I have a Somethin' Extra that has been modified with larger tail feathers and a K&B 61. It does the most perfect knife edge possible. There is no coupling at all, at any speed, and any rudder deflection. It has the stock flat wing tips, and wings rock like crazy going into a hover, but my cg is way fwd right now. It won't harrier because of the wing rock issue. I am moving the cg before I fly again, just to see if I can make it better. It's basically the same plane as the Twist.

Oh gosh, virginian,,, the UCD would be the LAST plane I would want to copy for knife edge, it has the worst coupling problem I have ever experienced. I couldnt mix the coupling out, I didnt have enough elevator throw. []

Im not trying to be condescending at all but it may sound like it.. Im going to share my personal experience with wingrock. I found that wingrock is something that I can handle with a good aileron setup and the right amount of expo on any plane. All of the planes I have flown with the exception of foamies all wingrock a good bit. My 30% Edge being the worst of them all...

BUT with a lot of practice and tweeking my setup I can fly with absolutely NO wingrock whatsoever with the exact same plane I started with that wingrocked uncontrollably. Difference is that I can stop the wingrock with the sticks now. You could watch me do an elevator maneuver and you would think that the Lanier Edge was the most stable airframe you had ever seen. But the truth is its the most wingrocking son of a gun that has ever been built. As the plane is descending in an elevator I am constantly watching the plane and making proactive control inputs to stop the rock before it ever starts. My aileron and rudder sticks are moving wildly but the Airplane is descending like its on vertical rails. Same thing with a harrier. Its like hovering, its takes a lot of stick time to really get good at it. Light wingloading will help but ultimately you have to learn to fly the plane. My buddy has a 35% Carden and he has the same thing... IT wingrocks like crazy if you let it, but wacthing him fly you would think it had no tendency to rock at all...

My point is that I am beginning to think that most if not all airframes have a goodbit of wingrock inherently in high alpha attitude but good pilots are always several steps ahead of the airplane,,, stopping a problem before it ever starts. So if you want a plane that has zero wingrock either get a foamy or work on perfecting lateral balance, cg and setting up geometrically correct servo setups so everything is moving as it should and then practice practice practice until the wingrock goes away.

Big Ned,

Regarding UCD 60's KE coupling, it really depends on what you are trying to accomplish.

If you try to do a long KE pass, then when CG is @ 5.75", KE flight requires almost no rudder input. Therefore, there's no coupling.

If you try to do a KE loop, w/ the 5.75" CG, KE looping requires low rate's full rudder, which will couple a little. But it's nothing that a little aileron and elevator stick won't correct.

If you try to do pinwheel, it's when the coupling is worst. Gosh, sometimes I need full elevator during the lower half of the double stall-turn, so it won't flatten out and get into a flat spin.

The rudder's pitch and roll coupling manifests differently depending on what the plane is doing. So trying to mix it out is futile.

I found something interesting. After I installed a pair of floats on the UCD 3D, it actually knife edges better, and straight KE pass requires as little rudder input as inverted flight requires down elevator. Also, the invered flat spins are much tighter and much flatter. It's simply amazing.

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Another thing I discover regarding wingtip conversion. After I cut off the wingtip on my Flip, I can no longer flat spin. Not sure if the reduced lifting area is the culprit, or is it some dynamics at the wingtip during yaw gyration.

wow, I had 3 U Can Dos and I fought coupling on all 3 of them. Im not sure if the newer versions have improved rudder but the original versions had a reputation for severe coupling issues. The worst was trying to enter a knife edge loop. I think on my earlier versions it was a lack of power running an OS91 FS. On the later versions I ran a Saito 1.20 and it wasnt as bad but it was still a problem. I reasoned that it was because it had so much power that it was climbing at lower rudder throw due to increased propwash and therefore more rudder authority. With less rudder input less coupling. But it was still a substantial problem, just less than with the 91. With my Edge you just roll it on KE, give a little rudder, adjust throttle and elevator for crosswind and attitude and watch it do its thing.

Again I think experience has a lot to do with it. I can fly my foamies on KE all day long and they are HARD to get to knife edge, much harder than a UCD. I know this because several of us at the field have foamies and most cant KE them at ALL, only 3 of us can. I also fly with less expo now so it "feels" like less stick input. As I gain experience I find many things that used to seem impossible much easier now.

I'm no expert in 3D, but can truly say that my Razzle is the better 3D plane. Maybe because it's bigger, maybe because of the wingtips. I don't know yet. Hopefully on the coming weekend I have a chance to find out, whether my efforts were for nothing, or helped the TWIST. I'll keep you in the loop.

The Funtana tip plates are on!!

I thinjk this will be bettter, cause it won't let air, moving on airfoil go away.
tell us results then.

The wing tips work!!!

They really helped the high alpha wing rock. The wing still will rock, but the rocking motion is much slower. Therefore, I can counter the wing rock using aileron, and it is very manageable.

Also, I do not recall experiencing any tip stall during the 2 flights I took.

It does slow down the low rate's aileron effect. Aileron now is less touchy on the low rate. High rate is still blinding fast.

Furthermore, it lands really slow now. Don't get me wrong: it landed slow before the tip plates, but it is like walking speed now. Must be the extra lift near the tips that didn't get lost that's retained by the tip plates.

I have not tried inverted harrier. It did not rock during inverted harrier before the tip plates, so I don't expect it to be much different now.

Awesome- thanks for sharing

I'll try on my giles202 tto and then tell u some results.
and I have better idea. i will do so: I will make separate wing tips. aileron will have separate tip and wing will have separate, so aileron wo't loose wind.

Word of caution on that one. I would strongly recommend you don't add any material to the ailerons themselves, but just let them sweep against the plates that attach to the wing tip. The reason? FLUTTER! Control surfaces as large as those are already prone to flutter, and adding weight and mass to them aft of their local cg will exaserbate the condition, probably with catastrophic results. Just make the tips wider to accomodate the aileron travel, even if they are a funny shape. I feel you will be much better off.

As for the wing rock upright and not inverted. That condition supports what I believe to be the real culprit with this airplane. It's not a function of the wing or wing tips, but rather a function of YAW stability, that is substantially reduced when the vertical tail is blocked by the fuselage and horizontal tail. I have already added a dorsal fin to my Funtana 90 to improve the knife edge flight, but now I think a VENTRAL fin may be the fix for the wing rock. The reason the tip plates helped, in my opinion, is because they added side area and perhaps increased yaw stability. Just a thought

what about plates on H stab and V stab?

Plates on the horizontal tail? What would they do? Make them big enough and they would add to the vertical surface area, and they wouldn't be blocked by the horizontal in high alpha flight. I don't think it would look very good.[]

Not24 and all,

What you are saying about the tail surface being blocked does make sense. At first I was thinking that wing rock was a function of the thick airfoil that 3D planes have in conjunction with the vorticies being generated off the wing tip shape. But I don't think that wing tip stall is the issue here because both tips stall at the same point. A rock assumes that the tip stall would alternate causing the rock. I have never seen a plane tip stall to one side and then recover. I have seen planes stall straight ahead and then pick up speed and then recover causing porpoise action. This I have seen with many different wing tip shapes.

I have noticed that profile planes usually harrier very well. My profile foamies are solid as well as the OMP profile planes that I see fly. These both have drastically different airfoil shapes.

But a profile will have great YAW stability. Its fuselage works like a "huge rudder" and is stable right side up or inverted.

The wing plates probably did add to the YAW stability as well as give wing tips more effectiveness at stall speeds. Sorta win/win. But keep in mind that they will still stall.

I wonder if a nice tall and looong rudder of the back would significantly add to the Yaw stabality on non-profile fuselages and greatly reduce the wing rock. This would help get more vertical stabilizer in the open during right-side-up harriers.

By the way, I have the UCD 60, Funtana 40, Funtana 90, H9 Edge 540, Quique Yak 54. The all have different wing tips and they all wing rock. By this point, I believe that most important is piloting skills. Practice, Practice, Practice.

My 2¢, tell me what you think.

Dave

I'll tell ya what I think. You ready? You are right about the profiles being better at Harriers, because of their fuselages, not their wing tips. That's what I think. What do I know? My Funtana rocks uncontrolably in a harrier, and I wish I had a four stroke in there to get that torque I need at low rpm's. I'm not too proud to modify the airplane till it flies the way I want it to. It may take a few months to get it right, but it will be much better when I am finished with it. Right now the weather sucks and the field is under water.[&o]

Just as an aside since you guys seem to be using his aircraft for both the tip plate as well as the swept tip concepts . . .Wayne isntalled tip plates like seanychen did on his original Raven (full scale) and he also swept the tips on all surfaces of his Turbo-Raven, and just so you know, in Wayne's parlance, these are called "Hollywood Tips" . . . why???

They are cosmetic.

The tips do alter the roll, stall, snap, and stability of an aircraft a little bit, but usually not in the direction that we would like. As in the pics YNOT posted, square, and shortened tips will increase roll rate, increase roll response and crispness, decrease roll damping, as well as roll inertia (though not by much) and in general give a 3D pilot better performance at some expense of stability in other aspects of the flight envelope. The square tips will also help for clean, crisp snap roll departures. Tip stall behaviors may change when removing tips, making the tendency a little worse and the departure more aggressive, but this won't be a constant for each wing design. The flat plates also going to dampen snap rolls a bit and reduce crispness, perhaps you will get a little better aileron response with these acting like vortex generators under some situations, and this *may* reduce the tip stall character and the rocking in harriers, but again, you will give up some snap roll performance, and perhaps some high alpha roll performce as well. The size that seanychen did are probably not going to be too much of an impact on the snaps, and they could be done so that they are easy to add and remove, so have fun experiementing (at lower speeds!) but I wouldn't expect to start seeing these on purpose built 3Ders.

Oh and the Raven also used to have strips near the root of the wing as well, sorta like the Tensor Side Force generators! (Wayne should have patented it!)

Keep in mind the Raven no longer flies with the Hollywood tips, or the tensor-esque root strips

Have a look at the Extreme Flight Mini 3D (http://www.extremeflightrc.com/produ...tml/Mini3D.htm). The wing is a very similar design to the UCD. Granted, the wing is different than the funtana, but I don't think that would matter. Watch the video, rock solid harrier. The bottom of the fuselage is tapered. Almost like a profile. Possibily giving more yaw stability.

Just an interesting observation.

Dave

Forgot to mention. . .those tip plates will also help when your knife edge passes get a little too low. . .

Hello,

I would like to bring forth my skepticism of yaw instability being linked to high-alpha wing rock. Take UCD for example. It has excellent yaw stability, but will start rolling back and forth while attempting high alpha vectored flight.

Another example, Goldberg Extreme 330 profile has also great yaw stability, but has considerable wing rock during harrier. But its brother Extreme 540, with a different wing, is much more stable during harrier. I'd say these 2 planes have similar yaw stability. I owned both.

Certainly there are many factors that contribute to aerodynamic stability but ...

The idea is, that at high alpha, the air flow is blocked by the elevator reducing the effectiveness of the rudder. That is why inverted harriers are more solid. The rudder is not blocked and gets direct airflow. The UCD has a flat bottom, so when at high alpha the rudder is blocked and the fuselage acts like a wing not a rudder making the high alpha unstable. Kinda like droping a piece of paper. The UCD is much more stable in inverted high alpha manuvers (I have one). The top of it is round and skinny, not flat, and the huge rudder is in the main air flow. Check out the Harrier 90. They made the back of the fuselage tall and skinny. No doubt for high alpha stability. The whole back half of the fuselage is like a vertical stabilizer.

As for the Goldberg Extreme 330 profile, my understanding is that is has a lot of bad tendencies and there are always exceptions to the rule. A forward CG or warped fuselage could also be hurting you there. But in general, the profiles are fantastic at high alpha.

At the same time, I am not completely ruling out wing design. I just don't think it is the main culprit for wing rock.

Dave

Hello Dave,

I agree with what you say regarding stability @ high alpha. I guess I am just not quite making the link between roll stability and yaw stability. I know they are related, because we correct wing rock (roll) w/ rudder inputs (yaw). In automobiles, when we turn too sharp, vehicle tends to roll because CG is higher than the lateral reaction force @ ground. I guess it's applicable for a low wing model as well.

Rudder on a plane definitely is meant to yaw under normal circumstances, and its effect on roll definitely has to do with the wing: shape, location, and orientation.

I haven't tried inverted harrier on my UCD yet. I should try it. Maybe I will be delightfully surprised.

Another thing to consider: I SUPERSIZED the rudder on Funtana 40, and it did didley squad for harrier wing rock.

I have a totally different thought on why Funtana is more stable in inverted harrier than upright harrier. Consider the CG location in height; i.e., the 3-dimensional CG location of a low-wing aircraft is a few inches above the wing's main spar. As the aircraft goes into upright harrier, the CG is shifted backward, and the downward weight vector is now aft of the wing's spar. Thus it becomes temporarily tail heavy.

Now consider the same low-wing aircraft inverted, the CG at inverted level flight is a few inches below the wing. As the aircraft goes into inverted harrier, the CG is shifted forward, and the weight vector is now forward of the main spar. Thus it becomes temporarily nose heavy.

It's just a thought.

Seanychen,

You have obviously put much thought into this issue of wing rock, but I believe you don't really understand the yaw thing yet. It's not yaw stability we are concerned with in an upright harrier. It's the lack of smooth air flow over the aft fuselage and the vertical. In high alpha flight, the ailerons are only working at all due to the prop blast over them , but they really aren't efficient as roll control surfaces anymore. To deflect the ailerons in a harrier, the result you get is due to the lack of symmetry from left to right, not necessarily the fact that one wing is creating more lift than the other. In other words, they become drag controls on the wings, and they respond accordingly. The rudder and vertical, on the other hand are the only surfaces on the plane that are not at a critical angle of attack, thus remaining effective. Since they are blocked by the lower fuse and the horiz tail when upright, even though they are not stalled, they have no clean air to work in, which makes them feel inadequate. Size, therefore, in this case at least, doesn't matter. My next mod will be to add a turtle deck to the lower fuse on the f90,which resembles the upper surface. Hell, it may even have an effect on the tucking during knife edge.