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Old Aug 09, 2012, 10:37 PM
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Wing rock: What causes it and how to stop it?

Any suggestions for a 3d newb?
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Old Aug 10, 2012, 02:42 AM
GPT
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Originally Posted by cttrulson View Post
Any suggestions for a 3d newb?
Is there any particular plane your referring to as some will rock badly no matter what you do.
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Old Aug 10, 2012, 02:57 AM
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JetPlaneFlyer has made an very intresting experiment with wing rock.
http://www.rcgroups.com/forums/showp...postcount=3865

This seems to indicate that it's related to the shape and/or the area of the rudder.
I've some wing rock on my Sebart Katana S 30E, it's easy to counteract with ailerons, but still, I will also try this experiment with bigger rudder area.
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Old Aug 10, 2012, 03:18 AM
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Wing rock is caused by instability around the yaw axis. At slow speeds (close to or under stall speed), yaw will make one wing go forward while the other recedes. This may cause a momentary reattachment of air to the wing that is moving forward and faster resulting in lift being re-established thus the wing comes up until the next yaw cycle reverses this process to the other wing...voila...wing rock.

Some form of stabilization will reduce/eliminate wing rock. Things that may help: a larger rudder, more fuselage side area, in some cases side force generators, as well stall and wing fences all may help.

It is best to purchase a good quality airplane that has already had the wing rock designed OUT of the plane. 3dhs and extreme flight seem to be the best at producing planes without wing rock.
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Old Aug 10, 2012, 04:12 AM
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As KE Spin says, my experiments show that wing rock is a form of Dutch Roll. The problem I think is that at high alpha the wings and fuselage and horizontal tail surfaces all add up to partially mask the vertical stabilizer. Other than a re-design of the plane the solution seems to be simply to add area to the vertical stabiliser/rudder.

The wing airfoil may also influence, 3DHS and EF use very sharp leading edged airfoils to enhance post stall performance.. But I tried that on my HK Slick and it didn't prevent wing rock though it may have gone toward eliminating the sudden wing drop from harrier that the HK Slick was occasionally prone to.

The HK Slick with standard side vertical stabiliser:
HK Slick 'a-rockin' (6 min 49 sec)


And with added area to vertical stab:
HK Slick 'A-rockin' or maybe not (2 min 22 sec)


As for as technique goes, I'm pretty much rubbish at 3D flying so maybe not the best to advise but I've found being very gentle with the rudder helps prevent the onset of wing rock.
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Old Aug 13, 2012, 09:30 PM
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Thanks for the instruction and remedies. I'm dealing with the HK Yak54 1100mm. I did not realize the primary cause was the size of the vert stabilizer. That would explain it though as it seems quite small in relation to the rest of the planes surfaces and size. I'm trying to get my worth out of this HK foam. So far I've been able to learn and execute some of the basics like knife edge, blenders and KE spin but I end up being to tentative on the slower harrier skills because of the rocking and tip stalling. I know if I upgrade to a Telink or Skywing this thing will just sit on the shelf. I should just bite the bullet and turn the Yak into a night flier. I'm sure my skills would advance more quickly. In the mean time I may experiment with SFG's and a larger vert. stab., that is some pretty convincing video JetPlaneFlyer.
Thanks again for taking the time to respond and help me out.
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Old Aug 13, 2012, 10:50 PM
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Hobbyking causes wing rock...
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Old Aug 14, 2012, 05:28 AM
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Originally Posted by ryanotown22 View Post
Hobbyking causes wing rock...
...since they started to sell copied airframes, the wingrock problem is solved at hobbyking, as well

Pete
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Old Aug 14, 2012, 05:49 AM
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So all this recent talk about the rudder being ineffective in the fuselage turbulence when in harrer, has made me think more about inverted harriers. So the reason an inverted harrier is often more stable than an upright harrier would be due to the fact that the vertical stab is now hanging below the fuselage, and hence in clear air; resulting in more lateral stability.

This may have been obvious to others, but I thought I'd share my brief epiphany.
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Old Aug 14, 2012, 06:19 AM
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So the reason an inverted harrier is often more stable than an upright harrier would be due to the fact that the vertical stab is now hanging below the fuselage, and hence in clear air; resulting in more lateral stability.
Yep, that's it.. Only slight comment is that the vertical stab gives directional stability (i.e. keeps the model pointing in the direction of travel). It usually doesnt contribite a great deal to lateral stability. Wing rock is a secondary effect.. Google 'Dutch Roll'
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Old Aug 14, 2012, 07:30 AM
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It usually doesnt contribite a great deal to lateral stability
so what adds more lateral stability, more fuse area, sfgs??

regards

Pete
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Old Aug 14, 2012, 07:39 AM
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The very early B17 bomber with the rounded rudder had the Dutch Roll problem. They added more area to the front and added the fin to the front to cure it.

Gord.
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Old Aug 14, 2012, 01:07 PM
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Originally Posted by 3D Peter View Post
so what adds more lateral stability, more fuse area, sfgs??

regards

Pete
Conventionally, dihedral is used to add lateral stability, high wing positions and swept back wings can also add lateral stability. You actually want neutral lateral stability for a 3D/aerobatic plane which is why you dont see the above features used. Any significant amount of positive leteral stability would give extreme rudder to roll coupling, which is a no-no for an aerobatic plane.
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Old Aug 14, 2012, 01:18 PM
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Originally Posted by JetPlaneFlyer View Post
Conventionally, dihedral is used to add lateral stability, high wing positions and swept back wings can also add lateral stability. You actually want neutral lateral stability for a 3D/aerobatic plane which is why you dont see the above features used. Any significant amount of positive leteral stability would give extreme rudder to roll coupling, which is a no-no for an aerobatic plane.
So is this why my T28 dives when I use rudder? Too much lateral stability?
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Old Aug 14, 2012, 03:11 PM
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Another thing we used to do with ails out to the end, was to cut the tips of the ails at about a 40deg. angle so they were angled in. Another fix was to end the ails a couple of ins. short of the tip. Couple of more things we might experiment with.

Gord.
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