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On the one side A321 neo has almost the same range as the A320 neo (250 NM difference), and a LR version of A321 neo will have an even longer range. The same goes for the Dassault Falcon 7x and the longer and longer-range Falcon 8x.

On the other side Boeing 737 MAX line shows a clear tendency: the longer the fuselage the shorter the range. The same tendency can be observed on most aircraft types.

I understand that fuel is generally in the wings which keep the same volume on a stretched derivative, but fuselage can accommodate fuel tanks and range can be a crucial point for aircraft. So why don't/can't aircraft manufacturers propose equivalent range stretched aircraft in general, as the A321 neo does?

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    $\begingroup$ My guess would be that the stretch is designed to accomplish a particular task. In some cases the task is to go farther, in others it's to carry more over the same (or shorter) range. Each manufacturer designs for the market they believe is emerging, to the niche they see as empty. For example, Boeing has ER & LR versions of the 777 which aren't any longer than the standard range, but have additional fuel tanks and increased MTOM. $\endgroup$ – FreeMan Feb 9 '18 at 12:56
  • $\begingroup$ Also compare the Falcon 7x and the longer and longer-range Falcon 8x $\endgroup$ – Cody P Feb 9 '18 at 20:08
  • $\begingroup$ @CodyP and the infinite range Falcon 9 :p $\endgroup$ – Antzi Feb 13 '18 at 7:39
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When aircraft are stretched, they usually just receive extra fuselage plugs on both sides of the wing: wing redesigns are incredibly expensive and take a long time. So the longer aircraft has a higher empty weight, and due to the unchanged wing design the fuel capacity remains the same - this reduces range. The aircraft is fuel limited. Conversely, if fuselage plugs are removed the same amount of fuel can take the aircraft further, as the B707-138 demonstrated, Qantas' first jetliner.

enter image description here

The A321NeoLR fixes the fuel limitation by adding extra fuel tanks in the cargo bays as this article explains, so that the aircraft now becomes weight limited. The extra fuel means that there can be less extra revenue from cargo. The B737-9 cannot follow suit, because it is has a shorter landing gear and has rotation limitations: from this article:

737 MAX9 is not suitable for stretch to an international version, not because the wing is not good enough but because the MAX9 cannot bring the wing to an angle at take-off where it can work efficiently; the landing gear is too short.

enter image description here

The longer fuselage limits the rotation angle before a tailstrike occurs, so max. TO weight has a hard limit that cannot be managed by trading cargo weight for fuel weight. Above photo is from this site, which also contains a table with geometric angle limitations for the different 737 versions: the -9 has a tail strike pitch attitude of 10 deg, and has increased flap deflection of 25 deg to limit lift-off attitude to 6.8 degrees. A small variation in centre of gravity at a high TO weight can cause a tail strike.

Boeing has launched the B737-10 which will address the rotation limit by a redesigned landing gear.

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    $\begingroup$ @ymb1 Thx, and the F70 and the B747SP. $\endgroup$ – Koyovis Feb 9 '18 at 13:47
  • $\begingroup$ True, but the -138 is more special though. $\endgroup$ – ymb1 Feb 9 '18 at 14:16
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    $\begingroup$ @ParadigmPilot - A321 has different flaps, but same wing. 777-300ER/200LR/F have wing extensions (raked wingtips), but not new wings. $\endgroup$ – ymb1 Feb 9 '18 at 14:23
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    $\begingroup$ please @koyovis explain the link between "shorter landing gear and has rotation limitations" and the impossibility of "extra fuel tanks in the cargo bay" for the 737, this is unclear to me $\endgroup$ – the world is not flat Feb 9 '18 at 16:22
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    $\begingroup$ @ymb1 Aha, a dropped penny. $\endgroup$ – Koyovis Feb 10 '18 at 2:51

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