yet another scratchbuilt twin boom pusher - Page 2 - RC Groups
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Mar 11, 2012, 04:11 PM
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xatled99's Avatar
Discovered that has reasonably priced fiberglass tubing. Ordered some 3/8". It weighs 2.45 oz for 54.5". Weight & balance calculations look good so far.
Last edited by xatled99; Mar 13, 2012 at 08:53 AM.
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Mar 13, 2012, 09:17 AM
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The tail volume coefficients are more or less in a happy place. There will probably be some fine tuning, but I at least have some confidence that the design will work. Preliminary plans are drawn up. Most of the parts should show up by the end of the week, and then the building will begin.

CG  = 3.350
wing: span=56.000, chord=9.000, area=504.000, AR=6.222
stab: span=16.000, chord=5.000, area=80.000, AR=3.200
fin:                            area=45.000
tail: length=20.000, arm=23.000

V_h = 0.406
V_v = 0.037
NP  = 3.775
SM  = 0.125

equivalent vtail:
area                = 125.000
dimensions          = 25.000 x 5.000
true AR             = 5.000
dihedral angle      = 36.870
projected half span = 10.000
projected AR        = 4.000
projected height    = 7.500
Last edited by xatled99; Mar 16, 2012 at 04:06 PM.
Mar 15, 2012, 06:15 PM
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Mar 15, 2012, 06:17 PM
USA: LakeGeorge, New York
Mar 15, 2012, 08:02 PM
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Firewalls cut, landing gear/wing/tailbooms laid out.
Mar 16, 2012, 06:55 PM
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Landing gear and motor mount. I used nylon standoffs from ace hardware; I had to drill them out a little to fit the 6-32 dubro hardware. An 11x6 prop should do the job according to ecalc.
Last edited by xatled99; Mar 16, 2012 at 11:46 PM.
Mar 16, 2012, 09:53 PM
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Tail framed in.
Mar 17, 2012, 12:11 AM
USA: LakeGeorge, New York
....are you using a 'Multiplex Twin-Star' wings? or just using for mockup?
Mar 17, 2012, 09:59 AM
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Boom mounting concept, work in progress. This should distribute the tail loads around the wing spar. The booms will need to be pinned in somehow.

Yes, I'm using a twinstar wing.
Last edited by xatled99; Mar 17, 2012 at 11:56 AM.
Mar 17, 2012, 05:28 PM
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If I had to do it over, I would have put the mounting brackets in before building the tail. Glue doesn't stick to the clamps so I had to use some 6-32 x 1/4" hardware.

I castered the nosewheel a bit.

The 11x6 prop is a bit tall; I may need to raise the motor mount.
Last edited by xatled99; Mar 18, 2012 at 09:06 AM.
Mar 17, 2012, 07:33 PM
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Awesome Progress!
Mar 18, 2012, 07:39 PM
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Learned that the wing and stab incidence angles are zero on this bird.

Going to need 3 1/4" wheels to make the fuselage level on the ground.

Moved the motor mount to the top of the firewall. Also realized that flush mounting the motor will buy a little more prop clearance on rotation.
Mar 23, 2012, 08:41 PM
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The new main wheels and wing dowels are installed and the access hatches are cut out. The CG looks good so far.

The prop collet that came with the motor was bunk, so I had to order an eflite one. I'm currently waiting on some pushrod hardware and a servo wire crimper and then I can start wrapping things up.
Mar 25, 2012, 01:07 PM
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Firewalls epoxied in. Glued in some 3/32" ply strips to prevent the rubber bands from gouging the foam. ESC and rx and servos are in, pushrods are made. Chopped off the nacelles. The eflite collet showed up, but the shaft is a different diameter. I'd already reamed the props, so now I need new props. Argh. Hoping to maiden by next weekend.
Mar 30, 2012, 09:46 PM
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Servos, pushrods, horns, etc. are all in. New props showed up and thankfully Just Worked with the eflite collet. Aileron Y harness is in. Still need to strap down the vtail wiring and program the radio. Looks like 300ish watts with 10x6, 400ish with 11x6, on a half charged pack. Wondering if a 3 blade would help with ground clearance.

Should be good to go for a maiden this weekend.

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