Is a tail rotor really needed?
Senis Semper Fidelis
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Is a tail rotor really needed?
This has been floating in my slowly diminishing grey matter for a few months now, so if I share it with you folk out there perhaps I may get an answer that will help me.
We all know the tail rotor is there for the countering of applied power and to control the tendency for the Heli to act like a gyroscope, but could this be replaced by a counter spinning flywheel mounted on the main rotor shaft, that could/would be controlled by a clutch/brake like system. In my mind this would act as a counter measure to the energy of the spinning main rotor and G/box , as though it was a contra spinning rotor but without the complexity's of a second rotor and control rods and systems.
I realise it may sound very agricultural what I am asking, but I know that this does work on a ground operated machine, where a huge spinning drum(the main rotor on a heli) is controlled by a counter spinning flywheel which controlls the energy required to do its work, and acts as a shock load absorber.
Can you people out there say if this has ever been tried, or even whether you feel it would work.
My regards, and have a nice weekend
PRB
We all know the tail rotor is there for the countering of applied power and to control the tendency for the Heli to act like a gyroscope, but could this be replaced by a counter spinning flywheel mounted on the main rotor shaft, that could/would be controlled by a clutch/brake like system. In my mind this would act as a counter measure to the energy of the spinning main rotor and G/box , as though it was a contra spinning rotor but without the complexity's of a second rotor and control rods and systems.
I realise it may sound very agricultural what I am asking, but I know that this does work on a ground operated machine, where a huge spinning drum(the main rotor on a heli) is controlled by a counter spinning flywheel which controlls the energy required to do its work, and acts as a shock load absorber.
Can you people out there say if this has ever been tried, or even whether you feel it would work.
My regards, and have a nice weekend
PRB
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vfrpilotpb,
The tail rotor does not absorb or balance energy at all. It is there to exactly counter the torque that the main rotor imparts on the fuselage as it is spun. A gyro has nothing to do with it.
Basically, the main rotor does not want to spin unless pushed. The proof is how quickly it slows down if the engine is decoupled. This continuous push to keep it spinning requires that an opposite push is needed to balance the system. If the helo was a boat, and you pushed its blades around by hand, you would have to dig your shoes into the deck and lean into the blades as you push them, and your feet would push the boat around in the opposite rototion.
The tail rotor is used to allow the "boat" to grab the water and push back to keep the boat pointing straight.
You ground machinery comparison isn't correct because that machine is tied to the ground, so this side push is free, and you can't see it. Watch the engine of your car rotate in its mounts as you goose the throttle. If the car were not sitting on the ground but floating in the air, the car would roll in the opposite direction!
The gyro in that ground machine is probably used to smooth out the rotation by adding mass, a common trick.
The tail rotor does not absorb or balance energy at all. It is there to exactly counter the torque that the main rotor imparts on the fuselage as it is spun. A gyro has nothing to do with it.
Basically, the main rotor does not want to spin unless pushed. The proof is how quickly it slows down if the engine is decoupled. This continuous push to keep it spinning requires that an opposite push is needed to balance the system. If the helo was a boat, and you pushed its blades around by hand, you would have to dig your shoes into the deck and lean into the blades as you push them, and your feet would push the boat around in the opposite rototion.
The tail rotor is used to allow the "boat" to grab the water and push back to keep the boat pointing straight.
You ground machinery comparison isn't correct because that machine is tied to the ground, so this side push is free, and you can't see it. Watch the engine of your car rotate in its mounts as you goose the throttle. If the car were not sitting on the ground but floating in the air, the car would roll in the opposite direction!
The gyro in that ground machine is probably used to smooth out the rotation by adding mass, a common trick.
"Just a pilot"
It's possible to fly without the tail rotor-but it's very hard on the pilot. I've done it twice.
Additional to above posts-consider the fact the proposed flywheel would be heavy as heck.
Effective only as it accelerated/decelerated.
Precession's effects on flight.
Weren't there buses built with flywheels as energy sources? Seen any lately?
Additional to above posts-consider the fact the proposed flywheel would be heavy as heck.
Effective only as it accelerated/decelerated.
Precession's effects on flight.
Weren't there buses built with flywheels as energy sources? Seen any lately?
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To:Vfrpilotpb
Let’s assume that your concept is feasible and that the spinning wheel is below the transmission. The wheel would have to be of a large mass and spin at a high rate of speed in order to counter the torque developed by the spinning main rotor. Now, let’s look a bit closer at the spinning mass. My god, it’s a gyroscope rotor and it has all of the characteristics of a gyroscope. Precession and rigidity in space. I believe it is like a Momentum Wheel that is used to stabilize satellites. Any time the pilot moved his cyclic the blades would respond due to (pick one) gyroscopic or aerodynamic precession and the spinning mass would also be effected and apply a torque load to the aircraft that may be in conflict with the pilots’ cyclic input.
Let’s assume that your concept is feasible and that the spinning wheel is below the transmission. The wheel would have to be of a large mass and spin at a high rate of speed in order to counter the torque developed by the spinning main rotor. Now, let’s look a bit closer at the spinning mass. My god, it’s a gyroscope rotor and it has all of the characteristics of a gyroscope. Precession and rigidity in space. I believe it is like a Momentum Wheel that is used to stabilize satellites. Any time the pilot moved his cyclic the blades would respond due to (pick one) gyroscopic or aerodynamic precession and the spinning mass would also be effected and apply a torque load to the aircraft that may be in conflict with the pilots’ cyclic input.
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I think you analogy in explaining the function of the tail rotor was, to quote another post, "Technically unsophisticated".
Lu may have finally actually understood and agreed upon something Nick said.
Stay on topic. Quit the wind up's.
[ 30 November 2001: Message edited by: RW-1 ]
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To: Sling Load
It was not a dig. I did it with a smile on my face but you couldn't see it.
Maybe I should have included a smiling gremlin.
It was not a dig. I did it with a smile on my face but you couldn't see it.
Maybe I should have included a smiling gremlin.
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Vfrpilotpb
It has been said that the tail rotor consumes between 6 and 12 percent of the engines power, and none of this power is producing lift or forward thrust. This loss of power still exists in fast forward flight because the vertical tail wants to swing out to the side and that creates additional drag.
This was a primary reason for developing helicopters with multiple main rotors.
Just a totally unbiased opinion, mind you.
[ 30 November 2001: Message edited by: Dave Jackson ]
It has been said that the tail rotor consumes between 6 and 12 percent of the engines power, and none of this power is producing lift or forward thrust. This loss of power still exists in fast forward flight because the vertical tail wants to swing out to the side and that creates additional drag.
This was a primary reason for developing helicopters with multiple main rotors.
Just a totally unbiased opinion, mind you.
[ 30 November 2001: Message edited by: Dave Jackson ]
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To: Dave Jackson
“It has been said that the tail rotor consumes between 6 and 12 percent of the engines power, and none of this power is producing lift or forward thrust. This loss of power still exists in fast forward flight because the vertical tail wants to swing out to the side and thereby it represents additional drag’.
I believe that the Blackhawk and the C H-53 tail rotors produce lift because they are canted. This provides a slight lift vector and it could be more that slight. Most helicopters have aerodynamic surfaces that will maintain the fuselage in a given direction with the loss of the tail rotor. Not being a “PILOT”
It is my understanding that in the stated conditions there is minimal if no pitch in the tail rotor. Now, if you slow down under the stated conditions you will have a problem and most likely have to auto rotate or make a very fast run-on landing.
Regarding your comment about tandem rotor helicopters I don’t know if I can agree with that. To design a second rotor with its’ own drive line and a second transmission doesn’t quit equate. On a single rotor helicopter you can survive a loss of a tail rotor especially under the stated conditions above. If you lose a rear rotor and that has happened when you open your eyes you are looking into the face of Saint Peter.
Tandem rotor helicopters despite their complexity offer superior lifting power and a wide CG range.
As a matter of interest my first helicopter ride was in an HRP-1 the first military tandem rotor helicopter.
“It has been said that the tail rotor consumes between 6 and 12 percent of the engines power, and none of this power is producing lift or forward thrust. This loss of power still exists in fast forward flight because the vertical tail wants to swing out to the side and thereby it represents additional drag’.
I believe that the Blackhawk and the C H-53 tail rotors produce lift because they are canted. This provides a slight lift vector and it could be more that slight. Most helicopters have aerodynamic surfaces that will maintain the fuselage in a given direction with the loss of the tail rotor. Not being a “PILOT”
It is my understanding that in the stated conditions there is minimal if no pitch in the tail rotor. Now, if you slow down under the stated conditions you will have a problem and most likely have to auto rotate or make a very fast run-on landing.
Regarding your comment about tandem rotor helicopters I don’t know if I can agree with that. To design a second rotor with its’ own drive line and a second transmission doesn’t quit equate. On a single rotor helicopter you can survive a loss of a tail rotor especially under the stated conditions above. If you lose a rear rotor and that has happened when you open your eyes you are looking into the face of Saint Peter.
Tandem rotor helicopters despite their complexity offer superior lifting power and a wide CG range.
As a matter of interest my first helicopter ride was in an HRP-1 the first military tandem rotor helicopter.
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The tail rotor is there for two reasons. One is to counter the torque on the main rotor, the second is for yaw control.
A counter rotating mass could do the job of countering the torque, but at a cost: weight. If the mass turned at the same speed as the rotor and the mass was a ring about 4 feet radius with a 20 foot radius rotor (pulled numbers out of air), then the counter rotating mass needs to weigh about 17 times more than the rotors. If the mass turned twice as fast, it would weigh 1/2 that. A transmission is also needed, the faster you spin the mass the beefier the transmission will have to be.
That would counter most of the torque, but it wouldn't automatically adjust to every condition of flight. That's okay because you still need yaw control.
Conventional yaw control wouldn't rob as much power as it does now, but the weight of all the components won't change.
Yaw control in the counter rotating mass is possible if you have movable masses inside that could be moved radially using the yaw control pedals. I doubt if this would be easy to control...there would probably be a noticeable lag between input and response.
Of course, the engines must spin that counter rotating mass, so efficiency may actually drop.
___________
In short, it is possible. My new cordless screwdriver uses this technology. I doubt if any overall increase in efficiency will be realized.
A counter rotating mass could do the job of countering the torque, but at a cost: weight. If the mass turned at the same speed as the rotor and the mass was a ring about 4 feet radius with a 20 foot radius rotor (pulled numbers out of air), then the counter rotating mass needs to weigh about 17 times more than the rotors. If the mass turned twice as fast, it would weigh 1/2 that. A transmission is also needed, the faster you spin the mass the beefier the transmission will have to be.
That would counter most of the torque, but it wouldn't automatically adjust to every condition of flight. That's okay because you still need yaw control.
Conventional yaw control wouldn't rob as much power as it does now, but the weight of all the components won't change.
Yaw control in the counter rotating mass is possible if you have movable masses inside that could be moved radially using the yaw control pedals. I doubt if this would be easy to control...there would probably be a noticeable lag between input and response.
Of course, the engines must spin that counter rotating mass, so efficiency may actually drop.
___________
In short, it is possible. My new cordless screwdriver uses this technology. I doubt if any overall increase in efficiency will be realized.
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Unfortunately, Lu is wrong yet again. A spinning wheel cannot counter the torque of the main rotor, because once the wheel is up to speed, it takes no torque to spin it, so it can't counter the torque of the main rotor. The main rotor is continuously making lift, so it has the drag that creates torque (torque is really rotating drag).
The fact that this silly spinning wheel concept can be considered by an individual is a mark of "technical unsophistication".
For MD600driver,
I hate to bear the bad news, but inside the tailcone of your nice little NOTAR helicopter is a perfectly fine tail rotor, with a gearbox, pitch change mechanism and driveshaft. It is based on a Eurocopter fenestron, which it strongly resembles. Also buried inside your tailcone is the nozzel mechanism, with its control links and the rotating barrel. Also, you have the required rudder stability system, and the rudder controls. In all, you have more parts, heavier weight, more failure modes, more power wasted, and a much poorer flight envelope. Other than that, it is a fine idea.
The fact that this silly spinning wheel concept can be considered by an individual is a mark of "technical unsophistication".
For MD600driver,
I hate to bear the bad news, but inside the tailcone of your nice little NOTAR helicopter is a perfectly fine tail rotor, with a gearbox, pitch change mechanism and driveshaft. It is based on a Eurocopter fenestron, which it strongly resembles. Also buried inside your tailcone is the nozzel mechanism, with its control links and the rotating barrel. Also, you have the required rudder stability system, and the rudder controls. In all, you have more parts, heavier weight, more failure modes, more power wasted, and a much poorer flight envelope. Other than that, it is a fine idea.
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Good point, Nick.
I was wrong too. :o The mass will counter changes in torque, but will do nothing for continuous application of power.
I can make this work. Add some paddles so there is drag acting on the mass. You could even vary the pitch of the paddles for yaw control. Hey, why not set up the paddles to create a bit of lift. Wait a minute....that's Kamov.
Seriously now, counter rotating fly wheels that balance continuous loads do exist. A mass-spring mechanism or the like that draw energy from the engines to supply the required centripetal acceleration to prevent the mass from flying off will accomodate a continuous application of power.
There are the same failure modes, weight problems, and control difficulties that I mentioned in my previous (sniff snifff...wrong) post, plus more complexity with the mass-spring or similar system.
I was wrong too. :o The mass will counter changes in torque, but will do nothing for continuous application of power.
I can make this work. Add some paddles so there is drag acting on the mass. You could even vary the pitch of the paddles for yaw control. Hey, why not set up the paddles to create a bit of lift. Wait a minute....that's Kamov.
Seriously now, counter rotating fly wheels that balance continuous loads do exist. A mass-spring mechanism or the like that draw energy from the engines to supply the required centripetal acceleration to prevent the mass from flying off will accomodate a continuous application of power.
There are the same failure modes, weight problems, and control difficulties that I mentioned in my previous (sniff snifff...wrong) post, plus more complexity with the mass-spring or similar system.
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heedm,
The spinning mass does not counter the steady torque of the rotor, it cannot, except for the tiny fraction of its power that is lost to friction. The wheel will only balance the torque while the wheel is being spun up, which is where it makes its pay in the screwdriver. It counters the twist jump (strating torque) of the tool when the tool is turned on. It cannot counter the running torque of the tool against the work (such as when a sanding disk is being pressed against a wall).
Your calculations would work to counter the torque of the rotor during rotor run-up, but not during normal powered flight.
EDIT I noticed your post after I wrote this, heedm. You are right on. One of the major problems with helo development was the fixation on torque balance via counterrotation in the early days. The simplicity of the single rotor helicopter (and NOTAR is one, too) usually outweighs the slightly greater efficiency of the double rotor (tandem or coaxial) designs that compete.
The tail rotor uses about 3 to 6% of the main rotor power in a heavy hover, and almost nothing in cruise.
[ 30 November 2001: Message edited by: Nick Lappos ]
The spinning mass does not counter the steady torque of the rotor, it cannot, except for the tiny fraction of its power that is lost to friction. The wheel will only balance the torque while the wheel is being spun up, which is where it makes its pay in the screwdriver. It counters the twist jump (strating torque) of the tool when the tool is turned on. It cannot counter the running torque of the tool against the work (such as when a sanding disk is being pressed against a wall).
Your calculations would work to counter the torque of the rotor during rotor run-up, but not during normal powered flight.
EDIT I noticed your post after I wrote this, heedm. You are right on. One of the major problems with helo development was the fixation on torque balance via counterrotation in the early days. The simplicity of the single rotor helicopter (and NOTAR is one, too) usually outweighs the slightly greater efficiency of the double rotor (tandem or coaxial) designs that compete.
The tail rotor uses about 3 to 6% of the main rotor power in a heavy hover, and almost nothing in cruise.
[ 30 November 2001: Message edited by: Nick Lappos ]
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heedm, the incorporation of 'jump takeoff' in gyrocopters is an interesting example of rotational inertia in a rotor system.
______________
Nick, are you putting a little western spin on your percentages?
The deputy chief designer of Kamov Company claims, with a little eastern spin
, that the coaxial configuration can save 10-12% over the single rotor with a tail rotor.
Would you agree that the torque of the main rotor must be offset in both hover and forward flight? In forward flight the 'angular drag' of the vertical stabilizer 'takes over' for the tail rotor?
[ 30 November 2001: Message edited by: Dave Jackson ]
______________
Nick, are you putting a little western spin on your percentages?
The deputy chief designer of Kamov Company claims, with a little eastern spin
, that the coaxial configuration can save 10-12% over the single rotor with a tail rotor.Would you agree that the torque of the main rotor must be offset in both hover and forward flight? In forward flight the 'angular drag' of the vertical stabilizer 'takes over' for the tail rotor?
[ 30 November 2001: Message edited by: Dave Jackson ]
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Dave,
The vertical stabaliser can take over, to a certain degree, in forward flight but what about all the poor aloutte 3 jockeys and the other helis with no vertical stabaliser. Apparently though the AIII in forward flight can lose its tail rotor and fly using the aerodynamics of the aircrafts body. Me thinks Ill not try that one.
Lu I stand to be corrected here but I believe the only reason for canting the tail rotor, I think all on Military helis, is so the the heli is level when in the hover for easier bussing and de-bussing from both sides.
The vertical stabaliser can take over, to a certain degree, in forward flight but what about all the poor aloutte 3 jockeys and the other helis with no vertical stabaliser. Apparently though the AIII in forward flight can lose its tail rotor and fly using the aerodynamics of the aircrafts body. Me thinks Ill not try that one.
Lu I stand to be corrected here but I believe the only reason for canting the tail rotor, I think all on Military helis, is so the the heli is level when in the hover for easier bussing and de-bussing from both sides.