Helicopter Swashplate Control 

Years ago I when I was at a university I would stop over and help a helicopter mechanic who maintained emergency choppers for medical evacuation to the hospital. I am a master mechanic by trade. This was just a perfect place to unwind with a fellow mechanic. We worked together like frick and frack. I found out he passed away which bummed me out. But I still have memories working with him. He was trained in the military. May God have mercy on his soul. Peace vf

Thanks! I appreciate that comment more than you know.

I just found this channel. This is great

​@@bzig4929you have done an awesome job, sincerely grateful ❤

Dumbing down is relative. I need dumber.

看完视频我感觉能制造了😂

thanks!

Sorry I read your comment wrong😅 my mistake

Well said sir!! Isn’t this an amazing channel?? I love the fact that you back him up with real knowledge and experience. Right on!!

The 120 degree swashplate and the angle between blades and blade actuators doesn't make it easier for people to understand. A simple 90 degree swashplate and no angle between blades and actuators would have been easier for people to understand. The 90 degree delay of gyroscopic presession could also easily have been explained. When I assembled my first RC heli I thought the manual was wrong because I didn't know about gyroscopic presession. Needless to say I had no control over the heli until I corrected my mistake ha ha.

@@dkjens0705 Even two bladed helicopters have the control horns at 45 degrees angles from dead aft or dead forward as this has to be done due to gyroscopic precession.

I think you have this stated incorrectly. Its not a matter of taking 90 degrees of rotation before there's any change. It's about gyroscopic precession; which is at 90 degrees to the force applied.

Glad it was helpful!

Glad you enjoyed it!

I'm not sure, but I think the software I use (blender) is used to make assets for gaming.

Glad you enjoyed it!

Thanks! Much appreciated coming from someone with your experience!

ive been in helos 20 yrs as a mechanic and found this to be the easiest explanation ive found. i would love to see a video on their explanation of gyroscopic procession as for as input goes. this has far reaching theory in that large heavy bikes are steered the same way. @@bzig4929

Borrowed from the Roger Rabbit film: "I've been a cab for 40 years!"

Don't get me wrong, the video, the animation and explanation are really good. But the notion of having large blades spin really fast, all the while controlled by high precision mechanisms, the entire assembly out in the open, susceptible to imbalance, constantly subjected to vibrations, is not particularly confidence inspiring. God forbid one of the many pins or joints or levers fails. Maintenance must be a nightmare.

Good suggestion! Also a challenge... helicopter mixing units are gloriously complex things.

Glad you liked it!

A few people have said this! I'm glad I was able to help people make that connection.

Thanks!

Thanks so much for those very nice words!

Welcome back!

Thank you!

I can relate to that. I've had a few employers tell me I ask too many questions about how something works. I'm an electrician, a really old one. Curiosity didn't kill the cat, it built a spaceship.

Short answer is... The centrifugal force loads as the blades rotate. I'm planning a future video to show the details on that. Thanks for watching!

Mechanically due to the pitch links they won't keep going up to that point. Like wings they are designed to take a certain amount of bending moment, and they begin to cone as collective is applied, when the system is at flight power and no collective is applied the blades fly at an angle called the "pre-cone angle" this is the blades producing enough lift for their weight but not yet enough to lift the helicopter off the ground. As the collective is increased the cone angle changes, and if the weight of aircraft exceeds the rating of the blades they can "egg beater", but this won't happen on the ground, you'll just run out of power(collective) and the blades will fly to a certain point and the drag they create will slow the whole system down, resulting in a low rotor RPM state and over torquing the system. Eggbeatering usually only happens if flight parameters exceed the limits of the system, such as if you are in a high speed descent, and you start to pull in collective, you aren't just trying to lift the weight of the helicopter but, you're also trying to arrest the momentum of the helicopter's movement as well, this can result in the blades snapping when they reach their limit and then looking like an old fashioned "eggbeater" to the outside observer. At this point the helicopter has the aerodynamics of a grand piano, and flies about as well, and there is nothing the crew can do to save themselves. This is usually the fault of the pilot and not the helicopter they have limits for a reason.

My vision with this is to do a series of videos that build on each other. The reason flapping and lead-lag exist are very specific and deserve a good explanation. I'm also trying to grow my animation skills and I need to learn how to do on-screen annotations for those topics. For the short answer... Flapping exists to correct for "forward flight dysemmetry of lift" and to allow control by tilting the tip path plane. Lead-lag allows for conservation of angular momentum as the blades flap asymmetrically. I love comments like yours! They really help me make the next videos better. Thanks.

Thanks for the comment!

I'm glad you find them useful. Thank you for watching!

that's my next video! I've started the story line and script and, once that's done, I'll start creating the video clips. Even though I'm reusing the same solid model, there is quite a bit of work to do to get them ready. In short... flapping allows the helicopter to fly fast and also allows control. But when it flaps the individual blade center's of gravity shift and this would create a problem with conservation of angular momentum... and this is what the lead-lag hinge solves. Constraining feathering under load... that's interesting... the blade pitch is close to the aerodynamic center, so loads are as low as they can be, but still significant. The answer, I believe, is robust components and lots of hydraulic pressure.

I had no idea they still used those in WWII! I found some photos online, but nothing that detailed. I'll keep looking.

Thank you very much!

I've been playing a future video on the aerodynamic reasons for flapping and lead lag. Droop stops will be part of that! Thanks for commenting.

The lead-lag degree of freedom can be eliminated with a type of rotor called a teetering rotor. In a teetering rotor, flapping occurs very close to the center of rotation. In the rotor system I animated, the flapping hinge is offset from the center of rotation and this causes two things that make a lead lag hinge necessary. The first is to relieve out-of-plane rotor forces when the rotor disk tilts on its virtual axis. This is due to Coriolis effect. The second reason is to allow for conservation of angular momentum. When the blades flap, their CG also moves inward. Much like an ice skater spins faster when she moves her arms inward, helicopter blades must spin faster when the flap away from neutral... The lead-lag hinge allows them to spin faster for the half cycle where they flap away from neutral, followed by spinning slower as they flap back towards neutral. Blades that don't lead-lag are called "stiff in plane" and these designs are possible, but not good for structural life of the blades.

@@bzig4929 excellent breakdown thankyou! I hadn't considered that at all.

I use Autodesk Fusion for 3d modeling, and then I import the models into Blender for materials, lighting and animation. Thanks for watching!

Thanks ✌️

Cool idea on the semirigid rotor! I'll need to figure out how to bend objects in the animation software. The main rotor, in this vid, is modeled after a ch-46, but the tail rotor and tail rotor drive is modeled after the S-92/Blackhawk. I had already done a ch-46, so I just copied that main rotor instead of creating a new one. The hawk also has the engine further forward with a nose gearbox... So the main transmission is also a little different.

@@bzig4929 Ah that's awesome, thanks for the clarification on the models it was based on!

The algorithm wants you to binge watch his catalog, either "play all" or just pick and choose. That's the highest scoring item in the equation, then sharing, then engagement. Your attention is absolute gold to YT. But commenting, liking and subs are pretty low scoring because they can't show you ads during BUT if you get replies, that's a conversation (comment, reply, reply) and that's focused attention.

It's just CF and the damping from the CF is sufficient that flapping doesn't need any springs or dampers. This doesn't address droop (negative flapping) when the rotors stop... This is handled with a mechanical droop stops that I didn't model in this simplified CAD model. Thanks for the question. I want to do a video on this exact subject... My day job keeps getting in the way.

Yes... CF loads. What's cool is that the CF loads increase as the blades flap away from neutral so it's a heavily damped system. Meaning that even aggressive maneuvering is unlikely to overlap the Rotors. My animation is greatly simplified and real helicopters have flap stops that are there for low rpm... Startup and shutdown. The stops are spring loaded so they are only in place at low CF (low RPM). if the blades were to contact a stop at high RPM - they can't because the CF loads overcome their spring force, and move them out of the way - but if they did, they would not protect the rotor. Loads are too high at flight RPM.

That concept is called "solidity". It's the ratio of the solid planform area of the rotor disk, to the empty platform area. Generally, for higher gross weight, you want higher solidity. So wider chord blades or more of them. I think the limiting factor to more-blades will be fitting the rotor controls into the narrowing space between the blades. The most blades is 7 on the ch53 and mi26. I could be wrong.

Good question! When you see how complicated these are, you'll understand why I didn't include that in the animation. If you do an image search on "helicopter mixing unit" you'll see what I mean. The complexity comes because each control on the flight deck has to influence all three hydraulic actuators, so they all have to get mechanically mixed before they connect to the pilot valves. And larger helicopters also do some non-traditional control mixing. The canted tail used in many Sikorsky aircraft would case a pitch change with pedal input if it were not dealt with at the design... So they mix in longitudinal cyclic commands with the pedal inputs. I may tackle the mechanical controls for a future animation, but it's a daunting task.

RC helicopters just use electric motors to actuate. They have a digital mixer in the remote.

good question... when rotating, the CF loads keep them from drooping or flapping excessively. As you shutdown the rotors, there is a spring loaded droop-stop that moves into position (moves in under spring tension, moves out under CF loads). If the droop stop malfunctions, the rotor won't be damaged as it would just come to rest against the limit of travel of the flap hinge... unless the blade hits another part of the aircraft as it's coasting to a stop. Droop stops are painted bright colors so a crew-chief, outside the aircraft, can visually check when they go in. Some aircraft procedures have the pilots pull the engines back to idle prior to shutdown for the purpose of getting confirmation that the droop stops are seated. I didn't animate the droop stops.