Dutch roll coordination technique

The proper use of the term "Dutch Roll" applies to a characteristic of
the lateral stability of an aircraft, inherent in all aircraft but
thoroughly investigated during the test flight and certification stage.
The manoeuvre can be seen by simply letting go of the stick in trimmed
level flight and yawing the aircraft. Ideally one would provide one yaw
impulse and then let the aircraft return itself to steady flight while
observing the dynamics of the recovery (how many oscillations, damping
etc.) but it is possible to keep the manoeuvre going by alternating the
impulse on the rudder pedals with each change in yaw direction.

Note that I have only mentioned the rudder above. This manoeuvre does
not involve aileron input. In fact a pilot could get himself into
trouble by trying to correct with aileron input and could produce
amplified pilot induced oscillations.

The dynamics are as follows:
With the first rudder input comes a yaw impulse. This causes the
opposite wing (starboard wing if port rudder input) to swing forward -
gaining a few knots (and lift) - and the other wing to swing back -
losing a few knots. This is why the aircraft seems to roll during the
yaw. If the pilot keeps alternating the rudder inputs this will cause an
oscillating yaw condition. Looking at the wing tip you would see it
describing an ellipse on the horizon. The way to stop this motion is not
to fight it. Simply ceasing control input will rapidly stabilise the
aircraft, remember that aircraft are designed to be laterally stable (in
most cases), loosing part of the tailplane or rudder could make this a
problem. Trying to fight the motion with control inputs will only
prolong the motion at best, and amplify it at worst. Your natural
instinct to correct in a particular direction with aileron is working
against you because at the point that you feel you should correct is the
point where the factors influencing the motion are changing direction
and you are now only adding to them. If a pilot got caught out he could
stall one wing tip while overcorrecting and end up in a spiral or even
spin. Unlikely but possible.

Incidentally this manoeuvre is best experienced in the tail of the
aircraft. The pilots are usually near the wing junction and as such are
on the centre line of a helix that the the passengers in the rear of the
fuselage are following.


Dennis O'Connor wrote:
Read, Stick And Rudder... Wolfgang Langewiesche

Denny

Matthew Jurotich" wrote in

When doing this correctly are the rudder and ailerons co-ordinated

or opposite? Why?

The proper use of the term "Dutch Roll" applies to a characteristic of
the lateral stability of an aircraft, i

One of the more famous aircraft subject to Dutch Roll was the Northrop
YB-49 turbojet Flying Wing bomber. The military test pilot Robert
Cardenas (who took over the project after Glen Edwards was killed)
recalled that the bombardier used to get seasick from the
oscillations.

(The YB-49 is cited as the predecessor of the B-2 Spirit stealth
bomber, because it was from Northrop and had the identical span. In
fact, the B-2 more closely suggests the German "nurflugel" designed by
the Horten brothers. www.warbirdforum.com/edwards.htm )


all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

Cub Driver wrote:
The proper use of the term "Dutch Roll" applies to a characteristic of
the lateral stability of an aircraft, i


One of the more famous aircraft subject to Dutch Roll was the Northrop
YB-49 turbojet Flying Wing bomber. The military test pilot Robert
Cardenas (who took over the project after Glen Edwards was killed)
recalled that the bombardier used to get seasick from the
oscillations.

(The YB-49 is cited as the predecessor of the B-2 Spirit stealth
bomber, because it was from Northrop and had the identical span. In
fact, the B-2 more closely suggests the German "nurflugel" designed by
the Horten brothers. www.warbirdforum.com/edwards.htm )


all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

Yup I would definately believe that. The lateral stability in those
tail-less designs was achieved through wing sweep rather than the usual
vertical fin. I would imagine that they had interesting spin
characteristics as well, although I don't remember it being mentioned
anywhere. The father of flying wing / tail-less designs was Alexander
Lippish.

I would imagine that they had interesting spin
characteristics as well,

I think it was Eric Brown who wrote about flying the British all-wing
aircraft, and having it almost rotate backward on him.

This is probably exactly what happened to the YB-49 that crashed near
Muric (now Edwards AFB) killing the pilot Danny Forbes, co-pilot Glen
Edwards, and the crew.

There are two files on the Warbird's Forum consisting of interviews
with Robert Cardenas, the military test pilot after Edwards, and a
very different view from Northrop test pilot Charlie Tucker
www.warbirdforum.com/edwards.htm


all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com