The Helicopter Speed Limit – Helicopter Physics Series – #7 – Smarter Every Day 51
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The Helicopter Speed Limit – Helicopter Physics Series – #7 – Smarter Every Day 51

October 13, 2019

Helicopters have a speed limit
that has nothing to do with laws. Well, unless you count the laws of physics. Hey it’s me Destin. Welcome back to Smarter Every Day.
The show where we do science. So today I’m gonna explain to you something pretty interesting about the dissymmetry of rotor flight. But before we get too serious, let’s just have a little fun. Check this out. Nighttime flying with Carl. ( rotor noise )
Sick! ( rotor noise ) ( excited shouts ) ( laughing ) Right there. ‘kay we’re going to do some light painting with a helicopter at night. ( rotor noise ) ( music ) ( music ) Did you see that?
Look real close. Go back to the image. If you look on one side you see this really tight radius of curvature. But on the other side you see a much larger radius
of curvature. What’s going on there? OK so to explain the effects of this
unsymmetric travel of the blades I’ve rigged one up on a stick here,
and I’m gonna try, let’s see if this works. There we go.
So as the advancing blade comes around, it’s moving faster relative to the air because
the helicopter’s moving so you add those two values together,
but the retreating blade, you subtract away the velocity of the blade from the forward
air speed and that’s the total relative velocity of the blade through the air.
This causes some funny things. OK Let’s start the blades and check things out.
As the chopper flies forward, the air flows over both sides of the helicopter.
The advancing blade is also travelling forward so this adds to the air velocity
of the rotor on that side. Now as long as the air speed of the rotor stays
under the sound barrier you’re OK. But if the helicopter goes too fast you’ll
create shock waves and start to damage things. The retreating blade sees
the same airflow of the vehicle movement but because the blade is travelling in the opposite
direction from that movement the actual air speed of that rotor is less.
This creates something called Dissymmetry of Lift, and to counterract this
the rotor on the retreating side is given more pitch to produce
more lift. This works up to a point, but if the helicopter goes too fast,
the pitch becomes too great and you lose lift creating what’s called a retreating blade stall. The cool thing about a retreating blade stall is that it is
a self correcting problem. If you think about it due to gyroscopic procession, if you have
a dissymmetry of lift between a left and right side of the helicopter, it won’t roll the helicopter
like you think it would, it actually pitches it. That’s good news because as you’re
flying along if you get too fast and you get a retreating blade stall, it’ll just slow
the helicopter down, automatically. OK There’s a lot of things I did not cover in this video series, but for the most part you should be way smarter than when we started on helicopters.
Smart enough in fact where you can make an educated guess as to which of these three helicopters
is the fastest in the US Army inventory. While you’re thinking about that please consider going to the Facebook page. I put all the photos from the night flights on there. Go download them, use them as your
desktop background, stuff like that. While you’re there please Like the Facebook page. Also if you have ideas for future Smarter Every Day episodes please Tweet me, I’d appreciate that, at SmarterYoutube. It’s been about a year since we started Smarter Every Day. If you have ideas for a one year episode I’m all ears. OK. Enough babbling. The answer is the Chinook.
It is the fastest in the US Army inventory. I’m Destin. You’re getting Smarter Every Day.
Have a good one. ( music ) [ Captions by Andrew Jackson ]

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  1. The CH-47 is not only the fastest US military helicopter, it's the fastest military helicopter in the world.

  2. Destin. Did you take drugs before making this one… .. 😮 (not to ignore the absolutely beautiful physics of it all but come on)

  3. That RC pilot is crazy skilled.
    I spent a year learning to fly collective pitch RC and am in awe of what this guy can do.
    It would take a decade to get that good.

    Massive Props to that guy.
    No pun intended.

  4. Hahaha I said the black hawk or the apatchie, (butchered the spelling) but I was so so wrong, I guess I was basing my guess off of the size

  5. Hey I've been very interested in all of your helicopter videos, this particular series makes me want to learn how to pilot a helicopter but more importantly, i would love you to do a video with the Redbull stunt Helo pilots

  6. So does the chinook have a tail rotor or do they spin differently I know it’s a google question but just found the videos and want to keep watching lol

  7. Airwolf… Designed by John Moffet and piloted by Stringfellow Hawke and it is capable of reaching speeds that rival the fastest jets… Cost $1billion

  8. I'm a huge fan of helicopters and have flown in most US helicopters except for the Apache, Cobra and Kiowa of course lol. I spent 11 yrs in the army (2000-201) with 2 tours in Iraq and one in Afghanistan. Personally my favorite is the Blackhawk because the ride is pretty comfortable and of course you can hang out if the side doors are open. I never cared much about riding in the Chinook because every time I flew in one it would be so jammed packed with soldiers and gear that you can forget about sitting down. I've flown in the old Huey a few times and it's not to bad. If could go back and do it all over again, I would definitely try to become a helicopter pilot, perferably an Apache pilot. I was lucky enough to see them in action several times in Iraq.

  9. Watching this seven years in the future, it’s awesome to see the growth of the channel man, you deserve it keep up the great work.

  10. I said before that this is the exact reason i love this channel. You always put videos up about stuff i didnt know I wanted to know 😆 As soon as i read this one I thought "hmm😕 I wander what the top speed of a helicopter is?" LMAO!

  11. But why is the ch-47 Chinook the fastest? Is it because of how fast the rotors are spinning? I think you have to make a video explaining yourself. That way I can get a little more smarter everyday.

  12. Without the lights in the video it would've been cool. With the lights and effects freaking best vid ever!!!

  13. Dont know about the blackhawk but i know the Chinook is considerably faster than the apache
    The fastest helicopter in the world is the British Westland lynx, it set the world record of 249mph way back in 1986 and remains unbeaten to this day!

  14. I have one question for you, how do you make that image with the RC helicopter blades going across the screen, or whatever you call it, by the way, I really like your channel.

  15. Oy… I love your videos. But too many big words. I didn’t understand half what you said.
    Maybe if you redid the vid and said the exact same thing in lay mans terms, I’d better understand.
    But goes to so how far you’ve come in 7yrs. All your newer vids I understand perfectly. I’m guessing I’m not the only one who’ve asked you to break it down for us simpler folks, huh? 😂😂😂

  16. What about choppers that have counter rotating twin roter configurations such as the Russian made Kamov Ka-50, doesn't that overcome the problem??

  17. still monitoring this videos comments? can you teach me about a cobra AH1 helicopter performing a barrel roll by matching the blade speed to the airspeed causing some kind of friction flip?

  18. Helicopters can fly at supersonic speeds. Shees, haven't you seen Airwolf?

    Seriously, if you have your MRBs going SLOW enough so that their tip plane speed is under the speed of sound you're golden. OR you could have them going FAST enough so even the root of the rotor plane is above the speed of sound. The problems exist when the MRBs have to withstand supersonic speed at the tips and subsonic speed at the root, and the constant vibration will tear them apart.

    Most MRBs do travel so that the tip is just below supersonic speed. That doesn't mean you can't speed them up… but it does mean if you do so it needs a significant speed so you don't have a supersonic boom in the middle of your blade. THAT requires gears (which modern helicopters don't use) or a "boost" function (see Airwolf 😉


  19. I don't have Twitter but if u can do one on paramotors. It's the fan thing u strap to ur back and u have a parachute glider above you

  20. I just started flying drones and one of the FAA rules is no night flying and each drone has to be registered with the FAA. I personally have no issues with what you guys did, but would the FAA?

  21. You didn’t show what happens to a two blade system like a UH-1H. In that case under retreating blade stall the helicopter rolls, not pitches up. This can cause total loss of control leading to the aircraft crashing.

  22. Awesome job! First time to your page and I am hooked. I can’t believe I haven’t found you earlier than this given my love of flying.

  23. 👍🏼 would you do a series on the physics of golf? The ones on here are old and not very good. Some night painting with swings of Mathew Wolf and Brooks Koepka would be sweet to compare…there also seems to be a distance barrier you could investigate along with all the aerodynamics stuff not to mention the counter intuitive nature how club path and face angles work. Thanks!

  24. I notice this great parallel; you quote book/chapter/verse, and, while well handling the responsibilities of husband and father, you do maintain the heart of a child. There is a good curiosity and a wasteful gossipy curiosity; you've equipped yourself well.

  25. CORRECTION: Although you said the chinook helicopter was the fastest in the Us army inventory that is false. The apache is 227mph and the blackhawk 225mph and the chinook is only 197mph top speeds although the AH-1Z Viper is 255mph and actually is the fasted U.S. military helicopter although its mainly used in naval and marine operations only. The apache and blackhawk are army as you said. The modern Apache guardian is stated as the best attack helicopter worldwide. The apache guarding has a top speed of 189mph conpared to the 197 chinook. This may be where you got your information.

  26. Good point, the helicopter with two blades can rotate them in the opposite direction, canceling the apparent wind effect on the retreating blade.

  27. The fastest, heaviest, and highest flying. I loved flying that beast. I beg to differ with your corrective action in RBS, the aircraft will pitch up as you said, but it will also roll to the stalled side….unless your in a Chinook.

  28. I think you put your arrows in illogical directions. Airspeed is experienced as airflow over the craft so it should be an arrow pointing against the direction of travel.
    I understood you but it would be more intuitive as I explain it

  29. Your model is annoying me at 3:03 because you installed the rotor head upside-down.
    Ally helo rotors rotate counter-clockwise when viewed from above. Enemy rotors rotate clockwise.

  30. Hi Destin, I am a big fan of your documentary videos. You make it really fun to learn and, I am getting a little smarter every day I watch them. Thank you! As for your anniversary documentary video, what about filming the blast of a big rocket launching and talk about the speed and dynamic of the hot gasses escaping the rocket’s engine. Perhaps you could also talk about thrust vectors and how much energy is lost by gasses that don’t flow in the same vector, because of the blast sound waves interference I imagine. I also imagine that the gasses are escaping the rocket's engine at supersonic speed. How crazy the shockwaves must get inside the combustion chamber? Well, I think you would make one episode even more cool than the Civil War cannons. Well, all your episodes are cool.

  31. The Cheyenne Shopper of the very late 1960s early 1970s was faster than the Chinook, shithook in military lingo. The Cheyenne flu mainly on its small wings as it speed approached about 330 miles an hour which I believe is it not a lot faster than the Chinook, but it was a helicopter that was more capable that the Apache is today. The money it took to build the very first Apache could have been spent on 3000 Cheyenne helicopters at Bay would have been upgraded through the years to be he Premier close air support weapon of all time. They were fast enough to get somewhere in a hurry and They Carried enough Ordnance to get the job done. You can also reduce the asymmetry issue bye depending on the wings more and just allow the rotor to go into auto rotation.

  32. Although you are correct in saying that the helicopter will pitch up, it doesn't necessarily correct itself. The helicopter will pitch up and begin to role in the direction of the retreating blade. At this point it is important to lower the collective, which will decrease the angle of attack, and aft on the cyclic, which will reduce speed to get out of a retreating blade stall!

  33. Great vid! TY for the share and great footage! Best of Regards! 👍 P.S. Not to be nit picky … Not a double helix… That is a helix inside of a helix not 2 intertwined helix's.

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