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« on: June 27, 2015, 05:26:21 PM »
bmblb
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......My 100th post and first ever entry into the RCI Sweepstakes. Here's an attempt to make a Gull Wing Flying Wing - 42in span - KFm 1 or 2 ...to be decided.

 ....some sketches and a plan. I am yet to decide on a pusher or a tractor....

 all comments welcome  Smiley

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2015 Sweepstakes Entrant -42" Gull Wing Flying Wing
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« Reply #1 on: June 27, 2015, 05:31:35 PM »
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here are the 'tiled plans' drawn on my floor tiles. I used this CG calc http://wingcgcalc.bruder.com.br/en_US/?

Panels are : 9+12+12+9
Sweep: at root: -1.5in, at tip +1.5in
Chord: Root - 9in, wing break one - 7.5in, tip - 6in

I am thinking whether to give the ailerons on the inner panel or the outer ones....want to avoid servo extn wires....

.... have drawn both options of the fins - inverted V and the vertical ones.....may be a big single fin in the center would also do....may be three.... Grin
    

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« Reply #2 on: June 27, 2015, 05:45:48 PM »
bmblb
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 ....wondering whether coro+foam would be better than foam+foam  Head Scratching
...hope to keep the WL around 6oz/sft....and will use a BW 1400KV rewound motor and 3S 610-850 mAh battery with a 5x5 or 6x4 prop....

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« Reply #3 on: June 27, 2015, 05:51:00 PM »
sundaram
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Re:

My vote is for Foam and Foam 😃
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« Reply #4 on: June 27, 2015, 05:55:22 PM »
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My vote is for Foam and Foam 😃
Thank you Sundaram Sir....i wanted to keep the taping to a minimum hence thought of coro+foam....also since each panel is 12in or less, with the spar reinforcement, maybe it would not be as floppy....perhaps this is why you suggested foam+foam.....

....any views on the elevon? on second thoughts....maybe at the tips
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« Reply #5 on: June 27, 2015, 06:30:47 PM »
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.....got hold of some really good bamboo sometime back and made spars over tea....5x2mm....feels quite strong......the braces will be out of credit card or 1mm ply.

IMG_20150627_181657110.jpg
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« Reply #6 on: June 27, 2015, 06:58:23 PM »
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......hope to cut the wing and laminate this evening.....as soooon as I have decided....all foam or Coro+foam....maybe I will try with a scrap piece of coro an see if its stiff and light enough ....if it works, saves me a lot of effort on taping.

IMG_20150627_185342950.jpg
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« Reply #7 on: June 27, 2015, 07:20:07 PM »
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here are screenshots of the cg calc.

.....for my scratchbuilts, I always struggle to draw the dihedral braces and often used an elaborate method.....until now.

in this calc, if you choose the chord as the thickness of the wing, and try out various angles/height in inches as the sweep , until you are satisfied with the angle, you can get the corresponding angle on the calc - simply use this to draw the braces....the angles are never whole, but you get an idea how much is ok.

the two pics show how !  Grin

...also. from the pic you can see the CG is right in the front, almost at the LE(0.41 in behind LE actually) - thereby necessitating location of the motor in the nose as CG would be an issue with the small battery....prop in slot becomes a little messy due to the gull/dihedral.

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« Reply #8 on: June 27, 2015, 08:09:00 PM »
K K Iyer
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@bmblb,
Hi Bhavesh,
Good to see another unconventional attempt.
I have no experience with flying wings, but lots with giving advice  Grin
What the hell, advice is cheap, so here goes...

Ailerons preferable on outer panels for two reasons:
1. More effective
2. More importantly, you'll need some reflex, which will need adjusting while trimming.

If the elevons are on the inner panel, and are reflexed, the outer panels will be at a higher AOA, and hence stall first. That's a recipe for tip stalls.

So if servo extension cables are needed, so be it.
Alternatively, if you can make a flexible pushrod with thin wire in a thin tube, you could use a single servo.
Ahmedt (on this forum) found some great thin wire (bicycle gear cable i think) that could be accommodated in tubes made out of ear buds...

Looks like you are keeping a static margin of 10%. See if you can locate relationship between static margin and reflex! Let me know.
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« Reply #9 on: June 27, 2015, 10:01:22 PM »
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@bmblb,
Hi Bhavesh,
Good to see another unconventional attempt.
I have no experience with flying wings, but lots with giving advice  Grin
What the hell, advice is cheap, so here goes...

Ailerons preferable on outer panels for two reasons:
1. More effective
2. More importantly, you'll need some reflex, which will need adjusting while trimming.

If the elevons are on the inner panel, and are reflexed, the outer panels will be at a higher AOA, and hence stall first. That's a recipe for tip stalls.

So if servo extension cables are needed, so be it.
Alternatively, if you can make a flexible pushrod with thin wire in a thin tube, you could use a single servo.
Ahmedt (on this forum) found some great thin wire (bicycle gear cable i think) that could be accommodated in tubes made out of ear buds...

Looks like you are keeping a static margin of 10%. See if you can locate relationship between static margin and reflex! Let me know.

Thank you, Iyer Sir.

Oh, you must try some wings - they are simple to build and fly really great. Besides, you just have 'one structure' to build (quite often a pusher )making things that much simpler.

As regards the elevon location, at the tips is the way to go - yet, I am mulling over the total area of the control surfaces and wondering whether I'd be able to get that in the tips without cutting in too much into the chord, thus rendering the tips unnecessarily 'draggy' (...not sure I could articulate this clearly).

...am with you on the tip stall bit - but I am wondering if the wing sweep and the gull wing itself has anything to contribute here favorably(?)

....suppose we preempt tip stall like behavior, then what would be the most suitable fin design - would these then act as vortex generators?....

.....i'd actually like to start with a single sufficiently sized fin in the center and see if it provides sufficient roll stability.

....and thanks....I will certainly look up static margin and reflex   Hats Off !
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« Reply #10 on: June 27, 2015, 10:28:43 PM »
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yet, I am mulling over the total area of the control surfaces and wondering whether I'd be able to get that in the tips without cutting in too much into the chord, thus rendering the tips unnecessarily 'draggy' (...not sure I could articulate this clearly).
 Hats Off !

....actually, I am just finding excuses to avoid the servo extension wires....lol ! this can be addressed with more throws.
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« Reply #11 on: June 28, 2015, 09:59:31 AM »
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....hopefully, I will be able to get some work done today..

 Smiley

IMG_20150628_093933941.jpg
Re: 2015 Sweepstakes Entrant -42" Gull Wing Flying Wing
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« Reply #12 on: June 29, 2015, 12:28:17 AM »
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.....got some work done today  Grin...here are the pics....

IMG_20150628_102136883.jpg
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« Reply #13 on: June 29, 2015, 12:30:47 AM »
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....enough for the day....here's the progress so far....

IMG_20150628_203319614.jpg
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« Reply #14 on: June 29, 2015, 06:11:00 AM »
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Coming along well, good luck  Thumbs Up

"The flight of the Bumblebee"  Interesting Tag Line! Wasn't that the name of the BBC Radio Signature Tune?
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« Reply #15 on: June 29, 2015, 08:56:36 AM »
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 Thank you, Sanjay Sir.....your build threads are a treat to follow.

Considering the long and vast history of BBC, its quite possible.....I just find this piece beautifully intense - several world class artistes have played it !!
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« Reply #16 on: June 29, 2015, 09:18:51 AM »
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Re:

Good work ... Coming out great. What's the construction material you are using ?
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« Reply #17 on: June 29, 2015, 11:37:50 AM »
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@docnayeem....thanks ! its 2.5mm coro and bamboo 5x3mm(and not 5x2mm as posted earlier) as I can use CA...

....just had to see the 'gull-wing' finished....some more pics

IMG_20150629_113156042.jpg
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« Reply #18 on: June 29, 2015, 11:44:55 AM »
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....more pics....satisfactory so far......fairly rigid. weighs 100g as of now. My target for the complete structure without the innards is 170g......lets see!

....foam+bamboo+hotglue would also work very well as already pointed out by Sundaram Head Scratching

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« Reply #19 on: June 29, 2015, 11:50:23 AM »
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....strangely, I am now able to upload only one pic at a time Huh?

IMG_20150629_112519169.jpg
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« Reply #20 on: June 29, 2015, 07:02:24 PM »
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.....i'd actually like to start with a single sufficiently sized fin in the center and see if it provides sufficient roll stability.

correction: yaw stability.
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« Reply #21 on: June 29, 2015, 10:48:33 PM »
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....stuck the bottom foam layer at....40%.....weighs about 130g. I added a 3mm ply brace on one side at each joint....that's what increased the weight....and hot glue !

....almost done with the wing.....just have to sand the airfoil !

....now for the fuse.....


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« Reply #22 on: June 29, 2015, 10:52:22 PM »
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.....just thinking about some options for the fuse....

IMG_20150629_224806942.jpg
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« Reply #23 on: June 30, 2015, 10:40:08 AM »
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......how to locate the neutral point Head Scratching ?

read through......but am a bit confused....are these steps correct?

1. Locate MAC and Distance of MAC from root.
2. Locate 25% of MAC from LE on the MAC.
3. Draw a perpendicular line from this C/4 MAC to the root chord arriving at the NP?

 @Iyer Sir......thank you.....some interesting reading  Salute

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« Reply #24 on: June 30, 2015, 11:14:06 AM »
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....here are some pics of the crude arrival of NP, and calculate the 'Static Margin'

...on the scale, 4.2cm is the NP and 6cm is the CG (NOTE: these numbers are NOT measurements....just so that you are able to see).....did not notice the alignment while clicking).

I am getting a static margin of 4.4% and HOPE I got my numbers right.

IMG_20150630_110442508.jpg
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