Plank 368 - RC Groups
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May 16, 2016, 11:20 AM
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Knoll53's Avatar
Build Log

Plank 368


I've always liked the durability of a plank for those flying sites with less than perfect landing zones. There are no acres of flat flying sites for me. So for a larger plane, I'll take a plank for all round fun.

Although less than 4m wing span, there is oodles of wing area. I am hoping to get some float out of this one.

Bottom flaps are for glide path control. I know that they will be draggy and I am hoping that they will add some lift at slower speeds as well.

I rolled a cf boom around the big end of a pool cue. It has lots of cf tow in it and is rigid and strong.

Still looking at the length of the pod. I'd like for it to balance with a minimum of lead. I'll build the tail first, then do a test balance.
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May 16, 2016, 12:23 PM
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turbonut's Avatar
Cool...
May 16, 2016, 01:38 PM
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Roll the boom


I've never rolled a boom before, so I shot a video to take notes.

First a mock up was built to test my methods and to test the strength of the part. I choose to wrap the main lay up with a double cf 50K tow spiral wrap. This turned out to be way too strong.
Plank368 boom mock up (10 min 22 sec)


Here's the layup for the actual boom, without the spiral wrap. It is just 4oz. glass on each side of the many strands of tow. The layup wraps around the mandrel 2 times. The 27" boom weights 120gm. I'm well on my way to a 6lb. plane.
Plank368 Boom Lay up (2 min 57 sec)
May 17, 2016, 08:57 AM
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EdSoars's Avatar
How can a tail boom be too strong? Too heavy, sure, but not too strong. Or am I missing something?

Watching with interest. I will probably never build a 3 meter, but I might scale this lovely creature down to 2m.

ed
May 17, 2016, 11:03 AM
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You got it ed. Too heavy and too costly. Design is a study in compromise between the many competing factors. Even for purely structural elements, cost and weight always figure in. For prototypes, I'm happy to error on the side of too strong. In this case, it is freaky rigid and "just" too strong.

This tapered pool cue mandrel would lend itself well to a really great spar. You could create a lay up schedule to put the exact amount of carbon where you need it.

Soon I will notch this boom for the main joiner attachment. We'll see if it is still too strong then.
May 17, 2016, 11:25 AM
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May 17, 2016, 12:32 PM
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For probably $10 in fabric costs, you have several layers of this fabric wrapped around a pool cue for a very strong and cool looking boom. 3K carbon lengthwise and red kevlar wrapped around the boom. Quick and easy.
May 20, 2016, 09:59 PM
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Hussle's Avatar
Will you wrap that tube join with tow?
May 21, 2016, 11:29 AM
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Yes the joiner and the rudder post are wrapped in tow. At the joiner it is about a 150K bundle.
May 23, 2016, 10:38 PM
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You are having too much fun sir. I enjoyed some of your slice and dice videos tonight. Like old times.
Jun 03, 2016, 11:39 AM
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Tail..............done


Hi Cable. Nice to see you back.

It seems big now, but I bet it won't once I start the wing.
Jun 03, 2016, 03:21 PM
Living on the Dark Side.
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Looking good Kent.
Jun 03, 2016, 06:41 PM
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Yes it only took 2 weeks......most of that time was just waiting for parts to arrive.

Got the laser cut wood parts the other day in all of their smoky goodness. I am looking for some inspiration and vision as to how to assemble them. There are no alignment jigs, but there are shear web "assemblies" that have the rib spacing set so I need to find a method that does not fight that layout.

Time to start building !


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