If it helps... I learned this stuff in the 80s/90s and I've been using it ever since, but trying to re-learn to the point of making a coherent (I hope) presentation has me going back over and over again to text books.
Your choice to not model the links between the collective/cyclic and the rotor system at this point is excellent. It avoids us getting distracted by trying to understand that complexity and focus just on what the controls do to the rotor system.
Coning is mostly influenced by the weight of the aircraft. This can be the actual weight, or the weight due to g loading. An autorotation is a 1g maneuver so coning is about the same as any other 1g flight condition.
Another solid video! You mentioned at 8:49 that absent of flapping, the dissymmetry of lift would cause higher lift in the advancing side and cause the helicopter to ROLL. You later mention that retreating blade stall causes a loss of lift on the retreating blade causing the helicopter to PITCH up caused by phase delay. Wouldn’t dissymmetry of lift also be subject to phase delay causing the helicopter to PITCH up? I also believe this action is the cause of Blow Back and what requires more forward stick input from the pilot. The amount of additional forward cyclic is proportional to the forward speed of the helicopter. This forward cyclic input in turn mechanically changes the pitch (less on advancing and more on retreating) of the blades and reduces (or eliminates) flapping due to dissymmetry of lift. (Pilot induced delta 3 hinge) One more crazy phenomenon. More induced flow at the rear of the disk in forward flight causing a reduction in AOA and lift resulting in a ROLL to the advancing side. Curious to hear your thoughts. I could very well have some (or all) of this wrong.
my thoughts... if there were no flapping hinge, the aircraft would roll due to FFDOL, but the flapping prevents this increased lift from ever happening. And you are correct... this is what leads to blowback of the rotor disk. Instead of a left roll, there is blowback due to FFDOL. But this doesn't cause the aircraft to pitch up... the rotor disk pitches up (blowback) but not the aircraft. The autogyro pioneers were the first to figure this out. I believe de la Cierva attempted a rigid rotor and only after seeing the controlability issues did he add the flapping hinge. I can see why you say "a pilot induced delta 3." Delta 3 creates a natural coupling between flapping an feathering. So if the pilot changes feathering based on the blow back... I get the analogy. It's interesting now that many are attempting to develop eVTOL aircraft without flapping hinges (like Joby, Archer, Beta) I understand, with side-by-side rotors, they won't see the issues de la Cievra saw on a single rotor autogyro, but all of those rolling moments have to go somewhere. If it isn't a control moment, it will be loads absorbed by the rotor masts and the airframe. I wonder if their flight test campaigns will point them to the same epiphany of Cievra. I think your last point is talking about transverse flow and this is one of the many subjects I didn't cover in the video. I have a book written by Sikorsky (the company, not Igor) "Sikorsky Helicopter Flight Theory for Pilots and Mechanics" This book deals with these subjects much more completely that I can do in 10-15 minute videos. It would probably take 10 hours to cover the materiel in the same depth as a book. Hopefully these videos stimulate questions and thoughts that point viewers to other sources and more study. Stay curious!
@@bzig4929 I truly appreciate the amount of effort you’ve put into this and the amount of knowledge you have on this subject. In my opinion, helicopters are one of the most fascinating mechanical things in the world! I have a copy of Helicopter Theory by Wayne Johnson. I’ll have to pick up a copy of Sikorsky Helicopter Flight Theory for Pilots and Mechanics. I still struggle to understand why the helicopter would roll due to FFDOL. I need to do some more research. If you want to pitch the rotor in any direction, you increase (or decrease) the lift 90 degrees (or whatever phase delay angle the system has) behind that intended direction. What scenario will a rotor tilt in the exact direction where the lift changes? That is where I am getting lost. As far as blow back pitching the rotor and not the heli, I can see that being true for a semi rigid head but not a fully articulated head. Any pitching of the rotor on a fully articulated head will induce a moment on the helicopter due to the offset hinge. Full transparency here, I most definitely could be misunderstanding something here! I too have thought a lot about these eVTOL aircraft. They make zero sense by the way. I can’t come up with a single scenario where they are successful. The blades must be subjected to significantly more stress than a helicopter blade due to their rigid design. It’s probably within the design envelope as traditional airplanes experience the same dissymmetry at high alpha with the descending blade having a higher angle of attack. The rolling moment gets thrown into the airframe and is balanced by the counter rotating blade on the other side of the fuselage. (At least that’s my theory) I don’t mean to challenge you in any way. I respect your opinions greatly. Many beers could be drank discussing helicopter theory but I think most people would lose interest fairly quickly. I look forward to your next video.
Something that came to mind the other day, I don't think centrifugal forces are the only forces applied to the rotor hub. Considering that while flapping, a blade has angular momentum, as that blade turns, and the flapping hinge changes the plane of rotation, some of that rotation must be converted to a linear force. Take this example: The advancing blade on the right has an upward flapping velocity. This is constrained by the flapping hinge. By the time that blade has rotated 90 degrees counter-clockwise, now at the forward blade position, all angular velocity from the right position is 90 degrees out of plane, meaning it is now applying a twisting force along the span of the blade. Constrained by the flapping hinge, this applies an additional linear force on the rotor hub.
I need to do another video about lead-lag. Lead-lag exists to correct the changes in angular momentum due to flapping. As the blade flaps up, the CG moves inward... making the blade want to advance. Because it can't, due to conservation of angular momentum, it leads forward. Then it lags aft when it flaps down.
@@bzig4929This explanation video will be cool. When writing the script, please take note that at least I am confused by your use of advance here. I would interpret that the same as leading, but that can’t be so, because you’re saying they are different.
@@bzig4929 Just a side note on why helicopters are far more expensive than fixed wing, per pound of payload capability. Each blade is continually flapping, AND lead/lagging, AND long axis twisting, for each single cycle of hub rotation. For a rotor speed of 324 rpm (+ 9% / -4%) for one model of light helicopter, so too are all the bearings hub and blade grip interface, constantly reversing at the same frequency. Obviously wear is far accelerated, and materials used must be top purity of hardness and/ or compliance. One axiom I've heard is: " A helicopter is a large collection of spare parts, all flying in formation, and wanting to fling themselves to pieces" 😱 The best damn helo pilot I've ever seen was a former Cobra pilot in Nam. In his middle age he flew AS315 Lama. I once saw him regularly hold a 100 foot long line with ballast ball and hook in high hover for 3-5 minutes at a pick, while pipeline handlers below were manipulating their choke cables. The ball was about 5 feet above their heads, and all that time never swayed more than 6" in radius. When he was signaled by the pipe handlers he gently lowered the hover by 7 feet, to ground the static braid and they hooked it up, and away he went. A true skyhook master. He had told me that he had "bent a bird", several years earlier. I did not ask him to elaborate, as his answer was terse. He had several 1000 hrs in Helos. Several years later, I asked his fueler guy what happened too him. FG said "He had another accident, some bearing had failed, but he wasn't hurt. However immediately retired, saying he wasn't going to risk a third time as that would be the end of him, and his mother needed him for home care." So that was that
I'm not really sure what "Sikorsky shake" is. All helicopters have vibration modes. But I think most pilots don't experience tip stall because they stay withing the limits on the aircraft. Sikorsky seems to take pride in high Vne aircraft so I think this would be especially true for that product line. Tip stall, in aircraft with hydraulics, is often not felt by the pilot until it gets pretty bad. I flew CH46s and that aircraft had an indicator... They put strain gauges on the control links at the rotor and fed that into a gauge for the pilots to show tip stall approaching.
@@bzig4929 I’ve only heard Sikorsky Shake a few times over the years, but my recollection is that several pilots described it as a common trait with all Sikorsky helicopters, and that the company even had to add a vibration damping system into their rotor systems. But a quick Google doesn’t find more than a couple of references. But Google can’t find a lot of things it used to. Maybe the dynamics of the Vertol twin rotors is different enough the dynamics are different?
Wonderful vid again. Amazing the engineering in a rotor head. I fly large RCs 700 size with 5-foot Dia rotor disc and I have a two blade and three blade 700. My favorite thing is take offs and landings. Can hold them in a perfect hover as well. If I had 15 million sitting around, I would own a Bell 429 or AS355.
if someone gave me a 429, out-right, I probably couldn't afford the operating costs :) RC helicopters are amazing. It's hard to believe the same physics of flight apply to RC helos, doing 3d aerobatics, as applies to manned helicopters.
@@bzig4929 Absolutely true, the bigger the RC the more it behaves like a full size. The blade chop on my two blade is amazing, luv that sound, kinda like a Huey. It also autos nicely. As for the operating costs on the 429, I heard to run a Sikorsky Sky Crane around 140k per hour!
@@rcas350pilot8Yes, and their pilots get insulted if you start asking silly questions like why wheels instead of skids and calling that beast a chopper. Don’t ask me how I know! (Skids are for kids, and don’t ever equate a Skycrane with a motorcycle.)
I may try that for a short. I'm processing the videos in davinci resolve... I think that can do 4k. The resuloution coming out of the animation software may also be limiting, but it will be fun to try.
here's an unlisted clip that I did in 4k. let me know of you think it looks any different. To me, it's about the same as my other videos, so the limitation is the rendered clips coming from the animation s/w. I suppose it makes sense that processing low-res clips in 4k is still low res. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-pPkUydVIXiI.htmlsi=AYRGYJGx9SVa-4MT
@@bzig4929 That 4K one definitely looks better, by a quite a noticeable margin on my 48" 4K OLED. Small details on the blades and tail rotor drive shaft are very much enhanced compared to a similar scene in the original at 1:50, for example. And on the later hub close-up too. It would be best to render at 4K high quality first, of course, but whatever you did worked for me at least. Your animation is so nice it's a shame to hide it!
