A Q on horizontal turns

"Ramapriya" wrote in message
oups.com...
Not having been in an aircraft boat-turn before, I find your example a
wee addling. The kids would get hurled across the seats because the
station wagon is trying to turn horizontally about its axis while being
restricted in its lateral movement by the tires that are grounded. In
an aircraft, there's just thin air outside, so I'd presume it'll mildly
keep sliding sidewards too (in the opposite direction) while turning
about its axis.

It's a little of both. It won't be as bad as the aforementioned station
wagon, because the rudder isn't capable of producing as much of a turn. In
fact, this is why it's so important to use aileron to bank the plane too for
a turn. But a turn does still happen to a lesser degree, and the passengers
would still feel the apparent force pushing them to the outside of the turn.

Pete

In article ,
"Peter Duniho" wrote:

"Ramapriya" wrote in message
oups.com...
Not having been in an aircraft boat-turn before, I find your example a
wee addling. The kids would get hurled across the seats because the
station wagon is trying to turn horizontally about its axis while being
restricted in its lateral movement by the tires that are grounded. In
an aircraft, there's just thin air outside, so I'd presume it'll mildly
keep sliding sidewards too (in the opposite direction) while turning
about its axis.

It's a little of both. It won't be as bad as the aforementioned station
wagon, because the rudder isn't capable of producing as much of a turn. In
fact, this is why it's so important to use aileron to bank the plane too for
a turn. But a turn does still happen to a lesser degree, and the passengers
would still feel the apparent force pushing them to the outside of the turn.

There's another thing that happens when you stomp on the rudder: while
the plane is yawing about its vertical axis, one wing is moving faster
than the other through the air and therefore generates more lift,
causing the plane to bank even without any aileron input. But the plane
yaws first and banks afterwards, so the effect is that the wing makes
this sort of circular stirring motion. It can be quite disconcerting if
you're not used to it.

BTW, Ramapriya, where do you live? Pilots are a generous lot, and you
can probably find someone to take you up so you can experience all this
firsthand.

rg

Ron Garret wrote:

BTW, Ramapriya, where do you live? Pilots are a generous lot, and
you
can probably find someone to take you up so you can experience all
this
firsthand.

I normally live and work in Dubai, United Arab Emirates. For about a
month or so more, I'll be in Khartoum (Sudan). Just yesterday, I've
lined up someone who knows the owner and pilot of a YAK-40. I'll go
check out his patience one of these days )

I also have my eyes on a long-disused YAK-40 lying within the airport
premises. I hear the owner might pay if someone takes it, so... )
Ramapriya

On Thu, 6 Jan 2005 at 09:35:46 in message
, Peter Duniho
wrote:

It's a little of both. It won't be as bad as the aforementioned station
wagon, because the rudder isn't capable of producing as much of a turn. In
fact, this is why it's so important to use aileron to bank the plane too for
a turn. But a turn does still happen to a lesser degree, and the passengers
would still feel the apparent force pushing them to the outside of the turn.

I have no special theory abut the sad crash - I just don't know enough
about it - but the comments about why the loading cases are 'not as high
as they should be' caused me to start writing.

I don't know how much steady yaw 'g' can be generated by an airliner. I
do know that there are smaller high powered aircraft that can fly 'knife
edge' and must therefore be capable of generating a steady one 'g' yaw
'acceleration'. I have doubts as to whether a station wagon can generate
much more than one 'g' in a turn.

But my point is this. Higher loads and angles of yaw can be generated by
control inputs that are in phase with the natural yaw frequency. A
single application of full rudder will generate a deflection in yaw
which may overshoot the final steady state yaw deflection which will
then be damped out. However if control inputs are added so as to
increase the yaw rate as the aircraft oscillates from one side to the
other then it is theoretically possible to generate very large loads
indeed. The maximum will be generated dependent on the amount of yaw
damping present and the energy inputs. An operating yaw damper does the
opposite; it operates so as to reduce the amplitude of yaw oscillations.

The same sort of thing can occur in pitch but conventional aircraft are
likely to have much better damping in pitch than yaw. The classic
phugoid oscillation in pitch is not often mentioned, the ones I am
referring to here are the short period stability oscillations.

I believe this driving up of the deflections might be described as
'pilot induced oscillations'.

I have not the data to answer the questions posed by this but the
possibility may be there. The fact that yaw dampers are often fitted to
assist the pilot (human or auto) seems to suggest that at some parts of
the flight envelope large deflections of yaw angle need to be reduced.
('Yaw dampers' may also be part of a system to produce automatic
balanced turns but that is not the effect I am alluding to.

Why can flutter be so destructive? Because at certain speeds the input
of aerodynamic forces changes in such a way as to drive the structure to
deflect beyond its limits in an oscillatory way.

Divergence means that a single structural defection will increase the
load on the structure so much that it bends enough to reinforce the
aerodynamic force and this can lead to catastrophic failure. It is
however rare in aircraft!

Peter:- believe me it was only after I had written this that I realise I
had entered quoting your post. Several posts before that made me want to
react. I am not reacting directly because of your post. I am not
following you about - honest!
--
David CL Francis

"David CL Francis" wrote in message
...
[...] I am not following you about - honest!

That's alright...I was just getting over my previous persecution complex. I
needed something new to obsess about.