Static rollover is no lift vector and about a 45 degree angle, pulled over by gravity. Dynamic is with a lift vector pulling lateral and the helicopter pivots to the point of 5-8 degrees and then pulled on over by the main rotor.
Thanks! Explanation also explains why helicopters have taken so long to reach today's level of sophistication. Complexities of helicopter flight also mean limitations. E.g. the presented retreating blade stall limits cruising speed severely. That is why tiltrotors are needed.
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 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...
Total bullshit, it was nothing but a static rollover start. If it would’ve continued to the critical angle, dynamic rollover cannot be stopped. Read the FAA is rotorcraft flying handbook.
I'm basically 15 and for some reason i enjoy learning about this stuff. Weird thing is that i actually get the stuff as i already have loads of aviation knowledge at such young age.
Awesome, I have a 17 year old going to his flight exam tomorrow for the helicopter license. I started his training when he was 14. You’ll learn fast at a young age.
The lift vector changes from vertical to more horizontal, which is a problem if there is a pivot point (like a skid). The cause could either be a stuck skid or that the cyclic is not centered for the pickup. In this video, a skid was stuck on fresh tar.
It is an interaction between rotor imbalance, and landing gear natural frequency and dampening, the main issue is when rotor frequency matches the landing gear natural frequency. Think the landing gear as a car suspension.
Also, I would imagine if you can do this in an R-22 you could help me do it in my R-44. Since I’m new to the aviation world, I wanna get as much safety training and dealing with any kind of mishaps as possible.
Three things needed rolling motion, exceedingly the critical angle, and a pivot point. Glad to see the response of dumping the collective before exceeding that angle!
Was this a supervised solo? I ask because the dual controls are still in. Lowering the collective immediately was the right thing to do. Curious though, the R-22 tends to pick-up right skid first (even with a 200 lb. guy in the right seat) Too much right cyclic? I am a 25 year Gold Seal/Master Instructor with a 99.8% pass rate on over 200 students. I tell my students ... "I'd rather you take 5 minutes and pick it up slowly than to raise the collective that fast." I know, everybody's got an opinion, right? I assume since you put the video on RU-vid you were looking for comments.
A fully articulated rotor system allows each blade to flap independently which creates moments where blade tip speeds vary from one another. The lead/lag hinge overcomes “Coriolis effect”. The helicopter flying handbook also has an explanation to reference.
Left pedal left pedal 😮 I’m still learning to pick up and don’t care how long it takes before the skids become light. Scary situation but good catch and way to start powering down to debrief and get the stress out before going back
Hi, back in '95 when I took my first CPL(H) in US the school gave me an interesting document (unfortunately lost), not sure if edited by RHC (Robinson) analyzing the different shape of the H/V curve during an approach. Summarizing the document was saying that since a descending helicopter controls a "gradual dissipation" of the high potential energy granted by his height from the ground, the standard H/V curve drown for high pitch settings doesn't apply. In that flight condition H/V curve is shrunk and higher from the ground leaving more room available for a safe flight condition and allowing to fly a linear tilted path (glide slope) that doesn't cut into it, as long as the approach path is not too steep. In all these years I searched for that or for a similar document with no results, did you ever run into this kind of information somewhere during your instructional career?
No I haven’t. I stress to my clients that the H/V diagram is not in the limitation section and we practice safe approaches without considering it. We use the reference for take off and slow flight. With the max performance take off being in the PTS, we often have to practice a take off in the shaded area. It is although, a speed/altitude configuration where the AVERAGE pilot MAY not be able to conduct a successful autorotation. I demonstrate autos for students in the shaded area to show how fast it all has to happen.
