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Dec 25, 2013, 06:22 PM
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special avian flight movement


unique footage 2:39 near the end of the above video > https://www.rcgroups.com/forums/show...w#post26992635
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Dec 26, 2013, 04:00 AM
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elevons vs mixed elevator+ailerons


Quote:
Originally Posted by xlcrlee
.... AND, the elevons acted exactly as one expects elevons to > down left elevon and slightly more up rt. elevon produces a smooth right turn....
Quote:
Originally Posted by Alien_Tech
Lee,
There is no differential used in the model, throws are equal both up and down.

To be clear, since elevons mix two TX [or fullsize pilot/aircraft] inputs, and since a level turn requires TWO forces -- enough up-elevator to keep the vertical projection of the lift vector strong/large enough to maintain level flight AND a centripetal radially-inward force to create and then maintain the turn -- my post* [re: those albatross-winged test models I made & flew months ago] described the result of those two vector-added inputs as exhibited in the elevons.

I.e., one stick with two independent and simultaneous stick movements: aileron-effect > left control surface down, right one up, and at the same time add a little more up on the right side than on the left side > elevator effect. Not so complex as it might seem ....

Lee



*
https://www.rcgroups.com/forums/show...n#post26952476
Last edited by xlcrlee; Dec 26, 2013 at 07:14 AM.
Dec 26, 2013, 08:42 AM
Pile-it
Alien_Tech's Avatar
Quote:
Originally Posted by xlcrlee
To be clear, since elevons mix two TX [or fullsize pilot/aircraft] inputs, and since a level turn requires TWO forces -- enough up-elevator to keep the vertical projection of the lift vector strong/large enough to maintain level flight AND a centripetal radially-inward force to create and then maintain the turn -- my post* [re: those albatross-winged test models I made & flew months ago] described the result of those two vector-added inputs as exhibited in the elevons.

I.e., one stick with two independent and simultaneous stick movements: aileron-effect > left control surface down, right one up, and at the same time add a little more up on the right side than on the left side > elevator effect. Not so complex as it might seem ....

Lee



*
https://www.rcgroups.com/forums/show...n#post26952476
Lee,

Many sets of doublets were performed (pitch & roll) with an instrumentation (alpha/beta vane & CPT's) package to ensure that there was no control interaction. Proverse yaw is present with aileron input only.
Dec 26, 2013, 10:17 AM
Registered User
Quote:
Originally Posted by Alien_Tech
Lee,

Many sets of doublets were performed (pitch & roll) with an instrumentation (alpha/beta vane & CPT's) package to ensure that there was no control interaction. Proverse yaw is present with aileron input only.
Do you mean that with the pitch held constant, from level flight the aircraft made a spirally descending circle with proverse yaw? The control indicications in the above post were re: constant altitude circles of my small cranked-wing Nürflügel models shown in that sketch. And now you mention it, I actually WAS having a lot of trouble with too much proverse yaw, but I took that to be a result of the gull-shape di+anhedral and the high aspect ratio for such very small models.

My main points in posting were/are:

1. showing the extensively tested most effective position of those elevons in that design, assuming that the entire outer wing was acting like a proportionally larger Boeing Dreamliner wingtip.

2. the exact placement and degree of washout is empirical and depends on the design which depends on its goal/function.

3. birds DO have "all-flying", even V-form*, combined horizontal+vertical tails, used for stability and control -- also to overcome often extreme adverse yaw! -- as may be needed in various flt-regimes.

4. some birds have forward vertical ["all-flying"] stabilizer/rudders .... on their heads, and almost all birds in fact also steer with their heads > further, I solved the too-strong proverse yaw in those test models by adding a fwd-vertical stabilizer that looked more like that of a pterosaur than a cockatoo [but I kept that only as information and gave it along with the models for the Fluid Mech folks at ETH to explore more extensively].


interesting/Lee




*since they drop their tails into positive AoA when "flapping"/Aerowing, plus also when Broadwinged Hawks sweep their wings forward when thermalling, slightly positive/upright V-formed, but inverted V-formed more during soaring/gliding when the tail is more often at an aircraft-normal neg AoA [but many freeflight models use a lifting tail, with the CG just ahead of the T.E.]
Dec 26, 2013, 10:47 AM
Registered User

combining test results


I readily admit that my analysis of my sketched-models' flying was more "black box" based on a huge storehouse of designed, flown and/or crashed models over more decades than I want to think about.

Your response, and my above question & response leaves me to wonder and ask if the anhedralled tips that I think I see in a lot of the Prandtl-d video were also involved in the proverse yaw .... which was sometimes almost disasterously too strong in my test-models. If in fact the pilot only gave roll input, as the wings banked the Prandtl-d would have to speed up [if it didn't, you guys need to get in touch w/DARPA quick]. Then, a bit tilted and speeding up, one would expect the wing to start to slip sideways in the direction of the lower wing, and anhedralled tips might easliy start to yaw the wing proversely. I did a lot of experimenting with the amount or di+anhedral while trying to get a self-stable turn/circle.


thoughtfully
Dec 26, 2013, 10:54 AM
Pile-it
Alien_Tech's Avatar
Lee,

No descending circle. A doublet is a maneuver designed to upset a particular axis in order to observe its dynamic response. It is performed from a trimmed state (full rapid deflections) the goal is to get a square wave input and measure the result. This is the only way to fully characterize the vehicle, prove proverse yaw, and to make sure the yaw isn't if fact due to sideslip.

More reading here: http://www.aero.polimi.it/~chimetto/...ntrolPulse.pdf

Red

Edit: there is no anhedral in the tips, not sure what you are referring to there. Once again, the aircraft is instrumented to separate the real from the perceived.
Dec 26, 2013, 11:48 AM
Registered User
Thanks, Red! [I hate mysteries, love clarity]. Got it!

My uninstrumented flt tests were definitely "steady-state" and not pulse perturbations. And yet the models seemed to fly a lot like birds with similar wing form*, tending to find "good" air and avoid sink by themselves. And THAT came out of my "discovery" of how to stabilize an aircraft with its own vortices while at the same time enabling a surprisingly high L/D. Perhaps the extreme conical camber I've now used in many designs, also often in peculiar places along the span as reversed conical camber [besides but including "backward" cones at the rear of upwardly flared Hoerner-type tips], does the same thing as the washout in a Horten-type Nurflügel. But I am reasonably sure that in both cases spanwise flow and vortices are involved.

Dunno, hope to someday find out ....


Lee



*the gull-like cranking was only to separate tricopter motors for a sailplane-like VTOL UAV, a concept which was dropped
Dec 28, 2013, 10:59 AM
Registered User
Quote:
Originally Posted by Alien_Tech
Hi Cable,

Nothing special, just carbon over a foam core.
Wasn't there some concern with the Horten designs about being too "slick" and this causing poor control?
Dec 28, 2013, 11:55 AM
Registered User

varying dihedral as used in Prandtl-d*


Quote:
Originally Posted by Alien_Tech
The other part of this that's not quite clear is that this isn't simply traditional washout. There is twist in the wing, similar to washout, but it's highly varied locally along with varying dihedral. This is what gets the vortex to shed early and get the same effects as Whitcomb's winglet.
The varying dihedral is what I think I saw in the video, and as it appears to me to show up in the T.E., why I made the references to the Hobie Hawk improved washout placement.

Quote:
Originally Posted by xlcrlee
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.

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

Quote:
Originally Posted by xlcrlee
I readily admit that my analysis of my sketched-models' flying was more "black box" based on a huge storehouse of designed, flown and/or crashed models over more decades than I want to think about.

Your response, and my above question & response leaves me to wonder and ask if the anhedralled tips that I think I see in a lot of the Prandtl-d video were also involved in the proverse yaw .... which was sometimes almost disasterously too strong in my test-models. If in fact the pilot only gave roll input, as the wings banked the Prandtl-d would have to speed up [if it didn't, you guys need to get in touch w/DARPA quick]. Then, a bit tilted and speeding up, one would expect the wing to start to slip sideways in the direction of the lower wing, and anhedralled tips might easliy start to yaw the wing proversely. I did a lot of experimenting with the amount or di+anhedral while trying to get a self-stable turn/circle.


thoughtfully
Quote:
Originally Posted by Alien_Tech
.... there is no anhedral in the tips, not sure what you are referring to there. Once again, the aircraft is instrumented to separate the real from the perceived.


I just mistook varying dihedral for slightly anhedralled tips


Lee





*and birds: can be seen in the videos & photos I posted
Last edited by xlcrlee; Dec 28, 2013 at 01:15 PM.
Dec 29, 2013, 10:00 AM
robinson727
Quote:
Originally Posted by Alien_Tech
Thought you guys might like to see this: http://youtu.be/Hr0I6wBFGpY
Alien.. You the guy flyin' the Prandtl D for Al Bowers?? He's a good friend and his work outstanding..
Dec 29, 2013, 12:54 PM
Pile-it
Alien_Tech's Avatar
Quote:
Originally Posted by robinson727
Alien.. You the guy flyin' the Prandtl D for Al Bowers?? He's a good friend and his work outstanding..
Hi Al,

Yep it's me. Al is fantastic!

Cheers
Red
Jan 01, 2014, 06:24 AM
Registered User

re: varying dihedral, spanwise washout placement and Prandt-d BSLD


note the wing form [front & rear views] which is greatly exaggerated and easy to see in the first ProtoWing shown [much lower Rn than RC Nurflügel]

also his comment that the AdvancedWing tends to stay in a turn [it IS hard to keep such a light & flexible construction constant, so one can expect aileron-like wing twists from flight to flight .... and I can therefore suggest a "proactive elevon" effect here]


Lee



Flight of the OmniWing Paper Airplanes (4 min 5 sec)






note: I happened to trip over this on the Internet, and more recently watched one of his "how to build" videos: from that I got the strong impression that his designs are highly empirical, the result of lots of attempts .... of course the birds were even longer at finding out what works best for them
Last edited by xlcrlee; Jan 02, 2014 at 07:55 PM. Reason: typ-oh
Jan 01, 2014, 10:46 AM
Herk
HerkS's Avatar
Very neat Lee - what do you think it would take to build a similar test bed that had radio control. Let's say something about 1.5 meters span? What would be the technical details for sweep, twist, taper ratio, CG location etc? I think it would be fun to build the concept in a larger version with control. Would you advise the inboard elevon setup that you discussed earlier? And other questions ---

If you wanted to work on something like that it might be a good idea to set it up on its own new thread - rather than hijack this one.
Jan 01, 2014, 11:56 AM
Registered User

you are right


Quote:
Originally Posted by HerkS
Very neat Lee - what do you think it would take to build a similar test bed that had radio control. Let's say something about 1.5 meters span? What would be the technical details for sweep, twist, taper ratio, CG location etc? I think it would be fun to build the concept in a larger version with control. Would you advise the inboard elevon setup that you discussed earlier? And other questions ---

If you wanted to work on something like that it might be a good idea to set it up on its own new thread - rather than hijack this one.
Sorry that it might seem that way.

I only want to shed light on the subject and raise awareness for further exploration of what Prandtl-d and others [incl. birds & moi] have found.

This thread started with some huge claims re: a new advance in aviation and some statements which seem, on the surface at least, to be not exactly correct. The points I have raised are valid, incl. the fact that birds actually do have adverse yaw [and a kind of all-flying vertical tail or tail with a variable vertical component, that they use a lot, however one wants to nit-pick], the many methods they use to overcome their adverse yaw, as well as concrete examples of how to incorporate this into an aircraft.

I think that the posted lower-Rn exaggerated examples [AcroBird, OmniWing] of how to twist wings and add "varying dihedral" show what to do, and it takes only a bit of judgement, luck and tests to figure out how to incorporate that into a normal-size/wt RC Nurflügel.

I totally agree with you > these efforts should have their own, or several, thread/s.


for any brave or curious:

Go for it ....!


Lee


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