X Prize Clean Aviation: $10 million

[RonL]

A Cessna? Talk about thinking inside the box...

I was thinking more on the line of meshing and morphing the technologies of the desired attributes of existing electric vehicles:

Speed:

105 mph. Batteries not included.

Altitude:

96,863 feet

Range: Lots of range on most vehicles. Though there are none that have both range and speed.



Rings? This one has lots of rings:

But seriously, I would imagine, based on the the Nuna and Helios examples above, that the most efficient and likely candidate to win the race would be some sort of flying wing.

Kind of like this little fella:

Only not quite so thick. I don't think we need to be carrying around 40,000 lbs of bombs.

All fine examples, and I love flying wings.

When I talk about outside the box, I'm generally thinking about things that can be done at my time and financial level, which is pretty small.

About the picture of the ring ducts, that is quite like what I was trying to describe only what I picture is smaller and not as bulky looking. Now if you can see in the minds eye those rings as part of the prop and in spin motion, they will store energy like a flywheel and I might dare say the drag of air flowing around and through them will be less than if motionless (?)

What I think to be most outside the box, is what happens at the motor/generator section.
If the housing and armature are allowed to spin in opposite directions twice the voltage (or more) can be applied, and if cooling based on air velocity will allow, the amp load might be doubled, you then have 4 times the power being applied between the two props.
The power being supplied is from batteries and is in modified wave form (or pulses).
The instant of change from power being supplied to power being generated, the load against the motor action being minus, becomes positive to the generator action and goes to the batteries in a continuous flow.
This might be just a very small difference, but something to look at.
Only electrical control can take advantage of those thermals you mentioned

The power switches happen in microseconds and changes in speed and rotating mass will have almost no change.
This is completely different than something bolted to a shop table.

Ron

 

[RonL]

Well Om,
Looks like you were right about me being out at 30,000 feet without a parachute

Everyone left to go win the prize before they got the "rest of the story".

Energy always has to be obtained and paid for, before being used. Because energy can be stored it can be compared to money in a bank account which generally earns interest, these accounts most often allow for deposits and withdrawals as long as a certain balance is maintained. A flywheel (a single or any group of rotating parts) is like the bank account. Electrical energy can be controlled with such precision that 95% or better efficiency is claimed for many motors on the market today. Motors and generators are generally one and the same for all practical purposes and as I understand, more speed always equates to more efficiency. (just a rule of thumb)

Thermal energy from air that flows through and around the aircraft, is the source of replacment for the losses in the electrical system.

A simplified description (of one) of several more parts that make up the whole.

Most are now aware of three phase brushless motors, they come in two versions, inrunners and outrunners, you have two options for each in what part mounts to the firewall or frame. The armature can be stationary and the housing rotates or the housing mounts and the armature rotates (not sure which offers the best advantages)
The design I'm putting in words here, is to use the armature mounted and the housing to be the rotating part, a body is machined and is made to hold two sets of neo. magnets, one set inside to work as an outrunner motor, and the second set of magnets (on the outside of the housing) work as the rotor inside a common alternator.
There are many ways to put this in motion with power input from other sources, a key factor is the outrunner motor action, spinning the rotor of the alternator at speeds of 15,000 rpm or more is independent of some slow moving power source.

It might be that everybody and their pets have been doing this for the last year or two, but I think it is a new idea.

Can electrical energy be levered through mechanical motion? I think yes. Along with heat being converted to work (air flow) it seems to me that battery quantity might not be as important as everyone is being led to believe

Guess my 30,000 feet is about used up

Ron

 

[OmCheeto]

All fine examples, and I love flying wings.

When I talk about outside the box, I'm generally thinking about things that can be done at my time and financial level, which is pretty small.

Well, I don't think anyone at the forum could afford to build our hypothetical plane.
But I can envision incorporating scaled down ideas into my electric boat design.
Or vice versa.

About the picture of the ring ducts, that is quite like what I was trying to describe only what I picture is smaller and not as bulky looking. Now if you can see in the minds eye those rings as part of the prop and in spin motion, they will store energy like a flywheel and I might dare say the drag of air flowing around and through them will be less than if motionless (?)

What I think to be most outside the box, is what happens at the motor/generator section.
If the housing and armature are allowed to spin in opposite directions...

I'll stop you right there and say, what?

How are you going to generate any meaningful torque on the prop if your housing is spinning? In my minds eye, your airplane is going to be an expensive tarmac ornament.

I doubt it. This is a speed contest, not a stay-aloft-a-long-time contest. Adding a bunch of wing adds a bunch of drag.

On any kind of aircraft at all I doubt if solar panels help for this one time, one trip contest. Panels might provide 8 kWh (10 M^2 x 200W/M^2 x 4 hours ), which is provided by 53 kg of rechargeable Li Ion batteries (150 Wh/kg), or 16kg of non rechargeable batteries. Dump the panels, go with extra batteries.

I don't know about that. I can imagine cubing the size of the Nuna and obtaining a doubling of speed to 200 mph. Add a few hundred kg of batteries, and we've got a race.

Though as I've said before, I know nothing about airplanes. I'll do a bit more number crunching this weekend to see what it takes to get a brick to fly.

 

[RonL]

I'll stop you right there and say, what?

How are you going to generate any meaningful torque on the prop if your housing is spinning? In my minds eye, your airplane is going to be an expensive tarmac ornament.

If a motor is mounted in such manor as to allow the housing to turn as well as the armature, and each has a prop of proper rotation mounted, any amount of power supplied to the motor will be split between the two parts based upon the thrust resistance of each prop.

P.S. Should work on your boat as well...Twin screw counter rotating props...


Ron

 

[minger]

If a motor is mounted in such manor as to allow the housing to turn as well as the armature, and each has a prop of proper rotation mounted, any amount of power supplied to the motor will be split between the two parts based upon the thrust resistance of each prop.

P.S. Should work on your boat as well...Twin screw counter rotating props...


Ron

I won't pretend to have been involved in this thread, but from quickly reading I'd point out that windage losses from spinning such a housing could be significant.

 

[OmCheeto]

If a motor is mounted in such manor as to allow the housing to turn as well as the armature, and each has a prop of proper rotation mounted, any amount of power supplied to the motor will be split between the two parts based upon the thrust resistance of each prop.

P.S. Should work on your boat as well...Twin screw counter rotating props...


Ron

Tell you what, let's build miniature models of our engines. We can compare thrust vs energy numbers on Monday.

Actually, the full size engines would probably be very small to begin with. Let's go with 12 inch diameter fans, as you mentioned the other day.

 

[RonL]

Tell you what, let's build miniature models of our engines. We can compare thrust vs energy numbers on Monday.

Actually, the full size engines would probably be very small to begin with. Let's go with 12 inch diameter fans, as you mentioned the other day.

I can see how the words didn't make for a clear picture.
The power tube size is based on motor/generator diameter, and is much like a super size canister vacuum.

High RPM motor/generator units transfer power to much larger props, 48" or more.

More than a weekend project for me
I'll be lucky to work on anything before late spring, if your interested in something to play around with on your boat ?, I'll send you a PM.

Ron

 

[mheslep]

Aviation Week did a piece on the VTOL Puffin
http://www.aviationweek.com/aw/blogs/business_aviation/index.jsp?plckController=Blog&plckScript=blogScript&plckElementId=blogDest&plckBlogPage=BlogViewPost&plckPostId=Blog%3A2f16318d-d960-4e49-bc9f-86f1805f2c7fPost%3Ad341a5a0-b4d4-4ae1-a99b-9488d0b1d281

A key design breakthrough is the redundancy in the electric propulsion system, says Moore. Detailed reliability analyses and powertrain build-up by M-dot Aerospace “showed that for each nacelle, we could achieve an FAA equivalency to a multi-engine rating. This is what allowed us to avoid having a cross-shaft, as each engine can fail any two components and still operate at the full 30-hp. rating [per nacelle].”
[...]
The rotors’ speed can be controlled through a wide range by varying the electric motor without the need for complex and heavy gear systems. Moore says that “electric motors have no lapse rate at high/hot conditions, nor with altitude, so that full power can be produced as you go to higher cruise altitudes.”
[...]
“Everything about electric propulsion is better than reciprocating or turbine engines for these small vertical-takeoff-and-landing platforms—except for battery energy storage,” says Moore. “And with billions of dollars going toward that problem, and exciting near-term technologies being developed by MIT, Stanford [University] and industry—how can we afford to not be looking at the incredible design freedom that electric propulsion offers to aircraft designers?”

 

[mgb_phys]

Everything about electric propulsion is better than reciprocating or turbine engines for these small vertical-takeoff-and-landing platforms

Except for the extension cord.

—except for battery energy storage

Yep like the only thing between me and an olympic gold is energy storage.

 

[Cyrus]

Aviation Week did a piece on the VTOL Puffin
http://www.aviationweek.com/aw/blogs/business_aviation/index.jsp?plckController=Blog&plckScript=blogScript&plckElementId=blogDest&plckBlogPage=BlogViewPost&plckPostId=Blog%3A2f16318d-d960-4e49-bc9f-86f1805f2c7fPost%3Ad341a5a0-b4d4-4ae1-a99b-9488d0b1d281

First of all, I'm glad they finally accurately quoted the electric system as not having a lapse rate, and not the entire system. That being said, the ability to not have a cross drive system is really great. This is classically a problem in terms of empty weight fraction in the XV-15 (precursor to the V-22), and its bigger brother, the V-22. If they can avoid having articulated rotor systems (think a helicopter mechanical controls) on each blade, that is also great because it reduces the complexity, cost and weight.

Their main problem; however, is that the FAA requires at least 30 mins reserve fuel. The Puffin flies for 5 minutes - total. This is really a fundamental problem.

 

[mheslep]

Their main problem; however, is that the FAA requires at least 30 mins reserve fuel. The Puffin flies for 5 minutes - total. This is really a fundamental problem.

5 minutes is the longest prototype test flight so far. The final design spec is ~20 mins, or http://www.scientificamerican.com/article.cfm?id=nasa-one-man-stealth-plane" (c. Reserve Fuel), and may apply only in air traffic control situations, i.e. in and out of FAA controlled airports.

 

[Cyrus]

5 minutes is the longest prototype test flight so far. The final design spec is ~20 mins, or http://www.scientificamerican.com/article.cfm?id=nasa-one-man-stealth-plane" (c. Reserve Fuel), and may apply only in air traffic control situations, i.e. in and out of FAA controlled airports.

To my knowledge, there have been no test flights of this prototype. The fuel issue still stands. I am looking outside my window right now, and it is IFR weather. If this is a 'flying car' in the most general sense, it is fundamentally not going to work because it is not robust to the environment.

When I get home, I will look through my FAR/AIM and give you the exact rules on fuel reserves required by law, and how it applies (I never really fly far enough to know this off the top of my head).

 

[mheslep]

To my knowledge, there have been no test flights of this prototype.

So then where did you get 5 minutes?

The Puffin, named because it resembles the bird, has not yet flown publicly, but Moore said its longest flight lasted five minutes.

The fuel issue still stands. I am looking outside my window right now, and it is IFR weather. If this is a 'flying car' in the most general sense, it is fundamentally not going to work because it is not robust to the environment.

<shrug>

"We're not trying to replace the car or the airplane," Moore said. "Cars are great at what they do, which is go a couple of miles at relatively slow speeds. Commercial air carriers are great at going long distances at faster speeds. But what happens when we want to go 100 or 200 or 300 miles? We have to take this very long drive

http://news.discovery.com/tech/nasa-aircraft-puffin-transportation.html

When I get home, I will look through my FAR/AIM and give you the exact rules on fuel reserves required by law, and how it applies (I never really fly far enough to know this off the top of my head).

Look forward to it, though AFAICT the source I supplied above are the current FAA regs.

 

[Cyrus]

The 5 mins are based on lab tests they have done, to my knowledge. (Edit: after reading your link, it does appear they have actually flow it. I wonder, why no pictures of the actual vehicle).

<shrug> ... really? You're answer to a 'flying car' that has to work in IFR conditions (and hence have fuel reserves for 30 mins, longer than the vehicle can even fly is ...<shrug>? This is called a fundamental problem, not ...<shrug>!

Clarification: now the article says it's not a flying car..however, one has to ask. What do you use a 5 minute, 50 mile range vehicle for? Let's be real here, at best this is a flying car (but worse than a car in performance!).

Obviously, the car is meant for use of 100 -300 mile trips, and the article states that the only way to do this (currently) is by car. But, what's wrong with taking the train?

 

[mheslep]

Clarification: now the article says it's not a flying car..however, one has to ask. What do you use a 5 minute, 50 mile range vehicle for?

https://www.physicsforums.com/showpost.php?p=2682088&postcount=101"

 

[Cyrus]

https://www.physicsforums.com/showpost.php?p=2682088&postcount=101"

Okay, better, but still not enough!

Note: (I will, rather reluctantly, admit that the more I read about this I am warming up to it).

There is also the problem that you could go 20 minutes. But you would have to leave the wife, kids, dog, and luggage at home...though that may not necessarily be a bad thing!

 

[Altrepair]

Here is a simple solution for motor weight and is cheap compared to HTS motors. Use 400 Hertz 3-phase AC induction motors. Remember people that like a transformer, higher frequencies reduce size and weight. Four-hundred hertz motors have been used in the aviation industry for years for the hydraulics or anything else that needed actuation. With 400 hertz motors you also gain insanely high RPMs. A two pole, 400HZ motor turns at about 24,000 RPM.

So I would give AC propulsion a call and ask for their AC induction motor with variable frequency speed drive package. Or talk with the engineers at 400hertz.net if you want a custom horsepower motor other than 268 HP from AC propulsion.

 

[mheslep]

Here is a simple solution for motor weight and is cheap compared to HTS motors. Use 400 Hertz 3-phase AC induction motors. Remember people that like a transformer, higher frequencies reduce size and weight. Four-hundred hertz motors have been used in the aviation industry for years for the hydraulics or anything else that needed actuation. With 400 hertz motors you also gain insanely high RPMs. A two pole, 400HZ motor turns at about 24,000 RPM.

So I would give AC propulsion a call and ask for their AC induction motor with variable frequency speed drive package. Or talk with the engineers at 400hertz.net if you want a custom horsepower motor other than 268 HP from AC propulsion.

The main loss component in normal electric motors is resistive, ie. IR loss in the windings. Along with the advantages of increasing frequency comes the disadvantage of increased resistive losses due to the frequency dependent http://en.wikipedia.org/wiki/Skin_effect" . Skin depth is proportional to 1/sqrt(frequency), so increasing the frequency from 60Hz to 400Hz decreases the skin depth 62%.

Windage is another loss secondary to IR, but at some high enough RPM windage will become dominant.

BTW, AC propulsion's motor ( i.e. Tesla's motor) is indeed a three phase induction design, though I don't know about frequency. At ~4KW/kg, I am not aware of any non-HTS electric motor at this scale (<500KW) with a greater power density.

 

[Altrepair]

The main loss component in normal electric motors is resistive, ie. IR loss in the windings. Along with the advantages of increasing frequency comes the disadvantage of increased resistive losses due to the frequency dependent http://en.wikipedia.org/wiki/Skin_effect" . Skin depth is proportional to 1/sqrt(frequency), so increasing the frequency from 60Hz to 400Hz decreases the skin depth 62%.

Four hundred hertz 3-phase AC induction motors have been around since before a lot people where even born that are members of this forum. All the issues of going higher frequency have been solved a long time ago when the aviation industry needed a lightweight electric motor solution. That is why in the aviation industry 400 hertz is standard since the generators and motors are light weight.

Windage is another loss secondary to IR, but at some high enough RPM windage will become dominant.

Turbo fan Jet engine turbines spin at insanely high rpms and thus suffer from windage losses too. I would say it is far worse since it has so many blades inside.

BTW, AC propulsion's motor ( i.e. Tesla's motor) is indeed a three phase induction design, though I don't know about frequency. At ~4KW/kg, I am not aware of any non-HTS electric motor at this scale (<500KW) with a greater power density.

[/QUOTE]

It is a 400 hertz design with copper rotor bars instead of aluminum. It is 4-pole instead of two, so it will turn at about 12,000 RPM. A standard off the shelf 400 hertz, 200 HP induction motor only weighs around 80 pounds compared to the 60HZ version that is in the thousands.

 

[Phrak]

It is a 400 hertz design with copper rotor bars instead of aluminum. It is 4-pole instead of two, so it will turn at about 12,000 RPM. A standard off the shelf 400 hertz, 200 HP induction motor only weighs around 80 pounds compared to the 60HZ version that is in the thousands.

Now way. How does power scale with frequency?

 

[mheslep]

Four hundred hertz 3-phase AC induction motors have been around since before a lot people where even born that are members of this forum.

Before all of the forum members were born.

All the issues of going higher frequency have been solved a long time ago when the aviation industry needed a lightweight electric motor solution. That is why in the aviation industry 400 hertz is standard since the generators and motors are light weight.

I'd say the issues are now well understood, not 'solved.' Certainly 400 Hz motors are lighter weight than similarly rated 60Hz motors. I only pointed out one known disadvantage that comes along with the other advantages (as with everything else): generally speaking a 400Hz motor will be a little less efficient than a similar 60 Hz motor because of IR winding losses. Thus on the factory floor a 400Hz motor will produce a higher electric bill per unit output than the similar 60Hz motor. For the case of a battery powered aircraft so equipped, the platform would have to carry a little more battery for a given power-time profile, even if the 400Hz motor weighs less. It's a trade off <shrug>. In a normal aircraft carrying thousands of megajoules of jet fuel, that efficiency loss doesn't matter (for auxiliary motors) so the 400 Hz weight savings dominates in traditional aviation.

 

[mheslep]

It is a 400 hertz design with copper rotor bars instead of aluminum. It is 4-pole instead of two, so it will turn at about 12,000 RPM.

I've never heard/seen a 400Hz spec for the Tesla. AC Propulsion http://www.acpropulsion.com/products-drivesystem.html" , I expect in the hundreds of hertz range. Do you have a reference for the 400 Hz claim?

 

[Altrepair]

Before all of the forum members were born.

I know the low frequency design of AC induction motors have been around since the 1800's, but I did not think the 400 Hertz design has been.

 

[Phrak]

I've never heard/seen a 400Hz spec for the Tesla. AC Propulsion http://www.acpropulsion.com/products-drivesystem.html" , I expect in the hundreds of hertz range. Do you have a reference for the 400 Hz claim?

The article says it all. The transmission is at a fixed gear ratio, so varying the frequency stands in place of shifting gears. I'm pleasantly surprised to hear about using induction motors. I'd always considered them too massive and underpowered for transportation. However, I can't say I understand the reasoning to inducing a 4 pole magnet in the rotor rather than using a 4 pole permanent magnet.

 

[mheslep]

Tesla Motors eventually included a transmission (2 gears I think) in their Roadster - still a big improvement over the transmissions used with combustion engines.

 

[Altrepair]

The article says it all. The transmission is at a fixed gear ratio, so varying the frequency stands in place of shifting gears. I'm pleasantly surprised to hear about using induction motors. I'd always considered them too massive and underpowered for transportation.

Until today when you learned of high frequency designs.

However, I can't say I understand the reasoning to inducing a 4 pole magnet in the rotor rather than using a 4 pole permanent magnet.

There would be no torque if current was not induced into the rotor bars which requires slip of the rotor relative to the rotating magnetic field of the stator. If instead magnets were used, it would be a synchronous motor which have no starting torque. So it would sit there buzzing with a very angry 60 HZ hum until damage occurs or some safety device trips. The large industrial synchronous motors start up as asynchronous induction motors since they also have rotor bars embedded into the rotor, till about 75% speed, at which point the DC field circuit is energized which causes the rotor to lock up in sync with the rotating magnetic field of the stator. Before they made them this way, a "pony motor" which is synonymous with a starter motor used for ICE's was used to bring up the speed of the synchronous motor.

I've never heard/seen a 400Hz spec for the Tesla. AC Propulsion http://www.acpropulsion.com/products-drivesystem.html" , I expect in the hundreds of hertz range. Do you have a reference for the 400 Hz claim?

If you look at the specs you see it says four pole, and if you know the formula to find the frequency of an ac induction motor when the poles and RPM are known then you can get a general idea of the frequency it is designed for. Another factor is also weight.

The Tesla uses AC propulsion's designs. The motor from AC propulsion weighs in at 110 pounds where as the 400 HZ, 200 HP motor from: http://www.400hertz.net/Products/ME-400-200-416.htm" weighs in at 85 pounds. The weight differences are due to more HP likely in the AC propulsion design and/or the frame the motor is in maybe weighs more, but both of them are are at least 12,000 RPM or greater and have about the same weight.

 

[Phrak]

Until today when you learned of high frequency designs.

I'm an electronics products design engineer in instrumentation, controls, and power conversion (and I don't push papers, I engineer). I know a little about DC motors and haven't done anything with AC induction motors beyond turning them on and off and advising against unreliable speed control using triacs.

There would be no torque if current was not induced into the rotor bars which requires slip of the rotor relative to the rotating magnetic field of the stator. If instead magnets were used, it would be a synchronous motor which have no starting torque.

Not really. An induction motor requires slip to generate a field on the rotor. No slip, no rotor field, no torque. For a permanent magnet rotor, no slip is required, and the torque is maximal at stall. DC motors that have permanent magnets are not driven by a constant AC frequency and neither is the tesla motor. DC motors are supplied with their own alternating potential mechanically or electronically.

 

[Phrak]

Tesla Motors eventually included a transmission (2 gears I think) in their Roadster - still a big improvement over the transmissions used with combustion engines.

Interesting. I was curious about how they managed one gear. The power and torque curves of an electric motor are OK, but not wonderful. I think another alternative is to vary the field winding current (where both stator and field are electromagnets), but I haven't looked into it. It could have drawbacks.

 

[Altrepair]

Not really. An induction motor requires slip to generate a field on the rotor. No slip, no rotor field, no torque. For a permanent magnet rotor, no slip is required, and the torque is maximal at stall. DC motors that have permanent magnets are not driven by a constant AC frequency and neither is the tesla motor. DC motors are supplied with their own alternating potential mechanically or electronically.

If you read the text of mine you quoted (There would be no torque if current was not induced into the rotor bars which requires slip of the rotor relative to the rotating magnetic field of the stator.) you would see I said it required slip. No slip means no current will be induced into the rotor bars. It is that simple. If the rotor followed exactly with the rotating magnetic field, no current will be induced since no magnetic flux lines will be passed through by the rotor bar conductors meaning no current could ever flow in the conductors, thus no magnetic field will set up on the rotor, meaning NO torque.



I did not say anything of PM DC brushless motors which have a feed back loop either by hall effect sensors or by back EMF, in which case the controller knows the position of the rotor to correctly time when to energize the next set of windings (the electronic version of the commutator).

Synchronous AC motors, though, have no starting torque and have totally a different torque curve and work differently, PERIOD, compared to PM brushless DC motors. You can argue that till the cows come home, but it is a fact. Either a pony motor is needed or it must be the type that has rotor bars embedded into the rotor such that it starts up as an asynchronous induction motor till sufficient speed is reached for the rotor to lock in step with the rotating magnetic field when the DC power source is supplied to the slip rings of the rotor that powers the electromagnets.

If I am not considered a credible source by you, then have a look here that backs up my claim of pure AC synchronous motors having no starting torque at all:

http://www.engineersedge.com/motors/synchronous_motor.htm"

http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee11/bdeee11_8.aspx"

http://www.tpub.com/content/neets/14177/css/14177_92.htm"

I did make one honest mistake by saying 75% synchronous speed, when it is actually 95% of synchronous speed before the DC circuit is energized to power the rotor electromagnets to lock the motor in step with the rotating magnetic field.

Finally, the AC induction motor in the Tesla roadster works on the same principle as your typical AC induction motor which requires sinusoidal current to work. The voltage feed to it from the vector-variable-voltage/frequency drive is variable length square waveform that has the on/off ratios such that it makes the current flowing through the motor windings sinusoidal due to its inductance.

Have a look: http://oee.nrcan.gc.ca/industrial/equipment/vfd-ref/images/figure-08.jpg"

Anyways, I think we are stirring the topic off course and so I shall refrain from posting about motor characteristics.

 

[mheslep]

If you look at the specs you see it says four pole, and if you know the formula to find the frequency of an ac induction motor when the poles and RPM are known then you can get a general idea of the frequency it is designed for.

Yes for a synchronous AC motor rpm = 120 x frequency / # poles. This motor can not be synchronous. Phrac noted the design is in fact variable frequency.