Naked Science Forum
General Science => General Science => Topic started by: Supervolant on 18/12/2023 12:45:09
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Hello Forum Members,
I am currently occupied in exploring innovative solutions for aerospace propulsion systems, with a specific focus on enhancing efficiency and reducing noise. I am reaching out to seek your expertise in evaluating the feasibility of a concept I've been pondering about.
In my quest to optimize aerospace propulsion, I am contemplating repositioning the electric drive motor from the center to the rim of the system, into the duct itself. This shift presents both advantages and challenges. Notably, it eliminates the tip gap between the rotor and stator, addressing significant pressure losses observed in current aerospropulsion systems. Additionally, this configuration enables the system to intake and expel air more efficiently, enhancing overall aerodynamic performance.
While I believe the rim-driven aspect is feasible, my next consideration involves the removal of classical roller ball bearings to reduce friction and associated inefficiencies. The proposed solution is a magnetic levitating setup. Imagine a high-speed maglev train executing an infinite loop. Makes sense?
To achieve a completely contactless setup and minimize friction to the bare minimum dictated by aerodynamics, the levitation unit must exert a force capable of not only lifting the rotor but also supporting the entire weight of the aircraft, including loads from aerodynamics and general aircraft control.
As someone more inclined towards creativity than mathematics, I am seeking assistance in performing basic calculations to determine the strength required for electromagnets to make this concept a reality.
Your insights and expertise would be immensely valuable in assessing the viability of this propulsion system modification. I appreciate any input or calculations you can provide on the strength of electromagnets needed for this ambitious concept.
This topic is something I am greatly passionate about. I am really looking forward to start a conversation and receive your input.
Thank you for your time and consideration.
- Robert
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Hello & Welcome back to TNS!
Responses might be slow & delayed, due to Holidays.
I'm No expert on the Topic, but it's Very interesting.
If already there are Electric motors involved, then you sure got a good power backup.
Could that same power not be used to create a Repulsion field effect?
Air pressure might be a Strong resistant force, What if a Birdy hits the system?
ps - wish there was an image in your Thread, I'm unable to Visualize.
(Policy against Advertising is Strict & Stringent)
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I am contemplating repositioning the electric drive motor from the center to the rim of the system, into the duct itself. This shift presents both advantages and challenges. Notably, it eliminates the tip gap between the rotor and stator,
Could you expound on this? It sounds like you are saying if you relocate the electric motor, the clearance between the rotor and the stator changes. That wouldn't make any sense.
You said this motor is part of the 'system'. What is the 'system'?
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It sounds as if the suggestion is to use the blades as spokes on a wheel, with a rim around the outside binding them together.
- Magnetic drive is applied to the rim
- There is no central bearing, but the rim is levitated away from the cowling on all sides.
- The gap between the blades and cowling is replaced by a gap between rim and cowling
A couple of random observations:
1) I am a bit concerned about the strength required of the rim.
- I understand that jet engine blades are grown by directional crystallisation, giving them great radial strength, allowing them to be light.
- I think the rim would require considerable strength and mass, which would be heavier than the current designs(?)
2) Magnetic levitation usually requires powerful magnets, which suggests superconducting magnets. These require considerable thermal insulation, which might be hard to fit inside an engine duct(?)
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Hello & Welcome back to TNS!
Could that same power not be used to create a Repulsion field effect?
Air pressure might be a Strong resistant force, What if a Birdy hits the system?
ps - wish there was an image in your Thread, I'm unable to Visualize.
(Policy against Advertising is Strict & Stringent)
Hello Zer0,
thank you! It's been a few years...
Indeed, the same magnets propelling the system can also generate the repulsion effect, theoretically enabling contactless magnetic levitation.
Air pressure will consistently play a role, and in the event of a collision with a bird, it is crucial to contain the damage without spreading it to other aircraft systems. Special containment rings are designed to address this concern.
Unfortunately, we may need to proceed without a picture for the time being.
I am contemplating repositioning the electric drive motor from the center to the rim of the system, into the duct itself. This shift presents both advantages and challenges. Notably, it eliminates the tip gap between the rotor and stator,
Could you expound on this?
It sounds like you are saying if you relocate the electric motor, the clearance between the rotor and the stator changes. That wouldn't make any sense.
You said this motor is part of the 'system'. What is the 'system'?
Hello Origin,
the electric motor would feature its stator and rotor configuration within the engine duct, departing from the conventional placement in the central hub typical of other ducted fan designs. Clearances, a subject open to engineering solutions, are not a primary concern.
With the 'system' is the propulsion system as a whole meant.
It sounds as if the suggestion is to use the blades as spokes on a wheel, with a rim around the outside binding them together.
- Magnetic drive is applied to the rim
- There is no central bearing, but the rim is levitated away from the cowling on all sides.
- The gap between the blades and cowling is replaced by a gap between rim and cowling
A couple of random observations:
1) I am a bit concerned about the strength required of the rim.
- I understand that jet engine blades are grown by directional crystallisation, giving them great radial strength, allowing them to be light.
- I think the rim would require considerable strength and mass, which would be heavier than the current designs(?)
2) Magnetic levitation usually requires powerful magnets, which suggests superconducting magnets. These require considerable thermal insulation, which might be hard to fit inside an engine duct(?)
Hello Evan,
It appears that you have a good understanding of the subject matter. I don't find any contradictions in the first part of your response; our perspectives are aligned.
Regarding your additional observations:
- I believe that there's no need for concern in this regard. In fact, this design offers several advantages over classical designs in terms of the strength and longevity of the rotor. The outer ring will function as a stress tuner, enhancing strength and operating in compression rather than tension, which is notably favorable for metallic parts.
While the system might potentially be heavier, our primary focus lies in the thrust-to-weight ratio of the entire system and its energy consumption. If these values prove more promising, irrespective of the weight, it is worth delving deeper into this design.
- Agreed, exploring superconducting materials/magnets may be an option. However, it's crucial to acknowledge the substantial increase in energy requirements associated with this design decision. As such, I believe it's best to consider alternatives to avoid such heightened energy demands that are, as you also rightfully pointed out, associated with space and weight increases.
Thank you for your insights.
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I don't think the propeller or turbine shaft is lifting the mass of the aircraft - that's the job of the wings! - but your problem is maintaining clearance in manoeuver, turbulence or ground run: the rotor is effectively a gyroscope that wants to continue pointing in the same direction, whilst the rest of the aircraft is jiggling up and down or rotating.
You also need longitudinal constraint - the rotor is transferring forward thrust to the airframe. The conventional axial roller bearing provides all the required constraints and doesn't let the rotor drop when switched off.
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I don't think the propeller or turbine shaft is lifting the mass of the aircraft - that's the job of the wings! - but your problem is maintaining clearance in manoeuver, turbulence or ground run: the rotor is effectively a gyroscope that wants to continue pointing in the same direction, whilst the rest of the aircraft is jiggling up and down or rotating.
You also need longitudinal constraint - the rotor is transferring forward thrust to the airframe. The conventional axial roller bearing provides all the required constraints and doesn't let the rotor drop when switched off.
Hello Alancalverd,
please excuse my oversight; I should have been more specific on this matter. Now, in the context of a vertical takeoff and landing (VTOL) aircraft, the rotor actually must lift the entire mass of the aircraft during takeoff and landing. And in case of a non-winged aircraft also throughout all other flight envelopes. Consequently, in order to remain contactless the magnets must possess the capability to compensate for this. The focal point of this discussion is to determine if the required magnetic strength is achievable.
Let's consider a scenario with four of these rotors and an aircraft weighing 2 tons, providing a simple and rudimentary example for ease of calculation. For hover, one rotor needs to generate a minimum of 500kg of thrust. Let's use a value of 750kg for vertical lift, necessitating each magnetic levitator to stabilize the rotor and withstand the entire aircraft weight. Additionally, considering accelerative g-forces, this hypothetical value may need to reach 1000kg of magnetic force. Is this feasible?
In the case of forward flight and high-g turns, these values could potentially increase by several factors. Therefore, the constraint must be applicable in all axes. For all other movements and 'jiggling' we will pretend that clever enough control algorithms can be made and take care off this challenge.
Yes convential roller bearing provide the neccesary support on common engines, however the goal is to create a contactless system that minimizes friction. One could use ball bearings, strategically placed around the rotor for auxiliary support when power is off or rotational speeds are yet insufficient to keep levitation stable.
Let me know what you think.
Thank you for your input.
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Ball bearings around the edge would be worse! the edge of the rotor is travelling much faster than the center, so the balls will be spinning much faster and thus generating more frictional and viscous losses!
Anyway for two magnetised surfaces very close to one another you can approximate the force as
F = B2A/2μ0
Suppose we have 1 sq m of 10T magnets almost in contact, then F = 100/8π x 10-7 = 4 x 107 newtons or thereabouts. Your aircraft weighs about 107N , so your magnet will support it, as long as it is travelling in a straight line at constant speed.
But have you ever seen a 10T magnet? You are looking at a supercon weighing about 500 tonnes. These travel by ship, not plane.
Frictional losses in the rotor hub bearings are among the smallest problems in aviation, way below sealing the toilet valve or demisting the windscreen.
If you want to power a helicopter, you are going to need many more mechanical bearings, and whilst frictional losses demand high-temperature lubricants, the limiting problem is fatigue. AFAIK the rotor hubs need as much maintenance as the engine bearings.
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Quite apart from the mechanical issues where would the power for these motors come from? The power requirements for aircraft are enormous, a quick mental calculation(could be inaccurate!) suggests a 747 needs ~120Mwatts. I know there are electric aircraft but they are very limited and I don't expect any realistic implementation unless a completely new source of power is discovered. Edited for bad spelling-excuse, there was a large Norwegian forest cat sitting on me as I struggled to reach the keyboard.
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Ball bearings around the edge would be worse! the edge of the rotor is travelling much faster than the center, so the balls will be spinning much faster and thus generating more frictional and viscous losses!
Anyway for two magnetised surfaces very close to one another you can approximate the force as
F = B2A/2μ0
Suppose we have 1 sq m of 10T magnets almost in contact, then F = 100/8π x 10-7 = 4 x 107 newtons or thereabouts. Your aircraft weighs about 107N , so your magnet will support it, as long as it is travelling in a straight line at constant speed.
But have you ever seen a 10T magnet? You are looking at a supercon weighing about 500 tonnes. These travel by ship, not plane.
Frictional losses in the rotor hub bearings are among the smallest problems in aviation, way below sealing the toilet valve or demisting the windscreen.
If you want to power a helicopter, you are going to need many more mechanical bearings, and whilst frictional losses demand high-temperature lubricants, the limiting problem is fatigue. AFAIK the rotor hubs need as much maintenance as the engine bearings.
Hello, thank you for your response.
As previously stated, the bearings are designated for auxiliary support and operate at low RPMs or when the power is off. No need to reiterate the obvious.
I recommend reading this NASA paper on the Development of a 32 Inch Diameter Levitated Ducted Fan
Conceptual Design for additional insights: https://ntrs.nasa.gov/api/citations/20070006851/downloads/20070006851.pdf
While I appreciate your calculations for a 100,000kg scenario, it's essential to recognize that not all technology scales uniformly. Let's consider a smaller-scale application with a 2000kg aircraft for the discussion.
I looked into 10T Magnets... With the new weight requirements maybe you see another strenght class more suitable?
https://www.nist.gov/image/10t-magnet
As rightly pointed out, current frictional bearing losses are relatively small. However, continuous improvement is crucial. Bearing maintenance costs and the need for frequent attention are important factors to consider.
Let's maintain our focus and work towards achieving a functional and efficient completely contactless maglev rim-driven motor. If there are specific aspects or parameters you'd like to delve deeper into, please feel free to share, and we can continue the discussion.
Quite apart from the mechanical issues where would the power for these motors come from? The power requirements for aircraft are enormous, a quick mental calculation(could be inaccurate!) suggests a 747 needs ~120Mwatts. I know there are electric aircraft but they are very limited and I don't expect any realistic implantation unless a completely new source of power is discovered.
Power requirements are not the primary focus of this discussion. While the prevailing discourse often questions the feasibility of electric vehicles (EVs), manufacturers continually demonstrate otherwise. Similar advancements are anticipated in the aviation sector. Noteworthy progress in hydrogen technology adds to the optimism. For the purpose of this discussion, let's assume an infinite power supply and direct our attention to the magnetic levitation aspect of the rotor.
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Apologies - of course 2000 kg is about 20 kN!
So with a bit of recalculation, and assuming 1 sq m of near-contact area, you need about 0.7 T field.
This is almost off-the-shelf for a small MRI machine BUT the magnet itself weighs around a ton. You can save weight if you accept total loss of liquid helium (which will cost a lot more than the fuel you burn in the engine) but nowadays it makes sense to use a recirculating chiller (which requires a continuous electrical supply).
And then there's a small problem of operating a superconducting magnet close to a turbine running at 2000 ?C. This is no big deal for a roller bearing - just use an oil cooler.
And you might just need to access the shaft rotation anyway: stuff like starter motors, generators, propellor gearboxes, air compressors....all rely on the presence of a shaft bearing you are trying (for no obvious reason) to get rid of.
As you approach sonic speeds, you need to slow down the air entering the combustion chamber. This usually requires a splitter of some sort, so there's already a structure to support the front bearing. Keep it simple!
I'm always wary of continuous improvement. It usually means adding complications and things that can go wrong - ask Boeing. Or ask me: the Powers that Be are reducing maintenance of ground-based navigation systems because GPS is better and cheaper. At least it is when flying over oceans or at high cruise altitude and in the absence of military exercises when the GPS is jammed (it is not intended or guaranteed for civilian use). Problem only arise at those crucial moments in your approach pattern when you make a moderately steep turn: suddenly the aerial can't see more than two satellites so the screen goes blank and up pops a message "GPS unreliable". When you are at 1000 ft, 150 knots, 15 degrees of bank and descending over buildings in cloud, this does not contribute to your sense of wellbeing.
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Apologies - of course 2000 kg is about 20 kN!
So with a bit of recalculation, and assuming 1 sq m of near-contact area, you need about 0.7 T field.
This is almost off-the-shelf for a small MRI machine BUT the magnet itself weighs around a ton. You can save weight if you accept total loss of liquid helium (which will cost a lot more than the fuel you burn in the engine) but nowadays it makes sense to use a recirculating chiller (which requires a continuous electrical supply).
And then there's a small problem of operating a superconducting magnet close to a turbine running at 2000 ?C. This is no big deal for a roller bearing - just use an oil cooler.
And you might just need to access the shaft rotation anyway: stuff like starter motors, generators, propellor gearboxes, air compressors....all rely on the presence of a shaft bearing you are trying (for no obvious reason) to get rid of.
As you approach sonic speeds, you need to slow down the air entering the combustion chamber. This usually requires a splitter of some sort, so there's already a structure to support the front bearing. Keep it simple!
I'm always wary of continuous improvement. It usually means adding complications and things that can go wrong - ask Boeing. Or ask me: the Powers that Be are reducing maintenance of ground-based navigation systems because GPS is better and cheaper. At least it is when flying over oceans or at high cruise altitude and in the absence of military exercises when the GPS is jammed (it is not intended or guaranteed for civilian use). Problem only arise at those crucial moments in your approach pattern when you make a moderately steep turn: suddenly the aerial can't see more than two satellites so the screen goes blank and up pops a message "GPS unreliable". When you are at 1000 ft, 150 knots, 15 degrees of bank and descending over buildings in cloud, this does not contribute to your sense of wellbeing.
Hello Alancalverd,
Thank you for your follow-up.
From what I gather, you are a pilot?
With the focus being to enhance current propulsion solutions, you mentioned, this often involves adding complications. The true brilliance of a concept lies in its ability to simplify and reduce part count while simultaneously improving performance. I believe we can all agree on that principle?
An excellent aerospace example is Relativity, showcasing their capability to 3D print entire sections and assemblies of rockets/engines, effectively reducing part count by a factor of 100x.
This principle of simplification also applies to the all-electric maglev rim-driven fan. In your previous response, you mentioned starter motors, gearboxes, and air compressors ? All are entirely absent in this concept. Consequently, there is no requirement to access or employ a shaft bearing in this setup. Additionally, a contra-rotating arrangement could eliminate the need for stator vanes to act as airflow straighteners.
You also talked about the system operating at 2000 degrees Celsius. This might be the case for current Jet engines, but not so much for an all electric solution. While there is heat generated from the electric motor, the goal is to dissipate and redirect it into the airstream, utilizing this 'waste heat' to further increase thrust efficiency.
To keep energy demands realistic, I propose steering clear of superconducting magnets. Is it feasible to stick to coils and magnets?
The overarching goal is fewer parts, simpler mechanics, enhanced energy efficiency, and increased thrust.
Best regards,
- Robert
ps: talking about Boeing and improvement seems to revolve around the company's pursuit of profit, regardless of the cost... With that being said, I rather not ask Boeing how to do things.
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starter motors, gearboxes, and air compressors ? All are entirely absent in this concept.
You might get away with a "maglev" starter ring, but how are you going to drive the propellor, bypass fan or heli rotor without a shaft bearing somewhere in the system? Pure jet is really restricted to fighter aircraft these days, and even jet jockeys appreciate a bit of air conditioning. You can of course run pneumatic and hydraulic pumps from the electrical system, but then you need an alternator on the turbo shaft.....
Is it feasible to stick to coils and magnets?
I have built room-temperature MRI machines running at 0.6 T. The lightest one, using a resistive magnet, weighed 150 tons and dissipated 200 kW of heat. We also had some permanent magnet 0.2T machines, but they were a lot heavier.
Supercon is always the lightest and most energy-efficient magnetic system.
It looks as though you are considering a ducted fan assembly rather than a combustion jet. The problem with a DF is a loss of efficiency at high angles of attack - essentially, it's not a very manoeuverable configuration compared with a prop or a jet. As they say, great for cruising (very quiet), sometimes an embarrassment during takeoff and landing.
You won't find anything simpler than a ramjet - no moving parts at all! But they do have their problems.
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@OP
NASA is Mostly Mind-blowing!
I Wonder thou, Why is it Not already Operational?
https://en.m.wikipedia.org/wiki/Halbach_array
Safety of an RR jet engine...
(It will Grind that Birdy into a Paste)
(A Lightning Bolt won't switch it Off)
(Frictional Heat abhors Ice jamming)
...remains Unchallenged!
ps - All the Best for
Future Endeavours.
Up upp & awayyy!
: )
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Problem with the Halbach array is that the strong field direction alternates, so the net field at any distance greater than the period of alternation is zero, and you can't use it to generate repulsion between moving objects. No big deal if you just want to stick a souvenir on a refrigerator, but you need a unidirectional convergent radial field to suspend Supervolant's rotating fan.
Also worth considering the aerodynamic efficiency of the system. The edges of the fan generate most of the thrust because they sweep a large area per rotation, so you want to keep the airflow around the edges as unobstructed as possible: close ducting induces drag on the fan tips. This means that your maglev can't use the "very near field" approximation of Reply #7 but will require a much larger field.
The center of the fan, on the other hand, produces very little thrust, so you might as well ignore it and put a ball bearing in the middle. Then you can drive the fan with any motor you like.
Short of going nuclear (and the Godiva nuclear airplane project wasn't much of a success) the highest practicable energy density is the oxidation of hydrogen, whether by combustion or in a fuel cell, and I don't see any battery system being able to compete. In the meantime, combining hydrogen with carbon does give us a very convenient range of fuels for every form of aviation.
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Thank you all for the input.
Considering current technology, the energy demands are too high for this concept to work out. I would like to add that this might be the ideal propulsion system if nuclear energy is an option. However, quite frankly, I think it's a really bad idea to put a thermonuclear reactor onto something that flies inside Earth's atmosphere.
I will be following a different approach.
Usually, I would now close the topic; however, I am always open to more good ideas and people who bring them.
I'll be checking in here once in a while!