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Dec 14, 2013, 10:41 PM
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slebetman's Avatar
Ah, forgot about EDF jets. If you look at the EDF forums you'll find that hotwire cutting segments is the most popular and most common method of building. And they're doing it with curves far more complex than non-linear twist.
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Dec 15, 2013, 05:05 AM
You know nothing....
Stuart A's Avatar
http://www.google.com/translate?u=ht...ngpair=ru%7Cen
Click on Ksena2 at the bottom of the models page.

Example of a wing from the Tetris site.A while ago I tried to persuade them to have a go at a Horten wing,but they didn't take the idea on board.
Last edited by Stuart A; Dec 15, 2013 at 05:16 AM. Reason: Page link not working
Dec 17, 2013, 08:18 AM
Registered User

cool


Has anyone noticed the various similarities [birds, vortex-control, etc.] to what I was discussing here? > https://www.rcgroups.com/forums/show...stabil+control


Some months ago, totally unaware of Prandtl-d, I applied this above set of concepts to several small freeflight albatross or gull-winged Nurflügel gliders whose wings look amazingly like the Prandtl-d [except cranked]. These were just concept models for a UAV project on which I was consulted; I later donated them to the ETHZ Fluid Dynamics Dept. for further study. They were fascinated with the flight characteristcs, as these gliders fly REALLY well, with NO vert. surfaces or winglets, etc., and do esp. well in slope or thermal lift!! > they apparently tend to find "good air" ["green" air] and avoid sink.


As a result of the hard work getting these very sensitive beasts [they look beautifiul] sorted out, re: R/C Nurflügel, please note
:

the preset control surfaces, variable for flight research into their effect, HAD to be elevons [only!] .... and they had to be placed 1/4 to 1/3 out from the centerline, about where the motors are in the Ptero shown in the above linked thread.



Further, many years ago when I was in love with my Hobie Hawks, I reasoned & proved that the original factory washout was in the wrong place! Out of the box they liked to snap-roll violently and "re-kit" themselves as they left your hand on a highstart launch. Not nice. But by using a hairdrier to re-bend the washout eight bays in from the tips, and then going linearly out from there to the tip, the L/D incr. and no more deadly snap-rolls on launch [could still do vert. snaps on command, though]. The outboard T.E. looked a LOT like that of the Prandtl-d ....

The factory re-did their jigs, with one part placed exactly at the 8th bay in, I saw in a released factory photo after I informed them and they obviously tried it. They never acknowleged my info, however. In the below photos, which do not show the jig that I saw then, I am not sure if I can see the jog in the T.E., but maybe ...


L
Dec 17, 2013, 11:38 AM
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Knoll53's Avatar
Quote:
Originally Posted by xlcrlee
the preset control surfaces, variable for flight research into their effect, HAD to be elevons [only!] .... and they had to be placed 1/4 to 1/3 out from the centerline, about where the motors are in the Ptero shown in the above linked thread.
Some things are best done with drawing. I'm not quite following what you are saying as to the location of the elevons. Could you post a sketch for us?



Quote:
Further, many years ago when I was in love with my Hobie Hawks, I reasoned & proved that the original factory washout was in the wrong place! Out of the box they liked to snap-roll violently and "re-kit" themselves as they left your hand on a highstart launch. Not nice. But by using a hairdrier to re-bend the washout eight bays in from the tips, and then going linearly out from there to the tip, the L/D incr. and no more deadly snap-rolls on launch [could still do vert. snaps on command, though]. The outboard T.E. looked a LOT like that of the Prandtl-d ....L
So for a nurflügel, I guess that it safe to say that you are not an advocate of the conventional BSLD where most of the wing twist occurs AT the wing tips, not 8 bays in.......I'm I following you correctly?

Kent
Dec 18, 2013, 08:52 AM
Registered User
Quote:
Originally Posted by Knoll53
Some things are best done with drawing. I'm not quite following what you are saying as to the location of the elevons. Could you post a sketch for us?





So for a nurflügel, I guess that it safe to say that you are not an advocate of the conventional BSLD where most of the wing twist occurs AT the wing tips, not 8 bays in.......I'm I following you correctly?

Kent
The Chief of Advanced Design at Grumman told me years ago that like the rest of aerodynamics, the exact application of washout varies with each design .... and must be physically tested in every case.

The Hobie's wingtips were originally twisted WAY too much to be effective, as they are narrow enough [chord] to start to become ineffective at the Rn's involved. I made an educated guess, and my solution luckily and happily worked!!

Below is a crude Internet-computer-drawn sketch I just now made of APPROX. where the elevons need to be placed when one uses a wing similar to the Parndtl-d, as I painstakingly found out with the small such Nurflügel models of which I posted above. What I discovered was that if, for ex. the wing turned left, the narrow [narrower than the sketch below, which was hard enough to make using this mouse] slightly more-anhedralled wingtips, which I propose were correctly placed within the control/stabilizing tip-vortices, acted like drag rudders inducing HUGE amounts of adverse yaw, if the outer left wing was twisted to give it even slightly more "lift"/AoA!! It would turn MORE left! Same if I even slightly reduced the AoA on the outer right wing! So I made a week of intense experimentation to find that the best control and L/D came with the elevons -- the ONLY control surafces for this type washout -- placed about as shown below.

And ... "your results may vary" > requires experimentation & testing. But like the little girl with the curl ... when you get it right, the results are astounding!


Lee



There was a little girl [Henry Wadsworth Longfellow]

There was a little girl,
Who had a little curl,
Right in the middle of her forehead.
When she was good,
She was very good indeed,
But when she was bad she was horrid
Dec 19, 2013, 07:46 AM
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wing tips & washout re: "vortex-control" wings


elaborated in the following post ....
Dec 19, 2013, 08:19 AM
Registered User

re: elevons, etc. for "vortex-control" Nurflügel


As my best indication so far is that birds & bird-like aircraft use the vortices for stabilization rather than control, I prefer to think of vortex-stabilization.

To wit, the Prandtl-d video states that they basically flattened "winglets", making them horizontal. Although I read in an erudite article [in German by a German PhD aerodynamicist] that his tests showed that for a high aspect ratio Nurflügel with slightly anhedralled swept and washed-out wings, the best overall flt [L/D, maneuverability, speed, winch] came when the winglets were untwisted, symmetrically airfoiled and w/zero AoA w.r.t the flt-path onflow ...

.... my understanding is that for fullsize aircraft the winglets should be washed-in.


Albatrosses & gulls are basically Nürflügel when they soar [tail-feathers retracted]. Further, a bird's flight feathers are spring-loaded, sprung, with copious curved "anhedral" and wash-in! ["feder" in German means both "spring", as in coil-spring, and "feather"!]. Like our hair, the feathers, similarly grown from modified skin-cells, can be formed and re-formed with moisture and heat > I've done this many times, as req., w/a hairdrier for my birds. The feathers' down-curve + axial-twist is maintained as they are wrapped around the bird's very warm body when not in use.

This 2-axis bend/twist allows correct AoA under fwd/downstroke flapping & gliding flt-loads, plus easy "*limp-rag" upstroke when "flapping" [which is actually circular/oval, so I now term this complex movement AeRowing!]. Next, the outermost long "pin-feathers" [formally used as ink-pens!] are very aeroelastic and are far from the bone & muscles ...


.... and they are NOT generally used for steering! [up/down or L/R]


Lee
Last edited by xlcrlee; Dec 25, 2013 at 03:32 AM. Reason: typo
Dec 19, 2013, 08:50 AM
Registered User

commenting on my comments >


1. What I learned at Grumman all those years ago [and it was in the context of fwd-swept wings, b.t.w.] was that the "real" reason for washout or washin, and its placement, was to assure optimum AoA at every wing section, which like the rest of aerodynamics, was a highly empirical subject. And that washout was NOT primarily used to prevent tip-stalling!

2. I assume that it is not a huge intellectual step to realize that a normally washed-in winglet, when rotated to become horizontal as stated in the Prandtl-d video, just might have the same washin ....

L
Dec 19, 2013, 08:54 AM
Registered User
especially if the thin, long outer wing and wingtip look like this one >
Dec 19, 2013, 11:14 AM
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Knoll53's Avatar
As hard as I try, I may not be able to fully understand what you are saying, but the theory is quite interesting. I'm still working on your post #35.

The red inboard elevons shown (thanks for the drawing! It IS worth a 1000 words) appear to be located and sized so that they would act as pitch neutral flaps. Their use would change the lift and drag for that portion of the wing. If set up as elevons, a downward deflection, for example on the left side, would create more lift on the left side and thus a weak roll to the right ( weak due to it's short moment arm).

If I'm following you correctly, you would not agree with this. Is your theory that a downward deflection of the left inboard elevon would create a coordinated turn to the left?

Kent
Dec 19, 2013, 03:46 PM
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iron eagle's Avatar
Interesting discussion.

One of the more interesting control surface setups I have seen was on a BWB aircraft. When looking at it there were about 8 control surfaces on both the top and bottom of each wing from the root to the tip. Everything from classical LE spoilers to a second row of "spoiler type of surfaces" adjacent to the ailerons/elevator/flaps/rudders. As you moved your controls the wing actually morphed to a degree depending how moved it, very interesting and responsive as well.
Dec 20, 2013, 07:55 AM
Registered User
Quote:
Originally Posted by Knoll53
As hard as I try, I may not be able to fully understand what you are saying, but the theory is quite interesting. I'm still working on your post #35.

The red inboard elevons shown (thanks for the drawing! It IS worth a 1000 words) appear to be located and sized so that they would act as pitch neutral flaps. Their use would change the lift and drag for that portion of the wing. If set up as elevons, a downward deflection, for example on the left side, would create more lift on the left side and thus a weak roll to the right ( weak due to it's short moment arm).

If I'm following you correctly, you would not agree with this. Is your theory that a downward deflection of the left inboard elevon would create a coordinated turn to the left?

Kent
Interestingly enough, the German aerodynamicist to whom I referred above, wrote [somewhat tongue-in-cheek, in German] that there is nothing so practical as a good theory.

I posted not only what the Grumman expert told me, but also the perhaps strange results of my extensive tests, what actually happened [re: those gull-winged "vortex-stabilized" Nurflügel test-models, as well as my Hobie improvement].

Have to leave this Internet place now for a meeting, but will write more, hopefully with a better, clearer explanation and illustration.


Lee
Dec 20, 2013, 10:12 AM
Registered User
So far as I can determine, the albatross-winged Nurflügel test-model, with long narrow tips placed within the vortex, acted like the Boeing Dreamliner .... insofar as the long narrow outer section is a somewhat aeroelastic wing-TIP -- which in this case, my results indicate would be the ENTIRE outer third or even HALF of the wing --and not a controllable part of the wing. Given the high aspect ratio, the most stable and tightest turns occurred with elevons placed as shown.

AND, the elevons acted exactly as one expects elevons to > down left elevon and slightly more up rt. elevon produces a smooth right turn.

As for "theory", beyond the established fact that every wing design and planform behaves uniquely [see bird planforms below], I can suppose that the elevon has an effect on the total spanwise flow & tip vortex. So it has an exhibited [as in flight-tested!] greater effect than merely its moment arm w.r.t. the centerline. In the right-turn example above, the left vortex and the connecting left wingtip vortex would perhaps open up and have thus LESS induced drag than on the now-tighter rt-side vortex system. [of course I am just guessing > Physics only tries to describe what, not "why", and to continually update or change theoretical models to better fit observed reality .... and "Reality is a Moving Target", I have decided!]


Lee
Last edited by xlcrlee; Dec 25, 2013 at 04:34 AM.
Dec 20, 2013, 10:39 AM
Pile-it
Alien_Tech's Avatar
Lee,

There is no differential used in the model, throws are equal both up and down.
Dec 20, 2013, 11:00 AM
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Knoll53's Avatar
Quote:
Originally Posted by Alien_Tech
There is no differential used in the model, throws are equal both up and down.
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


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