Tail rotor position
Choppie - as Bravo 73 says - getting to the pedal stops in extreme manoeuvres is usually Loss of Tailrotor Authority, LTA, (it is working fine but you can't apply any more pitch to it).
If you get to the stops doing normal manoeuvres then chances are you have Loss of Tailrotor Effectiveness,LTE, but you are unlikely to experience this in anything but a 206 - the TR is just not big or powerful enough for the aircraft.
If you get to the stops doing normal manoeuvres then chances are you have Loss of Tailrotor Effectiveness,LTE, but you are unlikely to experience this in anything but a 206 - the TR is just not big or powerful enough for the aircraft.
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Crab, you're right:
"Any helicopter that struggles with a 15 kt crosswind should never have been certified in the first place."
Everyone knows that the dividing line between good and non-certifiable helicopters is at 17 kts
"A wind velocity of not less than 17 knots must be established in which the rotorcraft can be operated without loss of control on or near the ground in any maneuver appropriate to the type (such as crosswind takeoffs, sideward flight, and rearward flight)" (FAR 27.143)
I've flown at least two non-Bell turbines that were maxed out in 18-20 kt xwinds at their critical azimuths, and they were duly certified.
"Any helicopter that struggles with a 15 kt crosswind should never have been certified in the first place."
Everyone knows that the dividing line between good and non-certifiable helicopters is at 17 kts
"A wind velocity of not less than 17 knots must be established in which the rotorcraft can be operated without loss of control on or near the ground in any maneuver appropriate to the type (such as crosswind takeoffs, sideward flight, and rearward flight)" (FAR 27.143)
I've flown at least two non-Bell turbines that were maxed out in 18-20 kt xwinds at their critical azimuths, and they were duly certified.
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Crab and BJC,
I agree with your points about LTE vs LTA, but regret to inform you that an entire class of helicopters have been certified with near-zero crosswind capability. For Cat B operations, 9 passengers or less, Bell has managed to certify the 407, 412, 212 with "wind + 45 degrees from the nose" and NO demonstrated cross wind pedal margin!
Look in AC 29-2, para .143 to see how to pull off this trick. It is a real shame, and an invitation to LTE for unsuspecting people.
The crummy tail rotors are the Cat B limiting element, and basically, the new interpretation of FAR allows them to operate above the weight at which the tail rotor has 17 knots of capability. According to the FAA, you can operate to limit pedal (just touching the stops) while landing, as long as when you are against the stop, the yaw rate is in the direction of the pedal.
This trick buys them about 5% more payload. The aircraft in question have TWO hover charts, one for "wind from any azimuth" and one for "wind + 45 degrees from the nose". The LTE hover chart has more payload, of course.
No wonder EC is eating their lunch.
I agree with your points about LTE vs LTA, but regret to inform you that an entire class of helicopters have been certified with near-zero crosswind capability. For Cat B operations, 9 passengers or less, Bell has managed to certify the 407, 412, 212 with "wind + 45 degrees from the nose" and NO demonstrated cross wind pedal margin!
Look in AC 29-2, para .143 to see how to pull off this trick. It is a real shame, and an invitation to LTE for unsuspecting people.
The crummy tail rotors are the Cat B limiting element, and basically, the new interpretation of FAR allows them to operate above the weight at which the tail rotor has 17 knots of capability. According to the FAA, you can operate to limit pedal (just touching the stops) while landing, as long as when you are against the stop, the yaw rate is in the direction of the pedal.
This trick buys them about 5% more payload. The aircraft in question have TWO hover charts, one for "wind from any azimuth" and one for "wind + 45 degrees from the nose". The LTE hover chart has more payload, of course.
No wonder EC is eating their lunch.
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Interesting, here's a key phrase:
"Rotorcraft certificated prior to Amendment 29-24 can update their certification basis to take advantage of this provision."
I imagine therefore that Bell won't be the only company to take advantage of this as FAR ammendments are generally accepted at face value by other certification authorities. No one willing to moan that Sikorsky or MD are also taking advantage of this, or can MD not play because they don't have tail rotors? This can only be good news for companies as they get increased capacity because they know that pilots are always able to land with the wind on the nose, right?
"Rotorcraft certificated prior to Amendment 29-24 can update their certification basis to take advantage of this provision."
I imagine therefore that Bell won't be the only company to take advantage of this as FAR ammendments are generally accepted at face value by other certification authorities. No one willing to moan that Sikorsky or MD are also taking advantage of this, or can MD not play because they don't have tail rotors? This can only be good news for companies as they get increased capacity because they know that pilots are always able to land with the wind on the nose, right?
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Interesting points raised!
BJC, I can assure you that Sikorsky has no interest in raising the MGW to swamp the tail rotor. In fact, the hover performance at max engine/transmission power leaves enough tail rotor thrust to achieve 35 to 50 knots sideward flight speed in the entire current Sikorsky fleet.
BJC, I can assure you that Sikorsky has no interest in raising the MGW to swamp the tail rotor. In fact, the hover performance at max engine/transmission power leaves enough tail rotor thrust to achieve 35 to 50 knots sideward flight speed in the entire current Sikorsky fleet.
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pot stirring
NickLappos,
Nice to see an OEM who doesn't design to the minimum FAR requirements for controllability! So, are you saying that since pedal margin wasn't limited at 17 kts that Sikorsky is unable to take advantage of this loop hole because the aircraft are engine performance limited instead?
No where did I see that smilie that shows a guy baiting a fishing hook and casting it....
All kidding aside (and because I don't want to get pounced by the Sikorsky fan club members in the forum) what an insane AC. I first got bit by this in a civil certified helicopter (I'm a military pilot) when I landed into wind and then tried to turn xwind to taxi to the ramp. Quite a surprise to encounter LTA in a brand new helicopter model in only moderate winds, even more surprising was it happening in proximity to other aircraft. I wish an instructor some where had pointed out the significance of this cert requirement before I had the opportunity to scare myself. I don't count encountering it in a 206/OH-58 as a surprise because you know it is coming...
Nice to see an OEM who doesn't design to the minimum FAR requirements for controllability! So, are you saying that since pedal margin wasn't limited at 17 kts that Sikorsky is unable to take advantage of this loop hole because the aircraft are engine performance limited instead?
No where did I see that smilie that shows a guy baiting a fishing hook and casting it....
All kidding aside (and because I don't want to get pounced by the Sikorsky fan club members in the forum) what an insane AC. I first got bit by this in a civil certified helicopter (I'm a military pilot) when I landed into wind and then tried to turn xwind to taxi to the ramp. Quite a surprise to encounter LTA in a brand new helicopter model in only moderate winds, even more surprising was it happening in proximity to other aircraft. I wish an instructor some where had pointed out the significance of this cert requirement before I had the opportunity to scare myself. I don't count encountering it in a 206/OH-58 as a surprise because you know it is coming...
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BJC,
The TR design is made to meet the needs of the mission/customer. For the S-76, we chose 35 knots of side flight with 10% remaining pedal travel, built a TR that could do that and met that handily. At 10,300 lbs, the S76 can go 51 knots sideways, at 11,700, it can go 35 knots.
For the Black Hawk, the design point was 45 knots sideward at 16,700 lbs at 4000 feet and 95 degrees F (7300' DA). That gives almost 60 knots sideways at sea level (I used to use the Doppler at 105Km/Hr to prove the point!)
The idea is to design each system to do the mission, and try to not use a flight manual caution as a safety device.
The TR design is made to meet the needs of the mission/customer. For the S-76, we chose 35 knots of side flight with 10% remaining pedal travel, built a TR that could do that and met that handily. At 10,300 lbs, the S76 can go 51 knots sideways, at 11,700, it can go 35 knots.
For the Black Hawk, the design point was 45 knots sideward at 16,700 lbs at 4000 feet and 95 degrees F (7300' DA). That gives almost 60 knots sideways at sea level (I used to use the Doppler at 105Km/Hr to prove the point!)
The idea is to design each system to do the mission, and try to not use a flight manual caution as a safety device.
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I feel a little better when I read Prouty saying repeatedly "for reasons I do not understand" when he is describing tail rotor vortices and LTE. A good description of the phenomenon (in his words) is at this link:
http://www.aviationtoday.com/rw/issu...ing/13637.html
NickLappos, too bad using a "flight manual caution as a safety device" is actually an accepted practice though. You probably never had to argue that point as a test pilot with management though
If you can honestly say that wasn't an issue then working in West Palm Beach just became my dream post-military flying job!
http://www.aviationtoday.com/rw/issu...ing/13637.html
NickLappos, too bad using a "flight manual caution as a safety device" is actually an accepted practice though. You probably never had to argue that point as a test pilot with management though
If you can honestly say that wasn't an issue then working in West Palm Beach just became my dream post-military flying job!
Prouty's repeated "for reasons I don't understand" in that R&W article is both amusing and enlightening. If the acknowledged guru of aerodynamics doesn't understand something, how are we mere mortals going to make heads or tails of it?
My own opinion is that the airflow interaction between the main and tail rotors is so chaotic as to be completely unpredictable in an absolute sense for every phase of flight every time. Witness Prouty's report of the Cobra performing a maneuver that the Apache could not (if I'm reading that passage correctly - it was worded strangely).
I have had a few pilots of Bells tell me that they prefer to land with right crosswinds as opposed to left because of their fear of LTE. They base this on the three wind diagrams "Umm...lifting" posted above in his post. I think it's funny. If you look at the first and third diagram in that post and sure enough, looks like left cross-winds can be dangerous!
But looking more closely, the real "danger" comes at wind speeds of above ten knots. I don't know about the rest of you, but in my experience with the 206, weathercock stability trumps tail rotor power. With a 10- or 15-knot left crosswind, the pilot may find himself with substantial right pedal applied. No way is the nose going to come around further to the right - at least, not until you get into a situation like Diagram #2 (which I don't think is *quite* that wide, but oh well). With a direct left crosswind, you don't have to worry about a spinning-wildly, out-of-control LTE situation. Keep full left pedal in and it probably wouldn't even go around one full turn, settling down into the wind. Still, it "concerns" a lot of pilots I've spoken with because of those dang diagrams.
If those diagrams are true, they're true for all helicopters, not just 206's.
For sure, left crosswinds in Bells and such make you work harder, dancing on the pedals as the t/r momentarily goes in and out of vortex ring state. The BO105 is particularly awful in this regard, and its t/r is way up high! Seems to me that in these conditions the airflow into the t/r is "confused" (would Prouty approve of that aerodynamical term?).
And finally, let me admit that all of my 206 experience (and I've got quite a bit) is at sea level or close to it. I've flown 206's with big and little tail rotors, and cannot recall a specific instance when I ran out of left pedal (touched the stop). It may have happened (the memory goes with age), but it was evidently a non-event. I've never spun, never had that edge-of-the-cliff feeling of impending disaster. Perhaps the JR suffers more at high altitudes. But all of these sky-is-falling people who condemn the 206 and claim that it has a "weak" or "insufficient" tail rotor must either never have flown one or are doing stranger things than this charter line dog has been doing for the last 25 years.
(Nick is quite vocal in his criticisms of the 206. He has, what, only about 6-or-7,000 r/w hours total? And I wonder how much of that time is actually in 206's? My logbook shows 6,600 hours of 206 time alone, increasing every day. Not that that makes me a Prouty - only that I have a lot of make/model time and I haven't died in an LTE accident. Yet. For reasons I don't understand.)
And finally, let me talk about the FH1100: Pilot friend of mine and I were out in one recently in a "fairly strong" wind (15-20 knots) and we could do nothing but hover into the wind. No left, no right, no nothing but straight or nearly so. Admittedly, with its Huey-like tailboom and fin the 1100 has more weathercock stability than a 206. Even so, I was surprised that we could not bring the nose around to the right without getting to full right pedal before getting much past 45 degrees. Odd.
My own opinion is that the airflow interaction between the main and tail rotors is so chaotic as to be completely unpredictable in an absolute sense for every phase of flight every time. Witness Prouty's report of the Cobra performing a maneuver that the Apache could not (if I'm reading that passage correctly - it was worded strangely).
I have had a few pilots of Bells tell me that they prefer to land with right crosswinds as opposed to left because of their fear of LTE. They base this on the three wind diagrams "Umm...lifting" posted above in his post. I think it's funny. If you look at the first and third diagram in that post and sure enough, looks like left cross-winds can be dangerous!
But looking more closely, the real "danger" comes at wind speeds of above ten knots. I don't know about the rest of you, but in my experience with the 206, weathercock stability trumps tail rotor power. With a 10- or 15-knot left crosswind, the pilot may find himself with substantial right pedal applied. No way is the nose going to come around further to the right - at least, not until you get into a situation like Diagram #2 (which I don't think is *quite* that wide, but oh well). With a direct left crosswind, you don't have to worry about a spinning-wildly, out-of-control LTE situation. Keep full left pedal in and it probably wouldn't even go around one full turn, settling down into the wind. Still, it "concerns" a lot of pilots I've spoken with because of those dang diagrams.
If those diagrams are true, they're true for all helicopters, not just 206's.
For sure, left crosswinds in Bells and such make you work harder, dancing on the pedals as the t/r momentarily goes in and out of vortex ring state. The BO105 is particularly awful in this regard, and its t/r is way up high! Seems to me that in these conditions the airflow into the t/r is "confused" (would Prouty approve of that aerodynamical term?).
And finally, let me admit that all of my 206 experience (and I've got quite a bit) is at sea level or close to it. I've flown 206's with big and little tail rotors, and cannot recall a specific instance when I ran out of left pedal (touched the stop). It may have happened (the memory goes with age), but it was evidently a non-event. I've never spun, never had that edge-of-the-cliff feeling of impending disaster. Perhaps the JR suffers more at high altitudes. But all of these sky-is-falling people who condemn the 206 and claim that it has a "weak" or "insufficient" tail rotor must either never have flown one or are doing stranger things than this charter line dog has been doing for the last 25 years.
(Nick is quite vocal in his criticisms of the 206. He has, what, only about 6-or-7,000 r/w hours total? And I wonder how much of that time is actually in 206's? My logbook shows 6,600 hours of 206 time alone, increasing every day. Not that that makes me a Prouty - only that I have a lot of make/model time and I haven't died in an LTE accident. Yet. For reasons I don't understand.)
And finally, let me talk about the FH1100: Pilot friend of mine and I were out in one recently in a "fairly strong" wind (15-20 knots) and we could do nothing but hover into the wind. No left, no right, no nothing but straight or nearly so. Admittedly, with its Huey-like tailboom and fin the 1100 has more weathercock stability than a 206. Even so, I was surprised that we could not bring the nose around to the right without getting to full right pedal before getting much past 45 degrees. Odd.
Prouty's repeated "for reasons I don't understand"
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I haven't been reading this thread for a while. It's taken an interesting turn.
Could someone help me out with what the argument actually is? Are we arguing if the 206 is a bad helicopter, if the 206 has a bad tail rotor, if LTE is a valid term, or is this something completely different.
In anticipation, here are my responses to the first three
- 206 might not be as competitive now, but it is definitely one of the more successful helicopters.
- Since the 206 is a successful helicopter, its hard to say it has an inherent fault. Sure a relatively low crosswind limitation is not desirable, but as NickL said, "The idea is to design each system to do the mission...", and the 206 has been able to do its job quite well, with the questionable tail rotor.
- LTE a valid term? Whatever you call it, it happens. If you don't give it a name someone else will. If the explanation of why things happen is wrong, that's bad. If you want to use an easy term to help pilots keep important points in their heads, I think thats a good idea.
Matthew.
Could someone help me out with what the argument actually is? Are we arguing if the 206 is a bad helicopter, if the 206 has a bad tail rotor, if LTE is a valid term, or is this something completely different.
In anticipation, here are my responses to the first three
- 206 might not be as competitive now, but it is definitely one of the more successful helicopters.
- Since the 206 is a successful helicopter, its hard to say it has an inherent fault. Sure a relatively low crosswind limitation is not desirable, but as NickL said, "The idea is to design each system to do the mission...", and the 206 has been able to do its job quite well, with the questionable tail rotor.
- LTE a valid term? Whatever you call it, it happens. If you don't give it a name someone else will. If the explanation of why things happen is wrong, that's bad. If you want to use an easy term to help pilots keep important points in their heads, I think thats a good idea.
Matthew.
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Attempt to explain
From Prouty
"A model helicopter mounted on a turntable in a low-speed wind tunnel permitted simulation of flight at all wind azimuths. The tail rotor was mounted on a separate support to investigate its performance at several positions with respect to the main rotor. Mounted far behind the main rotor, it suffered a thrust loss in left sideward flight due to the vortex ring state. But a position close to the main rotor produced no thrust loss — for reasons I do not understand."
Just as it is necessary to escape VRS in the main rotor by schedding it away through forward flight, the MR downwash provides for enough translational flow relative to the TR to reduce TR-VRS significantly.
delta3
"A model helicopter mounted on a turntable in a low-speed wind tunnel permitted simulation of flight at all wind azimuths. The tail rotor was mounted on a separate support to investigate its performance at several positions with respect to the main rotor. Mounted far behind the main rotor, it suffered a thrust loss in left sideward flight due to the vortex ring state. But a position close to the main rotor produced no thrust loss — for reasons I do not understand."
Just as it is necessary to escape VRS in the main rotor by schedding it away through forward flight, the MR downwash provides for enough translational flow relative to the TR to reduce TR-VRS significantly.
delta3
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The MR wash into the TR has nothing to do with TR Vortex Ring State, they occur at vastly different conditions.
The MR wash into the TR does cost about 5% of TR thrust, which is a blip on the HQ diagram for a helo with a right-sized TR and a disaster for a helo with a marginal TR. The issue is not the mystery of what happens, and "If I cant explain it, I can't control it." The issue is how the designer builds enough moxie in the design to handle the predictable effects that the real world provides. Like jack stall, LTE is predictable and preventable.
Evidence the fact that the OH-58D had LTE when the US Army first tested it, and they walked away from the aircraft. A few weeks later, a bigger TR was fitted, and the OH-58D has not had an LTE event since.
Mysteries like this are like picking your ears with a hammer and nail, if you are confounded by the blood, maybe the fault is not random circumstance.
For the record, IMHO the B-206 is a classic helo, and rightfully goes down in history as a great one. Like the S-61 however, just because it was great does not mean the waterline for safety is permanently set at the level that we have had to live with. If we mistakenly agree that the weaknesses of yesterday's helos is all that we ever need in future helos, we condemn all future pilots and passengers to suffer that way our fathers did. And for that we should be roasted slowly in hell.
The MR wash into the TR does cost about 5% of TR thrust, which is a blip on the HQ diagram for a helo with a right-sized TR and a disaster for a helo with a marginal TR. The issue is not the mystery of what happens, and "If I cant explain it, I can't control it." The issue is how the designer builds enough moxie in the design to handle the predictable effects that the real world provides. Like jack stall, LTE is predictable and preventable.
Evidence the fact that the OH-58D had LTE when the US Army first tested it, and they walked away from the aircraft. A few weeks later, a bigger TR was fitted, and the OH-58D has not had an LTE event since.
Mysteries like this are like picking your ears with a hammer and nail, if you are confounded by the blood, maybe the fault is not random circumstance.
For the record, IMHO the B-206 is a classic helo, and rightfully goes down in history as a great one. Like the S-61 however, just because it was great does not mean the waterline for safety is permanently set at the level that we have had to live with. If we mistakenly agree that the weaknesses of yesterday's helos is all that we ever need in future helos, we condemn all future pilots and passengers to suffer that way our fathers did. And for that we should be roasted slowly in hell.
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Allow me to strongly disagree.
Nick,
The point that I am making is that the MR downwash creates a 'benificiary' flow in the plane paralell to the TR. This benificiary flow has a positive effect on reducing the chance of a TR-VRS.
In the case of a light american style heli (I am referring to calculations of induced flows we made in a thread quite a long time ago) VRS will happen in the 10-15 knts wind from the left range, certainly if -as Prouty states- the disk is far away from the main rotor so that we get no interference and hence a 'clean' vortex.
The Mean Rotor down wash, washes that vortex away just in the same way as forward speed washes a MR vortex ring away. As you stated over and over again, even with small forward speed in case of the MR VRS the danger zone goes away. Well similarly even small components of beneficial MR downwash make the TR-VRS danger zone go away.
My point has -as far as I am concerned- no bearing on the question of sizing the B-206 tail rotor. Just as a MR-VRS has no bearing on lack or not of MR and engine power, the TR-VRS has no bearing on the power capability, it just depends on induced velocities. TR-power of course is needed in other TR-operating regimes.
delta3
The point that I am making is that the MR downwash creates a 'benificiary' flow in the plane paralell to the TR. This benificiary flow has a positive effect on reducing the chance of a TR-VRS.
In the case of a light american style heli (I am referring to calculations of induced flows we made in a thread quite a long time ago) VRS will happen in the 10-15 knts wind from the left range, certainly if -as Prouty states- the disk is far away from the main rotor so that we get no interference and hence a 'clean' vortex.
The Mean Rotor down wash, washes that vortex away just in the same way as forward speed washes a MR vortex ring away. As you stated over and over again, even with small forward speed in case of the MR VRS the danger zone goes away. Well similarly even small components of beneficial MR downwash make the TR-VRS danger zone go away.
My point has -as far as I am concerned- no bearing on the question of sizing the B-206 tail rotor. Just as a MR-VRS has no bearing on lack or not of MR and engine power, the TR-VRS has no bearing on the power capability, it just depends on induced velocities. TR-power of course is needed in other TR-operating regimes.
delta3
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delta,
If the TR gets to VRS at 15 knots, it means that the TR passes through the zero thrust point at this paltry speed. In other words, the helo needs no TR thrust because the weathercock stability is so strong at 15 knots that the fin provides all the anti-torque. I find this hard to believe.
Most TRs that I have analyzed reach the VRS point at 25 knots or more (30 to 35 knots for the S76, for instance.)
Also, it is my opinion that LTE is not achieved when the helo is at 15 knots, because at 15 knots the MR torque is low, since the MR is near/above ETL. LTE occurs when the MR torque comes rushing in as the speed decays to near zero. The concept of LTE as a mystery and caused by wondrous aerodynamic effects is a necessary component of the myth that single rotor helos can all get LTE, and the accompanying myth that we can't design to get away from LTE. Both myths are simply wrong.
I have a 1970 Russian helo aerodynamics text that shows the 5% decay in TR thrust available when the MR wake finds the TR. No big mystery, IMHO. Also, let me state that any TR that runs out of poop at 17 knots IGE will cause LTE if the helo is maneuvered near OGE under the same conditions, since MR torque is the biggest cause of LTE, because when MR torque is high, the TR thrust is fully consumed.
If the TR gets to VRS at 15 knots, it means that the TR passes through the zero thrust point at this paltry speed. In other words, the helo needs no TR thrust because the weathercock stability is so strong at 15 knots that the fin provides all the anti-torque. I find this hard to believe.
Most TRs that I have analyzed reach the VRS point at 25 knots or more (30 to 35 knots for the S76, for instance.)
Also, it is my opinion that LTE is not achieved when the helo is at 15 knots, because at 15 knots the MR torque is low, since the MR is near/above ETL. LTE occurs when the MR torque comes rushing in as the speed decays to near zero. The concept of LTE as a mystery and caused by wondrous aerodynamic effects is a necessary component of the myth that single rotor helos can all get LTE, and the accompanying myth that we can't design to get away from LTE. Both myths are simply wrong.
I have a 1970 Russian helo aerodynamics text that shows the 5% decay in TR thrust available when the MR wake finds the TR. No big mystery, IMHO. Also, let me state that any TR that runs out of poop at 17 knots IGE will cause LTE if the helo is maneuvered near OGE under the same conditions, since MR torque is the biggest cause of LTE, because when MR torque is high, the TR thrust is fully consumed.
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Point where TR-VRS occurs
Nick,
All depends on the loading of the heli and the size of the fin.
As you know I did all calculating experimenting with a R44 I and II.
Very light it requires little tail rotor, so the danger zone is in the low end.
Heavier it will require more tail rotor so the induced speed zone goes up in the ranges you indicate. (I did not check the precise speed here and now, and wish not to make a point of discord of that, if I have time I could dig into the archives, but that is not the point I am trying to make)
It now can look synical but a small tail rotor will have TR-VRS in a higher speed zone because its induced velocity will be higher (higher disk loading), so the under-powered B-206 will encounter it at higher left wind speeds....
There is by the way a big difference in my personal experience between R44-I and II MR-VRS risks. A light R44-II with the bigger MR is much more prone to MR-VRS because of the low disk loading. I would say 100% (my statistic, never had one in the R44-I but I had many in R44-II, so I always keep positive vario in that case)
d3
All depends on the loading of the heli and the size of the fin.
As you know I did all calculating experimenting with a R44 I and II.
Very light it requires little tail rotor, so the danger zone is in the low end.
Heavier it will require more tail rotor so the induced speed zone goes up in the ranges you indicate. (I did not check the precise speed here and now, and wish not to make a point of discord of that, if I have time I could dig into the archives, but that is not the point I am trying to make)
It now can look synical but a small tail rotor will have TR-VRS in a higher speed zone because its induced velocity will be higher (higher disk loading), so the under-powered B-206 will encounter it at higher left wind speeds....
There is by the way a big difference in my personal experience between R44-I and II MR-VRS risks. A light R44-II with the bigger MR is much more prone to MR-VRS because of the low disk loading. I would say 100% (my statistic, never had one in the R44-I but I had many in R44-II, so I always keep positive vario in that case)
d3
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Nick,
you said:
and then later:
how does that work?
you would need a whole lot of negative thrust I presume but in order to attempt that exercise (the sideways flight) you would have to transition through VRS somehow?
Philip
you said:
The TR design is made to meet the needs of the mission/customer. For the S-76, we chose 35 knots of side flight with 10% remaining pedal travel, built a TR that could do that and met that handily. At 10,300 lbs, the S76 can go 51 knots sideways, at 11,700, it can go 35 knots.
Most TRs that I have analyzed reach the VRS point at 25 knots or more (30 to 35 knots for the S76, for instance.)
you would need a whole lot of negative thrust I presume but in order to attempt that exercise (the sideways flight) you would have to transition through VRS somehow?
Philip
Last edited by Phil77; 1st Nov 2007 at 16:51. Reason: spelling
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Phil,
Yes, in racing sideward to the left at terrific speeds, you pass through VRS and then go to a windmill brake state on the TR (it is actually autorotating!) It is obviously where the TR downwash equals the sideward speed, in an S76 that is about 30 to 35 knots, in an Agusta 109 it is about 25 knots.
Pilots often see this in big winds in a pedal turn, when they experience a big pedal shift, usually when the aircraft behaves like it is jumpy and nervous in yaw.
delta3,
Sounds like you are doing very nicely with the simulation. Thanks for the insights!
Nick
Yes, in racing sideward to the left at terrific speeds, you pass through VRS and then go to a windmill brake state on the TR (it is actually autorotating!) It is obviously where the TR downwash equals the sideward speed, in an S76 that is about 30 to 35 knots, in an Agusta 109 it is about 25 knots.
Pilots often see this in big winds in a pedal turn, when they experience a big pedal shift, usually when the aircraft behaves like it is jumpy and nervous in yaw.
delta3,
Sounds like you are doing very nicely with the simulation. Thanks for the insights!
Nick
