Talk:Fuel economy in aircraft

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Comparison of Concorde and Boeing 747[edit]

The numbers in the table comparing these aircraft aren't consistent with each other. Each line of the table expresses the same underlying idea: fuel per passenger-distance. Therefore on each line, the ratio of the number in the left- and right-hand columns should be the same (or the inverse of that ratio in the 3rd line). But they aren't. There's something wrong here but I don't know what. Macboff (talk) 16:57, 15 January 2013 (UTC)

Discussion of fuel economy tables[edit]

(This discussion is moved here from a user-talk page, to be more than a two-person discussion):

Hello, thank you for your contributions to the Fuel economy in aircraft#Example Values section. Albeit enlightening, the car and buses comparisons do generate problems :

  • comparing fuel efficiency per seat and per pax needs the load factor, but this is dependent on the operator, not the aircraft
  • to be fair, I would add the speed of the transport or the time of travel, but how to include the travel time to the station or the cost of ownership of a personal car?
  • with all this, having a complete table would be very difficult

An apples to apples comparison with only aircrafts would be easier to maintain and expand. I would put a comparison table in the generic Fuel efficiency article between modes at a whole : air transport / rail / marine / car ... If that's okay with you I will transfer it later today. --Marc Lacoste (talk) 09:09, 17 July 2014 (UTC)

Thanks for your thoughts on this, Marc. I think the table needs some brief comparison to other transport modes for the economy figures for aircraft to be well understood. The figures for aircraft are quite high in comparison to mpg performance most people are familiar with -- the window sticker on a car in a showroom (or otherwise the oft mentioned EPA figures). The brief addition to table does this unobtrusively. Responding to your bullets, in order:
* The load factor aspect: The table as I first saw it didn't have the per passenger column. That was added after I added the Megabus line, which I flagged as the somewhat different metric (I couldn't find per seat data). I suggest deleting the Megabus line now that you have added one for Volvo bus, which is "per seat." As you said, adding the load factor or pax columns to the table is problematic because there are multiple operators, all operating differently. I think it is best to keep the table hardware-centric and therefore with the generalized data for "per seat" which allows rough performance comparison.
* The time factor: I think readers will be acutely aware of the time factor when viewing the comparison of modes. The table is about fuel economy and not time. Encyclopedias are about enlightenment, and as you said providing the brief context is enlightening.
* Complexity of the table. I suggest simplifying the table by eliminating the load factor and pax columns.
* Apples to apples comparison: I think with the deletion of Megabus and the two right hand (then blank) columns, the two car/bus lines provide an apples to apples comparison on the basis of fuel economy and should remain in the article. The generic Fuel efficiency article can of course provide a more detailed comparison among the various transport modes.}} Coastwise (talk) 16:09, 17 July 2014 (UTC)
I think using best cases for comparison isn't fair : the Prius could be 240mpg/seat, but the meaningful comparison would be between the whole air transport industry vs the whole personal car transport. In fr:Transport aérien I used Air France and Swiss as industry representative : they get 3,7 L/100 km per pax with a 80% load factor, implying 3L/100 km per seat. To compare cars, I used the whole french personnal car use : 29.6 billion litres for 424 billion km : 7 L / 100 km average, and there is 1.4 pax per car in average : pax consumption is 5 L / 100 km. (at 60km/h VS 800km/h) idem for bus transport : a modern volvo could be 560mpg/seat, and while megabus seems to have an excellent load factor, the UK average is 12.3 pax per bus/coach : (NB: this document could be the basis of an inter category table. There is something similar in France, too) --Marc Lacoste (talk) 21:35, 17 July 2014 (UTC)
That is an interesting report, Marc. Its stats for cars and buses seems to be an averaging of all kinds of uses though, and it seems to have a heavy weighting toward local use and commuting since those are predominant uses of such vehicles. In understanding the comparison to aircraft in the wiki table, a concept of comparable kinds of trips needs to be kept in mind, i.e what the report calls short haul (which it defines both as 250-940 miles (appx. conversion) and 500-2000 nm. For such car or bus trips I expect the load factor would be higher. The 1.4 passenger occupancy you quoted is for taxis, and the bus/coach one seems to be weighted by inclusion of smaller buses used on small distance trips. I think comparison of a Prius to a 787 on the line above it is fair -- both are best cases. From the Defra report, you could add a line for an average car at 36.5 mpg and an assumed seating for 4, or 146 seat-mpg (36.5*4). Megabus seems a fair comparison because it works on a model that is similar to regional airlines -- nearly 100 passengers and routes between points covered by short haul flights. I think for the table, speed is a non-issue. The difference in speed is inherently obvious, and which mode is chosen by a traveler is a matter of many factors that may include speed and fuel efficiency among others. But the topic of the article is solely fuel efficiency. With or without motor vehicles included, the table is only a rough guide. I still see no problem. I appreciate your discussion. Coastwise (talk) 23:39, 17 July 2014 (UTC)
The gaussian distribution is much wider for cars than for aircrafts : if we include a prius, we must also include a 9 MPG 1974 F150. I'm afraid there is more F150s on roads. It's really 1.4 pax per car avg : (french gov), so even a prius is only 70mpg per pax, and a F150 is 13! I'm afraid you want to think that aircraft are inefficient, but that's not the case, air transport is extremely optimized and consume less fuel per pax than cars at more than 10 times their speed, and could be comparable with buses, trains or ferries. I'm not air centric, for myself I ride a bicycle, use car sharing and never had a transoceanic flight. --Marc Lacoste (talk) 08:54, 18 July 2014 (UTC)

Marc, I think our discussion is best moved to the article's talk page. First, I really like the way you have broken the big table down into a series of smaller ones based on haul-length each model is intended for. Also, putting the comparison to other modes in sentence-form below the tables makes good sense.

Regarding the French study (I missed that link before), I don't read French so can't utilize that. What kind of trips (distance) are its pax load factors for? Is the data just for France, or is it EU wide, and do you know if comparable data is available for the US for long-distance highway travel? Concerning speed, I continue to think that is an issue apart from the topic of the article and table. If speed were relevant here, there is another angle to that. It is well-established through social research that travelers' sense of distance tends to be time dependent, with faster modes of transit leading to longer trips that are possible within personal time available. Thus in terms of fuel efficiency per holiday (instead of per mile), you can see where this perspective would lead. So, I suggest leaving speed out of this discussion, and leaving the focus of the article on the capabilities of the hardware.

The tables give both a sense of average aircraft performance as well as that of the current champion (Boeing 787). So, as I previously suggested, show the average auto (configured arbitrarily as a four-seater) and the Prius as the champion. Readers can do the simple arithmetic concerning their personal load factors to trips of comparable distance to the table data for the appropriate travel distance. The point is not to favor one mode of travel over another, but to provide perspective on what do these aircraft data mean. I am adding the average auto data to the concluding sentence, in hopes that this will help. Coastwise (talk) 20:08, 18 July 2014 (UTC)

I'm late : I didn't saw your reply until now. For the french study (it's from the USDOT equivalent), you can find the ref while searching for the term "taux d’occupation" (occupancy rate). I found this document for the french wikipedia, there should be comparable references for UK or US. I think it's representative for Europe, even for the western world. It's down from 1.5 in 1994 to 1.4 in 2008, but have no distinction between long or short distances.
Concerning speed, remember that the point of this article is not to make a podium for the most ecologic mean of transport, but to enable the reader to make his own opinion on transport, ecology, engineering, whatever domain he wants to check. Speed is a crucial parameter in transportation, at the center of the "capabilities of the hardware". (for myself, I'm close to your POV and find that intercontinental flights are too easy). From an engineering POV, a 2.4L/100km/seat aircraft at 900km/h is 100 times more aerodynamic per seat than a 2.4L/100km/seat car at 90km/h, and it's a stupendous feat.
I don't think it's the most precise thing to let "Readers can do the simple arithmetic concerning their personal load factors" : the point is to give a view on today's society as a whole, and the best way should be to compare the sector's averages (iata ~3.7L/100km/pax, cars ~5L/100km/pax, buses, trains...) It doesn't stop them from doing simple arithmetic. (again, for myself, i take pride for having a 3 to 4 pax average in my 4.5 litres per 100 kilometres (52 mpg‑US) car) (NB: if you want a champion, the VW 1L is the current one with .5 litres per 100 kilometres (470 mpg‑US) per seat, I think). Comparing best cases isn't the best way to compare IMHO. --Marc Lacoste (talk) 17:31, 2 December 2014 (UTC)
I understand what you are saying, but I still can't agree with your point of view. The tables review the performance of a wide range of aircraft models, including the very best. The comparison includes the average auto as well as the very best. As well, the comparisons are per seal mile in both cases. This is all basic information, and readers can evaluate it further however they may wish, or do further research if the information arouses curiosity. I don't see a problem here. Coastwise (talk) 05:47, 4 December 2014 (UTC)
If you can understand but disagree, I think my point is made : wikipedia isn't here to support your POV but to be accurate and NPOV. The current comparison doesn't include the average auto, only the best one, and the usual load factors are essential to grasp the efficiency of transport means. But that could be in the broader energy efficiency in transportation, indeed. --Marc Lacoste (talk) 08:13, 9 December 2014 (UTC)
No, your point isn't made at all. And this is not about POV. Also, the average auto is mentioned, and you have misstated what I said (understanding what you said does not constitute agreement with you.) Coastwise (talk) 15:52, 9 December 2014 (UTC)

Units Mangled?[edit]

The last column, fuel-efficiency per seat, gives metric L/km, but then gives English-units as mpg. (And if using mpg, it should be seat-miles per gallon.) The metric versions should be converted to km/L (so that high numbers mean high efficiency). Less clear, though, would be changing the column-name: while "fuel efficiency per seat" makes good intuitive sense at first, it doesn't match the unit-analysis, which is confusing. Should the title be "seat-fuel efficiency", or is that too unclear? — Preceding unsigned comment added by Not-just-yeti (talkcontribs) 16:05, 22 April 2016 (UTC)

The common European fuel economy metric is L/100-km. It is a mathematically natural metric, whereas MPG is not. That is, if you were to drive 50 miles at 100 MPG and 50 miles at 50 MPG, the MPG for the whole trip is actually less than the 75 average of those two numbers. This is because MPG is a metric of miles covered, whereas L/km is a real metric of fuel consumption. So I think the L/km units should remain as-is in the article, for both reasons (common usage and an appropriate metric). Coastwise (talk) 00:50, 23 April 2016 (UTC)

interesting works[edit]

Missing Aircraft[edit]

Where are the MC-21-200/300/400 jets? Where is the Comac C919? Where is the Sukhoi 130? Where is the Comac ARJ21? Where is the Mitsubishi MRJ 70/90? Where is the Embraer ERJ 135/140/145? — Preceding unsigned comment added by 2601:44:4200:1AB8:3444:C699:3A6F:E6CA (talk) 10:46, 15 December 2015 (UTC)

They are not mentioned due to lacks of references with the required data. - Ahunt (talk) 17:42, 15 December 2015 (UTC)

Minor correction[edit]

In this expression, referring to flight above Mach 0.85: "Above that speed, air begins to become incompressible"

That's backwards, it should read as compressible, not incompressible. — Preceding unsigned comment added by (talk) 18:11, 17 December 2015 (UTC)

No the text is correct. At low speeds air is compressible and as speed increases it becomes increasingly incompressible. That is what causes a sonic boom. - Ahunt (talk) 19:59, 17 December 2015 (UTC)
Respectfully, it's just the opposite! Incompessibility is a simplifying assumption; faster flows are more energetic and are therefore more able to compress the air, changing its density and thereby making the incompressible approximation invalid, which is why you only have to worry about compressibility at high speed. Here is a reference to clear things up: The first paragraph reads "A compressible flow is a flow in which the fluid density ρ varies significantly within the flowfield. Therefore, ρ(x, y, z) must now be treated as a field variable rather than simply a constant. Typically, significant density variations start to appear when the flow Mach number exceeds 0.3 or so. The effects become especially large when the Mach number approaches and exceeds unity." I would also refer you to the Wikipedia page for incompressible flow. Shock waves happen when disturbances exceed the local speed of sound; the ratio of aircraft speed to sound speed is the Mach number. I'd be happy to pull up more references if requested; every basic fluid dynamics text covers this. — Preceding unsigned comment added by (talk) 19:52, 18 December 2015 (UTC)
I should also explain--compressibility measures how much work is required to change the volume (or inversely, the density) of a fixed amount of air by a certain amount. It has to do with chemistry and thermal effects; it's not about speed, except to the extent that speed changes those. (I thank you for your edits by the way, ahunt, and I promise I'm not wasting your time here--not a pilot, but I do have a Ph.D. in aerodynamics, and I spent years studying and sometimes teaching this stuff.) — Preceding unsigned comment added by (talk) 21:58, 18 December 2015 (UTC)

Comment on aircraft table sorting[edit]

I find the tables to be mind-numbing in the amount of data presented, and have come to realize that much of the difficulty with them is the limited sorting capability of the table framework. However, if instead the following static sort is used, all of a sudden it all makes sense. Sort the list first by distance, and within each band of distance then sort by seat capacity. Apart from choice of aircraft, these are the factors that mainly affect economy. When the lists are sorted this way (I tried it in a spreadsheet), all of a sudden the data makes a LOT of sense instead of being a blizzard.

By static sort, I mean that sorting would be hard wired. Since it would be a double sort (distance and seat configuration), sorting by clicking the header would just mess things up, and it would not be possible to get back to the original sort.

I also advocate dropping the Fuel Burn column (lb/km) since the column to the right of it is the more important information for lay readers. It would also be good to add a column at the far right, Fuel Used Per Pax. (i.e. liters and gallons for the trip). The addition of this column is part of the reason that with the above manual sorting, the data finally speaks clearly. With this and the new sorting, the relationship of aircraft, distance and seating configuration to fuel economy becomes immediately apparent. Redoing the tables would be a lot of work, but I could help with it.

An alternative way to clearly show these relationships would be to combine all tables into one, sorted by aircraft model and seating configuration. There would be columns for each distance in the existing columns, with each of those cells holding the fuel burned (liters & gallons) for the trip. An accompanying table could be similar, but with l/100-km in the cells. However, these tables would likely be too wide for a web page. Coastwise (talk) 10:08, 16 February 2016 (UTC)

Your first proposal makes sense to me. Could you possibly create it here on the talk page to see if it works? - Ahunt (talk) 19:14, 16 February 2016 (UTC)

Main picture[edit]

current pic

I tried to illustrate the article which was quite dry before. The main picture still is problematic : it shows more contrails than fuel consumption. I tried to change it for a refuelling picture, but user:Ahunt put it back rightfully it's not illustrating very well the subject either, and the plane isn't identifiable for sure. But illustrating aircraft fuel consumption is hard: fuel burn is invisible! Better contrails pictures could be used :

But contrails are misleading, as they didn't show fuel burn. It could be more metaphorical :

Any ideas? --Marc Lacoste (talk) 07:59, 12 December 2016 (UTC)

My main concern about the bio fuel photo was that it is very much an edge case and also didn't really show the aircraft. I think to a casual reader it may not be clear what the photos was of. I think any of these photos you have proposed (except perhaps the last one) would be suitable. - Ahunt (talk) 17:01, 12 December 2016 (UTC)
Thanks for your reply. I was thinking the black smoke of turbojet/low bp turbofans airplanes would be a good illustration:

Not too far from transparent exhaust, high BP modern airliners? The first NASA convair seems the most striking. --Marc Lacoste (talk) 06:43, 13 December 2016 (UTC)

Those would be good if the subject of the article was air pollution, but don't really relate to fuel economy. I think the main attribute needed in the lead photo is something general that doesn't send a secondary message - Ahunt (talk) 16:14, 13 December 2016 (UTC)
True. So, do you think a metaphor (eg large airliners and tanks) or a contrail pic showing byproducts would be preferable? --Marc Lacoste (talk) 20:56, 13 December 2016 (UTC)
The contrail photos are more general and at least suggest the burning of fuel. - Ahunt (talk) 21:11, 13 December 2016 (UTC)
Another possibility would be a photo of a ground-crewman connecting a fuel hose to the fitting on the underside of an airliner wing. Coastwise (talk) 05:39, 3 February 2017 (UTC)
That's why I tried at first (see history, it's now the second pic), but it's only suggesting, not showing, so it wasn't really satisfactory either.--Marc Lacoste (talk) 08:04, 3 February 2017 (UTC)

Our efforts to select a good, illustrative pic are noted : it was used to illustrate an article in Aviation Week's BCA : Simulators Help Cut Emissions By Reducing Real-Time Training (pic only in the newsletter, the article is behind a paywall). This isn't the first time AvWeek uses a wikimedia picture, and I'm glad it's the case.--Marc Lacoste (talk) 16:01, 29 September 2017 (UTC)

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Concerning the edit on relative cruise speeds, jet vs. piston airliners[edit]

Marc, here is why I have undone your reversion to my edit that "jets have a cruise speed about 40 percent higher than" the fastest 1950s piston powered airliners. While you cite the L-1649 Constellation as having "250kts" cruise speed, several models cruised faster than that, and the L-749 had a cruise speed of 345 kts. The DC-7 had a cruise speed of 359 kts. Additionally, although some airliners have a maximum cruise speed of your cited 0.85 Mach, an operational cruise speed of 0.78 to 0.80 (515 to 529 kts) is common, due to fuel cost. Using those Mach-related speeds and the L-749 and DC-7 cruise speeds, jets commonly are operated at speeds in the range of 37% to 41% greater than those aircraft.Coastwise (talk) 09:04, 1 February 2017 (UTC)

The L-749 isn't in the piston vs jets comparison, and while the DC-7 is included (1.4MJ/ASK), it is noticeably less efficient than the modern jetliners (1.0-1.2MJ/ASK) (p.17). The included L-1049 is on par at 264 knots, and while jets aren't flying every time at their mach .85 high speed cruise, pistons weren't either (and there are Mach 0.9+ faster subsonic jets). Note that mach numbers for airliners are at -56°C, use convert for precise ground speed : Mach 0.85 (488 kn). Either way, we won't have a specific number but an order of magnitude. And giving percentages isn't the best way to comprehend the speed difference : to avoid misunderstanding (either jets are cruising at 185% or the pistons are cruising at 54%), stating 1.85 times is best, and rounding to two is straightforward.--Marc Lacoste (talk) 14:01, 1 February 2017 (UTC)
Marc, we need to avoid an edit war, so here I give further explanation of why I have again deleted your replacement of your statement (which you just reinstalled, now including a reference). FIRST, I have read your (interesting) reference three times, but do not find any support in it for your statement that "[n]onetheless, jets cruise two times faster" than the late model 1950s piston-powered airliners. SECONDLY, above in this Talk page your misuse of available data unreasonably skews your result to justify the statement. You compare a Connie L-1049 with a cruise speed of 264 kts to a jet at Mach .85 (488 kts), and in addition you fudge the latter's 85% higher speed to "twice" -- that's big mark-up and unreasonable. THIRDLY, your choice of the Connie at 264 kts instead of the DC-7 at 312 kts makes a huge difference in your calculation. A jet at Mach .85 is a cruise speed only 56% faster than the DC-7's cruise, barely half-again as fast, not twice as fast! FOURTHLY, the DC-7 was brought into production in 1953 and had later technology (and higher cruise speed) than the Connie, whose basic design was brought into production a decade earlier. Both the L-1049 and DC-7 are shown in comparison to jets (in terms of fuel efficiency) in Fig. 13.1 of Peeters et al. (2009). The most advanced technology in production at the time should be compared. Coastwise (talk) 09:40, 3 February 2017 (UTC)
1. In the ref, you can search for the included quote.
2. If rounding 1.85 as "twice" is too far, an "almost twice" is OK.
3. In Peeters et al (2005 not 2009), the p.17 first chart "Energy intensity per ASK", the L-1049 is at 1.1MJ/ASK, while the DC-7 is at 1.4MJ/ASK and modern jetliners are at 1.1MJ/ASK. If we want to support the article statement "only slightly more fuel efficient than the latest piston engine airliners", we have to select the L-1049 as the comparable, not the DC-7 which is 27% less efficient : the same difference as 29 points between 85% and 56%, fuel burn grows linearly with speed.
4. The DC-7 is not really higher tech than the Super Constellation, it just burn more to fly faster, as are early jets (the 707 burns twice as much for "almost twice" the speed).--Marc Lacoste (talk) 08:48, 4 February 2017 (UTC)

Another consideration is the Republic Rainbow (XF-12 / RC-2), which was a highly advanced late WW-II photo-recon plane, for which an airliner variant was intended. It never reached production for reasons explained in the WP article; however, the military version had a cruise speed of 363 kts, and the airliner was expected to have a cruise of 393 kts for which jets commonly cruise only 24-26% faster. That shows the relative potential piston aircraft would have had in terms of speed. For the aerodynamic and cooling/exhaust advances described in the article, it is likely that this aircraft would have been more fuel efficient than its contemporaries as well as current airliners; but I have seen no data. Without data this isn't for the article, but is a point to think about - particularly since structural advances of recent decades of course were not implemented. Coastwise (talk) 09:04, 1 February 2017 (UTC)

The near subsonic propeller airliner exists : the Tupolev Tu-114. While I understand your desire to demonstrate 50s piston airliners were already very efficient and the early jets were a step back, if jets won it was because their total cost (time cost + fuel cost) were lower or equal for a higher yield, and today's jets are much more efficient than those while retaining their speed (and if they could fly twice slower, they would be twice more efficient!), and propeller airliners are still less interesting for more than 300nm sectors. See cost index. --Marc Lacoste (talk) 14:01, 1 February 2017 (UTC)
You misunderstand my desire -- it is only accuracy and good documentation. Coastwise (talk) 09:40, 3 February 2017 (UTC)
I understand your good will, and a confrontation of referenced facts is certainly the scientific way towards unskewed truth.--Marc Lacoste (talk) 08:48, 4 February 2017 (UTC)

Marc, I have reverted your recent edit to what I had previously ('Nonetheless, jets cruise 40-80% faster than their predecessors'), which paraphrases a direct statement in a reference we have both used (Peeters et al. 2005). The reason you provided with your edit was, "I saw this too, but as detailed in the talk page, it's comparing the speed of the less efficient DC7, not the L1049 with comparable efficiency". This amounts to substituting your own judgment in place of a clear statement by the source, "serv[ing] to reach or imply a conclusion not stated by the sources" (WP:OR), and with a substantial upward rounding that is not "almost". Contrary to your reasoning, the 40-80% is not specific to the model you stated, but obviously to a range of aircraft. The four piston aircraft models referenced in Peeters et al. (2005) are tightly grouped in the paper's charts in terms of energy consumed per available seat kilometer (ASK), at a low level in relation to the curve for improvement in jet fuel consumption over the years. This tight grouping is more clearly shown in Fig 13.1 of Peeters et al. (2009), "Technical and Management Reduction Potentials", in: Gossling & Upham, "Climate change and aviation: Issues, challenges and solutions". Peeters et al.(2005)'s "40-80%" covers the relative speed of this well-performing group of aircraft in relation to the first sentence of the subject paragraph in the WP article. Coastwise (talk) 23:53, 9 February 2017 (UTC)

I understand your position. Then, if we detail the cruise range (40-80%), we have to detail the sentence "they have a comparable fuel efficiency as the latest piston engine airliners of the late 1950s". The energy intensity in MJ/ASK from [Peeters 2005] p.17 fig 5. (date retrieved with WebPlotDigitizer) of modern airliners (of the 90s) are A343: 1.134MJ/ASK; B772: 1.057; A333: 1.102; B772ER: 1.102; B738: 1.057. Average: 1.09MJ/ASK. 50s pistons are : L-1049 basis: 1.096 (+1%); L-1049H: 1.302 (+19%), L-1649G: 1.238 (+14%), DC-7C: 1.392 (28%) . So to be fair, We should have "Late 50s piston airliners are 1% to 28% more energy intensive than 90s jet airliners which cruise 40 to 80% faster". I'm afraid it would be too much detail, but it's precise.--Marc Lacoste (talk) 18:02, 10 February 2017 (UTC)
You reverted it with the summary : "original research (see: WP:No original research). Information in the cited source is adequate as-is.". It is certainly not OR as I only picked the [Peeters 2005] figures, I did not compute them again. Without those details, information is insufficient : if you want an overspeed range (40-80%), you must also show an energy intensity range (1-28%). You said "my desire -- it is only accuracy and good documentation".--Marc Lacoste (talk) 10:55, 22 February 2017 (UTC)
Marc, I responded to one or both of your statements in February, but now see that my response didnt' get saved. My apology, so here is a belated response. You have added more WP:OR to the WP:OR I identified above (see Feb. 3 and 9), by scaling off of charts in a publication. Please stick to characterizations or quotes of what authors actually say in cited publications, or to making more generalized observations (e.g. comparisons of an author's statements or between publications; or impressions of relationships in a chart or the rough [or sometimes precise, if on a grid line] numbers that a chart indicates).
You say "... if you want an overspeed range (40-80%) ...". Actually, I prefer not to state an overspeed range, but instead to deal in a general fashion with the difference in performance between piston and jet airliners. I included that phrase only to play ball with you, to find middle ground to a change you made that I felt was inappropriate. For more on how I have treated this difference in recent edits (which you have been reverting), please see my response of today in the next section below. Also, concerning generalizations, "about twice" is not a reasonable generalization of an 80% increase. Coastwise (talk) 22:24, 22 March 2017 (UTC)
Reading a chart isn't OR, as are routine calculations. When you say "I prefer [...] to deal in a general fashion with the difference in performance between piston and jet airliners", this is too much a shortcut  : we can't elude the fact that jets are faster than props, and this is the main explanation for the difference in energy efficiency, distance travelled by itself isn't sufficient. I understand your will to present Peeters's work as a counterpoint to the ICCT, but we should't be biased towards either. --Marc Lacoste (talk) 19:08, 24 March 2017 (UTC)

12 March 2017 edits[edit]

In twice reverting my recent edits, Marc LaCoste said in the respective reverts: (1) "reverted to pre 13 march rev : please provide detailed edit summaries for each change, thanks"; and (2) "if it's impossible to detail the changes, present them in the talk page per WP:EPTALK".

Below I will walk through the changes, and to folllow along open three browser tabs with the following content: A. The track changes; B. The original text; and C. My edits of 3/12.

The edits are listed by paragraph, in the order they occur on the track-changes page.

1. The intro paragraph is reworded and has some additional info.

2. The next changed paragraph (beginning "Each model of aircraft ... ) is reworded.

3. The next changed paragraph (beginning "Aircraft weight ...") is reworded.

4. The next changed paragraph (beginning "Flight altitude ...") is reworded and includes merges the paragraph that followed it in the original article.

5. The next series of changes merge the sections "Changes in commercial aircraft fuel economy since the 1950" and "Jet aircraft efficiency", and add information resulting in addtional information and subsections.

6. An intro paragraph was added to the section "Changes in commercial aircraft fuel economy since the 1950", foretelling topics of fuel economy from the individual aircraft model and the fleet perspectives; the latter is a new subtopic.

7. The content under the newly added subheading "The individual aircraft perspective" is the original topic, with edits. The photo was changed from the Comet to the B707 to match the thrust of the discussions in the document cited in both versions.

8. An original paragraph beginning "Today's turboprop airliners ..." was inadvertently lost in the editing and should be worked in somewhere.

9. Next encountered is the old heading "Jet aircraft efficiency". As mentioned above, the content was merged into the section being dicussed so the heading does not exist in the new version.

10. The heading "The aircraft fleet perspective" is added as a new topic. The old content to the left has been worked into to the sections on efficiencies of individual aircraft or the fleet, as appropriate.

11. Information on the Concorde was left out but if considered important could be added somewhere, in the subsection on individual aircraft. Information in the same paragraph on the A380, B747-400ER and B777-300ER is confusing in its detail and too focused on one part of the spectrum of airliners. It seems better left to the material in the tables at the end of the article, or if replaced in the section discussed here needs editing to be concise and demonstrate an important, broad point. As it is, I believe it detracts.

12. The added material about fleet fuel economy continues for a few more paragraphs in the track changes.

13. A subsection is added, "The effect of operations on fleet fuel economy", with underlying sections on tankering and operational factors.

14. Next a structural change was made, adding a major heading "==Technologies for improving fuel economy==", under which the original section on "Weight effect" follows, but renamed "===Weight reduction===" (i.e. as a technological matter).

15. Next, the subsection "====Aerodynamics====" was renamed "===Other technology potentials===" because it includes propulsion as well as aerodynamics. The section on "Fuel consumption factors" is renamed "Operational potentials", as a better description of the content and because fuel consumption factors are well discussed elsewhere in the article. The actual content of these sections was not changed.

16. No changes were made to the balance of the article. Follow three "Next Edit" entries in the track changes for minor edits and references corrections that I made minutes after posting the edit described here. Coastwise (talk) 05:30, 17 March 2017 (UTC)

It is worth mention that at the top of this Talk page the article is noted as being "Start Class" and "in need of immediate attention." I believe the changes I contributed (but at present are reverted) help address that. Among the criteria not met for B-class status are: "Coverage and accuracy; Structure; Grammar and style; and Supporting materials". My contributions in this and other instances are toward addressing those, and I believe further work is needed. Coastwise (talk) 16:36, 17 March 2017 (UTC)
Hello @Coastwise: and thank you for the complete details! The best way to include that could be through 16 edits, do you want to went through or do you prefer that I do it later (on Sunday)? --Marc Lacoste (talk) 18:51, 17 March 2017 (UTC)
Marc, I think your suggestion is excessively complicated, particularly since some sections were combined, and information from a few places was consolidated. I think the best way is to make the whole change and then you can review both the document as a whole and consider the individual sections. Coastwise (talk) 19:14, 17 March 2017 (UTC)
I've done it in a few minutes with a sock puppet account, almost everything is kept modulo line breaks or unimportant details: [1] You can see the article history is more clear, but I was unable to split the 5 to 13 changes, which seems to be the heart of your changes. I reverted it, could you detail the changes for each paragraph? thanks.--Marc Lacoste (talk) 11:39, 20 March 2017 (UTC)
I have made changes today in four passes. The first changes some headings and makes a minor adjustment to structure. The second replaces the remainder of my March 12/14 changes in one chunk. That is a major rewrite of two sections, including combining the sections, and rewriting them with the inclusion of much additional information and adding structure (subsections). Therefore, it is not possible to detail the changes to each paragraph. Just compare the original two sections (four short paragraphs total) to the new major section. You can easily do this with the two article pages in separate tabs -- it is the best (and really only way) given the nature of this revision. The third change today replaces original material inadvertently left out, and the fourth moves one paragraph to match the context. Coastwise (talk) 18:16, 20 March 2017 (UTC)
I reverted it again : you lost some references in the process supporting passages like "Modern jet aircraft have twice the fuel efficiency of the earliest jet airliners" or "Late 1950s piston airliners like the Lockheed L-1049 Super Constellation and DC-7 were 1% to 28% more energy intensive than 1990s jet airliners which cruise 40 to 80% faster" (it could look like it is done on purpose, since you and I were arguing over the redaction of those passages in the previous talk section). You should separate your additions to your modifications. Thanks.--Marc Lacoste (talk) 10:21, 21 March 2017 (UTC)
First, I see that my response to your February 10 and 22 in the Talk section above didn't get posted somehow, so I have made a fresh response there. It is pertinent to some of the following.
Concerning your March 21 post, the first part of what you say I "lost" (concerning the text citing to ICCT) was included in a different way, in saying "fuel economy improved 55%" (citing to Peeters et al. 2005, with page citation given). In reposting my text again today, I am adding a sentence to replace the "lost citation", expressed the same way as the Peeters material (i.e. the ICCT statement of a 51% improvement in fuel economy) and also providing a page citation for the ICCT reference. (And actually, your ICCT cite was in the first sentence of the main section, and the parallel Peeters 55% was in the first sentence of the Jet Aircraft Efficiency subsection -- one reason the article was not concise and in need of an edit.)
The second part of what you note that I lost was indeed intentionally omitted, since the material is covered in a different way in my changes. It added too much complexity, cluttering the article. Examples of how this is covered in the new text are:
* "By the 1990s the fuel efficiency of the latest jets was equivalent to the final piston-powered airliners, and now the Boeing 787 is roughly 20% better.[4]:294". The "roughly 20%" is an observation that anyone can easily make from inspection of the chart on that page.
* Concerning jets -- "The rapid adoption was because of jet airliners' markedly higher speed, altitude and range performance ...".
* Concerning jets in the fleet -- "The last piston-powered airliner models "were as fuel-efficient" as the average jet in the in the circa 2005 modern fleet, and later model jets such as the B777-200 or B737-800 were "slightly more efficient" than the average jet at that time.[2]:30 Subsequently, the B787 has entered service in the long-range component of the fleet and brings further efficiency gains, and is more efficient than the average jet in the present fleet.[4]:294" The quoted material is from the reference
I believe you have given no reason of any substance for reverting the revised text I have provided. I have bent over backwards to provide extra explanation you demanded (numbered items above). The reason for your latest reversion should have been handled either through small edits or by simply discussing your concerns here instead of reverting 9 paragraphs (which replace the original 4). Therefore, after the additional explanation here (and above regarding your above February Talk posts), I am once again posting my revised text. In doing so I am also moving one sentence from the subsection on individual aircraft to the very end of the subsection on aircraft fleets, where it fits best. Coastwise (talk) 22:28, 22 March 2017 (UTC)
The reason was given in the edit summary : you deleted referenced information. Before modifying it again, We should first obtain a consensus in the above section. You should separate your rewriting from your additions, they seemed interesting.--Marc Lacoste (talk) 19:13, 24 March 2017 (UTC)
Already asked and answered. We are at an impass. Coastwise (talk) 20:49, 24 March 2017 (UTC)
No we're not. Separate your additions from your modifications and we can discuss these mods, which aren't certainly impossible. I do appreciate your propositions, and we are closer in our views than you think.--Marc Lacoste (talk) 01:19, 25 March 2017 (UTC)
Thanks for your reassurance that our views are closer than it has seemed to me; however, I have presented my modifications in the only way I can and which I believe is appropriate. The modifications are apparent from the track-changes, in my view. Coastwise (talk) 06:07, 25 March 2017 (UTC)
I replaced your additions as an IP, I'll review them later.--Marc Lacoste (talk) 14:13, 25 March 2017 (UTC)

The aircraft fleet perspective[edit]

I'm afraid this new section gives too much coverage to the Peeters 2005 reference and doesn't fairly represent all significant viewpoints that have been published by reliable sources, in proportion to the prominence of each viewpoint in the published, reliable sources. Its main point is to remind post WW2 piston airliners were already very efficient, that the early jetliners were a step back and the mainstream idea that jetliner efficiency is growing is concealing that earlier technology was already efficient, in counterpoint to ICCT view. I think this as a counterpoint is a good thing and is noted "#Jet aircraft efficiency". But this new section is mainly paraphrasing multiple times the same idea, and as such renders the article as a difficult read in addition to giving it too much coverage. It also eludes the fact that jet airliners took over because they make more sense economically, as they replaced brand new piston airliners in less than a decade. I thus removed this sectin, which could be reinstated if it is resumed to one paragraph.--Marc Lacoste (talk) 13:40, 26 March 2017 (UTC)

Marc, the alleged redundancy you mention above exists only because you did not completely reinstate my edits (which you had reverted) in the edit you made yesterday as user You manufactured that redundancy yourself, by replacing only part of my edit. As I have said repeatedly, the edits I have made make sense only if they are reviewed as a whole, and my edit included entirely replacing the original text in the section "Changes in commercial aircraft fuel economy since the 1950s," including its "Jet aircraft efficiency" that you cite above, with a substantial rewrite. I believe all along your treatment of the my edits has been patently unfair, including making reverts for no reason of any substance (see my posts above), and this time your unreversion of only a part of my edit, in order to dismiss it as repetitive.
Further, since you believe by edit lacks balance (I disagree - it adds balance that was lacking in the article), the proper course is for you to add material instead of throwing out the new material.
For anyone reviewing this talk page, my edits in their most recent form can be found here, and there is discussion between Marc and me in the two above Talk sections. Coastwise (talk) 20:09, 26 March 2017 (UTC)

Updated layout[edit]

As the article structure isn't very clear and doesn't facilitate its reading, I propose an updated layout based on 3 main sections :

  1. The aircraft (flight theory to explain what impacts energy efficiency : Aerodynamics, Weight and Propulsive efficiency)
  2. Its exploitation (Speed, Altitude, Airlines and Operations)
  3. The history of fuel economy, Past: how was energy efficiency in the history of aviation; Present with the Example values (but they could be kept apart) and Future: was is envisioned to further enhance it?

I've done a draft in User:Marc Lacoste/sandbox/Fuel economy in aircraft, with the same material and additions for flight theory--Marc Lacoste (talk) 08:30, 28 March 2017 (UTC)

Without comments in a week, I've done it, the change history is available in User:Marc Lacoste/sandbox/Fuel economy in aircraft. --Marc Lacoste (talk) 07:26, 4 April 2017 (UTC)
When you posted I was writing the following to paste here. So I am reverting your change to enable further discussion first. Sorry, busy life here for the past week.

Marc, I think most of your reorganization is good, and I had been thinking along a similar line. Here are my thoughts on taking it a step further and addressing a still on-going matter:

1. Rename the "Aircraft" section, "Basic physics of flight efficiency"

2. Rename the "Aerodynamics" section, "Aerodynamics and speed" and move the "Speed" section to there. Both are the same topic.

3. Rename the "Range" section, "The effect of flight distance". Most people likely think of range as a maximum for a particular aircraft, whereas flight distance is a variable among routes or city pairs (e.g. affected by necessary fuel load) and is what is represented in the chart.

4. Move the "Altitude" section to be a subsection under "Propulsive efficiency". They are parts of the same topic.

5. Delete the "Airlines" section, as being far too detailed. This material is covered in your series of tables at the end of the article, and in a different, appropriately general way in material I cover next.

6. Rename the "History" section, "Efficiency of airliners and fleets", and replace the "Past" subsection with my sections that you have been deleting. (This "Efficiency ..." heading would also replace the "...1950s" heading at the top of those sections of mine.)

7. Move the "Operations" section to be a subsection at the end of that "Efficiency ..." section. Coastwise (talk) 08:17, 4 April 2017 (UTC)

  1. "Basic physics of flight efficiency" is too long, "flight efficiency theory" is a middle ground
  2. Aerodynamics and speed aren't the same topic : aerodynamics are related to the aircraft conception, speed to its exploitation
  3. "The effect of flight distance" is too long, "Flight distance" alone will do
  4. "Altitude" isn't related to "Propulsive efficiency", but to drag mainly (lower air density -> lower drag but lower compression too)
  5. the "Airlines" section is instructive and referenced, and isn't individual types fuel burn, but a whole organisation with operational constraints average : the real deal.
  6. a "fleet" subsection can be added the "History" section if you want, but please don't add 10 paragraphs at a time, do it one by one to review
  7. the "operations" are related to exploitation, perhaps it could go along with your additions if they are relevant.--Marc Lacoste (talk) 10:07, 4 April 2017 (UTC)
The shortened headings seem good. I'm short on time, so haven't given all this a close look yet. However, your #2 above is incorrect so I have made some changes to the Aerodynamics section accordingly. Aerodynamics is a matter of fluid dynamics, and how that results in lift and drag. Both of those are a matter of speed, as indicated in the chart in that section. I have added an intro to the section to explain that, and because aerodynamics is fundamentally a function of speed I have moved the Speed section from later in the article to be a subsection of this one. Coastwise (talk) 23:59, 5 April 2017 (UTC)
We should avoid confusing the design speed, which influences aerodynamics chosen (general config, wing sweep, fineness ratio...) and the exploitation speed, where the operator choose a cruise speed for optimum economics (to regain a late schedule or to optimise the cost index). Both are valid. We should also keep a concise text and prefer wikilinking to avoid repetition. --Marc Lacoste (talk) 08:04, 6 April 2017 (UTC)
While rewriting these sections, I remarked the article was confused (as its Skybrary reference) : maximum range isn't at minimum drag (at minimum drag, it's the longest endurance) but at the best velocity/drag ratio [2] (from [3]).--Marc Lacoste (talk) 08:46, 6 April 2017 (UTC)
Your placement of what you are calling 'design speed' and 'exploitation speed' (your own term, it seems) in widely separated sections is artificial. Both are matters of aerodynamics, for which speed is a fundamental factor. Both should be discussed in one place, under Aerodynamics, and the subsection there should be renamed "The effect of speed". On the chart there, it would be useful to add dots to indicate the difference between speeds for maximum endurance and maximum speed, which could be labeled "a" and "b" for use in the discussion. Coastwise (talk) 07:46, 9 April 2017 (UTC)
In the theory section, the speed is choosen by the aircraft designer : 300knots for a turboprop, Mach 0.8 for a jetliner, 150 knots for a STOL commuter, Mach 2 for Concorde. In the exploitation section, the speed is about the cruise choosen by the operator operator, between Long range cruise and high speed cruise, with the impact on fuel burn, like part 4.7: Cruise (p.19) in the Q400_Fuel-Efficiency-manual. I'll develop this part. --Marc Lacoste (talk) 19:32, 9 April 2017 (UTC)
Not so! The aerodynamics subsection (under Theory) discusses the relevant aerodynamics generally, and not aircraft design in particular. The only problem here (as pointed out above) is the errant "Design speed" heading and need to bring other content about speed up into the Aerodynamics section. Coastwise (talk) 20:16, 10 April 2017 (UTC)
The subdivision is between [The aircraft] and [Its exploitation]. Speed in the first section is about the flight enveloppe chosen by the designer (you can suggest a different name). Speed in the second section is about operations, not the design point. Car comparison : the first one is determined by the gear ratios, the second by the driver selecting a gear and pressing the throttle.--Marc Lacoste (talk) 07:05, 11 April 2017 (UTC)
You are taking us around in circles (saying what you have is right, because it is right). It is all the same physics. The distinction you are making is artificial and unnecessary, and makes the article less concise by scattering the topic to two places. Coastwise (talk) 16:06, 11 April 2017 (UTC)
I tried to 1: detail the concepts 2: give examples 3: explain the article sections. This isn't circular. The physics are the same, the goal isn't : it's the difference between the Aircraft design process and using it: Aviation#Operations_of_aircraft. The references below show what I mean. --Marc Lacoste (talk) 16:23, 11 April 2017 (UTC)
Here we are, like I said, full circle again. Your explanations are thin. The discussion in the Aerodynamics section is general, and not specific to design (despite your insistence on putting "design" in a header about speed). The field of aerodynamics (here relating to fuel economy) encompasses all the speed discussions in the article, and the altitude section as well. All of this should be in a concise discussion comprehensively IN ONE PLACE. In particular, the effect of speed is fundamental and should not be split between major sections. Coastwise (talk) 15:03, 17 April 2017 (UTC)

References to explore[edit]


--Marc Lacoste (talk) 10:06, 11 April 2017 (UTC)

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