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Apr 02, 2008, 11:40 AM
Flys like a chocolate teapot
Question

planks pitch stability


hi
does anyone know of a ratio of chord to wingspan that a plank with no other horizontal support will remain stable?
and is there anything i can do apart from dihedral, sweep and as low a COG as possible to help lower this ratio?
thanks
julian
ps im talking about an unpowered plank if that makes any diff
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Apr 02, 2008, 11:56 AM
Obsessed
screamin' eagle's Avatar
I don't know of any hard and fast rules, but I've built/flown a handful of different homebrew planks. To use a concrete comparison, I've done two different 60" flying wings. One had a 6 1/2" root chord and 5 1/2 inch tip chord. The other has a 9 1/2" root and 4" tip chord. Both are single tapered at both LE and TE. Both are very pitch stable, even for flying wings.
Apr 02, 2008, 12:02 PM
Phil.T-tailer
Phil.Taylor's Avatar
Quote:
Originally Posted by julian.i
hi
does anyone know of a ratio of chord to wingspan that a plank with no other horizontal support will remain stable?
chord:wingspan (i.e. aspect ratio) should have little or no effect on stability - which is chiefly a function on the airfoil pitching moment, in combination with reflex on the elevons. Plank airfoils like PW51 & MH64 are specifically desinged to be pitch stable.
EDIT - For more info see e.g. Martin Hepperles site:
http://www.mh-aerotools.de/airfoils/index.htm
follow "flying wings" & the links at the bottom of the flying wings airfoil page - he explains it all in there...
Phil
Last edited by Phil.Taylor; Apr 02, 2008 at 12:13 PM.
Apr 02, 2008, 12:03 PM
Flys like a chocolate teapot
are you using a zreo camber airfoil? or do you have to adjust the elevons up? or is the pitching moment of the airfoil totaly overcome by the low centre of gravity? ------edit------thanks Phil lol you got there first-------
cheers


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