Dutch Roll?

[Ron Hardin]

Do modern jet airliners still have a noticeable dutch roll? I haven't
flown in anything for a couple decades, and was wondering if it's been
damped out to zero by modern control theory, or still exists.

I first noticed it trying to take solar sights with an elaborate
protractor and bubble level setup on trans-Pacific flights, in
DC-6's and later 707's (something to do). It was a few degrees
in roll magnitude, quite noticeable. You'd think today it would
be gone completely, though, but I don't know.

It came to mind because my bicycle seems to do the same thing under
heavy baggage load. No doubt from a different cause.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

[Scott Skylane]

Ron Hardin wrote:

> Do modern jet airliners still have a noticeable dutch roll? I haven't
> flown in anything for a couple decades, and was wondering if it's been
> damped out to zero by modern control theory, or still exists.
>
> I first noticed it trying to take solar sights with an elaborate
> protractor and bubble level setup on trans-Pacific flights, in
> DC-6's and later 707's (something to do). It was a few degrees
> in roll magnitude, quite noticeable. You'd think today it would
> be gone completely, though, but I don't know.
>
> It came to mind because my bicycle seems to do the same thing under
> heavy baggage load. No doubt from a different cause.


Hmmmm, Dutch Roll in a DC-6? My understanding has always been that
Dutch Roll is a by-product of a swept-back wing. While the leading edge
of the big Dougs does angle back from the lateral plane, the wing as a
whole, is straight. Any lateral occilations you observed were probably
due to the crudeness of the autopilot.

As for the 707, I would guess that the Dutch roll characteristics you
observed where properties of a first generation jetliner yaw damper, ie:
less than perfect dampening.

In regards to transport category aircraft, anything of a newer
generation has, in my observation, perfectly eliminated any Dutch roll
tendencies.

Happy Flying!
Scott Skylane

[Ron Hardin]

Scott Skylane wrote:
>
> Ron Hardin wrote:
>
> > Do modern jet airliners still have a noticeable dutch roll? I haven't
> > flown in anything for a couple decades, and was wondering if it's been
> > damped out to zero by modern control theory, or still exists.
> >
> > I first noticed it trying to take solar sights with an elaborate
> > protractor and bubble level setup on trans-Pacific flights, in
> > DC-6's and later 707's (something to do). It was a few degrees
> > in roll magnitude, quite noticeable. You'd think today it would
> > be gone completely, though, but I don't know.
> >
> > It came to mind because my bicycle seems to do the same thing under
> > heavy baggage load. No doubt from a different cause.
>
> Hmmmm, Dutch Roll in a DC-6? My understanding has always been that
> Dutch Roll is a by-product of a swept-back wing. While the leading edge
> of the big Dougs does angle back from the lateral plane, the wing as a
> whole, is straight. Any lateral occilations you observed were probably
> due to the crudeness of the autopilot.
>
> As for the 707, I would guess that the Dutch roll characteristics you
> observed where properties of a first generation jetliner yaw damper, ie:
> less than perfect dampening.
>
> In regards to transport category aircraft, anything of a newer
> generation has, in my observation, perfectly eliminated any Dutch roll
> tendencies.
>
> Happy Flying!
> Scott Skylane

Actually it's from a mismatch of roll recovery time and yaw recovery time.
Plain ordinary dihedral, which a DC-6 has plenty of, is said to produce it.

Its presence certainly points to the autopilot, but only as having failed to
take it completely away. It develops naturally, and then grows to the granularity
of the autopilot, and then remains there, I think.

It can't be an instability in the autopilot, or it would grow bigger, which it
fails to do.
--
Ron Hardin


On the internet, nobody knows you're a jerk.