Helicopter Ground Resonance

[thedoorsbiggestfan]

thats Bonaventure hotel in LA

[upajos]

The alternative is to cut power and set the aircraft down firmly on the landing gear. Power from the engine is what drives the resonance to higher levels.

[jgdogg441]

@upajos Actually my good friend you would be wrong. As per this video /watch?v=RihcJR0zvfM cutting power and setting her down wont help a thing as the wheels/struts are trying to hold the helicopter still (friction) while the rest of the body is trying to shake itself loose. Also of note in the video I reference, the safety restraints are in fact slack to allow as much free movement as possible while still maintaining safety.

[pilotguitar21]

hmm....are we sure that this is ground resonance? looks like the heli has been idling long enough for the people to get out...ground resonance happens if there is a hard landing and shockwaves are sent from the skids and into the blades causing the blades to become out of phase with each other...looks like not the case here...looks more like harmonic resonance....he's idling at that range at which the main rotor and tail rotor and harmonizing with each other...making it worse and worse. maybe?

[glock21guy]

@pilotguitar21 Thought the same thing at first but then realized too that those people may never even have been in the heli. It was probably just filmed flying in while the people were waiting on the steps for the shot.

[Felipethug2010]

Saiu com a porta aberta.

kkk

[PIRINEOS12]

As far as I know in this event you have two options:1) If the rotor RPM are "high" you lift the heli (in the video case) 2 )If the RPM are low you turn off the motor .. Am I correct?.Good video.I guess the shoot was too expensive to repeat it ;)

[kellertv]

jettison the doors and pop the floats never fails.....

[jerrodcorey25]

JET RANGER SOUND EFFECTS = FAIL



[zeetek007]

Good thing the pilot knew what to do.

[helicopterwar247]

could have ruined a perfectly good gazelle

[ComputerGrant]

It wouldn't really matter much because MacGyver would be able to put it all back together again, but the pilot didn't know that.

[tubernation1]

Wow, good catch! Except for one thing, I could never sit through more than a couple of minutes of McGuyver! ;-)

[southamptonbythesea]

Quick response from the pilot, good thing he recognized what was about to happen!

[silverhelicopter]

this is a very early model Gazelle. Most Gazelle have the skids flexible connected to the frame. That way can not do this ground resonance

[Ranger4321]

This is probably a stupid question, but what causes the ground resonance?

[TheTBagg]

@Ranger4321 It can be a shock to the helicopter(like a hard or awkward landing) that causes the rotor head to go out of balance. Usually one blade leads or lags too much shifting the center of balance away from center of the rotor hub. That trend will continue with the center of balance moving farther and farther away from the center of the hub, which is why the vibration or oscillation will be more and more violent.

[kz4506]

yes soon as you feel vibration of this sort lift off and rotate the heli in the oposite direction to rotor , this will add load to the blades and straighten out resonance then land and go into negitave pitch quickly and feel the machine ,

[CapnJay214Supra]

I am a helicopter mechanic, and my boss just showed me this video as an example of the phenomenon. Chilling, especially when you consider that the actors exiting the bird seem oblivious to the danger.

[Maxamo86]

@CapnJay214Supra It is scary. I just read that passengers exiting the helicopter can aggrivate the problem as well.

[HHS81]

@ianrkav: The bo105 rotor (The Red Bull helicopters) is not a secret.

It is rigid rotorhead type Bölkow developed in the 60's in germany.

The Lynx uses also a rigid rotorhead. Rigid systems like that are known to allow such aerobatics like loopings and rolls.

[MyDogBob2001]

That is awesome. Glad the pilot knew enough to pull pitch. Although I like the jump out and scream like a girl.

[williamacro]

jajaja a gazelle with ranger sound

[Garrett85]

The music during the ground resonance effect is priceless ahahahhahahahahahahah, it sound like "all is ok" and the guys risk to have an helicopter rotor in the face ahahahahahahah

[veteran1970]

I bet the actors in that scene didn't even know it was happening

[ShadowGKCP]

it's not the ground it's the roof

[nightflyyerfan]

oh look! the heli dances!!!

[ianrkav]

What exactly is 'ground resonance' anyone?

[rea1001]

@ianrkav Im not sure, but I think there was a thing invented called google, and the internet that might have the answer to your question.

[ianrkav]

@rea1001 Well worra ya know. It seems you were right! The 'internet,' the thing we're communicating with now and how you viewed my original comment in the first place, does have a thing called 'Google.' It also has a thing called 'Wikipedia' too and by using all of these resources I was able to find the answer to my question!

Great world huh:-)

Interesting channel you have there by the way. Intruiging stuff:-)

[rea1001]

@ianrkav Sorry, didnt mean to be an ass, but by the time your question would have been answered, you could look up the information for yourself, instead of waiting days.

[ianrkav]

@rea1001 Don't worry my friend, no offence was taken. I actually thought it quite funny because you were right:-) I didn't stop to think at the time about Google, I just made an unthinking comment you know. I actually did look it up on wiki about an hour after:-)

Interesting channel. I saved 'Natural Law,' makes sense to me.

[dutto75man]

@ianrkav The rotor heads balance is offset due to faulty landing gear, roter head dampeners or by lowering engine power too quickely.

[ianrkav]

@dutto75man Mmm interesting! I have heard this only happens to multi rotor flexible heads and doesn't happen to choppers with just two blades on the main rotor and a stiff head. Is that true?

[dutto75man]

@ianrkav Yes thats correct, it can only happen to fully articulated rotor heads with dampeners (allow blades to move forward and back within their plane of rotation). The disadvantage of the two bladed system is if flown incorrectly it is susceptible to ''mast bumping'' which can lead to complete separation of the rotor head from the mast.

[ianrkav]

@dutto75man "Fully articulated" That was the term I was trying to remember, instead of 'flexible' as I used!:-)

Mast bumping, resulting in the rotor disc/blades flying off. That would be a bad thing wouldn't it!

So what exactly is the cause of and symptoms of mast bumping?

Thanks

[dutto75man]

@ianrkav Yeah fully articulated means the blades can flap, drag and feather. Semi articulated (two bladed system) can flap and feather only. Mast bump can happen in a negative G maneuver . Baically if the blade system isn't loaded by the helicopter itself the rotor head can strike the mast from its inner section. The whole blade system teeters like a sesaw and must be loaded so its balanced. Symtoms would be watching your rotor blades fly off to space. lol

[ianrkav]

@dutto75man I think I prefer the fully articulated head with at least 3 blades now:-) Tell me, I've seen the Red Bull helicopter, a Bo 105 I think it was, here on youtube performing aerobatics. What type of head would that have? 

[dutto75man]

@ianrkav either rigid or fully articulated. Choppers like the Lynx can do aerobatics but the Red Bull helicopters rotor head has been a carefully guarded secret for commercial purposes.

[ianrkav]

@dutto75man That would make sense. The aerobatics it does are pretty amazing! Thanks.

[kd4pba]

I think the bigger story here is the Stock Audio of what sounds like a Jet Ranger. No matter what Helicopter you see on TV they all appear to use the same sound clip.

[bionictrucker1]

@kd4pba You are so right. sometimes ya can also hear the sound of a Bell 47-G fer the sound clip and a good part of the time in helicopter movie film clips ya can here the sound clip of a Bell UH-1 Huey!

[SuperRugster]

WOW

[VolDep45]

Depending on the aircraft and situation, you either have to pick up off the ground or drop the collective to load the skids to stop the resonance. Ground resonance can be caused with worn landing gear struts (if so equipped) or keeping the aircraft lightly on the landing gear (collective not fully down).

[winterka100]

I don't fly choppers, but it seems like a good idea to load the blades up to break the cycle, as long as there is enough power available RIGHT NOW.

[TheFr3sh1]

why does this happen?  please

[Norgesmann]

@TheFr3sh1 Center of gravity moves out as the blades start to "chase" each other...

[Bugger90]

@Norgesmann the EC155? Lucky bastard! ;) I didn't know Bristow operated those, i thought they mainly did the S-76! What area of operations will you be visiting? Mexico? North Sea?

Yeah the 300 is a pretty sturdy aircraft :) I'm still in the education program though. I now have about 60 something hours on the Hughes. But we have modular here, so i already have a JAA PPL(h), so i can take that thing wherever i want on my own, until i have enough hours for a CPL :) Life's great!

[nipponhouseplayer]

Its all good ,Just as long as the check clears!

[charterpilot]

Ebalim you are so wrong...you must do what the pilot did and lift back off.

[ebalim]

all he needs to do is reduce the collective pitch or re-center cyclic

[Bugger90]

Reduce collective? Wherever you got your flying education, i hope they give refunds.

[Norgesmann]

@Bugger90 The best thing is to take of, but if RPM is too low there might not be time before you are fu*ked, then the corrective action is to shut down as quick as possible and apply rotor brake.

[Bugger90]

@Norgesmann and hope for the best of it, of course you're right, IF you're low on RPM. But this man had more than enough power at his disposal, so reducing collective, as ebalim suggested, would be a wrong move in this situation. And re-center cyclic is not going to do anything if you're already in ground resonance state. So in this situation, reduce collective = bad.

You fly 300s at Bristow, right? I fly Hughes 300 here in Holland too :) How are you liking Bristow thus far?

[ELX222]

@Bugger90 Not competely true, if your rpm is too low to take off then the best option is to lower collective and shut throttle.

[pf126p]

@Empriz Throttling down rarely works in time. The proper course of action, though counterintuitive, is immediate takeoff.

[PJDooWop]

pf126p is right. There's a video called "ground resonance - side view".. It shows an example of throttling down just after entering ground resonance, and it's not pretty

[17orlik]

There are two ways to handle with it as soon as possible takeoff or if you have a time decrease pitch of main rotr. in that case pilot made the best choise. Resonance can create main landing gear. Sir.

[HAIONSTRESS]

great find that was cool to see how quickly and correctly he acted

[metalheds]

bad lead lag dampers, soft landing pad, best coarse of action, lift off. Its called "ground resonnance" not flight resonance.

[Norgesmann]

@metalheds They don´t have to be bad, the schock, even from a dampened platform can be enough.

[NorwalkPost]

The corrective action is to jump out of the helicopter and RUN as fast as you can, screaming like a terrified girl all the way.

[micikas]

@NorwalkPost Agreed. Best place to do it is on a high building so you can backflip off of it and land soft on a bus.

[fuzzdemon]

Isnt it illegal to take off with a door open? lol

[cabdolla]

Nope. Not good for the airplane, but not illegal.

[aznwilly211]

well it was either that or die LOL

[pf126p]

@fuzzdemon You don't need doors at all! In the summer I fly without. The wind on your shoulders and in your mic gives you clear indication that it's out of trim! xD

[mcv218]

what causes ground resonance??

[kovona]

vibration from a imbalanced spinning rotor being bounced off the ground and back at the helicopter. Nasty stuff... Which is why always make sure the landing gears aren't flat and the skid shock absorbers are serviced.

[pf126p]

@kovona Imagine that. I've been flying 19 years I was not aware that skids had shock absorbers.

[aligerous]

Not technically shock absorbers but check out an MD-500 series. There's quite a bit of shock absorbing on that landing gear arrangement.

[panictactics]

The last thing you want to do is leave the ground. I would have jumped out and ran.

[lfguard10]

Actually it's the opposite. Leaving the ground is exactly what you want to do.

[aznwilly211]

to stop the standing wave?

[Mikitsubizunizu]

had that helo died, so would have the crowd below it. crazy helo pilots. XP

[sarnieken]

nicely spotted. thx for posting.

[marceloribeirobarros]

SUPER MY FRIEND ...SUPER !!!

[mason4300]

Nice find

[JflyG]

damn i never knew that.. crazy.. fixed wings =)

[JesperA86]

What building is that? Is it the GM building?

[flydef]

It's the Bonaventure hotel in Los Angeles.

[DerSarkast]

I'm surprised that they show this in a movie. It can be scary for some watchers

[lst1195]

what would have happened? whould the Gazelle have shaken apart?

[chris94kennedy]

Yup, i think i saw a video on youtube of a chinook getting ripped apart by ground resonance. Search it up i'm sure you'll find it =]

[uploadJ]

Keen observation; well done. 5/5

[YoureGuilty]

Well observed - nice.

[smash29]

Good eye!

[kajsing]

I have 200 hours of flying (so I'm new) and have only tryed it 1 time, it was under my training, and happened after a somewhat hard landing. nothing in it... just lift into hover.

[aSPITFIRE911]

AMAZING !! How offten does that occur ?

[helobelow]

You hope GR never occurs and if you land correctly or take off correctly probably never.

[TEXWAKE]

was this because he was at a high power? will this occur on a lower power as well?

[mountjoy23]

because it is a fully articulated head.

[Obelix6]

Yes this can happen at any power level because it is not realted to power. It can occur on a rough landing if the shock of the landing knocks the blades out of balance. the imbalance causes the helicopter to shake violently and will get progressively worse unless corrective action is taken. Corrective action is usually lifting the helicopter back into hover which brings the blades back into balance.

[Obelix6]

Fully-articulated rotor systems are more susceptible to this than other types because they have hinges that allow limited forward and backward movement of the blades.

[helobelow]

Very true...we call it a lead lag hinge which causes the blades to be spaced unevenly as they rotate. As conservation of angular momentum occurs the center of mass moves outward along the individual blades like an out of balance fan. It can only occur when a skid is in contact with a stationary object. Underslung systems are not suseptable to GR because the center of mass remains the same when CA momentum occurs. :--)

[hosscollar]

McGruber!

[R0darancabezas]

ay ay ay como se tambalea al despegar...

[howitzer24]

Now that I look closely the whole thing was shaking looking like it could crumble.

[antichicmusic]

wow...whoever discovered this footage,very cleverly observed!

[Highice007]

Can anyone explain "ground resonance"? I love the Gazelle, but don't know as much about avation as I would like.

[cmmndr312]

It happens when a shock is sent from one of the landing skids to the rotor mast. It creates an imbalance in the rotors that can hit a resonant frequency and shake a helicopter apart. One way to avoid this is to immediately hover the aircraft at the first sign. Changing rpm like powering down will increase the vibration as the rotor hits the resonant frequency of the ship and then it's all over...

[dustywar]

people exiting would of most likely been hurt or killed;(

[macanix]

Not really a big problem. You have 2 choices under these circumstances - 1) you have enough RPM to lift back off quickly or 2) you have low RPM and you apply the rotor brake. Both will kill the ground resonance.

[pf126p]

I can just imagine that pilot must have been shitting bricks, way up there and knowing what was happening, praying it rebalanced itself. It's scary enough atop a building with a small target, sudden ground effect and wind gusts. Holy crap. My hat's off to him.

[pf126p]

WOW.

[spidey692003]

Man imagine if he didnt get it up!!.... on top of a building too! Man that could of been a major catastrophy! nice skills. and good job finding that!

[FailedSquare]

It could have been the end of macgyver... my god!

[codyj702]

I thought Ground resonance only occurs on multi-bladed helicopters

[mountjoy23]

Fully articulated, lead, lag function has to be present.

[pf126p]

It IS multi-bladed... fully articulated... ;)

[codyj702]

multi-bladed as in multi-set bladed...like in a chinook

[pf126p]

Oooh, no. I thought you meant fully articulated - more than 2 blades. Ground resonance only occurs in fully-articulated systems, because it's a failure of the lead-lag setup characteristic thereof which the rigid and semi-rigid (2-blade) systems lack. The Chinook is indeed susceptible not because it has a dual setup but because it has a fully-articulated system. ;)

[bmakdad]

I know not of a helicopter with 1 blade.. :)

[silencecom]

Great piloting just in time too

[Focha]

Nice time reaction! It really safe that day. Thanks for posting.

[Chopper894]

Well spotted

[adooma1984]

The pilot lifted back up to prevent the helicopter from ripping itself apart