separator while the silicone cured).

So far the electronics have not overheated on a typical seven minute flight. They never did on the 1250s, and haven't yet on the 2000s. The batteries come out pretty hot after the flight. I'm reluctant to go to lipos because of the longer flight times.

The only thing I would do to improve the Puddle Master would be to add some "V" to the flat-bottomed hull. With the flat bottom, even the smoothest landings tend to bounce a bit. But I wonder if the v-hull would be harder to un-stick? As is, the flat bottom gets off the water very quickly. Lots of fun.