Trim Question - Needing left rudder on downline at idle  
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Trim Question - Needing left rudder on downline at idle - 8/28/2008 1:14:16 AM   
woodie


 

Posts: 325
Joined: 6/10/2002
From: Placerville, CA, USA
Status: offline 		Ok, Woodie here (aka Don Atwood).

I have a trimming or aerodynamic question for you aero gurus out there. All my recent pattern planes (all electric) have needed left rudder trim in downlines to stay straight. With the rudder at neutral, there is a noticeable right yaw at idle. Once you apply a little power, the yaw diminishes until it is pretty much gone at half power. My plane have been a Brio (very noticeable), a friends Brio (same issue), Integral (2) and a Genesis.

I have read the glo power Brios had the same issue so I don't know if it is primarily an electric power issue but it sure is noticeable on my models.

Any ideas or good explanations? Am I trimming wrong to create this? (or maybe I am just crazy) ;-)

thanks
Woodie
       Post #: 1

RE: Trim Question - Needing left rudder on downline at... - 8/28/2008 1:24:01 AM   
alex a v


 

Posts: 44
Joined: 9/30/2004
From: , PHILIPPINES
Status: offline 		Hi Woodie!

You might have applied right rudder trim to achieve straight and level flight, due to a lack of right thrust on the motor.
During the downline at idle, the rudder trim kicks in. As you apply power, the motor corrects and neutralizes the yaw effect.

Check your trims and your engine thrust angle to confirm this.

Alex

edited: "motor" instead of "engine"

< Message edited by alex a v -- 8/28/2008 1:32:45 AM >

(in reply to woodie)
       Post #: 2

RE: Trim Question - Needing left rudder on downline at... - 8/28/2008 1:30:00 AM   
riot3d


 

Posts: 570
Joined: 2/8/2005
From: oakland, CA, USA
Status: offline
quote:

ORIGINAL: woodie

Any ideas or good explanations? Am I trimming wrong to create this? (or maybe I am just crazy) ;-)




I think all of your plane has a crooked fin ... hehe

(in reply to woodie)
       Post #: 3

RE: Trim Question - Needing left rudder on downline at... - 8/28/2008 1:52:28 AM   
patternflyer1



Posts: 1364
Joined: 7/3/2003
From: Tracy, CA, USA
Status: offline 		Edited to a lower post for reasons of well, not paying attention.


Chris

< Message edited by patternflyer1 -- 8/28/2008 3:43:03 AM >

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RE: Trim Question - Needing left rudder on downline at... - 8/28/2008 2:29:56 AM   
billtulsa


 

Posts: 59
Joined: 1/8/2005
From: tulsa, OK, USA
Status: offline 		This is normal, and......

It gets worse the more aft you move the CG, and

It gets worse the bigger the propeller.

No matter what your rudder setting is or the amount of right thrust is set in the airframe this "shift" in yaw is going to happen on the down lines with these big props, Just mix it out, but you will need to play with it to find at what throttle stick position you need it to be removed completely. I have found that the mix only needs to be applied in the last 1/8 to 1/4 stick movement.

Bill C.

(in reply to woodie)
       Post #: 5

RE: Trim Question - Needing left rudder on downline at... - 8/28/2008 3:21:04 AM   
woodie


 

Posts: 325
Joined: 6/10/2002
From: Placerville, CA, USA
Status: offline 		Bill, that is what I am experiencing and have mixed out the yaw problem with a slight bit of left rudder at idle. The mix goes fades away at about 20% stick position. At cruise settings, the rudder is in neutral and I fly the right rudder inputs when needed.

Riot3D and Patternflyer1, as always I appreciate your input....... ;-) remember, I know where you live!!!!

Woodie

(in reply to billtulsa)
       Post #: 6

RE: Trim Question - Needing left rudder on downline at... - 8/28/2008 3:34:24 AM   
riot3d


 

Posts: 570
Joined: 2/8/2005
From: oakland, CA, USA
Status: offline
quote:

ORIGINAL: woodie

Riot3D and Patternflyer1, as always I appreciate your input....... ;-) remember, I know where you live!!!!




Ooops, I'm moving ...

(in reply to woodie)
       Post #: 7

RE: Trim Question - Needing left rudder on downline a... - 8/28/2008 3:42:10 AM   
patternflyer1



Posts: 1364
Joined: 7/3/2003
From: Tracy, CA, USA
Status: offline 		I shouldn't post on the fly. (no pun intented)

I misinterpreted your post Don. I thought I read it was going to the left on power off dl's..

So exactly the opposite of what I said. Too little right thrust. Need a little more IMO, therefore you have to add a little left rudder trim. lol..
I'm sure a cat like you has tried this though.. And that is what led you here. I'll say this, I haven't yet noticed one of my electrics go to the right in a downline. But then again, maybe I don't notice it.

Thanks for telling us in D7. Now we know where to downgrade you.. lol (my plane fly's perfect BTW) No visible downgrades. Not sure what they were looking at while at the nats. LOL

Chris

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       Post #: 8

RE: Trim Question - Needing left rudder on downline a... - 8/28/2008 4:10:23 AM   
riot3d


 

Posts: 570
Joined: 2/8/2005
From: oakland, CA, USA
Status: offline
quote:

ORIGINAL: patternflyer1

Thanks for telling us in D7. Now we know where to downgrade you.. lol




I can't do that, he's my coach ...

(in reply to patternflyer1)
       Post #: 9

RE: Trim Question - Needing left rudder on downline a... - 8/28/2008 4:59:11 AM   
woodie


 

Posts: 325
Joined: 6/10/2002
From: Placerville, CA, USA
Status: offline


I can't do that, he's my coach ...
[/quote]

Correction, WAS your coach....

My Brio was the worst, with a 22x12 prop, I had about 1/8" left rudder offset at idle, without it, the right yaw was very noticeable. When I went to 21" and 20" props, the yaw was slightly less but still there. That is where I started mixing it out at idle.

How about other designs (electric), other than the Brio, Genesis, Integral. Any of you noticing right yaw on downlines at idle?

Don (Woodie)

(in reply to riot3d)
       Post #: 10

RE: Trim Question - Needing left rudder on downline a... - 8/28/2008 5:12:11 AM   
ual767



Posts: 782
Joined: 12/3/2002
From: Chantilly, VA, USA
Status: offline 		Don, my Zeque is the same. More noticeable with larger diameter props. Right now I am running a 21" prop. I have slight right mixed for high power and slight left for low power.

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RE: Trim Question - Needing left rudder on downline a... - 8/28/2008 6:53:26 AM   
ExFokkerFlyer



Posts: 435
Joined: 5/3/2002
From: Fresno, CA,
Status: offline 		Obviously Don, you are too far to the right and you should spend more of your time watching the Democratic National Convention... that would skew your life, and your planes, further to the left and get rid of your trimming problem.

Jokingly,

Tom M

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(in reply to ual767)
       Post #: 12

RE: Trim Question - Needing left rudder on downline a... - 8/28/2008 2:20:58 PM   
woodie


 

Posts: 325
Joined: 6/10/2002
From: Placerville, CA, USA
Status: offline 		What? no rudder trim with your BM3? Truly a 'magic' plane?? ;-) I know where you live too!!!

Thanks for the feedback on the other designs guys, I feel better now.......

Don

< Message edited by woodie -- 8/28/2008 2:21:23 PM >

(in reply to ExFokkerFlyer)
       Post #: 13

RE: Trim Question - Needing left rudder on downline at... - 8/28/2008 3:59:22 PM   
Derek.Koopowitz


 

Posts: 353
Joined: 2/27/2004
From: Benicia, CA, USA
Status: offline
quote:

ORIGINAL: riot3d


quote:

ORIGINAL: woodie

Any ideas or good explanations? Am I trimming wrong to create this? (or maybe I am just crazy) ;-)




I think all of your plane has a crooked fin ... hehe



Actually I think he leans on the right rudder stick unconsciously. Keep doing it!!!

(in reply to riot3d)
       Post #: 14

RE: Trim Question - Needing left rudder on downline a... - 8/28/2008 10:12:29 PM   
TonyF


 

Posts: 908
Joined: 12/9/2001
From: Rosamond, CA, USA
Status: offline 		Never had an issue with anything once the right thrust was set properly. My best results have always to leave the rudder dead neutral, adjust right thrust for vertical uplines. Never had an issue with a downline.

But make sure the rudder is neutral, not just even with some tab on the top that may be crooked. Also, the rudder must be hinged dead on center. And a straight fin & rudder helps a lot.

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Team JR

(in reply to Derek.Koopowitz)