“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Monday, September 27, 2010

CA ISO system status

It's been a VERY hot day, with all-time temperature records broken in Southern California. How is the California Independent System Operator (CA ISO who manages our grid) handling it?

Not really so bad (click on graphic for a larger view).

Tuesday, September 21, 2010

The Airbus A319 saga - epilogue

Herehere, and here I've posted about various data-gathering exercises and calculations regarding the Airbus A319. The data was gathered on two flights, one on takeoff from Laguardia in New York to O'hare in Chicago, and the other on landing from Chicago at John Wayne Airport in Orange County, CA. I mentioned that the calculated landing speed seemed too low and that the landing roll seemed too short.

As it happens, my office window overlooks Long Beach Airport where Jet Blue provides service using the very similar Airbus A320. Rhett Alain over at his Dot Physics blog posted an article on an iPhone 4 app from Vernier Software and Technology called Video Physics. It allows the use of iPhone videos to do rudimentary analysis of the physics (position, velocity in the x and y axes) involved and to email the data files to a "real" computer for further analysis in Vernier's Logger Pro software.

I took video of a couple of Jet Blue's A320s on takeoff and landing and used the Vernier products to determine the speeds. As I suspected, my estimate of 152 knots for the A319 takeoff speed at Laguardia compared fairly well with the measured speed of 167 knots for the A320. The landing speed was another story. My accelerometer measurements and numerical integration with a taxi speed assumption let to a calculated landing speed for the A319 of 99 knots. My measurement for the A320 was 129 knots. This comports much more favorably with my knowledge of aircraft operations and what I've seen on the web.

I'll be travelling to Houston in November; I suppose it's possible that my iPhone will accidentally be measuring acceleration on takeoff and landing on that trip as well.

Saturday, September 18, 2010

Will ingenuity save us?

As is my wont, I entered a conversation on Joanne Nova's global warming skeptic blog site. The nature of my comments revolved around my contention that we won't be able to bring the underdeveloped world to the standard of living of the developed world since that would require increasing our primary energy consumption by about a factor of four, even without an increase in population.

The sentiment on that site is that progress is non-linear and unpredictable and that human ingenuity will result in breakthroughs that can make it possible for all seven or even nine billion people to live on Earth at western standards of living. People opine that gains in efficiency will enable more to be done with less - one person said that "a worker lying naked on a beach with an iPhone can be more productive than a whole office with several tons of gear in 1978." Really? Let's take a look.

I pulled statistics from an Energy Information Agency web site and Angus Maddison's web site and combined them into a spreadsheet. I was able to compile data from 1980 through 2006, surely a time when the efficiencies cited above would be in play. A couple of interesting charts emerged, the first shows per capita gdp as function of per capita energy use.
It looks an awful lot to me as if per capita gdp is purchased primarily with per capita primary energy use. Next, I looked at the ratio of per capita gdp to per capita energy use from 1980 to 2006.
Hmm. This is the the amount of gdp produced by a quantity of energy expended each year. The fact that it is increasing definitely shows a trend in favor of a more efficient use of energy to produce economic output but I see no indication of a breakaway trend; certainly nothing that will enable us to bring a western standard of living or anything close to the developing world at rates of primary energy use that are remotely feasible.

I'm hugely in favor of nuclear energy, solar, wind, geothermal, tidal, and other ways of extracting energy from the environment and I do believe that a standard of living that a Westerner such as myself could accept can be achieved for the world. Such things require focused effort, long-term planning, and massive investment.  I'd like to think the free market and ingenuity would find the solution, but I see little sign of it.

*Extensively edited to fix typos. I have GOT to be more careful about proofreading before hitting the PUBLISH POST button.

Sunday, September 12, 2010

More on Moller International and the "Skycar"

Back in March of 2009, I made a couple of posts (here and here) about the Moller Skycar. I questioned some of the claims made for the vehicle with respect to fuel economy and speed. The other day, a comment on the second of my posts related to Moller mentioned that my posts had been discussed on the Moller blog site. I'll quote the comment by a blog visitor and the answer by Bruce Calkins, Moller International's General Manager, in full:

A long time skeptic  - Query re: concerns about range and fuel efficiency
I was curious to know what Moller International thinks of the speculations by this blogger here: http://hamiltonianfunction.blogspot.com/2009/03/moller-sky-car.html and here: http://hamiltonianfunction.blogspot.com/2009/03/horsepower-fuel-efficiency-and_31.html I'm not sure I agree with all his assumptions, but he makes a pretty damning case. I would be interested to here the company's reaction.

Bruce Calkins  - Skeptics talk about fuel economy of the Skycar
There is a saying that a little knowledge is a dangerous thing. The blog entries seem to fit into this category. While the maximum hp and burn rate are correct, the assumption that we remain at that rate for anything more than the few short seconds while we are operating in VTOL mode is not. Our hp requirement in cruise is about 120 hp, with the corresponding fuel burn rate. Range projections are based on the reduced fuel burn rate. We are currently evaluating a hybrid fuel-electric propulsion system that might reduce the total installed power requirement replacing it with a temporary electrical "boost" system for the VTOL-mode operations. If you would like a more detailed paper on the subject, email me.
 Before I comment on this I want to state that Dr. Moller is, without a doubt, a brilliant man and an extraordinary aerodynamic engineer. Certainly, he's far beyond my expertise. That said, he and those with whom he works have a long history of making claims that are never fulfilled. A good place to start reading about this aspect is at Wikipedia's Skycar page.

Now, Mr. Calkins is stating that the Skycar will cruise using 120 horsepower. The Skycar specifications page states that the cruise speed at 25,000 feet is 305 m.p.h. and that "max mileage" is greater than 20 m.p.g. It's not stated what airspeed is utilized to achieve this mileage. It may be very much lower than 305 m.p.h. In my airplane, the maximum range airspeed (that is, the airspeed at which I can achieve the greatest number of miles per gallon) is about 24% lower than normal cruise speed. Interestingly, on another page the claim is that "M400 Skycar can cruise comfortably at 275 MPH (maximum speed of 375 MPH) and achieve up to 20 miles per gallon on clean burning, ethanol fuel." I'll use this and supplement it with information in a paper hosted on Moller's web site. However, one thing I note is that none of the referenced pages give a categorical statement that the Skycar can achieve a cruise speed of, say, 275 miles per hour while it's getting 20 m.p.g. Instead, statements such as that quoted above can be backed away from by saying "well, yes, it can get 20 m.p.g. at the minimum point on the thrust required as function of airspeed curve," typically not far above the maximum L/D (lift/drag) ratio airspeed.

But let's proceed. We'll start with the assumption of steady flight in cruise. The conservative claim above is that the Skycar will do 275 m.p.h. in cruise and Calkins states that it uses "about 120 horsepower." OK, as I've mentioned any number of times, power is equal to force times speed, so force is equal to power divided by speed. The Google calculator makes this division and  handily converts the units to newtons, yielding a thrust of 728 newtons.

Now, as we learn in high school physics or in airman ground school, for an airplane in unaccelerated flight (as the Skycar would be under the cruise condition assumed here) thrust=drag, and lift=weight. Hence, we're considering a total (lift induced plus parasitic) drag of 728 newtons for an aircraft travelling at 275 miles per hour. We need to determine if this is plausible. Without a lot of mathematical derivation, it's pretty easy to show that, in unaccelerated cruise flight, Thrust=Weight/(Lift/Drag). That means that Lift/Drag=Weight/thrust. Here we have (using 2400 pounds or 10,676 newtons as the "gross weight") that Lift/Drag=10,676/728=14.66. But the specifications page referenced above has the so-called maximum L/D (the maximum ratio of lift to drag) as 12.5. Now, this maximum ratio is at a specific airspeed, any other speed will produce a lower L/D ratio. 14.7 cannot be achieved.

The Moller International web site does not give sufficient data to go much further (wing span, wing area, flate plate area, etc.) so I can't really do much more than this. I will say that the figures claimed by Moller International are likely not outlandish but, in my opinion, they are very significantly exaggerated.

Monday, September 06, 2010

Unit ambiguity in the New York Times?

I've made several posts (here for example) decrying people's cluelessness with respect to scientific concepts and, in particular, with respect to units. But do we have an example in the New York Times? I follow the New York Times Twitter feed (nytimesscience) and read the following: When It Comes to Car Batteries, Moore's Law Does Not Compute http://bit.ly/bSuX3e. Naturally, I clicked on the link and it took me to an an article on the rate of advance in battery technologies, both with respect to energy density and charging rates. All very interesting, and the interview subjects were from IBM and Better Place.

But about midway through the article, I read the following:
He illustrated the challenge of building a battery with the energy density of gasoline by recounting that it took 47 seconds to put 13.6 gallons of gas in his car when he stopped to fill up on the way to San Francisco. That’s the equivalent of 36,000 kilowatts of electricity. An electric car would need to pump 6,000 kilowatts to charge its battery.
Does this make sense? Let's parse it.13.6 gallons of gasoline contains (at 125*10^6 joules/gallon) 1.7*10^9 joules. Putting this in the vehicle in 47 seconds yields a "rate of energy transfer" of 1.7*10^9 joules/47 seconds, or 36.2*10^6 joules/second or just over 36,000 kilowatts. OK, so far so good.

But where does the 6,000 kilowatts come in? Well, the internal combustion engine (ICE) in the gas powered car might use energy at something like 22% efficiency, so the 1.7*10^9 joules might translate to 3.74*10^8 joules of useful work. OK, an electric motor with the power to drive a car will typically have a minimum efficiency of 92%, so that means that we'll need 3.74*10^8/.92 = 4.07^10^8 joules of electrical energy put into the battery. Doing this in 47 seconds yields a charging rate of 8.6*10^6 watts or 8,600 kilowatts. Not really so far off, and I guess that that's where the figure came from.

Stepping back, it's a very good illustration of why we love fossil fuels. Suppose IBM and Better Place succeed in creating a lithium air battery with the required energy density and ability to accept a charge at the rate described above. Now, imagine a "charging station" with, say, 4 cars charging their batteries at the rate of 6 megawatts, and imagine that you're at a corner with another station across the street doing the same. As I drive around, this is not at all an unusual circumstance at some times of day. So, at this corner, we'll need to be able to supply at least 48 megawatts of electrical power. That's about 5% of the power from a gigawatt generating station (this is a big facility). Getting energy from a power plant to a charging station at this rate, with the ubiquity of today's gas stations, is an incredibly difficult transmission problem

As I've demonstrated in a previous post, I believe it will be possible to install sufficient capacity to supply electrical energy to a fleet of electric cars. But the ability to deliver it at an acceptable rate to batteries that can store it is definitely the sine qua non of the widespread adoption of electric vehicles.

Sunday, September 05, 2010

The Chevy Volt - is it for me?

I've already posted about the Chevy Volt and the mileage claims made for it. But the time is coming to replace the Land Rover LR3 HSE that I've been driving since 2006. The Land Rover is owned by my Company and, in the current economic environment, there's little excuse for being provided with such a vehicle. I've mentioned my partner and the BMW X5 he drove, also owned by our Company. He's purchased a Toyota Prius (NOT company owned).

So, I'm wondering what to drive. The choices really seem to be the Nissan Leaf, the Volt, and the Prius. I'm leaning against the Leaf because it's range is about 100 miles on a charge and, though my commute is about 62.5 miles round trip, I sometimes need to go to meetings from the office or go to places other than the office from home and there's no infrastructure to charge the Leaf "on the road."

The Prius is all well and good but, well.... my partner got one. So, what about the Volt? It has much to recommend it for my application - though it's only estimated to get 40 miles on a full charge prior to using the internal combustion engine (ICE) to supply energy to the electric motor and my one-way trip to work is about 30 miles, I can charge it at the office and use the ICE only in the circumstances described in the previous paragraph. So, decision made, right?

Not so fast. This vehicle has an MSRP of $41,000 for the base model. A tax credit (not sure how the money is actually collected) of "up to" $7,500 is available bringing the price after the credit down to $33,500. This is a high price for what is really a four passenger commuter car. So how does the energy situation compare to my current vehicle and to others I might consider?

In order to estimate potential savings some assumptions will need to be made regarding how often and for how far the ICE in the Volt would be used. So, I'll figure that I'll do my normal commute four days per week and that I'll plug the Volt in at the office (actually, down the street at the laboratory) during each of those days so that the ICE isn't used. On the fifth day, I'll assume I go to the office and then leave for a meeting 35 miles away, that is, 70 miles out and back from the office, and then another 32.5 back to the house. I'll also need to use the fact that the Volt is specified at 50 m.p.g. when the ICE is running the electric motor. I can, no doubt, do better than that but I'll use it.

Using these figures, I estimate that I spend $61.91 per week or $3,219.34 annually on gas in the Land Rover, and that I'd spend $22.94 per week or $1,193.04 annually for gas in the Prius, and $17.44 per week or $907.00 annually on gas plus electricity for the Volt.

Now, the Land Rover is paid for but not by me (except indirectly). The Company will get a minor cash infusion by selling it. I'd estimate that the Prius will cost about $7,000 less than the Volt after all is said and done (that is, purchase price out the door). The $286/year isn't going to make up that difference, so the rational thing to do is to buy a Prius, assuming that a pure ICE vehicle is ruled out. More to follow.

Saturday, September 04, 2010

A319 - the final chapter

I've discussed the accelerometer data I gathered on takeoff and landing in Airbus 319's, and I made some calculations with the data involving engine thrust and energy dissipated in braking. The final calculations I've made involve takeoff and landing rolls of the aircraft.

Excel makes it very easy to perform numerical integration of a time series of data such as that gathered by the Pasco Sparkvue software on my iPhone. The basic idea is that the sample rate was set at 20 Hz, so a data point was gathered every 0.05 seconds. I assume that acceleration is constant between samples, multiply the duration of 0.05 seconds and add it to the previous velocity to get the new velocity. Rinse and repeat. Do the same to integrate velocity to get distance.

On takeoff, initial speed is 0 and initial distance is 0. On landing, initial distance is 0 but initial speed is back-calculated by assuming a speed when braking stops. In my earlier posts, I assumed a speed at the end of brake application of 10 knots but that gave fairly unrealistic landing speeds and rolls. I adjusted to 15 knots which is acceptable by the A319 operating manual (max. taxi speed is 20 knots, 10 knots in turns). This gave a more believable touchdown speed and landing roll (though still, I suspect, too low and too short).

I calculated the distance from start of takeoff roll to rotation to be 4,350 feet and, as I mentioned in the earlier post, the rotation speed to be 152 knots. I find these numbers to be pretty credible. For landing, I calculated the touchdown speed to be 99 knots and the landing roll to be 2,800 feet. The latter two numbers are suspect, hopefully an A319 pilot will comment. Or, perhaps, I can install an A319 simulation in MS Flight Simulator and try it myself.