What's the latest news of the V22 Osprey?
I hate to stray from the "53: is it or isn't it heavy lift?" discussion but I have to digress to something 21st Century said about Majors Brow and Gruber who were involved in the infamous "Marana crash::
I hear this a lot, that the V-22 is way different now...how much "safer" the V-22 is now than it was "back then." And so I have to ask: Just HOW is the aircraft different from the one that Majors Brow and Gruber flew in April of 2000? Does it have a reliable VRS indicator now? You know, like the stall-warning horn in an airplane, that can physically sense when a wing is at a critical angle of attack? Does it even have an A-VRS indicator? Something that would tell the pilots when one proprotor is entering into VRS? Or does it just come with a computer program that tells the pilots when they are entering a critical range of speed and rate of descent, which is not nearly the same thing as an actual stall-warning sensor in an airplane.
I guess what I'm getting at is this: If two more pilots in one of these new, modernized, competely-different V-22s, pilots with perhaps not a lot of helicopter time, get into the very same kind-of-rushed, kind-of-behind-the-power-curve situation as Majors Brow and Gruber, could they still find themselves getting to A-VRS without sufficient warning?
You might counter this with, "Well, the synthetic warnings programmed into the FMS will give them plenty of warning!" And I will say, "Really?" Let me ask you how many times the stall-warning alarm went off in the cockpit of that Air France 447 Airbus that stalled its way down into the Atlantic Ocean? Answer: 75 times. THREE pilots in that cockpit, stall-warning going off and not ONE of those geniuses suggested lowering the nose and, you know, flying out of the stall. Because they were confused. But that will never happen to pilots in combat, will it?
And V-22 pilots will do okay with a warning that tells them only when they're getting into dangerous airspeed/rate of descent combinations.
So again, how is the aircraft different?
I think we can all agree with their advise that, “They introduced this aircraft and because of their life sacrifices, the Osprey of today is safe for the pilot, the crew and their passengers…”
I guess what I'm getting at is this: If two more pilots in one of these new, modernized, competely-different V-22s, pilots with perhaps not a lot of helicopter time, get into the very same kind-of-rushed, kind-of-behind-the-power-curve situation as Majors Brow and Gruber, could they still find themselves getting to A-VRS without sufficient warning?
You might counter this with, "Well, the synthetic warnings programmed into the FMS will give them plenty of warning!" And I will say, "Really?" Let me ask you how many times the stall-warning alarm went off in the cockpit of that Air France 447 Airbus that stalled its way down into the Atlantic Ocean? Answer: 75 times. THREE pilots in that cockpit, stall-warning going off and not ONE of those geniuses suggested lowering the nose and, you know, flying out of the stall. Because they were confused. But that will never happen to pilots in combat, will it?
And V-22 pilots will do okay with a warning that tells them only when they're getting into dangerous airspeed/rate of descent combinations.
So again, how is the aircraft different?
FH1100: should the Army and Navy and Marines have stopped flying Hueys because they can experience mast bumping? (If flown in certain profiles).
Hueys are still flying, today. I learned about mast bumping during flight school in about 1981. It was roughly 20 year old information at that point. (Don't recall just when in the sixties that the issue was documented, but some of my instructors were Viet Nam era Huey drivers who discussed how important knowing that limitation was for tactical flying ... )
Hueys are still flying, today. I learned about mast bumping during flight school in about 1981. It was roughly 20 year old information at that point. (Don't recall just when in the sixties that the issue was documented, but some of my instructors were Viet Nam era Huey drivers who discussed how important knowing that limitation was for tactical flying ... )
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FH since you always seem to be so concerned about VRS and A-VRS why don't you take the time to go AHS and read the following papers:
-V-22 Low-Speed/High Rate of Descent (HROD) Test Results
-V-22 High Rate of Descent (HROD) Test Procedures and Long Record Analysis
-The Nature of Vortex Ring State
As to whether the V-22 has a cockpit warning device I do not know. However the ROD limits imposed on the V-22 are the SAME as for every other helicopter in the USMC fleet. If you review the above papers you will find that with those limits, the V-22 has as much or MORE margin between the limit and VRS onset then do the helicopters. Currently helicopter crews honor those limits through crew coordination and by using established approach profiles, both in peace time operations and combat just the same as a V-22 crew does. Why do you imagine that a V-22 is more susceptible to a VRS incident then is a helicopter given the above information? Given the above should all helicopters have a VRS warning? How is it you have managed all these years to avoid VRS without a cockpit warning device? How many hours have been flown since the Marana incident and how many A-VRS mishaps have there been? The fact that the aircraft is being flown in combat as we speak and they aren't falling out of the sky due to A-VRS might be a clue.
-V-22 Low-Speed/High Rate of Descent (HROD) Test Results
-V-22 High Rate of Descent (HROD) Test Procedures and Long Record Analysis
-The Nature of Vortex Ring State
As to whether the V-22 has a cockpit warning device I do not know. However the ROD limits imposed on the V-22 are the SAME as for every other helicopter in the USMC fleet. If you review the above papers you will find that with those limits, the V-22 has as much or MORE margin between the limit and VRS onset then do the helicopters. Currently helicopter crews honor those limits through crew coordination and by using established approach profiles, both in peace time operations and combat just the same as a V-22 crew does. Why do you imagine that a V-22 is more susceptible to a VRS incident then is a helicopter given the above information? Given the above should all helicopters have a VRS warning? How is it you have managed all these years to avoid VRS without a cockpit warning device? How many hours have been flown since the Marana incident and how many A-VRS mishaps have there been? The fact that the aircraft is being flown in combat as we speak and they aren't falling out of the sky due to A-VRS might be a clue.
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FH1100,
When it is said that "because of their life sacrifices, the Osprey of today is safe for the pilot, the crew and their passengers…" there is much more to it than just the modifications made to the aircraft. As a result of the Marana crash an in depth study of VRS specific to the V-22 was conducted that resulted in greater knowledge, event-specific training, and the a/c mods. It is likely that the training for recognition/avoidance and recovery are more important than the a/c modifications (in the Marana case the aircraft was too low for recovery as would have been the case in an equivalent class helicopter, so recognition/avoidance would have been the key).
It is well known that it takes a higher rate of descent for a tiltrotor to get into VRS than a helicopter due to the higher disc loading and resultant greater downwash. The problem is the asymmetrical aspect unique to the tiltrotor that has been discussed at length on this and other threads.
It is easy to determine whether the training and modifications developed as a result of the Marana accident were effective or not -- almost 11 years after the tragic loss, not a single VRS incident in a V-22 has occurred. Unfortunately it was too late for Lt. Col John A. Brow and Major Brooks S. Gruber, and the 17 others on board that night. At least it is clear that their loss resulted in action that today allows pilots to avoid a repeat of the tragedy, even in combat operations as demonstrated in Iraq and Afghanistan. That unforgettable night in April of 2000 is 'burned' into the minds of all Osprey pilots. And if you don't believe that, ask one of them...
Here is an article that contains some of the information you were asking about:
Dispelling the Myth of the MV-22
When it is said that "because of their life sacrifices, the Osprey of today is safe for the pilot, the crew and their passengers…" there is much more to it than just the modifications made to the aircraft. As a result of the Marana crash an in depth study of VRS specific to the V-22 was conducted that resulted in greater knowledge, event-specific training, and the a/c mods. It is likely that the training for recognition/avoidance and recovery are more important than the a/c modifications (in the Marana case the aircraft was too low for recovery as would have been the case in an equivalent class helicopter, so recognition/avoidance would have been the key).
It is well known that it takes a higher rate of descent for a tiltrotor to get into VRS than a helicopter due to the higher disc loading and resultant greater downwash. The problem is the asymmetrical aspect unique to the tiltrotor that has been discussed at length on this and other threads.
It is easy to determine whether the training and modifications developed as a result of the Marana accident were effective or not -- almost 11 years after the tragic loss, not a single VRS incident in a V-22 has occurred. Unfortunately it was too late for Lt. Col John A. Brow and Major Brooks S. Gruber, and the 17 others on board that night. At least it is clear that their loss resulted in action that today allows pilots to avoid a repeat of the tragedy, even in combat operations as demonstrated in Iraq and Afghanistan. That unforgettable night in April of 2000 is 'burned' into the minds of all Osprey pilots. And if you don't believe that, ask one of them...
Here is an article that contains some of the information you were asking about:
Dispelling the Myth of the MV-22
By Lieutenant Colonel Kevin Gross, U.S. Marine Corpsv
Proceedings, September 2004
In 2000, two tragic accidents grounded the Marine Corps’ newest and most innovative aircraft, miring it in controversy and casting doubt on its future. Rigorous testing since then, however, has resulted in measures that should prevent the unusual aerodynamic condition that caused the first accident from happening again. (Photo by Mike Jones, U.S. Navy)
The MV-22 Osprey is a very capable medium-lift military transport aircraft the Marine Corps has needed for a long time. It is twice as fast, can carry three times as much, and goes six times farther than the CH-46E, the aircraft it is replacing. It is no reach to say that if the MV-22 continues its current run of success in testing and is fielded as planned, it will change everything about how maneuver warfare is conducted.
The Osprey, however, also is an airplane with an image problem, primarily resulting from two highly publicized mishaps that killed 23 Marines four years ago. The investigation into these accidents resulted in the discovery and subsequent resolution of an aerodynamic condition affecting all rotorcraft but unduly linked with the MV-22: vortex ring state (VRS).
On the evening of 8 April 2000, a flight of four MV-22s was conducting a night assault mission to a small airfield in Marana, Arizona, when the second airplane (or “Dash 2”) rolled nearly inverted on short final and crashed, killing all on board. During the subsequent investigation, it was discovered that the lead aircraft was almost 2,000 feet higher than planned at the initial point (the location where the conversion from airplane mode to VTOL [vertical take-off and landing] mode for landing begins). The lead aircraft entered a steep approach profile with a high rate of descent while it rapidly decreased speed for landing. During the rapid deceleration, Dash 2 no longer could remain in trail as briefed but came abeam of the lead’s right side. To return to the trail position, Dash 2 flew slower and with a higher rate of descent than his lead. At approximately 300 feet above ground level, with a more than 2,000-feet-per-minute rate of descent and with less than 30 knots forward airspeed, the mishap aircraft started a right roll that could not be corrected by the pilot.
The mishap investigation, having ruled out all other possibilities, soon focused on the extremely high rate of descent at low altitude as the primary cause of the accident. It was concluded that during the descent, the aircraft entered an aerodynamic condition called vortex ring state.
Vortex Ring State
Our search for the VRS boundary started with a thorough review of analytical and wind tunnel research and slow-speed, high-rate-of-descent flight testing. We soon discovered that the body of known actual flight-test data for VRS in other rotorcraft was very small. There were only two other rotorcraft flight research projects known to us at the time we began our initial flight testing, one by NASA Langley in 1964 and one more recently by the ONERA organization in France with a Dauphin helicopter. There was a larger amount of theoretical data available, however, from the private and academic sectors of flight-test research. The principal work we reviewed was from a paper published in 1965 by Kyuichiro Washizu and Akira Azuma of the University of Tokyo. [1]
VRS is an aerodynamic condition in which the tangential airspeed at the rotor is small (associated with low forward airspeed) and the airspeed perpendicular to the rotor is high (associated with powered rate of descent). VRS typically becomes a concern below 40 knots forward airspeed at high rates of descent. To reach this condition, power must be applied during the steep descent. Some might think that during VRS the rotor stalls, but that is not the case. VRS is a reingestion state, not a stalled state. Rotor lift creates a down flow of air, called induced velocity (Vi), and the up flow created by the nearly vertical rate of descent is called vertical velocity (Vv). When the induced velocity equals the vertical velocity, VRS may occur, causing a reduction in rotor lift or increased sink rate. VRS can occur as a rotorcraft settles down through its own vortex field at slow forward airspeeds.
This condition is not peculiar to the tiltrotor; in fact, every rotary winged aircraft is susceptible to it. A helicopter pilot flying a single rotor system exits VRS by lowering his collective (reducing power with his left hand) and pushing forward the cyclic (tilting his rotor disk forward to accelerate) with his right hand. A tiltrotor pilot has another, more-effective, option: he can move the nacelles into clean air.
Test Objectives
In developing the plan to understand VRS, Naval Air Systems Command directed the MV-22 Integrated Test Team at Patuxent River, Maryland, to conduct flight-test exploration of the Osprey tiltrotor’s high-rate-of-descent/low-airspeed boundary. The initial test plan was developed to conduct partial- and minimum-power descents to investigate the low airspeed descending flight characteristics and determine the effects of the thrust-control lever and cockpit-control inputs on handling qualities in this flight regime.
The objectives of the test effort were to define the boundary of VRS, derive a fleet operational envelope, define the recovery technique from VRS, determine applicability for warning systems, and document the condition in pilot training ground school simulations and the NATOPS (Naval Air Training and Operating Procedures Standardization) flight manual for the tiltrotor. The first two objectives initially were approached as two phases, to validate the current fleet low-airspeed rate-of-descent limit and document the VRS boundary, and to evaluate the capability to expand the current fleet limit. As the testing progressed, however, we soon realized that breaking the test effort into two phases was not necessary, and we added multiaxis control inputs and dynamic maneuvers to our test effort.
For the third objective, we knew that recovery from VRS, like the poststall departure recovery of a fixed-wing aircraft, requires proper and timely procedures. For the Osprey, the most powerful flight control is the pilot’s ability to change nacelle angle (thrust vector) at up to 8° per second through a thumb switch on the thrust-control lever. This ability to change nacelle angle (and hence inflow angle at the rotor disk) would lead to an effective and immediate recovery tool.
Flight Test
Our test-plan strategy was simple: approach the unknown boundary from higher air speed and down from above with increasing sink rate increments. For the purpose of pilot build up and standardization, only one pilot, chief test pilot Tom Macdonald of Boeing, flew each test point with a small group of copilots assisting. The aircraft was configured with nacelles full aft at 95°, flaps auto, and landing gear down. Each descent track was completed at the same target airspeed, with a package of data points at each 500-feet-per-minute descent increment, where we checked stability, handling qualities, ride quality, aural signatures, and descent arrest and recovery effectiveness.
Our testing was conducted at altitude with a target test band of 8,000- to 7,000-feet altitude to allow for recovery well before the hard deck of 3,500 feet above ground level. Each aircraft input at the target airspeed and rate of descent required one dedicated descent. With the addition of the Young Model 81000 low-airspeed system, we gained flight efficiency by omitting the sawtooth climbs to determine true winds in the test band for the next descent profile. By the end of our VRS test effort, we had flown 62 flights for 104 flight hours and exceeded 5,600-feet-per-minute rate of descent and flew as slow as ten knots calibrated forward airspeed.
During our testing, we experienced 12 roll-off events, 8 to the right and 4 to the left. The direction of roll off was not predictable from the cockpit. In fact, the cockpit characteristics approaching VRS were not as well defined as in single-rotor helicopters. We noticed a slight increase in vibration, rotor noise, and flight control loosening that would not in every instance foretell of an impending roll off. Each roll off, however, was characterized by a sudden sharp reduction of lift on one of the two proprotors, resulting in an uncommanded roll in that direction. We also noted that roll offs required nearly steady-state conditions to trigger them. Any dynamic maneuvering tended to delay or prevent a roll off from occurring. On many occasions, we entered the VRS boundary during dynamic maneuvers and then exited the boundary without encountering a roll off.
Improvements to the Osprey’s pilot display include an expanded rate-of-descent scale and a red line added behind the vertical sink scale. Both features should help prevent future encounters with vortex ring state. (Photo couresty of author)
Pilot recovery procedures from a VRS roll off are easy, immediate, and effective. The pilot fixes the thrust-control lever and simultaneously pushes the nacelle-control thumb wheel forward for two seconds. This two-second beep forward moves the nacelles 12° to 15° lower, which immediately takes the rotors out of the VRS condition as the aircraft accelerates rapidly. If required, the pilot then uses lateral stick to level the wings and then adds power to stop the rate of descent.
Avionics Improvements
Now that we knew where the VRS boundary was located, how the aircraft responded during VRS, and the proper recovery procedures and techniques, our focus turned toward avoidance of VRS. Boeing and Naval Air Systems Command avionics and crew systems engineers developed a simple yet eloquent method of keeping pilots away from VRS. We made two changes to our avionics displays that increased the pilot’s situational awareness during low-speed, high-rate-of-descent flight. First, we expanded the rate-of-descent scale from 1,000 feet per minute to 2,000 feet per minute in 200-feet-per-minute increments. Second, we added a red line behind the vertical sink scale at the rate-of-descent limit along with a visual and aural “sink” warning when the airspeed and rate of descent exceed the limits. The flight display used by the pilot as the primary performance instrument in the Osprey is shown above. The scale on the right side is the vertical speed indicator. The indicator’s arrowhead is pointing to an 800-feet-per-minute rate of descent. The airspeed box is on the left of the display and indicates 39 knots. With this combination of airspeed and rate of descent, the pilot has exceeded the existing rate-of-descent limit and now hears “sink rate, sink rate” in his headset and sees the red “sink” warning in the display near the top and to the right of center. It is important to note that this warning system is not a predictor of VRS, but a rate-of-descent limit to keep the pilot away from VRS.
Where We Go from Here
Our ultimate goal for this flight-test effort was to understand fully the aerodynamic effects of vortex ring state on the tiltrotor, to define the recovery procedures should the pilot encounter VRS, and, most important, to develop warning signals to keep pilots away from this condition. Pilot awareness of VRS and avoidance with rate-of-descent limits are the only tools available to prevent a high-rate-of-descent mishap from taking more lives. Our current rate-of-descent limit is 800 feet per minute below 40 knots calibrated airspeed (KCAS), increasing linearly to 1,600 feet per minute at 80 KCAS. Presently, Naval Air Systems Command is evaluating the potential to expand the rate-of-descent envelope in the 30-to-50-knot airspeed range to provide the user communities more capability during flight tests and approaches to landing.
So what have we found in our 14-months of low-airspeed, high-rate-of-descent testing in search of VRS?
By Lieutenant Colonel Kevin Gross, U.S. Marine Corpsv
Proceedings, September 2004
In 2000, two tragic accidents grounded the Marine Corps’ newest and most innovative aircraft, miring it in controversy and casting doubt on its future. Rigorous testing since then, however, has resulted in measures that should prevent the unusual aerodynamic condition that caused the first accident from happening again. (Photo by Mike Jones, U.S. Navy)The MV-22 Osprey is a very capable medium-lift military transport aircraft the Marine Corps has needed for a long time. It is twice as fast, can carry three times as much, and goes six times farther than the CH-46E, the aircraft it is replacing. It is no reach to say that if the MV-22 continues its current run of success in testing and is fielded as planned, it will change everything about how maneuver warfare is conducted.
The Osprey, however, also is an airplane with an image problem, primarily resulting from two highly publicized mishaps that killed 23 Marines four years ago. The investigation into these accidents resulted in the discovery and subsequent resolution of an aerodynamic condition affecting all rotorcraft but unduly linked with the MV-22: vortex ring state (VRS).
On the evening of 8 April 2000, a flight of four MV-22s was conducting a night assault mission to a small airfield in Marana, Arizona, when the second airplane (or “Dash 2”) rolled nearly inverted on short final and crashed, killing all on board. During the subsequent investigation, it was discovered that the lead aircraft was almost 2,000 feet higher than planned at the initial point (the location where the conversion from airplane mode to VTOL [vertical take-off and landing] mode for landing begins). The lead aircraft entered a steep approach profile with a high rate of descent while it rapidly decreased speed for landing. During the rapid deceleration, Dash 2 no longer could remain in trail as briefed but came abeam of the lead’s right side. To return to the trail position, Dash 2 flew slower and with a higher rate of descent than his lead. At approximately 300 feet above ground level, with a more than 2,000-feet-per-minute rate of descent and with less than 30 knots forward airspeed, the mishap aircraft started a right roll that could not be corrected by the pilot.
The mishap investigation, having ruled out all other possibilities, soon focused on the extremely high rate of descent at low altitude as the primary cause of the accident. It was concluded that during the descent, the aircraft entered an aerodynamic condition called vortex ring state.
Vortex Ring State
Our search for the VRS boundary started with a thorough review of analytical and wind tunnel research and slow-speed, high-rate-of-descent flight testing. We soon discovered that the body of known actual flight-test data for VRS in other rotorcraft was very small. There were only two other rotorcraft flight research projects known to us at the time we began our initial flight testing, one by NASA Langley in 1964 and one more recently by the ONERA organization in France with a Dauphin helicopter. There was a larger amount of theoretical data available, however, from the private and academic sectors of flight-test research. The principal work we reviewed was from a paper published in 1965 by Kyuichiro Washizu and Akira Azuma of the University of Tokyo. [1]
VRS is an aerodynamic condition in which the tangential airspeed at the rotor is small (associated with low forward airspeed) and the airspeed perpendicular to the rotor is high (associated with powered rate of descent). VRS typically becomes a concern below 40 knots forward airspeed at high rates of descent. To reach this condition, power must be applied during the steep descent. Some might think that during VRS the rotor stalls, but that is not the case. VRS is a reingestion state, not a stalled state. Rotor lift creates a down flow of air, called induced velocity (Vi), and the up flow created by the nearly vertical rate of descent is called vertical velocity (Vv). When the induced velocity equals the vertical velocity, VRS may occur, causing a reduction in rotor lift or increased sink rate. VRS can occur as a rotorcraft settles down through its own vortex field at slow forward airspeeds.
This condition is not peculiar to the tiltrotor; in fact, every rotary winged aircraft is susceptible to it. A helicopter pilot flying a single rotor system exits VRS by lowering his collective (reducing power with his left hand) and pushing forward the cyclic (tilting his rotor disk forward to accelerate) with his right hand. A tiltrotor pilot has another, more-effective, option: he can move the nacelles into clean air.
Test Objectives
In developing the plan to understand VRS, Naval Air Systems Command directed the MV-22 Integrated Test Team at Patuxent River, Maryland, to conduct flight-test exploration of the Osprey tiltrotor’s high-rate-of-descent/low-airspeed boundary. The initial test plan was developed to conduct partial- and minimum-power descents to investigate the low airspeed descending flight characteristics and determine the effects of the thrust-control lever and cockpit-control inputs on handling qualities in this flight regime.
The objectives of the test effort were to define the boundary of VRS, derive a fleet operational envelope, define the recovery technique from VRS, determine applicability for warning systems, and document the condition in pilot training ground school simulations and the NATOPS (Naval Air Training and Operating Procedures Standardization) flight manual for the tiltrotor. The first two objectives initially were approached as two phases, to validate the current fleet low-airspeed rate-of-descent limit and document the VRS boundary, and to evaluate the capability to expand the current fleet limit. As the testing progressed, however, we soon realized that breaking the test effort into two phases was not necessary, and we added multiaxis control inputs and dynamic maneuvers to our test effort.
For the third objective, we knew that recovery from VRS, like the poststall departure recovery of a fixed-wing aircraft, requires proper and timely procedures. For the Osprey, the most powerful flight control is the pilot’s ability to change nacelle angle (thrust vector) at up to 8° per second through a thumb switch on the thrust-control lever. This ability to change nacelle angle (and hence inflow angle at the rotor disk) would lead to an effective and immediate recovery tool.
For the fourth objective, several crew-alerting methods were discussed to determine the feasibility of active VRS avoidance. A few of the mechanical and tactile methods considered were a mechanical stick shaker, seat shaker, or rudder pedal shaker, but these were quickly rejected because of complexity, weight, and systems integration concerns. Instead, a visual and aural warning system was developed to alert the aircrew when the aircraft exceeded the NATOPS flight manual’s rate-of-descent limit.
For the fifth objective, data obtained from flight testing were used to develop pilot training courseware, update the simulation model to replicate VRS if deemed necessary, and update the NATOPS flight manual with a comprehensive narrative description of VRS to include pilot cueing to aid avoidance and emergency procedures for recovery should VRS occur.
Our first six-month period of flight testing started within two and a half months of the Marana mishap, and only weeks after preliminary mishap board results had been reported. On 11 December 2000, a second MV-22 mishap not related to vortex ring state occurred, taking the lives of all on board and resulting in the grounding of the Osprey fleet. Several investigative bodies evaluated the MV-22, the most significant of which was the blue ribbon panel.[2] The cause of the second accident was found to be the combination of a software anomaly and a hydraulic line failure. The grounding allowed the test team to analyze flight data collected to date, refine the test plan, and develop instrumentation, including a new low-airspeed measurement system. After evaluating several low-airspeed sensors, the test team selected the R. M. Young Model 81000 Ultrasonic Anemometer to provide the desired airspeed to as low as ten knots forward velocity. When integrated into the aircraft, this sensor provided the low-airspeed confidence required to complete our flight test. In addition to the normal aircraft display of flight information on the pilot primary flight display, we added two flip-down liquid crystal displays that indicated sideslip in one-degree increments and calibrated airspeed with one-knot accuracy from the ultrasonic anemometer. The addition of the flip-down digital displays, within the pilot’s central field of view, greatly reduced workload and increased test-point efficiency.Flight Test
Our test-plan strategy was simple: approach the unknown boundary from higher air speed and down from above with increasing sink rate increments. For the purpose of pilot build up and standardization, only one pilot, chief test pilot Tom Macdonald of Boeing, flew each test point with a small group of copilots assisting. The aircraft was configured with nacelles full aft at 95°, flaps auto, and landing gear down. Each descent track was completed at the same target airspeed, with a package of data points at each 500-feet-per-minute descent increment, where we checked stability, handling qualities, ride quality, aural signatures, and descent arrest and recovery effectiveness.
Our testing was conducted at altitude with a target test band of 8,000- to 7,000-feet altitude to allow for recovery well before the hard deck of 3,500 feet above ground level. Each aircraft input at the target airspeed and rate of descent required one dedicated descent. With the addition of the Young Model 81000 low-airspeed system, we gained flight efficiency by omitting the sawtooth climbs to determine true winds in the test band for the next descent profile. By the end of our VRS test effort, we had flown 62 flights for 104 flight hours and exceeded 5,600-feet-per-minute rate of descent and flew as slow as ten knots calibrated forward airspeed.
During our testing, we experienced 12 roll-off events, 8 to the right and 4 to the left. The direction of roll off was not predictable from the cockpit. In fact, the cockpit characteristics approaching VRS were not as well defined as in single-rotor helicopters. We noticed a slight increase in vibration, rotor noise, and flight control loosening that would not in every instance foretell of an impending roll off. Each roll off, however, was characterized by a sudden sharp reduction of lift on one of the two proprotors, resulting in an uncommanded roll in that direction. We also noted that roll offs required nearly steady-state conditions to trigger them. Any dynamic maneuvering tended to delay or prevent a roll off from occurring. On many occasions, we entered the VRS boundary during dynamic maneuvers and then exited the boundary without encountering a roll off.
Improvements to the Osprey’s pilot display include an expanded rate-of-descent scale and a red line added behind the vertical sink scale. Both features should help prevent future encounters with vortex ring state. (Photo couresty of author)
Pilot recovery procedures from a VRS roll off are easy, immediate, and effective. The pilot fixes the thrust-control lever and simultaneously pushes the nacelle-control thumb wheel forward for two seconds. This two-second beep forward moves the nacelles 12° to 15° lower, which immediately takes the rotors out of the VRS condition as the aircraft accelerates rapidly. If required, the pilot then uses lateral stick to level the wings and then adds power to stop the rate of descent.
Avionics Improvements
Now that we knew where the VRS boundary was located, how the aircraft responded during VRS, and the proper recovery procedures and techniques, our focus turned toward avoidance of VRS. Boeing and Naval Air Systems Command avionics and crew systems engineers developed a simple yet eloquent method of keeping pilots away from VRS. We made two changes to our avionics displays that increased the pilot’s situational awareness during low-speed, high-rate-of-descent flight. First, we expanded the rate-of-descent scale from 1,000 feet per minute to 2,000 feet per minute in 200-feet-per-minute increments. Second, we added a red line behind the vertical sink scale at the rate-of-descent limit along with a visual and aural “sink” warning when the airspeed and rate of descent exceed the limits. The flight display used by the pilot as the primary performance instrument in the Osprey is shown above. The scale on the right side is the vertical speed indicator. The indicator’s arrowhead is pointing to an 800-feet-per-minute rate of descent. The airspeed box is on the left of the display and indicates 39 knots. With this combination of airspeed and rate of descent, the pilot has exceeded the existing rate-of-descent limit and now hears “sink rate, sink rate” in his headset and sees the red “sink” warning in the display near the top and to the right of center. It is important to note that this warning system is not a predictor of VRS, but a rate-of-descent limit to keep the pilot away from VRS.
Where We Go from Here
Our ultimate goal for this flight-test effort was to understand fully the aerodynamic effects of vortex ring state on the tiltrotor, to define the recovery procedures should the pilot encounter VRS, and, most important, to develop warning signals to keep pilots away from this condition. Pilot awareness of VRS and avoidance with rate-of-descent limits are the only tools available to prevent a high-rate-of-descent mishap from taking more lives. Our current rate-of-descent limit is 800 feet per minute below 40 knots calibrated airspeed (KCAS), increasing linearly to 1,600 feet per minute at 80 KCAS. Presently, Naval Air Systems Command is evaluating the potential to expand the rate-of-descent envelope in the 30-to-50-knot airspeed range to provide the user communities more capability during flight tests and approaches to landing.
So what have we found in our 14-months of low-airspeed, high-rate-of-descent testing in search of VRS?
- Above 40 KCAS, VRS will not occur, regardless of sink-rate magnitude.
- The lower the disk loading (the ratio between an aircraft’s weight and rotor size), the smaller the sink rate where VRS might occur. Conversely, in the case of the MV-22 with higher disk loading, VRS may occur at a much larger sink rate.
- VRS requires a nearly steady-state condition. Any maneuvering tends to delay or prevent a roll off.
- As both sink rate increases and airspeed decreases, periodic rotor thrust fluctuations increase.
- As the VRS boundary is approached, handling qualities degrade because of unsteady flows at the rotor(s).
- Entry into fully developed VRS may be characterized by a sudden, sharp reduction of net thrust at the rotor.
- Recovery from VRS is immediate and effective using two seconds of forward nacelle tilt.
- There is a large margin of safety between rate of descent limit and VRS boundary below 40 KCAS.
- Kyuichiro Washizu and Akira Azuma, “Experiments on a Model Helicopter Rotor Operating in the Vortex Ring State,” University of Tokyo, presented at the American Institute of Aeronautics and Astronautics Symposium on Structural Dynamics and Aeroelasticity, Boston, MA, 30 August-1 September 1965.[back to article]
- “Report of the Panel to Review the V-22 Program,” Memorandum for the Secretary of Defense, John R. Dailey, Chairman, 30 April 2001. [back to article]
Last edited by 21stCen; 15th Dec 2011 at 16:52.
V-22 Myth Article
Very interesting article.
Two questions that come to mind, which are probably covered in the test reports, but which I have never seen discussed in online writings, are:
Thanks,
John Dixson
Two questions that come to mind, which are probably covered in the test reports, but which I have never seen discussed in online writings, are:
- What aircraft reactions accompanied those instances where they actually encountered vortex ring state?
- In any of the actual vortex ring state events, was the effect of prop pitch increase evaluated?
Thanks,
John Dixson
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BTW, Tom Macdonald, the V-22 Project Test Pilot for the V-22 had, during an earlier stage of his USN career, been stationed at the Naval Plant Representative Office at Sikorsky in Stratford Ct., where he certainly impressed all with his intelligence, flying skills and ability to navigate the shoal waters involving US Government flight acceptance of production aircraft!
Last edited by 21stCen; 15th Dec 2011 at 19:43.
Fatal Flaw
21st Century, I actually had read that article by Lt. Col. Gross some time ago, as it is from 2004. It does not dispel any "myth" about the V-22. In fact it confirmed something I've known about the V-22 with respect to A-VRS. Lt. Col. Gross reports:
Whoops! You mean to tell me that WHEN a V-22 gets into A-VRS the crew won't be able to know which way it's going to "break?" Yikes!
Let us acknowledge that the Marana V-22 did not get into a sustained 2000+ fpm rate of descent at 300 feet above the ground. If it did, it was only a momentary excursion. Otherwise, it would have hit the ground on its wheels in a couple of seconds. No, the RoD momentarily dipped to 2,000fpm+ and that was enough to excite one of the proprotors into VRS. Remember, Majors Brow and Gruber were trying to hold position on the lead V-22, "Dash-1" who was also having a hard time slowing down with the tailwind (and in fact they ended up crashing as well, something that gets glossed-over when speaking of the tragedy).
Lt. Col. Gross's article also does not answer my question, which was: How is the V-22 fundamentally "different" or "safer" now than it was back in 2000?
Answer: It is not.
Lonewolf asks:
Uhh, didn't they actually do just that? Why do you think the military flies UH-60's now and not UH-1Ns? Why are they developing the UH-1Y? Seems to me that if the 2-blade system was so great we'd still be using them. But what do I know...
jeffg asks:
I've never said the V-22 is more susceptible to VRS than a helicopter. I say the V-22 is more susceptible to A-VRS than a helicopter. ASYMMETRIC VRS: One proprotor goes into it while the other one does not. Why do some of you guys keep denying the importance of this?
jeffg persists:
I actually have gotten into VRS in a helicopter. It was quite unexpected, inasmuch as my attention was diverted elsewhere at the time and it caught me by surprise. (And nobody was shooting at me either!) However I have never accidentally or inadvertently stalled an airplane. Why? Because the stall-warning horn gave me sufficient warning that I was approaching a critical angle of attack.
21st Century notes:
Wait a minute. If an equivalent helicopter got into VRS at the same altitude as Majors Brow and Gruber, the helicopter would've settled vertically. If it hit the ground it would have done so upright, on its landing gear...not inverted like the V-22 did. See, for those of you who don't know, it's pretty hard for a helicopter to get into A-VRS.
Yes, I harp on this. Because only a true idiot...or someone who knows next to nothing about helicopters would downplay the importance of what I consider to be the fatal flaw of the tiltrotor design: Asymmetrical-VRS.
Now, I acknowledge that no A-VRS accident has happened since Marana. However, I will not go so as to say that another "Marana" accident will never happen again just because we're aware of it now.
The article that 21st Century posted by Lt. Col. Gross tells us that the V-22 crew now gets a "SINK!" warning on their PFD and an audible warning if the a/s drops below 40 knots and the RoD gets to 800 fpm. Great. Those are pretty conservative parameters.
The PFD and audible sink rate warnings are, in my opinion insufficient. I think that in practice, when the sh*t hits the fan, those warnings will be summarily ignored by V-22 pilots just like the stall-warning alert was ignored 75 times by the crew of AF447.
Bottom line: All those who claim that the V-22 is "a different aircraft now!" or "safer" than it was when first introduced are just putting out bullsh...uhh...propaganda. Yeah, yeah, we know more about VRS now. And we give the V-22 crews alerts. And if a V-22 pilot ever gets into A-VRS up at altitude he can just beep the nacelles forward and "fly out of it!" But we still can't tell the V-22 pilot with any certainty when one of the proprotors is close to VRS.
So it's still the same aircraft as it always was.
My book on the V-22 will be titled, "Fatal Flaw."
The direction of roll off was not predictable from the cockpit.
Let us acknowledge that the Marana V-22 did not get into a sustained 2000+ fpm rate of descent at 300 feet above the ground. If it did, it was only a momentary excursion. Otherwise, it would have hit the ground on its wheels in a couple of seconds. No, the RoD momentarily dipped to 2,000fpm+ and that was enough to excite one of the proprotors into VRS. Remember, Majors Brow and Gruber were trying to hold position on the lead V-22, "Dash-1" who was also having a hard time slowing down with the tailwind (and in fact they ended up crashing as well, something that gets glossed-over when speaking of the tragedy).
Lt. Col. Gross's article also does not answer my question, which was: How is the V-22 fundamentally "different" or "safer" now than it was back in 2000?
Answer: It is not.
Lonewolf asks:
should the Army and Navy and Marines have stopped flying Hueys because they can experience mast bumping?
jeffg asks:
Why do you imagine that a V-22 is more susceptible to a VRS incident then is a helicopter...
jeffg persists:
How is it you have managed all these years to avoid VRS without a cockpit warning device?
21st Century notes:
in the Marana case the aircraft was too low for recovery as would have been the case in an equivalent class helicopter...
Yes, I harp on this. Because only a true idiot...or someone who knows next to nothing about helicopters would downplay the importance of what I consider to be the fatal flaw of the tiltrotor design: Asymmetrical-VRS.
Now, I acknowledge that no A-VRS accident has happened since Marana. However, I will not go so as to say that another "Marana" accident will never happen again just because we're aware of it now.
The article that 21st Century posted by Lt. Col. Gross tells us that the V-22 crew now gets a "SINK!" warning on their PFD and an audible warning if the a/s drops below 40 knots and the RoD gets to 800 fpm. Great. Those are pretty conservative parameters.
The PFD and audible sink rate warnings are, in my opinion insufficient. I think that in practice, when the sh*t hits the fan, those warnings will be summarily ignored by V-22 pilots just like the stall-warning alert was ignored 75 times by the crew of AF447.
Bottom line: All those who claim that the V-22 is "a different aircraft now!" or "safer" than it was when first introduced are just putting out bullsh...uhh...propaganda. Yeah, yeah, we know more about VRS now. And we give the V-22 crews alerts. And if a V-22 pilot ever gets into A-VRS up at altitude he can just beep the nacelles forward and "fly out of it!" But we still can't tell the V-22 pilot with any certainty when one of the proprotors is close to VRS.
So it's still the same aircraft as it always was.
My book on the V-22 will be titled, "Fatal Flaw."
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FH1100
You certainly know how to turn a polite, straight forward discussion into one that is confrontational. To make it worse, you add your demonstrated lack of knowledge, exaggerations and distortions (see below).
FH1100 says:
And only a “true idiot” could fail to realize that nobody on this thread has EVER marginalized the danger of A-VRS. Those who fly tiltrotors understand it far better than you ever will. That’s why not one aircraft has experienced A-VRS inadvertently in the past 11 years. I’m not sure how many times that has to be repeated before the significance of it sinks in. That doesn’t mean it will never happen again. It does mean that the post-Marana actions to train the pilots and equip the a/c to avoid it have been effective to date.
FH1100 says:
That is true, and that is why all the post-Marana actions that have been successful so far were taken: to allow pilots to avoid the conditions that would permit A-VRS to develop.
FH1100 says:
The logic claiming that because reaching that extraordinary vertical descent rate at that low altitude was only 'momentary' has no relevance. Yes the a/c was ‘momentarily’ at just over 2400fpm at 285 ft above the ground as it entered into a Vortex Ring State, but prior to that it was at 1900fpm, 2000fpm, 2100fpm, etc., getting deeper into the VRS envelope while rapidly slowing the aircraft forward speed with a tailwind present, and at the same time power was rapidly being pulled in to arrest the descent. Whether it be a helicopter or a tiltrotor, this scenario was going to result in a fatal crash.
FH1100 says:
A CH-46 or CH-53 experiencing VRS with a rapidly increasing ROD starting from 2400fpm at 285ft AGL might allow it to hit wheels down, but the impact with the rotor system coming down around you and an inevitable rollover would almost certainly be fatal for all. And as far as recovery starting at 285ft with a 2400fpm descent and ROD rapidly increasing, sufficient time/altitude would not be available to lower collective and move the cyclic forward to exit the VR state before impact just as recovery for the V-22 was not possible at that point in time. Again, the key for both helicopters and tiltrotors is to avoid those conditions to begin with.
FH1100 says:
Wow, is this ignorance, arrogance or both? The pilots who have been flying the a/c and whose lives depend on it say, “it is a very different aircraft today.” You without any experience, knowledge, or connection to the program say, “it is not.” Those pilots who have flown the different a/c over time including the FSD, Block A, Block B, and Full Rate Production a/c including those with post production mods all attest to improvements that make the current production a/c very different from the a/c flown in 2000 (how many crashes have occurred due to hydraulic pipe chaffing like the one that occurred in 2000 is one easy example to back their claims). BTW, none of the pilots or support personnel I have spoken to or communicated with have ever claimed it is the perfect aircraft, in fact they all have their suggestions for additional improvements many of which they say are in the pipeline.
FH1100 says:
Wow, if that statement is true, you are an even a worse pilot than we have been led to believe! In the decades that I flew fixed-wing a/c I never once encountered a stall warning horn in normal flight operations that was needed to give me sufficient warning that the critical AOA was being approached. The only time I heard the stall warning horn was during training. We teach our students how to recognize and avoid stall conditions, and only engage them in imminent and full stall practice to instill immediate action responses in case they had screwed up and allowed the aircraft to be flown into a dangerous flight regime that should have been avoided. The stall warning horn is a last resort warning – if you rely on it to give you stall warning information on routine flights, you should not be flying. It is a very simple electronic device that is aerodynamically activated (AOA indicators are more advanced) – and they do fail!!
FH1100 says:
Nobody disagrees with that, but those flying the aircraft say that all efforts are being made to continue to do the best they can to see that the ‘goal’ of preventing a future reoccurrence comes true.
FH1100 says:
Agreed. Applying the standard US military helicopter limitations of 40kts/800fpm is certainly too conservative considering a tiltrotor will not enter VRS as early as a helo. The ex-CH-53 guys now flying the Osprey have said if they would at least make it 1200fpm the V-22 will still have a larger safety margin than a 53 over the 800fpm limit. However, looking at the safety record over the last 11 years it would be hard to argue changing it.
FH1100 says:
You should write that book, but it should be an autobiography instead as you’ve already chosen the perfect title.
You certainly know how to turn a polite, straight forward discussion into one that is confrontational. To make it worse, you add your demonstrated lack of knowledge, exaggerations and distortions (see below).
FH1100 says:
Because only a true idiot... would downplay the importance of… Asymmetrical-VRS
FH1100 says:
Whoops! You mean to tell me that WHEN a V-22 gets into A-VRS the crew won't be able to know which way it's going to "break?" Yikes!
That is true, and that is why all the post-Marana actions that have been successful so far were taken: to allow pilots to avoid the conditions that would permit A-VRS to develop.
FH1100 says:
Let us acknowledge that the Marana V-22 did not get into a sustained 2000+ fpm rate of descent at 300 feet above the ground. If it did, it was only a momentary excursion.
The logic claiming that because reaching that extraordinary vertical descent rate at that low altitude was only 'momentary' has no relevance. Yes the a/c was ‘momentarily’ at just over 2400fpm at 285 ft above the ground as it entered into a Vortex Ring State, but prior to that it was at 1900fpm, 2000fpm, 2100fpm, etc., getting deeper into the VRS envelope while rapidly slowing the aircraft forward speed with a tailwind present, and at the same time power was rapidly being pulled in to arrest the descent. Whether it be a helicopter or a tiltrotor, this scenario was going to result in a fatal crash.
FH1100 says:
Wait a minute. If an equivalent helicopter got into VRS at the same altitude as Majors Brow and Gruber, the helicopter would've settled vertically. If it hit the ground it would have done so upright, on its landing gear...
FH1100 says:
Lt. Col. Gross's article also does not answer my question, which was: How is the V-22 fundamentally "different" or "safer" now than it was back in 2000? Answer: It is not.
FH1100 says:
However I have never accidentally or inadvertently stalled an airplane. Why? Because the stall-warning horn gave me sufficient warning that I was approaching a critical angle of attack.
Wow, if that statement is true, you are an even a worse pilot than we have been led to believe! In the decades that I flew fixed-wing a/c I never once encountered a stall warning horn in normal flight operations that was needed to give me sufficient warning that the critical AOA was being approached. The only time I heard the stall warning horn was during training. We teach our students how to recognize and avoid stall conditions, and only engage them in imminent and full stall practice to instill immediate action responses in case they had screwed up and allowed the aircraft to be flown into a dangerous flight regime that should have been avoided. The stall warning horn is a last resort warning – if you rely on it to give you stall warning information on routine flights, you should not be flying. It is a very simple electronic device that is aerodynamically activated (AOA indicators are more advanced) – and they do fail!!
FH1100 says:
Now, I acknowledge that no A-VRS accident has happened since Marana. However, I will not go so as to say that another "Marana" accident will never happen again…
FH1100 says:
The article that 21st Century posted by Lt. Col. Gross tells us that the V-22 crew now gets a "SINK!" warning on their PFD and an audible warning if the a/s drops below 40 knots and the RoD gets to 800 fpm. Great. Those are pretty conservative parameters.
FH1100 says:
My book on the V-22 will be titled, "Fatal Flaw."
Last edited by 21stCen; 16th Dec 2011 at 18:15.
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What becomes abundantly clear reading FH1100s post is that he does not understand VRS(or A-VRS) nor has he taken the time to actually read and study the literature available about it. It's also obvious that FH1100 has absolutely zero comprehension of how military operations are flown, how pilots are trained and how crews are scheduled, how tactics are developed and how through training and tactics approach profiles etc. address issues such as VRS (yes A-VRS). Furthermore it's obvious that FH1100 has no concept of how tilt rotors are flown however he has come to his own conclusions based what he has read on blogs and pretty much nothing more. If only he would choose to pontificate about something he knew about, like being a raconteur.
FH, in your first post you asked
"Just HOW is the aircraft different from the one that Majors Brow and Gruber flew in April of 2000? Does it have a reliable VRS indicator now? You know, like the stall-warning horn in an airplane, that can physically sense when a wing is at a critical angle of attack?"
This implies that if it had such a device it would be safer, well it does but now that is not sufficient for you.* No it doesn't have an A-VRS sensor, but if one avoids VRS then one will avoid A-VRS. No it doesn’t sense how close a proprotor is to VRS but provides the pilot both visual and aural cues of approaching limits. Remember that no device can ultimately keep a pilot from exceeding limits. If that is your design criteria then I suggest that we ground every aircraft out there because everyone of them has limits that if exceeded will result in a fatal mishap.
*
In your second post you state:
'However I have never accidentally or inadvertently stalled an airplane. Why?'
So you triggered the stall warning then you inadvertently got too slow and if it weren't for the stall warning you would have stalled.
‘Because the stall-warning horn gave me sufficient warning that I was approaching a critical angle of attack.’
You admit that warnings work! If it worked for you why won't the VRS warning work for a V-22? They indeed have a warning device installed and there have been no further VRS(or A-VRS) mishaps since its installation. You should be happy. Apparently it works. Case closed. Oh wait, you always have a straw man argument to prove why it won't. Sorry, I can't counter those as they are pretty much devoid of reality. Will another V-22 crash at some point due to A-VRS? Probably. Will another fixed wing aircraft crash due to stall? Probably. Will another Biz jet run off a runway because the brakes failed? Probably. Should I continue?
But then you go and contradict yourself by implying that stall warnings don't work, stating the Airbus accident.* In fact you disrespectfully state:
'THREE pilots in that cockpit, stall-warning going off and not ONE of those geniuses suggested lowering the nose and, you know, flying out of the stall.'
Actually I believe if you were to read that report again you would find the facts to be slightly different. However are you suggesting the Airbus a dangerous aircraft with a fatal flaw and should be grounded because pilots failed to react properly?
‘The PFD and audible sink rate warnings are, in my opinion insufficient. I think that in practice, when the sh*t hits the fan, those warnings will be summarily ignored by V-22 pilots just like the stall-warning alert was ignored 75 times by the crew of AF447’
Yet you didn’t ignore the stall warning you received? I wonder why it worked for you but will fail for V-22 pilots? Maybe you’re just a better pilot then they are. No, apparently you think your 206 can do aerobatics (previous post) because your RFM doesn’t say it can’t, you’ve flown yourself into VRS and you apparently need the stall warning to keep you from stalling, I’d say you are about average like the rest of us.
So FH do you think stall warnings work or don't they? Your argument is a bit confusing since you take both sides.
‘Because they were confused. But that will never happen to pilots in combat, will it?’
Yes it will. They will get confused in the V-22 and make mistakes, sometimes fatal. Just as pilots have gotten confused in H-1s and made fatal mistakes. Just as they have CH-53s and made fatal mistakes. What’s your point? That they will only make mistakes in the V-22 or that only mistakes in the V-22 will be fatal?
“Uhh, didn't they actually do just that? Why do you think the military flies UH-60's now and not UH-1Ns? Why are they developing the UH-1Y? Seems to me that if the 2-blade system was so great we'd still be using them. But what do I know...'
That was completely ignorant. Payload, range, speed and other factors. Not safety. The two bladed rotor is perfectly safe but there are gains to be made with more blades. In fact don’t you fly a 206? Is it unsafe? Are you afraid to fly it because it only has two blades? What’s the safety record of the two bladed rotor system?
“I've never said the V-22 is more susceptible to VRS than a helicopter. I say the V-22 is more susceptible to A-VRS than a helicopter. ASYMMETRIC VRS: One proprotor goes into it while the other one does not. Why do some of you guys keep denying the importance of this?”
Thank you for the explanation but unlike you I’ve actually studied the issue. It would be nice if you did the same. Nobody denies the importance of it, we just understand it, unlike you.
'The article that 21st Century posted by Lt. Col. Gross tells us that the V-22 crew now gets a "SINK!" warning on their PFD and an audible warning if the a/s drops below 40 knots and the RoD gets to 800 fpm. Great. Those are pretty conservative parameters.'
The same exact parameters that apply to all rotary wing aircraft, not just tiltrotors. Sorry if you don’t like it, but it’s true.
“Wait a minute. If an equivalent helicopter got into VRS at the same altitude as Majors Brow and Gruber, the helicopter would've settled vertically. If it hit the ground it would have done so upright, on its landing gear...not inverted like the V-22 did. See, for those of you who don't know, it's pretty hard for a helicopter to get into A-VRS.”
2400 fpm is 40 ft/sec. If a 53 were at 285 agl at at 2400 fpm ROD and tried to recover from VRS, if the correct action was taken the pilot would lower the collective and push the nose over, both of which would increase the ROD so it would impact at at least 40ft/sec. I’m sure there is someone on here who can tell us what would happen to CH-53E if it settled vertically and upright onto the tarmac at 40 ft/sec. I’m going to guess that 40ft/sec is well beyond where the gear would yield and the OEM guarantees an chance of survivability. But I could be wrong. You are correct FH, the V-22 in A-VRS would roll over, the 53 wouldn’t. 21 century is right in that the end result would have been the same.
FH, in your first post you asked
"Just HOW is the aircraft different from the one that Majors Brow and Gruber flew in April of 2000? Does it have a reliable VRS indicator now? You know, like the stall-warning horn in an airplane, that can physically sense when a wing is at a critical angle of attack?"
This implies that if it had such a device it would be safer, well it does but now that is not sufficient for you.* No it doesn't have an A-VRS sensor, but if one avoids VRS then one will avoid A-VRS. No it doesn’t sense how close a proprotor is to VRS but provides the pilot both visual and aural cues of approaching limits. Remember that no device can ultimately keep a pilot from exceeding limits. If that is your design criteria then I suggest that we ground every aircraft out there because everyone of them has limits that if exceeded will result in a fatal mishap.
*
In your second post you state:
'However I have never accidentally or inadvertently stalled an airplane. Why?'
So you triggered the stall warning then you inadvertently got too slow and if it weren't for the stall warning you would have stalled.
‘Because the stall-warning horn gave me sufficient warning that I was approaching a critical angle of attack.’
You admit that warnings work! If it worked for you why won't the VRS warning work for a V-22? They indeed have a warning device installed and there have been no further VRS(or A-VRS) mishaps since its installation. You should be happy. Apparently it works. Case closed. Oh wait, you always have a straw man argument to prove why it won't. Sorry, I can't counter those as they are pretty much devoid of reality. Will another V-22 crash at some point due to A-VRS? Probably. Will another fixed wing aircraft crash due to stall? Probably. Will another Biz jet run off a runway because the brakes failed? Probably. Should I continue?
But then you go and contradict yourself by implying that stall warnings don't work, stating the Airbus accident.* In fact you disrespectfully state:
'THREE pilots in that cockpit, stall-warning going off and not ONE of those geniuses suggested lowering the nose and, you know, flying out of the stall.'
Actually I believe if you were to read that report again you would find the facts to be slightly different. However are you suggesting the Airbus a dangerous aircraft with a fatal flaw and should be grounded because pilots failed to react properly?
‘The PFD and audible sink rate warnings are, in my opinion insufficient. I think that in practice, when the sh*t hits the fan, those warnings will be summarily ignored by V-22 pilots just like the stall-warning alert was ignored 75 times by the crew of AF447’
Yet you didn’t ignore the stall warning you received? I wonder why it worked for you but will fail for V-22 pilots? Maybe you’re just a better pilot then they are. No, apparently you think your 206 can do aerobatics (previous post) because your RFM doesn’t say it can’t, you’ve flown yourself into VRS and you apparently need the stall warning to keep you from stalling, I’d say you are about average like the rest of us.
So FH do you think stall warnings work or don't they? Your argument is a bit confusing since you take both sides.
‘Because they were confused. But that will never happen to pilots in combat, will it?’
Yes it will. They will get confused in the V-22 and make mistakes, sometimes fatal. Just as pilots have gotten confused in H-1s and made fatal mistakes. Just as they have CH-53s and made fatal mistakes. What’s your point? That they will only make mistakes in the V-22 or that only mistakes in the V-22 will be fatal?
“Uhh, didn't they actually do just that? Why do you think the military flies UH-60's now and not UH-1Ns? Why are they developing the UH-1Y? Seems to me that if the 2-blade system was so great we'd still be using them. But what do I know...'
That was completely ignorant. Payload, range, speed and other factors. Not safety. The two bladed rotor is perfectly safe but there are gains to be made with more blades. In fact don’t you fly a 206? Is it unsafe? Are you afraid to fly it because it only has two blades? What’s the safety record of the two bladed rotor system?
“I've never said the V-22 is more susceptible to VRS than a helicopter. I say the V-22 is more susceptible to A-VRS than a helicopter. ASYMMETRIC VRS: One proprotor goes into it while the other one does not. Why do some of you guys keep denying the importance of this?”
Thank you for the explanation but unlike you I’ve actually studied the issue. It would be nice if you did the same. Nobody denies the importance of it, we just understand it, unlike you.
'The article that 21st Century posted by Lt. Col. Gross tells us that the V-22 crew now gets a "SINK!" warning on their PFD and an audible warning if the a/s drops below 40 knots and the RoD gets to 800 fpm. Great. Those are pretty conservative parameters.'
The same exact parameters that apply to all rotary wing aircraft, not just tiltrotors. Sorry if you don’t like it, but it’s true.
“Wait a minute. If an equivalent helicopter got into VRS at the same altitude as Majors Brow and Gruber, the helicopter would've settled vertically. If it hit the ground it would have done so upright, on its landing gear...not inverted like the V-22 did. See, for those of you who don't know, it's pretty hard for a helicopter to get into A-VRS.”
2400 fpm is 40 ft/sec. If a 53 were at 285 agl at at 2400 fpm ROD and tried to recover from VRS, if the correct action was taken the pilot would lower the collective and push the nose over, both of which would increase the ROD so it would impact at at least 40ft/sec. I’m sure there is someone on here who can tell us what would happen to CH-53E if it settled vertically and upright onto the tarmac at 40 ft/sec. I’m going to guess that 40ft/sec is well beyond where the gear would yield and the OEM guarantees an chance of survivability. But I could be wrong. You are correct FH, the V-22 in A-VRS would roll over, the 53 wouldn’t. 21 century is right in that the end result would have been the same.
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JohnDixson asks:
Hi John,
Your first question has been discussed on this thread on occasion and as JeffG suggested, the best source for more firsthand information is in the AHS papers he mentioned:
-V-22 Low-Speed/High Rate of Descent (HROD) Test Results
-V-22 High Rate of Descent (HROD) Test Procedures and Long Record Analysis
Regarding your second question, a non-manufacturer source familiar with the trials mentioned:
Hope that helps,
21stC
1. What aircraft reactions accompanied those instances where they actually encountered vortex ring state?
2. In any of the actual vortex ring state events, was the effect of prop pitch increase evaluated?
2. In any of the actual vortex ring state events, was the effect of prop pitch increase evaluated?
Your first question has been discussed on this thread on occasion and as JeffG suggested, the best source for more firsthand information is in the AHS papers he mentioned:
-V-22 Low-Speed/High Rate of Descent (HROD) Test Results
-V-22 High Rate of Descent (HROD) Test Procedures and Long Record Analysis
Regarding your second question, a non-manufacturer source familiar with the trials mentioned:
Prop pitch is not even a remote issue here. Tiltrotors use beta governors - unlike an engine governor on say, a UH-1. Just like a turboprop airplane, as you add power, the prop pitch changes to maintain the set rpm. Once you command helicopter mode within the conversion corridor, the rpm is ramped up automatically to helo mode rpm and there it remains governed and constant. At low power in the descent, the rpm still remains constant and the blade pitch has been increased by the governor, naturally.
Hope that helps,
21stC
Last edited by 21stCen; 19th Dec 2011 at 16:38.
Uhh, didn't they actually do just that? Why do you think the military flies UH-60's now and not UH-1Ns? Why are they developing the UH-1Y? Seems to me that if the 2-blade system was so great we'd still be using them. But what do I know...
Mast bumping was known issue in 1960's.
I trained in Hueys in early 80's.
Navy was still flying November Hueys well after the year 2000.
(A guy I know dinged a November tail pylon in Texas a few years before they all got retired).
The US Marines were still flying Huey's in COMBAT in 2004 (when I had a chance to participate in operations), typically in a two ship mix of one Cobra, one Huey.
The AIR FORCE is still flying TH-1H Hueys, and UH-1N Hueys, even as you and I speak. Those aircraft are expeced to be in service with USAF until 2020 something ... but that last is subject to change.
So, NO, "they" didn't actually "do just that," nor did they do it "due to "mast bumping" as a motive.
The Army bought the Blackhawk for a lot of reasons, which included more durable, more crashworthy, and more payload ... but that's a discussion for another time.
Cheers, and Merry Christmas
Lonewolf_50
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According to a briefing i attended last spring the Army is keeping 42 UH-1H's. Also, the DoS is buying refurbished and upgraded Hueys for use in several different places. Lots of life left in the two blade Huey!
Osprey crew awarded medals in historic fight | osprey, crew, marines - News Source for Jacksonville, North Carolina - jdnews.com
(I didnt post David Axe's rehash of this story because even though there was absolutely no information with which to slam the V22, he couldn't just grit his teeth and report on it without stuffing his treasure trove of weasel words in his attempt to continually taint public perception.)
Osprey crew awarded medals in historic fight
December 16, 2011 6:06 PM
LINDELL KAY - DAILY NEWS STAFF
Four Marines were awarded medals Friday for action taken during the first engagement of enemy forces by an MV-22B Osprey.
Capts. Thomas Keech and Matthew Cave, Sgt. Justin Barfield-Smith and Cpl. John Cederholm received the Air Medal with Combat Distinguishing Device for Valor for actions during a June 12 mission.
After several ground missions failed to re-supply Marines fighting in the Sangin River Valley of Afghanistan, an Osprey was sent into the combat zone. The four-man crew of Keech, Cave, Barfield-Smith and Cederholm flew in with food, water, medical supplies and ammunition for the 1st Battalion, 5th Marines, which had sustained heavy casualties throughout the day, according to award citations.
While unloading supply crates, the crew came under small arms and medium machine gun fire from Taliban forces. The pilots called in cover fire providing the crew enough time to unload supplies and re-board the aircraft.
The Osprey’s pilots told The Daily News on Friday that their aircraft was on the ground and under enemy fire for around three minutes, but it felt like time had ground to a halt and everything moved in slow motion.
As soon as the last crate was unloaded, the Osprey took flight with Cederholm firing the aircraft’s only weapon, a ramp-mounted machine gun, at approaching Taliban troops. Cederholm became the first Marine to ever engage the enemy from a MV-22B.
He downplayed the historical aspect of his mission Friday, saying he was just doing his job.
“I may have been the first, but I won’t be the last,” he said. “Others have done it since me and we will keep doing it as long as we have to.”
Cederholm’s father, Marine Col. Mike Cederholm, was present for the awards ceremony held at the VMM-264 hangar aboard New River Air Station.
“I’m so proud of my boy,” the elder Cederholm said of his son. “I’m in awe of these young men and women who continue to answer the call.”
Col. Cederholm said the four Marines receiving the award were representative of the around 250 members of Marine Medium Tiltrotor Squadron 264.
Cpl. Cederholm’s mother, Rebecca Cederholm, said she didn’t realize until the citations were read at the ceremony that her son had gotten off the aircraft to help ground troops unload supplies.
Each member of the four-man crew exhibited courage during their mission, according to their individual awards.
Cave and Keech landed the Osprey on the first run and provided accurate enemy positions to friendly forces, which allowed support aircraft to suppress Taliban forces with rocket fire. Barfield-Smith helped unload supplies and called out targets to Cpl. Cederholm once the Osprey was back in the air.
The pilots and crew showed their “skillful airmanship, steadfast aggressiveness, and exemplary devotion to duty in the face of hazardous flying conditions,” their award citations read.
Receiving the Air Medal is not uncommon among flight crews, but being awarded the combat distinguishing device for valor is rare, said 1st Lt. Kristin Dalton, the director of public affairs for MCAS New River.
December 16, 2011 6:06 PM
LINDELL KAY - DAILY NEWS STAFF
Four Marines were awarded medals Friday for action taken during the first engagement of enemy forces by an MV-22B Osprey.
Capts. Thomas Keech and Matthew Cave, Sgt. Justin Barfield-Smith and Cpl. John Cederholm received the Air Medal with Combat Distinguishing Device for Valor for actions during a June 12 mission.
After several ground missions failed to re-supply Marines fighting in the Sangin River Valley of Afghanistan, an Osprey was sent into the combat zone. The four-man crew of Keech, Cave, Barfield-Smith and Cederholm flew in with food, water, medical supplies and ammunition for the 1st Battalion, 5th Marines, which had sustained heavy casualties throughout the day, according to award citations.
While unloading supply crates, the crew came under small arms and medium machine gun fire from Taliban forces. The pilots called in cover fire providing the crew enough time to unload supplies and re-board the aircraft.
The Osprey’s pilots told The Daily News on Friday that their aircraft was on the ground and under enemy fire for around three minutes, but it felt like time had ground to a halt and everything moved in slow motion.
As soon as the last crate was unloaded, the Osprey took flight with Cederholm firing the aircraft’s only weapon, a ramp-mounted machine gun, at approaching Taliban troops. Cederholm became the first Marine to ever engage the enemy from a MV-22B.
He downplayed the historical aspect of his mission Friday, saying he was just doing his job.
“I may have been the first, but I won’t be the last,” he said. “Others have done it since me and we will keep doing it as long as we have to.”
Cederholm’s father, Marine Col. Mike Cederholm, was present for the awards ceremony held at the VMM-264 hangar aboard New River Air Station.
“I’m so proud of my boy,” the elder Cederholm said of his son. “I’m in awe of these young men and women who continue to answer the call.”
Col. Cederholm said the four Marines receiving the award were representative of the around 250 members of Marine Medium Tiltrotor Squadron 264.
Cpl. Cederholm’s mother, Rebecca Cederholm, said she didn’t realize until the citations were read at the ceremony that her son had gotten off the aircraft to help ground troops unload supplies.
Each member of the four-man crew exhibited courage during their mission, according to their individual awards.
Cave and Keech landed the Osprey on the first run and provided accurate enemy positions to friendly forces, which allowed support aircraft to suppress Taliban forces with rocket fire. Barfield-Smith helped unload supplies and called out targets to Cpl. Cederholm once the Osprey was back in the air.
The pilots and crew showed their “skillful airmanship, steadfast aggressiveness, and exemplary devotion to duty in the face of hazardous flying conditions,” their award citations read.
Receiving the Air Medal is not uncommon among flight crews, but being awarded the combat distinguishing device for valor is rare, said 1st Lt. Kristin Dalton, the director of public affairs for MCAS New River.
Times do change I guess....in days of yore....the cargo would have been an underslung load....the load would have been set down...released...and the aircraft moved over...landed and wounded/KIA or whatever people going out would have been loaded...and a quick departure made.
Our SOP was for the crew never...never... to get off the aircraft except in an absolute emergency. If you had to leave hastely....you did not want to leave a crewman on the ground....and have to operate the aircraft short handed or be forced to return to the LZ.
There are times externally carried cargo is a better idea than it being carried internally....when unloading time is critical due to the risk of being taken under accurate gunfire, mortars, rockets, or RPG's.
To gain airspeed...do we increase vulnerbility unloading at the LZ? Where is the trade-off point at which LZ Time outweighs Airspeed in transit?
Oh....I forget....we have been told Operational planning nowadays means we don't land in hostile LZ's like we did in that small Asian country far away.
The one thing that has not changed is the courage and dedication of the crews! In combat there are great acts of courage every day...some might even get noticed and it is good when they do.
I am confused however.....
Just this week, Vice President Joseph Biden, stated the "Taliban" is not our enemy in Afghanistan.....it is Al Qaeda that is the Enemy".
Have the Marines not received the Word?
Our SOP was for the crew never...never... to get off the aircraft except in an absolute emergency. If you had to leave hastely....you did not want to leave a crewman on the ground....and have to operate the aircraft short handed or be forced to return to the LZ.
There are times externally carried cargo is a better idea than it being carried internally....when unloading time is critical due to the risk of being taken under accurate gunfire, mortars, rockets, or RPG's.
To gain airspeed...do we increase vulnerbility unloading at the LZ? Where is the trade-off point at which LZ Time outweighs Airspeed in transit?
Oh....I forget....we have been told Operational planning nowadays means we don't land in hostile LZ's like we did in that small Asian country far away.
The one thing that has not changed is the courage and dedication of the crews! In combat there are great acts of courage every day...some might even get noticed and it is good when they do.
I am confused however.....
Cave and Keech landed the Osprey on the first run and provided accurate enemy positions to friendly forces, which allowed support aircraft to suppress Taliban forces with rocket fire. Barfield-Smith helped unload supplies and called out targets to Cpl. Cederholm once the Osprey was back in the air.
Look, the Taliban per se is not our enemy. That’s critical. There is not a single statement that the president has ever made in any of our policy assertions that the Taliban is our enemy because it threatens U.S. interests. If, in fact, the Taliban is able to collapse the existing government, which is cooperating with us in keeping the bad guys from being able to do damage to us, then that becomes a problem for us.
FFS, SASless, when a politician utters something like that, don't you first add a grain of salt before you make an assessment of what he said? (And two grains for "pull it out of my backside Joe" Biden, our erstwhile VP).
Yes, things do change over time. Go figure. Sometimes, change for the better and sometimes, not so much.
Other times, change is for the sake of change. *shrugs*
Yes, things do change over time. Go figure. Sometimes, change for the better and sometimes, not so much.
Other times, change is for the sake of change. *shrugs*
Just pointing out the incongruity of the situation...Gongs for combat against an Armed Enemy....but the VP (The Walking Gaff Machine) talking bollocks about how they are not the "Enemy" despite the threat they pose. I am sure the Marines present at that fight would clearly construe the Taliban as being the "Enemy" and very rightly so.
Just what says I should just giggle and fergeddaboutit when either the Prez or VicePrez talk stupid?
This is the number one guy's stand-in should we have a sudden change of command at the very top for crying out loud.
Just what says I should just giggle and fergeddaboutit when either the Prez or VicePrez talk stupid?
This is the number one guy's stand-in should we have a sudden change of command at the very top for crying out loud.
Back to 21st Century
Let me explain a bit further re the questions I posed.
First, however, someone forwarded my post to Tom MacDonald and I received a very appreciated response from Tom, and it was good reconnecting after many years. I probably should mention that in 1992 or so, I instigated an attempt to offer Tom a job flying at SA, which, unfortunately for us, but probably crucial to the Bell/Boeing V-22 Team, he did not take. In his response, Tom mentioned his intention to write an in-depth SETP paper at length on the subject, saying that the 2003 paper was limited by the 20 minute presentation time allotted by the SETP at their functions.
Anyhow, as to the first question on V-22 aircraft reactions to VRS, the underlying reason for the question is that there is a separate aerodynamic situation that perhaps some may mistake for VRS, and while it is clear that some posters have very obviously encountered true VRS, some others may have mistaken what I am about to describe for VRS.
This particular phenomenon was demonstrated to me just after I joined SA in 1966, by our Sr Exp. Test Pilot Byron Graham ( I was the ad hoc copilot, but that's another story ) He was doing a 53A flight loads survey at max weight and on the card was something called a " Rough Approach ". Up and away, he slowed the machine almost to a hover, and then began a descent. At about 20 KIAS and 1500-2000 fpm, that machine went from dead smooth to an ungodly N/rev hammering. Zero pitch or roll perturbations and zero effect upon cyclic control power/sensitivity. Other than the exceedingly high vibration levels, the aircraft was hands-off stable. Byron explained the SA aero people's analysis as being that the advancing blade tip is intercepting the tip vortex from the preceding blade. So, over the years, I can say that I saw probably a couple of hundred of these events, in 4,5,6 and seven bladed models. Behavior is the same, but the indicated speed/rate of descent for the event is controlled by the blade loading, attitude ( really the CG influence ) and the behavior of the particular airspeed system of that ship ( sometimes the speed is bouncing off zero ). Some forward speed is necessary, and the descent angle is very very steep, but not quite vertical.
The second question I proposed asked whether the V-22 testing included prop pitch increases after VRS was encountered. I was asking about pitch, and do understand that the V-22 has isochronous governing, and that the prop Nr is increased automatically when in helo mode. I suspect that answer will have to wait for the longer SETP paper. My curiosity derives from thinking, based on some hand-done CT/sigma ( blade loading ) calculations that the prop rotor is already at fairly high Ct/sigma values already when coming to a hover. Just curious.
Again, thanks to whoever sent my previous post to Tom MacDonald.
Thanks,
John Dixson
First, however, someone forwarded my post to Tom MacDonald and I received a very appreciated response from Tom, and it was good reconnecting after many years. I probably should mention that in 1992 or so, I instigated an attempt to offer Tom a job flying at SA, which, unfortunately for us, but probably crucial to the Bell/Boeing V-22 Team, he did not take. In his response, Tom mentioned his intention to write an in-depth SETP paper at length on the subject, saying that the 2003 paper was limited by the 20 minute presentation time allotted by the SETP at their functions.
Anyhow, as to the first question on V-22 aircraft reactions to VRS, the underlying reason for the question is that there is a separate aerodynamic situation that perhaps some may mistake for VRS, and while it is clear that some posters have very obviously encountered true VRS, some others may have mistaken what I am about to describe for VRS.
This particular phenomenon was demonstrated to me just after I joined SA in 1966, by our Sr Exp. Test Pilot Byron Graham ( I was the ad hoc copilot, but that's another story ) He was doing a 53A flight loads survey at max weight and on the card was something called a " Rough Approach ". Up and away, he slowed the machine almost to a hover, and then began a descent. At about 20 KIAS and 1500-2000 fpm, that machine went from dead smooth to an ungodly N/rev hammering. Zero pitch or roll perturbations and zero effect upon cyclic control power/sensitivity. Other than the exceedingly high vibration levels, the aircraft was hands-off stable. Byron explained the SA aero people's analysis as being that the advancing blade tip is intercepting the tip vortex from the preceding blade. So, over the years, I can say that I saw probably a couple of hundred of these events, in 4,5,6 and seven bladed models. Behavior is the same, but the indicated speed/rate of descent for the event is controlled by the blade loading, attitude ( really the CG influence ) and the behavior of the particular airspeed system of that ship ( sometimes the speed is bouncing off zero ). Some forward speed is necessary, and the descent angle is very very steep, but not quite vertical.
The second question I proposed asked whether the V-22 testing included prop pitch increases after VRS was encountered. I was asking about pitch, and do understand that the V-22 has isochronous governing, and that the prop Nr is increased automatically when in helo mode. I suspect that answer will have to wait for the longer SETP paper. My curiosity derives from thinking, based on some hand-done CT/sigma ( blade loading ) calculations that the prop rotor is already at fairly high Ct/sigma values already when coming to a hover. Just curious.
Again, thanks to whoever sent my previous post to Tom MacDonald.
Thanks,
John Dixson
Last edited by JohnDixson; 22nd Dec 2011 at 11:16. Reason: typo
My curiosity derives from thinking, based on some hand-done CT/sigma ( blade loading ) calculations that the prop rotor is already at fairly high Ct/sigma values already when coming to a hover.
Am I correct to assume those values are very high on the Osprey.....and by high mean they are approaching the level where blade stall might be encountered?
A few seconds of googling found this......
Aerodynamic Blade Loading: [CT/σ] [Ct/sigma]
is a simple concept that lets us see how far from stall the rotor is operating, similar to the coefficient of lift for an airplane's wing. It is the coefficient of thrust divided by the solidity.
For most modern airfoil sections, deep rotor stall is experienced at a Ct/sigma of about .20 to .21 at hover. As retreating blade stall takes over, the Ct/sigma for stall at 160 knots is about 0.10 and by 200 knots, it is about 0.06.
For a tilt rotor, the blades are purposely made with less chord than a helicopter, because the thinner blades are then operating at a higher angle of attack in a hover, and are more efficient. This means that they can save power in a hover by operating at a high Ct/sigma. The downside is that there is little margin left over for maneuvering at low speed. For helos, the blade chord is sized up to allow flight at high speed, so it is way oversized for a hover. Tilt rotors don't need the extra chord for high speed because they are on the wing by then, and the rotors are props!
The V-22 has a hover Ct/sigma of 0.175, which means that it will stall at only about 1.2 to 1.3 g's in helo mode (.21/.175). A typical helo has a hover Ct/sigma of about 0.09, so it never gets close to stall at low speed (ever pull 2.4 g's at 40 knots? It's a wild ride!)
~ Nick Lappos
The Sikorsky ABC has demonstrated blade loadings up to 0.185, but the full lift capacity of the rotor system has yet to be demonstrated ~ (1976)
From Prouty "Helicopter Aerodynamics - p.68" "Most rotors are at the peak of their efficiency in forward flight when CT/σ is about .08.
is a simple concept that lets us see how far from stall the rotor is operating, similar to the coefficient of lift for an airplane's wing. It is the coefficient of thrust divided by the solidity.
For most modern airfoil sections, deep rotor stall is experienced at a Ct/sigma of about .20 to .21 at hover. As retreating blade stall takes over, the Ct/sigma for stall at 160 knots is about 0.10 and by 200 knots, it is about 0.06.
For a tilt rotor, the blades are purposely made with less chord than a helicopter, because the thinner blades are then operating at a higher angle of attack in a hover, and are more efficient. This means that they can save power in a hover by operating at a high Ct/sigma. The downside is that there is little margin left over for maneuvering at low speed. For helos, the blade chord is sized up to allow flight at high speed, so it is way oversized for a hover. Tilt rotors don't need the extra chord for high speed because they are on the wing by then, and the rotors are props!
The V-22 has a hover Ct/sigma of 0.175, which means that it will stall at only about 1.2 to 1.3 g's in helo mode (.21/.175). A typical helo has a hover Ct/sigma of about 0.09, so it never gets close to stall at low speed (ever pull 2.4 g's at 40 knots? It's a wild ride!)
~ Nick Lappos
The Sikorsky ABC has demonstrated blade loadings up to 0.185, but the full lift capacity of the rotor system has yet to be demonstrated ~ (1976)
From Prouty "Helicopter Aerodynamics - p.68" "Most rotors are at the peak of their efficiency in forward flight when CT/σ is about .08.
A second source of information....a research paper done by a Naval Officer.
http://www.dtic.mil/cgi-bin/GetTRDoc...f&AD=ADA204856
The other issue that is important is Disk Loading and its effect upon Autorotational capability which has had a very major effect upon the Osprey performance.
Last edited by SASless; 22nd Dec 2011 at 13:16.
Nick and Ct
SAS, you are correct re Nick being the first to bring up this aspect.
I was interested and did a calc on my own recently, using what I have seen posted re the increased hover Nr and what has been posted re V-22 blade area.
The paper that Tom MacDonald will be writing ought to answer all of the conjectures and will, I am certain, be very interesting reading.
This thread seems to have two separate subjects, one being the strategic/tactical financial justification for the machine, and the second being the flying quality acceptability with the VRS issue wrapped up into that second area.
I'll leave the first subject area to others, and make a simple observation regarding the second. The USMC discovered a serious problem in the Marana incident. The Bell/Boeing/USMC test team did what appears to be an extensive and technically rigorous flight test to establish the boundaries of the problem and establish corrective action procedures. They did that and the USMC and USAF aviators are now happy with what they fly.
There will inevitably be some comment that Marana represented a failure of that same test team to discover that particular problem. In response, my experience is that prior to flight test beginning on any new model, the entire test planning sequence is reviewed at many levels for rigor, completeness and of course adherence to contractual/specification requirements. What I am suggesting is that none of the experts involved saw this one coming, and along those lines, it is not the first time it has occurred within the industry.
Thanks,
John Dixson
I was interested and did a calc on my own recently, using what I have seen posted re the increased hover Nr and what has been posted re V-22 blade area.
The paper that Tom MacDonald will be writing ought to answer all of the conjectures and will, I am certain, be very interesting reading.
This thread seems to have two separate subjects, one being the strategic/tactical financial justification for the machine, and the second being the flying quality acceptability with the VRS issue wrapped up into that second area.
I'll leave the first subject area to others, and make a simple observation regarding the second. The USMC discovered a serious problem in the Marana incident. The Bell/Boeing/USMC test team did what appears to be an extensive and technically rigorous flight test to establish the boundaries of the problem and establish corrective action procedures. They did that and the USMC and USAF aviators are now happy with what they fly.
There will inevitably be some comment that Marana represented a failure of that same test team to discover that particular problem. In response, my experience is that prior to flight test beginning on any new model, the entire test planning sequence is reviewed at many levels for rigor, completeness and of course adherence to contractual/specification requirements. What I am suggesting is that none of the experts involved saw this one coming, and along those lines, it is not the first time it has occurred within the industry.
Thanks,
John Dixson
Well said, John.
Repeated for emphasis, and truth, with the doubled comment that this was a new technology being undertaken.
You won't predict it all. R & D means R & D, and part of the "D" ends up being "discovery."
For a case in point, consider how long it took to get the T-45, a fairly simple aircraft in comparison, untracked for the USN jet training missions and roles, adapted from a simple light attack aircraft. Even with a well known design, things come up that need fixing. Ten years into its service, there were still issues with nose wheel steering and ground handling that were being addressed in ECP's by NAVIAR and the manufacturer.
For a case nearer and dearer to my rotary flying days, there was the matter of how to die in an S-70 / Blackhawk when the Horizontal Stab runs itself full down, uncommanded.
That too got fixed after the team looked into a rigorous root cause anaysis and effective engineering solution. But as with many technologies (the moving horizontal stab was relatively new feature, and its FBW control, when Blackhawk entered the field) what we enjoy today was earned in blood. 
As to Kadon bearings,
I'll leave the first subject area to others, and make a simple observation regarding the second. The USMC discovered a serious problem in the Marana incident. The Bell/Boeing/USMC test team did what appears to be an extensive and technically rigorous flight test to establish the boundaries of the problem and establish corrective action procedures. They did that and the USMC and USAF aviators are now happy with what they fly.
There will inevitably be some comment that Marana represented a failure of that same test team to discover that particular problem. In response, my experience is that prior to flight test beginning on any new model, the entire test planning sequence is reviewed at many levels for rigor, completeness and of course adherence to contractual/specification requirements. What I am suggesting is that none of the experts involved saw this one coming, and along those lines, it is not the first time it has occurred within the industry.
There will inevitably be some comment that Marana represented a failure of that same test team to discover that particular problem. In response, my experience is that prior to flight test beginning on any new model, the entire test planning sequence is reviewed at many levels for rigor, completeness and of course adherence to contractual/specification requirements. What I am suggesting is that none of the experts involved saw this one coming, and along those lines, it is not the first time it has occurred within the industry.
You won't predict it all. R & D means R & D, and part of the "D" ends up being "discovery."
For a case in point, consider how long it took to get the T-45, a fairly simple aircraft in comparison, untracked for the USN jet training missions and roles, adapted from a simple light attack aircraft. Even with a well known design, things come up that need fixing. Ten years into its service, there were still issues with nose wheel steering and ground handling that were being addressed in ECP's by NAVIAR and the manufacturer.
For a case nearer and dearer to my rotary flying days, there was the matter of how to die in an S-70 / Blackhawk when the Horizontal Stab runs itself full down, uncommanded.
That too got fixed after the team looked into a rigorous root cause anaysis and effective engineering solution. But as with many technologies (the moving horizontal stab was relatively new feature, and its FBW control, when Blackhawk entered the field) what we enjoy today was earned in blood. As to Kadon bearings,