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Rudder Question - 11/19/2012 12:50 AM   
Rubbernecker


 

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From: Forest, VA, USA
Status: offline 		Posted over on the other site as well, but just in case some don't frequent both. Thought I would post here instead of vintage since it applies mostly small planes. On designs like most of Ken Willard’s small stuff, the rudder is angled. This works fine if you are going to be using some type of pulse or escapement utilizing a u shaped wire over the rudder, but if you are using a servo with a pushrod, it creates a problem. The angled rudder causes the pushrod to bind. If you made the rudder the same area but made it vertical, would this cause a flying problem? In other words, is there any advantage to angling the rudder?

John


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RE: Rudder Question - 11/19/2012 1:15 AM   
soarrich



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Status: offline 		I think the angled rudder adds in a small amount of elevator effect.

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RE: Rudder Question - 11/19/2012 1:27 AM   
ffkiwi


 

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Status: offline 		An angled rudder isn't a problem to a servo if you use a balljoint on the rudder horn-with the popularity of Park Fliers and Indoor R/C, there is a whole range of 'miniaturised' horns, clevises, connectors, pushrods etc etc available from the big accessory names like Dubro and Goldberg-including miniature ball joints.

I don't think it makes a great deal of difference in terms of control effect though, providing you don't alter the respective areas of fin vs rudder-if you do, there may be some change in control response. There is one school of thought that argues that rudder height can have a greater influence than rudder area though...................

ChrisM
'ffkiwi'

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RE: Rudder Question - 11/19/2012 3:45 AM   
BMatthews



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Status: offline 		For reasonably small deflection angles the swept hinge line won't create enough of a binding action to produce any issues. But if you want it to be that little bit more proper then the ball joint idea is the best option. Or use a "pull-pull" thread system with two small control horns.

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RE: Rudder Question - 11/19/2012 4:24 AM   
guamflyer


 

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Status: offline 		what ffkiwi says is true and to the effect of rudder height, once I made my rudder too tall and it caused a symtom called spiral instability. the plane would spin and have a hard time coming out. I cut 1 1/2 inches off the top and the plane flew fine. I put a tall V tail on alot of my planes with no problems whatsoever. I've also used a rudder or fin that was 4" AT ROOT AND 1" AT TIP with no probs, it was 6 1/2 " tall.

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RE: Rudder Question - 11/19/2012 4:52 AM   
ffkiwi


 

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Status: offline 		From a purely FF perspective (ie my avatar!) it has been known for many years that fin and rudder area interacts with, and is inter-related to wing position. There are a few model designs out there which have optional wing positions-high, shoulder/mid or low wing. [the well known NZ Modelair 'Hummingbird' for example] The low wing versions all require a lower rudder height than the high wing version. If you attempt to fly the low wing with the full sized high wing rudder, you will find it spirally unstable. I've also found that with the odd FF low wing sport design that was a bit 'squirrelly', [APS 'Peril' and 'Jinty'-both Aeromodeller free plans from the mid 60's] gradually chopping a full chord strip 1/4" at a time from the top of the rudder usually cured the problem.........
The chief exponent of the rudder height theory is Australia's Stan Hinds, who produces some quite distinctive looking models with very tall, but narrow fins-he considers fin aspect ratio to be the critical factor. It seems to work for him...........

ChrisM
'ffkiwi'


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RE: Rudder Question - 11/19/2012 10:12 AM   
guamflyer


 

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Status: offline 		I Knew it wasn't just my Imagination....... thanks for validation....

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