Bell 206: JetRanger and LongRanger
In the S-300C it is quite obvious that you can lift out of a tight spot by increasing the ERPM to 3200 instead of 3100 ERPM with same or less M.P.
If the Limit M.P. for the day is say 23" you can lift more by increasing the ERPM momentarily during take off to 3200 and still be within the 190 hp power limit. Are the above posts saying that I'm actally not pulling 190 hp @ 3100Erpm and 23" (MPL for the situation) but rather less HP and first when I reach 3200Erpm and 23" (absolute limit) then I'm pullin the whole 190 HP from the engine?
If I increase Rrpm by 10% I thought I would get 20% more lift out of it. Right? But is this 20% more lift then costing 10 or 20% more horsepower to make?
Also me experience is that by beeping up the NR to just above the 100% (manufactures often allow 101-2% NR) then I can easily lift a load I was unable to lift before at a lower NR setting.
Maybe theoretically you are using more horsepower but you are not busting any limits and still getting the job done!
If the Limit M.P. for the day is say 23" you can lift more by increasing the ERPM momentarily during take off to 3200 and still be within the 190 hp power limit. Are the above posts saying that I'm actally not pulling 190 hp @ 3100Erpm and 23" (MPL for the situation) but rather less HP and first when I reach 3200Erpm and 23" (absolute limit) then I'm pullin the whole 190 HP from the engine?
If I increase Rrpm by 10% I thought I would get 20% more lift out of it. Right? But is this 20% more lift then costing 10 or 20% more horsepower to make?
Also me experience is that by beeping up the NR to just above the 100% (manufactures often allow 101-2% NR) then I can easily lift a load I was unable to lift before at a lower NR setting.
Maybe theoretically you are using more horsepower but you are not busting any limits and still getting the job done!
Shawn,
After beeping the old girl down and seeing the Q drop off a bit...do you then raise the collective back to your orginal Q setting for cruise? One must remember to decrease collective prior to beeping it back up....or you might find yourself over torquing as I recall.
After beeping the old girl down and seeing the Q drop off a bit...do you then raise the collective back to your orginal Q setting for cruise? One must remember to decrease collective prior to beeping it back up....or you might find yourself over torquing as I recall.
Pitching over the optimum angle or best Lift/Drag Angle only gives you more induced drag(porportionally) Also Lift is velocity square so increasig the rpm at optimum blade angle should give you more Lift I think.....
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In my short time flying the 412, I've been quite surprised to see that when we beep back the RPM for cruise, the torque goes down at a constant collective pitch - this is quite contrary to 'normal', and indicates that the rotor is more efficient at this lower RPM.
However, at the hover I suspect that the lift/drag and RPM/torque factors work as advertised.
If I remeber right, we had that dicussion a few month ago and somebody -probably Nick- explained that with a slight lower rpm the there would be less torque because the higher drag (square) at higher RPM would result in more torque or something like that. I can not find that thread but it was a heated discussion.
Otherwise I have to talk to my shrink again, the halluzinations are back.
Otherwise I have to talk to my shrink again, the halluzinations are back.
Shawn has said it right, though I think the answer is a little misleading in this situation, though it is very difficult to determine exactly what the original poster was trying to say.
Torque will increase with an increase in RRPM. But, if power is held constant (N1, TOT) then TQ must decrease witn NR increase. As usual with helicopters, this rule can vary too, dependant upon blade stall alpha, etc.
Beeping up does not always advantage your operation for several reasons, not the least of which is there are no free lunches. The most important consideration is the lift/drag ratio, ie when you get the most lift for the least drag (in otherwords, TQ) Most manufacturers have an operating RRPM slightly above the optimum lift drag ratio, so that a slight loss of RRPM will actually be benefitial to the aircraft, not further degrade your ability to cope with whatever is causing the RRPM loss.
Excluding tailrotor, there are two power limits to be considered in a limited power situation (what the yanks sometimes call max performance take off). Firstly, and most commonly is transmission limited (ie TQ limited) where the engine will produce more tq than the Xmsn can handle. In this situation, you will be weighing up and increase in RRPM giving you more lift at a lower tq versus the requirement for more power due to the degraded lift drag ratio. This is only going to be of minimal benefit, and you will reach power limits earlier with the higher RRPM.
Power limited situations (as opposed to tq limited) are those where the engine reaches a power limit such as temp, N1 or even fuel flow before the Xmsn reaches it's limit. In the UH1 for example, N1 limiting is common, and the result will be (in this case) RRPM bleed. In the short and long ranger it is more likely that you will get N1 overspeed whist RRPM stays 100% and you think you are sweet with the tq limit. When the UH1 bleeds, the rotor becomes more efficient initially (in terms of lift/drag) before tapering off. Thus when you get into RRPM bleed, you will get a slight improvement to help you get out of jail - but push things too far, and you pay big time.
So perhaps the 206 guy is giving a useful hint, but my feeling is that it's applicability is very narrow, and without understanding those applicability limitations, you are setting yourself up for grief.
As for who/what/where should HEMS be done, that is simply a matter for an appropriate risk management application. 206s have been flown safely on HEMS for decades, and should continue to do so, but perhaps it is about time that we apply risk management now we understand it, and limit the types, weights, wx, and especially visibility and light levels, etc that you dispatch a 206 into?
Torque will increase with an increase in RRPM. But, if power is held constant (N1, TOT) then TQ must decrease witn NR increase. As usual with helicopters, this rule can vary too, dependant upon blade stall alpha, etc.
Beeping up does not always advantage your operation for several reasons, not the least of which is there are no free lunches. The most important consideration is the lift/drag ratio, ie when you get the most lift for the least drag (in otherwords, TQ) Most manufacturers have an operating RRPM slightly above the optimum lift drag ratio, so that a slight loss of RRPM will actually be benefitial to the aircraft, not further degrade your ability to cope with whatever is causing the RRPM loss.
Excluding tailrotor, there are two power limits to be considered in a limited power situation (what the yanks sometimes call max performance take off). Firstly, and most commonly is transmission limited (ie TQ limited) where the engine will produce more tq than the Xmsn can handle. In this situation, you will be weighing up and increase in RRPM giving you more lift at a lower tq versus the requirement for more power due to the degraded lift drag ratio. This is only going to be of minimal benefit, and you will reach power limits earlier with the higher RRPM.
Power limited situations (as opposed to tq limited) are those where the engine reaches a power limit such as temp, N1 or even fuel flow before the Xmsn reaches it's limit. In the UH1 for example, N1 limiting is common, and the result will be (in this case) RRPM bleed. In the short and long ranger it is more likely that you will get N1 overspeed whist RRPM stays 100% and you think you are sweet with the tq limit. When the UH1 bleeds, the rotor becomes more efficient initially (in terms of lift/drag) before tapering off. Thus when you get into RRPM bleed, you will get a slight improvement to help you get out of jail - but push things too far, and you pay big time.
So perhaps the 206 guy is giving a useful hint, but my feeling is that it's applicability is very narrow, and without understanding those applicability limitations, you are setting yourself up for grief.
As for who/what/where should HEMS be done, that is simply a matter for an appropriate risk management application. 206s have been flown safely on HEMS for decades, and should continue to do so, but perhaps it is about time that we apply risk management now we understand it, and limit the types, weights, wx, and especially visibility and light levels, etc that you dispatch a 206 into?
I posted the latest AEL EMS Jetranger crash preliminary report in the "Third US EMS Crash" thread. It speaks to some of the things being discussed here.
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SASless - yes we then increase the collective to get more power, and on descent before landing, since we're already decreasing torque before we beep up, there is no danger of overtorquing.
For the jetranger problem - if you can beep to a higher rotor RPM (and stay within the power on limits of N2/Nr), then you will get a bit more power (power = torque time RPM). Whether you're on the good or bad side of the lift/drag vs. AOA curve is another matter. In general, if you're that tight on power, you're probably asking for trouble sooner than later.
For the jetranger problem - if you can beep to a higher rotor RPM (and stay within the power on limits of N2/Nr), then you will get a bit more power (power = torque time RPM). Whether you're on the good or bad side of the lift/drag vs. AOA curve is another matter. In general, if you're that tight on power, you're probably asking for trouble sooner than later.
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Rotor Droop
Just to throw another angle on it.
Quote from the book
Exceeding the limits of 810c TOT or 100% may cause N1 topping with resultant rotor droop.
And all the beeping in the world wont get you out of than one!!!!
Can you imagine @ 50feet and the N1 starts to die a death.
I think the bottom line is that as a pilot if you are depending on the beep to give you another 2/3% on the NR to get you out of a spot. Just shut down and drive home.
Quote from the book
Exceeding the limits of 810c TOT or 100% may cause N1 topping with resultant rotor droop.
And all the beeping in the world wont get you out of than one!!!!
Can you imagine @ 50feet and the N1 starts to die a death.
I think the bottom line is that as a pilot if you are depending on the beep to give you another 2/3% on the NR to get you out of a spot. Just shut down and drive home.
In the working world...N1 Topping, Max TOT/EGT, is not all that uncommon. Take helicopters high or hot or both and you can experience that on a daily basis. In Twins....both engines do not run the same either...so you can Q splits/Temp Splits/N1 splits and one or both engines hitting a limit before the other or different limits at the same time.
Throw in steep mountainsides....smoke...and a forest fire....add a 150-200 foot longline...and you have the making of a new extreme sport that Hollywood will not dramatize. We are all to old, fat, ugly, and obnoxious.
Hang on....that blonde thing....Nicole...errr....Anna Nicole could play the leading role!
Throw in steep mountainsides....smoke...and a forest fire....add a 150-200 foot longline...and you have the making of a new extreme sport that Hollywood will not dramatize. We are all to old, fat, ugly, and obnoxious.
Hang on....that blonde thing....Nicole...errr....Anna Nicole could play the leading role!
"When you increase Nr speed, you gain more lift from the rotor system at any given collective pitch setting"
Not necessarily correct.
EG:
The S76 will lift better at 96% - 100%NR than at 107%NR.
The major benefits at 100% NR is reduced T5, allowing more surplus power for departure.
Fuel burn per NM is also influenced by NR with 107% in certain environ's leaning out the burn rate.
Still personally, I would depart and land with 107% set constantly. I figured and extra couple of % was money in the bank if OEI was required.
With the JR. So long as you are within manufacturers NR Overspeed limits then have the NR up before you need it. To demand it all at once at the bottom of an approach is recipe for settling with power. The JR fuel system cannot and will not keep up demand. If you are not of the habit to approach with a loaded disc then you had better change your flying style.
Higher NR will accomodate more TR control as well since it is operating at (roughly) 6 times the revolutions of the MR. It will manifest problems will in advance of the MR.
All this information is from personal experimentation and via PPRUNE discussions with Nick Lappos, who has abandoned us for the dark side ....
Not necessarily correct.
EG:
The S76 will lift better at 96% - 100%NR than at 107%NR.
The major benefits at 100% NR is reduced T5, allowing more surplus power for departure.
Fuel burn per NM is also influenced by NR with 107% in certain environ's leaning out the burn rate.
Still personally, I would depart and land with 107% set constantly. I figured and extra couple of % was money in the bank if OEI was required.
With the JR. So long as you are within manufacturers NR Overspeed limits then have the NR up before you need it. To demand it all at once at the bottom of an approach is recipe for settling with power. The JR fuel system cannot and will not keep up demand. If you are not of the habit to approach with a loaded disc then you had better change your flying style.
Higher NR will accomodate more TR control as well since it is operating at (roughly) 6 times the revolutions of the MR. It will manifest problems will in advance of the MR.
All this information is from personal experimentation and via PPRUNE discussions with Nick Lappos, who has abandoned us for the dark side ....
I'll get me coat......
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Bell206 vs Kiowa vne
This is aimed mainly at any Australian Kiowa pilots.
The Bell 206 Jetranger has a vne of 69 knots with a front door removed. I dont think I've ever seen doors on an Army Kiowa, do you seriously hack around at no more than 69 knots when you are operating or is their some difference in the airframes that allows a higher airspeed.
Cheers,
Hollywood
The Bell 206 Jetranger has a vne of 69 knots with a front door removed. I dont think I've ever seen doors on an Army Kiowa, do you seriously hack around at no more than 69 knots when you are operating or is their some difference in the airframes that allows a higher airspeed.
Cheers,
Hollywood
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I am a former US Army OH-58A/C guy. The US Army Kiowas had a Vne of 100 KIAS, doors off. Supposedly, speeds faster then that resulted in a form of control reversal - the aircraft response would not always follow a predictable pattern for a given cyclic input. One of the practical reasons for this limit was the back doors, with the original handle design, would blow open in flight. In cruise this was not a problem; however, landings were a different story. The reason for the slower 206 Vne is probably due to several factors - actual airspeeds flown during certification, etc. Hope this helps.
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G'day centerpage,
I had heard of the control reversal problem. 30 knots is quite a difference between the military and civilian version of essentially the same fuselage. (At least they are to my knowledge, feel free to correct me!) I suppose I'm wondering if the main difference is the fact that one helicopter is operated by military personnel and the other is used predominantly to carry civilian paying passengers.
Anyone else?
Cheers,
Hollywood
I had heard of the control reversal problem. 30 knots is quite a difference between the military and civilian version of essentially the same fuselage. (At least they are to my knowledge, feel free to correct me!) I suppose I'm wondering if the main difference is the fact that one helicopter is operated by military personnel and the other is used predominantly to carry civilian paying passengers.
Anyone else?
Cheers,
Hollywood
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There is no such thing as control reversal in the doors off condition, and I really wish that someone would get that taken out of the flight manual supplement for doors off in the 206.
It stems from the original 206A model which when flown at very light weight with the doors off, had what is known as negative static stability.
This means that if you trimmed at 60 KIAS and noted the cyclic stick position (Longitudinally), and accelerated to 70 KIAS and held 70 KIAS and noted the longitudinal cyclic position, the position at 70 KIAS would be slightly aft of the 60 KIAS position.
But if you weren't measuring it, you'd never notice because the change is so small as to be barely measurable (and there is no force trim in the 206 for you to notice any stick forces).
As the 206 series increased in empty weight, or if you flew it at something other than empty with nearly no fuel, the problem evidently went away, but it stays in the supplement.
But there never has been a stick reversal (i.e. push the stick forward to make the nose go up).
The OH-58 was not subject to the same certification rules (or possibly interpretation of the rules) as the Bell 206.
The Canadian Air Force flew the Bell 206BII to 100 KIAS with the doors off and found no handling issues.
It stems from the original 206A model which when flown at very light weight with the doors off, had what is known as negative static stability.
This means that if you trimmed at 60 KIAS and noted the cyclic stick position (Longitudinally), and accelerated to 70 KIAS and held 70 KIAS and noted the longitudinal cyclic position, the position at 70 KIAS would be slightly aft of the 60 KIAS position.
But if you weren't measuring it, you'd never notice because the change is so small as to be barely measurable (and there is no force trim in the 206 for you to notice any stick forces).
As the 206 series increased in empty weight, or if you flew it at something other than empty with nearly no fuel, the problem evidently went away, but it stays in the supplement.
But there never has been a stick reversal (i.e. push the stick forward to make the nose go up).
The OH-58 was not subject to the same certification rules (or possibly interpretation of the rules) as the Bell 206.
The Canadian Air Force flew the Bell 206BII to 100 KIAS with the doors off and found no handling issues.
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I was taught that all the 'negative static stability' stemmed from the disruption of airflow (with doors off) to the horizontal stabilizer on the tail, which normally would produce lift downwards to assist in longitudinal stability.
...or something like that
...or something like that
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Just a question from a non pilot. Doors in or out of position must surely effect the centre of gravity, in addition to the air flow through the fuselage. So what problems does this pose?