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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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