Dynamic Rollover
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- Опубліковано 11 жов 2024
- Dynamic Rollover can happen with a pivot point, a rolling moment, and reaching the critical angle of 5-8 degrees. Picking up the helicopter with a two step process is so important and can prevent a roll over. The only action a pilot can take to attempt recovery during a roll over is to lower the collective. Visit www.clevelandhelicopterservices.com and check out our competitive pricing on helicopter pilot training and helicopter ferry services. Like us on FB at / clevelandhelicopterser...
EASY AND QUICK EXPLANATION TO UNDERSTAND, THANK YOU FOR YOUR TIME
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When you watch videos of these dynamic rollovers they're so quick, you better be Johnny-on-the-spot. Some kind of software fix for this would be nice but I'm not sure how far choppers are along w/ the fly-by-wire stuff. Just a little black box - once that tipping point is just about reached, emergency correction.. Be nice!
Interesting but where did you get a solid 5-8 degrees. I disagree with that. Critical rollover angle changes with the amount of the rolling moment. I submit to you it's possible to have a critical angle that is 0 if you develop a rolling motion high enough. Nothing a pilot can do past the critical angle to recover. The one thing the pilot can control best is the rolling moment. He does that with collective, not snatching it off the ground, and not snagging anything in a hover, and maintaining a slow hover.
That is straight out of the helicopter flying handbook, published by the FAA. When doing flight instruction it is important to stick with the Faa published information and not your opinion.
@@garycleveland2989 Someone deleted my reply...
@@garycleveland2989 5-8 degrees is what the HFH states about the cyclic authority on most helicopters, and also as a general guideline to abort an upslope maneuver. That is not the critical angle. Most helicopters have a slope landing limit of at least 5-8 degrees and more so how could that be the cause of dynamic rollover of exceeding 5-8 degrees slope or rotor disk angle or however else you want to put it. Critical angle is how it needs to be taught.
The rate of rolling motion is also
a consideration because, as the roll rate increases, there is
a reduction of the critical rollover angle at which recovery
is still possible.
Dynamic Rollover
A helicopter is susceptible to a lateral rolling tendency,
called dynamic rollover, when it is in contact with the surface
Tail rotor thrust
Tip-path plane neutral cyclic
Tip-path plane full left cyclic
Bank
Pivot point angle
CG
Weight
Main rotor thrust
Figure 11-5. Forces acting on a helicopter with right skid on the
ground.
during takeoffs or landings. For dynamic rollover to occur,
some factor must first cause the helicopter to roll or pivot
around a skid or landing gear wheel, until its critical rollover
angle is reached. The angle at which dynamic rollover
occurs will vary based on helicopter type. Then, beyond
this point, main rotor thrust continues the roll and recovery
is impossible. After this angle is achieved, the cyclic does
not have sufficient range of control to eliminate the thrust
component and convert it to lift. If the critical rollover angle
is exceeded, the helicopter rolls on its side regardless of the
cyclic corrections made.
Dynamic rollover begins when the helicopter starts to pivot
laterally around its skid or wheel. For dynamic rollover to
occur the following three factors must be present:
1. A rolling moment
2. A pivot point other than the helicopter’s normal CG
3. Thrust greater than weight
This can occur for a variety of reasons, including the failure
to remove a tie down or skid-securing device, or if the skid
or wheel contacts a fixed object while hovering sideward,
or if the gear is stuck in ice, soft asphalt, or mud. Dynamic
rollover may also occur if you use an improper landing or
takeoff technique or while performing slope operations.
Whatever the cause, dynamic rollover is possible if not using
the proper corrective technique.
Once started, dynamic rollover cannot be stopped by
application of opposite cyclic control alone. For example,
the right skid contacts an object and becomes the pivot point
while the helicopter starts rolling to the right. Even with full
left cyclic applied, the main rotor thrust vector and its moment
follows the aircraft as it continues rolling to the right. Quickly
reducing collective pitch is the most effective way to stop
dynamic rollover from developing. Dynamic rollover can
occur with any type of landing gear and all types of rotor disks.
It is important to remember rotor blades have a limited range
of movement. If the tilt or roll of the helicopter exceeds that
range (5-8°), the controls (cyclic) can no longer command a
vertical lift component and the thrust or lift becomes a lateral
force that rolls the helicopter over. When limited rotor blade
movement is coupled with the fact that most of a helicopter’s
weight is high in the airframe, another element of risk is added
to an already slightly unstable center of gravity. Pilots must
remember that in order to remove thrust, the collective must
be lowered as this is the only recovery technique available.
Critical Conditions
Certain conditions reduce the critical rollover angle, thus
increasing the possibility for dynamic rollover and reducing
the chance for recovery. The rate of rolling motion is also
a consideration because, as the roll rate increases, there is
a reduction of the critical rollover angle at which recovery
is still possible. Other critical conditions include operating
at high gross weights with thrust (lift) approximately equal
to the weight.
Refer to Figure 11-5. The following conditions are most
critical for helicopters with counterclockwise rotor rotation:
1. Right side skid or landing wheel down, since
translating tendency adds to the rollover force.
2. Right lateral center of gravity (CG).
3. Crosswinds from the left.
4. Left yaw inputs.
For helicopters with clockwise rotor rotation, the opposite
conditions would be true.
Cyclic Trim
When maneuvering with one skid or wheel on the ground,
care must be taken to keep the helicopter cyclic control
carefully adjusted. For example, if a slow takeoff is attempted
and the cyclic is not positioned and adjusted to account for
translating tendency, the critical recovery angle may be
exceeded in less than two seconds. Control can be maintained
if the pilot maintains proper cyclic position and does not
allow the helicopter’s roll and pitch rates to become too
great. Fly the helicopter into the air smoothly while keeping
movements of pitch, roll, and yaw small; do not allow any
abrupt cyclic pressures.
Normal Takeoffs and Landings
Dynamic rollover is possible even during normal takeoffs and
landings on relatively level ground, if one wheel or skid is on
the ground and thrust (lift) is approximately equal to the weight
of the helicopter. If the takeoff or landing is not performed
properly, a roll rate could develop around the wheel or skid
that is on the ground. When taking off or landing, perform the
maneuver smoothly and carefully adjust the cyclic so that no
pitch or roll movement rates build up, especially the roll rate.
If the bank angle starts to increase to an angle of approximately
5-8°, and full corrective cyclic does not reduce the angle, the
collective should be reduced to diminish the unstable rolling
condition. Excessive bank angles can also be caused by landing
gear caught in a tie down strap, or a tie down strap still attached
to one side of the helicopter. Lateral loading imbalance (usually
outside published limits) is another contributing factor.
Slope Takeoffs and Landings
During slope operations, excessive application of cyclic
control into the slope, together with excessive collective pitch
control, can result in the downslope skid or landing wheel
rising sufficiently to exceed lateral cyclic control limits, and
an upslope rolling motion can occur. [Figure 11-6]
When performing slope takeoff and landing maneuvers, follow
the published procedures and keep the roll rates small. Slowly
raise the downslope skid or wheel to bring the helicopter level,
and then lift off. During landing, first touch down on the
upslope skid or wheel, then slowly lower the downslope skid
or wheel using combined movements of cyclic and collective.
If the helicopter rolls approximately 5-8° to the upslope side,
decrease collective to correct the bank angle and return to level
attitude, then start the landing procedure again.
Use of Collective
The collective is more effective in controlling the rolling
motion than lateral cyclic, because it reduces the main rotor
thrust (lift). A smooth, moderate collective reduction, at a
rate of less than approximately full up to full down in two
seconds, may be adequate to stop the rolling motion. Take
care, therefore, not to dump collective at an excessively high
rate, as this may cause a main rotor blade to strike the fuselage.
Additionally, if the helicopter is on a slope and the roll starts
toward the upslope side, reducing collective too fast may create
a high roll rate in the opposite direction. When the upslope skid
or wheel hits the ground, the dynamics of the motion can cause
the helicopter to bounce off the upslope skid or wheel, and the
inertia can cause the helicopter to roll about the downslope
ground contact point and over on its side. [Figure 11-7]
Under normal conditions on a slope, the collective should
not be pulled suddenly to get airborne because a large and
abrupt rolling moment in the opposite direction could occur.
Excessive application of collective can result in the upslope
skid or wheel rising sufficiently to exceed lateral cyclic
control limits. This movement may be uncontrollable. If the
helicopter develops a roll rate with one skid or wheel on the
ground, the helicopter can roll over on its side.
Precautions
To help avoid dynamic rollover:
1. Always practice hovering autorotation into the wind,
and be wary when the wind is gusty or greater than 10
knots.
2. Use extreme caution when hovering close to fences,
sprinklers, bushes, runway/taxi lights, tiedown cables,
deck nets, or other obstacles that could catch a skid or
wheel. Aircraft parked on hot asphalt overnight might
find the landing gear sunk in and stuck as the ramp
cooled during the evening.
3. Always use a two-step lift-off. Pull in just enough
collective pitch control to be light on the skids
or landing wheels and feel for equilibrium, then
gently lift the helicopter into the air. 4.
Hover high enough to have adequate skid or landing
wheel clearance from any obstacles when practicing
hovering maneuvers close to the ground, especially
when practicing sideways or rearward flight.
5. Remember that when the wind is coming from
the upslope direction, less lateral cyclic control is
available.
6. Avoid tailwind conditions when conducting slope
operations.
snip
You should teach your students past the rote memorization part and get to the correlation part.
@@PilotLifeNet my channel was created to prepare my students for the oral part of their practical test. Answers must be brief and it is up to the examiner to pry further if desired. My channel is not monetized. If you wish to make a video expressing your detailed explanation, go for it.
@@PilotLifeNet HELLO, FOR MY OPINION . TOO TOO LONG BUT IS A GOOD SUPPLEMENT OF INFORMATION, BUT YOU PLACED SEVERAL REFERENCES TO FIGURES AND YOU DID NOT PLACE THEM...
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Thanks for explanation