Thursday, March 9, 2017

"Peak Speed" for the World's Airlines




So, it is true: planes fly slower nowadays! The video, above, shows that plane trips are today more than 10% longer than they were in the 1960s and 1970s for the same distance. Airlines, it seems, attained their "peak speed" during those decades.

Clearly, today airlines have optimized the performance of their planes to minimize costs. But they were surely optimizing their business practices also before the peak and, at that time, the results they obtained must have been different. The change took place when they started using the current oil prices for their models and they found that they had to slow down. You see in the chart below what happened to the oil market after 1970. (Brent oil prices, corrected for inflation, source)


It is remarkable how things change. Do you remember the hype of the 1950s and 1960s? The people who opposed the building of supersonic passenger planes were considered to be against humankind's manifest destiny. Speed had to increase because it had always been doing so and technology would have provided us with the means to continue moving faster.

Rising oil prices dealt a death blow to that attitude. The supersonic Concorde was a flying mistake that was built nevertheless (a manifestation of French Grandeur). Fortunately, other weird ideas didn't make it, such as the sub-orbital plane that should have shot passengers from Paris to New York in less than one hour.

If this story tells us something is that, in the fight between technological progress and oil depletion, oil depletion normally wins. Airlines are especially fuel-hungry and they have no alternatives to liquid fuels. So, despite all the best technologies, the only way for them to cope with higher oil prices was to slow down planes, it was as simple as that.

Even slower planes, though, still need liquid fuels that are manufactured from oil. We may go back to propeller planes for even better efficiency, but the problem remains: no oil, no planes, at least not the kind of planes that allow normal people to fly, something that, nowadays, looks like an obvious feature of our life. But, as I said before, things change!


Note added after publication. Out of curiosity, and also as the results of some comments received for this post, I went to look at the rated cruising speed of various passenger planes.  It seems that there is no detectable change in the reported values for similar planes, from the Comet to the Airbus 350. Still, the schedules indicate a slowdown of about 12% in the flight time. In part, I think it is to take into account the crowding of airports but also, in part, there has to be some leeway in how the plane is flown; it can be probably be slowed down, a little, from its rated cruising speed with a small improvement in fuel efficiency.

20 comments:

  1. Solar powered airships -- that would be nice and slow!

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  2. Interesting post. May I correct a few points. The performance of an aircraft is a function of Thrust v Drag and Weight v Lift. Engines provide the thrust the wings the lift. It is correct the faster you go the more thrust you need but the heavy the aircraft the more thrust you need or a big wing to generate lift to overcome weight (gravity). A turbine engine has to compress the air and a set of rotors at the back is the turbine which generates the thrust, the bypass engine was a clever work around for the problem of thermodynamics by extracting more thrust by using big fans at the front to push more air back and generate more thrust for a specific area of engine size. Pure turbines such as the Concorde or a jet fighter generate enormous amounts of heat so a bypass fan also helps with cooling the metal components. To get large loads (more passengers you need more and more thrust and the bypass fan enabled large amounts of thrust without more engines, like 8 instead of 4, which meant they were cheaper to operate because of reducing engine maintenance etc. But a bypass engine is also quite bulky and generates a lot more drag than a small profile turbine of high power output where fuel consumption is not an issue (such as a military aircraft) where performance or speed is king.

    The point to point times or speeds are comparable between the 1960's and today, what is now built into schedules is delays, delays on departure and delays in holding patterns on arrival, called it a congestion buffer. The graph on oil prices is pertinent and the main reason for airlines problems, each oil spike collected a lot of casualties in the airline business as they could not absorb or pass on the increased operating cost as the fuel used was fixed and at each spike, 1973, 1990 and 2008 a lot of airlines went to the wall. Those who go to the wall are those who cannot reduce costs because they are operating an aircraft with a lot of seats or high other cost and few customers. Those that survived were subsidised by governments or were able to change their cost structures to survive. In the meantime engine manufacturers went to significant effort to develop more fuel efficient engines for the amount of thrust they could produce. The designers went to enormous effort to develop fuel efficient airframes (less drag less weight). The fuel required for one flight in even say a 747 is enormous, they have to load hundreds of tons of fuel to carry 200-400 passengers. The whole air travel model is predicated on cheap fuel, raise the cost you go broke, reduce the cost you stay in business. Air travel as a mass commodity, if it ever was as few people on this planet ever get the opportunity to fly, is over but not yet recognised. It is not a viable mass transport system because of; its reliance on a high grade petroleum fuel, the sheer quantities of fuel the machines use, its technological complexity and the huge R&D investments required to get very marginal returns in efficiency. That is why there are basically only two manufacturers left and why the next major fuel price spike will finish a lot of them off for good. these are highly complex machines that require more and more upkeep as they age and the capital replacement cost over time becomes prohibitive. The Concord just about sent the UK and France broke and they never ever covered the costs. The technological frailty of the supersonic solution was exposed forever when a piece of metal from a tire went through a wing on take-off and the aircraft basically exploded, why, because it was flying fuel tank that used fuel to cool the whole metai structure at supersonic flight due to heat generated by skin friction of the air. It was a technological marvel and a maintenance nightmare. Complexity and oil, amazing the way the same problems come up time and time again when systems fail.

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    1. Thanks for the explanations Michael.
      A couple of questions:
      What is the chance of a long term role for short-haul propeller planes? I read that per passenger they use less fuel per passenger than a sea ferry, say Scotland to Ireland. Of course the ferry carries bulk cargo, these days motor cars, but that could change.
      Secondly, has bulk traffic - mass passengers in particular, I believe 80 millions per year thru London Heathrow - reduced the cost for elite traffic? Can we imagine for example, future oligarchs, their servants and necessary business associates having the means for intercontinental travel as the air travel system runs down?

      best
      Phil

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    2. Phil. There is no reason why pure jet aircraft could not be replaced by propeller aeroplanes providing they were turboprops. The issue has been speed, turboprops are more efficient than purejets but they are slower point to point. The key problem is that the modern world has been sold 'speed' especially on long haul routes. Speed, safety and comfort because with a pure jet you fly a lot higher than a turboprop and avoid weather, so it is both speed, safety and comfort that has made the purejet passenger aircraft so attractive. That was precisely the selling point of the Concorde, speed. It is my view that as the oil age winds down, air travel will return to being only available to the rich (private, corporate or government), which is paradoxically the way it began. One can argue all one likes on specific efficiencies of the type of aircraft but the reality is that they are highly capital intensive activities requiring highly specialised technically literate people to build, operate and maintain. Advances in aero-engineering have hit the limits of the laws of physics, simple. Mass or large scale air transport has hit the limits of growth common to all human systems, it cannot be scaled up and can only scale down.

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  3. Careful, Michael -- they don't want people like you helping the public "connect the dots". Just adds O2 to the fire. Even the best of them don't want it.

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  4. Careful, Michael -- they don't want people like you helping the public "connect the dots". Just adds O2 to the fire. Even the best of them don't want it.

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  5. Well Michael, partially... It's not so much a matter of airplanes and air travel. It's a matter of travel. Unless trains or intercity buses are electrified (at spectacular cost) and/or charging stations are placed along interstate highways so that liquid fuels aren't needed, the problem remains if aircraft are grounded but coast to coast travel still takes place. The last time I ran the numbers, a garden variety B737-700 can achieve something like 70 seat miles per gallon of fuel and on most flights that I take (and yes, I fly several times per year from Southern California to DC and elsewhere) there is a butt in every seat. A reasonably high mileage car (say, 35 m.p.g.) with two people in it doesn't do any better. And, for all their potential, trains are typically worse (let alone the issue of actually trying to get anywhere on one and yes, I have tried). So it will likely be all long-distance travel becoming unavailable, air transport being only one of the casualties.

    I flew from Houston to Orange County a couple of weeks ago in a B737-700. It held 137 passengers and burned about 17,000 pounds of fuel (I asked the Captain, I keep a record of all my flights, including A/C model, tail number, engine configuration, thrust, fuel burn). Jet A weighs about 6.8 pounds/gallon so it burned about 2,500 gallons of Jet A to travel some 1350 miles. That's 137*1350=184,950 seat (and passenger since all seats were occupied) miles. That's 74 seat (or passenger) miles per gallon. And the flight took about three hours.

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  6. By the way, I can't say with certainty, but I pretty confident that the airplane shown taking off as the narrator discusses "turboprop" engines is a Cessna 340. That aircraft is powered by two Continental turbocharged piston engines.

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  7. I like this though: http://www.solar-flight.com/projects/sunseeker-duo/ . It takes off and lands from any airfield, doesnt use a gram of fuel after building it and it seems lots of fun. They are building a 6 and a 10 seater now

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  8. Is Hyperloop the next Concorde, albeit a less expensive mistake?

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  9. Hello,
    I wonder how the business world will adapt to a life with less flights. For normal people, it will just mean that they'll have to stay around for the holidays, but business is so much based on the fact that you can have a meeting in Berlin and be back home in London for the night that I wonder how this will work.

    Best regards,

    Etienne

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    1. If (when) the airlines collapse, no one will fault peak oil. "We are sorry that we have to force the planes down because of the ongoing war (or the latest terrorist attack, or the latest emergency of whatever kind). Nothing to be worried about, folks; as soon as the emergency is over, the planes will restart flying. Guaranteed."

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    2. how biz adapts will be a moot point. when the planes ain't flying anymore because of fuel being too expensive, its likely the businesses using them will have gone bankrupt too. i'm sure we will keep airlines going as long as possible in spite of global warming, even at the expense of other economic activities. so when the crunch finally ends the airlines, i expect few people will be that bothered. i wouldnt be bothered now if they grounded every aircraft tomorrow. let the idiot majority stay home during the summer hols! poor things.

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  10. The video is well made, but I'm afraid your summary ("planes fly slower nowadays") is overstated, unless you assume the Concorde amounted to something significant in the past - of course it didn't, as it always was some kind of fancy rollercoaster (the video describes this well), and the vast majority of miles flown were on conventional planes.

    Regarding conventional planes, the trade-off between speed and consumption is a decision you have to make when designing the plane. Once the plane is built, you cannot really adjust it. As a consequence, if you want to know how the trade-off evolves with time, the main thing you have to do is take a look at the cruising speeds (and the cruising speed isn't a choice of the pilot, it really is embedded in the plane : for instance the "sweepback" of the wings does depend on it). And as the video says, the flight timetables convey no information : they have had more and more safety margins, that's all.

    For instance, the Airbus 330 had a cruising speed of Mach .82, and the more recent A350 has a cruising speed of Mach .85. It implies that, at least for long distance flights, there has been no "peak speed". But there is a "funny" thing : this design speed was decided before the oil price surge of 2008. And in the last years, Airbus developed an upgraded version of the older A330, which is currently having as much success as the supposedly better new plane... There may be several explanations to factor in, but my bet is that the old plane has a more relevant design speed, in respect to current oil prices. (Insights from the industry would be much appreciated!)

    Anyway, I doubt there will be a real "peak speed" for long-distance planes (ie new plane designs with speeds falling under Mach .80) : on long distances, the straightforward way to fuel savings obviously is to stack more and more people inside.

    Regarding shorter-range planes, the success of ATR since 2008 can be seen as a first sign of some "peak speed". But peak speed will truly be behind when some kind of bigger ATR, seating 150-200 passengers, will arrive on the market, and EasyJet et al. will decide that's the plane they need. Whether our technical society will collapse gently enough to allow this is an open question - but I must say I have my doubts!

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    1. Yes - and thanks for this comment. After I had written the post, I went to check the rated cruising speed of various planes and there is really no evidence that it has gone down over the years, from the Comet to the Airbus. Still, it is also true that the schedules indicate longer times for the same distance. I think it is due in part to the idea of taking into account the congestion of airports; but also there has to be some leeway in the way you fly the plane. It can be probably slowed down a little from its rated cruising speed. Not too much, of course.

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  11. Ugo, the conceptual idea of 'peak speed'is a distraction from the underlying issue identified about the price of fuel and the cost of fuel for airline or aircraft operations. Aircraft performance is a function of the laws of aerodynamics, speed is limited by the same laws, effectively if you want to double the speed you have to square the power. The most significant physical boundary of speed in flight is the speed of sound or Mach 1.0, this speed limit is a practical limit due to the problems that occur after you achieve that speed in terms of the airframe construction, the power required and the maintenance of control.There are significant engineering structural problems related to metals as the air friction at supersonic speeds generates significant heat, the faster you go the worse it gets to the point the integrity of the structure is compromised, so to solve that problem you need to resort to exotic alloys (aluminium and steel. To maintain that high speed requires very high levels of thrust due to the drag of the structure and the compressibility issue, that means an engine capable of generating very high power levels, the fuel consumption at that sort of speed and that sort of aircraft is well lets say breathtakingly large. The sheer tehcnical and engineering complexity of supersonic flight meant that it was not commercially viable because you had to charge Concorde fares (which in turn were not viable nor based on the true cost due to significant cross subsidisation).

    Airframes simply got larger and larger, so the issue of fuel consumption was disguised by the fact that the arithmetic of aircraft operation calculates the cost not on a seat basis but on the realities of flight or the best airmiles per gallon or litre, this again is constrained or assisted by the atmosphere at low altitudes where the air is dense, drag is high, at high altitudes where the air is less dense drag is lower, so paradoxically to achieve the best economy or air-miles per gallon, you fly as high and as fast as you can not slower, if you fly slower you actually use more fuel for the distance travelled. The quest for fuel efficiency was not driven by the cost of fuel specifically but by the need to be able to generate more thrust for less fuel burned. So the march of fuel efficiency gains was matched by the increase in the size and weight of the aircraft, for example if you look at the example of Boeing, the weight and carrying capacity jumps in a neat correlation as you move from the 707 to the 767 to the 747. From 120, to 240 to 400 passengers. The maximum speed of all three remains basically about the same in the range of about M 0.82 to M.086 that is a function of the laws of aerodynamics not of fuel costs. However the fuel required was decreasing for the rated power output but the fuel required was increasing rapidly, yes per pounds of thrust the engine was more efficient but you needed a lot more fuel because it was a bigger engine. It is in a way an example of both the laws of thermodynamics and Jevrons paradox.

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  12. All of this was predicated on a limited cheap resource, high quality turbine fuel. EAch oil spike destroyed the viability of people using less fuel efficient and older aircraft or those whose ability to sell the seats at a higher price was constrained by demand elasticity and substitution. For short or medium range distances the competition in the transport sector was the motor vehicle and trains. For long distance travel involving oceanic crossings there is no competition although there once was, ocean going passenger liners. Each oil spike has crashed the business model of airlines, the first spike took out the historical carriers, the second, new starts and subsidised historical carriers (like PanAm). The third was not so damaging but still had its casualties. In between time the overall size of the industry has grown, now that growth has a cost it is called congestion because the physical constraints of going from A to B mean you all have to use the same route, like a road airways can only accommodate so many aircraft at any one time in a 24 hour cycle. The work around this issue was to build more airports at different locations but the system is now basically saturated. So you need more seats in the same structure, hence the A380 or in a place like Japan the 747 used as a short haul domestic commuter. The key message is not speed but the inability of the resource base to support this luxury, finite ground space, finite oil, so once again yes there are the limits of physics but the limits to growth have been again reached and breached, population and finite resources. Nobody will ever build a supersonic or high orbital machine to carry people from place to place again.

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  13. I don't know why my comments weren't published. They insulted no one, contained nothing not demonstrably true, and were relevant and were not redundant. Two of them corrected factual errors in the video, one made a point which was, perhaps, not 100% in agreement with your viewpoint. I'd not have thought that your censorship (which, of course, you have every right to do on your own blog) would extend to comments such as those that I posted. My respect for you and your blog has decreased very significantly. I'd linked to your blog from mine, but will remove that link. I agree with censorship of spam, insults and ad hominem, threats, etc. but I do not condone and won't link to blogs that have a policy that would censor comments such as those that I made here. I know you don't get much traffic from my site, but it's a matter of principal. I don't expect to see this comment either but I assume that you'll read it.

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    1. Sorry, Rob. Some comments got stuck in the queue. Now I released them

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  14. It seems to be that the supersonic passenger plane is not old fashioned.
    Big ideas are in the pipeline.
    http://www.handelsblatt.com/technik/forschung-innovation/ueberschallflugzeuge-rueckkehr-der-koenigin-der-luefte/19507546-all.html

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Who

Ugo Bardi is a member of the Club of Rome and the author of "Extracted: how the quest for mineral resources is plundering the Planet" (Chelsea Green 2014)