Ohhh, so this is what it is! I've flown large-scale model helicopters before transitioning to drones and when making a fast descent, it sometimes felt like the 'pillar of air' the helicopter was sitting on just broke away underneath it and it took time and lots of collective to recover. I had little knowledge of aerodynamics back then, so I thought of it as a kind of stall. Seems like I wasn't that off. Thank's for the great explanation!
My understanding (and this may be a gross over simplification), is if you descend too quickly, the blade near the rotor hub begins to stall, resulting in loss of lift. Loss of lift results in an increased rate of descent, which propagates the stall along the blades unless you get back into forward flight?
Its amazing how clearly and succinctly you are able to explain concepts with some paper, a pen and 5 - 10 minutes. I know you've been inactive for a while, but if youre reading this I just wanna say thank you so much. Your content is helping me pass my CPL
Thank you for the nice videos, Jacob! The way I like to describe the difference is that VRS is an aerodynamic condition whereas settling with power is a performance condition. Settling will be your performance condition when in a VRS. That’s what makes the VRS hazardous! But VRS is not a prerequisite. There are several other ways to get into settling with no secondary vortex. These include heavy weight high density altitude approaches to landing, possibly to a pinnacle, where your power required is nearly equal to power available and you have no power margin to slow the helicopter any further. The desired flight path cannot be maintained without adding more power, power that is not available, and so the rate of descent will increase as translational lift is lost. In the best case you exceed engine limits to make a safe landing. In the worst case you have a hard landing and rollover. Another time it can happen is with low rotor rpm. Of course, settling can easily lead to the formation of a secondary vortex and a developed VRS once the increasing rate of descent induces a sufficient upflow. Sounds like the powerful Apache might actually be able to break out of incipient VRS with additional power. This technique is not taught in the world of light general aviation helicopters as it is considered counter-productive to recovery.
Ray Nixon. Well said. But I tend to disagree with some parts. Many people get wrapped around the word "Settling" whether it be with "insufficient" or "sufficient" power. Settling with power (sufficient power that is) is associated with a Vortex Ring State because increasing power intensifies the ring state and increases rate of descent. The airflow is simply not conducive to flying despite the aircraft having plenty of power available. Even with a large power margin, the rate of descent cannot be arrested due to the ring state only being further aggravated with power application. This is drastically different from settling with insufficient power. This condition occurs specifically from operating a helicopter with very little power margin and a sink rate is allowed to develop greater than can be arrested (based on aircraft climb/descent performance charts). As the helicopter decelerates less than ETL it falls even faster at a rate that's unrecoverable. This is simply poor planning, power management, and poor pilot technique. This condition doesn't even require a Vortex Ring State to be present in order to occur. I think it's important to distinguish the differences between these 2 types of settling because one deals with an aerodynamically turbulent environment and the other deals with power management. Thanks for your thoughts though. I appreciate the feedback.
Helicopter Lessons In 10 Minutes or Less Thank you, Jacob. It’s obvious now these two concepts are intertwined more than I had realized. I don’t know what it is about your videos that I like so much. They are simple, they foster such a clear understanding of the topics in a very short time frame, but your videos are also simply enjoyable and entertaining to watch. Please keep them coming. I am a flight instructor candidate like you and I’m looking for ways to deliver clarity. Btw, can you suggest where I might locate some of the Army training materials that you learned from, particularly what Army aviation has to say about settling and VRS?
Ray Nixon. Thanks! I use a combination of many sources for my videos. The printed books I use are linked in my videos in the bottom of the descriptions. As far as Army references you can try googling TC 3-04.4 Fundamentals of Flight.
Ray Nixon They are not intertwined. Settling with power is akin to not stopping fast enough in your car. All the brake pedal is applied but the car is moving too fast or too heavy(or a combination of both) to stop at your desired point or time. Same thing in the helicopter. Too fast or too heavy(due to load or conditions, think high and hot) for the power reserve available to arrest the descent rate. Hence SETTLING WITH POWER. The disk is still producing lift and lots of it, just not enough to arrest the sink rate at current conditions. Vortex ring state can occur at any weight and with any conditions. You need low airspeed(below ETL), a descent rate of 400-800 ft/min(dependent on model) and some power(no power would be an autorotative state so any amount of power is necessary to induce VRS). VRS involves an increase in rate of descent airflow from below. The ROD airflow cancels out some of the induced flow on top which causes the angle of attack to increase. If left unattended in ideal VRS conditions the blade roots will stall as the ROD airflow completely cancels the induced flow(at the root). this puts the relative airflow inline with the plain of rotation of the disk which means the angle of attack is well beyond max limits. Stalled blade roots means less lift which means an increased rate of descent. Increased rate of descent means more ROD airflow which cancels out more induced flow across the rest of the blades. ROD flow cancelling induced airflow equals very high angles of attack. The viscious circle continues until rectified or contact with the earth at a high rate of descent. Adding power aggravates the problem as you are simply increasing the angle of attack which will cause more blade area to stall. The difference between settling with power and VRS as others have pointed out is that VRS is an aerodynamic condition that is caused by poor piloting. Settling with power is a performance condition that is also caused by poor piloting. You can have settling with power without VRS. And you can have VRS without settling with power. The inability to arrest the sink rate is the only commonality between the two. Their causes and cures are not mutually exclusive.
I’m sure to speak for the silent majority. Please keep em videos coming as the topics and the narrative technique is top of the line. The competence is obviously undebatable.
It would be a great if you could do a video explaining skids and slides and how that looks and proper use of pedals and cyclic to correct it. I have the sift in July. You’re video are amazing as always.
Hi Jacob, very much appreciated that you do not state that VRS and settling with power are the same event. Closely related but they are not the same as the reached limit of power in settling doesn’t necessarily occur in VRS. Believe sidestepping out (vuichard) taught in Europe is a great way or recovering VRS.
I paused at 2:44. The blade root does have a slower "airspeed", therefore less lift.. But, the blade tip is pitched flat and producing near no lift, if even negative lift, at lower altitudes. How do we know this? Coning. When the aircraft gets into high altitudes (~15kftMSL) the blades cone, which means the tips of the blades are producing the lift in the thinner air. So, your drawing is accurate for how coning occurs, not for how low altitude lift is produced across the length of the airfoil. Further proof: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Pu48f7s5Ru8.html Watch how the tip dips below the middle of the length early after the upward flap is complete.
Some questions. 1. Did this used to be called 'Dirty Air"' 2. Does this only happen in a non moving hover state? 3. Once in a VRS and with enough altitude is it simply a matter of moving out of it to regain lift? 4. What IS the minimum altitude to recover? Ive seen video of, I think, a Royal Navy Helo hovering at an air show and this happened causing a crash even at full power. He was too low to avoid it.
So if I'm understanding you correctly when a helicopter is hovering it is stationary in altitude so there's no air coming up from the bottom to cause vortex ring State versus the cause of vortex ring state is when a helicopter is descending the air is being pushed up towards the blades and you develop early in late stage vortex ring state. So the reason the helicopter can stay in a hover is its altitude is constant and there's no air coming up is that correct? I wonder how these large helicopters can stay in a hover so long and not fall outoof the sky.
Awesome videos! Also I love the Apache clips. I wish you would make some video(s) showing those helos flying around just because they are the most cool helos out there :)
VRS isN'T SWP, because in the former the rotor is INeffective, while in the latter it provides lift efficiently - yet not enough for the *intended* spontaneous flight trajectory.
Hey Jacob. Thanks a lot for the tutorial. A small query- is there any chance of falling into vortex ring from OGE hover to touchdown in a confined area? Say, in tail cross wind? Thanks...
You could. But when you got into ground effect it would start to dissipate and break up some of the rotor vortices. If you got into VRS at 300’ AGL, there may not be enough time to recover by IGE. If you got into VRS at 50’ AGL you could probably recover in time.
Increase of throttle would increase thedrop rate, is that because of earlier stall at higher angles of incedence and attack? PS: yours are excellent video lectures!!!
zofe. Increasing throttle/collective could potentially aggravate the situation and cause the drop rate to increase because it exacerbates the formation of vortices in the rotor system. Thanks for the feedback!
No, they are two different things. In the Navy, both terms are used, but for two different conditions. See the comments below Mr. Ray Nixon's as an example of power settling.
Thanks for trying to educate pilots, but you got this one a little incorrect. VRS and SWP are two different conditions. VRS is when you descend too quickly into your own down wash causing the rotor tip vortices which is best illustrated by ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HjeRSDsy-nE.html video. SWP is when full power is not sufficient to hold an out of ground effect hover (OGE). SWP can turn into VRS if you don’t arrest the decent by getting back into ETL. The classic situation is taking off from airport and trying to land on top of mountain in confined area without checking OGE hover before descending into confined area. The density altitude combined with high gross weight causes SWP. Helicopter simply doesn’t have power to hold the altitude. To prevent SWP you should check to make sure you can hold altitude before descending into confined area.
Agreed with the video. VRS and SWP are two different things. The video explains it clearly. Sorry, "Gary" (if that is your real name!) you didn't get it and wanted to post your resumé. VRS - bad but you can get out of it. SWP - bad but you can get out of it only do it quicker. Posting your resumé on youtube - worse and you can't get out of it. E (no resumé necessary when you're not making up bs.)
Not generally you touch something that creates a pivot point. This could be a tower obstacle that you didn’t see while flying. Or if you have complications with a sling load or water bucket you could possibly roll over if the line get snagged on landing gear enough to drastically shift the center of gravity.
CAN YOU PLEASE MAKE A VIDEO TO EXPLAINED WHAT EXACTLY IS BLADE FLAPPING ANGLE AND HOW IT IS RELATED WITH THE AZIMUTHAL ANGLE. AND WHAT RELATION THEY ARE HAVING WITH EACH OTHER
Please pay attention! I have flown Sikorsky products for almost 3 decades and I get frustrated watching and listening to so-called informative videos. There are THREE terms that are relevant. TWO of them are: VORTEX RING STATE and POWER SETTLING and they are the SAME in terms of what happens on steep, low power descents in light or nil winds resulting in the helicopter descending in its own turbulent column of air with a rapid descent rate - resolved by forward or lateral cyclic to get out of the turbulent “dirty air” from rotor down wash. Actually you described it accurately. BUT, the THIRD term is SETTLING WITH POWER (subtle, but critical difference from “POWER SETTLING”). SETTLING WITH POWER is the MISMANAGEMENT OF AVAILABLE POWER. Typically a fast, flat Transition to the Hover (TTTH) with low torque/ power and a steep, nose-high flare. At the intended landing spot depending on weight, wind, DA there may not be sufficient power available to retard the descent rate as the helicopter is levelled for landing - new and inexperienced pilots trying to be “cowboys” and save time are usually the ones who get into trouble, although experienced pilots can as well. When I was in the Navy flying H-3s we would sail from a cold climate and rapidly enter the Gulf Stream for a huge temp difference - handling techniques that were OK in the cold may not work in warm temps. Of course, the solution is to plan the transition well back and “load the head” early and, as you approach there is time to assess if you have enough power to hover or if you need to wave off and burn off some weight; otherwise you end up bouncing off the water - resulting in having an awkward conversation with the Ship’s Captain explaining why you are a bonehead. In summary, your explanation was very good but would have been completely accurate if you wrote POWER SETTLING instead of SETTLING WITH POWER, but to make a point to explain the subtle, but significant difference in the terminology. And perhaps state that a separate video on SETTLING WITH POWER is forthcoming?
Roman Rajesh. The biggest difference for articulated rotor systems compared to rigid or semi-rigid rotor systems is the ability of the rotor to absorb/handle stresses placed on it. Articulated rotors have many more hinges or pivot points so that the blades themselves aren't absorbing the stresses of flight. Generally speaking, articulated rotor systems tend to be 4 bladed and low inertia systems by design while semi-rigid systems tend to be 2 bladed and high inertia. This affects autorotations with differences in response times needed to enter an autorotation before dropping rotor rpm. For instance, the older 2 bladed high inertia Huey helicopters can experience engine failure and have up to 3-4 seconds before rotor rpm begins to decay below normal limits. However, some of the newer articulated systems can have rapid rotor rpm decay with a second or 2 after engine failure due to its low inertia rotor system. I hope this helps answer your question.
ok sure:) To be clear " 4 bladed articulated heli is safer because it has more reaction time if motor fails and autorotation begins faster than 2 bladed heli. ?
Roman Rajesh. I wouldn't necessarily say one system is safer than another. A low inertia rotor system (typically associated with 4 bladed systems) can speed up and slow down faster than a high inertia rotor system. This can mean rotor decays faster but also can recover faster. High inertia rotor systems are more forgiving at the onset of engine failure, but can be harder to recover if rotor decays too much. Think of high inertia has bigger, heavier blades that are more resistant to change. They speed up and slow down slower. If the engine fails, these blades have a lot of momentum to keep them turning. The reverse is true for low inertia rotors. Low inertia rotors are lighter and therefore easier to speed up/ slow down. Great question! I hope this helps.
