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angles and dihedral

Old 10-11-2009, 11:56 PM
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Default angles and dihedral

Hi all, decided to replace the multiple repaired wing on my cheap parkflyer, an SDM "Skyhawk". Decided on a 2mm coreflute, cf sparred, 1.3 metre span with a symmetrical airfoil. Flat middle section, dihedral tips, similar in chord, span and design to the original. My question is related to airfoil and wing ancidence. The original wing had a very thin section under- cambered design. Would a fully symmetrical airfoil need a deffernt angle to provide the same sort of lift? It is very easily adjusted so it is no big deal to change things; I was just looking for a reasonable starting point. The plane is a floater any way, if that helps. Thanks in advance.... pictures of the original included.
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Old 10-12-2009, 04:37 AM
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a fully symmetrical wing needs angle of attack to produce any lift at all.
a non symmetrical wing, and especially a undercambered wing, will produce lift at 0 angle of attack.
however, in the air i dont thing you are going to notice. you will compenaste for it automatically by applying elevator, and its not going to be a headache.
but why do you want a fully symmetric wing, and in combination with dihedral?
the only reason that i knew for fully symmetric wings is to fly as good upside down, as the right way.
but dihedral dont work very well with that flying upside down business.
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Old 10-12-2009, 05:21 AM
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Default some more info...

Hi Moxus, thanks for that. The fully symmetrical wing is built in 3 sections, and will be used as a flat wing as well, with strip ailerons, at a future date. Just saved me building 3 different wings; sort of a modular concept. The experimental bug bit me a while ago and I can't shake it off...cheers...
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Old 10-12-2009, 06:12 AM
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Originally Posted by pattern14 View Post
Would a fully symmetrical airfoil need a deffernt angle to provide the same sort of lift?
The simple answer to that is that a symmetrical airfoil will never produce the same maximum lift as an undercambered airfoil.

As Moxus said; symmetrical airfoils are only usually only chosen on models that need to fly as well inverted as they do the right way up. When flying the right way up a symmetrical airfoil does not perform as well as one with suitable camber. A symmentrical airfoil is a bad airfoil to use on a thermal soaring type sailpane as flying speed and sink rate will be increased.

Also as Moxus said.. you will need a higher angle of attack compared to the old wing but elevator trim will look after it, you will most likely find that you need to fly noticably faster with the new wing than with the old anyway.

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