X Prize Clean Aviation: $10 million

[mheslep]

An MIT collaboration with the X Prize foundation may soon release a proposal for a fastest coast to coast flight using only electric power.
http://web.mit.edu/newsoffice/2009/x-prize-1217.html"

I am thinking some of the electric ducted fan technology discussed https://www.physicsforums.com/showpost.php?p=2292842&postcount=14", and some very high end battery technology is the key, probably primary batteries if they allow it. I'll follow up later.

Imagine flying all the way from coast to coast, completely guilt-free, in an airplane that doesn’t emit a single particle of greenhouse gas or air pollutants. That could happen someday, perhaps brought to reality thanks to the incentive of a $10 million prize that has been proposed by a team of MIT students.
[...]
The X-Prize Lab@MIT, a collaboration between the Institute and the X-Prize Foundation aimed at creating concepts for new prizes, led by instructor Erika Wagner of the Deshpande Center for Technological Innovation, just completed its third semester-long class devoted to developing new prize ideas. This time, the subject was energy storage, and the final presentations by the four teams of students in the class were held on Friday, Dec. 11.

Graduate students Daniel Codd (mechanical engineering), Wendelin Michel (AeroAstro), and Paul Tu (MIT Sloan School of Management) proposed the “Clean Aviation” X-Prize. The concept, they explained, would be to hold a race from California to New York, in which all the competing planes would have to be powered entirely by electricity and produce no emissions. The planes would be allowed two stops during the journey, which would have to be completed within 24 hours. The first to cross the finish line would get a $7.5 million prize, while the plane that covered the longest distance on a single leg of the flight would win $2.5 million.
[...]
this is not the first proposal for a green-aviation challenge, it’s the only one requiring an all-electric, emissions-free system. The plan calls for holding the race three years after the contest is announced, and then if no team is able to complete the challenge, holding a second contest two years later for a reduced prize. “It would be open to all possible entrants, from people working in a garage to Boeing.”
[...]
Ultimately, the decision about which, if any, of these proposals will be launched as X-Prize competitions rests with the X-Prize Foundation itself. The foundation was created and is run by Peter Diamandis ’83, SM ’88, who initially set it up to administer the first X-Prize, which led to back-to-back flights into space by the one-person rocket called SpaceShipOne, in 2004. The successor to that craft, the eight-person SpaceShipTwo, was unveiled last week and is expected to begin carrying ordinary citizens (and quite a few celebrities) into space in about two years, ushering in a new era in space transportation.
[...]

 

[mheslep]

From earlier "[url[/URL], I considered a Bombardier CRJ900, modified with ducted fans, at 12 kWh(41k BTUs) per mile based on its gross range data given a full load of fuel. Perhaps that could be cut that in half for a more efficient, slower, jet aircraft appropriate for this contest, or 6 kWh (21k BTUs )per mile? Distance for the contest is ~2500 miles, with two stops allowed, or ~850 miles per leg, 5100 kWh (17.4 million BTU )per leg.

[PLAIN]http://en.wikipedia.org/wiki/Zinc_air" non rechargeable batteries achieve about 0.5 kWh per kg, giving ~11 metric tons of battery per trip leg. However, power density of metal air batteries is low, at least for commercial models. This 11 m ton pack would provide only 1.1 MW.

Ducted fan concept:

 

[Cyrus]

This prize seems to ignore the realities of energy storage issues. Everyone under the sun in the UAV world is trying to get high energy electric systems. I do not see what this prize is supposed to do, it's certainly not going to 'start' people thinking about electric. As for your post above, does a 'superconducting motor replaces turbine' exist outside of the imagination?

 

[mheslep]

http://www.transportenvironment.org/Publications/prep_hand_out/lid/398" shows aviation fuel efficiency topping out at about 1MJ / seat-km in the large jumbos, or 2 seat-miles per kWh. I'm curious as to how that metric would scale down for smaller jet aircraft - fewer seats, more overhead.

 

[mheslep]

This prize seems to ignore the realities of energy storage issues. Everyone under the sun in the UAV world is trying to get high energy electric systems.

Why, what's wrong w/ petroleum for the UAV crowd?

I do not see what this prize is supposed to do, it's certainly not going to 'start' people thinking about electric. As for your post above, does a 'superconducting motor replaces turbine' exist outside of the imagination?

? That's not my sketch. AFRL built a 3MW motor. It's out of the paper in the link I referenced in the other thread.
http://www.masbret.com/asc08/ASC08_Tuesday_Plenary_Electric_Aircraft.ppt

 

[Cyrus]

Why would you want a loud, vibrating engine on a UAV?

 

[Cyrus]

I'm looking at that ppt, and I have to ask: why would you use an electric motor to power a ducted fan, and not just use a more efficient propeller?

Also, where are you going to get adequate energy storage?

 

[mheslep]

Why would you want a loud, vibrating engine on a UAV?

Ok you're talking about military applications. Doubt that matters for the higher altitude aircraft.

 

[mheslep]

I'm looking at that ppt, and I have to ask: why would you use an electric motor to power a ducted fan, and not just use a more efficient propeller?

Sorry I don't follow. What source of power are you suggesting, if not an electric motor? Edit: Perhaps you are asking: why use an electric motor instead of a traditional gas turbine? Electric motor can be >95% efficient, is quiet, as you mentioned above, and can run on electric charge that may have been generated on the ground and stored in the aircraft.

Also, where are you going to get adequate energy storage?

Post #2, for purposes of this prize. 11 metric tons of battery per 850 mile leg.

 

[FredGarvin]

Spurring on innovation is nice. That is what makes the world go round and improve. However, this, like every other electric application, is doing nothing more than shifting the sources of pollution. Most forms of clean electricity production are pretty much fixed. What's going to happen if this electric dream comes true with millions of cars and now aircraft. Crank up the coal plants. We certainly aren't doing much in nuclear and dams are pretty much fixed output. It's short sightedness at its best.

Back on topic...there is no way to make current energy sources viable and thus useful. Like the other X prize, it is nothing more than a stunt.

 

[Cyrus]

Sorry I don't follow. What source of power are you suggesting, if not an electric motor? Edit: Perhaps you are asking: why use an electric motor instead of a traditional gas turbine? Electric motor can be >95% efficient, is quiet, as you mentioned above, and can run on electric charge that may have been generated on the ground and stored in the aircraft.

Post #2, for purposes of this prize. 11 metric tons of battery per 850 mile leg.

No, I'm saying why would you power a fan, instead of a prop. Larger rotors are more efficient.

 

[Cyrus]

Ok you're talking about military applications. Doubt that matters for the higher altitude aircraft.

Why do you doubt this? The purpose of a UAV is to be a sensors platform. The formula for arc length is s=r d \theta. The higher you are...

 

[mheslep]

Spurring on innovation is nice. That is what makes the world go round and improve. However, this, like every other electric application, is doing nothing more than shifting the sources of pollution. Most forms of clean electricity production are pretty much fixed. What's going to happen if this electric dream comes true with millions of cars and now aircraft.

At least regarding the cars you must know that the power plants, even the worst of them, are much more efficient that any internal combustion engine going down the road. In moving cars to electric, conservative figures say CO2 pollution improves by almost a https://www.physicsforums.com/showpost.php?p=2507689&postcount=178" on average. SO2 may increase, if coal picks up all the additional load. In metropolitan areas pollution drops dramatically across the board, and the really bad stuff (benzene, etc) goes away completely. For me the biggest win is it does away with imported oil.

Edit: Last, how did I forget: electric ground vehicle transport is 1/3 the cost per mile of petrol based. It's break even amortizing in the cost of the batteries - at today's price of a gas, and that's only going up.

Crank up the coal plants.

Or the natural gas. Just as much gas electric power capacity in the US as there is coal; gas is more expensive but much cleaner. And local.

We certainly aren't doing much in nuclear and dams are pretty much fixed output. It's short sightedness at its best.

Nuclear http://www.world-nuclear-news.org/C-Shaw_eyes_US_reactor_uprate_market-0701104.html" and turbine upgrades are going through - another US 4GWe while nobody was looking. Also add another 5-10GWe a year wind - useless for baseload but fine for charging batteries.

Back on topic...there is no way to make current energy sources viable and thus useful. Like the other X prize, it is nothing more than a stunt.

Maybe so. First X prize didn't advance the art in any areas?

 

[mheslep]

No, I'm saying why would you power a fan, instead of a prop. Larger rotors are more efficient.

Oh. Prop aircraft are more efficient that turbofan jet aircraft? Still? I wouldn't know. This is a contest so speed matters, so my first hunch was to go with the fan. I was guessing something under 200-300 knots would be required to keep the losses to drag down, but I am vaguely aware that the altitude, lift, and air speed couple together in matter (that's beyond me) that complicates the energy efficiency issue.

 

[FredGarvin]

Oh. Prop aircraft are more efficient that turbofan jet aircraft?

At these low speeds, yes.

 

[FredGarvin]

At least regarding the cars you must know that the power plants, even the worst of them, are much more efficient that any internal combustion engine going down the road.

Are we talking efficiency or polluting/going green?

Maybe so. First X prize didn't advance the art in any areas?

Nope. Not a bit.

 

[mheslep]

Are we talking efficiency or polluting/going green?

Improving the first usually means improving the second, though 'going green' is not on the top of my to do list. I'm primarily after getting off imports and spending less on energy per mile. Electric transportation does that nicely, probably in aircraft too from what I can see.

Nope. Not a bit.

Hmm. Do you believe that's specific to the X Prize and its particulars, or every such contest: Lindberg crossing the Atlantic, etc?

 

[mugaliens]

No, I'm saying why would you power a fan, instead of a prop. Larger rotors are more efficient.

At what size aircraft operating at what altitude and for what distance? Why do highly efficient puddle-jumpers side with turboprops while highly efficient medium and long-haul aircraft side with turbofans?

 

[Cyrus]

Valid point, but for this competition I fail to see why one would use an electric duct fan.

 

[mheslep]

Valid point, but for this competition I fail to see why one would use an electric duct fan.

It is a first across the line, coast-to-coast speed contest. I see the decision (prop or turbofan) depending on the speed/efficiency curve of the chosen aircraft. If the efficiency allows it, go with a fan and get 3-400 knots.

 

[RonL]

From earlier "[url[/URL], I considered a Bombardier CRJ900, modified with ducted fans, at 12 kWh(41k BTUs) per mile based on its gross range data given a full load of fuel. Perhaps that could be cut that in half for a more efficient, slower, jet aircraft appropriate for this contest, or 6 kWh (21k BTUs )per mile? Distance for the contest is ~2500 miles, with two stops allowed, or ~850 miles per leg, 5100 kWh (17.4 million BTU )per leg.

[PLAIN]http://en.wikipedia.org/wiki/Zinc_air" non rechargeable batteries achieve about 0.5 kWh per kg, giving ~11 metric tons of battery per trip leg. However, power density of metal air batteries is low, at least for commercial models. This 11 m ton pack would provide only 1.1 MW.

Ducted fan concept:

Can you supply any information about what conditions the HTS motor has to operate in??

 

[mheslep]

Can you supply any information about what conditions the HTS motor has to operate in??

Depends of course on the size and performance envelope of the target aircraft. Here's the original thread:
https://www.physicsforums.com/showpost.php?p=2292842&postcount=14

and discussion of the original work
Overview:
http://www.drives.co.uk/fullstory.asp?id=2033

In Applied Superconductivity, IEEE Transactions:
http://ieeexplore.ieee.org/search/srchabstract.jsp?arnumber=5153109&isnumber=5166701&punumber=77&k2dockey=5153109@ieeejrns&query=%28%28masson%29%3Cin%3Eau+%29&pos=5&access=no"

http://ieeexplore.ieee.org/search/srchabstract.jsp?arnumber=5067019&isnumber=5166701&punumber=77&k2dockey=5067019@ieeejrns&query=%28%28masson%29%3Cin%3Eau+%29&pos=6&access=no"

 

[mheslep]

On a related note, NASA is due to release its small electric powered VTOL design today, Jan 20, at the American Helicopter Society.

https://www.youtube.com/watch?v=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/rhpPhvWvLgk&color1=0xb1b1b1&color2=0xcfcfcf&hl=en_US&feature=player_embedded&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowScriptAccess" value="always"></param><embed src="http://www.youtube.com/v/rhpPhvWvLgk&color1=0xb1b1b1&color2=0xcfcfcf&hl=en_US&feature=player_embedded&fs=1" type="application/x-shockwave-flash" allowfullscreen="true" allowScriptAccess="always" width="425" height="344"></embed></object>
http://www.scientificamerican.com/article.cfm?id=nasa-one-man-stealth-plane

It has the usual advantages associated with electric:

In principle, the Puffin can cruise at 240 kilometers per hour and dash at more than 480 kph. It has no flight ceiling—it is not air-breathing like gas engines are, and thus is not limited by thin air—so it could go up to about 9,150 meters before its energy runs low enough to drive it to descend.
[...]
At up to 95 percent efficiency, electric motors are far more efficient than internal combustion engines, which only rate some 18 to 23 percent. This means electric aircraft are much quieter than regular planes—at some 150 meters, it is as loud as 50 decibels, or roughly the volume of a conversation, making it roughly 10 times quieter than current low-noise helicopters.

and the usual disadvantages:

With current state-of-the-art batteries, it has a range of just 80 kilometers if cruising, "but many researchers are proposing a tripling of current battery energy densities in the next five to seven years, so we could see a range of 240 to 320 kilometers by 2017," says researcher Mark Moore, an aerospace engineer at NASA's Langley Research Center in Hampton, Va.

 

[Cyrus]

On a related note, NASA is due to release its small electric powered VTOL design today, Jan 20, at the American Helicopter Society.

https://www.youtube.com/watch?v=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/rhpPhvWvLgk&color1=0xb1b1b1&color2=0xcfcfcf&hl=en_US&feature=player_embedded&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowScriptAccess" value="always"></param><embed src="http://www.youtube.com/v/rhpPhvWvLgk&color1=0xb1b1b1&color2=0xcfcfcf&hl=en_US&feature=player_embedded&fs=1" type="application/x-shockwave-flash" allowfullscreen="true" allowScriptAccess="always" width="425" height="344"></embed></object>
http://www.scientificamerican.com/article.cfm?id=nasa-one-man-stealth-plane

It has the usual advantages associated with electric:

and the usual disadvantages:

I saw this last week at the DARPA conference I was at. I rolled my eyes then too. The comments on this link are borderline stupid. "No service -ceiling" oh yeah sure...right. I guess those propellers will work just the same in rarefied gas atmosphere...

Heh, I actually heard Dr. Moore talk last Thursday. He also had a samara wing vehicle. A lot of pie in the sky stuff.

I think it's good they are thinking outside the box, but in the end its a poor goal they are going after (flying cars). You should read my blog post on this nonsense. I would expect these kind of marketing ploys from companies, not NASA.

 

[Cyrus]

Probably should see a doctor about that eye problem.

Actually, I study VTOL so I know how to spot BS.

Yes I suppose 'no' service ceiling is hyperbole, but there is a valid point that the service ceiling is likely twice that of a similar combustion engine powered aircraft.

Whenever someone claims "no service ceiling," you know instantly they either have no idea what they are talking about (whoever wrote that article), or are being intentionally misleading. The aircraft is going to be limited by its ability to produce thrust at altitude, which is also a function of the propeller performance. Nice little fact that article left out. Also, there is a temperature lapse rate with altitude. Last time I checked, batteries don't like to operate in the cold, as it slows down the chemical reactions that produce electricity. Of course, we left out the fact that the energy density of batters is extremely low as compared to conventional fuels.

To continue, let's talk about rotor noise. That is a function of the disk loading, and the engine. The major contribution to the noise comes from the rotor itself though - hence you want low disk loadings.

Really? Why? Why should I consider NASA's Dr Moore to be spewing 'nonsense', 'pie in the sky' yet hold your 'blog post' authoritative?

Because this thing has a very high disk loading, it will have horrid, and I mean horrid auto rotative capabilities. You will come down like a fork lift. This thing does not have the markings of something people can practically use. You don't have to take my word for it though, I highly recommend you read some books on VTOL and judge it for yourself based on an informed viewpoint.

Because taking three hours to travel to a commercial airport, clear security, and board the aircraft is so practical?

Is this your only argument? If so, go reread the battery/range issue. If you think the FAA will let people fly around in this thing with almost no auto rotative capabilities, you're dreaming.

 

[Cyrus]

Don't get me wrong though. I think they can, and should, get a concept demonstrator built. Let's just be realistic and not pretend what it isn't - a personal vehicle people will use to go around town.

By the way, the installed HP required to hover (for a flying 4-seat car) is going to be -eeee-norrr-mous. Like, nearly a thousand horse power enormous.

Also, I don't think NASA is being dishonest, but they are definitely hyping it up for the public to get money for this thing. Given NASAs budget can you blame them? Ehh... I don't know. Dr. Moller has been saying his flying car will work for the last 30 years, yet still no car. Be weary of anything VTOL.

 

[russ_watters]

Maybe so. First X prize didn't advance the art in any areas?

Well it certainly led to some patents, but real, practical applications? No.

It is, however, a "stunt" that people want to try for themselves, so for a while anyway, the stunt itself provides a profit vector even without a practical application.

 

[FredGarvin]

Moller? All I can say is...meh.

I see he has changed his design from the 4 shrouded fans to two tilted props a la the Osprey. There's some major private innovation there. Take what has already been done. Well done Mr. Moller.

Cyrus is correct. Acoustics from that thing will be horrendous. Not to mention the dead notion that the average joe will be able to pilot a VTOL/STOL aircraft.

 

[mheslep]

Well it certainly led to some patents, but real, practical applications? No.

It is, however, a "stunt" that people want to try for themselves, so for a while anyway, the stunt itself provides a profit vector even without a practical application.

I think the technology release offered by these contests is rarely, if ever, a wholesale realization of the entire project. Rather, the uptake of technology is much more subtle, such as a piecemeal transfer of the into as upgrades into existing systems, or a redirect of existing R&D budgets.

I can't speak to the flow of technology from the X Prize. I worked on a team for DARPA's successful autonomous vehicle Mojave desert contest (~80 miles). There, we've seen no 'practical' examples of Detroit attempting to sell cars that drive them selves for 80 miles, nor will we in the near future. However, many of the ideas, practices, and algorithms introduced in that DARPA contest are suddenly everywhere in robotics research, nearly defacto standards, and some of the camera sensor work is going into current cars. Thus a fairly large push has come about in the robo world, DARPA's goal, all at the cost of couple $2-3 million for DARPA.

The all electric sports car Tesla might be another example. The two seater Tesla at $110,000 with 900 lbs of batteries is a 'stunt'; we will never see a mass production of that particular design. However, there's a good argument that the Tesla example convinced a GM VP (Lutz) that if some inexperienced Valley engineers could design, build and certify a high performance working car, GM certainly could, hence the Chevy Volt.

 

[Cyrus]

Moller? All I can say is...meh.

I see he has changed his design from the 4 shrouded fans to two tilted props a la the Osprey. There's some major private innovation there. Take what has already been done. Well done Mr. Moller.

Cyrus is correct. Acoustics from that thing will be horrendous. Not to mention the dead notion that the average joe will be able to pilot a VTOL/STOL aircraft.

In case I made things unclear, Moller is not working on the NASA vehicle shown in the video. He was simply at the DARPA workshop because of his background in flying cars. However, he is regarded by many as a fraud.

 

[FredGarvin]

Ahh. I misread. I thought he somehow got latched on to the NASA teet.

 

[mheslep]

Moller? All I can say is...meh.

Yes as Cyrus says Mark Moore is P.I. out of NASA Langley.

Cyrus is correct. Acoustics from that thing will be horrendous.

Is there a standard approach for characterizing the noise?

I'd read that increasing the number of blades and RPM increases the frequency signature which increases atmospheric attenuation - 8 blades shown here.

Re piloting VTOL, note this is not a tilt-rotor design, eliminating an additional control degree of freedom. I would expect that helps simplify control.

 

[mgb_phys]

Whenever someone claims "no service ceiling," you know instantly they either have no idea what they are talking about

I assumed that to mean no extension cord

Slighty on-topic.
Is there ANY circumstance in which a ducted fan is more efficient than a prop?
Sometimes they are more convenient for other reasons (lie the ducted rear rotor on helicopters)

 

[mgb_phys]

I can't speak to the flow of technology from the X Prize. I worked on a team for DARPA's successful autonomous vehicle Mojave desert contest (~80 miles)...Thus a fairly large push has come about in the robo world, DARPA's goal, all at the cost of couple $2-3 million for DARPA.

I think this was the smartest thing DARPA has done in decades.
Compared to the old way of just paying General Dynamics a couple of $Bn for some secret project that never sees daylight.
Even including the 10x as much spent by the universities and sponsors the RoI is incredible.

 

[mheslep]

I think this was the smartest thing DARPA has done in decades.
Compared to the old way of just paying General Dynamics a couple of $Bn for some secret project that never sees daylight.
Even including the 10x as much spent by the universities and sponsors the RoI is incredible.

We're in VIOLENT agreement on this. Generally, the robotics performance of the military contractors is atrocious, despite being hugely expensive, in comparison to the commercial vendors (e.g. Irobot) and academia.

 

[mgb_phys]

For everybody else - there is an excellent and entertaining talk by Sebastian Thrun from Stanford's team.

http://video.google.com/videoplay?docid=8594517128412883394

 

[FredGarvin]

Is there a standard approach for characterizing the noise?

I am not quite sure what you mean by standard approach. There is the area of aeroacoustics in which we look at the noise contributions due to aerodynamic influences. It is a relatively new area but a fair amount is known. In this case, it was mentioned that loading of the blades is a factor, as is relative mach number of each blade and blade tip. The spreding/attenuation over distances is very custom for each application in that the speeds and frequencies are always different. Plus, since this is unshrouded you don't have issues arising from waveguides, i.e. ducts. Things are different when a blade tip is sonic or supersonic. I can only assume they would be sonic, which means they will naturally attenuate/decay with increasing radius from the source.

There is a FAR (I can not remember the number off the top of my head) that governs the testing of noise signatures around airports. It is pretty detailed and measurements are required to simulate an aircraft arriving and departing and at altitudes, of I believe, 400 ft. It has been a while since I have read that FAR. I think it wouldn't be a killer for this application, but it would definitely be a concern.

 

[mheslep]

For everybody else - there is an excellent and entertaining talk by Sebastian Thrun from Stanford's team.

http://video.google.com/videoplay?docid=8594517128412883394

Seen it many times.

Thrun's team setup next to ours in the semi-final, so I had the opportunity to talk him and his team over several days. He's a fantastic engineer, great sense of humor.

 

[mheslep]

I am not quite sure what you mean by standard approach.

I was asking for indulgence in explaining how characterization of prop acoustics - fundamentals. Googling wasn't providing any useful fundamentals. This is a start:

There is the area of aeroacoustics in which we look at the noise contributions due to aerodynamic influences. It is a relatively new area but a fair amount is known. In this case, it was mentioned that loading of the blades is a factor, as is relative mach number of each blade and blade tip. The spreding/attenuation over distances is very custom for each application in that the speeds and frequencies are always different. Plus, since this is unshrouded you don't have issues arising from waveguides, i.e. ducts. Things are different when a blade tip is sonic or supersonic. I can only assume they would be sonic, which means they will naturally attenuate/decay with increasing radius from the source.

Well eventually I wanted to estimate dBl / distance given some prop assumptions. E.g. vehicle developing ~1000 lbs thrust at take off, RPM x, tip speed sonic, etc, add in latest
prop noise reduction techniques, then compare with known noise of 200HP turbine or piston engine.

 

[mgb_phys]

Thrun's team setup next to ours in the semi-final, ... He's a fantastic engineer, great sense of humor.

Rather letting the side down, as a German engineering prof though - stereotype-wise ;-)

 

[mheslep]

Rather letting the side down, as a German engineering prof though - stereotype-wise ;-)

Well he's been in the US for a long time. Then, Einstein apparently had a silly streak.

 

[Brian_C]

Sorry I don't follow. What source of power are you suggesting, if not an electric motor? Edit: Perhaps you are asking: why use an electric motor instead of a traditional gas turbine? Electric motor can be >95% efficient, is quiet, as you mentioned above, and can run on electric charge that may have been generated on the ground and stored in the aircraft.

Post #2, for purposes of this prize. 11 metric tons of battery per 850 mile leg.

I would suggest obtaining a formal education in the subject before making such outlandish claims. That 95% efficiency won't do you much good if it comes with a huge weight penalty. Gas turbine engines are really unparalleled when it comes to thrust/weight ratio and energy density.

 

[mheslep]

I would suggest obtaining a formal education in the subject before making such outlandish claims.

Thanks, I think I have a pretty good one, and a license to use it, though it is limited on the subject of aerodynamics. To be constructive, could you show how those numbers (11 metric tons / 850 miles) are outlandish? I think I've crunched and shown the basic numbers if you backtrack the post.

That 95% efficiency won't do you much good if it comes with a huge weight penalty. Gas turbine engines are really unparalleled when it comes to thrust/weight ratio and energy density.

Gas turbines are not an option for the prize, hence the thread topic "CLEAN AVIATION". Please see the https://www.physicsforums.com/showpost.php?p=2535479&postcount=1":

Superconducting motors operating with almost no losses could achieve power densities of 10–20kW/kg (and perhaps even higher) and torque densities of more than 35Nm/kg (compared to 10Nm/kg for the best conventional motors), the US researchers say.

Edit: maybe gas turbines hold the trophy for thrust/weight; the above challenges power/weight.

Maybe also see another thread for existing HTS propulsion research.
https://www.physicsforums.com/showpost.php?p=2292842&postcount=14

 

[Cyrus]

I took issue with a statement made by many of these articles: namely, that you don't need air intakes because it's electric. This is hog-wash because anyone that has flown an electric airplane knows they get very hot (battery, motor, and electronics). Cooling them is absolutely an issue. I do not buy that they don't need 'air intakes' for this vehicle. There will be significant power losses in the form of i^2R.

Also, how is this thing 'stealth' with big spinning rotors?

 

[mheslep]

I took issue with a statement made by many of these articles: namely, that you don't need air intakes because it's electric. This is hog-wash because anyone that has flown an electric airplane knows they get very hot (battery, motor, and electronics).

You mean RC airplanes? That's the 'because'?

Cooling them is absolutely an issue. I absolutely do not buy that they don't need 'air intakes' for this vehicle. There will be significant power losses in the form of iR^2.

I think the point here is that the air required for combustion, on the order of liters per second per HP*, completely dwarfs any air flow required for dissipating the couple hundred watts from this one man aircraft. Given the stated battery load (45kg) for Moore's VTOL, the [STRIKE]maximum[/STRIKE] continuous power is probably ~11kW (15HP). Though a small intake would suffice, no air intake at all is required dissipate 5% of that power as heat, just air flow over sufficient dissipative surface. I've built enclosed electronics boxes that conduct/convect away 500W from a two cubic foot box.

*quick math for gasoline combustion at 30HP requires 1 liter O2/sec, 5 liters air/sec, STP

Also, how is this thing 'stealth' with big spinning rotors?

How does one calculate the dBls / distance from these rotors?

 

[Cyrus]

How does the fact that a UAV is RC scale, or large scale, change the fact that there *will* be power losses by the engines that pose a thermal problem?

Please explain why you think this is not the case.

Also, what calculation did you do to get this 15HP number from? I don't believe this for one second.

Also, I did not say 'quiet' I said 'stealth': as in, radar cross signature.

 

[Cyrus]

Let's do a simple calculation using the momentum theory equation of an *ideal* rotor. A real rotor will inevitably require more power:

P = \frac{T^{3/2}}{\sqrt{2 \rho A}}

Assuming:

\rho = 0.002378 slug ft^-3
A = 28.27 Assuming a generous 6' rotor diameter
T = 300lbs (Assume 600lb GTOW)

That gives a power of about 25.7HP, very close to the claim on SIAM article of 60HP total (30HP each)!

 

[mheslep]

How does the fact that a UAV is RC scale, or large scale, change the fact that there *will* be power losses by the engines that pose a thermal problem?

Please explain why you think this is not the case.

Because the efficiency of electric motors and battery packs varies considerably. Larger motors can hit 95-98% efficient, but it is difficult to do that at small scale. Also I wouldn't imagine there is much room or effort made for thermal dissipation made on an RC, at least not the couple small ones I've toyed with. Small motor/battery mounted on poor heat conductors - plastic/composite - so yeah they'll get hot.

Also, what calculation did you do to get this 15HP number from? I don't believe this for one second.

SIAM said Moore's using a 45 kg battery load. Li Ion puts out http://en.wikipedia.org/wiki/Lithium-ion_battery" continuous (above I said maximum and corrected that to continuous) Edit: maximum battery discharge rate is typically be 10x (250W) for very short periods, i.e. peak up to 150HP. The motor would undoubtedly be the limiting factor - SIAM suggests it is 60HP.

Also, I did not say 'quiet' I said 'stealth': as in, radar cross signature.

Wasn't the 'stealth' reference in SIAM was on thermal signature? Obviously electric will be low compared to combustion.

Yes:

n addition, since electric motors are so efficient, they also generate far less heat. This not only gives them a lower thermal signature for military stealth, but means they don't need anywhere near the same amount of cooling air flowing over them that internal combustion engines do,...

 

[mheslep]

Let's do a simple calculation using the momentum theory equation of an *ideal* rotor. A real rotor will inevitably require more power:

P = \frac{T^{3/2}}{\sqrt{2 \rho A}}

Assuming:

\rho = 0.002378 slug ft^-3
A = 28.27 Assuming a generous 6' rotor diameter
T = 300lbs (Assume 600lb GTOW)

That gives a power of about 25.7HP, very close to the claim on SIAM article of 60HP total (30HP each)!

Thanks. How does one estimate the acoustic output of such a prop?

 

[Cyrus]

Thanks. How does one estimate the acoustic output of such a prop?

Want a PhD? Hehehe, honestly, I think its all empirical. The equations look like the NS equations: no closed form solutions.