What's the latest on tilt rotors?
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The information being released by the Marine Corps continues to give increasing indications that 'asymmetrical settling with power' was the cause of the April V-22 accident in Arizona. As pointed out above, when the vortex ring state develops on one side, the result would be a dropping of the wing on that side. The instinctive reaction of the pilot would be to use lateral cyclic stick in the opposite direction of the falling wing. This causes an increase of collective pitch on the rotor system that is in the vortex ring state. As we know, that is exactly the worst thing to do when a settling with power condition exists as it further worsens the resultant reduction in lift provided.
The existence of this phenomenon is certainly not a death blow for tiltrotor technology. It is a limitation that contributes to the defining of the normal operations flight envelope. Compare the above situation to what happens to an airplane when a poorly trained or inexperienced pilot allows the aircraft to stall while on approach for landing. If the airspeed is allowed to reduce to the point of aerodynamic stall (critical angle of attack is reached) the airplane will begin to lose altitude, and it is very likely a wing will drop. If the pilot then does what is instinctive -- pulls back on the yoke to stop the loss of altitude, and applies opposite aileron -- the aircraft will enter a stall/spin and at that point, lacking the altitude necessary for recovery, the pilot will be powerless to prevent the aircraft from impacting the ground. Unfortunately low time pilots repeat this scenario many times every year resulting in numerous unnecessary deaths. This does not prove that all airplanes are dangerous, or indicate that they should all be permanently grounded.
In the same way that a fixed-wing a/c should not go below 1.3 times the stall speed when on final approach, a single rotor helicopter should not descend at a rate of 300 fpm or more at slow speeds. Violating these limitations at low altitude has time and again resulted in the same devastating consequence experienced by the V-22 in Arizona when it was operated outside of its normal flight envelope. Does this mean that the use of all helicopters should be stopped? The characteristic of 'asymmetrical settling with power' in tiltrotors is by no means a fatal flaw necessitating the cancellation of an aircraft that more than doubles the range and speed capabilities of the helicopters they are replacing. When you develop an aircraft with dramatically increased capabilities at the high speed end, it is quite typical that there will be low speed limitation penalties that accompany the advances. However, it goes without saying that accidents with loss of life are not an acceptable price to pay for an increased capability to deploy troops further and faster than ever before.
The undeniable answer to preventing accidents in the future is training and experience. Pilots must learn to recognize the conditions that will put them outside the normal flight envelope, and apply correct recovery techniques when appropriate. All aircraft flying today have 'dangerous' characteristics in certain flight regimes that must be avoided, regardless of whether you are in an airplane, helicopter, or tiltrotor. When pilots are not properly trained to understand and recognize the conditions to be avoided, disastrous consequences are inevitable.
The Marine crew that perished in the April crash had a number of contributing factors working against them. The most obvious is a lack of experience in tiltrotors, having only 80 or 90 hours each in the V-22. Combine that with the extremely high workload environment of flying at night, flying with night-vision goggles, and flying in formation in a simulation of a high pressure rescue/extraction of civilian hostages in the final phase of an operations evaluation. Operating under these circumstances would be difficult for highly experienced tiltrotor pilots. Like many military operations, this type of flying will always be categorized as high risk, particularly when you throw in a real life high-threat location. But in time missions such as this will be able to be carried out successfully by those pilots who are now gaining experience in the military. It is terrible that 19 people lost their lives in an accident that should not have happened, but hopefully the lessons learned will save lives in the future.
Before any judgment is made on exactly what happened, why it happened, and how do we prevent it from happening again, we need to wait for ALL of the facts to be in. Fortunately there was a FDR, CVR, an eye witness on the ground, and the entire event was being filmed in infrared by an F/A-18 flying overhead at altitude. So it is likely that all the facts needed for complete analysis will be available, and that appropriate evaluation and recommendations will be forthcoming. The Marines more than anyone are interested in ensuring that this event never occurs again. The V-22's return to service shows their confidence in tiltrotor technology. That confidence comes from 45 years of tiltrotor research, including 11 years of flying the V-22.
R. Denehy, ATP - ASMEL, ASES, RH; CFI - ASM, RH; CFII - A&H
The existence of this phenomenon is certainly not a death blow for tiltrotor technology. It is a limitation that contributes to the defining of the normal operations flight envelope. Compare the above situation to what happens to an airplane when a poorly trained or inexperienced pilot allows the aircraft to stall while on approach for landing. If the airspeed is allowed to reduce to the point of aerodynamic stall (critical angle of attack is reached) the airplane will begin to lose altitude, and it is very likely a wing will drop. If the pilot then does what is instinctive -- pulls back on the yoke to stop the loss of altitude, and applies opposite aileron -- the aircraft will enter a stall/spin and at that point, lacking the altitude necessary for recovery, the pilot will be powerless to prevent the aircraft from impacting the ground. Unfortunately low time pilots repeat this scenario many times every year resulting in numerous unnecessary deaths. This does not prove that all airplanes are dangerous, or indicate that they should all be permanently grounded.
In the same way that a fixed-wing a/c should not go below 1.3 times the stall speed when on final approach, a single rotor helicopter should not descend at a rate of 300 fpm or more at slow speeds. Violating these limitations at low altitude has time and again resulted in the same devastating consequence experienced by the V-22 in Arizona when it was operated outside of its normal flight envelope. Does this mean that the use of all helicopters should be stopped? The characteristic of 'asymmetrical settling with power' in tiltrotors is by no means a fatal flaw necessitating the cancellation of an aircraft that more than doubles the range and speed capabilities of the helicopters they are replacing. When you develop an aircraft with dramatically increased capabilities at the high speed end, it is quite typical that there will be low speed limitation penalties that accompany the advances. However, it goes without saying that accidents with loss of life are not an acceptable price to pay for an increased capability to deploy troops further and faster than ever before.
The undeniable answer to preventing accidents in the future is training and experience. Pilots must learn to recognize the conditions that will put them outside the normal flight envelope, and apply correct recovery techniques when appropriate. All aircraft flying today have 'dangerous' characteristics in certain flight regimes that must be avoided, regardless of whether you are in an airplane, helicopter, or tiltrotor. When pilots are not properly trained to understand and recognize the conditions to be avoided, disastrous consequences are inevitable.
The Marine crew that perished in the April crash had a number of contributing factors working against them. The most obvious is a lack of experience in tiltrotors, having only 80 or 90 hours each in the V-22. Combine that with the extremely high workload environment of flying at night, flying with night-vision goggles, and flying in formation in a simulation of a high pressure rescue/extraction of civilian hostages in the final phase of an operations evaluation. Operating under these circumstances would be difficult for highly experienced tiltrotor pilots. Like many military operations, this type of flying will always be categorized as high risk, particularly when you throw in a real life high-threat location. But in time missions such as this will be able to be carried out successfully by those pilots who are now gaining experience in the military. It is terrible that 19 people lost their lives in an accident that should not have happened, but hopefully the lessons learned will save lives in the future.
Before any judgment is made on exactly what happened, why it happened, and how do we prevent it from happening again, we need to wait for ALL of the facts to be in. Fortunately there was a FDR, CVR, an eye witness on the ground, and the entire event was being filmed in infrared by an F/A-18 flying overhead at altitude. So it is likely that all the facts needed for complete analysis will be available, and that appropriate evaluation and recommendations will be forthcoming. The Marines more than anyone are interested in ensuring that this event never occurs again. The V-22's return to service shows their confidence in tiltrotor technology. That confidence comes from 45 years of tiltrotor research, including 11 years of flying the V-22.
R. Denehy, ATP - ASMEL, ASES, RH; CFI - ASM, RH; CFII - A&H
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PTI UAE
I find your contribution wholly unconvincing and a continuance of the denial process. Your comparison with the fixed wing stall/spin evolution is taking simile a bit too far IMHO (see later). There is always lacking any viable suggestion as to how Osprey crews are to avoid the AsymmVR condition - or recover. It will always be there - just a flick of the wrist away, and much much more insidious than an inept "stall/spin on finals" scenario. Anyway, specifically:
1. "a single rotor helicopter should not descend at a rate of 300 fpm or more at slow speeds.(???)" Unfortunately, I assure you that this sort of sedate operation will not work in an operational environment. I've got 13 months in SVN backing me up on this.
2. Pilots must learn to recognize the conditions that will put them outside the normal flight envelope (in a dynamic situation, as in Marana, just how do you do that? it's a momentary entry), and apply correct recovery techniques when appropriate (which are??). Don't be coy, just what are they?
3. All aircraft flying today have 'dangerous' characteristics in certain flight regimes that must be avoided, regardless of whether you are in an airplane, helicopter, or tiltrotor (quite trite. Not sure that this is a valid argument in support of asymmVR being an acceptably benign characteristic - rather sweeping assertion). In a FW, an ASI and an accelerometer will keep you out of trouble (except for coffin corner). What does the Osprey crew have? "Keep scanning that VSI Bloggs, watch out for any lag. It'll kill you"
4. When pilots are not properly trained to understand and recognize the conditions to be avoided, disastrous consequences are inevitable. AsymmVR will always be there - just a flick of the wrist away, and much much more insidious than an inept "stall/spin on finals" scenario. They'll have no aural/visual/instrument warning of its onset or imminence.
5. The Marine crew that perished in the 8 April crash had a number of contributing factors working against them. The most obvious is a lack of experience in tilt-rotors, having only 80 or 90 hours each in the V-22. If you're inferring here that AsymmVR had been identified as a possible outcome of exceeding the rather lose envelope laid down, you had better check your facts. My conclusion therefore is that, because it was a wholly unanticipated flight condition, it would not have mattered if they'd had ten times that MV-22 experience. And it would have happened in daylight just as easily. The formation station overshoot that precipitated the AsymmVR was no more likely at night than day.
6. But in time, missions such as this will be able to be carried out successfully by those pilots who are now gaining experience in the military. I guess we could discuss here the largish detachment of Apaches that went to Kosovo but weren't used because of the crew's inexperience and high accident rate.
7. and the entire event was being filmed in infrared by an F/A-18 flying overhead at altitude. Incorrect (retracted later by Gen McCorkle). But the eye-witness evidence is quite determinative.
8. The Marines more than anyone are interested in ensuring that this event never occurs again. That is the problem. It most assuredly will - because the susceptibility is built into the design concept and the propensity is in the style of operation. The solution is likely to be quite elusive. Warning systems of 2% chord L.E. pressure transducers will record the condition (delta t of spanwise lift distribution), but as found in RAE trials, cannot forecast it. There are too many variables close to the normal operation. What sort of buffer will there be in the new envelope and how can it be infallibly observed? (AsymmVR being automatically fatal and all). It is supposedly a combat area aircraft and is meant to be able to manoeuvre aggressively. Therein lies the conundrum.
9. The V-22's return to service shows their confidence in tilt-rotor technology. That confidence comes from 45 years of tilt-rotor research, including 11 years of flying the V-22. So why has the condition only now come to light (and detailed attention in flight trials, wind-tunnelling and modeling that's now underway)?
There is a light at the end of the tunnel in that you've brought yourself to address the problem as AsymmVR and not talked about settling, lead a/c wake, turbulence etc., as per most USDoD and Marine PR. But questions remain.
How do you differentiate between a "picking up the dropped wing" (with differential collective) instinctive response from either:
(1) a straight entry into asymmVR (because you're verging on the condition)
(2) or an entry that is a compound of picking up a gust-dropped wing (or even simply banking) whilst at the edge of the envelope (in the VR ball-park)?
"Late in the piece" (rolling) realization of asymmVR is around about the point where you would pull the crutch-handle, but what are they to do by way of recovery? Roll the long way round?
So in my opinion it's the dynamics of the condition's onset that needs to be understood -as well as the proximity of the condition to the required normal operation's parameters. I don't see asymmetric (engine fail) scenarios leading to asymmVR. Most of the ardent defences head off on that red herring - but it's irrelevant. Of course, for both the USN and USMC, the air-flow dynamics of what's happening at the carrier's fan-tail will also be food for thought.
My critics may hold that I'm a doomsayer but you have to review any such denial in the light of the well-witnessed and recorded circumstances of the Marana accident. If that accident hasn't got repeatability written all over it, then I'm a Monkey's Uncle. If I was a Pax River Osprey TP I'd be taking my pneumonia pills and doing some non-stop malingering. I kid you not. Finally, to compare:
Conventional helo:
Attempting to enter a high OGE (out of ground effect) hover whilst heavy could lead to VR, but it is more normally entered as an unhappy coincidence of your downwash with a steep approach path (i.e. at low IAS) when accompanied by a high Rate of Descent. Once the vortex forms and you don't move positively in relation to it, it will only be "stoked" by a higher collective power selection. It is quite recognizable when it happens (for some-one who's seen it and knows what's occurring). It takes quite a height sacrifice to escape that downward helix. If you're maintaining a pretty well level disc, a Vortex Ring will stay with you at quite surprisingly high speeds (20 to 30 kts of sideways, forwards, rearwards). You do need to shove the cyclic forward and tilt that rotor disc at a reasonable incline in order to "shed" it (i.e. it's "sticky"). Of course the whole new ball-game is that with the Osprey's asymmVR you don't get that chance. Your input is instinctive (as for a wing-drop) - but quite terminal.
Osprey:
The Marana MV-22 slightly overshot his starboard abeam position after a station change (tactically lose in trail and he swapped sides to the stbd echelon for the final approach). His required movement back to behind the leader's three o'clock (relative) position was sufficient to put him in the VR ball-park. Once you're there (in that ball-park) I guess it takes as little as a lateral stick movement to enter asymmVR (which they'd done to pick up their line to their own hover termination point .... and that's when they hit it). His earlier high ROD was probably not a factor. He hit it after that station change re-position. The Marines admit that wake turbulence from the leader had nought to do with it. On the promising side, now that they know about it, they'll be trying to avoid it. The problem is that a FW operating envelope is relatively easy to stay inside of - only asymmetric rolling g will give you un-instrumented and un-forecast grief. In the Osprey the forbidden and lethal edge of the asymmVR envelope will always be only a mishandle away.
Whatsoever their hopes and wishes, the actual entry into that asymmVR ball-park is so easy that sooner or later it must happen again. It just takes a whimsy of the wind and a bit of unaggressive manoeuvre to set it up. Marana proved that. Not doing the wind-tunnel and flight-tests for the possible condition just shows what compulsory optimism and gung-ho can do for a program. That oversight has led them into a total conundrum simply because the fatal flaw is designed into the basic concept.
So for your first post here on this forum PTIUAE, I don't think you've achieved what you were asked to. Feel free to provide any facts that will counter that opinion. You've been writing PR releases for too long methinks. Say hello to Tom.
[email protected]
[This message has been edited by UNCTUOUS (edited 24 May 2000).]
I find your contribution wholly unconvincing and a continuance of the denial process. Your comparison with the fixed wing stall/spin evolution is taking simile a bit too far IMHO (see later). There is always lacking any viable suggestion as to how Osprey crews are to avoid the AsymmVR condition - or recover. It will always be there - just a flick of the wrist away, and much much more insidious than an inept "stall/spin on finals" scenario. Anyway, specifically:
1. "a single rotor helicopter should not descend at a rate of 300 fpm or more at slow speeds.(???)" Unfortunately, I assure you that this sort of sedate operation will not work in an operational environment. I've got 13 months in SVN backing me up on this.
2. Pilots must learn to recognize the conditions that will put them outside the normal flight envelope (in a dynamic situation, as in Marana, just how do you do that? it's a momentary entry), and apply correct recovery techniques when appropriate (which are??). Don't be coy, just what are they?
3. All aircraft flying today have 'dangerous' characteristics in certain flight regimes that must be avoided, regardless of whether you are in an airplane, helicopter, or tiltrotor (quite trite. Not sure that this is a valid argument in support of asymmVR being an acceptably benign characteristic - rather sweeping assertion). In a FW, an ASI and an accelerometer will keep you out of trouble (except for coffin corner). What does the Osprey crew have? "Keep scanning that VSI Bloggs, watch out for any lag. It'll kill you"
4. When pilots are not properly trained to understand and recognize the conditions to be avoided, disastrous consequences are inevitable. AsymmVR will always be there - just a flick of the wrist away, and much much more insidious than an inept "stall/spin on finals" scenario. They'll have no aural/visual/instrument warning of its onset or imminence.
5. The Marine crew that perished in the 8 April crash had a number of contributing factors working against them. The most obvious is a lack of experience in tilt-rotors, having only 80 or 90 hours each in the V-22. If you're inferring here that AsymmVR had been identified as a possible outcome of exceeding the rather lose envelope laid down, you had better check your facts. My conclusion therefore is that, because it was a wholly unanticipated flight condition, it would not have mattered if they'd had ten times that MV-22 experience. And it would have happened in daylight just as easily. The formation station overshoot that precipitated the AsymmVR was no more likely at night than day.
6. But in time, missions such as this will be able to be carried out successfully by those pilots who are now gaining experience in the military. I guess we could discuss here the largish detachment of Apaches that went to Kosovo but weren't used because of the crew's inexperience and high accident rate.
7. and the entire event was being filmed in infrared by an F/A-18 flying overhead at altitude. Incorrect (retracted later by Gen McCorkle). But the eye-witness evidence is quite determinative.
8. The Marines more than anyone are interested in ensuring that this event never occurs again. That is the problem. It most assuredly will - because the susceptibility is built into the design concept and the propensity is in the style of operation. The solution is likely to be quite elusive. Warning systems of 2% chord L.E. pressure transducers will record the condition (delta t of spanwise lift distribution), but as found in RAE trials, cannot forecast it. There are too many variables close to the normal operation. What sort of buffer will there be in the new envelope and how can it be infallibly observed? (AsymmVR being automatically fatal and all). It is supposedly a combat area aircraft and is meant to be able to manoeuvre aggressively. Therein lies the conundrum.
9. The V-22's return to service shows their confidence in tilt-rotor technology. That confidence comes from 45 years of tilt-rotor research, including 11 years of flying the V-22. So why has the condition only now come to light (and detailed attention in flight trials, wind-tunnelling and modeling that's now underway)?
There is a light at the end of the tunnel in that you've brought yourself to address the problem as AsymmVR and not talked about settling, lead a/c wake, turbulence etc., as per most USDoD and Marine PR. But questions remain.
How do you differentiate between a "picking up the dropped wing" (with differential collective) instinctive response from either:
(1) a straight entry into asymmVR (because you're verging on the condition)
(2) or an entry that is a compound of picking up a gust-dropped wing (or even simply banking) whilst at the edge of the envelope (in the VR ball-park)?
"Late in the piece" (rolling) realization of asymmVR is around about the point where you would pull the crutch-handle, but what are they to do by way of recovery? Roll the long way round?
So in my opinion it's the dynamics of the condition's onset that needs to be understood -as well as the proximity of the condition to the required normal operation's parameters. I don't see asymmetric (engine fail) scenarios leading to asymmVR. Most of the ardent defences head off on that red herring - but it's irrelevant. Of course, for both the USN and USMC, the air-flow dynamics of what's happening at the carrier's fan-tail will also be food for thought.
My critics may hold that I'm a doomsayer but you have to review any such denial in the light of the well-witnessed and recorded circumstances of the Marana accident. If that accident hasn't got repeatability written all over it, then I'm a Monkey's Uncle. If I was a Pax River Osprey TP I'd be taking my pneumonia pills and doing some non-stop malingering. I kid you not. Finally, to compare:
Conventional helo:
Attempting to enter a high OGE (out of ground effect) hover whilst heavy could lead to VR, but it is more normally entered as an unhappy coincidence of your downwash with a steep approach path (i.e. at low IAS) when accompanied by a high Rate of Descent. Once the vortex forms and you don't move positively in relation to it, it will only be "stoked" by a higher collective power selection. It is quite recognizable when it happens (for some-one who's seen it and knows what's occurring). It takes quite a height sacrifice to escape that downward helix. If you're maintaining a pretty well level disc, a Vortex Ring will stay with you at quite surprisingly high speeds (20 to 30 kts of sideways, forwards, rearwards). You do need to shove the cyclic forward and tilt that rotor disc at a reasonable incline in order to "shed" it (i.e. it's "sticky"). Of course the whole new ball-game is that with the Osprey's asymmVR you don't get that chance. Your input is instinctive (as for a wing-drop) - but quite terminal.
Osprey:
The Marana MV-22 slightly overshot his starboard abeam position after a station change (tactically lose in trail and he swapped sides to the stbd echelon for the final approach). His required movement back to behind the leader's three o'clock (relative) position was sufficient to put him in the VR ball-park. Once you're there (in that ball-park) I guess it takes as little as a lateral stick movement to enter asymmVR (which they'd done to pick up their line to their own hover termination point .... and that's when they hit it). His earlier high ROD was probably not a factor. He hit it after that station change re-position. The Marines admit that wake turbulence from the leader had nought to do with it. On the promising side, now that they know about it, they'll be trying to avoid it. The problem is that a FW operating envelope is relatively easy to stay inside of - only asymmetric rolling g will give you un-instrumented and un-forecast grief. In the Osprey the forbidden and lethal edge of the asymmVR envelope will always be only a mishandle away.
Whatsoever their hopes and wishes, the actual entry into that asymmVR ball-park is so easy that sooner or later it must happen again. It just takes a whimsy of the wind and a bit of unaggressive manoeuvre to set it up. Marana proved that. Not doing the wind-tunnel and flight-tests for the possible condition just shows what compulsory optimism and gung-ho can do for a program. That oversight has led them into a total conundrum simply because the fatal flaw is designed into the basic concept.
So for your first post here on this forum PTIUAE, I don't think you've achieved what you were asked to. Feel free to provide any facts that will counter that opinion. You've been writing PR releases for too long methinks. Say hello to Tom.
[email protected]
[This message has been edited by UNCTUOUS (edited 24 May 2000).]
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Perhaps enough water has flowed under the bridge since the USMC MV-22 tragedy for us to be able to see the simple issues at the core of the accident.
Regardless of which organisation’s hat one is wearing I believe there is no arguing with the premise that IF asymmetric vortex ring (VR) is allowed to develop on an MV-22 when flying at low level in the helicopter mode, a high rate of roll will develop with catastrophic results.
From the purely pilot’s perspective, a similar situation can happen to a Harrier fitted with the original metal wing during a transition to or from the hover. Because the Harrier is directionally unstable at these speeds the pilot is responsible for keeping it pointing the way it is going by use of his feet. If he does not do this, or worse still actually tries to use his feet to control heading or track over the ground (instead of banking) then the aircraft’s dihedral effect will have it on its back in a trice.
The way the manufacturer tackled this lethal threat (sadly, as is the way of the world, only after the first fatal) was to develop warning systems that announced the ONSET of the problem while any lateral out of trim was still small and still being contained instinctively by the pilot using his lateral controls.
Now forget Harrier and think Osprey.
The prevention of roll induced by asymmetric VR needs two things:
1 An early warning that the flow on either proprotor is TENDING towards VR
2 A rapid AUTOMATIC configuration change to the aircraft to take it away from the detected incipient VR conditions.
Some years ago the Aerodynamic Research Flight at RAE Bedford carried out trials with a helicopter fitted with instrumented rotor blades so they could measure aerodynamic pressures at 2% chord. I rang the (now retired) scientist in charge of that research and he explained how they could detect the spread of VR as it developed along the blade. From this I
conjecture that perhaps a couple of such sensors (optimally positioned) on each Osprey blade might just produce the necessary error signal of DIFFERENT aerodynamic circumstances on parts of the SAME blade, to satisfy a solution to the warning system requirement. Given that each rotor has three blades the triple redundancy of such a system also appeals to me.
If early warning IS shown to be possible by whatever technique (but please leave the pilot out of this as he is more than busy enough doing a demanding military task) then I think the battle is won because I don’t see para 2 above as being difficult to sort out.
VR is by all accounts not a very stable state of affairs (as the RAE found when trying to stay in it for the trials I mentioned earlier) so I have a gut feel that a quick AUTO nudge forward
(5 deg?) of the engine nacelle tilt angle might be sufficient to kill the build-up of VR before it spreads to the whole blade.
If all this is allied with a unique and unmistakable warning to the pilot to initiate a go-around then perhaps the job of avoiding the accident might be completed.
Regardless of which organisation’s hat one is wearing I believe there is no arguing with the premise that IF asymmetric vortex ring (VR) is allowed to develop on an MV-22 when flying at low level in the helicopter mode, a high rate of roll will develop with catastrophic results.
From the purely pilot’s perspective, a similar situation can happen to a Harrier fitted with the original metal wing during a transition to or from the hover. Because the Harrier is directionally unstable at these speeds the pilot is responsible for keeping it pointing the way it is going by use of his feet. If he does not do this, or worse still actually tries to use his feet to control heading or track over the ground (instead of banking) then the aircraft’s dihedral effect will have it on its back in a trice.
The way the manufacturer tackled this lethal threat (sadly, as is the way of the world, only after the first fatal) was to develop warning systems that announced the ONSET of the problem while any lateral out of trim was still small and still being contained instinctively by the pilot using his lateral controls.
Now forget Harrier and think Osprey.
The prevention of roll induced by asymmetric VR needs two things:
1 An early warning that the flow on either proprotor is TENDING towards VR
2 A rapid AUTOMATIC configuration change to the aircraft to take it away from the detected incipient VR conditions.
Some years ago the Aerodynamic Research Flight at RAE Bedford carried out trials with a helicopter fitted with instrumented rotor blades so they could measure aerodynamic pressures at 2% chord. I rang the (now retired) scientist in charge of that research and he explained how they could detect the spread of VR as it developed along the blade. From this I
conjecture that perhaps a couple of such sensors (optimally positioned) on each Osprey blade might just produce the necessary error signal of DIFFERENT aerodynamic circumstances on parts of the SAME blade, to satisfy a solution to the warning system requirement. Given that each rotor has three blades the triple redundancy of such a system also appeals to me.
If early warning IS shown to be possible by whatever technique (but please leave the pilot out of this as he is more than busy enough doing a demanding military task) then I think the battle is won because I don’t see para 2 above as being difficult to sort out.
VR is by all accounts not a very stable state of affairs (as the RAE found when trying to stay in it for the trials I mentioned earlier) so I have a gut feel that a quick AUTO nudge forward
(5 deg?) of the engine nacelle tilt angle might be sufficient to kill the build-up of VR before it spreads to the whole blade.
If all this is allied with a unique and unmistakable warning to the pilot to initiate a go-around then perhaps the job of avoiding the accident might be completed.
How about, instead of re-engineering a 10° inboard tilt of the rotors when transitioning to hover, you just tack on a couple of JATO rockets, with an "Oh my God! Help Me!" trigger switch on the cyclic to accelerate out of a VR situation. Gotta be cheaper - and could be used in a few other tactical situations...
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That JATO solution would give an instantaneous clearance out of the vortex ring condition and (I guess) could be triggered by an FCS control follow-up circuit.
Scenario: Aircraft inadvertently enters AsymmVR during approach
i.e. 1. roll starts (within set FCS inputted parameters of airspeed, nacelle-tilt, Rate-of-descent and RadAlt height)
2. pilot makes normal instinctive differential-collective input to correct (as if for a gust-dropped wing)
3. FCS detects no roll-restorative response to side-stick applied in the correct sense (i.e. a decrease of some order of magnitude in the rolling moment, but in fact identifies an increase - which confirms that it's AsymmVR)
4. FCS decision is "Uh Oh, this is bad Kharma" and auto-fires "set 1" of emerg JATO (fuselage mounted and deployed together with gear extension ).
5. Aircraft accelerates out of vortex as roll-rate approaches bank of 60° (or thereabouts), regains differential collective controllability and aborts or does further circuit and approach (with "set 2" armed).
FCS = PFCS (primary flight control system) AFCS=Auto (both FBW aka fly-by-wire).
Flight control laws are all set by software and easily changed.
In fact, in order to gather useful empiric evidence of the AsymmVR condition, they would need to have something similar (to JATO) in order to ensure safety. i.e. it would probably be a sine qua non of any realistic trials and testing. When you think about the problems of replicating the condition in a full or quarter-scale tunnel, they are considerable. No tunnel is large enough that you can guarantee that the amount of air entrainment within a "stoked" vortex is representative of the free-flight unencapsulated open-air circulation.
The size of any such JATO kit need be no greater than 2000lbs of thrust for 15 seconds (= about 25kgs weight penalty per rocket, or about 100kgs overall). Perhaps simply having that four-simultaneous capability may also enable them to lower the safety margins in some other areas - to make up for it. It could also be used for emergency overweight STOVL departures (embassy bug-outs). Alternatively an underfuselage (over-fuselage) centre-line thrusting pair may do the job (and avoid the possibility of asymmetric firings). C130 had six JATO bottles per side but two per side would probably do the trick for the Osprey, two attached to each fuel sponson and firing a set at a time in the AsymmVR scenario.
Minus factor include the presence of explosive ordnance (particularly on a carrier), as well as the weight. A properly programmed FCS should preclude any nuisance firings.
There may be another vital VR factor at work here. The original XV-15 (upon which they did all the early proof-of-concept work) only had a 90 degree nacelle tilt capability. In the V-22 (all variants AFAIK) they increased this to 95 degrees in order to be able to back it up on the ground or reverse whilst hover-taxiing (an important capability on a crowded flight-deck as well as on a crowded tarmac). It makes sense to me that they may have had the use of that rearwards thrusting capability in order to slow more quickly on the approach in helicopter mode (i.e. it's unlikely to have been "gated out" because they had no way of knowing that it could severely exacerbate any AsymmVR problem). To explain this last point, think of it as being very similar to VIFFing in the Harrier (Vectoring In Forward Flight that the Harrier uses in Air Combat Tactics in order to turn inside an adversary - or for braking on the ground). The only airborne use for it in the V-22 would be to make the plane-to-helo conversion a much later and swifter, more dynamic process (i.e. good for tactical surprise).
However, here's the rub. The use of it would make the Osprey much more likely to encounter VR, simply because it (VR) would not require a terribly steep approach angle or high rate of descent if 95 degrees of rotor-disc tilt was being utilised to kill energy (potential i.e. excess height or kinetic as in speed). Five degrees may not seem much but when you're talking about a standard 3 to 8 degree approach angle, it's a lot. It would be enough, particularly with a tailwind, to ensure that you were descending in your own "bad air" even at much higher speeds than you would expect to encounter VR. Normally they just would not need to use it unless, say, they had a need to quickly kill excess energy - for instance if, as in the Marana case, the wingman had overshot his leader and had very little time to get back in position. The more I think about it, the more that makes sense. So on four counts it would explain why they'd not encountered VR earlier in the test & eval program (at all):
a. Firstly, as we know, no-one had expected that the Osprey was susceptible to it and so no-one had suggested testing for it.
b. Any testing that may have been done earlier (on the XV-15) would have been reassuring, but being limited to 90 degrees of nacelle-rotor tilt, quite invalid regarding the Osprey.
c. It may be that the Osprey is vulnerable to AsymmVR only when 90 degrees tilt is exceeded) - such as when a very rapid correction is needed (as in the Marana aircraft's overshoot of the leader's abeam position).
d. Any testing done on the V-22 may have preceded the decision to go to 95 degrees (which was done for ground-handling reasons)
At the very least, I'd be asking whether there was any prohibition (or even caution) for use of >90 degrees of nacelle rotor-tilt airborne. Was there any idea as to what implications it could have? I'd guess the answer (through the "smoke and mirrors" reply that you'd get) would be quite revealing. I may be wrong but I suspect that it is neither "locked out" nor "detented" when airborne. I'd guess that neither the PFCS or AFCS software has any inhibitors programmed in either. Whether or not they'd tell you that is debatable. It may all of a sudden be not FOI'able and even a matter of National Security. But it's worth asking these questions.
What I'm saying here is that it could simply be yet another case of "unintended consequences". Life and aviation is choc-a-bloc with those hind-sightable instances of human fallibility.
Scenario: Aircraft inadvertently enters AsymmVR during approach
i.e. 1. roll starts (within set FCS inputted parameters of airspeed, nacelle-tilt, Rate-of-descent and RadAlt height)
2. pilot makes normal instinctive differential-collective input to correct (as if for a gust-dropped wing)
3. FCS detects no roll-restorative response to side-stick applied in the correct sense (i.e. a decrease of some order of magnitude in the rolling moment, but in fact identifies an increase - which confirms that it's AsymmVR)
4. FCS decision is "Uh Oh, this is bad Kharma" and auto-fires "set 1" of emerg JATO (fuselage mounted and deployed together with gear extension ).
5. Aircraft accelerates out of vortex as roll-rate approaches bank of 60° (or thereabouts), regains differential collective controllability and aborts or does further circuit and approach (with "set 2" armed).
FCS = PFCS (primary flight control system) AFCS=Auto (both FBW aka fly-by-wire).
Flight control laws are all set by software and easily changed.
In fact, in order to gather useful empiric evidence of the AsymmVR condition, they would need to have something similar (to JATO) in order to ensure safety. i.e. it would probably be a sine qua non of any realistic trials and testing. When you think about the problems of replicating the condition in a full or quarter-scale tunnel, they are considerable. No tunnel is large enough that you can guarantee that the amount of air entrainment within a "stoked" vortex is representative of the free-flight unencapsulated open-air circulation.
The size of any such JATO kit need be no greater than 2000lbs of thrust for 15 seconds (= about 25kgs weight penalty per rocket, or about 100kgs overall). Perhaps simply having that four-simultaneous capability may also enable them to lower the safety margins in some other areas - to make up for it. It could also be used for emergency overweight STOVL departures (embassy bug-outs). Alternatively an underfuselage (over-fuselage) centre-line thrusting pair may do the job (and avoid the possibility of asymmetric firings). C130 had six JATO bottles per side but two per side would probably do the trick for the Osprey, two attached to each fuel sponson and firing a set at a time in the AsymmVR scenario.
Minus factor include the presence of explosive ordnance (particularly on a carrier), as well as the weight. A properly programmed FCS should preclude any nuisance firings.
There may be another vital VR factor at work here. The original XV-15 (upon which they did all the early proof-of-concept work) only had a 90 degree nacelle tilt capability. In the V-22 (all variants AFAIK) they increased this to 95 degrees in order to be able to back it up on the ground or reverse whilst hover-taxiing (an important capability on a crowded flight-deck as well as on a crowded tarmac). It makes sense to me that they may have had the use of that rearwards thrusting capability in order to slow more quickly on the approach in helicopter mode (i.e. it's unlikely to have been "gated out" because they had no way of knowing that it could severely exacerbate any AsymmVR problem). To explain this last point, think of it as being very similar to VIFFing in the Harrier (Vectoring In Forward Flight that the Harrier uses in Air Combat Tactics in order to turn inside an adversary - or for braking on the ground). The only airborne use for it in the V-22 would be to make the plane-to-helo conversion a much later and swifter, more dynamic process (i.e. good for tactical surprise).
However, here's the rub. The use of it would make the Osprey much more likely to encounter VR, simply because it (VR) would not require a terribly steep approach angle or high rate of descent if 95 degrees of rotor-disc tilt was being utilised to kill energy (potential i.e. excess height or kinetic as in speed). Five degrees may not seem much but when you're talking about a standard 3 to 8 degree approach angle, it's a lot. It would be enough, particularly with a tailwind, to ensure that you were descending in your own "bad air" even at much higher speeds than you would expect to encounter VR. Normally they just would not need to use it unless, say, they had a need to quickly kill excess energy - for instance if, as in the Marana case, the wingman had overshot his leader and had very little time to get back in position. The more I think about it, the more that makes sense. So on four counts it would explain why they'd not encountered VR earlier in the test & eval program (at all):
a. Firstly, as we know, no-one had expected that the Osprey was susceptible to it and so no-one had suggested testing for it.
b. Any testing that may have been done earlier (on the XV-15) would have been reassuring, but being limited to 90 degrees of nacelle-rotor tilt, quite invalid regarding the Osprey.
c. It may be that the Osprey is vulnerable to AsymmVR only when 90 degrees tilt is exceeded) - such as when a very rapid correction is needed (as in the Marana aircraft's overshoot of the leader's abeam position).
d. Any testing done on the V-22 may have preceded the decision to go to 95 degrees (which was done for ground-handling reasons)
At the very least, I'd be asking whether there was any prohibition (or even caution) for use of >90 degrees of nacelle rotor-tilt airborne. Was there any idea as to what implications it could have? I'd guess the answer (through the "smoke and mirrors" reply that you'd get) would be quite revealing. I may be wrong but I suspect that it is neither "locked out" nor "detented" when airborne. I'd guess that neither the PFCS or AFCS software has any inhibitors programmed in either. Whether or not they'd tell you that is debatable. It may all of a sudden be not FOI'able and even a matter of National Security. But it's worth asking these questions.
What I'm saying here is that it could simply be yet another case of "unintended consequences". Life and aviation is choc-a-bloc with those hind-sightable instances of human fallibility.
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UNCTUOUS
Please don’t misinterpret my comments as an attack on you personally. The best way to carry on a discussion in a forum is to concentrate on the issues at hand (as Mr. Farley has done quite effectively in his posting). My intent is not to embarrass you, but only bring to your attention the obvious flaws in your analysis that come from a lack of understanding of tiltrotor technology. I was in your position a number of years back, and could very well have come to the same conclusions that you have. However, my approach to reaching a final opinion differs from yours in that rather than theorize based on my limited knowledge, I prefer to go to the experts who work with the technology on a daily basis. It is incredible how much research on tiltrotor technology has been done by NASA and Bell over the years (courtesy of hundreds of millions of taxpayer dollars), and no, you will not find more than a fraction of the reports on the AHS or NASA web sites. The work is ongoing, a few months back I stood in one of the remarkable wind tunnels at NASA Ames where a fully functioning scaled replica of the V-22 was being assembled. This is only the latest in a number of long-term wind tunnel testing programs that included not only scaled models, but actual full-size aircraft with the XV-3 and XV-15 (and for the future there is talk of full size V-22 testing). There was a long list of very complex issues that were being closely examined during this research. It is not simply a matter of ‘running it through the wind tunnel’ as you stated in an earlier post. An incredible amount of data is accumulated by the numerous high tech monitoring systems that measure to a degree of accuracy most of us would not have thought possible. The dedication of the many people working on tiltrotor research at NASA is truly admirable, and their goal is no less than to contribute to the development of revolutionary a/c that combines dramatic technological advances that have been achieved on a number of fronts in aviation.
In my limited experience I have had the opportunity to fly the XV-15, the V-22 simulator at Pax River, and the incredible VMS simulator at NASA Ames Research Center (capable of pulling positive and negative Gs). This is of course nothing compared to the NASA, Bell and military test pilots that have spent years flying the XV-15 and V-22. I keep in regular contact with some of these individuals, and have great respect for the level of knowledge and expertise they have accumulated. I have included below some responses to my queries from a senior engineer/test pilot at NASA who has almost twenty years experience in tiltrotors. He knows far better than you and I what is known or not known on the subject of tiltrotor flight characteristics.
Some good news for you is that the V-22 crash is not being investigated only by Bell/Boeing and the Marines. The NASA rep that I have been in communication with just returned from the Naval Safety Center where he was leading a team which is “doing a NASA independent review of data from the V-22 accident.” NASA does not have to answer to, or coordinate with, the military investigators other than to present their final analysis. During his investigation, his people reviewed the available recorded data from the Crash Survivable Memory Unit (CSMU) of the a/c that went down in Arizona. He is not at liberty to release the details to the public at this point, but on initial review it was clearly evident to him that the pilots were “way outside of normal or reasonable boundaries or limits.” From numerous meetings and discussions with this individual, I can tell you that although he is an ex-military pilot himself, he does NOT fall in line with the opinions expressed by the military. During the past couple of decades that he has been working for NASA flying almost everything imaginable, he spent five years (1990 – 1995) as the NASA representative to the V-22 Integrated Test Team at Pax River. From that experience, he does not hesitate to point out where he disagrees with how the military have conducted their research and development program.
In the opinion of the NASA investigator, initial indications are in fact that the aircraft was in a situation that should have never have been allowed to develop. As a highly experienced tiltrotor pilots, he and his colleagues all agree they would never have allowed themselves to go so far outside normal operating parameters, or to use the control inputs in the way they were used in any circumstance. The outcome of having done so was inevitable. When these details are released (the sooner the better) it will be evident to all that asymm VR state is not a condition that is by any means entered ‘at the flick of a wrist,’ and it is not a condition caused by external environmental factors.
Asymmetric settling with power in tiltrotors has been known and understood by those at NASA and in the military for many years. The reason there was no in depth test and evaluation program by the Marines with the V-22 was because it was felt that the phenomenon was so far outside of the normal flight envelope that it would not be encountered. This was wrong – dead wrong. Combat conditions (or simulated combat conditions) all too often create situations that cause the pilots to enter regimes that the a/c was not designed for. In hind sight I would imagine it is painfully obvious to them that more wind tunnel and simulator testing was warranted, as well as actual flight testing when deemed safe based on the wind tunnel and simulator results. The lessons learned from this data need to be thoroughly understood by all pilots transitioning into tiltrotors so that it is completely clear what conditions/actions will produce fatal consequences.
The NASA pilot mentioned above has done extensive flight testing to explore the outer limits of the flight envelope and beyond in both fixed-wing and rotorcraft. Based on his experience he believes that at the very least the impending conditions of the phenomenon will be able to be safely tested in actual flight in a controlled manner that will provide answers without loss of life. Obviously with any flight testing there is an inherent element of risk, but the trials will be conducted at altitude where recovery can be accomplished safely. Regardless of the results of this testing program, the RECOVERY techniques practiced will have no direct application to the low altitude scenario that took place at Marana. The purpose is to more clearly define where and how the state develops, and how it can be RECOGNIZED before it progresses to the point of no return. This information can then be used to determine the solution to preventing a reoccurrence of this type accident in the future, whether that solution is to modify the aircraft, add warning or control devices, restructure pilot training with much greater detail and emphasis on understanding, avoidance, recognition and recovery, or restrict certain operations (or a combination thereof).
As to your questions/comments:
1. Nobody will be issued a private pilot license in the US without being able to recite verbatim the three basic requirements for getting into settling with power. From the FAA publication AC 61-13B (as well as other education and training publications that concur): “the following combination of conditions are likely to cause settling with power: 1) A vertical or nearly vertical descent of at least 300 fpm. Actual critical rate depends on gross weight, RPM, density altitude, and other pertinent factors……” I can’t speak to what the CAA/JAA etc. like to use as guidelines, but we all have to start somewhere to keep pilots safe. In demonstrating settling with power to students I have never been able to induce the condition with less than 500 fpm, however this does not mean it is not possible. Ray Prouty gives an excellent description of settling with power if you need further clarification.
2. Just as your initial assertion that tandem overlapping rotor systems (CH-46, CH-47) do not experience settling with power was shown to be false by those who fly the a/c, your claim that getting into asymm VR is a ‘momentary entry’ has been disproved by those who actually fly tiltrotors. According to the experience obtained by the NASA test pilot commenting below, your statement is in complete contradiction with the facts. In response to my question, he described his experience with the onset of the condition, as well as the basic recovery technique, “In the XV-15, on at least one occasion, I have come to a hover or near hover at altitude, 4 or 5 thousand feet, and picked up a pretty high sink rate with lots of power applied. Now, as a tiltrotor pilot, it was second nature to move the nacelles forward 10 degrees or more and apply appropriate power to fly right out of the condition. I have never encountered any asymmetrical conditions and you would have to work REAL hard to create them – way outside of normal or reasonable boundaries or limits.” Again the NASA pilot has seen the CSMU data, and as a former combat pilot himself, has made the assessment based on his experience that the Marana accident did not take place while performing a maneuver anything near ‘normal.’ No one would deny that the Marana V-22 crew had no recovery options available to them when they entered the asymm VR state at 285 ft above the surface. At altitude, in other than extreme conditions, forward movement of the nacelles has an immediate effect on changing relative wind/AOA conditions that cause settling with power, just as we in the helicopter world can escape the VR state by using forward cyclic and reduced power -- as long as circumstances permit it (not possible at extreme rates of descent and critically low altitude – sound familiar?). And note that so far, we are only discussing recovering at a stage when indications show an ‘impending or incipient’ asymm VR state. The forthcoming wind tunnel, simulator and flight tests will determine accurately what if any techniques can be used to recover from asymm settling. It may be that only avoidance of entering the extreme rate of descent and application of violent control inputs that the NASA investigator saw evidence of on the CSMU could have saved the V-22 crew. Perhaps Mr. Farley is correct in his suggestion that a warning device or automatic configuration change might be the answer.
3. Your comment here does not make sense. Nobody is saying that asymmetrical VR is anything less than deadly. Further, to deny that dangerous flight regimes exist in airplanes or helicopters is foolish, and I’m sure you do not subscribe to that belief. We cannot look at the tiltrotor with tunnel vision. Comparative relationships with other categories of aircraft should be drawn in order to correctly assess the capabilities and vulnerabilities as they relate to defining whether or not an aircraft is within our definition of ‘safe.’ For instance, when you say the design of a tiltrotor is deficient in that transmission failure or pitch lock have not been considered. The first thing I think of is what will happen to me if one these catastrophic events happens tomorrow when I’m flying along in a Bell 212 (or any other helicopter in existence) – it certainly has been considered by the design engineers, and there is no ‘back up.’ The answer is to minimize risk to the greatest degree possible by using the highest possible standards in the construction of the rotor and transmission components. And in the case of the transmission, add warning devices such as temperature gauges, pressure gauges, warning lights (temp & press), and chip detectors so that an impending failure will be recognized in order to provide the pilot with enough time to get the a/c on the ground before complete failure occurs. We can’t wear blinders when it comes to admitting that the only way to guarantee 100% safety in aviation is not to fly. That said, every effort must be made to ensure that we come as close to absolute safety as we possibly can. Regarding warning instrumentation, perhaps more can be done. But don’t be so hard on A/S and VSI indicators – sure, they’ve got limitations – but they’ve kept me and a lot of other helicopter pilots from getting into unanticipated settling with power for a lot of decades. Give us something better, and we’ll use it. But if you use the instruments we have knowing their limitations, they can provide you with good information.
4. As already shown above, those who have a great deal of experience in tiltrotors (which both you and I lack) attest to the fact that the asymm VR condition is far from insidious to say the least. Why do you think in all the thousands of hours of XV-3, XV-15, and V-22 flight testing, including pushing the envelope boundaries to what was believed to be their safest limits, the phenomenon had never been encountered in flight (an awful lot of ‘wrist flicking’ going on there)?
On the other hand, the all too frequent occurrence of the fixed-wing stall/spin scenario that I described in my previous post continues to be repeated again and again. For those of us with experience and a thorough understanding of the conditions that lead to a fixed-wing aerodynamic stall, we would not consider it an insidious event. However, for those with insufficient experience and inadequate training in airplane category aircraft (ex. 80 or 90 hrs) it can be very much more insidious than what it takes to get into assym VR in a tiltrotor, but just as fatal.
5. Again your statements are in complete contradiction with the opinions of those who do posses the facts. Those who possess actual experience say you are most definitely wrong in your assessment that experience would not aid pilots in strengthening their ability to better recognize and stay out of a position that would allow asymm VR to develop. A thorough knowledge of asymm VR should be possessed by all tiltrotor pilots (no doubt from April on that will be the case in the Marine Corp). It certainly appears something was lacking in the education and training process. Again, according to those with experience with tiltrotors, the vital element that was missing in this case it was the ability to recognize the extreme rates of descent combined with low airspeed that created the condition. Although the CVR did not record anything during the event itself, shortly before the accident the wing pilot transmitted. “Lead you’re too hot, lead you’re too hot!” As the lead a/c continued on at a higher airspeed, the wing a/c apparently did a dramatic full aft stick rapid deceleration that put the a/c into the deadly low speed/low altitude/ extremely high rate of descent combination that will kill you whether it is caused by settling with power or asymmetrical settling with power. Add to that a 28 degrees Celsius temperature, a 2100 ft msl altitude, quartering tailwind, massive right pedal and heavy left lateral stick inputs and things begin to pile up.
6. I don’t have enough knowledge of the facts to pass judgment on what took place in Kosovo.
7. Regarding the infrared video taken of the accident by an F/A-18 from above – I’m not saying this is the case, but when the military has a picture or video of one of their a/c crashing, and the press is clamoring to get at it, these things have had a habit of disappearing. (Mention of the existence of the tape came from a non-DOD source investigating the accident.) How many photos of the early F-117 crashes have you seen? Do you think none were taken? Think about it.
8. Again, your basic assertion that ‘the SUSCEPTIBILITY is built into the design concept’ has already been shown to be a false premise as attested to by those who have actual experience with the aircraft (have you even seen a tiltrotor?). Rather than being susceptible to the condition, it actually takes extreme rates of descent with radical control inputs to enter it. Mr. Farley seems to disagree with your theory that a warning device is not possible. Personally I don’t have the expertise to judge, but if it is deemed feasible and beneficial as a result of the upcoming wind tunnel testing at NASA, I should hope we will see one fitted as standard equipment.
9. I won’t beat a dead horse to death. By this point you should be aware that although the phenomenon was known of, it was not looked into because it was considered too far out of the normal flight envelope to investigate further. It was believed that the conditions required to encounter it were too extreme to consider. They were wrong. The fact that the accident did occur shows greater understanding is required and it will now be studied further. No matter how extreme the conditions must be to get you into it, the point is it can happen. All the options for making this the last accident of its kind that were discussed earlier must be completely researched and action taken (see above).
‘PR releases’?? ‘Say hello to Tom’?? I think you missed the mark again on this one UNCTUOUS. I am working with an offshore helicopter operator in the Persian Gulf, and will hold the position of managing director of Petroleum Tiltrotors International which currently has five 609s on order. This is why we are more interested than many that the correct lessons are learned from the tragic crash of the V-22 in Arizona, and that there is no ‘hidden fault’ in the technology. We are in a position to cancel our 50 million dollar order at anytime prior to delivery, and I can assure you that if we feel the a/c is not safe, we would do so. We are not going to risk our lives or the lives of our customers if all our questions are not answered fully.
I appreciate your interest in the subject, and especially appreciate your “asking the hard questions.” If tiltrotor technology is to be completely understood, we must all do this. And we need to demand complete answers without any room for doubt. Settling for anything less is unacceptable. If there is a requirement for additional warning devices that need to be added, we must insist on it. I am fortunate to be in the position to serve as Chairman of the 609 Industry Steering Committee (ISC) which is tasked with determining the scheduled maintenance requirements for the 609. The committee is comprised of operators that bring to the table some of the most experienced personnel in the rotorcraft industry (including Bristow, PHI, Canadian Helicopters, Scotia (CHC owned Brintel/Rotortech), and Shell Oil among others). We sit side by side with the FAA and Transport Canada in analyzing every relevant system and component on the aircraft. We are able to use whatever data we need from the V-22 development program to fully evaluate potential failures of systems, or potentially dangerous design characteristics, and we can demand a resolution to the problem. Bell cannot say ‘no’ to the regulatory members of or committee, as to do so would mean denial of certification. Thus far, to say that Bell has been totally cooperative is an understatement. We have complete access to their design engineers, test pilots etc., as well as independent expertise with our NASA contacts. Bell clearly recognizes that producing a safe aircraft is not just to their benefit, it means the survival of their program.
I am expecting additional information from NASA and Bell and will try to keep you updated as more information becomes available. Theories are great, but they work even better when we have the facts to support them. By the way, if you are really interested in some of the history of what has been learned during the development of tiltrotor technology, the NASA test pilot quoted above has co-authored a publication that is for sale by the Government Printing Office. It is part of the NASA Monograph Series (#17) entitled “The History of the XV-15 Tilt Rotor Research Aircraft” (NASA SP-2000-4517).
[This message has been edited by PTI UAE (edited 12 July 2000).]
Please don’t misinterpret my comments as an attack on you personally. The best way to carry on a discussion in a forum is to concentrate on the issues at hand (as Mr. Farley has done quite effectively in his posting). My intent is not to embarrass you, but only bring to your attention the obvious flaws in your analysis that come from a lack of understanding of tiltrotor technology. I was in your position a number of years back, and could very well have come to the same conclusions that you have. However, my approach to reaching a final opinion differs from yours in that rather than theorize based on my limited knowledge, I prefer to go to the experts who work with the technology on a daily basis. It is incredible how much research on tiltrotor technology has been done by NASA and Bell over the years (courtesy of hundreds of millions of taxpayer dollars), and no, you will not find more than a fraction of the reports on the AHS or NASA web sites. The work is ongoing, a few months back I stood in one of the remarkable wind tunnels at NASA Ames where a fully functioning scaled replica of the V-22 was being assembled. This is only the latest in a number of long-term wind tunnel testing programs that included not only scaled models, but actual full-size aircraft with the XV-3 and XV-15 (and for the future there is talk of full size V-22 testing). There was a long list of very complex issues that were being closely examined during this research. It is not simply a matter of ‘running it through the wind tunnel’ as you stated in an earlier post. An incredible amount of data is accumulated by the numerous high tech monitoring systems that measure to a degree of accuracy most of us would not have thought possible. The dedication of the many people working on tiltrotor research at NASA is truly admirable, and their goal is no less than to contribute to the development of revolutionary a/c that combines dramatic technological advances that have been achieved on a number of fronts in aviation.
In my limited experience I have had the opportunity to fly the XV-15, the V-22 simulator at Pax River, and the incredible VMS simulator at NASA Ames Research Center (capable of pulling positive and negative Gs). This is of course nothing compared to the NASA, Bell and military test pilots that have spent years flying the XV-15 and V-22. I keep in regular contact with some of these individuals, and have great respect for the level of knowledge and expertise they have accumulated. I have included below some responses to my queries from a senior engineer/test pilot at NASA who has almost twenty years experience in tiltrotors. He knows far better than you and I what is known or not known on the subject of tiltrotor flight characteristics.
Some good news for you is that the V-22 crash is not being investigated only by Bell/Boeing and the Marines. The NASA rep that I have been in communication with just returned from the Naval Safety Center where he was leading a team which is “doing a NASA independent review of data from the V-22 accident.” NASA does not have to answer to, or coordinate with, the military investigators other than to present their final analysis. During his investigation, his people reviewed the available recorded data from the Crash Survivable Memory Unit (CSMU) of the a/c that went down in Arizona. He is not at liberty to release the details to the public at this point, but on initial review it was clearly evident to him that the pilots were “way outside of normal or reasonable boundaries or limits.” From numerous meetings and discussions with this individual, I can tell you that although he is an ex-military pilot himself, he does NOT fall in line with the opinions expressed by the military. During the past couple of decades that he has been working for NASA flying almost everything imaginable, he spent five years (1990 – 1995) as the NASA representative to the V-22 Integrated Test Team at Pax River. From that experience, he does not hesitate to point out where he disagrees with how the military have conducted their research and development program.
In the opinion of the NASA investigator, initial indications are in fact that the aircraft was in a situation that should have never have been allowed to develop. As a highly experienced tiltrotor pilots, he and his colleagues all agree they would never have allowed themselves to go so far outside normal operating parameters, or to use the control inputs in the way they were used in any circumstance. The outcome of having done so was inevitable. When these details are released (the sooner the better) it will be evident to all that asymm VR state is not a condition that is by any means entered ‘at the flick of a wrist,’ and it is not a condition caused by external environmental factors.
Asymmetric settling with power in tiltrotors has been known and understood by those at NASA and in the military for many years. The reason there was no in depth test and evaluation program by the Marines with the V-22 was because it was felt that the phenomenon was so far outside of the normal flight envelope that it would not be encountered. This was wrong – dead wrong. Combat conditions (or simulated combat conditions) all too often create situations that cause the pilots to enter regimes that the a/c was not designed for. In hind sight I would imagine it is painfully obvious to them that more wind tunnel and simulator testing was warranted, as well as actual flight testing when deemed safe based on the wind tunnel and simulator results. The lessons learned from this data need to be thoroughly understood by all pilots transitioning into tiltrotors so that it is completely clear what conditions/actions will produce fatal consequences.
The NASA pilot mentioned above has done extensive flight testing to explore the outer limits of the flight envelope and beyond in both fixed-wing and rotorcraft. Based on his experience he believes that at the very least the impending conditions of the phenomenon will be able to be safely tested in actual flight in a controlled manner that will provide answers without loss of life. Obviously with any flight testing there is an inherent element of risk, but the trials will be conducted at altitude where recovery can be accomplished safely. Regardless of the results of this testing program, the RECOVERY techniques practiced will have no direct application to the low altitude scenario that took place at Marana. The purpose is to more clearly define where and how the state develops, and how it can be RECOGNIZED before it progresses to the point of no return. This information can then be used to determine the solution to preventing a reoccurrence of this type accident in the future, whether that solution is to modify the aircraft, add warning or control devices, restructure pilot training with much greater detail and emphasis on understanding, avoidance, recognition and recovery, or restrict certain operations (or a combination thereof).
As to your questions/comments:
1. Nobody will be issued a private pilot license in the US without being able to recite verbatim the three basic requirements for getting into settling with power. From the FAA publication AC 61-13B (as well as other education and training publications that concur): “the following combination of conditions are likely to cause settling with power: 1) A vertical or nearly vertical descent of at least 300 fpm. Actual critical rate depends on gross weight, RPM, density altitude, and other pertinent factors……” I can’t speak to what the CAA/JAA etc. like to use as guidelines, but we all have to start somewhere to keep pilots safe. In demonstrating settling with power to students I have never been able to induce the condition with less than 500 fpm, however this does not mean it is not possible. Ray Prouty gives an excellent description of settling with power if you need further clarification.
2. Just as your initial assertion that tandem overlapping rotor systems (CH-46, CH-47) do not experience settling with power was shown to be false by those who fly the a/c, your claim that getting into asymm VR is a ‘momentary entry’ has been disproved by those who actually fly tiltrotors. According to the experience obtained by the NASA test pilot commenting below, your statement is in complete contradiction with the facts. In response to my question, he described his experience with the onset of the condition, as well as the basic recovery technique, “In the XV-15, on at least one occasion, I have come to a hover or near hover at altitude, 4 or 5 thousand feet, and picked up a pretty high sink rate with lots of power applied. Now, as a tiltrotor pilot, it was second nature to move the nacelles forward 10 degrees or more and apply appropriate power to fly right out of the condition. I have never encountered any asymmetrical conditions and you would have to work REAL hard to create them – way outside of normal or reasonable boundaries or limits.” Again the NASA pilot has seen the CSMU data, and as a former combat pilot himself, has made the assessment based on his experience that the Marana accident did not take place while performing a maneuver anything near ‘normal.’ No one would deny that the Marana V-22 crew had no recovery options available to them when they entered the asymm VR state at 285 ft above the surface. At altitude, in other than extreme conditions, forward movement of the nacelles has an immediate effect on changing relative wind/AOA conditions that cause settling with power, just as we in the helicopter world can escape the VR state by using forward cyclic and reduced power -- as long as circumstances permit it (not possible at extreme rates of descent and critically low altitude – sound familiar?). And note that so far, we are only discussing recovering at a stage when indications show an ‘impending or incipient’ asymm VR state. The forthcoming wind tunnel, simulator and flight tests will determine accurately what if any techniques can be used to recover from asymm settling. It may be that only avoidance of entering the extreme rate of descent and application of violent control inputs that the NASA investigator saw evidence of on the CSMU could have saved the V-22 crew. Perhaps Mr. Farley is correct in his suggestion that a warning device or automatic configuration change might be the answer.
3. Your comment here does not make sense. Nobody is saying that asymmetrical VR is anything less than deadly. Further, to deny that dangerous flight regimes exist in airplanes or helicopters is foolish, and I’m sure you do not subscribe to that belief. We cannot look at the tiltrotor with tunnel vision. Comparative relationships with other categories of aircraft should be drawn in order to correctly assess the capabilities and vulnerabilities as they relate to defining whether or not an aircraft is within our definition of ‘safe.’ For instance, when you say the design of a tiltrotor is deficient in that transmission failure or pitch lock have not been considered. The first thing I think of is what will happen to me if one these catastrophic events happens tomorrow when I’m flying along in a Bell 212 (or any other helicopter in existence) – it certainly has been considered by the design engineers, and there is no ‘back up.’ The answer is to minimize risk to the greatest degree possible by using the highest possible standards in the construction of the rotor and transmission components. And in the case of the transmission, add warning devices such as temperature gauges, pressure gauges, warning lights (temp & press), and chip detectors so that an impending failure will be recognized in order to provide the pilot with enough time to get the a/c on the ground before complete failure occurs. We can’t wear blinders when it comes to admitting that the only way to guarantee 100% safety in aviation is not to fly. That said, every effort must be made to ensure that we come as close to absolute safety as we possibly can. Regarding warning instrumentation, perhaps more can be done. But don’t be so hard on A/S and VSI indicators – sure, they’ve got limitations – but they’ve kept me and a lot of other helicopter pilots from getting into unanticipated settling with power for a lot of decades. Give us something better, and we’ll use it. But if you use the instruments we have knowing their limitations, they can provide you with good information.
4. As already shown above, those who have a great deal of experience in tiltrotors (which both you and I lack) attest to the fact that the asymm VR condition is far from insidious to say the least. Why do you think in all the thousands of hours of XV-3, XV-15, and V-22 flight testing, including pushing the envelope boundaries to what was believed to be their safest limits, the phenomenon had never been encountered in flight (an awful lot of ‘wrist flicking’ going on there)?
On the other hand, the all too frequent occurrence of the fixed-wing stall/spin scenario that I described in my previous post continues to be repeated again and again. For those of us with experience and a thorough understanding of the conditions that lead to a fixed-wing aerodynamic stall, we would not consider it an insidious event. However, for those with insufficient experience and inadequate training in airplane category aircraft (ex. 80 or 90 hrs) it can be very much more insidious than what it takes to get into assym VR in a tiltrotor, but just as fatal.
5. Again your statements are in complete contradiction with the opinions of those who do posses the facts. Those who possess actual experience say you are most definitely wrong in your assessment that experience would not aid pilots in strengthening their ability to better recognize and stay out of a position that would allow asymm VR to develop. A thorough knowledge of asymm VR should be possessed by all tiltrotor pilots (no doubt from April on that will be the case in the Marine Corp). It certainly appears something was lacking in the education and training process. Again, according to those with experience with tiltrotors, the vital element that was missing in this case it was the ability to recognize the extreme rates of descent combined with low airspeed that created the condition. Although the CVR did not record anything during the event itself, shortly before the accident the wing pilot transmitted. “Lead you’re too hot, lead you’re too hot!” As the lead a/c continued on at a higher airspeed, the wing a/c apparently did a dramatic full aft stick rapid deceleration that put the a/c into the deadly low speed/low altitude/ extremely high rate of descent combination that will kill you whether it is caused by settling with power or asymmetrical settling with power. Add to that a 28 degrees Celsius temperature, a 2100 ft msl altitude, quartering tailwind, massive right pedal and heavy left lateral stick inputs and things begin to pile up.
6. I don’t have enough knowledge of the facts to pass judgment on what took place in Kosovo.
7. Regarding the infrared video taken of the accident by an F/A-18 from above – I’m not saying this is the case, but when the military has a picture or video of one of their a/c crashing, and the press is clamoring to get at it, these things have had a habit of disappearing. (Mention of the existence of the tape came from a non-DOD source investigating the accident.) How many photos of the early F-117 crashes have you seen? Do you think none were taken? Think about it.
8. Again, your basic assertion that ‘the SUSCEPTIBILITY is built into the design concept’ has already been shown to be a false premise as attested to by those who have actual experience with the aircraft (have you even seen a tiltrotor?). Rather than being susceptible to the condition, it actually takes extreme rates of descent with radical control inputs to enter it. Mr. Farley seems to disagree with your theory that a warning device is not possible. Personally I don’t have the expertise to judge, but if it is deemed feasible and beneficial as a result of the upcoming wind tunnel testing at NASA, I should hope we will see one fitted as standard equipment.
9. I won’t beat a dead horse to death. By this point you should be aware that although the phenomenon was known of, it was not looked into because it was considered too far out of the normal flight envelope to investigate further. It was believed that the conditions required to encounter it were too extreme to consider. They were wrong. The fact that the accident did occur shows greater understanding is required and it will now be studied further. No matter how extreme the conditions must be to get you into it, the point is it can happen. All the options for making this the last accident of its kind that were discussed earlier must be completely researched and action taken (see above).
‘PR releases’?? ‘Say hello to Tom’?? I think you missed the mark again on this one UNCTUOUS. I am working with an offshore helicopter operator in the Persian Gulf, and will hold the position of managing director of Petroleum Tiltrotors International which currently has five 609s on order. This is why we are more interested than many that the correct lessons are learned from the tragic crash of the V-22 in Arizona, and that there is no ‘hidden fault’ in the technology. We are in a position to cancel our 50 million dollar order at anytime prior to delivery, and I can assure you that if we feel the a/c is not safe, we would do so. We are not going to risk our lives or the lives of our customers if all our questions are not answered fully.
I appreciate your interest in the subject, and especially appreciate your “asking the hard questions.” If tiltrotor technology is to be completely understood, we must all do this. And we need to demand complete answers without any room for doubt. Settling for anything less is unacceptable. If there is a requirement for additional warning devices that need to be added, we must insist on it. I am fortunate to be in the position to serve as Chairman of the 609 Industry Steering Committee (ISC) which is tasked with determining the scheduled maintenance requirements for the 609. The committee is comprised of operators that bring to the table some of the most experienced personnel in the rotorcraft industry (including Bristow, PHI, Canadian Helicopters, Scotia (CHC owned Brintel/Rotortech), and Shell Oil among others). We sit side by side with the FAA and Transport Canada in analyzing every relevant system and component on the aircraft. We are able to use whatever data we need from the V-22 development program to fully evaluate potential failures of systems, or potentially dangerous design characteristics, and we can demand a resolution to the problem. Bell cannot say ‘no’ to the regulatory members of or committee, as to do so would mean denial of certification. Thus far, to say that Bell has been totally cooperative is an understatement. We have complete access to their design engineers, test pilots etc., as well as independent expertise with our NASA contacts. Bell clearly recognizes that producing a safe aircraft is not just to their benefit, it means the survival of their program.
I am expecting additional information from NASA and Bell and will try to keep you updated as more information becomes available. Theories are great, but they work even better when we have the facts to support them. By the way, if you are really interested in some of the history of what has been learned during the development of tiltrotor technology, the NASA test pilot quoted above has co-authored a publication that is for sale by the Government Printing Office. It is part of the NASA Monograph Series (#17) entitled “The History of the XV-15 Tilt Rotor Research Aircraft” (NASA SP-2000-4517).
[This message has been edited by PTI UAE (edited 12 July 2000).]
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UNCTUOUS
PS: Your most recent posting was incorrect with reference to the XV-15 nacelle tilt angle range. The XV-15 does extend back to 95 degrees tilt. Both in the simulator and the XV-15 we used this 5 degree aft tilt to act as a giant 'air brake' for rapid deceleration. In addition, it's used as a brake while ground taxiing (you don't need to touch the wheel brakes), and it's also kind of fun ground taxiing backwards (make sure you have lots of open ramp space!!)
PS: Your most recent posting was incorrect with reference to the XV-15 nacelle tilt angle range. The XV-15 does extend back to 95 degrees tilt. Both in the simulator and the XV-15 we used this 5 degree aft tilt to act as a giant 'air brake' for rapid deceleration. In addition, it's used as a brake while ground taxiing (you don't need to touch the wheel brakes), and it's also kind of fun ground taxiing backwards (make sure you have lots of open ramp space!!)
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PTI, just out of interest, is there any difference between tilting the nacelles back to achieve rapid deceleration and hauling back on the stick to achieve the same ?
By the way, I've got both a fixed-wing licence and a rotary CPL. Very low hours, but hey, I'm cheap and I don't mind supplying my own sun cream !
By the way, I've got both a fixed-wing licence and a rotary CPL. Very low hours, but hey, I'm cheap and I don't mind supplying my own sun cream !
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Robbo Jock
Its not really my business to reply to this -but pulling the stick back will change the wing angle of attack and also your view, as well as tilting the rotor thrust line.
Tilting the rotors back will not change the view and the wing aerodynamics will be less affected (some change inevitable due to them being in the downwash)
Being able to violently control forward speed without changing view can be a real godsend at times. Some times ones view is only just including the nearby osstacles and yanking the nose up then (in a chopper, tiltrotor or Harrier) can really add to the problem...
I hope you get the job
Its not really my business to reply to this -but pulling the stick back will change the wing angle of attack and also your view, as well as tilting the rotor thrust line.
Tilting the rotors back will not change the view and the wing aerodynamics will be less affected (some change inevitable due to them being in the downwash)
Being able to violently control forward speed without changing view can be a real godsend at times. Some times ones view is only just including the nearby osstacles and yanking the nose up then (in a chopper, tiltrotor or Harrier) can really add to the problem...
I hope you get the job
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Thanks for that, I hadn't considered the forward view. I was just thinking in terms of the rotor aerodynamics wrt vortex ring entry conditions. Tilting the rotors and tilting the whole plane would appear to achieve the same object - changing what could be considered a nice, flat, forward moving disc into one that is 'sinking' into its own downwash.
Obviously, you can haul the nose up a lot further than 5 degrees, but if you're on the edge of VR anyway (asymmetric or otherwise) tilting the nacelles or the nose is going to drop you right in it (literally and figuratively) isn't it ?
By the way, thanks for the wishes, but I think I'll be at the back of a very long queue for that one.
[This message has been edited by Robbo Jock (edited 06 June 2000).]
Obviously, you can haul the nose up a lot further than 5 degrees, but if you're on the edge of VR anyway (asymmetric or otherwise) tilting the nacelles or the nose is going to drop you right in it (literally and figuratively) isn't it ?
By the way, thanks for the wishes, but I think I'll be at the back of a very long queue for that one.
[This message has been edited by Robbo Jock (edited 06 June 2000).]
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Jeep
Those who will adapt most readily to tiltrotors are dual rated pilots, followed very closely by helicopter-only pilots. Airplane-only pilots on the other hand, would be a distant third, as they would have to learn rotorcraft basics (hovering skills etc.) while helicopter-only pilots will have no difficulty performing enroute fixed-wing tasks.
The main advantage of having rotorcraft pilots with at least some f-w experience is stall recognition and recovery ability when nacelles are in the horizontal position. There may be times during slow speed maneuvering in the airplane mode that not being able to recognize an imminent stall could spell disaster. There are a few negative-transfer habits that come from helicopter flying (stall recognition being the only one of a potentially critical nature), but nothing that good training and experience will not overcome.
The FAA in Part 61 (Certification of Pilots and Flt Instructors) has already issued powered-lift requirements, and I believe Part 141 is complete now also. Requirements for Part 142 still need to be determined. The Bell training facility will be operating under Part 142, and for entry into the program they are requiring pilots to be in possession of three ratings: helicopter, airplane, and an instrument rating in either helicopters or airplanes. I don’t know if they have determined whether or not a multi-engine rating will be req’d, and I’m not sure whether the category ratings (airplane & rotorcraft) will both have to be commensurate with the rating sought (i.e., is it OK to have a commercial helicopter license with only a private airplane rating when seeking a commercial tiltrotor rating).
As far as flying the aircraft itself: when you are in the helicopter mode, it flies just like a helicopter; when you’re in the airplane mode, it feels just like a twin-engine airplane. And although I can’t claim to be an expert, the transition phase feels suprisingly natural, and something that can be adapted to without much difficulty. I must say that in a hover the XV-15 felt much more stable than any helicopter I’ve ever flown. There is virtually no weather vaning tendency at all, perhaps a characteristic of all tandem rotor systems in general. You can hardly tell which way the wind is coming from – you set the cyclic and the a/c just sits there like a rock. As far as the airplane characteristics, the stall is very benign with no radical tendencies. Standard recovery procedures of lowering the nose and adding power apply, although if you are in an intermediate mode (i.e. 60 degrees as we practiced it) the more efficient recovery technique is to simply push the nacelle switch forward and fly out of it.
Those who will adapt most readily to tiltrotors are dual rated pilots, followed very closely by helicopter-only pilots. Airplane-only pilots on the other hand, would be a distant third, as they would have to learn rotorcraft basics (hovering skills etc.) while helicopter-only pilots will have no difficulty performing enroute fixed-wing tasks.
The main advantage of having rotorcraft pilots with at least some f-w experience is stall recognition and recovery ability when nacelles are in the horizontal position. There may be times during slow speed maneuvering in the airplane mode that not being able to recognize an imminent stall could spell disaster. There are a few negative-transfer habits that come from helicopter flying (stall recognition being the only one of a potentially critical nature), but nothing that good training and experience will not overcome.
The FAA in Part 61 (Certification of Pilots and Flt Instructors) has already issued powered-lift requirements, and I believe Part 141 is complete now also. Requirements for Part 142 still need to be determined. The Bell training facility will be operating under Part 142, and for entry into the program they are requiring pilots to be in possession of three ratings: helicopter, airplane, and an instrument rating in either helicopters or airplanes. I don’t know if they have determined whether or not a multi-engine rating will be req’d, and I’m not sure whether the category ratings (airplane & rotorcraft) will both have to be commensurate with the rating sought (i.e., is it OK to have a commercial helicopter license with only a private airplane rating when seeking a commercial tiltrotor rating).
As far as flying the aircraft itself: when you are in the helicopter mode, it flies just like a helicopter; when you’re in the airplane mode, it feels just like a twin-engine airplane. And although I can’t claim to be an expert, the transition phase feels suprisingly natural, and something that can be adapted to without much difficulty. I must say that in a hover the XV-15 felt much more stable than any helicopter I’ve ever flown. There is virtually no weather vaning tendency at all, perhaps a characteristic of all tandem rotor systems in general. You can hardly tell which way the wind is coming from – you set the cyclic and the a/c just sits there like a rock. As far as the airplane characteristics, the stall is very benign with no radical tendencies. Standard recovery procedures of lowering the nose and adding power apply, although if you are in an intermediate mode (i.e. 60 degrees as we practiced it) the more efficient recovery technique is to simply push the nacelle switch forward and fly out of it.
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PTI UAE, John Farley and any other thoughtful, informed observer:
I am a reporter with Helicopter News and Rotor & Wing. We cover the helicopter industry and have been tracking the MV-22 incident closely. These exchanges are highly illuminating. If it is OK with you, I would like to followup by phone/e-mail. We are totally cooperative trade press with no desire to play "gotcha." In fact, I am happy to run quotes by you or, if your prefer, not quote you at all. My main goal/motive is understanding and accuracy about the MV-22 and tiltrotor technology. Is there an e-mail address or phone number by which I can reach you? My e-mail is: "[email protected]." Many thanks.
HCN
I am a reporter with Helicopter News and Rotor & Wing. We cover the helicopter industry and have been tracking the MV-22 incident closely. These exchanges are highly illuminating. If it is OK with you, I would like to followup by phone/e-mail. We are totally cooperative trade press with no desire to play "gotcha." In fact, I am happy to run quotes by you or, if your prefer, not quote you at all. My main goal/motive is understanding and accuracy about the MV-22 and tiltrotor technology. Is there an e-mail address or phone number by which I can reach you? My e-mail is: "[email protected]." Many thanks.
HCN
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Robbo Jock
Sorry for the delayed response. I’m on holiday doing some island hopping, and only get into the business center periodically. John Farley gave you a good description of how tilting the nacelles has advantages other than just some of the ‘fun stuff’ you can do with the capability. Being able to control the angle of the fuselage is like having a new added dimension. For instance, standard practice on descent into a confined area is to use a 95 degree nacelle angle setting (5 degrees aft) which provides greatly enhanced visibility at a time when it is most needed. Doing this essentially brings the windshield down lower into your sight picture, and effectively increases the area you can see on approach. Those of us in the offshore industry will be especially appreciative of this ability. Approaching drilling rigs or platforms in a helicopter when the wind is such that the approach path puts the main structures and obstacles out of your sight picture can be very uncomfortable, and leaves little for visually judging your speed and rate of descent (especially at night). Being able to drop the nose 5 degrees while maintaining a normal descent profile makes a tremendous difference when visual references would otherwise be minimal. Another advantage of being able to tilt the nacelles beyond the normal swashplate range is that it allows a much steeper slope landing capability than conventional helicopters can offer. These are just a couple of added-value things helicopter pilots will appreciate when transitioning to powered lift a/c. It takes a little getting used to, but for an experienced tiltrotor pilot, taking advantage of these new capabilities will become second nature.
While sitting in the NASA VMS control room I watched a UH-60 pilot on loan from the Army perform a normal tiltrotor take-off and conversion (the Army still has lots of interest in the V-22, but not enough money for procurement). The room erupted with laughter as we watched the external visual display which shows the aircraft as it would be seen flying in real life (you can see the gear, flaps, nacelles, and flight controls move as well as see the attitude change as it flies over a runway, past the control tower, trees, bridges etc.) During the laughter the comment was made, “there’s another helicopter pilot take-off.” I had no idea what he had done wrong, as it looked perfectly natural to me. It was then explained to the Army Major that he had lowered the nose as he added power for departure. Standard procedure in the tiltrotor is to let the nacelles do the work for you. As the nacelles move forward, the ‘cyclic’ stick is used to simply hold the fuselage level, producing a smoother and more comfortable take-off for passengers than can be accomplished in a helicopter (or by an airliner for that matter!).
As for your concern over the additional 5 degrees contributing to an early entry into settling with power/asymmetrical settling, I would imagine that there would be at least some effect on the earlier development of the vortex ring state. By changing the disk angle by 5 degrees you are changing the disk plane relative-wind by that amount, and the blade resultant relative-wind by a lesser amount. I couldn’t quantify the effect (I’ll leave that to the aerodynamicists), but according to the pilots who have been flying tiltrotors for many years, getting into the phenomenon takes extreme conditions. I was taken through what I considered some pretty ‘wild’ maneuvers that are routinely done by test pilots, and we did not begin to encounter any problems. Those of us in the civilian world are going to be operating in a much more docile environment and a more restrictive envelope than our counterparts in the military. However, we are all very interested and will all benefit from the information that will be forthcoming from the wind tunnel, simulator and flight tests to further explore and define the conditions that allow an a/c to enter the state.
Regarding employment, we are not in the hiring mode yet, but we are collecting applications for pilot and engineer (mechanic) candidates now. If you would like to you can send your resume/CV to the address below, and I would recommend periodic updates if your experience level is low. BAAC has recently announced a program delay of 8 months (first flight is now scheduled for August next year) as the result of changing the manufacturer of the 609’s composite fuselage. Initial deliveries will probably be around the 1st quarter of 2003, so you have time to build your flight time!! Good luck to you, it’s definitely a worthwhile pursuit.
Send to:
Aerogulf Services Co. (LLC)
Attn: R.M. Denehy
Dubai International Airport
PO Box 10566, Dubai
United Arab Emirates
[This message has been edited by PTI UAE (edited 15 June 2000).]
Sorry for the delayed response. I’m on holiday doing some island hopping, and only get into the business center periodically. John Farley gave you a good description of how tilting the nacelles has advantages other than just some of the ‘fun stuff’ you can do with the capability. Being able to control the angle of the fuselage is like having a new added dimension. For instance, standard practice on descent into a confined area is to use a 95 degree nacelle angle setting (5 degrees aft) which provides greatly enhanced visibility at a time when it is most needed. Doing this essentially brings the windshield down lower into your sight picture, and effectively increases the area you can see on approach. Those of us in the offshore industry will be especially appreciative of this ability. Approaching drilling rigs or platforms in a helicopter when the wind is such that the approach path puts the main structures and obstacles out of your sight picture can be very uncomfortable, and leaves little for visually judging your speed and rate of descent (especially at night). Being able to drop the nose 5 degrees while maintaining a normal descent profile makes a tremendous difference when visual references would otherwise be minimal. Another advantage of being able to tilt the nacelles beyond the normal swashplate range is that it allows a much steeper slope landing capability than conventional helicopters can offer. These are just a couple of added-value things helicopter pilots will appreciate when transitioning to powered lift a/c. It takes a little getting used to, but for an experienced tiltrotor pilot, taking advantage of these new capabilities will become second nature.
While sitting in the NASA VMS control room I watched a UH-60 pilot on loan from the Army perform a normal tiltrotor take-off and conversion (the Army still has lots of interest in the V-22, but not enough money for procurement). The room erupted with laughter as we watched the external visual display which shows the aircraft as it would be seen flying in real life (you can see the gear, flaps, nacelles, and flight controls move as well as see the attitude change as it flies over a runway, past the control tower, trees, bridges etc.) During the laughter the comment was made, “there’s another helicopter pilot take-off.” I had no idea what he had done wrong, as it looked perfectly natural to me. It was then explained to the Army Major that he had lowered the nose as he added power for departure. Standard procedure in the tiltrotor is to let the nacelles do the work for you. As the nacelles move forward, the ‘cyclic’ stick is used to simply hold the fuselage level, producing a smoother and more comfortable take-off for passengers than can be accomplished in a helicopter (or by an airliner for that matter!).
As for your concern over the additional 5 degrees contributing to an early entry into settling with power/asymmetrical settling, I would imagine that there would be at least some effect on the earlier development of the vortex ring state. By changing the disk angle by 5 degrees you are changing the disk plane relative-wind by that amount, and the blade resultant relative-wind by a lesser amount. I couldn’t quantify the effect (I’ll leave that to the aerodynamicists), but according to the pilots who have been flying tiltrotors for many years, getting into the phenomenon takes extreme conditions. I was taken through what I considered some pretty ‘wild’ maneuvers that are routinely done by test pilots, and we did not begin to encounter any problems. Those of us in the civilian world are going to be operating in a much more docile environment and a more restrictive envelope than our counterparts in the military. However, we are all very interested and will all benefit from the information that will be forthcoming from the wind tunnel, simulator and flight tests to further explore and define the conditions that allow an a/c to enter the state.
Regarding employment, we are not in the hiring mode yet, but we are collecting applications for pilot and engineer (mechanic) candidates now. If you would like to you can send your resume/CV to the address below, and I would recommend periodic updates if your experience level is low. BAAC has recently announced a program delay of 8 months (first flight is now scheduled for August next year) as the result of changing the manufacturer of the 609’s composite fuselage. Initial deliveries will probably be around the 1st quarter of 2003, so you have time to build your flight time!! Good luck to you, it’s definitely a worthwhile pursuit.
Send to:
Aerogulf Services Co. (LLC)
Attn: R.M. Denehy
Dubai International Airport
PO Box 10566, Dubai
United Arab Emirates
[This message has been edited by PTI UAE (edited 15 June 2000).]
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HCN
The office can be contacted at [email protected], although it may be best to use [email protected] as I check this address periodically while travelling.
The office can be contacted at [email protected], although it may be best to use [email protected] as I check this address periodically while travelling.
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INCREDIBLE! As a first timer at PPRuNe, I must say I have seen a lot of discussion on the accident, but nothing anywhere like this!
Somebody should definitely set up a TILTROTOR category here to exploit the expertise and give those of us with questions the opportunity to ask the experts that are obviously present here!
The beginning postings were a bit sad and uninformed, but the latter told me more about tiltrotors than I have seen anywhere, AND I HAVE BEEN LOOKING.
THANKS
Somebody should definitely set up a TILTROTOR category here to exploit the expertise and give those of us with questions the opportunity to ask the experts that are obviously present here!
The beginning postings were a bit sad and uninformed, but the latter told me more about tiltrotors than I have seen anywhere, AND I HAVE BEEN LOOKING.
THANKS
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OK, well, here are some of my thoughts for people that are interested. It was really quite interesting to read the 2 page article posted recently about settling with power (or the Vortex ring state, as others may call it) that may have contributed to the Crash of the V22 operated by the US MArine Corps earlier this year. Well, to keep a long discussion short, I do not agree that it should be blamed on a design fault or the basic concept. Considering the effort that has been made by both, the U.S. military and Bell/ Boeing I would say that it is an excellent concept. The tiltrotor as in the V22 or the B609 will not replace the helicopter, nor will it replace the airplane. But it will fill a new market which may not be possible to be satisfied by any conventional aircraft. And there are allready many positive aspects before the aircraft is even out with the operators.
To come back to the original article, I believe that there have been some controversial results and maybe there will never be a definite conclusion to the accident. It does look however that there is nothing wrong with the aircraft. That is not up to me do discuss. I would like to mention though that it probably would be much more appropriate to target the training and qualification programs for the aircrew on the V22. Due to it's high cost and tremendous pressure on the operational status of the aircraft, I personally believe that the training requirements are not satisfactory enough for the operations conducted. After all it is a brandnew design and aspect of aviation. Just imagine yourself as a 100 hr. wonder trying to do an operational insertion of troops using night vision googles in an aircraft you may not feel quite comfortable with yet. I would say, well, you are asking for trouble. But what it comes down to is that it really couldn't be blamed on the aircraft or a design fault on it. I do agree that there are some sysytems which I personally think could be implemented to improve the safety of the aircraft. But I guess that the designers would sure have thoguth about it. Anyway, any airplane, if you misshandle it, can be stalled. Any helicopter, if you misshandle it, can enter the Vortex ring state. What it comes down to is pilot tarinig, recognition and avoidance of these flight conditions. I also do not necessarily agree with the fact that flying out of it is the only way to recover from the above condition. Yes, it is so according to the text book, but anybody who has done some slinging or other operations involving a lot of OGE hovering will know that there is other ways around it.
Anyway, I think to put a moral to the story,
the Tiltrotor concept is very new and the media and people have always tried to find fault with new things. Just remember the millennium bug- the world was gonna break down- did it? Well, it wasn't that bad after all.
Modern aircraft design is very, very advanced and especially on the B609 there is tremendous effort being made to counteract and correct problems before the aircraft will come out. The B609 industry steering committee is doing a fantastic job and the input from the members involved does help to make the cost cheaper and the aircraft safer and easier to maintain for the future operators. What will happen, well, just like with the millennium bug we will not know until the aircraft is flying. The test flying so far is really going great from what I understand. The effort made by the manufacturer and industry members certainly helps a lot to predict most of the aspects.
And think back, it took more than 25 years for the Bell 212 to proof it's reliablity. So give the concept some time.
What I would like the concerned people to consider though is to maybe revise the standards of training and the requirements for the aircrew. As for the B609 I do believe this issue may not be of such importance since the operational flying will maybe not be as challenging. However, the military may well be better of to, and I am sure this is done, considering the training syllabus and minimum training before going "hot".
I would appreciate any feedback on my thought and welcome anybody to challenge my view-points.
To come back to the original article, I believe that there have been some controversial results and maybe there will never be a definite conclusion to the accident. It does look however that there is nothing wrong with the aircraft. That is not up to me do discuss. I would like to mention though that it probably would be much more appropriate to target the training and qualification programs for the aircrew on the V22. Due to it's high cost and tremendous pressure on the operational status of the aircraft, I personally believe that the training requirements are not satisfactory enough for the operations conducted. After all it is a brandnew design and aspect of aviation. Just imagine yourself as a 100 hr. wonder trying to do an operational insertion of troops using night vision googles in an aircraft you may not feel quite comfortable with yet. I would say, well, you are asking for trouble. But what it comes down to is that it really couldn't be blamed on the aircraft or a design fault on it. I do agree that there are some sysytems which I personally think could be implemented to improve the safety of the aircraft. But I guess that the designers would sure have thoguth about it. Anyway, any airplane, if you misshandle it, can be stalled. Any helicopter, if you misshandle it, can enter the Vortex ring state. What it comes down to is pilot tarinig, recognition and avoidance of these flight conditions. I also do not necessarily agree with the fact that flying out of it is the only way to recover from the above condition. Yes, it is so according to the text book, but anybody who has done some slinging or other operations involving a lot of OGE hovering will know that there is other ways around it.
Anyway, I think to put a moral to the story,
the Tiltrotor concept is very new and the media and people have always tried to find fault with new things. Just remember the millennium bug- the world was gonna break down- did it? Well, it wasn't that bad after all.
Modern aircraft design is very, very advanced and especially on the B609 there is tremendous effort being made to counteract and correct problems before the aircraft will come out. The B609 industry steering committee is doing a fantastic job and the input from the members involved does help to make the cost cheaper and the aircraft safer and easier to maintain for the future operators. What will happen, well, just like with the millennium bug we will not know until the aircraft is flying. The test flying so far is really going great from what I understand. The effort made by the manufacturer and industry members certainly helps a lot to predict most of the aspects.
And think back, it took more than 25 years for the Bell 212 to proof it's reliablity. So give the concept some time.
What I would like the concerned people to consider though is to maybe revise the standards of training and the requirements for the aircrew. As for the B609 I do believe this issue may not be of such importance since the operational flying will maybe not be as challenging. However, the military may well be better of to, and I am sure this is done, considering the training syllabus and minimum training before going "hot".
I would appreciate any feedback on my thought and welcome anybody to challenge my view-points.
Guest
Posts: n/a
Tiltrotor
Yes, you are right, the tiltrotor is definitely a niche aircraft that will not replace airplanes or helicopters (although there may be some instances where companies currently using a both a turboprop and a helicopter may be able to use the tiltrotor in place of the two a/c). The two basic requirements that exist for the tiltrotor to be effective in a particular civilian operation are:
1) There must be an absolute need for vertical take off and landing capability at one or both ends of the flight. – If not, a turboprop airplane would be able to perform the operation more economically flying airport to airport.
2) The distances to be flown must be greater than a minimum of about 100nm. -- If not, a helicopter will be able to perform the operations more economically due to its lower initial acquisition cost (DOCs for the 609 are expected to be slightly higher than a 412).
The key to the potential success of the first civilian tiltrotor also rests with its ability to operate using the existing helicopter ground infrastructure. When the Civil Tilt Rotor Development Advisory Committee (CTRDAC) prepared their feasibility report for Congress in the mid 90s, they referred mainly to a 40 or 75 passenger a/c. The projected saturation of major metropolitan airports by the year 2010, and the lack of available real estate for new airports meant some alternative method of mass transport must be developed. Although the report came back with a resounding affirmative response for the projected success of the tiltrotor in a future transport role, the CTRDAC pointed to the critical need for publicly funded infrastructure development.
In order to be successful, vertiports that will be needed to support transport tiltrotor operations will have to be built either in, or very close to city centers (preferably with over water approaches that do not overfly congested areas). This can only be accomplished with public support. Public support can only be gained with understanding and confidence in the technology, and so Bell/Boeing (now Bell/Agusta) decided that a small civil tiltrotor should be introduced that can operate using the existing helicopter infrastructure. This way the general public will have time to learn about and become familiar with the capabilities of tiltrotors before the introduction of a large-scale transport version.
The 609 will be 44 feet long and 60 feet across (proprotor tip to tip). These dimensions are not far off from those of a Bell 212 which are 48 feet across (blade diameter) and 58 feet long (main rotor tip to tailrotor tip). I’m sure there will be some offshore platforms that 609s will not be able to land on safely, but by far the majority of platforms, drilling rigs and helipads currently being used by helicopters should present no problems. And it sure is nice being able to visually see the furthest extremity of your aircraft when you’re maneuvering on the ground rather than trying to estimate how much distance exists between the nearest obstacle and your tailrotor!!
Yes, you are right, the tiltrotor is definitely a niche aircraft that will not replace airplanes or helicopters (although there may be some instances where companies currently using a both a turboprop and a helicopter may be able to use the tiltrotor in place of the two a/c). The two basic requirements that exist for the tiltrotor to be effective in a particular civilian operation are:
1) There must be an absolute need for vertical take off and landing capability at one or both ends of the flight. – If not, a turboprop airplane would be able to perform the operation more economically flying airport to airport.
2) The distances to be flown must be greater than a minimum of about 100nm. -- If not, a helicopter will be able to perform the operations more economically due to its lower initial acquisition cost (DOCs for the 609 are expected to be slightly higher than a 412).
The key to the potential success of the first civilian tiltrotor also rests with its ability to operate using the existing helicopter ground infrastructure. When the Civil Tilt Rotor Development Advisory Committee (CTRDAC) prepared their feasibility report for Congress in the mid 90s, they referred mainly to a 40 or 75 passenger a/c. The projected saturation of major metropolitan airports by the year 2010, and the lack of available real estate for new airports meant some alternative method of mass transport must be developed. Although the report came back with a resounding affirmative response for the projected success of the tiltrotor in a future transport role, the CTRDAC pointed to the critical need for publicly funded infrastructure development.
In order to be successful, vertiports that will be needed to support transport tiltrotor operations will have to be built either in, or very close to city centers (preferably with over water approaches that do not overfly congested areas). This can only be accomplished with public support. Public support can only be gained with understanding and confidence in the technology, and so Bell/Boeing (now Bell/Agusta) decided that a small civil tiltrotor should be introduced that can operate using the existing helicopter infrastructure. This way the general public will have time to learn about and become familiar with the capabilities of tiltrotors before the introduction of a large-scale transport version.
The 609 will be 44 feet long and 60 feet across (proprotor tip to tip). These dimensions are not far off from those of a Bell 212 which are 48 feet across (blade diameter) and 58 feet long (main rotor tip to tailrotor tip). I’m sure there will be some offshore platforms that 609s will not be able to land on safely, but by far the majority of platforms, drilling rigs and helipads currently being used by helicopters should present no problems. And it sure is nice being able to visually see the furthest extremity of your aircraft when you’re maneuvering on the ground rather than trying to estimate how much distance exists between the nearest obstacle and your tailrotor!!
Guest
Posts: n/a
Tiltrotor
Has anyone out there got any hard facts on what sort of licence / qualifications will be required for tiltrotors?? I've heard suggested that F/W & Helo' will both be req'd ? I'd be interested in various coutries positions. (I'm in Aussie)
Cheers
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Cheers
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