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RBS
As always, thank you Nick, for your learned explanation.
I have stalled a 47, 205, 206, 212, 214ST, 500C, 500D, 55, 55T, 58, 58T and 61 (never stalled the 76). Many have probably encountered it whether they recognize it as RBS or not. It is easy to induce (any combination of high DA, high GW, high speed, high power, rapid change in attitude and/or turbulence). It is also easy to recognize and recover from. |
@NickLappos
199kts seems to me a pretty extreme space to occupy for a test flight. Did the S76 (or S70) ever go that fast during developmental test flying? |
Max Test Speeds
Nick can best answer for the S-76.
The S-70 has a Vne of 193 KIAS and was tested there in accordance with US Army requirements, Prior to production, the Army desired a test to achieve a free stream advancing tip Mach number of 1.0, and that was accomplished flying out of Burlington Vt, and the test instrumentation recorded a KIAS of 199. |
John is right, many helicopters are tested in a dive to around 200 knots, the absolute requirement is to go to at least 1.2 Vh for a military machine (so if Vh is 161, Vdive is 193, in case you're wondering where John Dixson got the 193 from!)
For civil helos it is 1.11 times Vne (or actually, you operators get to fly to 90% of the maximum speed tested). The S-76 flew a number of world records at 186 to 188 kts in level flight, and the most it has gone in a dive is about 210 knots (John, remember the Kollsman airspeed gauge with the stop at 155 knots, with Pasquarello and Mills flying? There is a great story there......) The test point at 199 for the 525 tells us they have probably got about 165 max level flight speed, and that test point is fairly normal. |
Nick,
Going a little OT: Happy Birthday :ok:
Originally Posted by NickLappos
(Post 9437238)
remember the Kollsman airspeed gauge with the stop at 155 knots, with Pasquarello and Mills flying? There is a great story there......
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Nick and John probably remember stories of WPB Approch /Tower asking Airliners to increase their airspeed on the ILS due to overtaking aircraft behind them.....and the responses from them when told the traffic was a helicopter.
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Ah, yes....
"Helicopter 12345, reduce airspeed 20 kts for the Lear on final two miles ahead." |
No further word yet from Bell?
High stakes when a multi billion dollar new platform has an inflight separation vs crew making contact with a power line, or both. Textron has said the aircraft was exceeding expectations and had achieved over 200 knots, so speculation is speculation, be it RBS, separation, or wire strike. What would your shareholders like to hear? Condolences to all involved. |
Originally Posted by blackdog7
(Post 9437724)
High stakes when a multi billion dollar new platform has an inflight separation vs crew making contact with a power line, or both. Textron has said the aircraft was exceeding expectations and had achieved over 200 knots, so speculation is speculation, be it RBS, separation, or wire strike.
http://www.verticalmag.com/news/two-...-flight-tests/ Photos of the crash site show a compact debris field, with only small fragments of the fuselage visible. WFAA reported eyewitness claims that the aircraft hit a power line and exploded, but the Texas Department of Public Safety said the aircraft did not strike the line and electricity transmission was unaffected. The NTSB was headed to the crash scene at the time of the report. Early media coverage at the scene detailed an interview with two farmers that claim to have seen the helicopter come into contact with wires or a utility pole before the aircraft impacted the ground, however, followup reports stated that there had been no power outages in the area and all wires in the vicinity appeared to be intact. The crash resulted in a substantial fire that consumed a majority of the helicopter wreckage and singed the top of a utility pole close by. Helicopter debris was mainly localized at the crash site, however the tail boom of the 525 was reported to have been located 1,500 feet southeast of the main wreckage and appears from media footage shot from overhead to have no fire damage and a serrated angled tear at the point of separation. |
So a chase aircraft, a platform stuffed full of sensors, and we have to base conclusions on conflicting news reports?
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SAS, there is a true and related anecdote re a 1972 hard IFR S-67 and Frankfurt Tower and an ILS clearance that I'll send via PM or email.
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Blackdog7
The accident is being investigated by the NTSB. You obviously do not know what that means. Bell has turned over all data and only the NTSB can issue updates. When I say all I mean all, even copies. Failure to do this is a criminal offense. Look at the Gulfstream Roswell crash. Bell and vendors will assist, but the reports are NTSB. The Sultan |
Originally Posted by JohnDixson
(Post 9436517)
Viper, that sounds like pitch-lag instability, not stall.
Part 2: I looked in vain online for an old H-3 flight manual. There used to be a write-up on pitch-lag instability in the USN military manual. Anyway, re H-3 pitch-lag: The H-3 rotor has some alpha-1 coupling in the geometry. In the H-3, as the blade lag angle increases ( which occurs with increased power ), the pitch angle decreases a bit. Hardly noticeable, but coming back into a hover on the 61, the pilot needs to nudge the collective up a bit more when he applies collective to come to the hover. Really a non-issue. However, if a blade damper has a problem ( e.g. sticky relief valve ) then at higher speeds, and having nothing to do with stall*, the rotor can excite a pitch to lag angle instability. Pilots unfamiliar with the excitation may well call it a 1:1 or 1/rev, but in fact it is 2/3 per rev. Fix is to look at the dampers and check their timing. * USN H-3 had a cruise guide indicator. The main rotor servo ( typically highest loads on the newer machines have highest loads on the aft longitudinal servo, but I honestly don't recall which servo on the H-3 had the highest loads ) had an LVDT ( linear,variable,differential transducer ) which measures the loads on that servo and feeds an indicator with range markings. Like the same system on the S-65 series, anything over 30% in indicative of increasing degrees of stall. On the H-3, with a damper problem, one can see pitch-lag when the cruise guide will be barely indicating anything. It will be at higher power, thus faster speed, but its not a simple 1/rev. An easy way to evaluate the difference is that with a simple 1/rev, ( and assuming it is large enough to get one's attention )there is usually one blade out of track and quite visible from the cockpit. With pitch-lag, the main rotor feels and appears to wobble at a slightly slower frequency, and one can see that. Rotor heads subsequent to the S-61 have a very flat alpha-1 geometry, that is, almost zero blade pitch change as the lag angle changes, and as a result have been absent this particular instability. Interesting stuff - I have no doubt that you are correct. Our machines were 1960s vintage and while very well maintained, tended to be cranky when pushed too hard. Best, V7 :ok: |
Originally Posted by blackdog7
(Post 9437742)
So a chase aircraft, a platform stuffed full of sensors, and we have to base conclusions on conflicting news reports?
And why are you jumping to conclusions? That asked, I concur with your point that good information should be available due to both telemetry and the chase plane. I am not sure that Bell is required to release that to the press, so all we have to work with is what is available through the press. (Sultan, I just realized, made this point somewhat differently). I am confident that the NTSB is already working with Bell on assessing that information Bell should have on hand ... per Sultan's post. |
"We" would be everyone who has speculated or commented on this thread.
Certainly not jumping to conclusions and am well aware of NTSB requirements and investigations. Also aware of the warped reality of the value of human life and how multi-billion dollar programs can steamroll right over them to soothe investors. Best of luck to Bell and TXT with the 525 program. |
blackdog7,
I am afraid you have no idea what you are talking about. I well know the people at Bell and at the NTSB, I can assure others (not you) that they want nothing but the truth to come out of all this. As for you, blackdog7 (+10 points for an apt name), I have often felt that people who have deep belief in unethical conspiracies are simply showing us what is inside their own heads, a squirming mess of conflict, lies and few scruples, so that these troubled people project that same unseemly world onto others they deal with. I pity you. |
Sorry Nick
A little too close to home I guess. I pity you too! |
The software used on almost every new FBW aircraft model has resulted in some problems. The most recent example is that of the A400 turboprop engine software which resulted in a fatal crash. The software code of the F-35 has also been plagued with problems. It would not seem unusual for Bell's first effort with a commercial FBW aircraft model to experience similar software problems.
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The software used on almost every new FBW aircraft model has resulted in some problems. The most recent example is that of the A400 turboprop engine software which resulted in a fatal crash |
Originally Posted by 212man
(Post 9438401)
Ergo, nothing to do with FBW.....
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During a crash investigation the company can't release any information even to employees not directly involved in the investigation. Bell cannot even comment on the investigation other than to confirm that one is in progress. Soothing investors and customers is not a license to release anything. After the NTSB releases a report, Bell may be able to make comments, but not before.
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Given that this is a helicopter model in development, and not one that anybody is currently flying beyond the OEM and development team, the need or urgency to release an interim report or bulletin with alerts to users as the investigation progresses (like in the recent Bergen crash) isn't present. I'd suggest patience to all.
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We only go forward because these men didn't go backwards...
RIP brave men 👏👏👏 |
Originally Posted by Lonewolf_50
(Post 9439857)
Given that this is a helicopter model in development, and not one that anybody is currently flying beyond the OEM and development team, the need or urgency to release an interim report or bulletin with alerts to users as the investigation progresses (like in the recent Bergen crash) isn't present. I'd suggest patience to all.
It rather depends on the complexity of the task on hand. And this is obviously more complicated for a new model especially when it crashed during expansion of the envelope. The difficult task in that case is to find out whether it was due to a mechanical malfunction an unanticipated effect (aerodynamic, aero-elastic, etc.) or something in the interaction man -machine while in yet unproven terrain. On the plus side they might have more data due to instrumentation and chase aircraft. For Bell finding the real cause will indeed be urgent because it will be important for the future of this type. |
I am not referring to speed of investigation, but the urgency (in time) of issuing any bulletin or report. Since nobody else is flying this helicopter the only people with an interest are already involved in the investigation.
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Originally Posted by Lonewolf_50
(Post 9440295)
I am not referring to speed of investigation, but the urgency (in time) of issuing any bulletin or report. Since nobody else is flying this helicopter the only people with an interest are already involved in the investigation.
OK, fair enough! Indeed for any one else besides Bell themselves there is no urgency in obtaining the information what went wrong. |
Latest On Accident
From Rotor And Wing:
The No. 1 525 prototype’s main rotor blades appear to have struck its tail and nose during a high-speed, engine-out test that ended with the July 6 crash that killed its two pilots, Rotor & Wing International has learned. “We saw signs consistent with a blade strike on the tailboom,” the National Transportation Safety Board’s investigator-in-charge for the probe, John Lovell, told R&WI, adding that investigators also believe “the nose was struck.” The fly-by-wire Bell Helicopter super-medium, twin-engine helicopter broke up in midair during a flight to expand its operating envelope that included a test of the 525’s performance in one-engine-inoperative conditions as the aircraft approached its never-exceed speed (Vne), Lovell said. Bell early last March said it had flown the 525 above 200 kt in a shallow dive. A flight tracking service, Flightradar24, had reported July 6 that its last data set on the 525 flight put the aircraft at 199 kt at 1,975 ft. Prior to the breakup, Lovell said, “data indicates that main rotor rpm dropped significantly.” He also said some of the aircraft’s main rotor blades “appeared to have dropped from their normal plane” of rotation. Test pilots in a Bell 429 chase aircraft reported that some of the main rotor blades were moving out of plane before the aircraft broke up over Italy, Texas, about 30 nm south-southwest of the flight’s launch point, Bell’s Xworx research center at Arlington Municipal Airport. The Sultan |
careful with your assumptions
FR24 shows groundspeed
A flight flown at Vne in IAS terms can give a completely different TAS or Groundspeed value depending on local ambient winds and density altitude. There is no credible reason why an aircraft should be operating for certification purposes at Vne+40 kts, but in any case the report quoted states that they were approaching Vne, so the speeds quoted are meaningless or misleading. Nobody here has the info required to work out what happened, so it would be better to stay quiet on any reasons why the aircraft and crew were lost, both on this programme and on the AW609 (but then again this is a rumour site so anything stated here should be taken with a huge dose of salt). Thoughts from the southwest of the UK are of course with the crews families and the Bell employees involved. DM |
DM
Bell stated they were out at 200 kts and that would be from the card not FR24. As to reasons why the requirement is to demonstrate operations at 1.11 Vne. So if Bell was looking to expand to 180 knots, 200 would be the test point. Being out their testing engine failure is high risk, not something a line or armchair pilot would ever get close to. Some of us have. The Sultan |
Sultan, are you suggesting there was a mixup re the specific tests to be conducted at the power on Vne ( actually 1.11 times that value ) and the OEI Vne as described in Advisory Circular 29-2C Para 29-1505?
As you implied, that testing is rather critical and typically the flight test cards and briefings are carefully ( very carefully ) constructed, so I kind of suspect I've misinterpreted your writing. |
Sultan's ego must place a large load on his Rotor System....perhaps the Vibrations are getting to him.
I suppose he fails to grasp the experience level and background of a great many who attend this Forum. Save your gratuitous remarks and stick to what ol' Joe Friday insisted upon will you...or as close to facts as you can get anyway. Do you know exactly what the Task was that day, the details of the plan and brief, and the profile and Test Points being sought when the accident happened or are you just passing along some talk overheard at a Tavern somewhere? |
JD
160 was the original Vne so I was just responding to why would anyone fly beyond VNE. Two reasons are expansion of the original envelope and the need to demo 1.1 Vne. As to AEO vs OEI Vne's those are defined in the end by testing the actual characteristics of the aircraft. That appears to be what Bell was doing. They may actually have a goal of a 200 Kt Vne. I was just throwing out the rationale of why testing at such speeds. Finally. Not an expert on the nuances of Part 29, but you have to be able to transition from AEO Vne to OEI Vne so engine loss at Vne is required testing. The Sultan |
Sultan: Not at 1.11Vne.
Look The Advisory Circular defines the testing requirements and is online. Have a read and you'll see what they had to do, and, important to your implication, not do. Re the R/W note above. Doing the OEI Vne testing by itself would explain some Nr droop, but typically not result in the comment " significantly "*. The comments re the blades going out of track and the possibility of both nose and tail strikes opens up all sorts of possibilities, but one needs the telemetry data to make sense of what was going on. *The FAA does not require simultaneous twin engine cuts on a twin engine Cat A machine. The military does, dependent on the rules set up for the particular aircraft. One day the Project Pilot on the CH-53D asked me if I was doing anything ( I wasn't ) and he needed me to help him do the twin cuts at max speed, max weight, with appropriate pilot delay time. Now that defined significant rotor speed droop ( high 70 % as I recall ). I still have a copy of the data traces. The aircraft rolled left very quickly and in fact my right leg got whacked pretty good when Frank put in full right cyclic. But the blades remained in track etc. Now, we had done a buildup at incremental speeds up to the max speed point and things had gone quietly, so the reaction at the final data point was without prior evidence that we were on the edge ( of rather severe stall ). This is not a suggestion at all re the Bell 525 situation, simply an observation that significant Nr droop ( depending on how the writer defines " significant " ) needs an explanation. We can be certain that all of these aspects have already been examined in detail by the Bell investigative folks. |
Also, OEI is not AEI so it's not clear if this was being flown with one engine or not. I'd venture to suggest that at only 3000' or so, it would not be a dual cut. If it was indeed following a dual cut, it would be interesting to see if there are any similarities to the fatal AB139 accident that occurred during high speed autorotation testing (both bailed but FTE struck).
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212, for a Cat A aircraft, Part 29 does not require a simultaneous dual engine cut. It does require single engine cuts from dual engine flight and requires cutting the second engine from whatever speed the applicant selects for the OEI maximum speed ( usually OEI VH ). Part 29 also requires testing to whatever the applicant selects for the Vmax autorotation speed. That can have its own set of things to watch out for. After one reads all the testing required in that sub part G of the advisory circular and then comparing to the limited info in the referenced article, there is no certainty of exactly what the initial conditions were.
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JD
Nothing I said or read say both engines were cut. As to Part 29 Sikorsky should read it for 30 minute loss of lube. This was development/envelope expansion. Is not AEO all engines operating? The Sultan |
Yes AEO is - I wrote AEI.
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As to Part 29 Sikorsky should read it for 30 minute loss of lube. |
Not that startling given who wrote it!
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Originally Posted by 212man
(Post 9453873)
Yes AEO is - I wrote AEI.
@TheSultan: John D has been sharing in good faith ... I'd encourage all of us to do likewise. @SASless: winding up Sultan? Let's keep it classy. |
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