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Floatplane waterproofing

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Ace05/06/2020 10:38:55
321 forum posts
22 photos

I need a new hack and have always fancied flying off (fresh) water so am combining both with a Wot4 Mk3 kit fitted with airbrakes. Powered by either a Laser 100 or ASP 91 with interchangable landing gear / floats. Covering will be heatshrink.

Tail closed loop, elevator and throttle sealed with Vaseline. Fuel lines and wing seat with RTV. Waterproof ailerons / float rudder servos.

Although a reasonable pilot I am a water novice so the odd bath is likely and no matter how well I think it's sealed I expect some water to find it's way in.

1) So is spraying the inside with water based varnish to prevent any water ingress soaking into the balsa worthwhile before sealing the fuz up? Or would that then prevent any ingress from evaporating? 2) Would it be prudent to also spray the whole outside before covering? Any covering gaps/damage or seam lifts won't then allow in water? 3) My other Laser engines have an open forward vent which would probably suck in water to the fuel. Would the ASP be a better choice although I would prefer the laser if practical?

Thanks Ace

Frank Skilbeck05/06/2020 10:48:00
4729 forum posts
101 photos

My Mk 2 Wot 4 did many hours service as a float plane with a Laser 61, way back on 35 MHz. Had a couple of dunkings, the only precautions I took was to put the receiver in a balloon with some vaseline on the neck and a tie wrap. Some sealant on the wing seat is useful to stop water ingress from the spray.

I had a forward facing vent just behind the prop, no issues with water spray, if you had a dunking then the procedure was to tip the water out, make sure the electrics weren't wet and run the engine as soon as possible.

Wot 4 is no more but it was dumb thumbs event trying to fly in very strong winds, Laser 61 is doing sterling service in a Flair Fokker D7.

Alan Gorham_05/06/2020 11:01:34
1287 forum posts
145 photos

I usually paint the fuel tank bay and the part of the fus that the wing seats on with Solarfilm Clearcoat. That fuel proofs the tank bay and gives some water protection to the place where water is likely to come in if tipped up. It's a waste of time waterproofing the wood anywhere else in a Wot4 fuselage as they float nose down with everything from the wing TE back out of the water if capsized. Likewise, your proposed sealing of the control linkage exits in the rear fus is a waste of time. The first question I would ask is: "Did you build it with waterproof glue?".

I would seal the covering overlaps with something like Clearcoat though because you can get them lifting after prolonged exposure. Usually on film covered floats I find.

The place I would pay most attention to water ingress would be your aileron servo linkage exits.

John Lee05/06/2020 12:12:21
744 forum posts
72 photos

It's great fun Ace. Have a look at the tips in the Windermere Model Waterlines Flyers website. Link

Alan Gorham_05/06/2020 12:19:58
1287 forum posts
145 photos
Posted by Ace on 05/06/2020 10:38:55:

Waterproof ailerons / float rudder servos.

Do you mean you have a separate servo for water rudders? I'm guessing it must be mounted in the floats?

The Wot4 definitely doesn't need water rudders for good steering on the water. It has good air rudder authority and with the size of motor you are talking of fitting, a blast of throttle will give you enough air over the rudder to turn with. Beware of over-complications. Simpler is cheaper and doesn't fail as much.

Ace05/06/2020 12:50:05
321 forum posts
22 photos

Cheers Frank, Alan, John.

Laser tank vent up high and tucked in behind spinner sounds like a proven workable solution. May look at a latex glove which will accommodate the 2.4 whisker aerials only when floats on as it may overheat or attract condensation during prolonged hack duty.

Not started yet, thought I would ask questions first as no Ullswater crying. Will be using waterproof Aliphatic and PVA. Wing is foam, twin servo wells lined and varnished with RTV lead seal. Clearcoat in short supply so being saved for small seam seals, PV67 my choice for larger area fuelproofing. Capsized float angle is something I am pretty sure I will experience.

Good info on rudder authority as I am a big believer in KISS which is why its good to ask questions first thumbs up

Cheers John, the WMWF site is a wealth of information and was a useful along with some US sites.

Edited By Ace on 05/06/2020 12:51:53

Alan Gorham_05/06/2020 13:32:48
1287 forum posts
145 photos

If you get the Silicon seal well done on the wing seat then there is no need to put the Rx in any kind of bag as no water will get in that way. I have never bothered and in fact I think it will cause more problems through condensation forming in the Rx.

Not sure why you need RTV sealant. I use the small sized tubes of bathroom silicon from the poundshop. Works fine.

I was asking the question about your wings, because if they are built up then they may ship water through the aileron linkage exits and need drying out. Not so much of a problem on a foam wing.

If you are capsizing then you will find the engine will stop very quickly so you are unlikely to draw water into the tank vent. Think about the fact that the carb inlet is a much easier entry point and nobody takes any precautions with them..

If you are proposing to fly at a big site like Ullswater, then you have plenty of space to make your takeoff and landing approaches dead into wind and this alone will minimise the risk of turning the model over. The rescue boat is usually quite prompt at Ullswater, meaning the model will only spend around 5 mins or so turned over. I honestly wouldn't get too paranoid about trying to waterproof everything on a model like a Wot4.

Geoff S05/06/2020 14:29:32
3664 forum posts
26 photos

My first foray into radio control was model yacht racing because I'd had to give up my dinghy racing passion after what turned out to be a life-changing cycle accident. In a breeze, downwind sailing could result in the only parts of the model out of the water being the mast and sails - the hull and its electronic contents being submerged.

Normal practice was to house the receiver and battery (27Mhz 2 channel and 5 cell 500maH nicads) in a screw-top pot with holes for arial, rudder servo and sail winch outlet. Sail winches were probably designed to be water resistant anyway but I used normal Futaba servos (148s probably) but I took them apart and sprayed the circuit board with a sealant (can't recall what but probably 'borrowed' from work) and sealed the case joint with silicon.

After every race there was water in the hull which was drained but I can't recall any problems with water affected electical components. Receivers and modern servos are probably more (fresh) water resistant with surface mount components than the cheap 27 Mhz stuff I and most were using (only 2 channel control is permitted in International 1 metre yachts) so I doubt if there will be a problem if minimal care is taken with the installation. Of course the consequences of gear failure are rather higher with an aircraft than a boat


Alan Gorham_05/06/2020 14:35:25
1287 forum posts
145 photos

Actually I would argue that modern SMT based gear with smaller pin and lead pitches is more susceptible to water damage/malfunction than older stuff.

However, my point is that a floatplane is not a model boat and water ingress into the electronics is much less of an issue if minimal but carefully thought out precautions are taken.

Ace05/06/2020 16:45:52
321 forum posts
22 photos

Vent concern was more to do with sucking float tip and prop spray while on the surface contaminating the fuel leading to an unreliable engine. That said the amounts in a 9/11 oz tank will be tiny. Laser it is.

Agree cheap silicone would do fine but "free" RTV is better wink

I suspect miniaturization and complexity probably leaves our equipment more vulnerable. However I will only be in fresh water, saltwater would be far more serious. Will make every effort to keep any water out and try without an electrical cover. After all if it gets a dunking its already down. I can always take a latex glove with me.

Robin Colbourne05/06/2020 22:09:40
590 forum posts
17 photos

RTV just means 'Room Temperature Vulcanizing', i.e. it cures on exposure to atmospheric moisture at room temperature. Therefore bathroom silicone sealant is RTV, although it often has fillers in to reduce the cost and possibly enhance certain properties, so isn't 100% silicone.

What 100% RTV Silicone means

Ace06/06/2020 01:03:05
321 forum posts
22 photos

Thanks Robin for those who were wondering what the difference was thumbs up

For me - Better because it's "free" wink  Our 100% also has a cross link additive which enhances its's ability to stick like snot to a horse hair blanket. If it wasn't free I would also use cheap poundland silicone.

Edited By Ace on 06/06/2020 01:11:00

Ace06/06/2020 10:43:45
321 forum posts
22 photos

Out of curiosity I did a test for the weight penalty of varnishing the bare wood interior over and above the usual engine/tank bay, 4 sides x 2g = 8g. However as it was water based this relaxed the fibers and bowed the sheet slightly, returning to flat once dried. The test sheet was very thin 1/32" balsa and of course was completely unrestrained and not part of a ridged structure. I doubt the 1/8" sheet in a ridged wot4 fuz would react the same! It also took the film well so may also consider running a brush width under where all the intended film joins will be on the whole airframe. Of course 8g behind the c o g will mean 32g up front but then the laser 100 is over and above normal so useful wt is always better than lead. Will see how I feel when I get to the decision point of the build.

test 1.jpg

Varnish (ed) was a spelling mistake not a water smudgeembarrassed

Water test thumbs up

Edited By Ace on 06/06/2020 10:48:54

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