Note that the gull/Möve [click on thumbnail photo below] basically IS a Nurflügel .... but his wings have a different shape, incl. conical camber to utilize spanwise flow for both control AND stability in a much more aerodynamically efficient way that is actually OPPOSITE to the Horten, B-2, etc. It is VORTEX control !

If you could do that with a model Nurflügel it would have a much higher L/D and could fly both a lot faster AND a lot slower, with more control and the "strange" ability/feature of automatically heading into green air [lift], be it mechanical or thermal!!.

I know this for a FACT and after I discovered it have used this principle in a simple way in some of the mass-mkt toys I created.

B.t.w., I am a Physicist & Engineer; two friends of mine, both top level Aerodynamicists, one ex-Boeing, now at the top of an international Aerospace research organization, the other, high level at EADS .... both think I am "on to something new and unexplored" [except of course by birds, around for ca. 85,000,000 years to sort this out, and Pterosaurs, who could conform their wings 3-dimensionally using lots of muscles in their skin membranes, like we have in our faces].



Lee


[NOTE: this of course also works as a pure Nurflügel, but I cannot post that unproduced version]

R/C Pterosaur (1 min 6 sec)

TRU Pterodactyl (0 min 22 sec)

Looking for a better photo to post, I just now discovered that the Acrobird is still being sold, although those b***tards at ITC have neither informed me nor sent any royalties since its inception.

I have only a few early samples myself, and although I think the prices they are asking are a lot for a foam plane, if anyone wants to get one to see what the above post entails, there are seemingly many sources for it, found by Googling "acrobird stunt glider". ITC "lost" the very expensive mold-form that I and the head of the prototype dept. at GFT [factory in Huisui, China] spent 2 solid weeks making, the head of the foam-molding sub-contractor company told me that he initially made something like 150,000 pc. for ITC, and ITC swore they only made and sold about 1,000 pc.

If for some reason anyone gets their hands on one, because of ITC's cheating and cutting me out of the loop (I only lent them the form to cost out production prices, and they put it into production without my consent or any contract), the idiots forgot to compensate for molding "springback", and the wings wind up with a lot less dihedral than designed.

This is easily fixed over a bread toaster [with care!]: the wings should be more or less flat across, no anhedral, with only a very slight dihedral. On the samples I got, the corrected tips need to be about 1cm higher than how it was shipped.

At any rate, after the looping/circling toy-nonsense, you can watch it seek and fly into lift, or turn into an offset, non-orthogonal onset wind on a slope [which is rising air on the slope!].

Among many sources I just found >

http://de.shopping.com/acrobird-stun...vw==/info?sb=1

http://www.amazon.de/Unbekannt-Acrob.../dp/B000WXNLOW

etc.


Lee

Lee:
More explanation would be nice ... I am not clear on the concept.

There is no "free lunch," the energy necessary to generate a vortex is not insignificant and contributes to overall drag. Do you have an analysis that compares the drag figures for "conventional control" vice "vortex control?"

Originally Posted by Cap_n_Dave

Lee:
More explanation would be nice ... I am not clear on the concept.

There is no "free lunch," the energy necessary to generate a vortex is not insignificant and contributes to overall drag. Do you have an analysis that compares the drag figures for "conventional control" vice "vortex control?"

First, I mentioned that it does need more investigation. But my education and practical experience with aircraft & aerodynamics over almost 70 years now [strange, but true], plus whatever abilites I inherited from my engineer/inventor grandfather & father [latter was an aerodynamicist, promoted to Chief of Engineering at Republic when he quit; last project the SeaBee] as well as specific knowledge [which research has shown can be passed via the gene coating], starting with talking to aerodynamic engineers when I was 9 mos. old [presumably regarding non-technical matters, although the first word I consciously remember is "Fowler flaps"] and reading my father's engineering books as soon as I could hold them .... leads me to make those posted statements.

Of course I compared the airborne behavior of these "special" wing forms with "normal" ones of similar size and wing-loadings, etc.

-------------------------------------------------------------------------------------------------------

To specifically respond to your statement, when something becomes more efficient, it isn't getting something for free.

These birds simply use the naturally consequential vortices & spanwise flows that HAVE to exist on a wing moving in an airflow .... in a better way systemically [net effect]. And, as a physicist, I know that "You get Nothing for Nothing" [0 = 0].

Depending on the oncoming flow, one wing's tip vortex expands and provides a better L/D, and the reverse for the other side. Disregarding entropy for the moment, the net effect is the SAME induced tip drag. But with a normal Horten/B-2 control & stabilization set-up [incl.passive!], EACH tip gets more drag with a control input .... AND requires some sort of "up-elevator or -von" setting to maintain proper AoA.

It seems that the vortex itself is used for pitch stabilization as well, at least in my toys & models [not the ones shown].

The upshot is that when I made the first pre-Acrobird prototype as a toy for my bird, I was amazed that it could slowly circle the room more than two times when thrown. And outside in a nearby park, after the looping nonsense [why it has a tail], it would slowly meander every which way when it got closer to the ground and find little bits of lift to keep it up for a surprisingly long while. It acted like it had a brain and flew like a real gliding bird would, showing me that a lot of birds' behavior is due to the physical shape of their wings and not "fly-by-wire" stabilization, etc.

Normally staid Swiss who witnessed this were astounded as well, and shouted the Swiss equivalent of "holy sheep, that's amazing; I never saw anything like that before", if you get the meaning of my drift.


Lee

http://archive.org/details/nasa_techdoc_19660010456

...

Interesting, but that's not exactly what I meant. The Acrobird's wings are cambered only because I wanted it to fly slowly. Similarly, my F-22's wings have conical camber, esp. because I needed to deal with low Rn [20 cm span] with 18g wt., so the wings are shaped basically in a smoothly curved version of the F-22 landing configuration, approximating the curvature of L.E. and T.E. flaps.

Micro Fighter /StarScream RTF R/C F-22 ORIGINAL version (0 min 42 sec)

Indoor Aircraft Carrier Landing (0 min 5 sec)

The gulls have far less camber and curve their wings spanwise [anhedral] for different reasons, incl. automatically turning into a slope wind and destabilizing for rapid maneuverability when landing [mucho more anhedral] .... and it's a very effective way to kill off lift and lose altitude fast for landing. Further, when outstretched the anhedralled wing ends are like downturned tips on a Horten. That is because, even though the gull has a tail, it is basically retracted in this mode, and the rear-swept wingtips are now the horizontal stabilizers. Because the airflow is reversed [up/down] there, as in the T-tails of 727s, etc., horizontal tail anhedral actually provides positive stability. Especially re: spiral stability. Same with an inverted V-tail: MUCH more stable in turns & gusts [I had a long flight in a V-tailed Bonanza and did not like the Dutch-roll action!]. Free flight models often have this feature, even if it's in the form of putting the vertical stabilizer on the bottom.


What I found has to do with the use of tip-vortices, which of course vary from one wing shape and camber [or camber mean-line: http://en.wikipedia.org/wiki/NACA_airfoil] to another.


When the B-2 was first displayed in public, my neighbor in Seattle didn't believe it could fly, so I traced the planform from the nearly top-view newspaper photo and quickly made a paper model. I cambered the wing -- for Rn purposes! -- and twisted in washout and downturned the T.E. at the root center [deltas work better that way, easily demonstrated with Rogallo and other hanggliders].

The quick & dirty B-2 paper model was twisted something like the hangglider in the photo below, plus the downturned center rear .... which you will note in later photos of B-2's in flight that the center T.E. sections are often also depressed.

This small model flew very stably without a hangglider-like pilot-weight hanging under for [esp.fore-aft: pitch] pendulum stability. And without reflexed T.E. or elevons. And without opened drag rudders [Horten / on B-2 only closed for stealth mode].


Lee

+ opened rudders

Lee

I have a large Horten with 2 turbines that has flown for several years. When we first flew it we did not use the drag rudders at all. Indeed the 2 other Hortens of the same design flying with EDF power did not have drag rudders fitted. We have only really needed them to assist with landing and in very strong cross winds. They are not deployed both open like the photo of the B2. They only open up on the side that more drag is needed. They are variable in amount projecting and of course are in pairs on both the upper and lower surface.

John

When you speak of auto soaring, whether it was the bird toy in thermals or the automatically turning into a slope wind, it doesn't make sense to me. Can you explain further?

For slope soaring, maybe you imagine that if you fly along the slope with the hill on your right, you would feel wind blowing in from your left wing (the wind that is hitting the slope). This is not the case - you would not feel any sideslip from wind relative to the ground. Sideslip is measured relative to the aircraft body. Aerodynamic forces do not care about what direction or speed the ground is moving beneath you - only the relative air on the body.

For thermal soaring, I do know of a trick to make a glider "auto soar" by carefully tailoring wing twist along the span. Basically you design the wing to stall asymmetrically and then trim it to fly a very stable glide near stall. When such a plane encounters a vertical gust which increases AOA on the plane, it will always stall one wing first, creating a nice turning action that causes it to naturally turn around updrafts. This has been successfully designed, built and flown. But this requires careful tailoring of both airfoil section and spanwise lift distributions at low reynolds numbers, along with a very good understanding of the dynamics (have to have stable spiral mode) of free flight models.

B.t.w., my "quick & dirty" B-2 paper model flew very stably AND "clean" .... w/o the need for opened drag rudders! OK, it didn't have a supercritical airfoil nor an unstable rearward CG requiring computer stabilization either.

Sometime after I made that model, after playing a game with my Scorpio neighbor that he created called "Stealth Frisbee" [you couldn't see it till it was in your face: funny], WhiteWings approached me to make a diecut coverstock pop-out version of the B-2. Coincidentally, after that request, on a day when I'd been carrying some of the 777 coverstock planes I made for Boeing to the Boeing Field museum store I happend to run into the chief pilot instructor of the B-2 program. He'd just flown the "Spirit of Washington" B-2 to the field [they use state's names to help maintain govt. funding] and was just then one of the first non-Boeing types to be up in the new 777.

He was surrounded by lots of people, but when he spotted the 777 coverstock models I was carrying, he asked for and got a bunch of those 777 gliders which he took back with him in the B-2! [they are almost photgraphically accurately printed and can fly with scale aeroelastic! wings up to 26m straight ahead and then flare nose slightly up into a nice landing > selective Rn control w/various flying surfaces allows that] and in return I received a lot of super drawings & photos from the USAF and Northrup and made an absolute scale [within the limits of publicly released and "smudged" otherwise secret drawings] planform and almost photographically accurately printed B-2 glider.

[ Although I produced them for WhiteWings, THEY were selling them, not me. I told them to send a bunch to Whiteman http://en.wikipedia.org/wiki/Whiteman_Air_Force_Base to show gratitiude for their help. Apparently they were much liked, with everone flying them, and they used them up. One morning at maybe 05:00 PST, some Major who'd obviously misunderstood my time zone, called and woke me and said "The General wants more bombers". Of course generals always want more bombers! ]

Since I knew no normal person could duplicate the twists & curves I'd put into my "Stealth Frisbee" model, I created the diecut version with a flat-plate airfoil [flat], using fold-around drag rudders that were flat on the bottom [the user-inserted locking "opened drag rudder" tab projected downward from the undersurface, providing pure drag plus some "down", and was of a size and area to result in the appropriate rudder + up-elevon mix I wanted] with the visible scale rudder surfaces projecting upward so that they were also elevons in the UP position. Also, for the SAME aerodynamic reason as in the fullsize aircraft, the very front of the nose is user-curved downward, having the other function of being a nice shock-absorber in "one-point landings" or "Facial Encounters of the First Kind".

These B-2 gliders, without twisted wings and stabilized approximately in the "normal" Horten fashion, flew very nicely .... but not so well as my first one, reflected in a lower L/D and somewhat reduced stability.

THAT is the point of this thread ....!


Lee

Originally Posted by flyzguy

When you speak of auto soaring, whether it was the bird toy in thermals or the automatically turning into a slope wind, it doesn't make sense to me. Can you explain further?

For slope soaring, maybe you imagine that if you fly along the slope with the hill on your right, you would feel wind blowing in from your left wing (the wind that is hitting the slope). This is not the case - you would not feel any sideslip from wind relative to the ground. Sideslip is measured relative to the aircraft body. Aerodynamic forces do not care about what direction or speed the ground is moving beneath you - only the relative air on the body. ....

Actually, your understanding reflects a misunderstanding of most pilots and engineers. The actual explanation lies in the physics of the situation which is hiding in Einstein's General Theory of Relativity [ not the common Special Theory of Relativity!]. I ran into a satellite physicist [physics tries to DESCRIBE observed reality: it does not "explain" it] who told me that "there are two ways of looking at it .... and only one way works!". He said that is why they launch satellites in ONE direction w.r.t. the Earth's rotation.

If the Earth was a pure fluid planet the "common" understanding reflected in your statement would hold. However, the reality is that the Earth's mass is enormously greater than the comparitive microscopically THIN layer of air. The momentum of aircraft and birds is locked into the EARTH's momentum frame-of-reference, not the air's. THAT is what is actually behind the "dynamic soaring" use of the wind velocity gradient that allows Albatrosses to cross the Pacific.

Again.there is no "understanding in physics", like cooking, there is only acceptance of "this is what usually [the circles around the observed data points] happens when you do this, when this happens first".

Strange but true, the "green air"-seeking ability of this type wing form. But it is NO different than butterflies, using sensors, microprocessors and inertial navigation [locked onto the EARTH, the only way without radar, or GPS, etc.,to differentiate air currents!!], to find lift and soar cross country.


Lee

Originally Posted by John Wright

Lee

I have a large Horten with 2 turbines that has flown for several years. When we first flew it we did not use the drag rudders at all. Indeed the 2 other Hortens of the same design flying with EDF power did not have drag rudders fitted. We have only really needed them to assist with landing and in very strong cross winds. They are not deployed both open like the photo of the B2. They only open up on the side that more drag is needed. They are variable in amount projecting and of course are in pairs on both the upper and lower surface.

John

Sure. And that adds more drag in a turn. The bird's long-ago evolved method [trial & error > intelligence reflects how quickly a working solution is derived for a new problem] does not add drag in a turn, instead rather seems to redistribute it.

Lee

Originally Posted by flyzguy

.... For thermal soaring, I do know of a trick to make a glider "auto soar" by carefully tailoring wing twist along the span. Basically you design the wing to stall asymmetrically and then trim it to fly a very stable glide near stall. When such a plane encounters a vertical gust which increases AOA on the plane, it will always stall one wing first, creating a nice turning action that causes it to naturally turn around updrafts. This has been successfully designed, built and flown. But this requires careful tailoring of both airfoil section and spanwise lift distributions at low reynolds numbers, along with a very good understanding of the dynamics (have to have stable spiral mode) of free flight models.

OK, you are "starting to get it". The birds' [and "my"] system does in fact involve using the effect of a changing onflow-vector, but since it involves the tip-vortices specifically, it applies to BOTH wings differentially, in a way that does not need to stall either wing to get an automatic course-change action [not a circle!!].

I didn't invent anything new: so far as I can tell it was used even by reptile Pterosaurs millions of years before birds evolved from a different line [warm-blooded, feathered (to keep eggs & parents warm), hollow-boned, meat-eating dinosaurs .... like T-Rex (the animal, not the helicopter) and Velociraptor].


Lee

note the similarity in wing twist washout [lesser at much higher Rn of course] of the RQ-170 and the hangglider; compare to N1M