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-   -   longitudinal dihedral (http://www.rcuniverse.com/forum/aerodynamics-76/10207362-longitudinal-dihedral.html)

pl365322 12-20-2010 02:22 AM

longitudinal dihedral
 
Hi guys!
As I am setting up a Discus CS 2.6m from Jamara, I measure the longitudinal Vé at 0°. I guess that is wrong. I thought about 1 to 1.5° should be best.
Any advise?
Thanks.

Tall Paul 12-20-2010 09:14 AM

RE: longitudinal dihedral
 
How are you measuring this?

Lnewqban 12-20-2010 10:34 AM

RE: longitudinal dihedral
 
http://fatlion.com/sailplanes/decalage.html

http://fatlion.com/sailplanes/divetesting.html

http://www.ppssrc.com/articles/soaring_faq.html#590334 (See 7.6)

pl365322 12-20-2010 11:35 AM

RE: longitudinal dihedral
 
Paul,
I am measuring that, the plane fuse straight, measuring the difference between elevator and wing incidence.

Tall Paul 12-20-2010 12:41 PM

RE: longitudinal dihedral
 
1 Attachment(s)
Wing incidence... if the most forward part of the leading edge and the trailing edge are at zero relative to a fuselage reference line, or the mid-line of the horizontal, then you have zero incidence.
If the wing has any tilting up, then its incidence isn't zero.
Usually only a aerobatic plane with a symmetrical section might have zero longitudinal dihedral.

BMatthews 12-20-2010 05:29 PM

RE: longitudinal dihedral
 
The only discus models from your description that I can find show a fixed stabilizer with movable elevator.  And it doesn't appear to have flaps.  First off ensure that the elevator is sitting at zero to the stabilizer.  Otherwise you'll get a false reading. 

The other issue is that on a high speed sort of model where you're expected to move the CG more towards the rearward limit you do not require a lot of Longitudinal Dihedral (LD).  So the designers may have expected you to just use a few clicks or turns of up trim on the Tx or a clevis in the pushrod system for the elevator.  If this bothers you then add a wedge shaped shim to the stabilizer that provides a one degree negative angle to the fixed stabilizer and adjust the elevator pushrod to do the same to the movable elevator so it is all smoothly faired. 

From there go and fly and test the CG location until it's as far back as you can comfortably tolerate and then look at the elevator trim position and adjust the wedge shimming as required.

BMatthews 12-20-2010 05:33 PM

RE: longitudinal dihedral
 
OK, you asked the same question in two forums.  I'm locking this one and requesting that any further discussion about posts in this thread be directed to the other one here....

http://www.rcuniverse.com/forum/m_10207368/tm.htm


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