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Dihedral /rudder confusion

Old 09-07-2009, 10:21 PM
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Default Dihedral /rudder confusion

Been flying 3 channel motor gliders (R/E/Motor) and 2 channel gliders (R/E) for a while, my latest builds been reducing the dihedral with the intention of doing mild aerobatics. As I reduce the dihedral angles the rudder has less and less effect, and in some cases I have had to have the rudders out of proportion.
I know the dihedral by changing lift forces levels the aircraft and causes more stable flight. A rudder with no dihedral cause change of direction by "slew".
Why is it that the increase in dihedral will make the rudder more effective in turning?
Hoping for clarity
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Old 09-07-2009, 10:32 PM
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Dihedral works due to sideslip. if you hold the model in front of you and yaw it sideways you will see that the dihedral causes the leading wing to have a higher angle of attack which increases its lift (see attached illustration).

So to produce a turn the rudder yaws the model. The yaw generates a side slip and the dihedral rolls the model in the direction of the yaw. It's the roll (not the yaw) that makes the model turn because the wing's lift is angled to the outside of the turn which 'pushes' the model round the turn. Yaw on it's own wont turn the model, without the dihedral to cause the roll the model will just side slip without actually changing direction of travel.

You need plenty of dihedral on a R/E model. Decreasing the dihedral wont make it more aerobatic. In fact the opposite will be true, it will just get more sluggish to rudder input. if you want to run low/zero dihedral the you need to add ailerons.

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Old 09-07-2009, 10:36 PM
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Here is a nice description.
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Old 09-08-2009, 04:16 PM
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Thanks that cleared up the confusion in my tiny mind. The two replies made it understandable.
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Old 09-21-2009, 11:22 AM
Keith C
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Some time ago i watched a combat event. The overall winners were two brothers who built planes with aluminum rails for the fuse. and paper covered foam wings. They were R-E only. They looked very strange with what i,m guessing at no less than 20 deg. dihedral. They out turned all the aileron planes.
Happy flying , Keith C.
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