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Aerotow from water


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Yesterday the first test flight of the Cularis with floats was completed successfully on Levisham and ended with a nice landing on the ... er .. bracken?! I got some photos from my phone: ht

Found this video on Youtube - John, have you seen it? Phil.    

Erm - just put the electric thingie in the front?

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oipigface

Mark took most of the pictures just after the second attempt at a flight started, and they don’t show the beast at its best. It won’t loop or roll, but it could have been designed to do stall turns. 
We tried the first flight in 5m/s air, which wasn’t quite enough, and I landed at the bottom of Levisham having established that a lot more up trim was needed. By the time I got back from the retrieval, the wind had increased to 8m/s. 10 clicks of up, and it soared out of Mark’s hand with a bit of up elevator applied. 5 minutes of trimming and trying various things and I had learned that the extra 200g or so means that it likes to fly much faster than without the floats. I’ve never tried to fly it with ballast, but perhaps I should. All that drag underneath requires more elevator trim, and turns are much better with some rudder assist, so I’m going to program some in.

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  • 2 weeks later...
oipigface

Since the competition at the Bwlch was cancelled today, I spent most of it in the shed, limiting myself to just 5 frames of the snooker.
I’ve now finished fitting the 1/64” ply tops to them, and they are gratifyingly light and stiff. The downside was that I managed to glue one of the bellcranks to the top, so I had to do some surgery to release it, and mend one of the closed loop threads which had suffered under the strain. It was quite easy to open the bottom up for access. 
Most of today I’ve spent working on the water rudders. I’ve been thinking a lot about how to prevent epoxy getting into the shaft bearings, which are flush with the tops, but exposed. The photos show what I decided to do.

582C94DB-CCBF-49D4-9B18-B4B039488744.thumb.jpeg.775000532fa0a8b7290a3102448b57e1.jpeg

First, I covered the rear ends with masking tape, then I cut out a circular piece using the flange of each bearing as a guide.  Then I put a tiny drop of oil in each ball race. The internal shafts are 4/2mm CF tube, and I’m going to glue the external parts of the shafts (which carry the tillers) into them using 2mm rod. Because of this, I didn’t want to get any release agent inside the shafts, so I stuck a piece of rod into each of them, before spraying them liberally -3 coats - with R5.

BD4A3A2E-DDFD-4616-8C04-E01DFB68701C.thumb.jpeg.5bc5392f50c060ac4498dd3d2502f583.jpeg
Half an hour later, I removed the masking tape to reveal two wax encrusted bearings, which I then covered with little circles of masking tape. 
And now I’ve got my fingers crossed that that will do the trick.

I’m almost ready to do the final covering with fibre glass and epoxy now. 

 

 

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SilentPilot

Congratulations, it seems to fly well :) 

Have you had it on water yet? I’m no expert at float plane dynamics but I think the floats might need to be further apart. The long wings aren’t the only problem, I’m looking at the triangle formed from the two floats and the fuselage, it seems narrow and tall.

The high CG (relative to the floats while on water) and the moment arm from the long wings could make it unstable.

Coming along nicely though! 

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Phil.Taylor

Found this video on Youtube - John, have you seen it?

Phil.

 

 

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Marc RC pilot

Amazing! Hat off to these guys. What a lovely place.

Nice one Phil

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oipigface
On 18/08/2020 at 11:12, SilentPilot said:

Congratulations, it seems to fly well :) 

Have you had it on water yet? I’m no expert at float plane dynamics but I think the floats might need to be further apart. The long wings aren’t the only problem, I’m looking at the triangle formed from the two floats and the fuselage, it seems narrow and tall.

The high CG (relative to the floats while on water) and the moment arm from the long wings could make it unstable.

Coming along nicely though! 

Those aren’t the floats that I am building for an attempt at ROW. They are the ones I had fitted to an electric powered Easy Glider. They are also mounted on the Easy Glider undercarriage, The new ones are 50% longer, and the undercarriage I have made to go with them is proportionately larger, and has bracing wires. So they will be longer, taller and farther apart. Whether I’ve got it right or not remains to be seen. 
The floats make the CG lower rather than higher, and they make it more stable rather than less. That’s why it won’t roll or loop.

 

9 hours ago, Phil.Taylor said:

Found this video on Youtube - John, have you seen it?


Well, I have now. Bit annoying really, but not surprising! One interesting thing about what they’ve done is the fore-and-aft floats, which must improve its stability, and eliminate any possibility of a nose-over on landing. I can’t recall any full-size machine like that.

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SilentPilot
11 hours ago, oipigface said:

The floats make the CG lower rather than higher, and they make it more stable rather than less. That’s why it won’t roll or loop.

Sure the actual CG will be lower with the floats down there, plus the low down drag, but my observation was based on the glider sat on the water not in flight.

Sitting on water instead of solid ground means the relative CG is quite high over the floats. High and narrow isn't good!
It reminds me of the warnings we had when driving tankers. Never park with two wheels (not strictly two wheels, more the entire side of the vehicle) on a grass verge. Any kind of give in the ground and the CG of the load moves more over the sunken wheels, this then sinks it more, this then moves the load... you can see where I'm going here, a vehicle can go from parked level to rolled over by the time you get back!

I worry that floats might have the same problem. Though I do trust your judgement in getting the geometry right to avoid this problem.

My own worry is having the tow line on top of the wing. I've not decided yet whether to make a tail release (which could really still suffer the same problem) or have a third float under the tail, possibly on a drop-off dolly type so I don't carry it in flight, but then we'd need to be sure the glider was airborne well before the tug to fly over the dropped off float...

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oipigface

Bit of a milestone this morning. After many layers of chopped strand mat, even more layers of release wax, much elbow grease and quite a lot of cursing, I have finished the mould for the nose cones. This is my first two-part mould, so I’m feeling quite pleased with myself. The floats themselves just need a rub down and a second coat of resin.77C3A42F-0CF8-48E5-875A-3922C1E52948.thumb.jpeg.c8e2aa987f385d737416141274afcf92.jpeg".
 

3FCA8F14-C85D-4F1B-920C-ACE3973FEDEF.thumb.jpeg.1f8fc18db6171595ea2382e4b4e112f4.jpeg

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oipigface

Right, chaps! Good advice needed.
Here’s a couple of photos of my first attempt at using my mould (or any mould come to that):

E7336C5C-B418-47ED-BF62-89CF8DA4D366.thumb.jpeg.e4d5f7e757f7009db93997625dda2143.jpeg

196873DB-A418-45F6-87E6-579E4EC9FD0A.thumb.jpeg.0b560ccbc6177ef6c5334e086048e49b.jpeg
 

I’m quite pleased with the result, mostly because I managed to get the weave straight enough, and it matches the front end of the floats well enough. (You can see from the picture that I awarded myself a glass of something nice.)  I’m not happy with the finish, though, because these nose cones are supposed to be waterproof but if you look through them from the inside, they are full of little pinholes.

87650A28-7E5C-43BF-9685-E00FA8679F30.thumb.jpeg.9a754664e749716fcba5fd05e4269683.jpeg

I first noticed this when I demoulded the top, which I had laid up with two layers of 98g carbon cloth. I thought that maybe it needed another layer with a closer weave, so I put a layer of 25g glass cloth in between the layers in the bottom. It seems to have made little or no difference. In fact what seems to be happening is that epoxy from the gaps in the weave is staying on the mould. Squint carefully at the first picture and you may be able to see this. 
So what am I doing wrong, chaps? I’m using L285 laminating epoxy. I’m pulling about 80% vacuum, in a hotbox at around 40C for 90 minutes, followed by another couple of hours outside the box. The top I demoulded after leaving the part overnight in the vac bag. The bottom was sooner than that.

Another thing that may be wrong is the vac bag. This part is very deep and curvy, and it’s hard to get the bag pleated well. 

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Graham Woods

Pin holes are a pain. One can spray the mould with a layer of paint, Schwabbellack or gel coat. The holes will probably still be there albeit under the paint but it should be waterproof. As one can imagine the holes are air filled bubbles which come from poor wetting out or using too coarse a weave. A 'veil' cloth of 25gsm glass can help with larger forms. The paint can be 'two-pack' or even from a humble aerosol  can. The moulds should ideally have a layer of mould release of course. If the carbon weave needs to be seen the use a clear lacquer spray instead of pigmented paint is possible. The pin holes will now be under the clear lacquer. One could use Rustoleum or Halfords clear lacquer. A clear lacquer coat could be subsequently sprayed if necessary and there would be no pin holes to fill.

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SilentPilot

Looks like a rather large glass of Scotch there!

Is that what is hindering proceedings?

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oipigface
39 minutes ago, SilentPilot said:

Looks like a rather large glass of Scotch there!

Is that what is hindering proceedings?

It’s not Scotch, it’s Tenneseean.  I poured it after demoulding.

 

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oipigface
1 hour ago, Graham Woods said:

Pin holes are a pain. One can spray the mould with a layer of paint, Schwabbellack or gel coat. The holes will probably still be there albeit under the paint but it should be waterproof. As one can imagine the holes are air filled bubbles which come from poor wetting out or using too coarse a weave. A 'veil' cloth of 25gsm glass can help with larger forms. The paint can be 'two-pack' or even from a humble aerosol  can. The moulds should ideally have a layer of mould release of course. If the carbon weave needs to be seen the use a clear lacquer spray instead of pigmented paint is possible. The pin holes will now be under the clear lacquer. One could use Rustoleum or Halfords clear lacquer. A clear lacquer coat could be subsequently sprayed if necessary and there would be no pin holes to fill.

So do you think I should be using more layers of lighter cloth? I could always paint it with lacquer or whatever, but I would rather get it right.

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Graham Woods
14 hours ago, oipigface said:

So do you think I should be using more layers of lighter cloth? I could always paint it with lacquer or whatever, but I would rather get it right.

You could use some lighter carbon if you have it but then it really needs to be a twill or satin weave to go round such small compound curves. What you have done looks ok except it looks a little 'dry' to me, resin wise. I'm no expert but I think you may be setting yourself a very hard task. Just use a clear lacquer or spray paint in your mould.  :yes:

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oipigface
1 hour ago, Graham Woods said:

You could use some lighter carbon if you have it but then it really needs to be a twill or satin weave to go round such small compound curves. What you have done looks ok except it looks a little 'dry' to me, resin wise. I'm no expert but I think you may be setting yourself a very hard task. Just use a clear lacquer or spray paint in your mould.  :yes:

Thanks, Graham. I ordered some clear gelcoat from Easy Composites this morning. The problem seems very common. I thought I put a load of epoxy into it. I’m having a break today, but I’ll have another go soon.

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oipigface

First float finished:

587CB61E-22F9-427F-AF40-F233D78C7DE5.thumb.jpeg.214b36ea4da348f55964778428484bbd.jpeg

 

...complete with functioning and (maybe) waterproof rudder.

9B1D70A3-7188-4ED3-8A6C-A2337D10DB82.thumb.jpeg.88c76d64f53c346dc7a1c682c4f26e20.jpeg

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oipigface

... and finally two useable nose cones! I must have had more than a dozen attempts with paint, gelcoat and lacquer in my search for a classy naked carbon finish, but I’ve given up now that I have finally produced two pairs of useable mouldings. The finish on one of the tops was pretty good, but I wasn’t able to replicate it on another or on a matching bottom. I joined the two pairs together, rubbed them down, filled them a bit and squirted some white primer at them. They are held on with magnets and sealed with waterproof tape. 
  They’ll be OK. Time to look for a boat!

   The good finish was achieved using gelcoat in the moulds, and adding epoxy-soaked cloth while it was still green. The result seems VERY sensitive to the timing of the application of the cloth.

 

07669F37-9DC3-49D6-8A64-CF111022A8D3.thumb.jpeg.0b92c79c558d03a3e2376297a2f6e8da.jpeg
 

50CB2DC0-0380-480F-97BF-C9F4B43D4FB8.thumb.jpeg.c4e394e13116f853e1869c1ab1c4f34e.jpeg

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