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).]