Tail Rotor Power Consumption
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I have a dream........
Thanks Nick for taking the time.
Were the blades on tail thrust device for the X-49 variable pitch?
Maybe at a higher the pitch needs to be less/more to allow a better induced flow & reduce drag?
At lower speed the pitch is more/less to give greater control where drag is not an issue, possibly give stability as well
Or maybe that might make the fan very inefficient and pointless.
Ok so the X-49 didn't really gain that much due to drag due to mass, a less than desirable yaw control & a marginal gain in airspeed.
A mechanical drive so far gives us the X-49 or a tail rotor type helo.
Why not a gas thrust vectored system?
The thrust comes from the power plant turbine engine that is also coupled to the gearbox that provides drive to the main rotor.
Or could even be a separate engine
Also...
Gas is ducted down the shorter tail and nozzle vectored to provide anti torque thrust.
Using a similar type nozzles like the Harrier.
The NOTAR uses a fan driven from the engine to provied a cold gas thrust for the tail vectoring nozzle.
Why not a hot gas?
Also the engine(s) that is providing the thrust could also be thrust vectored to give stability and might help should there be a tail thrust vectoring control failure?
And lets use the thrust vectored nozzle for assisting high load take offs would be an alternative and an efficient way of managing gases at low airspeed.
Again if it can get a stuck wing off the ground straight up.....
Now I am not thinking it will fly at speeds that jets do but it may just be a little faster than what we are doing now as I am not talking engines for thrust the size of a large fighter jet, but perhaps something the like on a personal jet.
Now, if we can de-couple the gearbox in flight and use the some gas from the engine to be diverted to the rotor system for tip thrust jet drive.......
Damn, my napkin is all soggy and the picture is all blurry... ooh a peanut.
Were the blades on tail thrust device for the X-49 variable pitch?
Maybe at a higher the pitch needs to be less/more to allow a better induced flow & reduce drag?
At lower speed the pitch is more/less to give greater control where drag is not an issue, possibly give stability as well
Or maybe that might make the fan very inefficient and pointless.
Ok so the X-49 didn't really gain that much due to drag due to mass, a less than desirable yaw control & a marginal gain in airspeed.
A mechanical drive so far gives us the X-49 or a tail rotor type helo.
Why not a gas thrust vectored system?
The thrust comes from the power plant turbine engine that is also coupled to the gearbox that provides drive to the main rotor.
Or could even be a separate engine
Also...
Gas is ducted down the shorter tail and nozzle vectored to provide anti torque thrust.
Using a similar type nozzles like the Harrier.
The NOTAR uses a fan driven from the engine to provied a cold gas thrust for the tail vectoring nozzle.
Why not a hot gas?
Also the engine(s) that is providing the thrust could also be thrust vectored to give stability and might help should there be a tail thrust vectoring control failure?
And lets use the thrust vectored nozzle for assisting high load take offs would be an alternative and an efficient way of managing gases at low airspeed.
Again if it can get a stuck wing off the ground straight up.....
Now I am not thinking it will fly at speeds that jets do but it may just be a little faster than what we are doing now as I am not talking engines for thrust the size of a large fighter jet, but perhaps something the like on a personal jet.
Now, if we can de-couple the gearbox in flight and use the some gas from the engine to be diverted to the rotor system for tip thrust jet drive.......
Damn, my napkin is all soggy and the picture is all blurry... ooh a peanut.
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Helofan, you have some interesting ideas but they would all suffer from poor efficiency. This translates as increased fuel burn and reduced payload/range.
The key to good propulsor efficiency is to have it handle a high mass flow rate of air. At high speeds you get a high mass flow rate, so can get away with a small diameter fan. At lower speeds to get the same mass flow rate you need a proportionately larger area. This is where any fan designed for a large speed range will suffer, being too heavy for high speed and too inefficient for low speed.
When X2 flies, likely sometime next year, it will outperform the X-49. It has a pusher prop which, by the constraint of physics, must be a compromise. My guess is that the test pilot will use the main rotor to accelerate up to 100 Ktas, then gradually feed in more propellor pitch to get to 250Ktas. It's interesting to note that some of the larger development variants have 2 pusher props, widely seperated. This will address the need for positive yaw control, which would otherwise be provided by a tail rotor.
John, are you penciled in as one of the X2 TPs when the machine is ready?
The key to good propulsor efficiency is to have it handle a high mass flow rate of air. At high speeds you get a high mass flow rate, so can get away with a small diameter fan. At lower speeds to get the same mass flow rate you need a proportionately larger area. This is where any fan designed for a large speed range will suffer, being too heavy for high speed and too inefficient for low speed.
When X2 flies, likely sometime next year, it will outperform the X-49. It has a pusher prop which, by the constraint of physics, must be a compromise. My guess is that the test pilot will use the main rotor to accelerate up to 100 Ktas, then gradually feed in more propellor pitch to get to 250Ktas. It's interesting to note that some of the larger development variants have 2 pusher props, widely seperated. This will address the need for positive yaw control, which would otherwise be provided by a tail rotor.
John, are you penciled in as one of the X2 TPs when the machine is ready?
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This subject is getting way off the topic of tail rotor power; but a response is ....
Graviman,
In your first paragraph, are you moving the vortex, or moving the goal posts?
___________________
Where are the 'extras' in this COMPLETE drivetrain?
This drivetrain also INCLUDES the rotorhubs and flight-controls, plus there is no need to include any "extra drivetrain/structure mass/cost" for a tail-rotor.
Are you saying that Germans are poor engineers?
_____________________
What 'standard' has the X2 set?
The 'standard' was set 30 years ago by the Sikorsky ~ S-69 (XH-59) ABC. The upcoming X2 will be compared against the S-69.
In your first paragraph, are you moving the vortex, or moving the goal posts?___________________
the expensive of extra drivetrain/structure mass/cost would put most engineers off.
Where are the 'extras' in this COMPLETE drivetrain? This drivetrain also INCLUDES the rotorhubs and flight-controls, plus there is no need to include any "extra drivetrain/structure mass/cost" for a tail-rotor.
Are you saying that Germans are poor engineers?
_____________________
the standard has to be against X2
What 'standard' has the X2 set? The 'standard' was set 30 years ago by the Sikorsky ~ S-69 (XH-59) ABC. The upcoming X2 will be compared against the S-69.
Last edited by Dave_Jackson; 26th Jan 2008 at 01:54. Reason: Removed humor.
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The Propulsor and the Helicopter
From Ga6riel on Rotary Wing Forum
The graph was probably intended for fixed-wing aircraft. However, it raises an interesting thought.
On the fixed-wing craft, the propulsor is responsible for overcoming; the parasitic drag of the fuselage, plus the induced and profile drag of the wings.
On the helicopter, the propulsor is only responsible for overcoming the parasitic drag of the fuselage. This is because the induced and profile drag of the rotor(s) will be overcome by the mechanical power going directly to the main-rotor(s). One caveat will be that the advancing blades have a higher velocity than that of the fuselage and this higher profile drag must be countered by the propulsor. Of course, with slower rotor rpm the profile drag to be counter by the propulsor will be reduced.
Perhaps this might imply that a given propulsor will propel a very clean helicopter at a faster speed than it would propel a comparable fixed-wing craft.
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Dave, blade vortex interaction is a fact of life. At the very least it means that the tip cannot be profiled to use as high a Cl/Cd as in a free stream. Even X2 designers have recognised this by using that neat tip profile (the tip vortex is thus a larger diam, so reducing its rotational velocity). An intermesher in hover puts the BVI further away from the tip, so would need to limit lift produced at this radius (ie max lift radius would move inboard).
My original question remains: how much power is lost in the Kmax from blade vortex interaction through lower blade tip? There must be some estimates somewhere?
Regarding powertrain: i have always agreed that the FL-282 has a very well thought out gearbox. I sent you some photos from Coventry air museum at one point. But you seem to be championing the interleaver over the intermesher, which from your layouts will need a more complicated drivetrain - perhaps it is you that is changing the goalposts.
But the general point remains. The conventional has very well understood dynamics up to 165Ktas. Since each new project is a risk you will have some convincing to do that the intermesher should be the config and not conventional.
For example R22 handles well enough, once you learn the quirks (mostly a cyclic response lag). If you don't wish the pilot to learn the quirks then SCAS is the way to go. If you don't like the sometimes messy development of hydraulics then electric actuators are becoming more powerful each year. This makes it hard to justify moving away from the positive yaw response provided by a tail rotor for some purist aerodynamic handling advantage.
Above 200Ktas it is a different story. The benefit of lateral symmetry (at least projected to plan view) is that the retreating side no longer needs to balance the advancing. Agreed S-69 has set the standard for X2 to beat.
Regarding your last post: it is unlikely that rotor aerodynamics will ever be as efficient as a wing, because as rotor technology moves on so does fixed wing technology...
My original question remains: how much power is lost in the Kmax from blade vortex interaction through lower blade tip? There must be some estimates somewhere?
Regarding powertrain: i have always agreed that the FL-282 has a very well thought out gearbox. I sent you some photos from Coventry air museum at one point. But you seem to be championing the interleaver over the intermesher, which from your layouts will need a more complicated drivetrain - perhaps it is you that is changing the goalposts.
But the general point remains. The conventional has very well understood dynamics up to 165Ktas. Since each new project is a risk you will have some convincing to do that the intermesher should be the config and not conventional.
For example R22 handles well enough, once you learn the quirks (mostly a cyclic response lag). If you don't wish the pilot to learn the quirks then SCAS is the way to go. If you don't like the sometimes messy development of hydraulics then electric actuators are becoming more powerful each year. This makes it hard to justify moving away from the positive yaw response provided by a tail rotor for some purist aerodynamic handling advantage.
Above 200Ktas it is a different story. The benefit of lateral symmetry (at least projected to plan view) is that the retreating side no longer needs to balance the advancing. Agreed S-69 has set the standard for X2 to beat.
Regarding your last post: it is unlikely that rotor aerodynamics will ever be as efficient as a wing, because as rotor technology moves on so does fixed wing technology...
Last edited by Graviman; 26th Jan 2008 at 11:33. Reason: Reread tidy-up only.
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Graviman;
So does mine. Are you talking about the vortex generated by the lower blade tip (which happens to be outboard of the other rotor) or are you talking about the lower blade tip cutting through a previously generated vortex.
A partial answer to your question is; the Kmax rotor has a low tip speed and a relatively low disk loading.
I'll research and champion anything that offers the possibility of an improvement over the existing.
Perhaps your perspective is from applied engineering, as opposed to design engineering.
Dave
My original question remains:
A partial answer to your question is; the Kmax rotor has a low tip speed and a relatively low disk loading.
But you seem to be championing the interleaver over the intermesher, which from your layouts will need a more complicated drivetrain - perhaps it is you that is changing the goalposts.
Perhaps your perspective is from applied engineering, as opposed to design engineering.
Dave
Last edited by Dave_Jackson; 1st Feb 2008 at 17:02. Reason: Removed confrontational remark.
Originally Posted by Graviman
John, are you penciled in as one of the X2 TPs when the machine is ready?
-- IFMU
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It may be costly and inefficient but it could work, lets let the gen II folk figure out how to make it efficiant, lets just make it work.
I am a multi gazillionaire, I dont care that I cant go as far or carry as much, I just want a different ride to the rest.
Its kinda like owning a V8 when a 2 liter will do the same thing with 2/3 less fuel. It might be over kill, but heck it sure is fun to drive.
( the only thing that should come in 2 liters is milk and orange juice )
You are right this thread has taken a different fork again.
Sorry all.
Back to the theories of tail rotor ( anti torque ) alternatives etc...
HF
I am a multi gazillionaire, I dont care that I cant go as far or carry as much, I just want a different ride to the rest.
Its kinda like owning a V8 when a 2 liter will do the same thing with 2/3 less fuel. It might be over kill, but heck it sure is fun to drive.
( the only thing that should come in 2 liters is milk and orange juice )
You are right this thread has taken a different fork again.
Sorry all.
Back to the theories of tail rotor ( anti torque ) alternatives etc...
HF
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Helofan, the point is that the conventional cannot be faulted for technical reasons. It is flawed, and a small percentage of power is lost driving the tail rotor. But any of the proposed alternatives have flaws too, either through lack of yaw authority or weight. The job of an engineer is to figure out which flaws the customer will accept.
I have no doubt Dave would gladly spend some of your gazillions for you:
http://uk.youtube.com/watch?v=CkDKb65daaA
http://uk.youtube.com/watch?v=6xeLhP...eature=related
I have no doubt Dave would gladly spend some of your gazillions for you:
http://uk.youtube.com/watch?v=CkDKb65daaA
http://uk.youtube.com/watch?v=6xeLhP...eature=related
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Grav,
Fear not, Dave's theories are sullied by neither experience nor practicality. It is always amusing to me that he assumes those rotorcraft experts who built 20,000 helicopters (which is 20,000 more than he) are all wrong. With some internet search and a grainy photo of a 1941 rotorhead, he can demolish any argument!
The pursuit of symmetry that is his mantra seems to be sparked by some internal asymmetry, frankly! Even Charlie Kaman, the inventor, dumped the syncropter configuration that Dave is wedded to, Dave has never tried to find out why.
Fear not, Dave's theories are sullied by neither experience nor practicality. It is always amusing to me that he assumes those rotorcraft experts who built 20,000 helicopters (which is 20,000 more than he) are all wrong. With some internet search and a grainy photo of a 1941 rotorhead, he can demolish any argument!
The pursuit of symmetry that is his mantra seems to be sparked by some internal asymmetry, frankly! Even Charlie Kaman, the inventor, dumped the syncropter configuration that Dave is wedded to, Dave has never tried to find out why.
Last edited by NickLappos; 27th Jan 2008 at 14:07.
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As you said, Nick - at least Piasecki is doing something. We've got a terrible record for R&D in the helicopter world compared to the fixed wing world.
Personally, I'd like to see more done with electric ducted fans on the side of the fuselage - some very high efficiencies have been developed with these devices. Also probably easier to schedule power with electrics...
Personally, I'd like to see more done with electric ducted fans on the side of the fuselage - some very high efficiencies have been developed with these devices. Also probably easier to schedule power with electrics...
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Shawn, I think part of this is that it costs 4 times the amount to develop a helicopter as a fixed wing, for a given payload mass. So i would expect helicopter design to be 4 times as conservative, or for there to be 1/4 of the R&D.
Electric drive definately offers many new possibilities.
Electric drive definately offers many new possibilities.
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Shawn said: "Personally, I'd like to see more done with electric ducted fans on the side of the fuselage - some very high efficiencies have been developed with these devices. Also probably easier to schedule power with electrics..."
Good idea. If these side thrusters could be rotated 90 degrees for vertical lift for takeoff the craft might lift an additional 30%. Could be attached to an existing helo. I have been considering this idea for some time.
slowrotor
Good idea. If these side thrusters could be rotated 90 degrees for vertical lift for takeoff the craft might lift an additional 30%. Could be attached to an existing helo. I have been considering this idea for some time.
slowrotor
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Nick;
The subject of this thread was 'Tail Rotor Power Consumption'; until; in Post #12 you said "Dave, as usual, your analysis is sandbagged in favor of your pet configuration" and then followed it up in Post #14 with "Two of those sources drink the same KoolAid that you do".
Your technical responses are underwhelming.
Then in Post #51 you go on to say "Even Charlie Kaman, the inventor, dumped the syncropter configuration that Dave is wedded to, Dave has never tried to find out why."
Perhaps it is you who should try to find out why.
Every concern that I have been able to discover about the intermeshing configuration, plus potential solutions.
To hell with me, let Charles Kaman, a former employee of United Technologies, talk to you in his own words. ~ from his book 'KAMAN: Our Early Years'.
"A tail rotor, used to counter the torque of the main rotor, used precious power without providing lift. But proposing an alternative to the tail rotor would have been premature--and out of the question for United Aircraft--as Sikorsky was completely committed to the tail rotor configuration."
"I remember once during the war encountering Reggie Brie, the British chief pilot, after a flight in one of the Sikorsky R-4 trail blazers. His arm was in muscular spasm from his effort to overcome these control forces."
Nick, a couple of questions.
~ Did, or did not, Sikorsky take a slow-motion film of Igor movements while piloting an early craft?
~ Is this relevant? "[Arthur Young (Bell)] Impressed by Igor Sikorsky's film, he concentrates on main rotor/antitorque tail rotor configurations." - from Charles Lumsden.
At a meeting with Erle Martin, Charles Kaman said " Erle, I'd like to develop this system [Synchropter] for United Aircraft. I'll continue to function with my own basic job, and I'll do this work on over-time or extra time, or however. All I ask is that you pick up the costs and provide me with the place and technician to do the basic spade work."
'His answer was swift, decisive and clear. "Charlie, we have our inventor at United Aircraft. His name is Igor Sikorsky. We don't need another one."'
________________________
Nick;
If you believe so strongly in the main&tail rotor configuration, you may wish to tell Boeing that they have be building helicopters wrong for the past 50 years.
Knowing where you're coming from, I love your arguments ~ flawed as they are.
Dave
The subject of this thread was 'Tail Rotor Power Consumption'; until; in Post #12 you said "Dave, as usual, your analysis is sandbagged in favor of your pet configuration" and then followed it up in Post #14 with "Two of those sources drink the same KoolAid that you do".
Your technical responses are underwhelming.
Then in Post #51 you go on to say "Even Charlie Kaman, the inventor, dumped the syncropter configuration that Dave is wedded to, Dave has never tried to find out why."
Perhaps it is you who should try to find out why.
Every concern that I have been able to discover about the intermeshing configuration, plus potential solutions.
To hell with me, let Charles Kaman, a former employee of United Technologies, talk to you in his own words. ~ from his book 'KAMAN: Our Early Years'.
"A tail rotor, used to counter the torque of the main rotor, used precious power without providing lift. But proposing an alternative to the tail rotor would have been premature--and out of the question for United Aircraft--as Sikorsky was completely committed to the tail rotor configuration."
"I remember once during the war encountering Reggie Brie, the British chief pilot, after a flight in one of the Sikorsky R-4 trail blazers. His arm was in muscular spasm from his effort to overcome these control forces."
Nick, a couple of questions.
~ Did, or did not, Sikorsky take a slow-motion film of Igor movements while piloting an early craft?
~ Is this relevant? "[Arthur Young (Bell)] Impressed by Igor Sikorsky's film, he concentrates on main rotor/antitorque tail rotor configurations." - from Charles Lumsden.
At a meeting with Erle Martin, Charles Kaman said " Erle, I'd like to develop this system [Synchropter] for United Aircraft. I'll continue to function with my own basic job, and I'll do this work on over-time or extra time, or however. All I ask is that you pick up the costs and provide me with the place and technician to do the basic spade work."
'His answer was swift, decisive and clear. "Charlie, we have our inventor at United Aircraft. His name is Igor Sikorsky. We don't need another one."'
________________________
Nick;
If you believe so strongly in the main&tail rotor configuration, you may wish to tell Boeing that they have be building helicopters wrong for the past 50 years.
Knowing where you're coming from, I love your arguments ~ flawed as they are.
Dave
Last edited by Dave_Jackson; 30th Jan 2008 at 04:14. Reason: Corrected a quotation mark
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A slightly different tack. A little while ago I was told that the fenestron design was not only using the effect of the fan as anti-torque but the load was shared with the force created by the curved surface around the ducting (courtesy of Mr Bernoulli). Obviously this is only in the hover and at low speeds as the aerofoil of the fin is helping in forward flight. Any comments?
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Jim,
Your assertion is quite correct - the issue is a hover power one, and the fenestron would be a loser because of its high disk loading, which consumes more power than a large open tail rotor. But the designers cleverly made the housing shape to expel the plume of air efficiently, like a rocket nozzle, so that the air "sees" an equivalently larger disk. This controlled efficient expansion of the air from the fenestron almost halves the power consumption, and makes the fenestron a real player as far as power consumed.
The design cost is still an issue, the wider ducting weighs more and has quite high drag. On the S76 fantail, the ducting added about 2 square feet to the total drag of the aircraft over a tail rotor. That is about 12 to 15% drag increase, a real design issue.
When the Boeing-Sikorsky team built the Fantail demonstrator, I joked that since the ducting was worth half the thrust of the device, why not just build two ducts and leave the fan off. I got some pretty silly stares from the engineers on that one! It took 600 hours of wind tunnel work to shape the duct properly to reduce the fan's power usage.
Dave, It is a shame, but you are starting to sound a bit manic, frankly.
Your assertion is quite correct - the issue is a hover power one, and the fenestron would be a loser because of its high disk loading, which consumes more power than a large open tail rotor. But the designers cleverly made the housing shape to expel the plume of air efficiently, like a rocket nozzle, so that the air "sees" an equivalently larger disk. This controlled efficient expansion of the air from the fenestron almost halves the power consumption, and makes the fenestron a real player as far as power consumed.
The design cost is still an issue, the wider ducting weighs more and has quite high drag. On the S76 fantail, the ducting added about 2 square feet to the total drag of the aircraft over a tail rotor. That is about 12 to 15% drag increase, a real design issue.
When the Boeing-Sikorsky team built the Fantail demonstrator, I joked that since the ducting was worth half the thrust of the device, why not just build two ducts and leave the fan off. I got some pretty silly stares from the engineers on that one! It took 600 hours of wind tunnel work to shape the duct properly to reduce the fan's power usage.
Dave, It is a shame, but you are starting to sound a bit manic, frankly.
Last edited by NickLappos; 30th Jan 2008 at 10:59.
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So electric motors either driving a fan or a fixed pitch ( or even variable would be nice ) power generated by the aircraft is out of the question?
If its safety thats an issue in this sort of device, it could be backed up by an emergency ducting system coming off the engine gases?
Should I stick to Leggo blocks and my little miniature Air Hog helicopter?
I'm a good driver!
HF
If its safety thats an issue in this sort of device, it could be backed up by an emergency ducting system coming off the engine gases?
Should I stick to Leggo blocks and my little miniature Air Hog helicopter?
I'm a good driver!
HF
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Helofan,
Some of the new generation high rpm pancake motors offer very good power to weight. There is also the possibility of designing in redundacy into the motor, which if brushless DC (IGBTs in place of commutator) will already be very reliable. This redundancy cannot be designed into a single tail rotor driveshaft, which is probably the conventional Cat A weakest link. I think e-drive fenestrons is a very real possibility in the near future.
Some of the new generation high rpm pancake motors offer very good power to weight. There is also the possibility of designing in redundacy into the motor, which if brushless DC (IGBTs in place of commutator) will already be very reliable. This redundancy cannot be designed into a single tail rotor driveshaft, which is probably the conventional Cat A weakest link. I think e-drive fenestrons is a very real possibility in the near future.
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Nick said;
Dave, It is a shame, but you are starting to sound a bit manic, frankly.
Dave, It is a shame, but you are starting to sound a bit manic, frankly.
However, when you provocatively and repetitively personalize your attack in a defamatory manner, I will respond.
Dave