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mdnanwelch7(at)hotmail.co
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 Posted: Mon Feb 18, 2008 6:44 pm Post subject: Wings and their characteristics |
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You'ze guys,
I don't begin to have all the facts about airfoils like Rick does, but it is my understanding that an abrupt stall tendency is sometimes mitigated by washout.
For those unfamiliar with the term, washout is the practice of building the wings with a deliberate slight spiral twist outward. As each rib is fastened to the spar, starting at the root end, there is a very slight twist as you progress outward, with the trailing end of the rib rises. Usually the washout is around 2", or so, and can be seen quite easily if you view the end of the wing, looking toward the fuselage.
The stall characteristics of any airfoil are critical at a specific angle (regardless of the airfoil). By having "washout" the root of the wing may be, in fact, STALLED, while the outer portion of the wing is still flying, albeit barely!!
Notice that when a wing is designed with built-in washout, that the tips of the wing are twisted UP, not down.
The most apparent reason for this direction of twist, rather than twisting the wing down, is because as "stall"
progresses outward along the wing, the last to stall is the outer portion....hence, still giving you aileron control.
Although I haven't backed my statements up with documentation, as Rick so eloquently does, this is more of a "shade tree mechanic" understanding.
Mike Welch
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jindoguy(at)gmail.com
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| Posted: Mon Feb 18, 2008 7:30 pm Post subject: Wings and their characteristics |
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Mike, it's a good understanding, however you base it. The Hershey bar wing (untapered) like the Kolb's has this tendency naturally without twist. The other way you can get the same effect is to use aerodynamic twist and use a different or thicker version of the root airfoil.
Rick
On Feb 18, 2008 8:42 PM, Mike Welch <mdnanwelch7(at)hotmail.com (mdnanwelch7(at)hotmail.com)> wrote:
[quote] --> Kolb-List message posted by: Mike Welch <mdnanwelch7(at)hotmail.com (mdnanwelch7(at)hotmail.com)>
You'ze guys,
I don't begin to have all the facts about airfoils like Rick does, but it is my understanding that an abrupt stall tendency is sometimes mitigated by washout.
For those unfamiliar with the term, washout is the practice of building the wings with a deliberate slight spiral twist outward. As each rib is fastened to the spar, starting at the root end, there is a very slight twist as you progress outward, with the trailing end of the rib rises. Usually the washout is around 2", or so, and can be seen quite easily if you view the end of the wing, looking toward the fuselage.
The stall characteristics of any airfoil are critical at a specific angle (regardless of the airfoil). By having "washout" the root of the wing may be, in fact, STALLED, while the outer portion of the wing is still flying, albeit barely!!
Notice that when a wing is designed with built-in washout, that the tips of the wing are twisted UP, not down.
The most apparent reason for this direction of twist, rather than twisting the wing down, is because as "stall"
progresses outward along the wing, the last to stall is the outer portion....hence, still giving you aileron control.
Although I haven't backed my statements up with documentation, as Rick so eloquently does, this is more of a "shade tree mechanic" understanding.
[quote][b]
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