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Old Jul 16, 2015, 11:40 PM
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The Xperiment--A 48" Cruciform Balsa Build

A few years ago I started experimenting with a fully symmetrical F3P model. From the original thread:

" Looking at the trends in newer F3p planes it seemed like there was a drive towards more fuse area over the CG, and in most cases semi or fully symmetric fuse profiles.

This is great as coupling is all but gone, and knife edge should behave more like wings level flight. But even if fuse area was increased to match wing area, because of the difference in aspect ratios, you'd still need to fly at a higher angle of attack in KE, compared to wings level. To get the plane to approach complete neutrality, the fuse starts to look like the wing.

So that's what I tried, a completely cruciform plane. And to get it to be able to land somewhat like a normal plane, I shifted the wing from 0/90 to 45/45, while leaving the tail group at 0/90. This keeps the rudder/elevator in normal plane axes, and gives a sort of conventional stance on the ground without the need for some sort of ridiculous gear. To make determining the orientation easier I painted the top and bottom to look like the top and bottom of a regular plane, and the sides to look like a conventional fuselage. "

VID00063 (0 min 51 sec)


After several years of flying the bigger green one, I've set out to make a proper balsa version. Rather than start completely from scratch, I'm using the tails and wings from an existing ARF. I originally wanted to build it using the 60" EF Extra parts, but 3DHS was having a sale on the spares for their 47" SHP, so that's what I went with. Seeing it all together, a 60 In model would have been enormous, so I'm glad I stuck with the 48"class.

The fuselage is framed up from a core of 1/16ply, which gets built around the x-spar. I notched both spars, then wrapped them thoroughly with carbon tow. The rest of the fuse is 1/16 balsa, with a few stringers here and there. Fuselage was drawn in SolidWorks, and I'll post the cut files, for anybody who's interested in building one. I designed it around the motor box for the 3DHS Yak55, and will be using the Yak cowl

Fuse is framed, just need to notch and join the stabs, cover and install the electronics. I had some concepts for gear, but I think for now this will be a hand launch/catch deal. The aft fuselage provides for a convenient hand hold :P

-A
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Old Jul 17, 2015, 01:05 AM
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Looks interesting, orientation must be a bitch though!
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Old Jul 17, 2015, 01:56 AM
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Quote:
Originally Posted by luke352 View Post
Looks interesting, orientation must be a bitch though!
It is That part of what makes it look cool while flying, it can make quick changes in direction that just don't look normal. Got to stay on top of it though!

-A
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Old Jul 17, 2015, 12:45 PM
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Old Jul 17, 2015, 01:16 PM
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JUNK RADIO
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nice I like it..
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Old Jul 17, 2015, 08:27 PM
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Wings and tail fitting are done

-A
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Old Jul 17, 2015, 09:24 PM
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Fly it 'till it breaks.
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Just looking at that thing is oddly satisfying. I'm very interested to see how this turns out. Really nice work so far. Keep it up! Thanks for sharing :-)
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Old Jul 17, 2015, 10:30 PM
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Thanks man!
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Old Jul 18, 2015, 03:58 AM
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Thumbs are overrated.
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awsome! I love poeple who think outside the box, keep it up.
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Old Jul 20, 2015, 12:04 AM
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Got everything covered and the tails setup, just need to drop in servos, and set up the linkages. Should fly it by mid week

Finished fuse ended up at about 270g with the spar. For comparison, I weighed my 48" Laser fuse, and it was about 350g

-A
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Old Jul 20, 2015, 08:37 AM
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iumop ap!sdn w,I
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Wow, I love it! Youve done a great job on it.

Are you going to put wheels on the wing tips? Just wondering how you are going to land it?
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Old Jul 20, 2015, 08:55 AM
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Thanks! I've got some plans for tip mounted gear or little landing stilts that extend/retract from the rear fuse, but I'll see how it flies first. First flights will be hand launch and catch. I typically fly at a field by the bay, which has some rather tall reeds/grass that I could plop it into safely if it's a handful.

-A
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Old Jul 20, 2015, 09:27 AM
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Nice! I taught myself how to fly with the plop it into a tall farmers field method. Nice to have that as a backup. Can't imagine having to hand catch it on the maiden!
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Old Jul 24, 2015, 10:09 AM
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Servos went in last night, just need to finish a bit of wiring, and it should be ready for maiden tomorrow!

-A
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Old Jul 26, 2015, 02:06 AM
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All done!

Maiden tomorrow morning. Hopefully I'll have some nice video to post in the afternoon. Still need to do the silver vinyl for the side of the fuse, but I'll finish it up if it survives the first outing .

-A
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