T/R Loss of Effectiveness
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You want maximum rotor RPM whenever t/r thrust is an issue. When the main rotor slows, the tail rotor slows much more. You want at least 100% Nr.
The 206 weathervanes strongly. Once upon a time (that's how fairy tales start, you know) I was on an offshore platform and had a chip light. Returning to service required a 30 minute penalty run with "some pitch". No further clarification on how much pitch was required or permitted. So being bored at about the 20 minute mark, I started experimenting. I had about a 20 knot wind blowing, and started picking up to a hover, with my feet not actually touching the pedals, to see what would happen. Eventually, I was going from flat pitch to an OGE hover and back to flat pitch, with my feet flat on the floor. As long as the power change was slow and smooth, the nose didn't move at all, up and down and up and down. This tells me that there is no chance of LTE in a 206 as long as the nose is into the wind and the pilot is smooth. But poor pilot technique can get you into trouble in any aircraft.
The 206 weathervanes strongly. Once upon a time (that's how fairy tales start, you know) I was on an offshore platform and had a chip light. Returning to service required a 30 minute penalty run with "some pitch". No further clarification on how much pitch was required or permitted. So being bored at about the 20 minute mark, I started experimenting. I had about a 20 knot wind blowing, and started picking up to a hover, with my feet not actually touching the pedals, to see what would happen. Eventually, I was going from flat pitch to an OGE hover and back to flat pitch, with my feet flat on the floor. As long as the power change was slow and smooth, the nose didn't move at all, up and down and up and down. This tells me that there is no chance of LTE in a 206 as long as the nose is into the wind and the pilot is smooth. But poor pilot technique can get you into trouble in any aircraft.
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The feet flat on the floor is a technique I've used for years when I instruct on occasion....whether on takeoff, landing, in the cruise, or in the hover, they are to remove their feet from the pedals and land the aircraft safely....could be a neutral pedal situation, or a jammed left or right....good fun!
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These are recent questions from the EASA exams - would appreciate any comments:
What has the worst effect (counter-clockwise rotor system) once you experience "tail rotor vortex ring state"?
a) making a right pedal turn (to swing the nose to the right)
b) making a left pedal turn (to swing the nose to the left)
c) raising the power lever
d) decreasing the power lever
What is the best procedure (clockwise rotor system) once you have experienced "tail rotor vortex ring state"?
a) making a right pedal turn (to swing the nose to the right)
b) making a left pedal turn (to swing the nose to the left)
c) raising the power lever
d) decreasing the power lever
Phil
What has the worst effect (counter-clockwise rotor system) once you experience "tail rotor vortex ring state"?
a) making a right pedal turn (to swing the nose to the right)
b) making a left pedal turn (to swing the nose to the left)
c) raising the power lever
d) decreasing the power lever
What is the best procedure (clockwise rotor system) once you have experienced "tail rotor vortex ring state"?
a) making a right pedal turn (to swing the nose to the right)
b) making a left pedal turn (to swing the nose to the left)
c) raising the power lever
d) decreasing the power lever
Phil
Phil
must be a trick question. in first question answer would be lower collective as you would hit the ground with the ac spinning presumably very quickly! which makes the answer to q2 interesting !
But is this like the new nag question, what does 1 cm on the 1:500k chart represent on the ground, CAA answer 500,000 NM !!!!!!
must be a trick question. in first question answer would be lower collective as you would hit the ground with the ac spinning presumably very quickly! which makes the answer to q2 interesting !
But is this like the new nag question, what does 1 cm on the 1:500k chart represent on the ground, CAA answer 500,000 NM !!!!!!
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Well, it seems to me there are several answers - like most EASA questions they only tell half the story.
Talking of Nav, have they changed the one where sunset is when the centre of the Earth's disk goes below the horizon?
Phil
Talking of Nav, have they changed the one where sunset is when the centre of the Earth's disk goes below the horizon?
Phil
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Don't give me this, "The tail rotor gets into horizontal VRS!" bullcrap. It does not. And don't give me this, "The main rotor vortices interact and interfere with the tail rotor thrust!" bullcrap either. Those are all just girly, whiny excuses instead of just admitting that your piloting skills are so poor. KEEP THE DAMN NOSE STRAIGHT WITH THE PEDALS, ALRIGHT? I know you're already preoccupied making your two inept hands try to do the right things on the controls - I know that. But don't forget about your feet! They're in the fight as well. Use 'em or lose 'em.
FH1100 Pilot, hope you're not referring to me here, it sounds like it. let's see, 7000 Hrs without having scratched an aircraft, both fixed and rotary, mostly military and on a diverse range of operations, doesn't exactly seem to match up to "poor piloting skills" or "inept hands", as you so subtly put it. Don't know why you would assume I have some sort of lack of competency with LTE or landing into wind, I was merely interested in a conversation about some causes theories on LTE. It's an interesting subject.
Are you seriously saying when tracking rearwards no wind conditions, there is no loss of lateral and or longitudinal stability due to the effects of main rotor wash on the T/R and the horizontal/vertical stabilisers? I thought the 205 was well known for that?
Yes it seems there is a lot of "bullcrap" at times on this forum, in this case it seems from your direction......? Pity because you did make some good points, when you weren't making derogatory personal comments.
FH1100 Pilot, hope you're not referring to me here, it sounds like it. let's see, 7000 Hrs without having scratched an aircraft, both fixed and rotary, mostly military and on a diverse range of operations, doesn't exactly seem to match up to "poor piloting skills" or "inept hands", as you so subtly put it. Don't know why you would assume I have some sort of lack of competency with LTE or landing into wind, I was merely interested in a conversation about some causes theories on LTE. It's an interesting subject.
Are you seriously saying when tracking rearwards no wind conditions, there is no loss of lateral and or longitudinal stability due to the effects of main rotor wash on the T/R and the horizontal/vertical stabilisers? I thought the 205 was well known for that?
Yes it seems there is a lot of "bullcrap" at times on this forum, in this case it seems from your direction......? Pity because you did make some good points, when you weren't making derogatory personal comments.
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Bullcrap ... a bit strong
you certainly do get large tailrotor thrust variations when the aircraft is flying through the air slowly (15kts ish) in the same direction as the tail rotor is blowing air. This has been attributed to TR VR but it may not actually be the case, it may be just that thrust variations result from the tail rotor encountering it's wake. There is (should be) of course no difficulty in applying pedals as required to maintain heading, inputs may need to be nimble and authoritative, but there is likely to be lot's of Tail Rotor Authority to achieve what is required.
Pilot have historically been surprised by the response of the tail rotor and sometimes crash as a result (as we have seen with one of our poster's EC120.) (should they hang up their certificate or just get with the program as far as Authoritative tail rotor control is concerned?)
Another frequent cause of the mis-nomer (LTE) has been inadvertently having a negative airspeed and being surprised by natural weathercocking, as the helicopter yaws beyond the comprehension of the pilot.
It is fair to call these other versions of LTE Lack of Tailrotor Education, same nemonic, different problem (more pilot related). LTEd
Apart from countering torque the other use of a tail rotor is do fly the aircraft sideways or backwards through the air. If the tail rotor is not powerful enough to do this then it doesn't have sufficient authority to achieve the sideways flight intended, this just means it won't do it, the helicopter will default into wind with lot's of margin available to control the more into wind result.
you certainly do get large tailrotor thrust variations when the aircraft is flying through the air slowly (15kts ish) in the same direction as the tail rotor is blowing air. This has been attributed to TR VR but it may not actually be the case, it may be just that thrust variations result from the tail rotor encountering it's wake. There is (should be) of course no difficulty in applying pedals as required to maintain heading, inputs may need to be nimble and authoritative, but there is likely to be lot's of Tail Rotor Authority to achieve what is required.
Pilot have historically been surprised by the response of the tail rotor and sometimes crash as a result (as we have seen with one of our poster's EC120.) (should they hang up their certificate or just get with the program as far as Authoritative tail rotor control is concerned?)
Another frequent cause of the mis-nomer (LTE) has been inadvertently having a negative airspeed and being surprised by natural weathercocking, as the helicopter yaws beyond the comprehension of the pilot.
It is fair to call these other versions of LTE Lack of Tailrotor Education, same nemonic, different problem (more pilot related). LTEd
Apart from countering torque the other use of a tail rotor is do fly the aircraft sideways or backwards through the air. If the tail rotor is not powerful enough to do this then it doesn't have sufficient authority to achieve the sideways flight intended, this just means it won't do it, the helicopter will default into wind with lot's of margin available to control the more into wind result.
Listen Per, I wasn't referring to you specifically in my post...but if the shoe fits...
I've had guys tell me about what a terrible, weak, defective tail rotor the 206 has. To which I usually chuckle and ask, "Got much time in the 206, do you?" And then they usually shuffle their feet and admit that, well, no they do not. But they've read plenty!
Yeaaaah.
I see your 7,000 hours of combined f/w and r/w flight time, Per, that's very nice. 7,000 hours is a lot of flight time. Oh yeah, I've got 7,000 hours IN THE 206. I'm starting to get a feel for the aircraft.
Look, we know that helicopters don't always fly forward, right? Even though the fuselage may be stationary, it and the rotor may be "flying" backwards due to a strong tailwind. It shouldn't take a rocket scientist to think of how that wind will interact with the various control surfaces back there - control surfaces that are designed to *usually* see wind from the front.
If you're in a heavy 206 at an OGE hover with the wind off your five o'clock, you're not just asking for trouble, you're BEGGING for it. If you don't notice that your left leg is sticking pretty much straight out, then you'll probably be surprised when the dang thing snaps around.
But the tail rotor does not "stall" like an airplane wing - it's always producing thrust. And if the dumb pilot doesn't neutralize the pedals (crazily, some do!), he has a fair chance of stopping the rotation before it winds up. But like Gomer says, momentum is everything. You must, must, must hold the left pedal at FULL and reduce a bit of torque until the rotation stops, which it should/might as the nose comes around into the wind (then get the torque back in). Don't let it just keep going around and around as if you've had a tail rotor failure. Do not accept that you're just going to crash because your tail rotor is now in irrevocable "sideways" VRS or some crap. The tail rotor is still working.
But think about this silly "sideways" VRS thing. *IF* that were even possible, AS SOON AS the fuselage started to rotate around the mast the tail rotor disk would be at a different angle to the relative wind. Voila! Within a couple of degrees of yaw you are now *out* of "sideways VRS." That "sideways VRS" crap is the most ridiculous excuse for crashing a helicopter I've ever heard.
And yes, a wind from the left front can blow the MR vortices into the tail rotor in a 206. Yes, your feet will be "busy" as the TR thrust fluctuates a bit. But the left wind will help with the anti-torque, so you won't have as much left pedal in as if the wind were off your right-front, right? Win-win!
Any pilot who crashes a 206 with a wind from the left-front and blames it on the dreaded VRS is just making an excuse for his poor planning, performance, and decision-making.
Again Per, sorry if some of these fingers point at you. It's not intended that way. But some of you young guys who have these preconceived notions about the horrible 206 tail rotor ought to listen to guys like me and Gomer and others on this board who actually have flown the things enough to know the truth.
I've had guys tell me about what a terrible, weak, defective tail rotor the 206 has. To which I usually chuckle and ask, "Got much time in the 206, do you?" And then they usually shuffle their feet and admit that, well, no they do not. But they've read plenty!
Yeaaaah.
I see your 7,000 hours of combined f/w and r/w flight time, Per, that's very nice. 7,000 hours is a lot of flight time. Oh yeah, I've got 7,000 hours IN THE 206. I'm starting to get a feel for the aircraft.
Look, we know that helicopters don't always fly forward, right? Even though the fuselage may be stationary, it and the rotor may be "flying" backwards due to a strong tailwind. It shouldn't take a rocket scientist to think of how that wind will interact with the various control surfaces back there - control surfaces that are designed to *usually* see wind from the front.
If you're in a heavy 206 at an OGE hover with the wind off your five o'clock, you're not just asking for trouble, you're BEGGING for it. If you don't notice that your left leg is sticking pretty much straight out, then you'll probably be surprised when the dang thing snaps around.
But the tail rotor does not "stall" like an airplane wing - it's always producing thrust. And if the dumb pilot doesn't neutralize the pedals (crazily, some do!), he has a fair chance of stopping the rotation before it winds up. But like Gomer says, momentum is everything. You must, must, must hold the left pedal at FULL and reduce a bit of torque until the rotation stops, which it should/might as the nose comes around into the wind (then get the torque back in). Don't let it just keep going around and around as if you've had a tail rotor failure. Do not accept that you're just going to crash because your tail rotor is now in irrevocable "sideways" VRS or some crap. The tail rotor is still working.
But think about this silly "sideways" VRS thing. *IF* that were even possible, AS SOON AS the fuselage started to rotate around the mast the tail rotor disk would be at a different angle to the relative wind. Voila! Within a couple of degrees of yaw you are now *out* of "sideways VRS." That "sideways VRS" crap is the most ridiculous excuse for crashing a helicopter I've ever heard.
And yes, a wind from the left front can blow the MR vortices into the tail rotor in a 206. Yes, your feet will be "busy" as the TR thrust fluctuates a bit. But the left wind will help with the anti-torque, so you won't have as much left pedal in as if the wind were off your right-front, right? Win-win!
Any pilot who crashes a 206 with a wind from the left-front and blames it on the dreaded VRS is just making an excuse for his poor planning, performance, and decision-making.
Again Per, sorry if some of these fingers point at you. It's not intended that way. But some of you young guys who have these preconceived notions about the horrible 206 tail rotor ought to listen to guys like me and Gomer and others on this board who actually have flown the things enough to know the truth.
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If you are needing Full Left Pedal to counteract Hover Torque and you reduce the Throttle...along with reducing Torque you also reduce the efficiency of the Tail Rotor as the RPM drops. Question for you is which reduces quicker....the Torque or the counter torque force?
If the tail rotor thrust decreases quicker than the Torque decreases....you would have a bigger problem than before you went rolling off the Throttle.
If the tail rotor thrust decreases quicker than the Torque decreases....you would have a bigger problem than before you went rolling off the Throttle.
Indeed you are correct sir.
The retard of the throttle I mentioned it is actually the procedure for a High Pitch TR Control Jam, as this CAA paper ( http://www.caa.co.uk/docs/33/CAPAP2003_01.pdf) points out:
HP TRCFs in the hover result in a yaw rate build-up over the failure time. Reducing collective pitch increases the yaw rate, however, reducing MR speed, in conjunction with raising the collective, proved very effective in increasing MR torque and reducing TR thrust, the combination leading to a significant reduction in yaw rate and recovery from the low hover . (Section 9 page 4)
So yes, the TR thrust decreases quicker then the MR torque! I Did not think well before writing.
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SP
Stuck High T/R Thrust
that's more or less right.
there's a transient effect and a steady state effect
there is a large increase in the yaw rate initially while the throttle is being reduced (transient), once a low RRPM is established the yaw rate then will decrease as the t/r will be less effective but the torque required by the rotor will be similar (or possibly slightly greater)(steady state).
one yardstick for a helicopter design is whether, at reduced RRPM, the t/r capacity to arrest yaw continues after the m/r ceases to be able to provide lift=weight (and in turn if that could continue after the engine ceases to be able to produce enough torque)
the order of those limiting factors is nice to know
Stuck High T/R Thrust
that's more or less right.
there's a transient effect and a steady state effect
there is a large increase in the yaw rate initially while the throttle is being reduced (transient), once a low RRPM is established the yaw rate then will decrease as the t/r will be less effective but the torque required by the rotor will be similar (or possibly slightly greater)(steady state).
one yardstick for a helicopter design is whether, at reduced RRPM, the t/r capacity to arrest yaw continues after the m/r ceases to be able to provide lift=weight (and in turn if that could continue after the engine ceases to be able to produce enough torque)
the order of those limiting factors is nice to know
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In all deference to FH1100 Pilot's credentials, and excellent logic about how the aircraft has plenty of TR control, the accident record says otherwise. What pilots should do (FH1100 Pilot, too) is recognize that, when we have to get out the rubber stamp and blame the pilot, we should do so sparingly and wisely. If 95% of LTE accidents occur in one type of helo, then either the pilots are selectively crappy who fly it, or the aircraft has a weakness that pops up every now and then.
Yes, he can fly it for 7000 hours safely, and for that he gets a special recognition (I am serious) but not everybody has those skills, and a GOOD machine doesnt kill its occupants for being less than perfect.
As long as we are comfortable blaming pilots, we wont get better machines. How do I know? The genuises who gave us thet 206 double down on the issue by inventing the "wind from the nose" approvals where the TR is even MORE compromised! They applied that to get more lift for the 412 and other models, and gave a new generation of pilots reasons to get "pilot error" stamped on their headstones.
LTE can be designed out, a lot of good military designed helos show that to be true. In fact, the original Bell AAH competitor had the same yaw problems, and had its yaw system redesigned due to poor yaw TR control, as did the UH-1Y. The pilots who flew them after the fix could thank military test pilots for having higher safety standards than some ppruners who are all too willing to blame pilots.
Yes, he can fly it for 7000 hours safely, and for that he gets a special recognition (I am serious) but not everybody has those skills, and a GOOD machine doesnt kill its occupants for being less than perfect.
As long as we are comfortable blaming pilots, we wont get better machines. How do I know? The genuises who gave us thet 206 double down on the issue by inventing the "wind from the nose" approvals where the TR is even MORE compromised! They applied that to get more lift for the 412 and other models, and gave a new generation of pilots reasons to get "pilot error" stamped on their headstones.
LTE can be designed out, a lot of good military designed helos show that to be true. In fact, the original Bell AAH competitor had the same yaw problems, and had its yaw system redesigned due to poor yaw TR control, as did the UH-1Y. The pilots who flew them after the fix could thank military test pilots for having higher safety standards than some ppruners who are all too willing to blame pilots.
