Lecture 8: Helicopter Aerodynamics
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- čas přidán 28. 06. 2024
- MIT 16.687 Private Pilot Ground School, IAP 2019
Instructor: Philip Greenspun, Tina Srivastava
View the complete course: ocw.mit.edu/16-687IAP19
CZcams Playlist: • MIT 16.687 Private Pil...
This lecture focused on the aerodynamics of helicopters.
License: Creative Commons BY-NC-SA
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I found Philip Greenspun on the internet years ago purely by accident. Being a fixed wing pilot, I was impressed by his aviation accomplishments. I am equally impressed by his teaching skills. Nicely done.
And here I was waiting for a good explanation of gyroscopic precession...
I think VSauce’s explanation is probably the best I’ve ever seen.
czcams.com/video/XHGKIzCcVa0/video.html
“Let’s ignore it because no one understands it anyway” 😂😂?
Oh glad your comment was top row, I was searching for this too. Good day
🤣🤣 bad luck
Here's the best explanation I've ever seen and it finally clicked for me.
Basically if you wanted to till the orbit of a satellite, you would have to add the thrust to change the angle 90 degrees before the position you wanted to have the max "up" deflection. Here's the video though.
czcams.com/video/n5bKzBZ7XuM/video.html
A helicopter is a Hilly Ka Flopter. A main rotor system is a Twirly Flipter. A tail rotor's a Fizzy Gig. Hoppy Flopter & Hilla Ka Flopter are also names for complete helicopters along with Twirly Gig & Flying Soap Bubble. The collective pitch is a Up Lever. Keep this in formation in your heart & never forget it, for its gospel truth. Helicopters beat the air into submission.
Took a look at this before having to teach a lesson about helicopters to some of my younger Air Cadets. SO useful, I now understand so many more things about how these aircraft work.
05:00 "Where the airflow becomes turbulent". Turbulence is actually one phenomenon that helps delaying blade stall as the flow remains attached for a longer chordwise length. I think the correct term is here "separation", not turbulence
Its more complicated than either, but the zone in question does become turbulent. The turbulent boundary layer you are thinking of is an increased energy state, while the separation bubble is a decreased energy state. The turbulent boundary layer is better thought of as micro vortexes than chaotic "turbulence". Similar to the way wingtip vortices are refered to as wake turbulance.
Separation as normally explained is not really a complete notion, or you would have a perfect vacuum over the wing and extremely high lift. The laminar bulk flow separates and space is filled with chaotically turbulent fluid with little net bulk flow direction.
If we are talking about a transition to a turbulent boundary layer before an adverse pressure-gradient on the aft portion of the upper surface of a lifting wing, then yes, turbulence improves lift.
Under any other situation, its not going to improve lift.
E.g. A wing will generate vastly more lift with laminar flow than turbulent over the forward portion of an airfoil: Liebeck.
Helicopers have strange blade oscillations which create a situation of an extreme hysteresis loop, one that not only causes the stalled airflow to re-attach at a much lower angle of attack than it initially stalled at, but actually allows the blade to generate a higher Lift Coefficient than is theoretically possible with its airfoil series. E.g. Naca 23012 achieves CLmax of 1.65 steady state, but can actually exceed CLpeak of 2.1-2.3 when oscillated approximately 5 cycles per second. (Or pitched up abruptly in an airplane, it can also achieve substantially higher CLmax and cause an over stress unless a modified lower Va speed is used than would ordinarily be computed).
Fantastic lecture, I loved the examples peppered throughout, answered all of my general questions.
Interesting topic, great speaker, nice presentation and some good questions.
Overall a great video, thanks!
Very helpful to future students! Great work! Thank you!
It is an honor to watch this!
Why tailrotor control at the pitch pull in autorotation? On larger heli’s like the Huey, etc., friction from the transmission may add need for OPPOSITE yaw correction. (In a Huey, that would RIGHT pedal.). Feels strange.
Helicopters! Amazing flying machines!
The swash plate could also be called the air flogger, and the formula loosely translated to.... enough air flogged into submission, lift is created.
I'm writing this on my exam in the explain lift section.
Professor, rigging depends on the aircraft and the mast is NOT tilted to the side, but the controls are sometimes, depending on aircraft may or may not be rigged. For example a S72 has control mixing to take care of some of these “issues.” A B206 has no mixing and the pilot has to make the right control inputs. Drift is controlled with slight tilt of the rotor disk!
Very interesting video.
What is involved in landing on a surface that isn't coplanar with the rotor system axis?
You touch down skids level, then as you lower collective and as the craft tilts, lets say left, you apply an equal amount of right cyclic against the grounded skid to where youre correlating the downward and lateral forces. Takeoff is the same where you should come just off the ground in a stationary hover. Rule of thumb is to keep the blades parallel to the horizon at all times. If you were to pull collective with the blades parallel to the ground, you would shoot up and off at that angle, and if you snagged a skid on the way, thats called dynamic rollover, which is a bad time.
It's so fascinating. I like helicopters more than an aeroplane
very very interesting. i wish there had been more questions asked.
In autorotation, the rushing air going up will keep the blades spinning? With that, you keep the blades at close to 0° angle of attack as possible and when the helicopter is 40-50 feet above the ground, increase the blades angle of attack as much as possible on the collective while pulling back on the cyclic stick?
That tictac makes all of this obsolete
Sikorsky blades h-3, s-61, s-64 etc have symmetrical mrb's. H-60 has asymmetrical mrb's. How much difference is there in lift between these two profiles?
thank you for sharing
What balances the unbalanced pitch torque of tail rotor ?
HELIKOPTER HELIKOPTER
Thank you for this brother, this lecture is very helpful, I learned a lot. May GOD bless you.
The only helicopter i got to fly the correlator was your wrist and the rpm's redlined at 2800 and below and 2900 and above. seemed very difficult to a low time pilot
This is a great playlist of lectures. I’ve learned a lot with it. I think it’s interesting and kind of funny how I know about gyroscopic precession and these college students don’t lol, not that they aren’t smart because they are at MIT, I just study and love learning about airplanes and helicopters.
stay thirsty my friend
They know for sure if theyve been there for a semester, which they probably have since this was an IAP, spring. They've all have taken 8.01 by now probably.
I didn't know it was called a swashblade, but I had an indoor rc helicopter that had one.... I know nothing about helicopters but after investigating it, I figured out its function. The interesting thing about it was that it was so small and it also was only 3 channel....so, it had throttle, yaw and pitch. no roll. The way they accomplished flight was to attached the part of the swashblade that, in a real helicopter would be attached to flight controls.... they put two magnets there. then, they put the magnets and suspended them in the middle of a copper coil.
Brilliant idea, to me at least! you control its pitch and qnd coordinat some yaw with it and it would fly excellently, indoors with airflow.
As the right control stick moved, it changed where on the copper coil was getting more and less electricity....which would cause a magnetic field in a chose area of the coil. As the rotor system spun, the swashblade would be pitched towards the direction of the electrical current.....or, the way you were asking it to fly.
Made it super easy to fly and helped me intuitively learn how to master the little thing. I kept trying to give it lots of throttle, pitch back, then yaw 180° while flying away....like a helicopter on M*A*S*H* or something but.... my kids, bless them... asked if they could shoot at the helicopters with nerf guns and, like the fun dad I am, said "What The F- Absolutely not! Are you insane?" ......And was immediately vetoed by Mom. So, those helicopters were, sadly, lost in action.
I tried my hardest....but... I just.....the fire was too heavy and I couldn't avoid all the rounds. The LZ was all lit up..... Nerf Darts flying in from seemingly nowhere.
in the end: all four helicopter units were lost to enemy.... I mean, my darling children.... fire.
That was almost a decade ago, so.... good thing I forget things and don't take them personal!1! 🙃 😄 🤣
I'm kidding. They were kids and I love that they got that experience. I plan to buy three more (one for me and both kids) very soon (I have to donate plasma haha) so they can learn about how they work. I do At Home Public Charter School with my son, RC aircraft and model rockets are science this year (if, like all schools, I can get the funding.... but, unlike other schools, I am 100% of the funding, so, might not happen, unfortunately).
kaman uses rotor servo flaps instead of a rotor swash plate.
The chart at 30:00 was interesting... How many careers have being an instructor as the first rung on your professional path?
"Blades of Glory " ? Of course. Wow.
Omg love choppers!!!!!!
Great lecture. Couldn't help but notice the student on Facebook to the right :)
I would be the guy to say, “yes, I am interested in you going back to the concept…I have time.
I would also ask him about the skill & risk involved in an emergency Afgany take off!
15:40 can someone please make ne understand this..
Or please leave a link.. I can't find a video or other resources on it
If you're asking about the drag chart and why total drag gets lower at a higher airspeed, here's a good video from Jacob at Helicopter Lessons in 10 mins or less.
He's an Apache pilot and great instructor, so I recommend all of his other videos too if you're interested.
czcams.com/video/BVW-l-iUJJw/video.html
Where are the analytical performance equations. Hover power , minimum power speed, maximum power horizontal speed.
Climb performance in forward flight, autorotation glide angle etc.
This is MIT , the place to learn just that.
Hint: Hover power is
P=(L^1.5)/D × sqrt(2/{pi×density})
+ 3/4 × vtip×L×Cd/Cl
L lift
D rotor diameter
vtip rotor tip speed
Cl blade lift coeff
Cd drag coeff
pi 3.1416
density = 1.225 kg/m³ sea level
Cl = 0.1 × blade AOA
Cd ~ 0.01
Using consistent units
m, Newton, Watts, sec
You will get a good estimate for selected AOA in deg
Just to be constructive
Thousands of moving parts spinning in close formation around an oil leak waiting for metal fatigue to set in.
Nice..
He had no clue how the wing/rotor makes lift that is for sure!
3:54 this is NOT how lift is generated. If Bernoulli's principle was responsible, you would need a wing with a ridiculously huge chord and too much drag to ever work. It's primarily generated from the coanda effect. I expect more from MIT
Wind is energy. I would hardly call using all available energy…cheating, it’s more like being a better pilot knowing of and managing all sources of your energy.
I am a wildlife vet. Most of my career have been flying in what you call "dead-man's curve"; needles to say I've lost a lot of pilot and Vet friends. I am a pilot-want-to-be but still a Vet. Haha. But quite scary that I was always doing the pre-flight inspections... Helicopter pilots seems to get lazy with those...
Helicopter Aerodynamics. I always thought that was an oxymoron. Complicated machine.
I might be basic, but why don't they put a safety glide system or a parachute on these things? They seem to crash enough and kill everyone on board to start questioning; maybe there is a way of making these things more survivable. I am beginning to study this because I am tired of all the fatal crashes I see every few months in the news. The most recent one was in Canada.
I don’t believe there’s anything you can really do if a helicopter goes down
I don’t want a parachute anywhere near those rotors, thanks.
helicopters can land much more safely than an airplane in an emergency. They don't need a parachute. Look up what autorotation is. Any helicopter can completely lose the engine and land safely. And all helicopter pilots are trained to only fly over places they can land safely with an autorotation. The fatal crashes that happen are due to pilot error, like smashing into a mountain, or on takeoff, and I highly doubt a parachute would help, especially since they already have parachutes in the form of autorotation
@OMG!!! PRODUCTIONS kobe's pilot flew into instrument meteorological conditions in a helicopter unequipped to do so, ignored his instruments, and slammed into the ground. Nothing would have saved him except common sense or an IFR rating. Least of all a dumb idea like a parachute
@@moonasha hey, you have some points but there is nothing wrong with thinking outside of the box and building something better. if we all just settled some status quo, we would be still in caves.
Nice video other than perpetuating the myth of how a wing generates lift. Newton 2nd Law: accelerate air down. It is not momentum transfer or the wrong bernoulli crap presented here. Fortunately I have seen some MIT videos that actually got this right...can somebody please help this guy?
At 26:?? Was he saying that you can’t autorotate the ‘copter without causing damage? ‘cause this guy has been literally dead on about everything!
Now compare Airwolf and Blue Thunder to each other.
Airwolf for looks and Blue Thunder for more possible....
A military helicopter pilot I knew told me that they have the aerodynamics of a brick!
Choppers actually don’t want to fly, we need to force them into a fragile balance to fly. If one important component goes south, it all goes south.
rubber belts...!? : (
The tail rotor thrust while on the pad is pointing in the wrong direction. The main rotor is turning CCW, which results in the copter body rotating CW. Therefore you need to apply thrust to the left of the boom to counteract fuselage rotation.
Earn Money Sleeping... hahaha I never heard that🤣🤣🤣
Helikopter helikopter
HELIKOPTER HELIKOPTER
PARAKOFTER PARAKOFTER
Anyone feel like this is a way for philg to brag that he owns a helicopter? Genuinely enjoy the engineering parts of this course though.
3:40 why does he say the energy of the air has to be the same like it would otherwise break physics? I don’t follow. I can run air through a compressor and the air coming out has more energy to the tune of what the compressor adds in. What am I missing?
Put a helicopter within a round cylinder with high walls, that helicopter will not go up and will go down real fast!
Helikopter Helikopter
This is not helicopter aerodynamics. What about Translational lift, Transverse flow effect, dysemmetry of lift, Coriolis effect, gyroscopic prosession and many more?
what am i doing here
im a doctor
Sad to see MIT professor teaching helicopter stuff and not understanding basics of how main rotor works :(
His PhD is in computer science, not engineering. I believe he was a guest lecturer here.
Has Bill Burr seen this? Hi Billy Boy! 👋
Oh the things i watch so i can build a helicopter in kerbal space program...
That is an oxymoron..
1:25 stopped watching here.
It's an interesting topic but unfortunate that the instructor is satisfied with muddled explanations apparently so he can make one snarky comment after another. Be clear and thorough, then if time allows add in some humor.
Good information although very basic. Also this due should learn how to teach...... like not breathing hard into the mic and please never, never, never be drinking water or who knows in this case a beer while teaching and being mic. Thank you
I wasn't sure if he was drinking or gargling. Either way, it definitely degraded the audio and was both distracting and annoying.
Thanks firstly for the noisy, repulsive, overly intimate water slurp and gulping.
Meh! He began the presentation correctly and then forgot the purpose of it and went on into regulations, flying techniques and career possibilities.
Before even getting to the flight controls and “being a big fan of Blades of Glory” he should have mentioned the flapping and consequent lead-lag aerodynamic phenomena and he could have used the classic skate dancer example to explain that.
Too much jumping around, defeats the initial purpose of the lecture.
guy loves drinking water
Tip for lecturers: DON'T DRINK WATER DURING YOUR LECTURE. That sound was so disgusting and off-putting that I couldn't watch past 1:10. Dislike.
Yep, it stopped me too. He could have at least tried to be quiet. But it sounded like a commercial for listerine.
My problem with 'copters is redundancy in engine failure. With a plane you can glide, a heli you are a brick.
Theres auto rotation
Yeah. No. Auto rotation is a real thing and works.....
@@getsome418 Which literally is gliding.
As both an airplane and a helicopter pilot, I'll tell you I will take the helicopters 4 to 1 glide ratio with a 0 MPH landing speed (into a back yard if needed) over an airplanes 8 to 1 glide ratio with a 70 MPH landing speed all day long. I dont think many people appreciate that until theyve flown both. I cruise around at 500' just thinking ' well I can go here or there or this spot or even theres a clearing behind me I can make a 180 into' whereas flying fixed wing, yea I can make it into a field straight ahead if Im high enough assuming Im not over a city, but also If I dont land with the corn rows, Im gonna eat the dirt at 60MPH when I somersault as soon as the nose gear touches down, but regardless if you dont hit a long straight road with no powerlines the airplane is going to be a writeoff. The helicopter, if you know what youre doing, the passengers wont even understand why you landed there.
Great course, but please never drink into the mic it is awful
too much umm
his voice is too slimey and his mic picks up WAY TOO much mouth noise -- impossible to listen to
Poor "educator"! Nothing to learn here!
An MIT professor is lecturing? Sounds like this guy really doesn’t have a very good grasp on heli aircraft operations. He’s pencil in the eye boring….
With regard to the history of aviation, don't forget this guy !
en.wikipedia.org/wiki/George_Cayley
HELIKOPTER HELIKOPTER
Helikopter Helikopter