Mast Bumping in Helicopters
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- Опубліковано 1 бер 2018
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This video's topic covers Mast Bumping. This subject can be a sensitive subject for some because it usually deals with expensive repairs of rotor components and, in some cases, catastrophic damage resulting in death. That said, it's a subject that requires understanding if it can affect your helicopter. I say "if" because it only applies to semi-rigid or "teetering" rotor systems. If you're not familiar with what exactly a semi-rigid system is, I'd recommend watching my Types of Rotor Systems video ( • Types of Rotor Systems... ). Mast bumping, just like the name implies, is where the main rotor hub contacts or bumps the rotor mast. This causes damage to the mast and can cause complete rotor separation in extreme cases. Mast bumping can occur for a few reasons. The first being takeoffs and landings from sloped terrain.
If a helicopter attempts a takeoff or landing to or from a slope there can be points where cyclic limits may be reached. By applying cyclic in the direction of slope with little or no collective applied it is easy to see of this can happen. To help prevent this, be sure to have some collective applied prior to displacing the cyclic for a slope takeoff and try to avoid landings which require maximum cyclic displacement in any direction. This type of mast bumping is far less severe than the other type : low-G flight.
Low-G flight is usually accomplished with a "pushover" or the leveling off / dive entry following a cyclic climb. You'll notice those maneuver being demonstrated in the introduction to this video prior to the Apaches conducting diving rocket engagements. Keep in mind that fully articulated and rigid rotor systems can do this type of maneuver. Semi-rigid rotor systems cannot without risking mast bumping. If a semi-rigid system attempted this it could have catastrophic damage resulting in main rotor separation.
Let's take a look at why:
1. As the helicopter reaches the crest of the climb, the helicopter reaches weightlessness also known as "zero-G's." Main rotor thrust is drastically reduces as it unloads.
2. At this point, the tail rotor still provides thrust to offset the tail rotor. But now there is no main rotor thrust to counteract. So the aircraft side-slips and rolls towards the right.
3. The pilot recognizes this right roll and tries to correct with left cyclic. But this has little effect because the main rotor is unloaded.
4. The pilot applies even more left cyclic and the rotor reaches its flapping limit. The rotor hub and mast make contact. This force can be sufficient enough to bend or break the mast. The result: the main rotor flies away and the fuselage falls to the ground.
The best way to prevent mast bumping is to avoid pushover-type maneuvers when flying semi-rigid rotor systems. If you ever find yourself in this situation by recognizing a feeling of weightlessness/right roll you should immediately and smoothly apply aft cyclic to load the rotor and establish level flight.
The biggest takeaway from this video is that mast bumping is a very dangerous condition in helicopters with semi-rigid rotor systems. Well that wraps up the subject. Thanks for watching! Don't forget to hit like and subscribe below. As always, safe flying!
If you enjoyed the video or have any questions or comments, hit the like button and comment below.
If you're just getting started and want more information, pictures, and more explanations, I'd recommend reading the Rotorcraft Flying Handbook - amzn.to/2ifPlnZ. If you've already got a basic understanding, and want to further your professional helicopter education with advanced helicopter concepts, I'd recommend reading Cyclic and Collective, by Shawn Coyle - amzn.to/2ifQGLx
This is how my Dad would explain some engineering point, get a bit of paper and a pencil and break it down, great stuff!
Awesome explanation Jacob. Thank you for putting all this time in
Excellently presented explanation without complicated and unecessary comments!! Well- done!!0
Straightforward plain English with no gobbledygook. Very nice
I know nothing about helicopters other than I used to ride in them in the navy. This video was totally AWESOME for a primer on mast bumping!
I was trying to find out what happened in the 2002 catastrophic crash of SAR 71 near Hamburg. I found the perfect technical explanation here. Thank you!
I know more about Helicopters now. I would never have watched this. I was drawn in by the precise explanation and presentation. Very nicely done.
Bless you Jacob: for all your teaching!
best heli info i've found on youtube (helps for RC heli) thankyou
Really good info as always man, thank you! Just covered this in ground school but it’s good to see a more in-depth explanation
Keep them coming; excellent and to the point.
Very well explained................
Superb video, well explained definition, diagrams were helpful in understanding this condition. Thank you!
Aweosme !!Thanks so much for these videos !!! Definitely helps us inspiring warrants and pilots !!
Very good explanation.
I have learned so much from your videos.
The normal range of the cyclic does not exceed the gap between the droop stops and the rotor mast. Mast bumping occurs when the fuselage is not loaded with the rotor system. This unloaded state allows the fuselage to already be tilted, which allows for situations where the cyclic can exceed the gap. For example, in a low-g situation, translating tendency causes an extreme right roll of the fuselage. Sometimes up to 100 degrees in 1 one second. If the pilot can correct the right roll in 0.1 seconds, the fuselage has already moved 10 degrees to the right. To correct, the pilot moves the cyclic to the left 20 degrees to correct, but in the R22 the gap between the droop stops and the mast is 12 degrees. In that situation, the teetering hinge strikes the mast. While reaching the cyclic stop during a slope landing is not recommended and requires you to pick another spot, mast bumping is not a concern.
Matt Henderson. Well said. I've not flown and therefore cannot speak for the R22 and its droop stops. But mast bumping can have the possibility of occurring in other types of rotor systems with maximum cyclic displacement. Thanks for the input.
@@helicopterlessonsin10minut10 Really cool.
By the time all that info would pass through my brain, the tail would already be long gone and I’ld be racing it to the ground!
Speaking of ground, thats where I plan to stay😉
What happened to, down collective, right pedal,
a bit of aft cyclic, then a bit of forward cyclic,
then up collective, left pedal to regain trim attitude?
Very well done, Thanks!
Very cool video.
Thanks for the awesome explanation.
With Best Regards
I fly Huey gunships and we are able to do those kind of maneuvers and never had MB... not even close. You can do that, but you must be very
conscious of what is going on with the aircraft at that particular time. Marines flew semi rigid rotor attack helicopters till 2012 in several wars. Awesome video!
He doesn’t mention it in this video, but mast bumping is mostly a problem with Robinson helicopters. Even strong turbulence in level flight can trigger mast bumping and cause the blades to separate, sever the tail, or impact the cockpit.
The problem is so bad that the FAA forbids anyone from flying the R22 or R44 unless they are specifically trained on the mast bumping and why you must never go low g in a Robinson. (SFAR 73.)
Very interesting. Thanks for posting. Not a pilot but good to learn. 👍😎🇳🇿
Subscribed! supercat380 said it all! Great lesson about mast bumping!
I believe "mast bumping" is what happened to the Robinson R-44 that crashed here a few days ago in Rowlett, Texas. . . . then the main rotor blades severed off the tail section of the robbie chopper as it fell out of the sky, killing the CFI pilot & student pilot!!! R.I.P.
Good vídeo 👍🏾🚁
Great explanation. However I request you to highlight which couple causes the Roll to occur as well how will the roll and yaw tendency differ for a clockwise rotating main rotor. And at which stage should collective input occur during recovery.
Thanks
Exactly what happened in rowlett
Thank you
I fly an autogyro which also has a teetering rotor system. They have teeter-stops which prevent mast-bumping (although, the problem now becomes stop-bumping instead). A condition which can cause stop-bumping in a gyro (and I would assume would cause similar in a heli) is outrunning the retreating blade and causing retreating blade-stall - We have to be very, very careful of taxiing with an active rotor because of this - It can cause the gyro to roll over and turn an otherwise flight-worthy aircraft into instant FOD.
Oh... by the way, I think you'll find that your low-G condition happens before apogee. We also have to be careful not to pull low-G manoeuvres - Gyros rely on a loaded rotor-disc for autorotation - Unloading the rotor-disc is a pretty sure-fire way to become ballistic. Given your explanation, I would imagine that it is also accompanied by a roll toward the retreating blade, which I had never considered before. Not that I am going to perform in-flight experiments to find out, of course !!!
Merci beaucoup !
Eric (Paris)
Here's a question: But WHAT happens if this "peak" is somewhere at a mountain-top with thin air and you CAN'T "load" the rotor?! Or if your RPMs are already too high.
Disclaimer: Not a pilot, just have a basic understanding of what you say here and some curiosities.
Ultimately you just have to think ahead of the aircraft and never get yourself into a position you can’t get out of. Like driving a car, you don’t want to drive so fast that you realize can’t make a turn while you’re in the turn.
@@helicopterlessonsin10minut10
Awesome answer. Thank you so much for replying!
Took Jacob 7.6 min to succinctly explain mast bumping. The U.S Army took 25 min, 1/2 doz soldiers and contractors to poorly explain the same concept.
The British would need about 15 hours to try explain the same subject, and it still would not be explained!!
And that includes a 1 minute introduction
Just imagine… something improving over decades benefiting undoubtedly from the original Army material as well a more modern learning concepts and presentation formats.
Kind of like just the device I’m typing this on is more advanced than the best Army supercomputer from the same era.. better than the best Air Force inertial reference and navigation platform from the same era… and way better than any CIA spy camera!
Love your video.. can you do a video explain about tail rotor buzz? Thank you very much!
Affiq Azri. I'll add it to the list. Thanks for the suggestion.
Very well presented. In a full scale helicopter on a slope, the helicopter must have been landed there so unless a skid or wheel has sunk in or the aircraft slid then bumping is overcotrol by the pilot but something one might do gently to see where your limits are. So you ease off a wee bit and then make a positive break with the ground accepting you will not be able to go upward absolutely vertically initially as you break contact with the ground. A friend of mine was killed in Oman in 1978 or 9 whilst flying a Bell 205 Huey and it was thought he instinctively pulled back to avoid some seagulls - he was skimming across the sea near the desalination plant or he wasn't paying attention and suddenly realised he was about to hit the jetty - all terribly sad. The wreckage suggested mast bumping. So how do you contour fly a Huey over prolonged distances at ultra low level - as I did as a military pilot. Firstly one is aware of the danger of negative G. One tries to vary height with the collective rather than zooming by inputting aft cyclic. If you shoot over the edge of a cliff you initially dump the collective quickly but not as a snatch. You may go Weightless but that doesn't matter as long as the cyclic is centered. As you feel the Weightless sensation subsiding you can then gently but quickly push the cyclic forward so that the helicopter goes into a nose dive. It is all a matter of feel. I don't ever remember any instructor dwelling on this but I do remember throwing the Huey as I have with any helicopter I've flown - Wessex, Bell 206, Westward Scout etc.... - all over the sky, showing off as one did as a young military pilot, without ever worrying my rotor shaft might snap. The important thing is to appreciate what the rotor head is doing. What you NEVER do if you have that Weightless sensation is to input any aft cyclic because the blades have become a bit unstable and there is a real risk of one striking your tail boom - and that's curtains!😡. Now how you deal with this in a model helicopter when you have no seat of the pants feelings I'm not quite sure. I suppose you apply what I used to apply leaving greater margin for error. Flying the Bolkow 105 with a rigid rotor head one had none of those worries but as I always had paramedics on board I didn't think it was fair to turn upside down and having an iota of self preservation I would have wanted someone to demonstrate it to me and then watch me do it. Torque turns and very steep wingovers maintain positive G - albeit only a little. I always thought the Gazelle was light enough and fast enough to be able to do a barrel roll - where you maintain positive G throughout - BUT if ons cocked it up it could be a case of curtains 😢. I hope someone enjoys this ramble from an Old and Bold pilot who is still alive! - but now flies model aircraft.
Do you think you can prepare a lesson concerning the different shapes of rotor blades ie.. swept tips etc. Thank you sir and fly safe.
you are wonderful
I 100% agree with you but the faa helicopter handbook clearly says you will roll left in low G. Studying for cfi checkride and confused why the faa handbook is different
Would like to see a video with whats involved in a commercial flight test. For Helicopters
Please explain how more cyclic or more power, give you clearance. The rotor head can tilt x no. Of degrees before contact. How does more power or cyclic change the angle of contact.
OK your channel is awesome. Hands down. This video was helpful to understand what may have happened in the recent Robinson crash. Although her tail came off, that might also have something to do with it :P
Hi Jacob, nice series of videos so the average Joe can understand. What do you mean by the main rotor disc being "unloaded"? How is the main rotor thrust reduced at the crest?
Jeff. Think of loading and unloading the rotor as increasing the lift it is currently producing. When the aircraft starts a cyclic climb, the G forces increase and the rotor “loads” as it cones. It’s as if the helicopter weighs more with these increased G forces. The rotor “loads” up the weight. When the aircraft pitches over forwards the rotor unloads the weight of these G forces. In essence, it unloads the weight. I hope this helps.
Truly excellent tutorial - thanks. Came here after a search of mast bumping while reading a crash report of a fatal incident involving an R44. Subbed! Now for a question from someone more familiar with the physics of fixed wing flight....Cannot the rotor mount in simpler designs be such that this contact is prevented through either clearance or physical means? Or does the nature of rotary flight require a degree of tilt and blade flexibility that such range of motion is required?
Got a whole video covering rotor design that should answer your questions. Check out my “Types of Rotor Systems” video.
Dumb question here, but can you reduce the rolling and side-slipping during a push-over with pedal input?
Why are those rotors designed to depend on center of gravity and allowed to swing freely instead of being spring-loaded to not move beyond a safe range?
TiagoTiago. Good question. I don't design helicopters but it sounds like a good design feature. The only reason I can think that it might not work is that if the semi-rigid system has too much spring-loading, the blades may begin to absorb the flapping stresses instead of the flapping hinge. Thanks for the feedback!
Bell 206 is it articulated or ridged or semi ridged?? it was and still is my favorite Helicopter as well as the Long Ranger. ??
Could you please make a video on Low G and the effects on the helicopter? And what to do to correct it
Joao. I’ll add that one to the list also.
Whats with mast Bumping on helicopter that either on a slope or a low g flight? Saw some Videos with helicopters that drestroys itself on a even ground!
@Matt Henderson There was concern for a recent R44 double fatality that Mast bumping may have been a cause, but the ATSB has not released their final report on the incident. All we do know for sure is that the rotor came down about a block away from the air frame which dropped into a backyard fortunately missing a house.
Rotor separation is definitely a result of mast bumping. But so could poor maintenance practices. It’ll be interesting to see what the investigation board finds.
Hello! Thank you for the videos- short and sweet. May I request more on aerodynamic hazards for the Robinson R22? I’m working through my private. Thanks!
K. S. Thanks for the feedback! Unfortunately I've never flown or studied that specific aircraft and therefore don't claim to known everything about that bird.
Helicopter Lessons In 10 Minutes or Less
Thank you. I will continue to appreciate your videos!
I have run into a couple of pilots who are proned to mast bumping.I found it was their technique really, as it varies from pilot to pilot, not machine to machine.My origional flying instructor back 40 years ago , suggested to me that it was all in the hands of the pilot. Not a bad answewr really. Or what about the P of F formula ie., CLHALFEROWVSQUAREDS!!!!
Why 2 blades rotor can not have fully articulate blades to prevent mask bumping?
Gud..no bullshit..to the point. Thanx.
Can uh please explain me about ARDDs
when you loose the rotor in flight, the helicopter has the aerodynamic qualities of a cinder block, pull aft on the cyclic to level out, correct the roll, do not reduce collective and when you land, thank youtube for putting this video on for all to see.
"when you loose the rotor in flight", aft cyclic won't do much.
@@yeolefatdad8872 something to hold onto while you get a many wonderful 360 view of the surrounding around you.
Not so great auto rotations seems to also be a cause. While flaring if you contact a stinger or the rear of the skids while in to much a rearward tilt, the disc usually become unloaded and the quick fwd tilt of the fuselage has caused the rotor hub to contact the mast.
Johbros. Great point.
One thing to consider, if you bump the rear of the skids Upon landing and the rotor bumps the mast and caused damage, you are already on the ground.
Hey Jacob,
I live out here in Texas and an R-22 crashed in Rowlett, TX due to tailboom separation. I imagine this was from mast bumping. Can you please explain what you think they were doing to cause this? Thanks
It could be possible that a low g situation occured ,or they were flying very slowly or even hovering and entered a vortex ring state also known as settling with power. The rotorcraft would have started to the right, and possibly the wrong cyclic input sealed their fate.
Just speculation, but it appears from the flight profile that they were practicing recovery from settling with power. When the helicopter enters settling with power, the nose will drop. The control inputs to recover are to lower collective, some right pedal to compensate for loss of torque, forward cyclic to gain airspeed, fly into "clean" air, then raise collective to arrest the descent. What appears to have resulted was tail cone separation about 2 feet forward of the tail rotor gear box. Its possible that whoever was on the controls applied aft cyclic when the nose dropped. The aircraft would have been tail high and, as the main rotor was tilted aft, the main rotor blades struck and separated the tail. Another possibility, though less likely, is demonstration of a low G pushover, which is prohibited in the R-44. Actually, all Robinson helicopters. This could have also resulted in a nose low attitude and caused excessive blade flapping, resulting in a tail separation. These are just my opinions based on the little evidence and not accusations toward the crew. God bless their families.
@@herbie509 Thank you for your analysis Craig. I’m a fixed wing guy so I value a rotorhead’s examination greatly.
@@Back2Africa_Overlandthank you sir.
muito bom
Can this happen in an autorotative descent ?
Thank you 😊 #HLI10OL #SkyBaum
Thank you sir. If you don't want to reduce collective during recovery would increasing collective be of any benefit? Thank you again sir.
David Wallace. Yes. Increasing collective would load the rotor system and give it positive thrust again.
Helicopter Lessons In 10 Minutes or Less Thanks for your prompt response, sir.
Do you think mast bumping is what caused the recent crash of the Robinson R-44 in Texas?
It is not correct that the main rotor thrust is decreasing when you push over. Why should it? It has more or less the same collective setting and the same rpm. It is the the gravity force m*g of the whole helicopter which is decreasing due to dynamic change in the track curvature and all the forces: rotor thrust, tail rotor thrust and m*g will get out of equilibrium or trim state, resultung in a roll initiated by the tail rotor thrust with some lever arm over the the C.G. That is why nothing happens when you push as much as possible and as fast as possible with the R-22/R-44/R-66 at hover or low speed. The helicopter had virtually no track to build a curvature apon, so there will be no inertial forces reducing the m*g and leading to untrimmed state.
I’m not a pilot so I’m ignorant about this but why wouldn’t there be some kind of software that limits this?
Do these types of main rotor heads not have bump stops and what about collective stops to prevent over travel of the collective? I have over 20 years of experience working on Apaches from the Alpha models to the current Echo model.
The bell 47 has dynamic stops on the rotorhead
Jacob when’s the next video due? We miss you
DDT DDT. Haha thanks for your concern. I've been swamped with work the past few months but I'll try to start pushing more out in December. I've also been working on a another project I think you guys will like.
What causes the loud chop, chop, sometimes heard with Hueys. UH-1H?
Fucking capet bangers
Why Robinson's are banned from mountain flying in New Zealand.
I'm here trying to figure out why the Robinson crashed because its blade(s) flexed or moved enough to contact the fuselage (top of canopy).
Any ideas or input you'd like to share on that crash or the mechanics of it?
Thanks for the video.
I haven’t seen the crash investigation or the video so unfortunately I can’t comment.
@@helicopterlessonsin10minut10 I'll have to find which incident I was referring to. There was another Robinson that went down into the water near Miami today. From what I've read Robinsons have an issue with Mast Bumping.
Hard-stops before exceeding mechanical limits have been part of steering and suspension systems in cars since day 1. Why are they not part of the rotor pivot?
They are on the bell 47 helicopter
I miss my Bergen Gasser!!!!!!!!!!!!!!
Looks like Ft.Hood.
Pretty sure this is what's happening when my rotor separates on my Huey and Ka-50 in DCS.
Even I understood that
why have I heard that it's good practice in a low g roll to not only gently bull back on the cyclic, but to also gently lower the collective?
W. McMaster. Generally the advice is to pull aft cyclic to load the rotor and adjust flight controls for normal flight. The collective is generally not lowered unless there is a risk of over torquing or engine limiting. (But in this case the rotor should be sufficiently loaded.) You have to be careful reducing the collective here because above all you want to keep the rotor loaded. Suffice it to say, it depends on the situation and where your collective / rotor currently sits. Thanks for the feedback!
But how exactly does raising the collective prevent bumping on sloped takeoffs?
Not sure why an engineer wouldn't just design these helicopters to not be able to physically articulate past the point of causing catastrophic damage. Why does it need to be able to move so much past the point of being able to use it?
Thank you very much for explaining how functioned a helicoper. But I would like german subtitles so that I can understand it better, that would be great🚁🤔👍
This video explains sorta what happened to Kobe helicopter 🚁 while he was attempting to climb the foggy 🌫 morning weather
Yup...
Kobe’s crash was caused by the pilot flying into fog, getting disoriented, and crashing without realizing it. The Sikorsky S76 does not have a semi-rigid mast, so there is no risk of mast bumping in low-g conditions.
The most common helicopters that crash due to mast bumping are the much more common (and affordable) Robinson R-22, R-44, and R-66 helicopters. Many Robinson pilots have died due to mast bumping, which can cause catastrophic rotor separation, or it can cause the rotor to sever the tail or strike the cockpit - any of these will be fatal. Mast bumping can happen not only due to a low-g pushover (which must never be done in a Robinson helicopter), but it can even happen in level flight with strong enough turbulence. The faster you’re going, the less turbulence it takes to do this, so you must slow down the windier it is - and land if it’s not safe to continue.
Helicopters look more complicated than fixed wing aircraft
They are! It’s like taking the engine from a plane, replace the prop with the wings and bolt it on pointing up!
Not spin them at several hundred rpm😂
Friends only let enemies fly Robinson. 😉 _cough_ Bo105 is the way to go _cough-cough_
Why more mast bumping in robinson but hardly in bell 206 ?????????????????????????
Not answered Yet ????????????
Well.....I have heard of cow tipping on farms but never mast bumping in helicopters.
I think point number 2 is misworded.
THAT'S what mast bumping means?
My creepy uncle lied to me.
Lol
Extreme cases can cause a clean underwear shortage onboard....
😁
I bumped my head in a helicopter crash. I can no longer say Cabernet Sauvignon or "free refills" so I can't go to Paris or McDonalds.
The only reason for mast bumping is faulty design.
you've gotten to the bottom of why this is a sensitive subject for some people.
"Budget car can't turn as quick as Bugatti" - ooooh news worthy!
*rolls eyes*
Why does design allow this? Car doors and steering have LIMITED movement.
Aircraft do have limiters in the form of a Droop Stop and flap limiters. But with enough force these can be overcome and mast bumping can offer. It’s a severe downfall of the semirigid rotor design and why many military helicopters today no longer use the design. Once again, you really only get into this condition with rather aggressive maneuvering.
Easy
Video about mast bumping: starts with a helicopter not susceptible to mast bumping.
Sorry I couldn’t put up a video of mast bumping with a helicopter that’s susceptible to it. It’s a little hard to keep a steady camera during main rotor separation for that type of video.
@@helicopterlessonsin10minut10 not a mast bump, but amusingly related: ua-cam.com/video/yWaezf0MPE4/v-deo.html
F that. I'd rather not get into a death can suspended in the air by a room fan in the first place.
"room fan" lmao
"...Hi everyone---my name is Kobe Bryan and I approve this Video."
A hot chick bumped my mast and I blew my rotor...
mast bumping.......shit....for those of us in hueys its mast BUMP.......as in one fucken time
What a bullshit design flaw.