# Comparisons between the A340 and 747-200 wing: sweep angle and span

Here is a picture of the wings of the A340 (launched in the late 1980s) and the Boeing 747-200/400 (launched in the early 1970s / 80s) superimposed upon each other (source: https://www.amazon.com/Evolution-Airliner-Ray-Whitford/dp/186126870X).

I was hoping to use this image to inquire about technological improvements in wing design between 1970 and 1990. The reason for the comparison between these two airliners in particular is that they seem as close to a "fair" comparison that can be made between airliners over very different time periods, specifically because they're designed to carry relatively the same amount of people.

Specifically, there were two facts about the wing planform that I wanted to ask about.

1. Greater aspect ratio. The A340 has a much greater aspect ratio because it has the same span but much lower total wing area. This improved the L/D ratio by reducing induced drag. What allowed engineers to use a higher aspect ratio wing for the A340? I.e., could the engineers at Boeing in the late-1960s have designed a plane with the same aspect ratio as the A340 if they wanted to (in which case, the higher aspect ratio on the A340 was a design choice, and not a result of any improvement in techniques, methods, materials etc.).

2. Less wing sweep. Wing sweep is desirable because it lets you fly faster without incurring extremely large drag penalties (increases critical mach number), but it does so at the expense of lift. Therefore, if you can get away with a lower sweep angle for a given speed, that's something that would be good for fuel efficiency. How were engineers able to get away with reducing the wing sweep of the A340 while having it fly at generally speaking, the same cruise speed as the Boeing 747?

Thanks so much!

Both less wing sweep and increased aspect ratio are acommodated by the progress in application of rear loading supercritical wing profiles in the couple of decades between design of he two types.

Pic above is from Torenbeek, earlier used in this answer, and depicts the increased thickness of the supercritical profile - which enables higher aspect ratio. But the main difference is actually the higher allowed Mach over the wing => less wing sweep required => way less constructive and aerodynamic problems.

Aspect Ratio is $$b^2/S$$. Start sweeping the angle of any given wing and the span reduces, so there is a feed-forward loop in the two parameters considered in the question.

• Thanks! That makes sense to me. A follow-up question if you don't mind. As far as I'm aware, the first supercritical sections were introduced on the generation of aircraft launched in the late70s - early 80s (767, 757, A300, A310). Did the aircraft of the late-80s - early 90s (A340, 330, 777) incorporate "improvements" to their supercritical sections? If so, what specific improvements were made? Apr 18 at 6:01
• Yeah that's a hard one, the manufacturers keep that information close to their chest. I don't have any academic research docs from that period. Apr 18 at 8:33
• @interested22 please ask your follow up question as an actual question. There's no place to answer it down here. Plus, while Koyovis might not have info, others might and they might not see your question down here in the comments. Apr 18 at 14:10