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Nov 16, 2019, 11:26 PM
rab
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Build Log

Martin B10


Last year I built a Saab Viggen following flite test plans that used a hot wire cutter. I then thought that I could probably adapt some stick and tissue plans to that build technique. I have a pdf of plans for a Martin B10 that interested me. To my eye the plane looks rather steam punk.

This will be rather ambitious for my limited experience, but I am not afraid of a do over. Also this will be slow going, there are several things to figure out. The biggest unknown is how best to make the wing de-mountable for the trip to the field.

I am aimed at a 40 inch wing span and an 18 oz weight. We will see how close I come to my weight target.
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Nov 17, 2019, 07:46 AM
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Looks like you're off to a good start.
Nov 19, 2019, 11:09 AM
Jer. 29:11
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That's an interesting technique. I'd love to learn what works for you (and what doesn't). Please keep us posted!
Nov 20, 2019, 08:39 PM
rab
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Perhaps some explanation is in order. To make the hot wire cutter I went out on the internet bought some nichrome wire, a servo tester, and a brushed esc. The pvc pipe, speaker wire, watt meter, battery and connectors I already had laying around.

The foam I bought at home depot, it started as a 4' by 8' by 2" sheet. After a bit of experimenting I settled on a 3s battery and about 16 watts for a good cut. I also found that the foam cuts well on my table saw and I find that a good way to get squared up stock.

Templates: I've been using aluminum flashing, using 3m 77 to paste it on the aluminum. I use an old scissors to cut the aluminum.

I found that I can use 3m 77 to fix the template to the foam for the cut. But I give the glue a moment to gas after the glue is sprayed on the aluminum. The propellant does dissolve the foam. Waiting a moment or two give the propellant a chance to evaporate away. After the template can be pulled off with little damage to the foam.

As you can see my technique with the hotwire is not outstanding. Some gentile sanding/shaping will be required.
Nov 20, 2019, 09:35 PM
Jer. 29:11
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Your fuselages look promising! Thank you for sharing your techniques.
Nov 29, 2019, 05:56 PM
rab
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Muddling on. I've glued the fuselage segments together. If I knew better where the electronics are going I'd have prepared for them. As is I'll be making openings as I get things figured out. I suspect that this one will like the CG pretty far forward. I'll make a small profile glider soon to get a rough idea.
Jan 17, 2020, 08:30 AM
rab
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Slow going. Mostly due to planning and experimenting - the remedy for not knowing what I am doing.

You may notice I've cut out some tail feathers, I plan to glue balsa strips to the edges. I plan to do the same to the wings. I also have a bunch of vacuum forming to do, canopies, nacelles, the bee hive, and maybe the nose. I think I'll use fiber tape on the top and bottom of the wing rather than embed a spar in it. Rather cover with light weight fiberglass I want to cover with doculam, that experiment came out good.

I've also followed some excellent advice from GPW, cut out more than one. Since I don't expect the first one to fly well until it has some scars from crashes.

- Allen
Jan 17, 2020, 06:32 PM
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Quote:
Originally Posted by rab
Slow going. Mostly due to planning and experimenting - the remedy for not knowing what I am doing.

- Allen
Looking good!

You might find the video T_om has published to be helpful

Foam Fuselage Hot Wire Cutouts (5 min 20 sec)


and also the thread he made...
https://www.rcgroups.com/forums/show...en-Complete%29

I know I did
Jan 18, 2020, 11:08 AM
rab
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Helpful , yes I agree.

- Allen
Jan 24, 2020, 10:18 PM
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Some small progress on the tail feathers.

I plan to do something similar for the wings.

Also debating when to do the covering. Do I cover the foam in stages as I go. Or wait to the end?

- Allen
Jan 27, 2020, 06:30 PM
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I am very interested in your project. Foam is really easy to damage so would recommend cover each piece as it is finished. For example, cover (I use fiberglass and epoxy) the stab and elevators when you are finished with them.

Jim
Jan 31, 2020, 01:36 PM
rab
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Yes, I will cover assemblies independently. I've used fiberglass and WBPU, fiberglass and Glidden gripper. But not fiberglass and epoxy (at least not on model airplanes). I intend to cover this one with a soft doculam, that seems to bond well and can be painted. I think I can use it to get a smoother finish with less weight.

I'm wrapping the edges of the wings and tail for dent resistance on the edges and also for ease of shaping, I've learned that if I use strapping tape or fiber tape on the leading edge of a foam wing it greatly increases the wings resistance to fracture. I'm expecting the balsa/doculam leading edge will also resist fracture.

- Allen
Jan 31, 2020, 02:48 PM
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I've used Doculam many times and it is one of the reasons I have moved to fiberglass and epoxy. I could never get paint to stick very well to Doculam. Also, fiberglass and epoxy adds tremendous strength to the foam.

We call it epoxy but what we really refer to is finishing resin. I use Zpoxy. You mix it equal parts resin and hardner. Then thin it 50/50 with denatured alcohol. Lay the fiberglass on the surface and paint the epoxy over it. Goes down really easily. Let it cure overnight. Does not add a lot of weight but does add tremendous strength.

Some people use thin paper and white glue. I have tried it as well and it also adds a lot of strength. But not as good of a surface in my opinion. Both methods allow for good paint jobs.

Jim
Jan 31, 2020, 02:55 PM
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BTW, I am building something similar on my thread in scale models. Will be making the fuse on my Zero the same as yours. But instead of doing a left and right half, I will be doing a top and bottom. https://www.rcgroups.com/forums/show...-from-MA-plans Look toward the end of the thread for the latest part of the build on the Zero.
Feb 01, 2020, 12:06 PM
rab
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This thread got my attention a few years ago. https://www.rcgroups.com/forums/show...3Zeke%C2%94%29 It was only ten years later that I finally set up a hot wire cutter. The hot wire cutter was the big stumbling block for me.

- Allen


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