Prandtl-d - Page 4 - RC Groups
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Dec 20, 2013, 11:44 AM
Pile-it
Alien_Tech's Avatar
Quote:
Originally Posted by Knoll53
Can you post a little more info. about your control surfaces? Maybe a simple line drawing showing the layout. From the pictures it appears that you have just two conventional elevons placed at the wing tips.

In my version, there were 4 control surfaces. Crow was used for landings per the attached drawing and I found it ineffective. In fact, I can remember one landing where it seemed to glide better WITH crow.........that was a long...long landing. I never did spend much time testing or tweaking that set up, so my initial observations are certainly incomplete.

thanks,
Kent

Yes there are just two elevons out at the tips. I'll see if I can't find some detail shots.

Red
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Dec 21, 2013, 08:47 AM
Registered User

relativity theory


I still don't claim to know exactly what was going on with my test models, but here are some facts and my conjecture:


1. The tighter the tip-vortex, the more drag; the more open, the less drag and greater L/D.

2. The inboard elevons in my [cranked-wing] test models acted exactly as normal and were the most effective placement as tested in these designs [see sketch in my previous post].

3. Any tiny incr. in wash-in [incr. AoA] in the outer wing sect. of my designs, once they were optimized for a SUPER glide [L/D], greatly incr. the drag on that side, yawing the wing in that direction, and the opposite when even micro-washed-out!

4. I suppose [can be tested in flow studies] that when the left [inboard] elevon is lowered, the washout on that wing is incr., relative to that of the rt. wing when the rt. elevon is simultaneously raised, which would incr. its washout. That would mean [as in 3.] that there's a more open vortex on the left side and a tighter vortrex on the rt., w/more drag on the rt. side and less drag on the opened-vortex left side. Further, down-elevons on both sides reduces the optimized AoA of both wingtips [which appeared in my tests to be at a slightly positive AoA w.r.t the flight path, but still negative w.r.t. the root sect.] and perhaps reduced the overall L/D = "down". And since up-elevons can only add a very little "up" to a critically optimized aircraft [these high aspect ratio soaring birds are very efficient but correspondingly just barely stable, and very definitely "fly-by-wire"!!]. Anyway, one would "tune" the aircraft design to allow some effective "up", however.

Dunno .... but they did work like normal elevons in those tested designs. And that would fit with my observation of how and with which [inboard] feathers gulls & albatrosses use for control/steering.


The fact that these birds operate at Rn's extremely and critically lower than the Dreamliner might account for the more outboard aileron placement on the Boeing, relative to its still-long wingtip. Plus, the jet's wings must be proportionally stronger and thus heavier [more mass] to deal with the "rock-solid" air through which they must fly. So the birds' relatively much lighter outboard wing is likely easier to steer w/ more inboard control-feathers [also closer to bone & muscle].

As would an R/C model wing ....

An easy test would be for someone to tape on slightly anhedralled long, narrow, swept tips [see below crude "mouse-drawn" sketch] on a Horten model and see just what happens re: elevon effectiveness.

My guess is that a fighter aircraft becomes an albatross.


In any case, maybe, re: Prandtl-d, to fly like a bird .... you have to BE a bird!



Lee
Dec 22, 2013, 08:23 AM
Registered User

form = function


The American architect, Louis Sullivan, Greenough's much younger compatriot, who admired rationalist thinkers like Greenough, Thoreau, Emerson, Whitman and Melville, coined the phrase in his article The Tall Office Building Artistically Considered in 1896 (some fifty years after Greenough's death). Here Sullivan actually said "form ever follows function", but the simpler (and less emphatic) phrase is the one usually remembered. For Sullivan this was distilled wisdom, an aesthetic credo, the single "rule that shall permit of no exception". The full quote is thus:


"It is the pervading law of all things organic and inorganic, of all things physical and metaphysical, of all things human and all things superhuman, of all true manifestations of the head, of the heart, of the soul, that the life is recognizable in its expression, that form ever follows function. This is the law."



^ Sullivan, Louis H. (1896). "The Tall Office Building Artistically Considered". Lippincott's Magazine (March 1896): 403–409.
Dec 22, 2013, 01:11 PM
Pile-it
Alien_Tech's Avatar
If anyone got the latest AMA mag with the false cover advertising the AMA Expo, you'll notice that one of the speakers will be Albion Bowers "On the Minimum Induced Drag of Wings: Why Birds Don't Have Vertical Tails". The talk is specifically about this project, and the model will be there.
Dec 22, 2013, 05:15 PM
Registered User
iron eagle's Avatar
Quote:
Originally Posted by Alien_Tech
If anyone got the latest AMA mag with the false cover advertising the AMA Expo, you'll notice that one of the speakers will be Albion Bowers "On the Minimum Induced Drag of Wings: Why Birds Don't Have Vertical Tails". The talk is specifically about this project, and the model will be there.
It would be nice if the AMA offered a transcript of that.
Dec 22, 2013, 07:52 PM
Pile-it
Alien_Tech's Avatar
Quote:
Originally Posted by iron eagle
It would be nice if the AMA offered a transcript of that.
Maybe they will video tape it and put it online?
Dec 23, 2013, 07:13 AM
Registered User

birds steer like airplanes steer like birds


If one wants to mimic a bird's turning [and even lift distribution]: which bird and which part/aspect of that bird's broad flight regime?


1. My budgie Kiki turns his long tail-feathers sometimes as much as ~30° to one side when making an abrupt turn at high speed.

2. Broadwinged Hawks [eagles, etc.] greatly incr. the AoA of the inboard wing and skew ["roll"] their outspread tail to provide a strong yawing force to counter the extreme adverse-yaw in a tight, slow, flat minimum-sink thermic circle [in which the turn radius starts to approach the wingspan]. Most birds also roll/skew their tails similarly when gliding or soaring [as do many R/C Ornis]. Of course when "flapping" [a common misnomer for most birds' lift+propulsive wing motion which is far more complex than merely "up/down", as a flap, and which I have now decided to call AeRowing] with the tail depressed at a positive AoA to compensate for the powerful fwd/downstroke ... the bird simply puts more effort into one wing than the other in order to turn [we do similarly when walking or when rowing a boat].

3. Gulls have a very difficult time making smooth small thermal circles, and they often continually re-stabilize with a somewhat "choppy" movement.

4. Gulls often use ther HEADS as steering rudders to help them turn [and as "elevator" trim for precise up/down corrections].

5. Gulls form their wings into a McDonald's-like rounded "M" to easily maneuver when landing, totally changing their lift distribution. And what of the R/C "Butterfly" landing lift distribution?

6. Birds can pull in, extend or change the sweepback of one wing > rudder-effect.

7. Modern aircraft can continually re-configure their wings in flight .... paralleling what birds do.



Happy/Merry!!



Lee






Holy Modal Rounders - If You Want to Be a Bird - Legendado e Traduzido Para Maria Inês Palombello (2 min 44 sec)
Dec 23, 2013, 07:29 AM
Registered User

Christmas Present for the World >


I personally think that the most wonderful thing to come out of all of this is the perhaps patentable benefit of adding thrust-producing* winglets or tips to windmills, and thus using this thrust to turn the windmill without even needing wind [it's thrust, right?]. These could even be made small enough to put inside one's house or apartment: a renewable free "green" energy source!!


SilLee



P.S. I really hate Entropy: along with Gravity, I consider it my personal enemy.

*http://ntrs.nasa.gov/archive/nasa/ca...2007033776.pdf
Dec 23, 2013, 07:49 AM
Herk
HerkS's Avatar
Quote:
Originally Posted by xlcrlee
I

P.S. I really hate Entropy: along with Gravity, I consider it my personal enemy.
We need gravity - - it is the power plant - the engine - that makes soaring flight possible.

Entropy is another issue. That would make a fun forum on it's own. The question though was explored by Isaac Asimov many years ago. It's a good read.
https://docs.google.com/file/d/0Byou...RJVEg4YnM/edit

Enjoy -- Herk
Dec 24, 2013, 09:26 AM
Registered User

what you mean "we" ....?


Quote:
Originally Posted by HerkS
We need gravity - - it is the power plant - the engine - that makes soaring flight possible.

Entropy is another issue. That would make a fun forum on it's own. The question though was explored by Isaac Asimov many years ago. It's a good read.
https://docs.google.com/file/d/0Byou...RJVEg4YnM/edit

Enjoy -- Herk
http://newsgroups.derkeiler.com/Arch.../msg05570.html

YOU may need Gravity, I still consider it my personal enemy: soaring becomes Superman-like [OK, getting back "down" -- a useless concept in this case -- is another story. Anyway my bird Kiki now can fly his Magic Carpet inverted and use his wings oppositely if needed. So powered flight would still work. To "land".

again,
Happy/Merry
L
Dec 24, 2013, 01:32 PM
Registered User

don't tell these birds ...


.... that they don't have vertical stabilizers or adverse yaw on occasion >



some birds HAVE vertical stabilizers [some aircraft don't, right?!]
.... my gull-winged Nurflügel test-models had a MUCH easier time circling when a Pterosaur-like vertical stabilzer was added where the "head" would be!

almost ALL birds also steer L/R & up/down with their heads

almost ALL birds roll their tails to provide yaw input



in the first seconds note how the bird skews his/her tail, providing yaw input >

Eagles on thermals (1 min 55 sec)




same YAW steering when required >

Where Eagles Soar DVD (1 min 37 sec)





note skewed/rolled inverted-V tail [which includes verticality] >

http://galerie.chip.de/k/tiere-unter.../milan/332833/




leaky
[Lee+Kiki]
Dec 24, 2013, 05:32 PM
Registered User

more yaw'n action ;-)


jest watch 'em tails twitchin' 'n twistin' ever' which way >



Birds of prey gliding high above lakes and mountains in Spain - David Attenborough - BBC wildlife (3 min 6 sec)




an' turnin' they haids fur steerin'[google translate: "and turning their heads" etc.]
Dec 24, 2013, 05:44 PM
Registered User

'nuff said


as Kiki likes to say, "See! Watch!"* >


Red Kites in Slow Motion - The Slow Mo Guys (2 min 37 sec)




*ALL the control inputs in slo mo

Dec 24, 2013, 09:34 PM
Registered User

better drawing of my test model


I am visiting my friend and her computer has a better mouse, so here is closer to what the test model I made several months ago [badly drawn in Post #43] actually looks like >


L


b.t.w., the little "tail" in the rear is at a positive AoA of about 7° ..... and IT [not the elevons] acts a bit like a flap, slowing the glide, but also strangely flattening it even more!
Last edited by xlcrlee; Dec 25, 2013 at 04:31 AM.
Dec 25, 2013, 07:57 AM
Registered User

soaring bird correcting for adverse yaw


typical > wing closest to center of circle held at higher AoA, adverse yaw compensated by skewing/rolling tail to provide opposite yaw force [fullsize & R/C sailplanes do the same, for the same reason]

note this in below video at 0:26
can be seen frame by frame


a coordinated right turn can be seen at 0:32 > the left wing is at a much higher AoA than the rt. wing = right aileron input and the depressed tail is tilted left [positive AoA, rt.side higher, lifting vector up and left] = right yaw input .... the SAME control inputs used by an aircraft




Birds of prey gliding high above lakes and mountains in Spain - David Attenborough - BBC wildlife (3 min 6 sec)
Last edited by xlcrlee; Dec 27, 2013 at 05:58 AM.


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