What's the latest on tilt rotors?
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Bell 609
Lets get the ball rolling with a simple one.....With the arrival of the Bell 609 in the near future,does anyone care to speculate what kiind of licence will we require to fly the thing, do we all go out and sit the ATPL(A) and Perf A type stuff or what? It strikes me that "Tilt Rotor"may become the industry standard for off-shore operations, so I for one would like to get all the right "ticks-in-boxes" sooner rather than later. Cheers
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I have heard the rumour that the British CAA have said that the Helicopter ATPL licence and IR is what they will require for the 609.
My personal guess is that this will not just be a Britishh CAA decision. I reckon that European legislation will be involved in any future decisions about licencing requirements, and I expect a higher grade of examinations to be required for the Helicopter ATPL as a result
My personal guess is that this will not just be a Britishh CAA decision. I reckon that European legislation will be involved in any future decisions about licencing requirements, and I expect a higher grade of examinations to be required for the Helicopter ATPL as a result
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I heard, early in the development process for the 609, that there was a substantial discussion about how the power lever (for want of a better word) was to work. The rotor types on the team wanted it to work 'up and backwards' for increased power and the fixedwing boys wanted it 'backward to forward' for increased power. Can someone tell me what they decided? It would seem to me that the answer to this kind of question would indicate the final design philosophy and also indicate who was going to be most popular poling the thing.
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We have a Bell 206L3 in our stable and attend recurrent training at Bell Helicopter, Fort Worth, Tx. every year. During my visit last spring, I flew with a instructor named Keith? who is as sharp as a new razor with rotary, and is apparently headed for the tiltrotor program. We hear that the feds (FAA) are working on a "POWERED LIFT" rating on pilot certificates for this class of aircraft. I always felt that if I won the lottery big time, I would pay for my own CONCORDE type rating just for the fun of it before retirement. Now with the impending Bell 609, the CONCORDE just took back seat. This is the cat's ass flying machine, and if you can get trained in it, I feel that you will be in a great position for future employment. Right now, it looks like EMS and OIL RIG service will start this new era, but I don't think it will take long for the corporate world to catch on to this aircraft's capabilities. It won't be long before the captains of industry are landing at their company sites in one of these machines to do business.---CY
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Sorry, forgot to mention this, but in regard to the tiltrotor one of the instructors at BELL said that some pain in the ass general demanded that power be applied with control movement in a certain direction for military models. However, BELL has it figured out that they will build it for normal people to fly also. It's a simple manner of inverting the power quadrant (or something like that).
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Whilst sheltering from the rain (I know, I'm a wimp) in 609 chalet sales guy mentioned 18 firm orders, about half of which were corporate biz-jet; rest EMS or rigs. At projected cost of $8-10 mil I would expect oil comps to get cold feet- doesn't really matter if workers take twice as long on helicopters to reach rigs
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Flew the V22 Osprey Simulator at USMC New River a couple of years back, and the thrust lever worked in the opposite sense that us guys are familiar with. I believe that this may have had something to do with the decision to let fixed wing guys take the lead in flying it.
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I understand CHC has 10 on order for delivery early next century, Northern Mountain has 1 on order as does Skylink Aviation. This from an arcticle I read about a pilot from Cougar helicopters (who I believe has a fixed wing commercial background). He recently had the chance to fly the XV-15, and felt that "the 609 definitely leans towards the rotary end of the operational spectrum" YIPEEEEE!!!!
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MV22 Osprey Accident Theory
The articles I keep seeing (see box below) and the direct transcripts of Marine Aviation Chief Lt General Fred McCorkle's press brief - lead me to believe that they are at risk of believing their own (and Boeing/Bell) hype about "there being nothing wrong with the design". So I have sent via two different routings, the following "heads up" to Col Dennis Bartels who is leading the investigating team. I've no doubt that he has all sorts of AMES people to hand and a wealth of technical advisors. However Bartels' own background is totally in the CH46 and as I've said, tandem overlapping rotored birds don't catch the vortex ring "flu".
http://www.usmc.mil/marinelink/announce.nsf decision to resume flights
http://www.usmc.mil/marinelink/announce.nsf MV22 mishap info
http://www.defenselink.mil/news/Apr2..._t411dasd.html LtGen Fred McCorkle's briefing
So in the interests of not seeing any more Marines "hit the dirt", I deemed it cheekily appropriate for them to have an outside opinion. Even when military crashes are involved I doubt very much that, under the "party system" of manufacturer participation in the investigation, you can expect all the potential bad news to surface. And now that you also are privy to this disclosure having been made, just stow it away so that you can ask them the hard questions when this accident is replicated at some time in the future.
To: Col Dennis Bartels (of Dept of Avn, HQMC Aviation Mishap Board (AMB) OPNAVINST 3750)
Subject: There is an INBUILT DESIGN Problem with the V-22 Osprey
I understand that V22's are shortly to be restored to flight status and that the accident profile is to be re-flown. All that I have read, by way of official releases and media reporting, leads me to believe that the phenomenon of vortex ring, as it applies to the V22, is not thoughly understood. Perhaps it would just make me feel less complicit in future accidents if you would read the following dissertation on the hazard.
The best way to visualize vortex ring (VR) is to imagine forcing a plunger slowly down a loose-fitting water-filled pipe. You get a spill-over inflow around the periphery of the disc's upper surface (about the top quarter/third outer annulus). This is analogous to what happens below translational speed in a helo. That spill-over air is the rotor-disc version of that self-same lift-dependent vortex that spills off the end of a FW's wingtips. In a FW it is greater at low alt, low IAS, high AUW, high AoA. It is greater in the Rotary Wing (RW) because of centrifugal flow. In fact if you've heard of "behind the drag curve", that is what happens in a FW, below min drag IAS, when it starts taking more power to fly more slowly. In a FW the vortices get "left behind" and above translational speed in a helo the vortices are simply shed and left behind (as in the FW). But unfortunately, in a RW, below translational speed on a steep approach, the spill-over can become entrained air (i.e. your downwards flight-path approximates your rotor downwash) . So the drop to below translational speed on a steep approach is the entry to the VR high-threat area - so to speak. The instinctive reaction to a higher Rate of Descent is to increase collective (more blade angle and more fuel to generate more power to maintain N2 RPM). The result is greater spill-over, greater entrainment and the effect sneaks further in along the rotor disc. That area of the disc is in effectively now what, in a FW, would be a negative angle of attack - i.e. power increases only drive you downwards faster. And the outer area of the disc, because of the blade's higher rotational velocity, is where most of your lift (and lift dependent drag) comes from. It is really ALL bad news - nil good. In a straight "chopper", because of ingrained pilot instincts, the situation can rapidly deteriorate - but it is not irretrievable if you act quickly enough.
The lack of rotor interaction (as in the CH46 and Chinook's contra-rotating and overlapping discs) may well be why the V22 is more prone to vortex ring than those conventional dual-rotor helo's. I've never heard of a Chinook or Sea Knight falling foul of it, probably because vortex figures-of-eight are a physically impossible non-entity. So with side-by-side non-overlapping tilt-rotors you've got a big problem; what happens when, due to environmentals or piloting factors, the vortex ring effect hits asymmetrically? (high-rate steep descent, relative wind, gust-blanking of one nacelle, tight-cored thermal, or simply localized wind effects causing you to suddenly drop below translational speed as you descend). In the Osprey, the inducement of such a condition may be due to simply picking up a gust-dropped wing with lateral stick movement. The power and blade-angle on that dropped wing's nacelle is increased - and maybe just enough to trigger the condition (i.e. enter VRing). Entry into a VR condition means that the wing will drop further/faster, requiring a larger correction (and remember we said that that was bad news). The effect, as in the MV-22, would be a quick roll past 90 deg and a nose-drop to the downward vertical. I doubt that recognition + reaction time + nacelle swivel-rate (12 secs) could possibly resolve that asymmetric case - for a life-saving "burst-out" of the recirc bubble. It’s illustrative if the MV-22’s response to an attempted “wing-levelling”, in an assy VR condition, could be likened to a FW's auto-rotative entry into a spin. Every incident of asymmetric vortex ring will be a killer because of the control system and instinctive pilot response. e.g. Right wing drops and pilot applies left stick to pick it up. This feeds in greater blade angle and power on the side locked into the Vortex Ring condition (which increases the adverse roll-rate). If you wish, liken it to trying to pick up a dropping [auto-rotating] wing with aileron in a conventional FW aircraft.
Once a recirculation bubble forms and you are IN that vortex ring condition in a conventional helo, the recognition feature is that a higher collective setting will undesirably beget a higher rate-of-descent. The only way out is to utilize available altitude as your escape path and jam that cyclic forward, breaking out of that recirc bubble by accelerating through translational speed (i.e. by doing this, the vortex ring is "shed"). Unfortunately I can think of no similar solution for the V-22 with its rotor configuration. I doubt that nacelle-tilt rates (i.e. a 12 second transition), once you take into account recognition and reaction time, would be anywhere sufficient for escape (according to the loadmaster witness, the MV22 "hit the ground two to three seconds after flipping"). The asymmetric nature of the Osprey's vulnerability would seem to make it a very conclusive condition.
Terrain can be a factor in that it can cause localised wind effects that hit you unexpectedly in the descent and create the conditions for vortex ring (i.e. you can suddenly lose "translational" lift due to tree-line or terrain shielding of the relative wind). Translational lift is where the blades aren't in true air-chopping hover mode any more, i.e. you experience a lift gain and drag loss because the rotor-disc entity is now generating the lift. As you pass through about 15-18 knots airspeed, you notice a distinct change in rotor-slap noise and an apparent surge in power (both during accel and decel to the hover). But unexpectedly drop below translational speed during a steep approach, and it can be "Hello Mr Vortex Ring". That is the problem they will face in envisaged V-22 ops - conversion to rotor-borne flight may be a direct transition straight into the VR hazard area. Relative wind could be the big bugbear for the Osprey's gust response. To explain, just think about the exposure of the RH nacelle as against the LH nacelle in a wind-gust from (say) 2:30 to 3:00 o'clock. One's part-blanked, one's not.
In a true "chopper", late realization is the big hazard because you are intentionally descending anyway - yet as ground-rush sets in, you belatedly become aware that your rate is high so you pull in a little power (to decrease the ROD). You become momentarily confused because the rate increases (rather than decreases) so you pull in a little more power etc etc. Got the idea? Very quickly you are in a world of hurt. Of course it would now appear that the MV22 accident crew wore it just on one side. That's insoluble.
The Osprey rotors are contra-rotating and that could be a complicating factor also. This (contra-rotating props) brings up another consideration. As all glider pilots know, Coriolis has its influence upon which direction thermals rotate (clockwise or counter-clockwise, dependent upon hemisphere). Might be drawing a long bow, but if you were to be unfortunate enough to fly, below translational speed on approach, through a thermal (rapidly rotating and fast rising air), would the effect upon each contra-rotating rotor be the same? Given that:
a. You may already be in the ball-park for vortex ring formation and,
b. the effect upon each V-22 rotor might be quite dissimilar, and that
c. You could fairly expect that a lateral stick input will be required (as in any gust upset)....the inference being that he lateral stick input will be altering blade angle and power on both sides - perhaps enough to trigger the condition asymmetrically.
d. Military operations (formations) may lead to VR as a function of wake turbulence from a preceding Osprey in the same flight.
I am wondering if it would do any good to mount the Osprey's engines so that, as the rotor shafts rotate upward from the forward flight mode to the vertical/hover mode, they would also tilt inward so that the rotor wash would be directed outward to some degree. The hovering tilt-inward solution? It would require the nacelle gear-boxes to be re-splined but it may be possible to go for about ten degrees at great technical cost. It would also effectively rob the aircraft of 1-2% power in the hover - where it needs it. I'm not sure that it would make a great difference, sort of similar to wing-taper, winglet end-plates or greater aspect ratio in a FW to reduce losses due to wake vortices. Moreover, you might end up with a part-disc effect and out-of-balance air-loads on the rotor (and cyclical stresses on the transmission gear-boxes).
I myself think that sucking some power out of the disc for a powerful bleed-air fed wing-tip reaction jet nozzle may be the answer. Perhaps such a jet could also be used for induced-flow empowering of the ailerons at slow speed. Short of that, perhaps an emergency JATO to achieve a rapid exit from a recirc bubble.
It will be interesting to see how they resolve this and whether they will try to optimistically avoid any redesign. I remain unconvinced that the asymmetric VR condition will not repeatedly revisit the Osprey Fleet. The fact that they haven't hit the condition before may simply be due to the fact that a specific VR investigation was never designed into any Osprey Flight Test Schedule. Now that it's in "operational development" as an operational Marine a/c, you have to expect that uninvestigated foibles may well emerge.
[This message has been edited by UNCTUOUS (edited 11 May 2000).]
http://www.usmc.mil/marinelink/announce.nsf decision to resume flights
http://www.usmc.mil/marinelink/announce.nsf MV22 mishap info
http://www.defenselink.mil/news/Apr2..._t411dasd.html LtGen Fred McCorkle's briefing
So in the interests of not seeing any more Marines "hit the dirt", I deemed it cheekily appropriate for them to have an outside opinion. Even when military crashes are involved I doubt very much that, under the "party system" of manufacturer participation in the investigation, you can expect all the potential bad news to surface. And now that you also are privy to this disclosure having been made, just stow it away so that you can ask them the hard questions when this accident is replicated at some time in the future.
To: Col Dennis Bartels (of Dept of Avn, HQMC Aviation Mishap Board (AMB) OPNAVINST 3750)
Subject: There is an INBUILT DESIGN Problem with the V-22 Osprey
I understand that V22's are shortly to be restored to flight status and that the accident profile is to be re-flown. All that I have read, by way of official releases and media reporting, leads me to believe that the phenomenon of vortex ring, as it applies to the V22, is not thoughly understood. Perhaps it would just make me feel less complicit in future accidents if you would read the following dissertation on the hazard.
The best way to visualize vortex ring (VR) is to imagine forcing a plunger slowly down a loose-fitting water-filled pipe. You get a spill-over inflow around the periphery of the disc's upper surface (about the top quarter/third outer annulus). This is analogous to what happens below translational speed in a helo. That spill-over air is the rotor-disc version of that self-same lift-dependent vortex that spills off the end of a FW's wingtips. In a FW it is greater at low alt, low IAS, high AUW, high AoA. It is greater in the Rotary Wing (RW) because of centrifugal flow. In fact if you've heard of "behind the drag curve", that is what happens in a FW, below min drag IAS, when it starts taking more power to fly more slowly. In a FW the vortices get "left behind" and above translational speed in a helo the vortices are simply shed and left behind (as in the FW). But unfortunately, in a RW, below translational speed on a steep approach, the spill-over can become entrained air (i.e. your downwards flight-path approximates your rotor downwash) . So the drop to below translational speed on a steep approach is the entry to the VR high-threat area - so to speak. The instinctive reaction to a higher Rate of Descent is to increase collective (more blade angle and more fuel to generate more power to maintain N2 RPM). The result is greater spill-over, greater entrainment and the effect sneaks further in along the rotor disc. That area of the disc is in effectively now what, in a FW, would be a negative angle of attack - i.e. power increases only drive you downwards faster. And the outer area of the disc, because of the blade's higher rotational velocity, is where most of your lift (and lift dependent drag) comes from. It is really ALL bad news - nil good. In a straight "chopper", because of ingrained pilot instincts, the situation can rapidly deteriorate - but it is not irretrievable if you act quickly enough.
The lack of rotor interaction (as in the CH46 and Chinook's contra-rotating and overlapping discs) may well be why the V22 is more prone to vortex ring than those conventional dual-rotor helo's. I've never heard of a Chinook or Sea Knight falling foul of it, probably because vortex figures-of-eight are a physically impossible non-entity. So with side-by-side non-overlapping tilt-rotors you've got a big problem; what happens when, due to environmentals or piloting factors, the vortex ring effect hits asymmetrically? (high-rate steep descent, relative wind, gust-blanking of one nacelle, tight-cored thermal, or simply localized wind effects causing you to suddenly drop below translational speed as you descend). In the Osprey, the inducement of such a condition may be due to simply picking up a gust-dropped wing with lateral stick movement. The power and blade-angle on that dropped wing's nacelle is increased - and maybe just enough to trigger the condition (i.e. enter VRing). Entry into a VR condition means that the wing will drop further/faster, requiring a larger correction (and remember we said that that was bad news). The effect, as in the MV-22, would be a quick roll past 90 deg and a nose-drop to the downward vertical. I doubt that recognition + reaction time + nacelle swivel-rate (12 secs) could possibly resolve that asymmetric case - for a life-saving "burst-out" of the recirc bubble. It’s illustrative if the MV-22’s response to an attempted “wing-levelling”, in an assy VR condition, could be likened to a FW's auto-rotative entry into a spin. Every incident of asymmetric vortex ring will be a killer because of the control system and instinctive pilot response. e.g. Right wing drops and pilot applies left stick to pick it up. This feeds in greater blade angle and power on the side locked into the Vortex Ring condition (which increases the adverse roll-rate). If you wish, liken it to trying to pick up a dropping [auto-rotating] wing with aileron in a conventional FW aircraft.
Once a recirculation bubble forms and you are IN that vortex ring condition in a conventional helo, the recognition feature is that a higher collective setting will undesirably beget a higher rate-of-descent. The only way out is to utilize available altitude as your escape path and jam that cyclic forward, breaking out of that recirc bubble by accelerating through translational speed (i.e. by doing this, the vortex ring is "shed"). Unfortunately I can think of no similar solution for the V-22 with its rotor configuration. I doubt that nacelle-tilt rates (i.e. a 12 second transition), once you take into account recognition and reaction time, would be anywhere sufficient for escape (according to the loadmaster witness, the MV22 "hit the ground two to three seconds after flipping"). The asymmetric nature of the Osprey's vulnerability would seem to make it a very conclusive condition.
Terrain can be a factor in that it can cause localised wind effects that hit you unexpectedly in the descent and create the conditions for vortex ring (i.e. you can suddenly lose "translational" lift due to tree-line or terrain shielding of the relative wind). Translational lift is where the blades aren't in true air-chopping hover mode any more, i.e. you experience a lift gain and drag loss because the rotor-disc entity is now generating the lift. As you pass through about 15-18 knots airspeed, you notice a distinct change in rotor-slap noise and an apparent surge in power (both during accel and decel to the hover). But unexpectedly drop below translational speed during a steep approach, and it can be "Hello Mr Vortex Ring". That is the problem they will face in envisaged V-22 ops - conversion to rotor-borne flight may be a direct transition straight into the VR hazard area. Relative wind could be the big bugbear for the Osprey's gust response. To explain, just think about the exposure of the RH nacelle as against the LH nacelle in a wind-gust from (say) 2:30 to 3:00 o'clock. One's part-blanked, one's not.
In a true "chopper", late realization is the big hazard because you are intentionally descending anyway - yet as ground-rush sets in, you belatedly become aware that your rate is high so you pull in a little power (to decrease the ROD). You become momentarily confused because the rate increases (rather than decreases) so you pull in a little more power etc etc. Got the idea? Very quickly you are in a world of hurt. Of course it would now appear that the MV22 accident crew wore it just on one side. That's insoluble.
The Osprey rotors are contra-rotating and that could be a complicating factor also. This (contra-rotating props) brings up another consideration. As all glider pilots know, Coriolis has its influence upon which direction thermals rotate (clockwise or counter-clockwise, dependent upon hemisphere). Might be drawing a long bow, but if you were to be unfortunate enough to fly, below translational speed on approach, through a thermal (rapidly rotating and fast rising air), would the effect upon each contra-rotating rotor be the same? Given that:
a. You may already be in the ball-park for vortex ring formation and,
b. the effect upon each V-22 rotor might be quite dissimilar, and that
c. You could fairly expect that a lateral stick input will be required (as in any gust upset)....the inference being that he lateral stick input will be altering blade angle and power on both sides - perhaps enough to trigger the condition asymmetrically.
d. Military operations (formations) may lead to VR as a function of wake turbulence from a preceding Osprey in the same flight.
I am wondering if it would do any good to mount the Osprey's engines so that, as the rotor shafts rotate upward from the forward flight mode to the vertical/hover mode, they would also tilt inward so that the rotor wash would be directed outward to some degree. The hovering tilt-inward solution? It would require the nacelle gear-boxes to be re-splined but it may be possible to go for about ten degrees at great technical cost. It would also effectively rob the aircraft of 1-2% power in the hover - where it needs it. I'm not sure that it would make a great difference, sort of similar to wing-taper, winglet end-plates or greater aspect ratio in a FW to reduce losses due to wake vortices. Moreover, you might end up with a part-disc effect and out-of-balance air-loads on the rotor (and cyclical stresses on the transmission gear-boxes).
I myself think that sucking some power out of the disc for a powerful bleed-air fed wing-tip reaction jet nozzle may be the answer. Perhaps such a jet could also be used for induced-flow empowering of the ailerons at slow speed. Short of that, perhaps an emergency JATO to achieve a rapid exit from a recirc bubble.
It will be interesting to see how they resolve this and whether they will try to optimistically avoid any redesign. I remain unconvinced that the asymmetric VR condition will not repeatedly revisit the Osprey Fleet. The fact that they haven't hit the condition before may simply be due to the fact that a specific VR investigation was never designed into any Osprey Flight Test Schedule. Now that it's in "operational development" as an operational Marine a/c, you have to expect that uninvestigated foibles may well emerge.
[This message has been edited by UNCTUOUS (edited 11 May 2000).]
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UNCTUOUS, all very good stuff, mate! I always thought they would have a long way to go before they discovered all the aerodynamic "funnies" of such a beast. Vortex ring of one or both discs was something I have wondered about in the past, especially during the transitional phases of flight. Another possible difficult malfunction is nacelles stuck forwards / down for landing...
Does anyone know if they are utilising mainly rotary experienced pilots on "uppers" to cope with the higher cruise IAS, or mainly fixed wing jocks with extra training to cope with the slow speed stuff?
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The best insurance is to Fly safe!
Does anyone know if they are utilising mainly rotary experienced pilots on "uppers" to cope with the higher cruise IAS, or mainly fixed wing jocks with extra training to cope with the slow speed stuff?
------------------
The best insurance is to Fly safe!
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http://199.97.97.163/IMDS%AEROWORLD%read%/home/content/u sers/imds/feeds/comtex/2000/05/09/up/0000-4039-us-marine-crash
Wishful and wistful GUNG HO
I am not an opponent of tilt-rotor technology however I do firmly believe that LtGen McCorkle is erring in that he has already:
a. attributed the cause to pilot error
b. averred that there is absolutely nothing wrong with the Osprey design
c. Spoken of having his pilots re-fly the accident profile tomorrow (a mite hazardous at this stage in my opinion)
d. Reassured all and sundry that there can be nothing wrong with the V22 if he and Gen Mick Ryan are going to be on the first one airborne now that the suspension (not a grounding) has been lifted.
Now I see all the above as a bit dunder-headed, if not Colonel Blimpish. It's got nothing to do with aviation safety nor sensible, prudent investigation. It is all crazily designed to protect the Osprey program from falling back into the clutches of a precocious Congress. Just look at some extracts from McCorkle's Press Briefing:
"The commandant is confident the MV-22 is fully airworthy, with no design flaws," said Lt. Gen. Fred McCorkle.
"When he hit 15 degrees angle of bank he was in big trouble," he said.
"By the time he realized he was in trouble, it was already too late," McCorkle said. Nevertheless, "it's beyond me why they didn't" pull out of it, he said.
COMMENTARY: Those HIGH angles of bank will get you every time.
OK Marines, listen up. The Commandant has said it was PILOT ERROR and there'll be no more of these accidents. Semper Fi!
Military Pilot Error: Henceforth to be known as a "McCorklism".
The Problem with Press Reporting
If it wasn't so serious, such hierarchy pronouncements would be laughable. They're worthy of a three stooges script.
Therefore my cynical COMMENTARY: Those HIGH angles of bank will get you every time. ( 15 degrees? )
I'll now repeat myself a bit here:
"And no doubt all the pilots will be careful not to get in that VR groove again. Sooner or later however, because it's there as a lethal trap, someone else will overcook it a bit and fall (OS)prey to it. They are calling it pilot error simply because at some stage of the approach he did wind it up to 1700fpm. However I'm willing to bet that the point of actual onset (of the VR condition) hasn't been picked and that it was shortly before the loadmaster saw him "flip at about 285ft, impacting 2 to 3 seconds later" (which exact figure obviously came from the CSMU) (aka crash survivable memory unit). If you think about it, he was unlikely to be descending at anywhere near 1700fpm at <300ft and the "flip" at 300ft or thereabouts was likely to have been the exact onset point of the asymmetric VR condition. You don't have to be Mandrake to work that one out - it falls straight out of the onset scenario. It just bears out my point that you can hit VR during a steep approach simply as a function of many different factors. Pick up a bit of a tail-wind due to local wind shear or terrain shielding and you end up arcing over (parabolically) in order to keep your LZ sight picture. That's enough to put you in the VR frame."
This breakdown simply contradicts the impression given by the Marines Press Briefing which intentionally conveyed the illusion that the accident crew brought it upon themselves by allowing their descent rate to wind up to as high as 1700fpm (but at what stage?). Elsewhere it's said that the (average?) rate of descent was 1000fpm (which isn't horrendously in excess of the allegedly recommended max of 800fpm). In other words, if the V22 is so handling sensitive that an extra piddling 200fpm is going to be disastrous, it's an accident going everywhere to happen. A combat aircraft has to be fairly forgiving as well as robust in its handling qualities - or it's a sitting duck.
"Analyses of the data retrieved from the data recorder, called a Crash Survivable Memory Unit (CSMU), along with extensive engineering investigations have confirmed that all aircraft systems and software were operating properly at the time of the accident."
OPERATING PROPERLY? Does this clearly say to you that the aircraft was not at fault? It does to the Marine Commanders. Think about the possible incongruities here.
http://www.usmc.mil/news/news99.nsf/...b?OpenDocument
But, just possibly, there is a design flaw built into the tilt-rotor concept. This should be the concern. Have you asked Bell-Textron and Boeing FSR's to put their hands on their hearts and swear that the V-22's susceptibility to asymmetric (or symmetrical) vortex ring was tested as part of the Developmental Flight Test Schedule (now completed)? Have you seen it in writing? Why would there be some or any reticence about showing you such a document, the test-profiles flown and the data-points - if they indeed exist? Why are they only now talking about carrying out some wind-tunnel testing? Surely that data exists already? GOT THE IDEA?
If you had simply mentioned "vortex ring" in the issue (immediately after I brought it up) you'd have had the scoop of the year - well before it hit the news. You decided not to - your decision. After all, it is a $36Billion contract and people tend to think thrice before stirring Bell (let alone Boeing). So I quite understand. I also understand that, not being a pilot, it is hard for you to grapple with some of these concepts. I am not a XXXXX employee nor a US citizen so I can understand your further reservations that I might be putting you in harm's way. It might be better to stick with straight reporting of Press briefings. Perhaps you can pick up on this thread after the next V-22 accident.
<As I understand your analysis, the "lack of rotor interaction may well be why the V-22 is more prone to vortex ring" than conventional (CH-46 and Chinook) helicopters. I understand what you are saying here, but am unclear as to why this is the case. >
To me, the tandem overlapping rotor case (CH46, CH47) is quite clear and calls up a mind's eye view of two circularly incomplete (because of the overlap) interlocking vortices, helically rotating in opposite directions (because of the contra-rotating rotors) - and because of that, essentially cancelling each other out (because of the overlap and contrary rotation). For a vortex ring to form and strengthen, it must retain its circular integrity (you can't have a recirculation bubble shaped like a figure-of-eight or distended ellipsoid). Just as Nature abhors a vacuum so does aerodynamics detest a discontinuity. Any tendency toward a strengthening recirculation would be dissipated by the mutually beneficial turbulent interaction of the contra-rotating and overlapping tandem rotor configuration.
You don't have to state anything as being fact. You can simply postulate a theory and ask the embarassing questions (espec about flight-test schedules and wind-tunnel testing) and see if they are able to rise to the occasion. I'm sure Woodrow and Bernstein would approve of that tactic, - and, as a bonus, it keeps you clear of the arcane aerodynamics.
Declaring a new design concept to be unflawed after it's just killed a whole bunch of people in very benign circumstances is both wishful thinking and very cavalier.
[This message has been edited by UNCTUOUS (edited 12 May 2000).]
Wishful and wistful GUNG HO
I am not an opponent of tilt-rotor technology however I do firmly believe that LtGen McCorkle is erring in that he has already:
a. attributed the cause to pilot error
b. averred that there is absolutely nothing wrong with the Osprey design
c. Spoken of having his pilots re-fly the accident profile tomorrow (a mite hazardous at this stage in my opinion)
d. Reassured all and sundry that there can be nothing wrong with the V22 if he and Gen Mick Ryan are going to be on the first one airborne now that the suspension (not a grounding) has been lifted.
Now I see all the above as a bit dunder-headed, if not Colonel Blimpish. It's got nothing to do with aviation safety nor sensible, prudent investigation. It is all crazily designed to protect the Osprey program from falling back into the clutches of a precocious Congress. Just look at some extracts from McCorkle's Press Briefing:
"The commandant is confident the MV-22 is fully airworthy, with no design flaws," said Lt. Gen. Fred McCorkle.
"When he hit 15 degrees angle of bank he was in big trouble," he said.
"By the time he realized he was in trouble, it was already too late," McCorkle said. Nevertheless, "it's beyond me why they didn't" pull out of it, he said.
COMMENTARY: Those HIGH angles of bank will get you every time.
OK Marines, listen up. The Commandant has said it was PILOT ERROR and there'll be no more of these accidents. Semper Fi!
Military Pilot Error: Henceforth to be known as a "McCorklism".
The Problem with Press Reporting
If it wasn't so serious, such hierarchy pronouncements would be laughable. They're worthy of a three stooges script.
Therefore my cynical COMMENTARY: Those HIGH angles of bank will get you every time. ( 15 degrees? )
I'll now repeat myself a bit here:
"And no doubt all the pilots will be careful not to get in that VR groove again. Sooner or later however, because it's there as a lethal trap, someone else will overcook it a bit and fall (OS)prey to it. They are calling it pilot error simply because at some stage of the approach he did wind it up to 1700fpm. However I'm willing to bet that the point of actual onset (of the VR condition) hasn't been picked and that it was shortly before the loadmaster saw him "flip at about 285ft, impacting 2 to 3 seconds later" (which exact figure obviously came from the CSMU) (aka crash survivable memory unit). If you think about it, he was unlikely to be descending at anywhere near 1700fpm at <300ft and the "flip" at 300ft or thereabouts was likely to have been the exact onset point of the asymmetric VR condition. You don't have to be Mandrake to work that one out - it falls straight out of the onset scenario. It just bears out my point that you can hit VR during a steep approach simply as a function of many different factors. Pick up a bit of a tail-wind due to local wind shear or terrain shielding and you end up arcing over (parabolically) in order to keep your LZ sight picture. That's enough to put you in the VR frame."
This breakdown simply contradicts the impression given by the Marines Press Briefing which intentionally conveyed the illusion that the accident crew brought it upon themselves by allowing their descent rate to wind up to as high as 1700fpm (but at what stage?). Elsewhere it's said that the (average?) rate of descent was 1000fpm (which isn't horrendously in excess of the allegedly recommended max of 800fpm). In other words, if the V22 is so handling sensitive that an extra piddling 200fpm is going to be disastrous, it's an accident going everywhere to happen. A combat aircraft has to be fairly forgiving as well as robust in its handling qualities - or it's a sitting duck.
"Analyses of the data retrieved from the data recorder, called a Crash Survivable Memory Unit (CSMU), along with extensive engineering investigations have confirmed that all aircraft systems and software were operating properly at the time of the accident."
OPERATING PROPERLY? Does this clearly say to you that the aircraft was not at fault? It does to the Marine Commanders. Think about the possible incongruities here.
http://www.usmc.mil/news/news99.nsf/...b?OpenDocument
But, just possibly, there is a design flaw built into the tilt-rotor concept. This should be the concern. Have you asked Bell-Textron and Boeing FSR's to put their hands on their hearts and swear that the V-22's susceptibility to asymmetric (or symmetrical) vortex ring was tested as part of the Developmental Flight Test Schedule (now completed)? Have you seen it in writing? Why would there be some or any reticence about showing you such a document, the test-profiles flown and the data-points - if they indeed exist? Why are they only now talking about carrying out some wind-tunnel testing? Surely that data exists already? GOT THE IDEA?
If you had simply mentioned "vortex ring" in the issue (immediately after I brought it up) you'd have had the scoop of the year - well before it hit the news. You decided not to - your decision. After all, it is a $36Billion contract and people tend to think thrice before stirring Bell (let alone Boeing). So I quite understand. I also understand that, not being a pilot, it is hard for you to grapple with some of these concepts. I am not a XXXXX employee nor a US citizen so I can understand your further reservations that I might be putting you in harm's way. It might be better to stick with straight reporting of Press briefings. Perhaps you can pick up on this thread after the next V-22 accident.
<As I understand your analysis, the "lack of rotor interaction may well be why the V-22 is more prone to vortex ring" than conventional (CH-46 and Chinook) helicopters. I understand what you are saying here, but am unclear as to why this is the case. >
To me, the tandem overlapping rotor case (CH46, CH47) is quite clear and calls up a mind's eye view of two circularly incomplete (because of the overlap) interlocking vortices, helically rotating in opposite directions (because of the contra-rotating rotors) - and because of that, essentially cancelling each other out (because of the overlap and contrary rotation). For a vortex ring to form and strengthen, it must retain its circular integrity (you can't have a recirculation bubble shaped like a figure-of-eight or distended ellipsoid). Just as Nature abhors a vacuum so does aerodynamics detest a discontinuity. Any tendency toward a strengthening recirculation would be dissipated by the mutually beneficial turbulent interaction of the contra-rotating and overlapping tandem rotor configuration.
You don't have to state anything as being fact. You can simply postulate a theory and ask the embarassing questions (espec about flight-test schedules and wind-tunnel testing) and see if they are able to rise to the occasion. I'm sure Woodrow and Bernstein would approve of that tactic, - and, as a bonus, it keeps you clear of the arcane aerodynamics.
Declaring a new design concept to be unflawed after it's just killed a whole bunch of people in very benign circumstances is both wishful thinking and very cavalier.
[This message has been edited by UNCTUOUS (edited 12 May 2000).]
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Amazingly enough, if you go to the web-site for the American Helicopter Society, you'll find 50 odd academic papers on Osprey aerodynamics - but there were obviously no studies done on the V-22's susceptibility to "vortex ring" (let alone asymmetric vortex ring). If you go to NASA AMES and NASA Langley sites and search similarly, you'll find zip. There are plenty of learned treatises on literally every other aspect of the Osprey's aerodynamics - but the one "biggy" slipped through the cracks.
They did run a quarter-scale model through the AMES wind-tunnel at NAS Moffett. http://quest.arc.nasa.gov/aero/team/...g/ly12-29.html
But it appears that vortex ring wasn't on the test schedule.
[This message has been edited by UNCTUOUS (edited 14 May 2000).]
They did run a quarter-scale model through the AMES wind-tunnel at NAS Moffett. http://quest.arc.nasa.gov/aero/team/...g/ly12-29.html
But it appears that vortex ring wasn't on the test schedule.
[This message has been edited by UNCTUOUS (edited 14 May 2000).]
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Good job no-one thought of these arguments before Mesrs Wright did their stuff at Kittyhawk a century ago...Imagine the headlines...
Hmm. Inherently unsafe...too slow you'll fall into the ground...Spinning, omigod!!!!fall out; the altitude'l kill you...landing, ground cushion makes it impossible. Travel over 30 MPH and you'll all suffocate.
Send for my horse! (careful, might fall off it!)
Where will we all be if we give up innovating in the name of progress?
"Folks, welcome aboard this Bloody Uncomfortable Mk 29 horse and cart, our fright time from London to Manchester is eleven days....."
Good on Boeing, the Marines Corps, Uncle Sam and all others involved in this project. I hope it works, despite the doom-sayers.
Remember the Harrier?
Hmm. Inherently unsafe...too slow you'll fall into the ground...Spinning, omigod!!!!fall out; the altitude'l kill you...landing, ground cushion makes it impossible. Travel over 30 MPH and you'll all suffocate.
Send for my horse! (careful, might fall off it!)
Where will we all be if we give up innovating in the name of progress?
"Folks, welcome aboard this Bloody Uncomfortable Mk 29 horse and cart, our fright time from London to Manchester is eleven days....."
Good on Boeing, the Marines Corps, Uncle Sam and all others involved in this project. I hope it works, despite the doom-sayers.
Remember the Harrier?
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UNCTUOUS
A very well argued treatise on a little understood subject.
However you are incorrect in one area. Vortex Ring does occur in contra-rotating tandem helos. During a trial some five years ago by RWOETU(Rotary Wing Operational Evaluation and Training Unit) a pilot known to me experienced what was subsequently, positively confirmed as VR. It occurred during a very high (5000'+) hover. and was in all respects identical to a conventional Helo VR state. High ROD, Low IAS,Power applied. Since then the recommended recovery is as you stated, except that a bias towards the left side is helpful(clean, air to the advancing blades). I thought you might be interested.
A very well argued treatise on a little understood subject.
However you are incorrect in one area. Vortex Ring does occur in contra-rotating tandem helos. During a trial some five years ago by RWOETU(Rotary Wing Operational Evaluation and Training Unit) a pilot known to me experienced what was subsequently, positively confirmed as VR. It occurred during a very high (5000'+) hover. and was in all respects identical to a conventional Helo VR state. High ROD, Low IAS,Power applied. Since then the recommended recovery is as you stated, except that a bias towards the left side is helpful(clean, air to the advancing blades). I thought you might be interested.
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Capt Tercrue
Thanks. I spoke to some buddies with a lot of time on the Chook (CH47) and they'd not run into it in many hours on type. I can remember talking to some CH54 (Skycrane) types in SVN after they'd hooked out my busted bird and they said they were very fearful of VR because of their normal profiles. My interest dates from a personal encounter. But I can't see how an overlapping tandem-rotored helo could generate a consistent vortex, yet I admit that I'd not found anything academic that said yea or nay. But more importantly, it would seem that it has been overlooked as a potential pitfall for the tilt-rotor breed. The TP's at Pax River will probably have some exciting rides whilst coming to terms with it. I wish them luck.
Pants
If you look at the following URL's I think the answer will jump off the page.
Unfortunately they thought about engine failure but disregarded pitch-lock, VR (espec asymm) and transmission failure. Nacelle-tilt gear-box failure can be accommodated because the blades are composites and will simply break off (harmlessly and hopefully symmetrically) during any enforced "run-on" landing.
http://www.navair.navy.mil/V22/fltcntls.htm
http://www.navair.navy.mil/V22/propul.htm
http://www.navair.navy.mil/V22/convert.htm
Thanks. I spoke to some buddies with a lot of time on the Chook (CH47) and they'd not run into it in many hours on type. I can remember talking to some CH54 (Skycrane) types in SVN after they'd hooked out my busted bird and they said they were very fearful of VR because of their normal profiles. My interest dates from a personal encounter. But I can't see how an overlapping tandem-rotored helo could generate a consistent vortex, yet I admit that I'd not found anything academic that said yea or nay. But more importantly, it would seem that it has been overlooked as a potential pitfall for the tilt-rotor breed. The TP's at Pax River will probably have some exciting rides whilst coming to terms with it. I wish them luck.
Pants
If you look at the following URL's I think the answer will jump off the page.
Unfortunately they thought about engine failure but disregarded pitch-lock, VR (espec asymm) and transmission failure. Nacelle-tilt gear-box failure can be accommodated because the blades are composites and will simply break off (harmlessly and hopefully symmetrically) during any enforced "run-on" landing.
http://www.navair.navy.mil/V22/fltcntls.htm
http://www.navair.navy.mil/V22/propul.htm
http://www.navair.navy.mil/V22/convert.htm
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