Rudder for final runway alignment (?)

Steve Foley writes:

Try it in a 172. You CAN turn with rudder only. It's not coordinated, but it
still turns.

If I _hold_ the rudder, I do indeed enter a turn. But I've been
trying (perhaps incorrectly) to just apply it briefly just above the
runway in order to improve my alignment. It works, but only until I
release the rudder, at which point it snaps back. If I hold the
rudder long, the turn becomes more persistent, but then the aircraft
starts to roll, which is what I'm trying to avoid in the first place
when I'm only 30-50 feet above the runway.

I'll grant that I've been trying some truly reckless approaches that
would be unthinkable in real life, standing the aircraft on one wing a
few hundred feet from the threshold, coming in at a 45° angle, and
then trying to align. But I figure that if I can do that to any
extent, then more serious approaches should be all that much easier.
Obviously if I start ten miles out, it's not a problem to be right
down the centerline if the weather isn't too bad. These wild
maneuvers are the kinds of things you can do safely only in
simulation. Surprisingly, there aren't too many crashes, despite the
recklessness of it all.

Plus I get impatient waiting for the next airport to draw near. I've
found that Hawaii seems to have a ton of little airstrips that are
good for touch-and-go practice. Today I discovered that Heathrow and
London City Airport are rather conveniently placed for alternating
touch-and-go practice between them without too many wild approaches.

--
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On Thu, 21 Sep 2006 07:38:09 +0200, Mxsmanic
wrote:

RK Henry writes:

Some argue that it's preferable to use the rudder in an instrument
approach for minor heading changes. In fact, when I took my instrument
rating check ride, the examiner chided me for rolling to minor heading
changes instead of just using the rudder, though he signed me off
anyway.

If I try to use the rudder alone for a heading change in flight, the
aircraft just snaps back to its previous heading when I center the
rudder again.

Is there the heading hold engaged on the autopilot? Does the airplane
tend to bank when you apply rudder? If not, this may be a modeling
error in your sim. I'm not aware of any real airplane that returns to
its exact original heading without intelligent intervention. Being
able to turn the airplane using only the rudder is usually inherent in
the airframe design. A simulator that doesn't model that behavior is
incomplete.

RK Henry

RK Henry writes:

Is there the heading hold engaged on the autopilot?

No, these are with A/P shut off. The usual scenario is that I've
impatiently done a full circle after take-off and I'm trying to
scrunch back in on the same runway from a very short distance away
(half a mile or so, sometimes less). It helps me to get more landings
in over a short period. Especially in small aircraft, going 20-40 nm
to find another airport for another touch-and-go is very
time-consuming.

Does the airplane tend to bank when you apply rudder?

If I hold it, yes, it starts to bank. But holding it also turns the
aircraft too far, and I don't want to bank because I'm so close to the
ground. The aircraft starts to slip and slide and I come dangerously
close to the ground while still misaligned or too far from the
threshold.

If not, this may be a modeling error in your sim.

MSFS is pretty reliable on these points, especially with the
hyperrealistic Dreamfleet models. I tend to assume that any mistake
is mine, rather than the sim's.

I'm not aware of any real airplane that returns to
its exact original heading without intelligent intervention.

It's not exact, but if I push the rudder sharply and quickly, the
aircraft yaws 10-15 degrees, and if I immediately release it, it yaws
back in the opposite direction almost as if it were pulled, which I
don't understand. If I hold the rudder for more than a second or so,
the plane starts to bank.

Being able to turn the airplane using only the rudder is usually inherent in
the airframe design. A simulator that doesn't model that behavior is
incomplete.

I'm sure the simulator is modeling it correctly. It would be inherent
in the basic aerodynamics of the model, so if this didn't work,
nothing would work.

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"Mxsmanic" wrote in message
...
Is it cheating/advisable/forbidden/useless to use the rudder alone to
accomplish the very last seconds of runway alignment on landing? As I
approach the landing point it becomes very difficult to turn in the
usual way just to improve alignment. Using rudder alone can line me
up perfectly right quick, but I don't know if that's the proper
technique, and I have to hold the rudder going in.

I know that the rudder can (and should?) be used to deal with
crosswinds, but I'm talking about landing in calm air and just being
an aircraft-width or so away from the centerline (which on narrow
runways or with large aircraft might mean one set of wheels on the
grass). As I get closer I'm afraid to roll the aircraft because a
wing might fall too low, or ground effect might do something
unpleasant, or something like that.

The actual line up just prior to touchdown is a marriage of subtle control
pressures dealing with several things at one time. Depending on the airplane
you're flying, the amount of bank available to you at the last second might
well be limited as you have noted. For many airplanes, it is perfectly
acceptable and indeed can even be critical to use rudder to insure
proper alignment of the aircraft with the runway at touchdown.
Its probably not wise to consider the act of touchdown as a 0 wind
condition. Although it is possible to actually have a 0 wind condition, in
reality, you will almost always have some wind component acting on the
airplane through the touchdown. That's why landing an airplane is considered
the marriage of all your controls acting at once to achieve the touchdown
correctly.
Some airplanes like airliners for example with underslung engines can't be
banked close to the ground. Others like the F16 or the T38, require a
straight in crab, set up for whatever is necessary, right through the
landing.
Generally, you will set up a landing with whatever the airplane is telling
you is needed at any given instant in time during the approach and the flare
through touchdown. If its truly calm, its a simple line up and landing. If
needed, you can use whatever combination of crab or slip and correction from
the slip through touchdown. Remember, its aircraft specific!
To answer your question, generally yes, you can, and indeed should, use
rudder to align the airplane at touchdown. General rule; keep the tail lined
up with the nose and don't scuff the wheels with a side load and you're
right in the ball park.
Dudley Henriques

Mxsmanic,

In these kinds of your posts, could you please spell out clearly that
you are talking about playing a flight simulator, not real flying? it
would save people a lot of time tailoring their answers.

--
Thomas Borchert (EDDH)

Thomas Borchert writes:

In these kinds of your posts, could you please spell out clearly that
you are talking about playing a flight simulator, not real flying? it
would save people a lot of time tailoring their answers.

It's not necessary in most cases. Simulators, as their name implies,
behave like real aircraft for the most part, especially for all of the
more basic aspects of flying. While certain types of extremely
complex or aircraft-specific modeling are sometimes absent, all sims
tend to be very good indeed at all the normal flight maneuvers. Some
sims let you crank down the realism at your discretion, but the basic
calculations are there and are correct. Simulation isn't _that_
difficult.

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Mxsmanic,

It's not necessary in most cases.


yes, it is.

--
Thomas Borchert (EDDH)

I've just learned that (based on this thread) Monty Python's Flying
Circus is considering re-writing "The Argument."

Jay B

On 09/23/06 11:46, Jay B wrote:
I've just learned that (based on this thread) Monty Python's Flying
Circus is considering re-writing "The Argument."

Jay B


Damn it! I paid for an Argument!

.... no you didn't.

;-)


--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA

I've just learned that (based on this thread) Monty Python's Flying
Circus is considering re-writing "The Argument."

No, that would be "abuse". "Argument" is three doors down.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.