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

Sheer genius
 

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..........

: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.

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.

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.

... :oh: ok

"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.

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. Rotors that turn slower and have larger chords.

Perhaps it's time to re-thing the Blade Loading Coefficient [coefficient of thrust / solidity].


Dave

In other words...
"You can fly all the way to the crash site?"

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?

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.

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.

Graviman
 

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.

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..........

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.../t-196414.html
more technical info:
http://www.sae.org/technical/papers/760892

Another potentially usefull general resource, other than PPRuNe Rotorheads:
http://www.geocities.com/capecanaver...49/index22.htm

Check out "MH53 into an antenne" on 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:

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!

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