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Apr 24, 2015, 03:55 AM
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Build Log

Kawanishi H6K Mavis


Time for a new project!

After trying out Rhino on a few different models I have decided on one to carry through into production.

The model I've chosen is the Kawanishi H6K Mavis as I don't think I've seen it modeled much before, plus I love the old flying boats.

I've attached the jpg of the Rhino model for an idea of the beast.

I've done quite a bit of thinking about this one and have finally settled on a sectional foam construction method for the fuselage, a la Keith Sparks PBM Mariner. The wing will be hotwired foam.

I've chosen this methods as:
  • I thought it looked interesting and I'm always up for something new,
  • I've discovered that I hate strip planking balsa,
  • I wanted something that will not rot if a bit of water penetrates the hull, and
  • foam makes sense to me for water duties as it is inherently waterproof


The real life plane was a monster at 40m wingspan, so I've decided to do at a decent scale of 1:20 for a 2m (78") span model and a fuse length of about 1.3m.

So far I have the sections cut out and am proceeding with the hollowing out and sticking together. Once that's sanded back I'll move onto the wing which should be relatively simple affair.. 4 panels, 2 of which are constant chord and the other 2 have an even taper. Perfect for hotwire.


Slow and steady, here we go.
Mat
Last edited by Wormboy; Apr 24, 2015 at 06:31 AM.
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Apr 24, 2015, 04:29 AM
71% of the world is runway . .
Bart83's Avatar
Hi Mat ,

This is awesome ! i see you have developed a steep learning curve in Rhino , well done !

Your foam method is also very intresting , would love to try that one time. For the wings i know a great simple composit building method. Tell about it later , im sure you will like it.

Cheers,

Bart
Apr 24, 2015, 06:30 AM
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Hi Bart,
Thanks for the compliments. Rhino was actually quite intuitive once you develop a basic understanding of the language and terms.

I've been wanting to try out Sparkys sectional method for a while now and went out and purchased both his book and mariner plans to get it firm in my head. It also helped thinking about how to embed hard points for servos and motor mounts.

I'm looking forward to hearing about your wing construction method.
Apr 24, 2015, 09:54 AM
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RickC_RCAV8R's Avatar
Wormboy :

You are my hero ! I use this exact building technique all the time and it WORKS ; great in fact . Strong , light weight fuselages and wings . Easy to seal up for paint and water proofing . See my blog for my builds . I am doing a Pfalz D3a right now and have done the V22 Osprey . It looks like you are doing the same process as I do for construction .

TIPS : Do a thinned down EPOXY mix after your filling stage . I use drywall filler and then the epoxy mix . Equal portions of 99% Isopropyl alcohol and the A/B mixe epoxy . This stuff can now be sprayed on as it has the consistency of apple juice .

Use full strength epoxy on the inside of the segment joints . Use an old T Shirt cotton cut up in strips if necessary to lap these joints .

If you think of it , plan your cutting templates to include the mounts for various equipment as it makes for extremely strong mounts rather than be added later .

Keep updating . Great job and project . RickC
Apr 24, 2015, 10:47 AM
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Thanks for the tips Rick.
I've had a scroll through your osprey build and it looks great. Nice job.

Just one question at the moment, although I'm sure there will be more later.
You mention you use fabric for lapping the joints on the inside. Is your outside finish just thinned epoxy on foam or is it glassed? I'm planning to glass the outside of the Mavis to toughen up the skin as it will receive a bit of wear and tear which will dually serve to strengthen the joints, but hadn't planned to lap the inside . Bearing in mind that there are 45 sections from front to back, there may be a bit of a weight issue lapping inside as well as glassing outside and think it will probably be overkill.. thoughts?
Apr 25, 2015, 12:46 AM
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Here's another approach to scratch modelling the Kawanishi H6K

http://th00.deviantart.net/fs71/PRE/...li-d5oeojr.jpg
Apr 25, 2015, 01:16 AM
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RickC_RCAV8R's Avatar
Wormboy :

The cotton fabric material that I use is basically a 3/4 inch wide tape , if you will . I simply apply these with the thinned down epoxy to fasten them . My Osprey was finished with about 4 coats of the thinned epoxy mixture as they are extremely thin when applied . I just did a rough 400 grit sanding before applying a primer and paint . Used a whole 25ml tube .

I have used 1/2 ounce fiberglass over blucor Styrofoam in building floats but found out that the glass will unstick itself after about a year or so from the foam . It adds a lot of weight even for the 1/2 oz . cloth . It wears great but is just too damned heavy for a large structure . If I were in your position , I would just glass the extreme wearing locations only .
Apr 25, 2015, 02:35 PM
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RickC_RCAV8R's Avatar
Mat:
I thought of an alternative covering rather than fiberglass that is nearly as tough , but a LOT cheaper to obtain . Send your girlfriend into the store for a couple of pairs of 'Nylons" . Yup , if they can stretch over the leg and thigh easily , they sure can stretch over wings and most fuselages . They also tend to re-adjust their tension as to wrap the structure without any wrinkles . I epoxy over and thru the nylon and trim the excess areas later . It does work and is strong like Hell ! (Fit the obvious Jokes here ........)

The bonus is that if you have a fetish for this type of thing ...............................Nyuk yuk yuk .
Apr 27, 2015, 01:58 AM
71% of the world is runway . .
Bart83's Avatar
Hi Mat ,

Here are some idea's for you.

First of all these are idea's are not mine but i've seen them on other builds.

For the wing , it might be good to take a look at the full composit Do24T build by Rolf Breitinger from Germany. He build his full composit wings in a relative simple method.
He cuts wing core's from foam using a hot wire method. This gives the actual wing form , a bottom and upper ''mold''. Then on a flat surface he prepares the wing ''skin''. This is a thin film. On this film comes a layer release way/film. Then a layer of gellcoat followed by some layers off glass cloth and epoxy. then another layer off thin clear foil is aplied. This complete sandwich is then being placed between the wing core and mold and allowed to dry. The result is a very strong full composit wing. He uses 6mm foam formers in that.

If you want i can contact mr Breitinger for some exact instructions ( will have to translate form german )

Cheers,

Bart

(19 min 4 sec)
Apr 27, 2015, 04:22 AM
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Thanks for the ideas and info gents, I think with the enormous wing that the Mavis has, even at full scale, I will have a bit of leeway with regards to weight. That being said, I still plan on making it reasonably light.

With regards to glassing the high wear parts, unfortunately being a seaplane a significant portion of the plane will be subjected to water and wear. By the time I get done with those bits I may as well go the whole hog.

Bart, the method mr Breitinger has used seems just one step shprt of a vacuum bagged wing such as is used for composite gliders. I will keep it in mind and I do have a fellow modeller locally that uses this technique. My original plan was just applying glass over foam, but was also considering adding a 1.5mm balsa skin between foam and glass. I will see how I'm feeling once the cores are cut.

I think I'll move this over to the waterplanes forum tonight.
Apr 27, 2015, 06:39 AM
71% of the world is runway . .
Bart83's Avatar
Hi Mat ,

Dont know were but is somewhere i read about using a nylon stocking as coverting cloth. Cheap , easely follows the shape of the wing. You can just use expoy or PU for finishing.

Good thing you live so far away Mat , otherwise there would be a change of a dogfight between my Do24K and your Mavis.

Cheers,

Bart
Apr 27, 2015, 07:19 AM
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Moved this build over to a proper build thread in Waterplanes
78" Kawanishi H6K Mavis

Nice painting Bart, I'm glad the Mavis was faster... it had to have some redeeming qualities as it was otherwise a sitting duck being both poorly armored and armed.

Both Bart and Rick, good suggestions on the nylons, however the trailing edge of my wing cores will be slightly concave to accept the flaps and frise ailerons. I'm not sure the stretch in the nylon will allow me to maintain that concave surface. Worth thinking about though.


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