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Old Jan 09, 2007, 09:04 PM
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Montreal, QC, Canada
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Build Log
Nakajima A6M2-N (Rufe)

Seeing the build off contest thread raised my interest to share the building of my latest design; a disguised Zero.

We don't see enough people designing, let alone designing scale (stand off scale even) projects. It has been more and more my interest.

Nakajima A6M2-N ?
Yup, a Zero by any other name.
Small differences.
No folding wings, redesigned rudder and of course the disctinctive main float.

So there are a couple of different aspects to my project, when compared to most of the other projects listed.
1- It is CAD and CNC cut alright, but everything is foam instead.
2- those Zero get wet.
3- very light model at a target of 8oz.
4- construction technique is radically different.

Like many others, I'm using 3D views from Russian source.
http://www.airwar.ru/enc/fww2/a6mn.html
http://www.airwar.ru/enc/fww2/a6m.html

Target specs:
Wing Span: 29"
Wing Area: 138+ in^2
Weight: 8 oz (targeted).
Power: CD-ROM, 7x3.5E prop
Battery: 2S lipos 800mAh

It's designed/built as a stand off scale.
Plan to have the floats come out to test fly and also fly off grass.
And wheels in for indoor flight.

Seeing that CNC cutting balsa is fair, I guess that CNC cutting foam should be fair as well...

Let's see if I can include a couple of shots of the construction process.
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Old Jan 09, 2007, 09:27 PM
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I always wanted to build one of those with a GWS Zero and GWS floats. The stuff's all there, and the floats look pretty good. They have a nice foam core float design, with an attractive light plastic hull bottom, made with flexible plastic.

They are the right size for the build. 10 bucks a pair.
Have you seen those floats?

Edit: I found a neat site for this:
http://www.masali.com/Inside/Models/...%20Gallery.htm

I think I learned something from the pics at that site. The plane could use a servo, connected to maybe the gear retract channel. Use it to shift ballast, or most efficiently, a sliding battery tray. Make it tail heavy for takeoff, as a bit tail heavy initially takes off well anyway, and then shift the weight once in the air. Seems like the plane wanted to tilt forward too far in the water, unless it was just far too nose heavy.

Bill
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Old Jan 10, 2007, 07:58 AM
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Wouldn't A zero onfloats be called a "Ruffe"?
Either way cant wait to see it, neat building technique too.
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Old Jan 10, 2007, 11:35 AM
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Quote:
Originally Posted by ShawnM4kq
Wouldn't A zero onfloats be called a "Ruffe"?
Either way cant wait to see it, neat building technique too.
Rufe, I think.

Bill
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Old Jan 10, 2007, 12:51 PM
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Yeah! Go the foamie!
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Old Jan 10, 2007, 03:38 PM
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Montreal, QC, Canada
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I started to look at this project over the Xmas break and had the first cut file on written on Dec 27th. At the time I was not aware of this contest. I heard about it last weekend. First images of the cutting were on Dec 31st. 2006.

According to Charlie, this is voiding my entry to the competition.

If this stands, I do not know how to change the title of the thread, if someone can tell me how...

----

Anyhow, a few more pictures of the cutting process.
Fuselage is in 6 sections. Barely any sanding required a basic assembly.
Losts of sanding at the pre-painting to get smooth surface.
LD
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Old Jan 10, 2007, 03:50 PM
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Montreal, QC, Canada
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Have I missed the rules about when you should have started on this ?
All I see is:

5. Each airplane will be an original design by the competitor. Previous work is allowed as long as the subject has not been published or sold.

Here is an exemple of what can be done with stupid pieces of foam...
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Old Jan 10, 2007, 05:41 PM
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Santa Clara, CA, USA
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Quote:
Originally Posted by dionnel
According to Charlie, this is voiding my entry to the competition.

LD
Well, I'm not a sponser, but I am a competitor, and I certainly have no problem with your entry. Starting in late December is certainly fine with me. The more the merrier! It seems you're early enough in the build that a late Dec start date shouldn't matter.

Jim
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Old Jan 11, 2007, 05:00 PM
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Montreal, QC, Canada
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Quote:
Originally Posted by scratchandbash
They are the right size for the build. 10 bucks a pair.
Have you seen those floats?

...
The plane could use a servo, connected to maybe the gear retract channel. Use it to shift ballast, or most efficiently, a sliding battery tray. Make it tail heavy for takeoff, as a bit tail heavy initially takes off well anyway, and then shift the weight once in the air. Seems like the plane wanted to tilt forward too far in the water, unless it was just far too nose heavy.

Bill
Yes, I have seen these GWS floats.
Again, I plan to make my own using my hot wire CNC machine.
Beside the prop, receiver, servos and speed controller, everything will be homemade.

First set will be slightly oversized to make sure I'm on the good side of the floatation.
And I will play with step position and float angle before I start adding a servo and move a mass around.
With an overall weight target of 8oz, there won't be much to move around anyway...

LD
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Old Jan 11, 2007, 11:00 PM
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Quote:
Originally Posted by dionnel
Yes, I have seen these GWS floats.
Again, I plan to make my own using my hot wire CNC machine.
Beside the prop, receiver, servos and speed controller, everything will be homemade.

First set will be slightly oversized to make sure I'm on the good side of the floatation.
And I will play with step position and float angle before I start adding a servo and move a mass around.
With an overall weight target of 8oz, there won't be much to move around anyway...

LD
Yes, there is not much nose lenght. I built a very light Coverite covered GWS bash Zero. With a DD 300, needed for weight, and the batt clear in front, I have the cg where I think it will be good, but have no more adjustment other than ballast.

I may remount the elevator servo from the rear of the wing saddle area, to the front. Definitely need to keep things forward. I think 8oz would easily be doable with light foam, but the challenge is to keep the tail light enough to not kill the target weight with needed nose weight.

BTY, the Macchi is beautiful!
Bill
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Old Jan 15, 2007, 06:50 PM
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Montreal, QC, Canada
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Since I'm doing a Rufe, better have a Rufe tail.
Recut the stab and rudder parts.

As far as I know the diffference between a Zero and a Rufe was the floats and the increased area rudder and tiny sub fins. The wings were also not folding on the Rufe.

LD
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Old Jan 15, 2007, 07:11 PM
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Montreal, QC, Canada
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Next goes the main float.

Just to stay on the save side, I decided to increase the volume to make sure the whole thing will... float...
Even wavelets are very big for this size of a plane.
Bottom is flat and the step height is slightly increased.
A middle under the front hull will be glued afterward to help keep a straight line on water.

Shape is complex and difficult to do on a hot wire CNC.

I opted to make a profile cut followed by shape cuts.
Profile cut is done to give the side outline.

Then the part is rotated 90 and all the remaining cuts are done there.
Those 3 cuts in a half-circle motion are giving the top rounded shape - giving the shape of the bulkheads.
The 3 cuts are done without moving the float from the surface, one after the other.
The front cut provide the main front taper.
The back cut gives the rear taper.
The middle cut is done last and is not tapered for the middle section.

From the bottom the shape looks a lot like a compact surf-board.
After those cut, trimming the corners and then 5min of shading gives a quite decent shape close to the original.

LD
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Old Jan 16, 2007, 04:52 PM
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OK, I slightly renamed the thread as it is officially not part of the Build off contest. But I plan to continue adding to it case there are people out there who might be interested by something else than balsa and laser in this Star War era.
LD
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Old Jan 16, 2007, 05:07 PM
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Been looking at the motor aspect a bit.
Plan to use a home-made CD-ROM based on 23.8 stator.
Rotor coming from an old sp400 case turned and trimmed down and 12 5x5x1 N45SH magnets. Stator will be held by a bearing holder in turn fixed to an annular motor mount.
Looking at 3 strands of #28 guage wire with 13 or 14 Turns.
To drive a 7x3.5 HD GWS 2 bladed prop from a 2S 800mAh 20c li-po pack.
With a target weight around 8.5oz, that should give me about 100w/lb with the floats on.

Basic controls will be :
- throttle
- ailerons
- elevator
- rudder coupled to a water rudder

Big pieces left to do are:
- figuring out how to attach the main float to allow adjustments and removal
- make a plug for the canopy.
After that everything will go quickly.

LD
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