Anti-flail devices

[ronnie barker]

Hi there my name is Mr G Barker i am a member of the British military (MOD) who works on the Apache and i am undertaking a project on re-designing the excisting Anti-flail device for the Apache helicopter for my foundation degree. I am trying to find out if anyone on this site knows of any aircraft that uses anti-flails for there drive shafts, and if so do you know where i can obtain the information about these. I am looking ideally for an helicopter with a split ring anti-flail.

many thanks Mr G Barker

[dangermouse]

on who's behalf are you doing this work

Boeing?
Agustawestlands?
the MoD?

a bit more clarity may get you some responses, however a wild shot in the dark about a military aircraft safety device without any credibility as to the requirement for the info is not likely to get you any answers

You dont live any where near a location that would need to know that info and the manufacturers wouldnt need to ask on this site anyway

DM

[ronnie barker]

This engineering project is part of my engineering degree, and thus i am not expecting the results to be implemented, unless ofcourse we manage to find out as much information that the MOD, find this to be to good an idea and save enough manhours to make it feesable and cost effective. Any further clarification to this please feel free to reply.

We are planning to try and make the Anti-flail device a split ring device, (by modifying the excisting the present item) so that the removal of the whole item is not required and this the removal of the drive shaft can be removed in atleast half the time.

[riff_raff]

ronnie barker,

There was much development work done recently for the EU's ERICA tilt rotor program regarding anti-flail devices for its composite cross-wing drive shaft system. Try searching for relevant tech papers on the internet.

Good luck,
riff_raff

[nodrama]

Dangermouse,

You are barking up the wrong tree.

Suffolk happens to be the home of a large British Army helicopter base, including a well established maintenance facility.

RB is most probably an ex or soon-to-be ex military aircraft technician who has embarked on a degree course to enhance his civilian job prospects. He is using the Apache as his subject airframe as that is the type that he has experience of.

RB, you wouldn't happen to be REME 'Ronnie' Barker, about 40, used to be big into motorbikes?

[ronnie barker]

i am not the ronnie barker you are thinking about, and i am on a career course which incorporates the degree. Not leaving the army for atleasrt another 8 years. This project is for the mod no for me personally.

[nodrama]

They are subject to a patent application by Bell, but have you seen these...?

Patent EP1327084 (http://www.freepatentsonline.com/EP1327084.pdf)

Patent US6676526 (http://www.freepatentsonline.com/6676526.pdf)

[riff_raff]

nodrama,

That Bell patent for an anti-flail device only looks effective if you have a failure of the flex coupling itself. It would not appear to be helpful if you experienced a shaft structural failure between the couplings, due to some event like an impact. If the shaft is used on a military aircraft drivetrain, damage due to a projectile impact is something you must seriously consider.

And more importantly, some sort of driveline de-couple device would be especially desireable, in order to isolate the driveshaft failure. And to prevent the flailing shaft from beating a hole through any adjacent (flight critical) structure. Such a de-couple device would not really be helpful for a conventional rotorcraft like a CH-53 or CH-47, but for a tilt-rotor like the V22 (which doesn't have such a device), or even Sikorsky's X2 compound, it would be a very effective improvement to the drivetrain's fault tolerance.

Regards,
riff_raff

[nodrama]

Very typical for this site:

very few people will offer up any useful info for a geniune question, but as soon as someone does or an attempt to help out is made, some bright-spark pops his head out of the woodwork and analyses and critics the suggestion......I could have put money on it :rolleyes:

Hopefully your info will be of use to Ronnie though.

[riff_raff]

nodrama,

OK, I'll take your criticism to heart. Here's my suggested approach to drive shaft flex coupling fault tolerance, and why I think it's better than what you suggest:

ronnie is apparently conducting a design study on an improved anti-flail device for use on a rotorcraft drive shaft flex coupling. These devices are normally external annular constraint devices (like your Bell patent "cup" suggestion) or internal shaft prolongs that pass through the bore of the nearest hanger bearing structure. Conventional anti-flail devices are passive devices that only (hopefully) prevent excessive excursions of an already failed shaft. Generally, with flight critical subsystems like a tail rotor drive shaft, it is very desirable to have at least single fault tolerance. But a flex coupling with only one load path, backed up with an anti-flail device, does not provide any functional fault tolerance.

Since ronnie wants to exercise his creative skills to improve a helicopter drive shaft coupling installation, what I would suggest to him is rather than designing an improved "band-aid" approach to a failed flex coupling event, why not set his mind to designing an improved, more reliable flex coupling? What I have in mind is a flex coupling configuration that would have multiple load paths, and thus would have functional fault tolerance that existing flex couplings lack. Maybe an inner/outer concentric flexure of some sort?

Now I don't know if it is even possible to design such a thing. But to me, designing a flex coupling that is less likely to structurally fail would be much more satisfying (and interesting) than designing a better anti-flail device for a failed coupling. It's a case of addressing the problem (ie. inadequate coupling fault tolerance) rather than the symptom (ie. a failed coupling). Who knows, if ronnie is a bright guy he just might come up with a device that serves a need far beyond his intended application.

Regards,
riff_raff