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« on: July 06, 2015, 10:35:01 AM »
bmblb
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....my gull wing flying wing (http://www.rcindia.org/electric-planes/2015-sweepstakes-entrant-42'-gull-wing-fling-wing/) for 2015 Sweepstakes is almost ready...while 'drawing the lines' I got tempted to make a bird type plane.

....so here are some pics of the progress so far....

IMG_20150705_195402599.jpg
Fenix - 48 in KFm2 bird like plane - 2015 Sweepstakes entry
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« Reply #1 on: July 06, 2015, 10:40:25 AM »
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......I decided to use bamboo for the spar....here's a perfect piece - (but its also perfect for my crossbow project)....so will have to shave one.

IMG_20150705_200154329.jpg
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« Reply #2 on: July 06, 2015, 10:47:47 AM »
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....some more pics.....the spar came out good !

IMG_20150705_234310228.jpg
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« Reply #3 on: July 06, 2015, 10:50:54 AM »
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......how time flies Grin....I realized it was 3am......and stopped after sticking the KFm layers.

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« Reply #4 on: July 06, 2015, 11:02:17 AM »
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....I decided to try a technique I read about for curved wingtips - and it worked beautifully !

Use a heat-gun and bottle for the radius.

Very important :

1.If you decide to use this method, ensure you have a large slab of stone - the ones they use for flooring....or couple(=2 for weight) of regular floor tiles with a clean edge - place this along the whole chord - aligning in a way that there's a clear half inch margin AFTER your aileron.

you can choose bottles of various radii depending on your choice - but ensure it is cylindrical - wine bottles work well.

2. Coro becomes brittle if heated too many times....try to get it right in 1-2 tries. It is necessary to tape it after done to prevent tears.
3. Cut the aileron after moulding the tips.

IMG_20150706_105140067.jpg
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« Reply #5 on: July 06, 2015, 11:21:15 AM »
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....the wing tips will continue with the KFm step as normal....another layer of foam comeing there and it will be thinned out to the extreme tips.

Controls:

Stage one: Just elevons should work fine.....depending on how this goes>
Stage two: flaperon+ elevator

Also, there will be no vertical fin specifically......if the curved wing tips are found to be inadequate then I will introduce a fin - using 1.5mm clear acrylic sheet - as soon as I can find it(any leads welcome here)

.....And this would be a prop in slot leaving both nose and tail for all the creativity ! Grin
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« Reply #6 on: July 06, 2015, 01:14:00 PM »
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.....the pelican just takes my breath away  Bow

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« Reply #7 on: July 06, 2015, 01:48:29 PM »
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Working with bamboo:

...had the unique opportunity to watch an old man cutting bamboo strips for curtains on the footpath, while stuck in Bengaluru's notorious traffic jams - a good 10+ mins without moving an inch.

 and I just wanted to try my hand at it and got hold of some youngish bamboo....and made myself two knives( actually completed the one with shoe lace handle(4mm) after 22years - and the other with the PVC tube handle(6mm) in a day.....a fair amount of bellowing, holding, hammering, quenching, and all of grinding and honing was done by self. The blue sheath is a pvc tube again, moulded using the heatgun- check the belt clip)....so what does this have to do with working with bamboo ?

you need a heavy knife with a thick blade and a sharp tempered edge ! the NT cutter is dangerous for bamboo ! the old man just made a notch, split it and ran his blade right through, prying a bit at the knots !

and - avoid using CA if you can - it makes bamboo brittle !

... Grin I just wanted to show off my knives  Grin

IMG_20150706_132041849.jpg
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« Reply #8 on: July 06, 2015, 06:20:30 PM »
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Great knives - you made them yourself ?  What metal did you use ?

Just a piece of information/tip for those interested in making their own knives -

use old leaf springs from heavy vehicles - known as "spring patti " locally.

The original Maruti 800 - (japanese one) had leaf springs of excellent quality
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« Reply #9 on: July 06, 2015, 11:49:18 PM »
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@ saikat.....glad you enjoy making knives.....have shared some youtube links on PM.....quite amazing !
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« Reply #10 on: July 06, 2015, 11:57:06 PM »
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.....finished the wing and quite thrilled with the results....here are some pics.




IMG_20150706_170233557.jpg
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« Reply #11 on: July 07, 2015, 12:00:32 AM »
bmblb
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....the right wing tip was done FIRST and came out better than the left.....although the angle is same on both sides, the kink cant be undone. On the bottom, the curve is quite similar when you run your fingers over it.

learning - use same techniques for both sides - used my palm for the right and a set square for the left - hence the sharp bend.

 the foam piece in the blue background is the wing tip filler.
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« Reply #12 on: July 07, 2015, 07:53:02 PM »
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Good going bmblm. intresting.
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« Reply #13 on: July 10, 2015, 08:04:48 PM »
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....thank you!

 here are some pics of the progress.....

....notice in the front view.....the LE thickens towards the tips....I have added a 3mmx25mm foam strip sanded so as to give a 'slat' kind of an effect - just like the REAL birds - the wing has an AR of about 6+ bordering on the side of 'high' AR, as far as flying wings are concerned, so I have read.

....with the high propensity to 'Tip Stall' with such type of wing.....as I learnt from my previous build, it made sense to include the wing cuff.

.... it feels really nice to run your fingers underneath the wing, and feel the camber change Grin Grin

......and in the side view, the dented nose is evidence of the several test launches....to get the cg....this has been tricky  Bang Head

....but fun

 

IMG_20150710_070146076.jpg
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« Reply #14 on: July 10, 2015, 08:23:05 PM »
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....drying after two coats of paint !

IMG_20150710_092127400.jpg
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« Reply #15 on: July 10, 2015, 10:36:47 PM »
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........just for the record, I maidend the Fenix this afternoon around 5pm at Hoskote. Grin

my hand-eye coordination right now is less than desirable to do anything meaningful....

I got a video.....but let me give you a blow-by-blow account tomorrow  Wink

the date/time stamp on the video is from 2008....so you will have to ignore that....

let me enjoy the videos  Grin
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« Reply #16 on: July 10, 2015, 11:13:25 PM »
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  watch !

 

 

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« Reply #17 on: July 11, 2015, 10:28:23 AM »
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Long Live Omar Sheriff !!!
He passed away. Featured in todays newspapers...
Well done BMBLB
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« Reply #18 on: July 12, 2015, 11:43:09 AM »
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Long Live Omar Sheriff !!!
He passed away. Featured in todays newspapers...
Well done BMBLB

....May his Soul rest in peace. I got goosebumps reading this post....
updates follow after sometime.


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« Reply #19 on: July 12, 2015, 01:27:52 PM »
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What happened to the flying bird
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« Reply #20 on: July 12, 2015, 10:54:12 PM »
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here are a few pics of the completed bird.

at 415g RTF, it is un-put-down-able  Grin

notice the slats.....

IMG_20150709_170619326.jpg
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« Reply #21 on: July 12, 2015, 11:12:52 PM »
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Maiden Flights:

....I'd have had about 20+ test glides (just bare plane) to get the CG and get a hang of the plane......first without fin and THEN with the fin.
it is un-flyable without the fin with just elevons!! the best glides were about 60-75 feet....gentle, flat....nice !

Once fully rigged, it weighs about 415 g, with a WL of 5.03 oz/sft this is with the 850mAh(68g). Wink

the CG is where it should be and feels quite good in the hand  Grin

Launch 1: 25% throttle, 30% throws. Climbed nicely but no response to control inputs...so cut off and landed gently - insufficient throws AND no reflex, as I learnt.

Launch 2: 45% throws, and set the elevators at 5mm deflection (Up) from neutral and launched at a little more throttle....climbed nicely, but the prop came off.

Launch 3/Flight 1 - 00:30 - 02:35
Launch 4/Flight 2 - 03:05




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« Reply #22 on: July 12, 2015, 11:52:57 PM »
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Summary:

The V-Tail KFm Eagle is a fantastic first "Bird Type Plane" to build and fly - it looks great in the sky....but I wanted something different for my first BTP.....something with a wider flight envelope, and should resemble the flight of a Bird of Prey !

The Fenix dives, climbs, rolls and glides beautifully....the sweep really looks neat when coming in fast and low. As you can see from the videos, its quite stable.

...just listing down some points here:

1. 'Self-designed' Head Scratching
2. Does look and fly like a bird
3. Justifiably uses a subtle yet VERY effective feature of 'Slats'/wing cuffs which are essential to mitigate tip stall, especially for a moderate - high AR(for flying wings). You actually need to fly with and without to know the difference !
4. Explored design/stability concepts like Static Margin and Neutral Point.
5. Actually saw the need for 'Reflex' (I think this is what the upward deflection of Ele is called??)
6. Coro+Foam fusion for durability
7. Curved wing tip - been done with foam before, possibly first in coro  Grin ( here I come, EasyStar)
8. Wing Loading well within range, actually lighter considering coro !!
9. CG arrived at by test glides as the tail feathers push the CG further back than just the wing in addition to using the calc.
10.And a few interesting/simple things for further observation  Wink

Hope you enjoyed this !



 
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« Reply #23 on: July 12, 2015, 11:58:19 PM »
K K Iyer
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 Clap Clap Clap
Ah, so birds can loop...
Given enough power Grin
A fine achievement. Congrats.
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« Reply #24 on: July 13, 2015, 12:27:48 AM »
sundaram
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loved the flight  Clap Clap Clap superb
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« Reply #25 on: July 13, 2015, 12:35:42 AM »
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Clap Clap Clap
Ah, so birds can loop...
Given enough power Grin
A fine achievement. Congrats.

Thank you Iyer Sir.....

That's why I called it The Fenix ....just kidding, I was just pushing it....(the blow by blow account comes later)
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« Reply #26 on: July 13, 2015, 12:43:43 AM »
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loved the flight  Clap Clap Clap superb

thank you Sir.....it is indeed a nice feeling.

....these are hopefully my baby steps to the Grand Masters of BTP!

I meant to seek your inputs and will re post as soon as I am able to locate a pic for comparison.
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« Reply #27 on: July 13, 2015, 12:34:26 PM »
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Query:

(a)....the multicolored flying wing(MCFW) flies well (aerobatic) without the fins too, but not the Fenix despite the curved wing tips.

....If Fin gives roll stability, then the Fenix should have better roll stability due to the flattish fuselage AND the curved wingtips.

(b) The upward deflection of the elevons necessary for take off - is this really called 'reflex' or is it a case of misunderstood concept and/or misused term or both?

any/all comments welcome !


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« Reply #28 on: July 13, 2015, 03:32:01 PM »
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@bmblb,
Here's my 2 cents worth:
one is a swept wing, and the other is not.

When a swept wing, in level flight, gets yawed to the left, it slips to the right and two things happen:
1. The right wing presents, to the airflow, a larger frontal area than the left wing. The resultant higher drag produces a force counter to the original yaw.
2. The right wing sees a higher angle of attack and hence higher lift and drag both.

The result is a yaw correction to the right and roll inducement to the left.

When a swept wing, in level flight, gets banked to the left, it slips to the left.
The result is a roll correction to the right and yaw inducement to the left.

Hence sweep works like dihedral. There is a conventionally accepted thumb rule that i don't recall exactly (like 5 or 10 degree sweep equals 1 degree dihedral, that had been mentioned in a thread a few months ago, probably by Gusty sir)

(Effect of fuselage depends on whether the centre of side area is above/below/ahead of/behind the CG)

The upward deflection of the elevons for takeoff is just 'up elevator'. No connection with 'reflex'.

A reflexed airfoil is one where the camber, which is concave from below, becomes convex as it approaches the trailing edge. This has the same effect as decalage in a wing and stab layout. This may be built in, or achieved by setting the elevons in a raised position (for level flight). Up elevator for takeoff is over and above this.
(Coeff of moment being positive etc not being introduced into the discussion at this stage, as not reqd)

People with formal education on the subject, like rcpilotacro, or a recent member who is completing his aero degree, are requested to see if the above explanations are ok.
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« Reply #29 on: July 13, 2015, 11:47:10 PM »
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....Thanks ! better to clarify than misuse terms !

however, I was wondering on these lines.

1. The MCFW is evidently a swept back wing, yet, the BTP is not essentially a plank either - unless we use simple arithmetic to cancel out the forward and aft sweeps, leaving with a negligible sweep back - then why have such a wing at all (agreed that the birds change the sweep depending on how they want to fly - there are birds - well, most of the birds actually - whose wings' standard form for most part of their flying behaviour  is indeed sweep forward and then sweep back....of course changing in extreme dives and glides (perhaps for structural and collapsible reasons as well?)

....or do the sweeps (forward and aft) actually add up rather than negate, and is so designed ( by Him) so as to have a longer span, without compromising on the stability by virtue of the 'total sweep' ? I am just guessing here !!!

2. As regards 'reflex' which is a case of simple up elevator here, - what factors in a plane necessitate such a pronounced deflection to start with? For a layman, if the control surfaces are neutral and there's sufficient down thrust(?), it should fly level, right ?

or is it a case of insufficient 'down thrust' and needs another washer?

In other words, if I were to make the same plane fly with the elevons at neutral, then what should change in the plane? **

2.1....this should show up in the test glides as well, correct? why are the test glides flat, then? or is it that 60-70( I believe the glides are much longer) feet glide is too short to assess this?

Couple of more points on the curved wing tips and the fuse sides....maybe later.
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« Reply #30 on: July 14, 2015, 12:32:18 AM »
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The upward deflection of the elevons for takeoff is just 'up elevator'. No connection with 'reflex'.

A reflexed airfoil is one where the camber, which is concave from below, becomes convex as it approaches the trailing edge. This has the same effect as decalage in a wing and stab layout. This may be built in, or achieved by setting the elevons in a raised position (for level flight). Up elevator for takeoff is over and above this.
(Coeff of moment being positive etc not being introduced into the discussion at this stage, as not reqd)

.....Iyer Sir, I naturally came across and read about reflexed wing....

What I meant is exactly what you have written above!

.....note that the plane sank(no level flight here) inspite of the ele input.....however, AFTER the ele setting was set at Up ele permanently, THEN ele input resulted in a climb, otherwise level flight(EDIT: with a tendency to dive).

...it was necessary to get this sequence right....and guess it is reflex after all as the usable ele input was only after the 'over and above' ele setting.
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« Reply #31 on: July 14, 2015, 01:06:04 AM »
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Maiden Flights:

Launch 1: 25% throttle, 30% throws. Climbed nicely but no response to control inputs...so cut off and landed gently - insufficient throws AND no reflex, as I learnt.

Launch 2: 45% throws, and set the elevators at 5mm deflection (Up) from neutral and launched at a little more throttle....climbed nicely, but the prop came off.

Correction:

.....hate doing this as it may be perceived that facts are being twisted to suit theories rather than the other way around.

Nevertheless,.....

Here's the sequence of events - what was typed above is an oversight in excitement, as I now recall(the blow by blow account) :

Launch 1: On launching at about 25% throttle, the plane took the path of launch but did NOT climb.....instead on increasing throttle AND giving ele input, it flew ahead without noticable/ proportionate increase in alt, as though there was no ele input at all !!!....and therefore cut throttle and landed.

Launch 2: Two corrections were made. The ele setting was set at 'Up' by 5mm or so from neutral. This is visible in some parts of the video when the plane is flying level(EDIT: and without any control input - a trimmed flight). And the throws were increased - this is evident from the maneuvers.

In addition, there were a few loops where recovery was longer (the heavy breathing is mostly repeated sighs of relief  Grin) - would these recoveries be faster if the 'Up deflection' was set at more than what it now is AND with the same ele input?

....If so, then I think it resembles the definition of reflex ?



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« Reply #32 on: July 14, 2015, 09:29:27 AM »
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or is it a case of insufficient 'down thrust' and needs another washer?

In other words, if I were to make the same plane fly with the elevons at neutral, then what should change in the plane? **

Need inputs here ! It is possible I may be grossly incorrect with the reference of the 'thrust line' in this scenario.

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« Reply #33 on: July 14, 2015, 10:09:55 AM »
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Test Glides  Grin Grin Grin
 
 There are some gaps(Edit: meaning details intentionally omitted) in my account of the test glides. Any guesses from the recent posts/edits ?
..........
 2.1....this should show up in the test glides as well, correct? why are the test glides flat, then? or is it that 60-70( I believe the glides are much longer) feet glide is too short to assess this?
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« Reply #34 on: July 14, 2015, 11:13:48 AM »
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@bmblb,
Now have to introduce CoM!
Will phone.
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« Reply #35 on: July 15, 2015, 11:24:55 PM »
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@bmblb,
Now have to introduce CoM!
Will phone.

.....at the end of our conversation, I had a couple of pages filled with something I will have to sit at to figure out/understand in moooore detail.

....it is not often that one finds people taking such interest...

thank you very much, Iyer Sir ! Sorry, I had a overnight travel and got back earlier this evening (and was just in time yesterday for the bus after 3 hours of flying..)
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« Reply #36 on: July 16, 2015, 12:51:16 AM »
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Hence sweep works like dihedral.

I must apologize before hand for how this sounds - the intention is NOT to sound cheeky.

......if sweep(assumed to be swept BACK) works like dihedral, then swept forward works like 'anhedral'? again, cancelling out each other?




 ..... OR.....



....does it work like a gull wing Huh?



OR



....like a polyhedral wing.....just adding the dihedral in the same direction?

...there really must be a reason for this shape of a wing !!!
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« Reply #37 on: July 16, 2015, 02:55:43 PM »
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....here's another video from Tuesday.

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« Reply #38 on: July 16, 2015, 04:07:19 PM »
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Just happened to see the videos today. Don't know how I missed it earlier. Loved the way the "buzzard" fler
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« Reply #39 on: July 16, 2015, 09:56:30 PM »
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Wow. Terrific!
Nothing succeeds like success!

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« Reply #40 on: July 16, 2015, 10:40:52 PM »
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"..there really must be a reason for this shape of a wing !!!"

But for some reason, not seen many wings like the Minimoa in the last 80 years...

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« Reply #41 on: August 26, 2015, 09:27:05 AM »
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ta da  Grin !

IMG_20150719_091504388.jpg
Re: Fenix - 48 in KFm2 bird like plane - 2015 Sweepstakes entry
* IMG_20150719_091504388.jpg (57.66 KB, 800x450 - viewed 371 times.)
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