Can you fly with one blade missing?

[manfromuncle]

Sounds daft, but bear with me..

I remember reading a story once, possibly from the Korean war, where a heli was shot down and the pilots removed the damaged blade and managed to get it airborne again (albeit with some serious shaking!) to avoid capture by the enemy.

Anyone heard of this story? Do you think it's possible?

I might have read it in this:

http://www.amazon.co.uk/Tales-Helicopter-Pilot-R-Kirkland/dp/1560989521

But I don't have the book here so I can't check.

[HillerBee]

Impossible. The imbalance would roll the helicopter over in seconds. Blades on a Hiller or Bell47 in those days weighed around 85 pounds. An imbalance on a Hiller of a .1 ounce make them already shake like .....

[Flying Bull]

Don't think so.
You might have a chance if you have 4 blades and remove 2 - but thats only a guess.
Going through all the accidents, where a helicopter touched someting with the blade - and knowing how tiny the bolts on the main gear box are - and having had vibrations, only to a lost sctoth tape - one blade off would rip out the gear box in moments.
Greetings Flying Bull

[kiilik]

Hey. I have heard the same story, that a copter crew was shot down in vietnam. They flew with "Killer egg" four bladed, similar to 500. So they removed damage blade and the oposite blade and took off before captured.

Dont know is it true:rolleyes:

Regards Kiilik

[ericferret]

I believe that a Bell 205/212 lost a blade in the Philipines, aircraft flying in formation reported that the aircraft had "blown up".


A number of years ago a Hughes 500 was involved in a mid air with a Bell 47(Bristows)
in Kent.

The 47 blade got a bit mangled but the aircraft landed safely.

The 500 lost 9 inches off one blade tip including all the weights and went on to land with no casualties.

The damage to the 500 was substantial due to the vibration.

The instrument console sheared off at the base, and there was little structure left retaining the tailboom. It was possible to move the boom end up and down about 18 inches.
Tough aircraft!!!!!!!!!!!

[Rotating Star]

A rotor sytem with an odd number of blades and missing one of its blades would shake itself to bits well before flight rpm.
With an even number of blades (eg 4), if you remove 2 opposing blades you would need twice the angle of attack on the remaining blades to produce the same amount of lift. Assuming you could raise the lever high enough would the resulting pitch angle cause the blades to stall?
Any deciples of Prowty out there care to enlighten us?

[donut king]

Someone should try it!!!!

[ericferret]

www.flying-circus.org/roll%20call/aviation%20unit/aviation%20unit.html

Someone did
One Tom Wiktorek to be exact.

[NutLoose]

Yes it can be done........................ and THE PROOF to show it, see

http://www.popasmoke.com/visions/image.php?source=4225

[docstone]

I recall a video of a US Super Stallion loosing as blade whilst mid-air refuelling - all seems well until the helo appears to catch up with the refueler and as he tries to compensate the refueling line disconnects and flies upwards taking out at least one blade.

The helicopter certainly doesn't fall out of the air or appear to tear itself apart - quite what happened next isn't covered on the video, hope all walked away (probably with a few hefty dry cleaning bills).

[NLJ]

docstone,

the video I think you are referring to can be seen here:
http://www.youtube.com/watch?v=iyAMC7miuy4
The blades remain intact, but the refuelling probe gets trimmed!

[mechchick]

I would not like to do the vibe run....and I think the 2 pers (well now theres a quandary there wouldnt be any 2 pers with 1 blade missing lol) would just about kill the drivers kidneys!!

Given that the blades cone when under load and the loading is spread across the disc (in a perfect world) I can see that you would lose altitude very quickly (no autos on one blade - you are the deadmans curve then!!)
and it would probably be safe to make the assumption of the flight ending in a large smoking hole...

Dunno I will ask our test pilot what he reckons - I bet I know what his reaction will be F:mad: off!!!

[nodrama]

Both a British Army Lynx and a Gazelle, and a Bristow 76 have lost a MR blade in flight in previous years. No survivors. I think to get a helicopter back on the ground and walk away would depend greatly on what stage of flight it happened and on a great amount of luck.

[skadi]

As far as I remember my BO105 groundcourse several years ago, the centrifugal force on one blade at 100% NR is about 10 metric tons!!!
So loosing one complete blade would result in an massive imbalance and total destruction of the dynamic system in a very,very short time .

skadi

[Graviman]

Any deciples of Prowty out there care to enlighten us?


Any out of balance would seriously affect fatigue life, and it would not be long before the rotor parts failed. Any unusual vibration is bad - get the machine down.

In theory removing half the blades, if system is still in balance, doubles the blade pitch. This means machine limits are halfed, so any manouvre will stall the blades with a good chance of overtorque on the transmission. Not generally a good idea.

[212man]

Bristow 76 and in a mid air with a Bell 47(Bristows)

Sadly, one and the same pilot. One of life's true gentlemen:(

[NickLappos]

The problem with the loss of a large piece of rotating mass is not the loss of lift (most rotors have enough collective pitch to give the remaining blades the angle necessary to make up the lost lift.)

The vast problem is the whirling imbalance, which is usually several times the mass of the helicopter. For a 10,000 lb helo, the blade might have 30,000 lbs of centrifugal force (physics jocks please forgive me) so that the loss of a blade can give you as much as 3 g's of lateral imbalance.

This is not just a pilot shaking problem, it is also a primary structural nightmare. The fuselage usually has a lateral natural frequency of about 3 to 5 Hz. To see this vibration on your helo during your next walk-around, try to shake your helo by grabbing the tail and giving it some tugs laterally. Find the natural frequency by shaking it where it "likes" the frequency and shakes a bit more, like "pumping" a swing to make it get higher. For many helos, this natural fequency is lower than 1 per revolution, so it can be excited by the big imbalance due to the loss of the blade. For larger transports, this frequency is the torsional-lateral tuning of the vertical tail and the tailcone.

If a blade is lost, the shaking can literally tear the aircraft apart, typically by collapsing the tail cone where it attaches to the fuselage. Look at this terrible video carefully, and note how each airframe failed in the same way, at the same place, long before the ground was struck:

http://www.thatvideosite.com/video/868

[Mark Nine]

During my 'Battle Damage Repair' course in the Army, we were told it was possible to saw up to 1 metre off the end of all 4 Lynx main rotor blades if they were damaged.
Knowing what I do about M/R track and balancing, you would have to be spot-on with the measuring of the saw line to prevent a massive unbalance.
Centrifugal pull of one Lynx M/R blade = 55 tons!!!!

[Flying Bull]

Hi Mark Nine,
The Lynx can take it (partly).
There where two near similar incidents, one with two german Navy Lynx and relative short later with two british Lynx, they just didn't belive and had to try themselves ;-)
While doing formation flying - they flew just a little bit to close and touched rotorblades....
On both occasions all helicopters managed to land - the germans on their frigates, the british did it over land - so no deck landing required.
From the german side:
One helicoter lost parts on all four main rotor blades....
the other one had bend edges.
The one with the bend edges had the worst vibrations.
Couple of years later one Lynx lost a part out of one blade - about an meter or so from the point where the folding gear is normally attached.
They decided to ditch and were rescued later.
But prolonged flight isn't recommended ;-)

Greeting Flying Bull

[skadi]

Flying Bull wrote:
The one with the bend edges had the worst vibrations.



I suggest, that in this case the vibrations came from the disturbed aerodynamis ( out of track etc. ) rather than from mechanical imbalance due to different masses. Same reason as for the partly loss of scotch tape .

skadi

[Dave_Jackson]

Yes a helicopter can fly with one blade missing.

However, it requires a special rotor.

The swashplate must be replaced with a swishplate (http://www.synchrolite.com/Swishring_Name.html), plus the normal blades must be replaced with gay blades.
The swishplate has the ability to control gay blades as they continually depart and return to the 'group'.

[ericferret]

The Bristow S76 that crashed off Yarmouth lost about 12 feet of one blade.

The head and main transmission were torn out of the airframe.

There is a full report on the AAIB website.

For the record that was the second Bristow 76 to loose a blade, the previous aircraft accident was caused by spindle failure again not survivable.

[Scissorlink]

I also read about an OH6A pilot who got shot in a blade and had to land behind enemy lines. After removing the opposite blade (leaving two from four) and stripping the machine bare he managed to get it airborne and stagger back across to safety, have no idea where I read it and I have tried to find it a few times...Is it in "tales of a helicopter pilot"??

SL

[riff_raff]

As Mr. Dave Jackson should be aware, a rigid rotor configuration would be more survivable than a hinged rotor configuration in a blade-off condition.

Right?:ok:

[NickLappos]

I flew chase for those flights, back in the day. Same config, one shot is from below, so the rotation appears backward.

The 3 bladed flights were flown to confirm the behavior of the rotor at lower blade loadings, so that performance for the next gen of Sikorsky helos could be examined. The ability to recover was also tested, of course, but at the cost of flight test, that was not the biggest driver.

The vibrations were simply awful, BTW. The normal 53 needs no vibration suppression gear, but since vibes go up when number of blades go down, the three-bladed 53 was another world. The pilots (Jim Kay and Al King) had difficulty reading the instrument panel.

[Mark Nine]

I think what cross-land is trying to point out is that the rotor blades are a different style. Look at the point where the extension arm changes to the lift section. On the six bladed aircraft, the change is 90 degrees, (old design) and on the trial aircraft the change is 45 degrees, (a newer design).

[NickLappos]

Mark and cross,
You are both right, I missed that detail!

The 3 bladed flight was flown with cut down IRB's with SC 1095 airfoils and titanium spars. The original 53D has NACA 0012 airfoils and aluminum spar blades. Using the newer blades gave better data for the real purpose of the test, to determine the performance for the newer Sikorsky designs.

[Fareastdriver]

When the BV 234 was first introduced to the North Sea one of the assurances given to the Shell passengers was 'Twin Rotor Safety'. They honestly believed that it could fly on one rotor.

[TheMonk]

If I'm not mistaken, there is/was a one-bladed helicopter that flew. Bolkow 101 I think.

Monk

[John Eacott]

Like this? The Bo-103

http://www.luftrettung-hamburg.de/assets/images/BO_103.jpg

And the Bo-102 Helitrainer

http://www.geocities.com/capecanaveral/launchpad/5249/Bo103vistas.gif


http://www.eurocopter.com/site/docs_wsw/fichiers_communs/images/histbo102g.jpg

[Gaseous]

I bet its easy to track:} - and I bet you cant fly that with one missing:}:}

[TimmoWhakatane]

I dont really see the point of a single bladed design as wouldnt you still have the same rotating mass but less lift?

What are the benefits? :confused:

[Dave_Jackson]

For the interested :8, or the very bored :bored:

Research and development work on a Single-Bladed All Electric Rotor (http://www.unicopter.com/ElectroRotor.html)

It appears that the single-bladed rotor will work well in hover and in vertical climb. Forward-flight is the problem. It's unfortunate because it would have been a simple and fun project to build.

Dave

[Graviman]

I would hate to be the guy that lifed the hub bearings on the BO-103!!:eek:

Even though the mass balance is there, effectively it is as if the cyclic was going around the box at Nr. The vibration must have been awful. The mass could have been set lower than hub to generate an equal and opposing hub moment to the lift, but this would only work for 1g. Any actual cyclic input would still lead to out of balance moments, hence a means of 1P vibrational energy getting into the structure.

I wasn't sure if that hub was teetering - it's hard to tell from the hiller bar. However, cyclic vibration is why hingeless hubs always have 3 or more blades...

[Dave_Jackson]

Mart,

Vibration should only have been a problem during any attempt at forward flight. It should not have been a problem during vertical; climb, hover and descent.
See the links at the bottom of this page http://www.unicopter.com/B465.html

Dave

Here is the Boelkow hub plus additional information on the craft. http://www.unicopter.com/B472.html

[bugdevheli]

A friend of mine was test starting the engine on a 22. The machine was minus its main blades, but had tail rotor blades. The engine fired and a split second later one tail rotor blade broke loose, the next second the tail rotor gearbox plus a section of the boom departed and was found later about eighty yards away. The belt drag on the pulleys was enough to spin the drive train up.:O:O:O:O

[manfromuncle]

I wouldn't mind seeing the video of that!

[Frober]

We lost a S-61N in the North-Sea in 1978 due to a spindle brakedown followed by a blade loss. They found helicopterparts on the seabed covering about 1 sq.km. due to domolation. 21 souls lost.
Another S-61N (Brazilian) actually flew into the sea due to severe vibrations in June 1997. The pilots lost control completely. The wreck was picked up from 800 meters depth. There are 2 theories:

-One blade abration strip came loose. The weight is 340 grams, but due to angle of speed it induces much, much more. Heavy lateral imbalance!
-Another theory is that on blade broke and lost approx. 1/3. This was found on the seabed about 100 meters from the wreck. The rest of the blades were twisted around the hub as they met the water.
2 of 20 lost their life.

Conclusion: NO :=

[Backward Blade]

I am a bit of a practical man if I do say so myself. And yes I did bear with you for the last couple of days. SO...experimentation aside, and/or removing a blade on the ground for test purposes is one thing, the fact of the matter if you lose a blade in flight you're screwed! Occupational Hazard.

BWB

PS

I found the research many of you did enjoyable to say the least. Burned alot of my time while weathered out in the bush. thx

[arjens]

After reading here how death is almost unavoidable when the MR becomes unbalanced, wouldn't it be a life safing option when it is possible to "just eject" the oposing blade?

That would probably give enough stability to safely autorotate ...

[Thomas coupling]

Some scarey people out there....:eek:

[Fred Bound]

"....wouldn't it be a life safing option when it is possible to "just eject" the oposing blade?"



BRILLIANT!

May I be the first to suggest to arjens that he puts his idea to the test in a 206, or maybe a 350.

Or ANY helicopter for that matter..........

[arjens]

:eek: okok..

I know it wouldn't be applicable to e.g. a 206. But how else could you ever escape from this? Maybe thats a better question then.

[TRC]

If a helicopter sheds a substantial part of a main rotor blade - let alone a whole one - in flight, the occupants will be killed instantly. The massive lateral g generated by the imbalance will break the necks of all on board in a fraction of a second.

Not much more than a fraction of a second later, the entire transmission will depart the airframe. So if you survive the initial shedding of the blade, you will not survive the loss of the rest of the main rotor and everything else that gets torn out.

I can't think of any safety measures that could be incorporated into a helicopter design that would operate/deploy/whatever, in the time that would be available in such an event.

[Fareastdriver]

TRC
That about sums it up, really, doesn't it?

[TRC]

That about sums it up, really, doesn't it?


I'd have thought so, but after 48 posts on the subject I somehow doubt it.

[arjens]

... :oh: ok

[diethelm]

"Can you fly with one balde missing?"

Yes you can, for a very, very short period of time. However each specific aircraft is only capable of doing it once and each pilot and occupant can only do it once per lifetime. However, it is highly unlikely that the remains of you, the occupants and the aircraft will land in a normal or acceptable manner.

In addition, you may in a Robinson R22 perform a loop, roll or other aerobatic maneuvers. However, like losing a blade, you can only do it once per lifetime/aircraft. This landing too, is likely to be somewhat abnormal.

[Dave_Jackson]

Wings seldom fall off.

Considering today's technological advances, such as strong lightweight composite construction and elastomeric bearings, perhaps its time that manufactures made a significant move toward 'absolutely' rigid rotors (http://www.unicopter.com/B329.html#ARR). Rotors that turn slower and have larger chords.

Perhaps it's time to re-thing the Blade Loading Coefficient [coefficient of thrust / solidity] (http://www.pprune.org/forums/showthread.php?t=250086#11).


Dave

[Dolmangar]

Yes you can, for a very, very short period of time. However each specific aircraft is only capable of doing it once and each pilot and occupant can only do it once per lifetime. However, it is highly unlikely that the remains of you, the occupants and the aircraft will land in a normal or acceptable manner.
In other words...
"You can fly all the way to the crash site?"

[Graviman]

I would just like to alter the direction of the thread to:

What design modifications would improve helicopter crew chances after blade damage?

High bypass gas turbines are designed to continue running in the event of a blade failure. The trick is to mount the bearing system in a compliant mount, much lower than the rotating frequency, and critically damp the system.

A large heli rotor rotates at ~4Hz, so the compliant mount requires at least a linkage and spring arrangement to mount the mgb (more weight :uhoh:). The full weight of a blade would shift rotor cg, too far for even this to handle. So what about designing a weak link in the blade, just at the position that such a mounting system could handle? Maybe include dampers on tensioned wire to absorb tail lateral modes?

It won't stop blade shedding accidents, or events where rotor system takes a severe impact. It might just avoid accident where the rotor just takes a knock from becoming catastrophic.

Any thoughts?

[TRC]

It won't stop blade shedding accidents, or events where rotor system takes a severe impact. It might just avoid accident where the rotor just takes a knock from becoming catastrophic.

Any thoughts?


Graviman, the theory maybe fine but the practice isn't.

The point here that is being missed is not what to do when a blade loses interest in it's primary job, but how often it happens.

Airbags were developed in cars to reduce the injury to occupants in accidents that occur on a very regular basis, Christ knows how many per day. To provide a system that offers a chance of survival to helicopter occupants in the extremely rare event of a blade coming off would render just about all helicopters unviable - either through the cost of the system or, with the smaller variety - too heavy to be worth flying.

If someone could come up with a design for a system of a 'compliant mount' that would accept and cope with the loss of the weight of a main rotor blade at operating RPM - and cope with the resulting aerodynamic abnormalities without a weight and cost penalty, then I for one would be very impressed. I'm not holding my breath.

The statisticians amongst us might be able to tell us how many helicopters have been lost to blade shedding - i.e. how many events per many million flight hours.

I would prefer to see smoke hoods rather than lifejackets in commercial airliners first.

[Graviman]

TRC, i agree entirely with what you are saying (interesting about the smoke hoods). It is not an easy task, and clearly the blade root has to be strong enough or the machine goes down. Also i agree that total blade loss it is a rare event, but i am considering events where blade suffers some damage from impact - which is generally at the tip.

Statisticians can only work with data that they have. Is there any modification worth considering, even if the statisticians later reject it?

For example mgb could be mounted on a linkage system, which allowed large longitudinal/lateral movements but good rotational coupling - basically a subframe. This system does introduce mass, and is limited in how much movement it allows. It is also only suitable for the new generation of hingeless rotors. It also offers the product advantage of good vibration isolation, with potential for vertical isolation too. If much more that the tip gets damaged the movement will destroy the powertrain, but the rotor remains attached long enough to autorotate to a survivable landing.

What i am really asking is there any merit in a design study of this and potentially other systems. From your response so far the answer is no, but the question is one worth asking.

[TRC]

Also i agree that total blade loss it is a rare event, but i am considering events where blade suffers some damage from impact - which is generally at the tip.

Tip damage usually occurs on or near the ground as a result of striking an object on the ground. Also, a tip-strike is unlikely to cause catastrophic drive-train damage, so the need for a lengthy autrotation is unlikely.

For example mgb could be mounted on a linkage system .......... with potential for vertical isolation too.

At least one manufacturer has come up with something like this. The Bell 'Nodamatic' system as found on LongRangers and I think the 222 (and some others I think) reduces main rotor vertical vibration quite well. It is quite bulky and relatively heavy, and all it does is damp out vibrations measured in fractions of an inch per second. What it would look like and weigh if it could cope with the kind of massive destructive forces that the loss of a component weighing up to several hundred pounds rotating at 350 RPM or so - I can't begin to imagine.

I can't think of anything else to say..........

[Graviman]

TRC, 'nuff said - thanks for the discussion. Clearly the view is that rotorstrikes are unavoidably serious, and that any attempt at a design modification would be impractical so cannot be justified.

Googling for some more info on the Bell Nodamtic system i got (no suprise):
http://www.pprune.org/forums/archive/index.php/t-196414.html

The Nodamatic suspension is designed to eliminate the two per rev vertical beat that is common to Bell single rotor helicopters. When the Bell blades are aligned with the longitudinal centerline they lose lift and as such the fuselage drops. The Nodamatic allows the transmission to move in relation to the fuselage and the suspension system has calibrated weights that respond to the vertical bouncing of the transmission in relation to the fuselage. The moving of the weights causes a counter force to resist the movement and it cancels out the vertical beat in the fuselage. The way the Nodamatic is hinged I would assume it would allow lateral movement of the transmission when not in operation but not fore and aft. The primary movement is up and down during flight but I would think that if the trannie can be displaced laterally when static that some lateral movement could take place when maneuvering. I think.

more technical info:
http://www.sae.org/technical/papers/760892

Another potentially usefull general resource, other than PPRuNe Rotorheads:
http://www.geocities.com/capecanaveral/launchpad/5249/index22.htm

[Mark Nine]

Check out "MH53 into an antenne" on www.alexisparkinn.com/helicopter_videos.htm (http://www.alexisparkinn.com/helicopter_videos.htm)
to see just how much you can accidently knock off the end of your blades and still get away with it.:eek:

[Graviman]

Just shows that it is possible, and potentially required, for continued flight after rotor impact. Perhaps that one was lucky to have trimmed all it's blades into balance, so structure did not resonate...
http://www.alexisparkinn.com/photogallery/pave_low.jpg
Going for minor overhaul!

[wobble2plank]

I seem to remember there was a Lynx (NL ?) that had a tie bar failure in flight which resulted in the loss of the crew and airframe.

The post crash accident report stated that the rapid roll onset broke both the pilots necks shortly after the blade departed. Water ingress into the sleeve and spindle joint allowed the delaminating of the 'dog bone' tie bar which led to the failure.

Result: Loss of blade in a Lynx=Catastrophic, not even enough time to 'blow' the other blade (even if you get the right one ;-) ). Mass inspection and replacement of tie bars which incidentally, Westlands only supplied in batches of 5 (????????)

W2P