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Old Aug 13, 2012, 06:27 AM
Don't worry be happy :)
Stark's Avatar
Joined Sep 2001
642 Posts
Yippee!
Fix for wing rock, Sebart Katana S 30E

I was reading the tests by JetPlaneFlyer to fix a wing rock problem and got inspired to try the same modification myself.

My Sebart Katana had a fair bit of wing rock att high alpha and the modification of the rudder removed it almost completely. I have to fly with very high angle of attack to get any wing rock!

It's not perfect though, because it increases the pitching to the belly slightly in knife egde and I don't know how I should solve that, yet. I have about 20% of up elevator to rudder mix.
If you have a tip about this issue I will be happy to try it!
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Last edited by Stark; Aug 13, 2012 at 06:45 AM.
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Old Aug 13, 2012, 07:41 AM
iumop ap!sdn w,I
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Joined May 2005
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Looks like you added most of the new rudder area above the wing. Try adding more below the wing (maybe to the bottom of the rudder) and see if that helps with the KE.

Could also move both ailerons slightly up or down to help with pitching in KE. Mixing it out on the Tx would be easier though.
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Old Aug 13, 2012, 07:50 AM
Extremely Twisted
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United States, NH, Epping
Joined Oct 2005
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Try some vortex generators: http://www.rcgroups.com/forums/showp...postcount=7100

As well as some SFG's. With those on, see if you can remove the rudder extension.
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Old Aug 13, 2012, 08:28 AM
Don't worry be happy :)
Stark's Avatar
Joined Sep 2001
642 Posts
Quote:
Originally Posted by G.P. View Post
Looks like you added most of the new rudder area above the wing. Try adding more below the wing (maybe to the bottom of the rudder) and see if that helps with the KE.

Could also move both ailerons slightly up or down to help with pitching in KE. Mixing it out on the Tx would be easier though.
Thanks! I will make a test with more area below the wing.
I tried with the ailerons slightly up for some time ago, but I didn't like it. But I will try it again.

Quote:
Originally Posted by cwojcik View Post
Try some vortex generators: http://www.rcgroups.com/forums/showp...postcount=7100

As well as some SFG's. With those on, see if you can remove the rudder extension.
Thanks! I have thought about the vortex generators, but haven't found a suitable material to make them of yet. But I'm still looking.

Yes! I've made two round SFG in five minutes using a small bowl from the kitchen to cut them to shape. About 4-5 inches in diameter. I will post a picture of them later.
It's a slight improvment in harrier and a big difference in knife edge. I can fly much slower with them and still hold the altitude. But I can probably make them alot bigger.

Thanks for all the tips.
Do you have more ideas so feel free to write them down!
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Old Aug 13, 2012, 10:20 AM
Grumpy old git.. Who me?
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Quote:
Originally Posted by Stark View Post
It's not perfect though, because it increases the pitching to the belly slightly in knife egde
Great to hear that the increase in vertical stab area worked for you too.

The cause of the increase in tuck to belly in KE could be simply that the weight added to the tail had moved the CG back. Make sure the plane is still trimmed neutral and doesnt climb when inverted. The weight of the foam although not a lot is places way back so will need the bettery moving a fair way forward to get back to the same CG as previously.

Steve
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Old Aug 13, 2012, 03:01 PM
Don't worry be happy :)
Stark's Avatar
Joined Sep 2001
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Quote:
Originally Posted by JetPlaneFlyer View Post
....The cause of the increase in tuck to belly in KE could be simply that the weight added to the tail had moved the CG back. ...
Thanks Steve! You're right, the CG was to far back after the change, but a heavier prop and the battery all the way to the front made it neutral again. Still I need more up elevator to rudder mix than before in knife edge.

Here are the pictures of the sideforce generators. Diameter is 11 cm.
They has a very distinct effect, despite there small size. The plane flies more like my Twisted Hobbys foamie and the rudder is far more powerful.
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Last edited by Stark; Aug 13, 2012 at 03:12 PM.
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Old Aug 20, 2012, 02:18 PM
Don't worry be happy :)
Stark's Avatar
Joined Sep 2001
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An update:

I added fairings to the landing gear in the same fasion as the Katana S 50E V2.
The SFG:s made the plane behave like a foamie. But I lost one of the SFG, removed the other and for now I like the plane better without them. It flies more like an airplane...
The tall rudder made the plane somewhat instable when inverted so I removed about an inch.
I'm happy with the plane for the moment. Great rudder authority in high alpha and less wingrock and better in Knife Edge.
This is a great learning experience!
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Old Aug 20, 2012, 02:44 PM
Grumpy old git.. Who me?
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It's fascinating to play around with this sort of stuff and see what the effect is, especially when you do actually manage to get the right end result. The rudder shape looks fine now, not like the barn door job I tested on my HK Slick.

Soon as I get chance I'll build a new rudder for the HK Slick and see it I cant get a compromise that sorts out the wing rock and still looks ok. I might take some cues from the way you have done yours making the rudder wider near the bottom.
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Old Aug 20, 2012, 03:13 PM
Don't worry be happy :)
Stark's Avatar
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Quote:
Originally Posted by JetPlaneFlyer View Post
It's fascinating to play around with this sort of stuff and see what the effect is, especially when you do actually manage to get the right end result. The rudder shape looks fine now, not like the barn door job I tested on my HK Slick....
Yeah, but you is the pioneer who showed me the way! Thanks!
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Old Aug 23, 2012, 02:58 PM
Don't worry be happy :)
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Joined Sep 2001
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This is a video from yesterday evening.
Filmed by my friend Tony using an Iphone.
Flying with the modified rudder and fairings on the landing gear.

Kvälls flygning med Katanan (10 min 13 sec)
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