Floats. The knowledge of the cognoscenti is keenly sought.

[David Davis 2]

There is a small but enthusiastic group within my club who are keen on flying off water. They mostly use small foamy electric powered ARTFs which are not really my thing. However, their enthusiasm did result in me buying a set of VQ floats described as being suitable for 40-60 models on the box. The floats are 93cms or 36.6" long.

 

My problem is deciding upon which to fit them to. These are the candidates:

 

1. Senior Telemaster, an eight-foot wingspan four channel trainer powered by a Thunder Tiger 91 FS. Pros: in serviceable condition, I flew it yesterday for the first time in two years. Cons: it's rather heavy and the fuselage length is 63" or 1.6 metres long so perhaps the floats are too short.

 

2. Uproar, an early aerobatic design by Chris Olsen. 66" (1.68 metres) in the wingspan. Cons: needs a new wing.

 

3. WOT 4. Restored by a clubmate. Cons: needs radio and engine or electric motor installing.

 

I could also build a Telemaster 40 if none of the above are suitable. I have a wing, the sole survivor of a crash!

 

Should I fit a more powerful engine to a float plane than I would normally use for a model equipped with wheels?

 

[PeterF]

Other than the 40-60 size range does it give a weight range or can you find the weights of models that use that size of float as some sort of guide.

[Ernie]

Hi David, we used to fly off water at a spectacular wee loch called Monike near Dundee.

I remember that there were a couple of pitfalls.  I had a flair cub at the time, and it did look fine sitting on the water. BUT, after no time at all, it started to sag, because the glue i'd used wasn't waterproof. Also, depending on wind direction etc. there is not always the possibility of taking off and landing as normal. Think about doing all that stuff towards yourself. 

ernie

[Ace]

DD - The governing factor will be the float length. Ideally the float step needs to be just behind the cog with roughly 2" protruding out in front of the prop to prevent nosing over.  

[Don Fry]

The step is placed in the same place as the main wheels of a tail dragger, for the same reasons. You don’t need an overhang at the front, many full size don’t, but caveat, models operate in non scale rough water, and an overhang helps. 
If it flys well on wheels, it should fly well on floats, you notice less performance, but not the end of the world.

[Nick Cripps]

Alastair Sutherland published some guidelines on the design of floats in his column in RCMW some years ago. His rule of thumb was to make the volume of each float in cubic inches equal to four times the weight of the model in ounces. You could roughly measure the dimensions of the float and work out the weight of model from that. Another rule of thumb is that the length of the float should be around 75-80% of the fuselage length but the position of the step and having a couple of inches of float protruding ahead of the prop are more important.

 

There's also some good information on the Windermere Model Waterplane Flyers site WMWF.

[David Davis 2]

Given that the length of the fuselage should be 25% or so longer than the float and given that the floats are just over 36" long, that puts the Uproar in the frame with its 45" long fuselage length from the firewall to the rudder. The WOT 4 measures 36" and the STM is over five feet in length.

 

 

I have a choice of engines. An Enya 50 is in pole position but I also have an Irvine 46 and a 52. There are also a number of 48-54 fourstrokes skulling about currently unemployed.

 

Edited March 10, 2022 by David Davis 2

[Frank Skilbeck]

5 hours ago, Don Fry said:

The step is placed in the same place as the main wheels of a tail dragger, for the same reasons. You don’t need an overhang at the front, many full size don’t, but caveat, models operate in non scale rough water, and an overhang helps. 
If it flys well on wheels, it should fly well on floats, you notice less performance, but not the end of the world.

 

Don, no the step should be in the same place as the main wheels on a tricycle undercarriage, just under the c of g (see Multiplex float instructions here)

 

BTW a Wot 4 makes an excellent float plane, mine did many years service with a Laser 61 for power.

Edited March 10, 2022 by Frank Skilbeck

[Nick Cripps]

Good spot, Frank, I missed that! The step should be 1/2-3/4 inch behind the step to allow the model to rotate correctly for take-off.

 

And, yes, the Wot 4 makes a great waterplane:

 

[Nick Cripps]

1 hour ago, Nick Cripps said:

The step should be 1/2-3/4 inch behind the step

 

Doh! ?‍♂️

 

The step should be 1/2-3/4 inch behind the CG.

[SIMON CRAGG]

This might be of use to you:

 

https://www.hooked-on-rc-airplanes.com/rc-float-plane.html

[Nick Cripps]

Chuck Cunningham's article that was published in RCM is a good source of information too:

Float Flying

[John Bisset]

I made some floats for my Wot 4 a few years back, hotwire cut from foam and covered with Solartex.  I modified them after the first few flights to extend the float noses, because there was so much spray thrown up.  Float noses slightly longer than -  ahead of aircraft nose worked well for me and avoided spray and reduced dig in potential. 

[Martin Harris - Moderator]

Anyone got any comments regarding potential aerodynamic effects?  For many years I've dragged out [appropriate expression?] my Limbo Dancer fitted with a pair of floats donated to me "in case they might be useful".  Lots of fun for sliding around on and off of snow but they do have some very odd effects on flight characteristics with rather disconcerting pitch effects at any speed - no doubt due to the excessive angle between them and the chord line!

 

 

 

[Frank Skilbeck]

Yes, that does seem very excessive, I usually set mine up so they are either parallel with the wing or only have a very slight negative pitch.  If you ever flew off water with them set up like that you would run the risk of the floats digging in, apart from any aerodynamic issues. Been a long while since I flew my Wot 4 off floats, but those were parallel to the chord line and apart from the additional drag I don't recall any unusual aerodynamic effects.

[Martin Harris - Moderator]

I do fly off water Frank - but it's in a crystalline form!  Makes for easy take-offs though...

[Martin Harris - Moderator]

Like this...

 

[Nick Cripps]

I set floats up with the top surface parallel to the tailplane. You could go a degree or so negative but I think your Limbo Dancer is a bit extreme, Martin!

 

You certainly notice the effect of the extra weight of floats on a model and, being well below the cg, they tend to make the model more stable in roll. The other effect is the increase in side area often helps knife-edge.

[Martin Harris - Moderator]

8 minutes ago, Nick Cripps said:

You could go a degree or so negative but I think your Limbo Dancer is a bit extreme, Martin!

Yes, I know but I only use it to play in the rare event of snow down here and the fun is based around getting on and off the ground rather than any general flying.  My real point was to draw attention to aerodynamic considerations when fitting floats.

[Nick Cripps]

45 minutes ago, Martin Harris - Moderator said:

the fun is based around getting on and off the ground rather than any general flying

Same with waterplane flying but getting the float angle correct is more important when flying from water. Floats set at large negative angles can cause a model to leap off the water before a decent flying speed is reached causing the inevitable stall and a callout for the rescue boat. Probably no big deal on a Limbo Dancer with its low weight and high power but risky on higher-loaded models.

I appreciate you were asking for aerodynamic affects but thought it worthwhile pointing out for any others who might be tempted to follow your example without thinking it through.

[Martin Harris - Moderator]

Yes, in no way am I advising anyone to follow my arrangement, which was done for expediency without major modifications to the floats or airframe and just happened to work adequately to provide lots of fun so has remained as it was. You have to react fast when conditions are good for snow flying!  I had used more conventional skis in previous years but couldn't find them...