Sikorsky X2 coaxial heli developments.
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Rigid Rotor,
#2
The concerns about the efficiency of the X2 relate to;
The aerodynamics in respect to the effects of reverse velocity, the high profile and parasitic drag and the rotor/propeller interaction.
~ and ~
The power train in respect to independently controlling the speed and torque distribution to the rotors and the propeller. You have commented on the use of a load splitter such as spider gears or 3-way planetary gear, to which I agree. However IMHO, there also must be a means of controlling the specific power distribution to the rotors v.s. propellers in addition to changing their collective pitch setting.
All of the above has been elaborate on in the previous 700 posting and the many linked web pages.
To my knowledge, Sikorsky has not addressed or solved these specific problems.
The primary shortcoming of the V-22 is that of limited capacity (hover). The primary shortcoming of the X2 will be forward speed (cruise). Both craft will/would spend more of their time in forward flight then in hover, which works to the disadvantage of the X2.
#3
I suspect that the Armed Services have become very despondent over the V-22 and the Comanche. When this is combined with the current and future economy, it is doubtfully that any external money will be forthcoming for the X2.
Perhaps Sikorsky should spend more time under the hood (Engineering) and less time polishing the paint job (Marketing).
Dave
Could you elaborate on #2 & #3?
The concerns about the efficiency of the X2 relate to;
The aerodynamics in respect to the effects of reverse velocity, the high profile and parasitic drag and the rotor/propeller interaction.
~ and ~
The power train in respect to independently controlling the speed and torque distribution to the rotors and the propeller. You have commented on the use of a load splitter such as spider gears or 3-way planetary gear, to which I agree. However IMHO, there also must be a means of controlling the specific power distribution to the rotors v.s. propellers in addition to changing their collective pitch setting.
All of the above has been elaborate on in the previous 700 posting and the many linked web pages.
To my knowledge, Sikorsky has not addressed or solved these specific problems.
The primary shortcoming of the V-22 is that of limited capacity (hover). The primary shortcoming of the X2 will be forward speed (cruise). Both craft will/would spend more of their time in forward flight then in hover, which works to the disadvantage of the X2.
#3
I suspect that the Armed Services have become very despondent over the V-22 and the Comanche. When this is combined with the current and future economy, it is doubtfully that any external money will be forthcoming for the X2.
Perhaps Sikorsky should spend more time under the hood (Engineering) and less time polishing the paint job (Marketing).
Dave
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While in engineering (critique) mode
Mart,
Here is an engineering challenge for you.
The earlier S-69 used a pair of jet engines to provide forward thrust. On the X2 the single propeller must produce the large thrust during high speed and high drag flight.
This thrust will be accompanied by a large torque, which must be counteracted by the fuselage. Airplanes have a large wing area to handle this torque, however the X2 has a very small blade area. What effect will this laterally unsymmetrical loading have on the craft?
From pictures it appears that Kamov's solution is coaxial propellers.
Dave
Here is an engineering challenge for you.
The earlier S-69 used a pair of jet engines to provide forward thrust. On the X2 the single propeller must produce the large thrust during high speed and high drag flight.
This thrust will be accompanied by a large torque, which must be counteracted by the fuselage. Airplanes have a large wing area to handle this torque, however the X2 has a very small blade area. What effect will this laterally unsymmetrical loading have on the craft?
From pictures it appears that Kamov's solution is coaxial propellers.
Dave
The Osprey has about the same installed power as a CH53E. It has payload slightly in excess of a Blackhawk. That would be about 12,300 hp and a 14,360lb useful load. This was from Nick's old presentation. On another 174 hp, the CH53E ekes out 36,515 lbs of useful load. The Blackhawk is listed as 10,484 lbs useful for its 3780 hp. Clearly, the Osprey is in the Very Large Engine camp.
Maybe at speed, tilt rotor technology can be more efficient than X2 technology. We will have to see what the numbers are when the X2 boys are done. Partly you have to look at the mission to determine efficiency. If you are just going to use the VTOL capability to takeoff, then go boring a long distance with little payload, then land VTOL, it is a lot of effort to build/pay for/maintain a tilt rotor compared to going a few extra miles to a runway with a real turboprop. If you are flying somewhere for a rescue, with a bunch of hovering, I bet the X2 technology comes ahead in efficiency pretty quickly.
If they achieve 250 kt cruise can you really say that cruise is a shortcoming?
Regarding the propeller torque effect in high speed cruise, I recon it would be about the same as any large turboprop - nothing. There is ample control power in both airplanes and helicopters to deal with things like that. You are getting blade area confused with control power.
You crack me up! Spend a little less time polishing that website and build something! Or keep polishing the website but why slag off the folks who are actually doing something?
-- IFMU
Maybe at speed, tilt rotor technology can be more efficient than X2 technology. We will have to see what the numbers are when the X2 boys are done. Partly you have to look at the mission to determine efficiency. If you are just going to use the VTOL capability to takeoff, then go boring a long distance with little payload, then land VTOL, it is a lot of effort to build/pay for/maintain a tilt rotor compared to going a few extra miles to a runway with a real turboprop. If you are flying somewhere for a rescue, with a bunch of hovering, I bet the X2 technology comes ahead in efficiency pretty quickly.
If they achieve 250 kt cruise can you really say that cruise is a shortcoming?
Regarding the propeller torque effect in high speed cruise, I recon it would be about the same as any large turboprop - nothing. There is ample control power in both airplanes and helicopters to deal with things like that. You are getting blade area confused with control power.
Perhaps Sikorsky should spend more time under the hood (Engineering) and less time polishing the paint job (Marketing).
-- IFMU
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IFMU
Interesting rebuttal.
Should technical discussion stop?
Perhaps people will stop reverse engineering Sikorsky's 'something'', if Sikorsky stop marketing their 'something'.
My original post said 'speculation'. That remark still stands.
And, when asked to support a position, I will.
Dave
Interesting rebuttal.
....... who are actually doing something?
Perhaps people will stop reverse engineering Sikorsky's 'something'', if Sikorsky stop marketing their 'something'.
My original post said 'speculation'. That remark still stands.
And, when asked to support a position, I will.
Dave
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Time out guys. :)
Gents,
There are some interesting technical discussions going on here, which is a good thing.
There is some mud slinging going on, which is a bad thing.
Can i just ask that we keep the debate about technical merits nice and peacible?
I ask this because i know that there are many technical contributors out there who have to make a judgement about whether or not to contribute to this thread. By discussing pros/cons at a technical level without flames it attracts these folks. If the thread descends into acrimony and flames any technical contributors will clam up and we all suffer.
This in not aimed at anyone in particular - i can just see some squabbles brewing.
Thanks.
There are some interesting technical discussions going on here, which is a good thing.
There is some mud slinging going on, which is a bad thing.
Can i just ask that we keep the debate about technical merits nice and peacible?
I ask this because i know that there are many technical contributors out there who have to make a judgement about whether or not to contribute to this thread. By discussing pros/cons at a technical level without flames it attracts these folks. If the thread descends into acrimony and flames any technical contributors will clam up and we all suffer.
This in not aimed at anyone in particular - i can just see some squabbles brewing.
Thanks.
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Re- controlling the prop torque-
- The closest example we have for inference is perhaps the AH-56 Cheyenne – I understand it did pretty well and had achieved a dash speed of around 210 Kts during flight testing. Of course, it did have wings with asymmetric incidence angles – perhaps to offset the prop torque?
- So then, given the fact that the Cheyenne (a single rotor configuration) managed the prop torque (with a bit of help from its wings), there’s perhaps little reason why the X-2 with two rigid rotors (and far superior control power) can’t manage it.
- The Cheyenne had a collective mounted twist grip to control its prop pitch – the pilot could dial in the required prop pitch angle and haul up on the collective – that’s quite the dream solution for a pilot to accelerate an attack helicopter!!
- However, I understand it also incorporated an automatic system to reduce prop pitch, so as to prevent main rotor RPM decay, in the event of engine failure – I’m sure the X-2 will be having something similar...
- So then - just a question from a simple dim-bulb test pilot -
-what's the fuss all about?
- The closest example we have for inference is perhaps the AH-56 Cheyenne – I understand it did pretty well and had achieved a dash speed of around 210 Kts during flight testing. Of course, it did have wings with asymmetric incidence angles – perhaps to offset the prop torque?
- So then, given the fact that the Cheyenne (a single rotor configuration) managed the prop torque (with a bit of help from its wings), there’s perhaps little reason why the X-2 with two rigid rotors (and far superior control power) can’t manage it.
- The Cheyenne had a collective mounted twist grip to control its prop pitch – the pilot could dial in the required prop pitch angle and haul up on the collective – that’s quite the dream solution for a pilot to accelerate an attack helicopter!!
- However, I understand it also incorporated an automatic system to reduce prop pitch, so as to prevent main rotor RPM decay, in the event of engine failure – I’m sure the X-2 will be having something similar...
- So then - just a question from a simple dim-bulb test pilot -
-what's the fuss all about?
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Post #728 is simply one person's speculation.
Speculation on this forum, be it about new rotorcraft or rotorcraft accidents, is open to reasoned rebuttal.
A short historical perspective:
Some of the more obvious improvements to the Advancing Blade Concept were presented in reports at the conclusion of the S-69 project. These consisted of; replacing the four engines with one, utilizing a pusher propeller, and significantly reducing the twist on the blades, etc.
At the time, some people were disappointed that the development was not continued. They believed that the ABC presented a unique and potentially viable way of providing rotorcraft with a meaningfully higher cruise speed. Later so did I, and therefore spent a few thousand hours researching, conceptualizing and developing potential methods of creating functional and practical solutions.
It eventually became apparent that my limited neuronal count was unable to find satisfactory answers to the concept's remaining limitations. However, I was willing to freely provide these ideas to others, on the Net and at an AHS convention, with the hope that they might 'spark' a better idea in others. I then moved on in search of other potential areas for VTOL improvement. Shortly thereafter, Sikorsky, with great fanfare, revived the thirty-year-old project.
Over time it became apparent that X2 was little more than a regurgitation of the old and that Sikorsky was not, in my opinion, addressing these meaningful limitations. At this point I began to question the motivation behind this 'project'.
If Sikorsky is has secretly developed one or more advancements, which overcome the ABC's limitations, AND the X2 was designed 'bolt-ready' to accept these advancements, I will sincerely apologize and eat crow.
Dave
Speculation on this forum, be it about new rotorcraft or rotorcraft accidents, is open to reasoned rebuttal.
A short historical perspective:
Some of the more obvious improvements to the Advancing Blade Concept were presented in reports at the conclusion of the S-69 project. These consisted of; replacing the four engines with one, utilizing a pusher propeller, and significantly reducing the twist on the blades, etc.
At the time, some people were disappointed that the development was not continued. They believed that the ABC presented a unique and potentially viable way of providing rotorcraft with a meaningfully higher cruise speed. Later so did I, and therefore spent a few thousand hours researching, conceptualizing and developing potential methods of creating functional and practical solutions.
It eventually became apparent that my limited neuronal count was unable to find satisfactory answers to the concept's remaining limitations. However, I was willing to freely provide these ideas to others, on the Net and at an AHS convention, with the hope that they might 'spark' a better idea in others. I then moved on in search of other potential areas for VTOL improvement. Shortly thereafter, Sikorsky, with great fanfare, revived the thirty-year-old project.
Over time it became apparent that X2 was little more than a regurgitation of the old and that Sikorsky was not, in my opinion, addressing these meaningful limitations. At this point I began to question the motivation behind this 'project'.
If Sikorsky is has secretly developed one or more advancements, which overcome the ABC's limitations, AND the X2 was designed 'bolt-ready' to accept these advancements, I will sincerely apologize and eat crow.
Dave
Happy Birthday Igor Sikorsky
Meanwhile, a flurry of news on X2 announced on the anniversary of Igor Sikorsky's birthday:
Sikorsky-s-X2-chases-world-speed-record
Chasing a world speed record, Sikorsky Aircraft's chief test pilot finally got the opportunity Tuesday to open up the Stratford company's latest helicopter, flying the X2 at 181 knots.
Kevin Bredenbeck took the aircraft out for a high-speed spin, putting the 216.5-knot speed record clearly on the horizon.
In 2005, Sikorsky unveiled its unique design that includes stacked, overhead counter rotating blades and a propeller at the rear of the aircraft instead of the traditional tail rotor. The company announced plans to go after the 250-knot goal in 2009, when it moved the project to its West Palm Beach, Fla., facility for high-speed testing.
The world's fastest helicopter flight was clocked at approximately 216.5 knots, or 249 mph, in August 1986 by John Eggington and Derek Clews aboard a Westland Lynx in England, according to the Federation Aeronautique Internationale of France.
Sikorsky said it could hit 250 knots, or 287 mph, within months, but much will depend on performance review and weather conditions. But the helicopter is meeting expectations, according to the program manager.
"The X2 technology demonstrator today exceeded average helicopter speeds of a conventional helicopter, generally 160-170 knots," said Jim Kagdis, program manager of Sikorsky Advanced Programs. "The demonstrator is proving out the technologies very well, from the active vibration control system to the fly-by-wire controls. There are no show-stoppers here so far, and now the program turns a corner, as this completes phase three of four. We are flying forward to the 250-knot cruise speed."
Analysts have said the X2 is one of the bright spots in a helicopter industry in need of more creativity and excitement.
If all goes as expected, the X2 could challenge for a number of potentially large military contracts, especially for reconnaissance.
Sikorsky announcement
-- IFMU
Sikorsky-s-X2-chases-world-speed-record
Chasing a world speed record, Sikorsky Aircraft's chief test pilot finally got the opportunity Tuesday to open up the Stratford company's latest helicopter, flying the X2 at 181 knots.
Kevin Bredenbeck took the aircraft out for a high-speed spin, putting the 216.5-knot speed record clearly on the horizon.
In 2005, Sikorsky unveiled its unique design that includes stacked, overhead counter rotating blades and a propeller at the rear of the aircraft instead of the traditional tail rotor. The company announced plans to go after the 250-knot goal in 2009, when it moved the project to its West Palm Beach, Fla., facility for high-speed testing.
The world's fastest helicopter flight was clocked at approximately 216.5 knots, or 249 mph, in August 1986 by John Eggington and Derek Clews aboard a Westland Lynx in England, according to the Federation Aeronautique Internationale of France.
Sikorsky said it could hit 250 knots, or 287 mph, within months, but much will depend on performance review and weather conditions. But the helicopter is meeting expectations, according to the program manager.
"The X2 technology demonstrator today exceeded average helicopter speeds of a conventional helicopter, generally 160-170 knots," said Jim Kagdis, program manager of Sikorsky Advanced Programs. "The demonstrator is proving out the technologies very well, from the active vibration control system to the fly-by-wire controls. There are no show-stoppers here so far, and now the program turns a corner, as this completes phase three of four. We are flying forward to the 250-knot cruise speed."
Analysts have said the X2 is one of the bright spots in a helicopter industry in need of more creativity and excitement.
If all goes as expected, the X2 could challenge for a number of potentially large military contracts, especially for reconnaissance.
-- IFMU
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Hi, I'm an engineer working on X2. I find the discussions going on here interesting. Though I can't really comment on what hasn't been publicly disclosed, I will say this, the people working on it are some of the best in our company, if not the industry.
The ABC struck me as a good idea and I wanted the company to revive it as well, and soon after the X2 program was started in 2005. Seeing it from the ground up has been a once in a lifetime experience, and being there for first flight was one of my most cherished memories.
Dave, I've gone through your site, and appreciate your collection of information there. However, I feel you've been knocking our small team unfairly. Not quite sure what limitations you are referring to but let's go through them shall we?
1) Vibration - ABC vibration was wicked at high speed. I mean the instrument panel was a blur! We are using AVC (in a novel way for Sikorsky), as has been stated in the press releases. Besides that we have a 4 bladed rotor, which helps. Test pilot comment is that its like sitting on a couch watching TV.
2) Loads - ABC vibratory loads were quite bad, due to hingeless rigid rotor at high speed. It also had high maneuvering loads. Obviously we have better materials to handle the high loads now as well as fly-by-wire.
3) Performance - L/D ratio was just as poor as every helicopter, 3-4. Though we don't have the 250 knot data yet, I expect we will double that. I know you've gone through Mr. Bagai's blade patent. I work with him and can tell you that figuring out the final solution was not easy. The shaft fairing, which can be seen in the popular sci article is another important invention for reducing drag.
4) Workload - the ABC required 2 pilots to fly. X2 has 1.
5) Acoustics - The ABC J-60's were loud. A prop can be clutched.
So...I'm sorry its not a Synchro (honestly, I doubt there would be much difference with a synchro ABC vs. coax...we can discuss if you wish), or that it doesn't go 400 knots like the Russians claim their magic VTOL does. Ideas are a dime a dozen in this industry. What matters is putting your thought into action, design, build, test, and fly!
The ABC struck me as a good idea and I wanted the company to revive it as well, and soon after the X2 program was started in 2005. Seeing it from the ground up has been a once in a lifetime experience, and being there for first flight was one of my most cherished memories.
Dave, I've gone through your site, and appreciate your collection of information there. However, I feel you've been knocking our small team unfairly. Not quite sure what limitations you are referring to but let's go through them shall we?
1) Vibration - ABC vibration was wicked at high speed. I mean the instrument panel was a blur! We are using AVC (in a novel way for Sikorsky), as has been stated in the press releases. Besides that we have a 4 bladed rotor, which helps. Test pilot comment is that its like sitting on a couch watching TV.
2) Loads - ABC vibratory loads were quite bad, due to hingeless rigid rotor at high speed. It also had high maneuvering loads. Obviously we have better materials to handle the high loads now as well as fly-by-wire.
3) Performance - L/D ratio was just as poor as every helicopter, 3-4. Though we don't have the 250 knot data yet, I expect we will double that. I know you've gone through Mr. Bagai's blade patent. I work with him and can tell you that figuring out the final solution was not easy. The shaft fairing, which can be seen in the popular sci article is another important invention for reducing drag.
4) Workload - the ABC required 2 pilots to fly. X2 has 1.
5) Acoustics - The ABC J-60's were loud. A prop can be clutched.
So...I'm sorry its not a Synchro (honestly, I doubt there would be much difference with a synchro ABC vs. coax...we can discuss if you wish), or that it doesn't go 400 knots like the Russians claim their magic VTOL does. Ideas are a dime a dozen in this industry. What matters is putting your thought into action, design, build, test, and fly!
Chief Bottle Washer
Helierez,
Welcome to Rotorheads, and thank you for taking the time to give us a factual post
Welcome to Rotorheads, and thank you for taking the time to give us a factual post
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Helierez, many thanks for your thoughts - i'd be interested to learn more about the concept work for X2.
I am just starting to hold my breath a little now. This is getting exciting!
----
Dave, nobody would fault your enthusiasm and efforts to stimulate development in the helicopter industry. As designers & engineers we both know that to take an idea forward requires many stages of investigation: evaluation, optimisation, validation, development, costing, & fabrication. This requires everyone involved to buy in to the numbers, which means that ideas tend to get driven towards the conservative. In helicopters, which among other things save lives, this is a good thing. I am quite sure your questions will have been considered at great depth during the early stages of X2.
One of the reasons i am developing my own helicopter performance calculation methodology is to allow me to ask exactly these sorts of questions and then produce the numbers. Good engineering relies on accurate numbers, without which any answer given cannot be complete.
Chasing a world speed record, Sikorsky Aircraft's chief test pilot finally got the opportunity Tuesday to open up the Stratford company's latest helicopter, flying the X2 at 181 knots.
----
Dave, nobody would fault your enthusiasm and efforts to stimulate development in the helicopter industry. As designers & engineers we both know that to take an idea forward requires many stages of investigation: evaluation, optimisation, validation, development, costing, & fabrication. This requires everyone involved to buy in to the numbers, which means that ideas tend to get driven towards the conservative. In helicopters, which among other things save lives, this is a good thing. I am quite sure your questions will have been considered at great depth during the early stages of X2.
One of the reasons i am developing my own helicopter performance calculation methodology is to allow me to ask exactly these sorts of questions and then produce the numbers. Good engineering relies on accurate numbers, without which any answer given cannot be complete.
Last edited by Graviman; 27th Jun 2010 at 12:35. Reason: Helierez post was removed at one point - shame.
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X2 vs. tilt-rotor for heavy lift
The Army spent a good deal of money performing trade studies and simulations comparing an X2 configuration against both twin and quad tilt rotor configurations for their 20ton Joint Heavy Lift program. I believe the results of those studies suggested the twin tilt rotor configuration was best. However, the study requirements also may have been focused more towards speed, altitude and range, which would naturally favor a fixed wing airframe.
Full tilt ahead: What will follow the V-22?-07/11/2006-Washington DC-Flight International
Of course, the X2 was a more mature technology than either of the JHL tilt rotor candidates. And the X2 is currently in flight test (with private funding), while the QTR and OSTR concepts have not progressed much beyond powerpoint slides (paid for with $30 million of DoD money). So you've got to give Sikorsky's X2 group credit for that.
Full tilt ahead: What will follow the V-22?-07/11/2006-Washington DC-Flight International
Of course, the X2 was a more mature technology than either of the JHL tilt rotor candidates. And the X2 is currently in flight test (with private funding), while the QTR and OSTR concepts have not progressed much beyond powerpoint slides (paid for with $30 million of DoD money). So you've got to give Sikorsky's X2 group credit for that.
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riff-raff,
I think that two of the five entrants were dropped from the competition, then Sikorsky was given some funding to prepare a presentation on their Variable-Diameter Tilt Rotor concept.
Variable-Diameter Tilt Rotor Dusted Off for JHL Study
Dave
I think that two of the five entrants were dropped from the competition, then Sikorsky was given some funding to prepare a presentation on their Variable-Diameter Tilt Rotor concept.
Variable-Diameter Tilt Rotor Dusted Off for JHL Study
Dave
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Dave,
Actually, three of the original five were dropped. Two concepts from Sikorsky and one from Boeing.
The three concepts that were dropped probably had the lowest technical risk. But apparently, they also did not give the performance leap that the program was looking for.
As for the VDTR, Sikorsky spent a great deal of time and money looking at that. And in the end they apparently came to the conclusion that the rotor's mechanical system would be too complex and unreliable. So I don't know why the JHL program would go back down that path. A variable speed drivetrain is much easier to do than a variable diameter rotor.
Regards,
riff_raff
Actually, three of the original five were dropped. Two concepts from Sikorsky and one from Boeing.
The three concepts that were dropped probably had the lowest technical risk. But apparently, they also did not give the performance leap that the program was looking for.
As for the VDTR, Sikorsky spent a great deal of time and money looking at that. And in the end they apparently came to the conclusion that the rotor's mechanical system would be too complex and unreliable. So I don't know why the JHL program would go back down that path. A variable speed drivetrain is much easier to do than a variable diameter rotor.
Regards,
riff_raff
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riff-raff,
Totally agree.
IMO, the engine should be operating near its optimal RPM at all times. During hover the rotors should be receiving 100% of the allocated power, and, this power allocation should smoothly transition, so that the Xrotors areX propeller is receiving 80-90% of the allocated power during cruise.
A major limitation is that existing variable power transmission devices, which would control this allocation, can consume a meaningful percentage of the engine's power.
This web page is the conceptualization a potential variable controller for an ABC helicopter. Theoretically, it will not consume power during hover and during cruise. However, it will consume approximately 3% of the power at the mid-range between hover and cruise. It also has some detail concerns. It was openly presented 5-years ago so that anyone can freely copy it, or improve on it.
One might hope that Sikorsky would openly or secretly develop a variable controller. One might also assume that this 'unexciting device' would be developed and tested before completing the envelope to wrap around it.
Dave
A variable speed drivetrain is much easier to do than a variable diameter rotor.
IMO, the engine should be operating near its optimal RPM at all times. During hover the rotors should be receiving 100% of the allocated power, and, this power allocation should smoothly transition, so that the Xrotors areX propeller is receiving 80-90% of the allocated power during cruise.
A major limitation is that existing variable power transmission devices, which would control this allocation, can consume a meaningful percentage of the engine's power.
This web page is the conceptualization a potential variable controller for an ABC helicopter. Theoretically, it will not consume power during hover and during cruise. However, it will consume approximately 3% of the power at the mid-range between hover and cruise. It also has some detail concerns. It was openly presented 5-years ago so that anyone can freely copy it, or improve on it.
One might hope that Sikorsky would openly or secretly develop a variable controller. One might also assume that this 'unexciting device' would be developed and tested before completing the envelope to wrap around it.
Dave
Last edited by Dave_Jackson; 2nd Jun 2010 at 18:14. Reason: Corrected big typing error
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Dave,
Depending upon what your definition of "meaningful percentage" is, I might agree or disagree. Here's a traction CVT that I've been working on. I did a design study for a split path MRGB variator sized for roughly 400 ft-lb at the variator input and a drive ratio of 2.0. The variator components would have added about 105 lbs to the MRGB. The variator input-to-output efficiency would have ranged between 93% and 95% during variable speed operation. With a traction drive, these losses are primarily due to EHL contact spin loss.
Being a split path configuration, only half the power passes through the variator. So worst case, the variable speed device itself would produce less than a 4% loss. Not as good as a gear system, but not too bad either.
The biggest issue with using a traction device like a CVT (ie. a power transfer device lacking positive engagement) in an aircraft drivetrain is how do you demonstrate that it has adequate fault tolerance/reliability?
Regards,
riff_raff
A major limitation is that existing variable power transmission devices, which would control this allocation, can consume a meaningful percentage of the engine's power.
Being a split path configuration, only half the power passes through the variator. So worst case, the variable speed device itself would produce less than a 4% loss. Not as good as a gear system, but not too bad either.
The biggest issue with using a traction device like a CVT (ie. a power transfer device lacking positive engagement) in an aircraft drivetrain is how do you demonstrate that it has adequate fault tolerance/reliability?
Regards,
riff_raff
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riff_raff,
Your patent for a variable speed transmission c/w elastohydrodynamic lubrication is intriguing and thought provoking.
This is just rudimentary musing but, ~ Without a differential in the power-train, the propeller on the X2 may work reasonably well with only a disengagement clutch and a feathering system.
The range of horsepower to be transmitted by the rotors will be large but their rotational speed change will be relatively small. Might a reduced version of your transmission serve the rotors? Any small slippage can be compensated for by the central processing unit.
In addition, could the backside of your cone (30) provide positive transmission when it is fully 'pressed against the backing crown gear (48). If this is possible, there shouldn't be any loss during hover, a medium loss during transition, and a very small loss during cruise, because in cruse the rotors will be receiving a significantly small percentage of the total power.
Dave
Your patent for a variable speed transmission c/w elastohydrodynamic lubrication is intriguing and thought provoking.
This is just rudimentary musing but, ~ Without a differential in the power-train, the propeller on the X2 may work reasonably well with only a disengagement clutch and a feathering system.
The range of horsepower to be transmitted by the rotors will be large but their rotational speed change will be relatively small. Might a reduced version of your transmission serve the rotors? Any small slippage can be compensated for by the central processing unit.
In addition, could the backside of your cone (30) provide positive transmission when it is fully 'pressed against the backing crown gear (48). If this is possible, there shouldn't be any loss during hover, a medium loss during transition, and a very small loss during cruise, because in cruse the rotors will be receiving a significantly small percentage of the total power.
Dave
Join Date: Nov 2004
Location: Cambridgeshire, UK
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Hmmm...
N41AX
N525SA
Same machine with different registry?
Riff,
Thanx for answer on hydraulics thread - wasn't sure what "EMAD" or "AMAD" mounting stood for in mechanical drive pumps?
I imagine you can't go into many details in public space, but is your CVT a lighter / higher power version of the torotrak transmission? Torotrak | Home
How close to production is it or are you just doing the concept work?
Keep an eye out for the Milner drive - large contact area: Milner CVT for High Torque Applications
Mart
N41AX
N525SA
Same machine with different registry?
Riff,
Thanx for answer on hydraulics thread - wasn't sure what "EMAD" or "AMAD" mounting stood for in mechanical drive pumps?
I imagine you can't go into many details in public space, but is your CVT a lighter / higher power version of the torotrak transmission? Torotrak | Home
How close to production is it or are you just doing the concept work?
Keep an eye out for the Milner drive - large contact area: Milner CVT for High Torque Applications
Mart
Last edited by Graviman; 3rd Jun 2010 at 11:54. Reason: Picture of torotrak CVT.
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There was me wondering if another X2 had come out to play!
BTW roughly what size of team was involved in developing X2?
I'm guessing there was a core concept team that then subcontracted systems to specialist groups like yourself.
Was the team based at Elmira or Stratford?
Mart
BTW roughly what size of team was involved in developing X2?
I'm guessing there was a core concept team that then subcontracted systems to specialist groups like yourself.
Was the team based at Elmira or Stratford?
Mart
Last edited by Graviman; 22nd Oct 2010 at 11:52. Reason: Was getting confused - Terex HQ is in Bridgeport, Ct...