Exceeding Vne
Brother John can confirm this story as well....as it happened more than once with various pilots involved.
The Sikorsky Completion Center was well out into the middle of no where....in the area of West Palm Beach.
As part of the Conversion Training we conducted for customer pilots we included some ILS Approaches to West Palm Beach Airport.
One evening.....a Eastern Airlines 727 was ahead of us on approach and seeing an opportunity that was impossible to pass up.....we laid whip to the horses and began to overtake the 727.
Approach Control (being well familiar with this) requested Eastern to increase speed due to overtaking traffic.
Eastern complied.
A minute or so later....ATC requested Eastern to increase speed again......Eastern agreed.
Another minute and ATC yet again asked for a speed increase to be queried by Eastern as to what kind of traffic was overtaking them.....to be told by ATC....."A Helicopter!".
There was a moment's pause....then Eastern with an odd sound to his voice asked....."Helicopter? What kind of Helicopter?".
To be told by an anonymous helicopter pilot....."A damn fast one!"!
Yes....the 155 number was just that!
The Sikorsky Completion Center was well out into the middle of no where....in the area of West Palm Beach.
As part of the Conversion Training we conducted for customer pilots we included some ILS Approaches to West Palm Beach Airport.
One evening.....a Eastern Airlines 727 was ahead of us on approach and seeing an opportunity that was impossible to pass up.....we laid whip to the horses and began to overtake the 727.
Approach Control (being well familiar with this) requested Eastern to increase speed due to overtaking traffic.
Eastern complied.
A minute or so later....ATC requested Eastern to increase speed again......Eastern agreed.
Another minute and ATC yet again asked for a speed increase to be queried by Eastern as to what kind of traffic was overtaking them.....to be told by ATC....."A Helicopter!".
There was a moment's pause....then Eastern with an odd sound to his voice asked....."Helicopter? What kind of Helicopter?".
To be told by an anonymous helicopter pilot....."A damn fast one!"!
Yes....the 155 number was just that!
The London to Paris competition had GBHBF (The Spirit of Paris) taking part. After it was over Sikorsky advised us that they would have authorised a 100/100% cruise if we had asked them.
A bit late; it was all over.
I would do that regularly at Aldergrove to Tridents. A light Puma would get up to 160 knots on a 3 degree glide path.
A bit late; it was all over.
"Helicopter? What kind of Helicopter?".
212 hello! AFCS hardcover testing was sometimes boring and once in awhile “ interesting “ . The guys doing the S-61 certification were having trouble getting th required delay times doing the forward hardover at most forward CG and at max climb. ( this was a year or so prior to me joining ), so the Ch Experimental Pilot ( Byron Graham ) and the Ch Pilot Dmitry ( Jimmy ) Viner went to fly the data point. Byron was beyond good, flying skill-wise and he was flying. Winter, with 3-4 inches of snow on the ground. Took off to the south, threw the hardover in just over the Merritt Pkwy bridge southbound. Byron took the delay time and then some, and when he brought the cyclic back he cut the tail drive. Made the neatest zero thrust landing and there is a widely circulated ( internally ) picture of the tail wheel path thru the snow-dead straight.
Boring? Due to the S-92 AFCS architecture, it required 2000+ hardovers, none of which were particularly attention getting.
With the advent of FBW controls, that sort of failure mode testing will largely, if not totally, be a thing of the past.
Boring? Due to the S-92 AFCS architecture, it required 2000+ hardovers, none of which were particularly attention getting.
With the advent of FBW controls, that sort of failure mode testing will largely, if not totally, be a thing of the past.
Sas, to your first sentence in Post 18. So right. To meet that requirement for the UH-60 ( an area where the military requirement mirrored the FAA ) we had to install a pitch bias actuator. After a number of years in service and with a PBA whose reliability record was below par, the Army did an eval and came to the conclusion we had talked about at the very beginning: the attitude vs speed slope was such that if you put the ship on an attitude, it held speed...QED. So the PBA came out.
Well, the 76 was not much different here, but the FAA.......what was the Sergeant’s name in Hogan’s Heroes again?
Well, the 76 was not much different here, but the FAA.......what was the Sergeant’s name in Hogan’s Heroes again?
Last edited by JohnDixson; 27th Nov 2018 at 14:56. Reason: grammar
I shall not make a confession here but we had the Puma speed beat....well beat! Like you would have stepped outside to see what had you bogged down....beat!
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During the ‘70s, we were occasionally asked to do an air test of some sort in the Puma HC1. Part of the test was to fly at VNE which was 167 knots which was only achievable in a dive. It was a white knuckle ride with the centre (plastic) windscreen panting. Seem to remember the ASI kissing 167 for just a fraction of a second before recovering to a more sensible flight regime.
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Thanks for the replies, discussion, resources, and stories! I appreciate it.
To summarize what I’ve been reading, potential dangers of exceeding power-on Vne include: negative effects on controllability, reduced service life on aircraft components, and resultant inaccuracy of time-change component schedules. If it’s exceeded by 10%, you *may* run into problems with compressibility, excessive vibration/aircraft stress, blade stall, or some combination of all of the above. Did I miss anything big there?
To summarize what I’ve been reading, potential dangers of exceeding power-on Vne include: negative effects on controllability, reduced service life on aircraft components, and resultant inaccuracy of time-change component schedules. If it’s exceeded by 10%, you *may* run into problems with compressibility, excessive vibration/aircraft stress, blade stall, or some combination of all of the above. Did I miss anything big there?
The Lynx Mk7/9 had a Vne of 156Kts yet it held the speed record of over 200kts (heavily modified aircraft) - it would exceed 156 (without the TOW booms) with ease in level flight and I was advised by an ex-TP that it only started to become a handful above 180 Kts.
Of course I never tried it.............................................
I'm sure Shy will remember the dive to Vne (168Kts) in the Gazelle - and then the subsequent pull into jackstall
Of course I never tried it.............................................
I'm sure Shy will remember the dive to Vne (168Kts) in the Gazelle - and then the subsequent pull into jackstall
Crab,
Nearly reliable sources suggest it became a handful for you when you first put your hand on the door handle!
Nearly reliable sources suggest it became a handful for you when you first put your hand on the door handle!
Sas - yes, it kept going upside down when I flew it
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Originally Posted by [email protected]
I'm sure Shy will remember the dive to Vne (168Kts) in the Gazelle - and then the subsequent pull into jackstall
Think about this: The manufacturer has to design the helicopter to be flown by pilots of all skill-level from Private up through ATP. Not every guy that flies their new machine is going to be Chuck Aaron. They have to assume that some dope will take the thing up with it loaded to max gross and with it also at one of the (longitudinal or lateral) c.g. limits. And maybe they'll fly it up at its limiting airspeed. Sooooo...let's see what the FAR's say about this.
(e) The rotorcraft, after (1) failure of one engine in the case of multiengine rotorcraft that meet Transport Category A engine isolation requirements, or (2) complete engine failure in the case of other rotorcraft, must be controllable over the range of speeds and altitudes for which certification is requested when such power failure occurs with maximum continuous power and critical weight. No corrective action time delay for any condition following power failure may be less than—
(i) For the cruise condition, one second, or normal pilot reaction time (whichever is greater); and
(ii) For any other condition, normal pilot reaction time.
(f) For helicopters for which a VNE (power-off) is established under §27.1505(c), compliance must be demonstrated with the following requirements with critical weight, critical center of gravity, and critical rotor r.p.m.:
(1) The helicopter must be safely slowed to VNE (power-off), without exceptional pilot skill, after the last operating engine is made inoperative at power-on VNE.
(2) At a speed of 1.1 VNE (power-off), the margin of cyclic control must allow satisfactory roll and pitch control with power off.
Yikes! Remember, these conditions must be met without "exceptional pilot skill."
Can you imagine being a test-pilot for a manufacturer and having to bring it up to max gross, and then load it to a "critical" c.g. (i.e. one of the limits). Then you go out and set max cruise power, and dive to power-on VNE...and then cut the engine. I'm no test pilot, but I would assume that you'd have to run that test at all of the corners of the c.g. envelope. At "critical" MRRPM. And VNE.
Scary stuff, when you think about it.
Back when we were trying to get the FH1100 back into production, an operator called and asked how fast the ship would go? I said "127 mph" (which is its VNE). And he said, "No, seriously, how fast will it really go?" I guess he was comparing it to a Bell 206, which as a VNE of 150 mph and figured it would go just as fast. And maybe it would. But an 1100 is not a 206. I told him honestly that I never took one above published VNE. Because as I said, I'm no test-pilot.
An FH1100 with a RR250-C20B would certainly go faster than 127 mph. But the mast on the 1100 is not tilted forward (as on a 206) and it has a tiny horizontal stab to help pull the tail down. Just doing 127 produces a pronounced nose-down cabin attitude of around -10 degrees. Making it go faster would make the nose drop even further. Now, can you imagine if the engine quit at "something above" VNE? Your Private Pilot natural instinct might be to quickly lower the collective. And if you did that before pulling back on the cyclic the nose would drop even further and the airspeed would increase. You'd probably cut the tailboom off or bump the mast off trying to get the nose up. I had talked with enough of the original FH1100 test pilots to know not to mess with the limits. They put the fear of God into me - and I'm an atheist!
As people have said, VNE is about more than just retreating-blade stall. A lot more.
§27.143 Controllability and maneuverability.
(We'll disregard letters 'a' through 'd' for now so we can focus on the really meaty part of this standard, which is 'e' and especially 'f'.)(e) The rotorcraft, after (1) failure of one engine in the case of multiengine rotorcraft that meet Transport Category A engine isolation requirements, or (2) complete engine failure in the case of other rotorcraft, must be controllable over the range of speeds and altitudes for which certification is requested when such power failure occurs with maximum continuous power and critical weight. No corrective action time delay for any condition following power failure may be less than—
(i) For the cruise condition, one second, or normal pilot reaction time (whichever is greater); and
(ii) For any other condition, normal pilot reaction time.
(f) For helicopters for which a VNE (power-off) is established under §27.1505(c), compliance must be demonstrated with the following requirements with critical weight, critical center of gravity, and critical rotor r.p.m.:
(1) The helicopter must be safely slowed to VNE (power-off), without exceptional pilot skill, after the last operating engine is made inoperative at power-on VNE.
(2) At a speed of 1.1 VNE (power-off), the margin of cyclic control must allow satisfactory roll and pitch control with power off.
Yikes! Remember, these conditions must be met without "exceptional pilot skill."
Can you imagine being a test-pilot for a manufacturer and having to bring it up to max gross, and then load it to a "critical" c.g. (i.e. one of the limits). Then you go out and set max cruise power, and dive to power-on VNE...and then cut the engine. I'm no test pilot, but I would assume that you'd have to run that test at all of the corners of the c.g. envelope. At "critical" MRRPM. And VNE.
Scary stuff, when you think about it.
Back when we were trying to get the FH1100 back into production, an operator called and asked how fast the ship would go? I said "127 mph" (which is its VNE). And he said, "No, seriously, how fast will it really go?" I guess he was comparing it to a Bell 206, which as a VNE of 150 mph and figured it would go just as fast. And maybe it would. But an 1100 is not a 206. I told him honestly that I never took one above published VNE. Because as I said, I'm no test-pilot.
An FH1100 with a RR250-C20B would certainly go faster than 127 mph. But the mast on the 1100 is not tilted forward (as on a 206) and it has a tiny horizontal stab to help pull the tail down. Just doing 127 produces a pronounced nose-down cabin attitude of around -10 degrees. Making it go faster would make the nose drop even further. Now, can you imagine if the engine quit at "something above" VNE? Your Private Pilot natural instinct might be to quickly lower the collective. And if you did that before pulling back on the cyclic the nose would drop even further and the airspeed would increase. You'd probably cut the tailboom off or bump the mast off trying to get the nose up. I had talked with enough of the original FH1100 test pilots to know not to mess with the limits. They put the fear of God into me - and I'm an atheist!
As people have said, VNE is about more than just retreating-blade stall. A lot more.
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Actually it's not
The rule is applicable to all phases of flight (you must be able to survive engine failures and safely fly into and in autorotation),
The second part (f) is specific in requiring satisfactory handling within a power off envelope, including getting there from a power on Vne failure ( which is a test case that focusses your mind)
If your power on envelope is the same as power off , only (e) applies.
as with defining any Vne there is more than one factor to take into account, but as before the clue is in the title: never exceed
The second part (f) is specific in requiring satisfactory handling within a power off envelope, including getting there from a power on Vne failure ( which is a test case that focusses your mind)
If your power on envelope is the same as power off , only (e) applies.
as with defining any Vne there is more than one factor to take into account, but as before the clue is in the title: never exceed
Last edited by dangermouse; 29th Nov 2018 at 07:02.
FH properly expands the considerations re the speed limit test requirements, but we need to also realize that the FAR’s recognize the establishment of an OEI Vne. Thus for the 92, the twin engine power on Vne is 165 and the OEI Vne is 120, which is also the power off Vne. So doing the second engine cut test is performed at the OEI Vne. Makes the second cut test a lot less eventful than implied above ( the collective position is far lower, thus the Nr decay rate is lower etc ).
I can only comment re the 76 and 92 here, but the power on Vne for both was achievable in level flight, not a dive, so the cut of the first engine at Vne was also a bit less exciting than implied above.
I can only comment re the 76 and 92 here, but the power on Vne for both was achievable in level flight, not a dive, so the cut of the first engine at Vne was also a bit less exciting than implied above.
Last edited by JohnDixson; 29th Nov 2018 at 11:29. Reason: Additional information
Originally Posted by [email protected]
I'm sure Shy will remember the dive to Vne (168Kts) in the Gazelle - and then the subsequent pull into jackstall
Avoid imitations
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Originally Posted by [email protected]
I'm sure Shy will remember the dive to Vne (168Kts) in the Gazelle - and then the subsequent pull into jackstall
These days I fly a heli that will easily exceed its 167 kts Vne in level flight, let alone in a descent - slippery little beast. It was quite amusing to once be asked to make "best speed" to fit in between two airliners in the instrument pattern - then to be asked to slow down because I was catching a preceding Boeing 767 on finals.
Have a question for the Gazelle pilots here: did Eurocopter ever upgrade the hydraulics and servos to provide a force capability commensurate with that rotors’ control loads?
Avoid imitations
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John, I doubt it. During my time instructing on the type I was always under the impression that the hydraulic system was designed so that structural loads couldn't easily be exceeded. There was a pressure relief valve built in so that would be the first thing to "pop" off if feedback forces became too much, rather than something more vital.
Thanks, Shy, but it seems I totally misunderstood the use of “ jackstall” in connection with several events involving Gazelles. I thought it signified a condition wherein the maneuver control loads exceeded the force capability of the servos, hence the cyclic became stalled or immovable. What did it in fact mean?