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Old Mar 28, 2012, 01:19 AM
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roo_ster's Avatar
United States, TX, Dallas
Joined Mar 2011
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First Scratch-Build: Twin Boom

Howdy:

Just assembled & flew my first scratch-build. It is an obvious imitation of some of the successful twin-boom designs found on this forum, with some of my own "innovations."

Specs & Hardware
WS: 27" KFm3
Motor: Emax CF2812 (http://www.headsuprc.com/servlet/the...ushless/Detail)
Prop: GWS 8x4HD
Servos: T-Pro MG90 "9g" (really 13g)
ESC: ExceedRC 30amp
Batt: 3S 1000mah 20C+ lipo
Mass: 380g/13.4oz without lipo, 477/16.8oz with 1000mah 3S 45C lipo
3ch: AET

Flight
Flies great. I maidened it in 10-15mph winds. Would never have maidened an ARF or PNP costing real $$$ in that. It was like a feeling of freedom, "If it crashes, I am likely out a dollar's worth of foam and a few dollars' worth of other materials."

Back to flying...

It likes more speed than a floaty delta I own, but is more predictable in that it is not nearly so floppy. It looks and is crude, but the wing & elevator are rigid and the vert stabs are no slouches. The triangular fuse & booms are not as stiff as I'd like and I will build the next with those improvements in mind.

It has crazy-level throws (ail & el) that I dial down to 50% or so, with 25% expo. Very responsive and on the edge of my ability to handle smoothly. It is not self-correcting, but goes where it is pointed. It does all the AET aerobatics. It handles the wind just fine and is limited more by its own power plant than the wind. Not sure if it can go vertical indefinitely, it kept getting blown off vertical too much to be sure.

I programmed my DX6i for spoilerons and they work like a charm on landing. Slow it WAY down and it sort of floats/parachutes until I flare right before impact. Needs a smidge of up trim on the el.


Build Materials & Techniques

Bluecore, skewers, round & square wooden dowels, hot glue, Welders glue, Gorilla PU Glue, packing tape, Extreme tape, shiny scotch tape, popsicle sticks, music wire, blue painters tape.

The wing is a flubbed KFm3 with a 1/4" square wooden spar, glued together with GG. (first step is only the thickness of the spar & top & bottom foam) The leading edge is a skinny dowel tacked down in three spots with hot glue, slathered with water, slathered with GG, and clear packing taped over. The GG expanded in the void space inside the tape and gave me a round, hard LE. The wing is hella stout.

Fuse & spars are scored bluecore, folded and glued on one seam, with extreme tape on one corner. I followed up a few places with skewer cross-members. Next build will have some internal foam reinforcement and better seam-work to stiffen them.

Horiz stab benefits from a skewer, GG, and packing tape. I made the vert stabs extra big

All the hardware is on top. Next build, some of it will get buried and go under. The ail servos are too far back. To balance fore & aft CG, the 3S 1000mah lipo had to go out on top of the fuse. CG for good flight is 35-40% back from the leading edge. First flight I taped a bag of Skittles on the front, to get CG to 20% back from LE. Too far forward, Skittles had to go.

The Emax 2812 is on a stick mount with heat sink. Though not recommended for 3S, the GWS8x4 never got the lipo, ESC, or motor warm despite ~75% throttle 5 min flights. I think it'll ride.

I let my 7YO son decorate it. It has stars, bombs, guns, stick-man pilot, and more. In honor of my UM and parkflier T-28s, he named it "Navy Pliean." ( My daughter decorated my bluecore delta, which awaits electronics. Fewer bombs, more flowers...but still enough bombs & guns to put a hurtin' on the Bad Guys) I figure I am fooling no one with my mad build skilz and letting them have fun with the planes before I install electronics is fun for all. They'll get to see "their" plane flying.
















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Last edited by roo_ster; Mar 29, 2012 at 11:58 AM. Reason: Mass
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Old Mar 29, 2012, 11:59 AM
Standing Athwart History
roo_ster's Avatar
United States, TX, Dallas
Joined Mar 2011
640 Posts
Mass: 380g/13.4oz without lipo, 477/16.8oz with 1000mah 3S 45C lipo
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Old Mar 29, 2012, 03:25 PM
Mobius Cables... I got em'
chanyote66's Avatar
United States, TN, Oak Ridge
Joined Dec 2011
3,873 Posts
nice build, I made a similar design out of Dollar tree foam that was fun! Now im into Flying wings because of time to build, amount of materials and fewer electronics. I still fly my "drone designed twin boom's every once and a while.
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Old Mar 29, 2012, 05:23 PM
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roo_ster's Avatar
United States, TX, Dallas
Joined Mar 2011
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Quote:
Originally Posted by chanyote66 View Post
nice build, I made a similar design out of Dollar tree foam that was fun! Now im into Flying wings because of time to build, amount of materials and fewer electronics. I still fly my "drone designed twin boom's every once and a while.
Would you have any suggestions for a scratch-build flying wing?
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Old Mar 29, 2012, 05:41 PM
Mobius Cables... I got em'
chanyote66's Avatar
United States, TN, Oak Ridge
Joined Dec 2011
3,873 Posts
Quote:
Originally Posted by roo_ster View Post
Would you have any suggestions for a scratch-build flying wing?
yup... Im doing a build now, check it out!

$TREE FLYING WING FIGHTER/FPV

The "Iron Feather" Version is fun to fly for low speed and the "Strato V" is great for high speed!

You could use the same stuff you have here but i recommend prop savers! they help a lot with flying wings, unless you are skilled enough to catch it.
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Old Apr 20, 2012, 12:27 PM
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roo_ster's Avatar
United States, TX, Dallas
Joined Mar 2011
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Some updates:

1. Low-temp hot glue doesn't like inside auto heat. Trying out some Arrow Brand BSS6-4 Slow Setting for Woodworking from a hi-temp gun as suggested by jackerbees.

2. Elevator needed a stiffener, so it got a bamboo skewer along its trailing edge. Much better loops after that.

3. Up-propped to a GWS8x6DD/HD and it is all good. My power system handles the more aggressive than suggested prop fine and the difference is remarkable.

4. Poor design of thin, unsupported elevator control rod lead to some ugly flutter in the elevator when flying in 20mph+ winds and the GWS8x6. The model handles the wind fine, otherwise. Will have to re-design elevator control surface & control rod. Too much play.

5. Lack of proper elevator control in the middle of a flutter caused me to nose it in the grass (chopped throtle, though). The nose in front of the lipo is sort of scrunched, but not broke. I was impressed that there was no more damage. I think I'll try the heat gun trick and if it doesn;t work, chop off and scab back on a new nose. I do want that nose out there, as it cushioned my lipo (which stayed firmly in place with the Velcro-berand industrial application velcro.

If I can conquer the flutter, I might try one more thing before I retire the air frame. I want rudders and will try a single servo mounted midships in front of the motor with two bell-cranks turning the force 90deg.
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