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Old Dec 17, 2010, 10:52 PM
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kamakasi's Avatar
Joined Nov 2005
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Dihedral vs. Poly-Dihedral

don't want to start a math war but is there a noticeable difference in the flight characteristics between a sailplane with dihedral vs one with poly-dihedral with the EDA's being equal.
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Old Dec 18, 2010, 02:59 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
11,416 Posts
"EDA's being equal".. i'd say no, no great difference. The polyhedral plane should be slightly more efficient but we are talking about very small margins.
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Old Dec 18, 2010, 03:47 AM
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The 'Wack, BC, Canada
Joined Oct 2002
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Yeah, but to get the same EDA (I'm assuming that EDA means Effective Dihedral Angle) the one with plain dihedral will have to have the tips further up in the air than the polyhedral wing. The greater angle in the tips of the poly wing means that you're getting a bigger shift in angles of attack from a given yaw angle out in the tip panels where there's more leverage to roll the model.
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Old Dec 18, 2010, 05:02 AM
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eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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Then there is always elliptical dihedral.




Also more threads in the 'Similar Threads' list.
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Old Dec 18, 2010, 11:36 AM
greg
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somerset, nj
Joined Feb 2005
371 Posts
AMA articles

Blaine Beron-Rawdon wrote series of articles entitled "Dihedral" in the Aug-Nov 1988 Model Aviation magazine. The AMA has a digital archive where you can search for them. Try looking for "Dihedral" in 1988.
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Old Dec 18, 2010, 12:50 PM
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Joined Oct 2000
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I've found poly is fine with a conventional rudder-elevator control system.
And not so fine with a vee-tail, but OK with an inverted vee-tail, these with rudder-vators.
The rolling input from the rudder on the vee-tail rolls the plane opposite the turning direction, and creates problems taking off and landing.
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Old Dec 18, 2010, 09:50 PM
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it seems the biggest difference is aesthetic. while 3 to say 5 degs. looks ok. with a single break 9 or 10 degs as you would find on a large res ship looks ridiculous. I know you should do the math and trust the #'s but my current projects name will pretty much say it all WAG-TLAR. I have the Sailplane Designer's Handbook by Eric Lister and while some of the airfoils are dated the equations and such are valid. This is how I went about determining the tail movement and fuselage dimensions. The planned wing span is 160" with an aspect ratio of 18.5 to 1 basically a big thermal ship I don't want to say XC and open myself to the argument as the mean cord is just over 9". I'm still messing around with the airfoil. I don't really need another bit floater I have my Sail-Aire for that. I want to start playing with ballasting and getting the wing loading up to a range where "stored momentum" has a meaning. The attachment shows a cheesy front view so you can get an idea of the form I have chosen for the dihedral. The ship is going to be Rudder, Elevator and Flaps. Don't know if I'll install spoilers but you can bet the provisions will be there. Oh. the dihedral shape comes from applying PHI (1.61803399) to the angles. The wife went back to college to finish out her ancient art's degree (going to be a prof.) so the suggestion was hers
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