Brian Whatcott wrote:

On Fri, 17 Jun 2005 00:20:28 -0700, Ed Sullivan
wrote:

On Fri, 17 Jun 2005 01:06:53 GMT, Gord Beaman
wrote:


stick.

Ok, thanks...I know that sweepback will increase fore and aft
stability by making the critical fore and aft CG limits 'farther
apart' but I sure can't see how it affects lateral
stability...anyhoo...if you find out could you tip me off?
Thanks Ed.

This is not a complete explanation, but it might help.

http://avstop.com/AC/FlightTraingHan...Stability.html

It does help - but in a disconfirming sense - let me quote:

"The contribution of sweepback to dihedral effect is important
because of the nature of the contribution. In a sideslip the wing into
the wind is operating with an effective decrease in sweepback while
the wing out of the wind is operating with an effective increase in
sweepback. The reader will recall that the swept wing is responsive
only to the wind component that is perpendicular to the wing's leading
edge. Consequently, if the wing is operating at a positive lift
coefficient, the wing into the wind has an increase in lift, and the
wing out of the wind has a decrease in lift. In this manner the swept
back wing would contribute a positive dihedral effect and the swept
forward wing would contribute a negative dihedral effect. "

This suggests that sweepback is directionally destabilizing..... (?)

Brian Whatcott Altus, OK

Yes, I see your point Brian and on a slightly different tack, I
always saw dihedral like this.

A wing has max lift when it's 90 degrees to gravity, (or 'down')
it has zero lift when pointed straight 'up'...now, when a gust
knocks a wing (with dihedral) 'down' (towards level) then it's
lift increases while the other wing's lift will decrease (as it
goes upwards 'toward' the 'zero lift angle'. Hell, if you had
'enough' dihedral then you couldn't roll the a/c because of this
powerful effect, the ailerons wouldn't have enough authority to
overcome it. Taking things to a ridiculous extreme you could have
say, 45 degrees of dihedral where it'd be possible to have a gust
of wind take one wing 'down' to 90 degrees so that it has the max
lift that it's capable of while the other wing is pointed
straight up and has 'no' lift at all.

I imagine that the correction then would be somewhat sudden.



-Gord.

"You are completely focused on RPM as the
single factor producing rotational velocity"

-Dude Henrickles