Biplane wing dihedral

Ed Sullivan wrote:

On Sat, 11 Jun 2005 00:04:10 -0400, vincent p. norris
wrote:

Friend of mine said at lunch today that the upper wings of biplanes
have no dihedral. Hementioned specificlaly the Stearman PT-17.

I believe he was mistaken. I know the Sopwith Camel upper wing was
flat but I think the PT-17 and most other biplanes have dihedral in
both wings.

Any expert comments?

Thanks. vince norris


Some biplanes have sweptback wings which provide the same effect as
dihedral. My parasol Jungster II has sweepback and no dihedral.

Ed Sullivan

Why is that Ed?...dihedral provides lateral stability by making
the 'downgoing wing' increase it's lift while the 'upgoing'
wing's lift decreases, so how does the 'sweep-back' provide
lateral stability?
--


-Gord.

"I'm trying to get as old as I can,
and it must be working 'cause I'm
the oldest now that I've ever been"

On Thu, 16 Jun 2005 02:09:30 GMT, Gord Beaman
wrote:

Ed Sullivan wrote:

On Sat, 11 Jun 2005 00:04:10 -0400, vincent p. norris
wrote:

Friend of mine said at lunch today that the upper wings of biplanes
have no dihedral. Hementioned specificlaly the Stearman PT-17.

I believe he was mistaken. I know the Sopwith Camel upper wing was
flat but I think the PT-17 and most other biplanes have dihedral in
both wings.

Any expert comments?

Thanks. vince norris


Some biplanes have sweptback wings which provide the same effect as
dihedral. My parasol Jungster II has sweepback and no dihedral.

Ed Sullivan

Why is that Ed?...dihedral provides lateral stability by making
the 'downgoing wing' increase it's lift while the 'upgoing'
wing's lift decreases, so how does the 'sweep-back' provide
lateral stability?

The reference escapes me, but I have read that so many degrees of
sweep back is the equivalent of an estabilished amount of dihedral.
All I know for sure is that this little sucker only has a 21' span and
it is as steady as a rock. It will go for miles without touching the
stick.

Ed Sullivan wrote:

On Thu, 16 Jun 2005 02:09:30 GMT, Gord Beaman
wrote:

Ed Sullivan wrote:

On Sat, 11 Jun 2005 00:04:10 -0400, vincent p. norris
wrote:

Friend of mine said at lunch today that the upper wings of biplanes
have no dihedral. Hementioned specificlaly the Stearman PT-17.

I believe he was mistaken. I know the Sopwith Camel upper wing was
flat but I think the PT-17 and most other biplanes have dihedral in
both wings.

Any expert comments?

Thanks. vince norris


Some biplanes have sweptback wings which provide the same effect as
dihedral. My parasol Jungster II has sweepback and no dihedral.

Ed Sullivan

Why is that Ed?...dihedral provides lateral stability by making
the 'downgoing wing' increase it's lift while the 'upgoing'
wing's lift decreases, so how does the 'sweep-back' provide
lateral stability?

The reference escapes me, but I have read that so many degrees of
sweep back is the equivalent of an estabilished amount of dihedral.
All I know for sure is that this little sucker only has a 21' span and
it is as steady as a rock. It will go for miles without touching the
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.
--


-Gord.

"I'm trying to get as old as I can,
and it must be working 'cause I'm
the oldest now that I've ever been"

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

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

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

On Fri, 17 Jun 2005 20:07:30 GMT, Gord Beaman
wrote:

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'.///
I imagine that the correction then would be somewhat sudden.

-Gord.

I think that I must have read this thread once too many times...in
that when I read what I posted, I see that the "Traing" text implies
just the opposite of what I thought it did. Oh my: he says sweep
back is like dihedral, but the argument seems to point the other way.

Think I will shut up, now!

Brian W

I think that I must have read this thread once too many times...in
that when I read what I posted, I see that the "Traing" text implies
just the opposite of what I thought it did. Oh my: he says sweep
back is like dihedral, but the argument seems to point the other way.

Think I will shut up, now!

Brian W

I'm really sorry I started this. Perhaps my parasol also benefits from
the pendulum effect. It does have a slight dutch roll tendency, but
the controls are so light that this is overcome easily. According to
what I have read my aircraft has far more sweepback ( 15 degrees )
than is healthy subsonic, but it doesn't seem to care. It does very
reliable moderate aerobatics and yet is not a monster on cross country
trips.

Ed Sullivan, me too

On Fri, 17 Jun 2005 15:45:41 -0700, Ed Sullivan
wrote:




I think that I must have read this thread once too many times...in
that when I read what I posted, I see that the "Traing" text implies
just the opposite of what I thought it did. Oh my: he says sweep
back is like dihedral, but the argument seems to point the other way.

Think I will shut up, now!

Brian W

I'm really sorry I started this. Perhaps my parasol also benefits from
the pendulum effect. It does have a slight dutch roll tendency, but
the controls are so light that this is overcome easily. According to
what I have read my aircraft has far more sweepback ( 15 degrees )
than is healthy subsonic, but it doesn't seem to care. It does very
reliable moderate aerobatics and yet is not a monster on cross country
trips.

Ed Sullivan, me too

I take it back here is some more confusing
info:http://www.av8n.com/how/htm/roll.html

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

Aren't a/c with sweptback wings subject to dutch roll?

vince norris