Gyroscopic Action.?

Question

1)What us Gyroscopic action and gyroscopic precession and how is it related to the aircraft's propeller?

2) Why in tail wheel aircraft is the magnitude of this force dependent on how abruptly the tail is raised?

Thanks in advance

Answer 1

Gyroscopic action is the force that keeps a spinning top from falling. Precession is the coupling of that effect in two axis.
If you were to hold a fast revolving wheel -- like a bicycle wheel that you are holding by an axis -- and you sit on a chair than can revolve, and that you turn the wheel so that it goes from being vertical to horizontal, the effect is that you, on the chair, would start spinning.
This precession is what allows or to a degree forces a bike to lean in a turn. You turn left? The whole bike leans left. You lean left? You will turn left.

In the case of a propeller driven aircraft, a tail dragger, the plane of the propeller is an an angle to the vertical, but when you reach enough speed, the tail will lift, and the plane of the propeller will change and become vertical. This will create yaw that must be balanced by a proper application of rudder.
The faster the tail will lift, the more pronounced that force will be, and the more rudder application will be needed to counterbalance it.

Answer 2

Gyroscopic force occurs on a spinning object (disk, wheel, whatever) when you try to alter the direction of the axis of spin.

As mentioned, this is why a top does not fall over if spinning - it will precess (wobble in circle) instead. If you have a wheel spinning in front of you on the vertical axis, and you try to push the axis away from you, it will instead try to lean to the left or right (clockwise-right, cc-left). The best illustration is when driving a motorcycle at a good speed. Its subconscious so few people notice unless they look for it, but to turn left, say, you actually flick the handlebars a little to the right causing the bike to lean left so you can turn. The effect is far more noticeable on a motor cycle because the wheel is more massive and spinning faster than, say, a bicycle.

(This is one reason why those 3-wheeler ATV's were so deadly. Experienced motorcycle riders would try to turn subconsciously the same way - and not realize the problem until they wandered into the wrong ditch. I know, it almost happened to me.)

Our physics class demonstrated this by holding a spinning bicycle wheel with lead weights on the rim, while sitting on a rotating stool. Move the axis and you will turn in funny directions.

On a top, as gravity tries to pull it over, the leaning top instead turns its axis 90 degrees away. Continue this process and the leaning top precesses in a circle instead of falling over.

The propeller on a small plane is turning counter-clockwise from the pilot POV IIRC (haven't flown it about 7 years.) When a taildragger goes from leaning back to level (pitch change), this gyroscopic force will cause the aircraft to want to turn (yaw) - rightwards, if I recall .

The faster the pitch up, the stronger the gyroscopic force, and the stronger the tendency to yaw.

Answer 3

Gyroscopic Action

Answer 4

TORQUE AND P FACTOR
To the pilot, “torque” (the left turning tendency of
the airplane) is made up of four elements which
cause or produce a twisting or rotating motion
around at least one of the airplane’s three axes. These
four elements are:
1. Torque Reaction from Engine and Propeller.
2. Corkscrewing Effect of the Slipstream.
3. Gyroscopic Action of the Propeller.
4. Asymmetric Loading of the Propeller (P Factor).
TORQUE REACTION
Torque reaction involves Newton’s Third Law of
Physics—for every action, there is an equal and
opposite reaction. As applied to the airplane, this
means that as the internal engine parts and propeller
are revolving in one direction, an equal force is trying
to rotate the airplane in the opposite direction.
When the airplane is airborne, this force is acting
around the longitudinal axis, tending to make the airplane
roll. To compensate for this, some of the older
airplanes are rigged in a manner to create more lift
on the wing that is being forced downward. The
more modern airplanes are designed with the engine
offset to counteract this effect of torque.
Generally, the compensating factors are permanently
set so that they compensate for this force at cruising
speed, since most of the airplane’s operating lift is at
that speed. However, aileron trim tabs permit further
adjustment for other speeds.
When the airplane’s wheels are on the ground during
the takeoff roll, an additional turning moment
around the vertical axis is induced by torque reaction.
As the left side of the airplane is being forced
down by torque reaction, more weight is being
placed on the left main landing gear. This results in
more ground friction, or drag, on the left tire than on
the right, causing a further turning moment to the
left. The magnitude of this moment is dependent on
many variables. Some of these variables are: (1) size
and horsepower of engine, (2) size of propeller and
the r.p.m., (3) size of the airplane, and (4) condition
of the ground surface.
This yawing moment on the takeoff roll is corrected
by the pilot’s proper use of the rudder or rudder trim.


GYROSCOPIC ACTION
Before the gyroscopic effects of the propeller can be
understood, it is necessary to understand the basic
principle of a gyroscope.
All practical applications of the gyroscope are based
upon two fundamental properties of gyroscopic
action: rigidity in space and precession. The one of
interest for this discussion is precession.
Precession is the resultant action, or deflection, of a
spinning rotor when a deflecting force is applied to
its rim. , when a force is
applied, the resulting force takes effect 90° ahead of
and in the direction of rotation.
The rotating propeller of an airplane makes a very
good gyroscope and thus has similar properties. Any
time a force is applied to deflect the propeller out of
its plane of rotation, the resulting force is 90° ahead
of and in the direction of rotation and in the direction
of application, causing a pitching moment, a yawing
moment, or a combination of the two depending
upon the point at which the force was applied.
This element of torque effect has always been
associated with and considered more prominent in
tailwheel-type airplanes, and most often occurs
when the tail is being raised during the takeoff roll.
This change in pitch attitude has the
same effect as applying a force to the top of the
propeller’s plane of rotation. The resultant force
acting 90° ahead causes a yawing moment to the
left around the vertical axis. The magnitude of this
moment depends on several variables, one of
which is the abruptness with which the tail is
raised (amount of force applied). However, precession,
or gyroscopic action, occurs when a force is
applied to any point on the rim of the propeller’s
plane of rotation; the resultant force will still be
90° from the point of application in the direction
of rotation. Depending on where the force is
applied, the airplane is caused to yaw left or right,
to pitch up or down, or a combination of pitching
and yawing.
It can be said that as a result of gyroscopic action—
any yawing around the vertical axis results in a
pitching moment, and any pitching around the lateral
axis results in a yawing moment.
To correct for the effect of gyroscopic action, it is
necessary for the pilot to properly use elevator and
rudder to prevent undesired pitching and yawing.

ASYMMETRIC LOADING (P FACTOR)
When an airplane is flying with a high angle of
attack, the “bite” of the downward moving blade is
greater than the “bite” of the upward moving
blade; thus moving the center of thrust to the
right of the prop disc area—causing a yawing
moment toward the left around the vertical axis.
That explanation is correct; however, to prove
this phenomenon, it would be necessary to work
wind vector problems on each blade, which gets
quite involved when considering both the angle
of attack of the airplane and the angle of attack of
each blade.
This asymmetric loading is caused by the resultant
velocity, which is generated by the combination of
the velocity of the propeller blade in its plane of
rotation and the velocity of the air passing horizontally
through the propeller “disc.” With the airplane
being flown at positive angles of attack, the right
(viewed from the rear) or downswinging blade, is
passing through an area of resultant velocity which
is greater than that affecting the left or upswinging
blade. Since the propeller blade is an airfoil,
increased velocity means increased lift. Therefore,
the downswinging blade having more “lift” tends
to pull (yaw) the airplane’s nose to the left.
Simply stated, when the airplane is flying at a high
angle of attack, the downward moving blade has a
higher resultant velocity; therefore creating more lift
than the upward moving blade.Thismight be easier to visualize if the propeller shaft was mounted perpendicular to the ground (like a
helicopter). If there were no air movement at
all, except that generated by the propeller
itself, identical sections of each blade would
have the same airspeed. However, with air moving
horizontally across this vertically mounted
propeller, the blade proceeding forward into the
flow of air will have a higher airspeed than the
blade retreating with the airflow. Thus, the blade
proceeding into the horizontal airflow is creating
more lift, or thrust, moving the center of thrust
toward that blade. Visualize ROTATING the
vertically mounted propeller shaft to shallower
angles relative to the moving air (as on an airplane).
This unbalanced thrust then becomes proportionately
smaller and continues getting smaller until it
reaches the value of zero when the propeller shaft is
exactly horizontal in relation to the moving air.
Each of these elements of torque effects vary
in values with changes in flight situations. In one
phase of flight, one of these elements may be more
prominent than another; whereas, in another phase
of flight, another element may be more prominent.
The relationship of these values to each other will
vary with different airplanes—depending on the
AIRFRAME, ENGINE, AND PROPELLER combinations
as well as other design features.
To maintain positive control of the airplane in all
flight conditions, the pilot must apply the flight controls
as necessary to compensate for these varying
values.

Answer 5

Well, you can look up several terms.

"P-Factor"
what causes "Left Turning Tendencies"

that should sum up what you need for the effects of the propeller and and the aircraft.

Answer 6

Here it is described;
http://en.wikipedia.org/wiki/Gyroscopic_precession#Torque-induced_precession.
After reading this I would make the assumption that the tail being lower than the center of gravity simply makes the condition more severe.

Answer 7

I was wondering much the same thing