Talk:Fuel economy in aircraft

Comparison of Concorde and Boeing 747

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

(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 : defra.gov.uk (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)

interesting works

• Matthew Kling and Ian Hough (2011). "Air Travel Carbon & Energy Efficiency" (PDF). Brighter Planet.

Missing Aircraft

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?