Payload Range Diagram

After my last post a debate started about the range of the B737MAX-8 and -9, precisely whether these ranges can only be achieved with an additional fuel tank. It seems like (and Scott Hamilton pointed us to that) that Boeing already said that the MAX-9 range of 3595nm is reached with an additional fuel tank. Boeing did not say anything about the MAX-8 fuel tank configuration to reach 3640nm of range, but it seems logical that this will also be only achievable with the additional fuel tank.
A further hint to that is the difference between the different OEW and MTOW gains, relative to the NG.
OEW is said to be 5500lbs more but MTOW is raised by 7000lbs. These 1500lbs difference could mean 1500lbs more payload for a given range or 1500lbs more fuel (assumed there is a tank that can hold the fuel). With an estimated nautical air mile performance of 0.08nm/lbs fuel that would mean an additional 120nm of range. So the additional range due to the better aerodynamics of the aircraft and the better SFC of the engine would be 540nm-120nm = 420nm. This represents about 13.6% of today's B737-800NG range or 13.75% of today's B737-900ER's range. Boeing seems not to be overpessimistic at this point about the performance improvements, I would say...
As well, 3760nm of range at least for the A321neo seems a little bit odd, unless there is another fuel tank installed in the aicraft. A full somparison of range (estimations) and more can be found at Leeham News. They are not quite macthing the ranges given by Boeing for the MAX.

To better understand what options airframers have to improve the payload-range performance of an aircraft, here are some basics.
Let's start with a nominal aircraft. You can fill up the tanks and go without any payload and fly a certain distance (A). If you add payload you won't go as long as before as you need more thrust to lift the aircraft. At one point (B) the Maximum Take Off Weight (MTOW) is reached. You can only add more payload if you drop fuel. This will lower your range further, as you start with less fuel in the first place and the added payload - other than the fuel - does not disappear over time (well, unless you are flying paratroopers...).
Note that netween points B and C you always take off with MTOW. Point C is where you have reached the maximum payload - you cannot load more passengers or cargo into the aircraft.

Now what happens if you add a fuel tank? The tank itself has a weight. So the payload could be a little bit less (depending on where the tank is located). So until you reach MTOW at the new point B you can fly longer. This option does not make sense for you (as an airline) if you always fly with a lot of payload, as you cannot make use of the extra tank.

If you raise the MTOW without adding a fuel tank you can add more payload until you reach the new MTOW - or you can fill up more fuel and fly longer distances with high payloads (re the first comment: given that you also raise MZFW). This option has no benefit for short range missions.

Only if you simultaneously raise the MTOW and add an additional fuel tank you have more range for every mission.

Lastly, a better engine SFC leads to more range for every given payload.

Now everyone can build it's own "Dreamliner". Take a given (existing) aircaft, add MTOW, fuel tanks and/or new engines and see what happens...I wait for some clarifications on how Airbus and Boeing want to reach the advertised ranges of the neo and MAX aircraft.


  1. 1. Adding a fuel tank does not allow to increase range between B and C. Indeed, between B and C, the aircraft is MTOW limited, so you can not load more fuel in the aircraft. Adding a fuel tank increases range between A and B.
    2. Increasing MTOW does not increase max payload as this is a MZFW limit

    1. Thanks - corrected. I should have added in the first place that raising MTOW wtihout adding a fuel tank ABD without raising MZFW does not really make sense...

  2. "2. Increasing MTOW does not increase max payload as this is a MZFW limit"

    "I should have added in the first place that raising MTOW wtihout adding a fuel tank ABD without raising MZFW does not really make sense..."

    Now, since I'm not an engineer and don't know much about the difference in MTOW and MZFW, something in my head is trying to make sense of this. How can you increase MTOW and not for the same token increase MZFW? If the take off weight increases, does not increase the maximum zero fuel weight of the aircraft? or is it that just fuel could be added?

    Thanks for your outstanding blog ATP.

    1. Raising MZFW is equivlent to raising payload.
      - You can add a fuel tank without raising MTOW to add range with a payload less than max payload (only business travellers with leight bags, no cargo, like the LCF-JFK A318 service from BA).
      - You can increase MTOW at the same time to make use of the extra tank even with a heavy (close to max) payload (without raising MZFW.
      - You can raise MZFW only to carry more passenger and/or cargo over shorter distances (as range will fall).
      - You can MZFW and MTOW to carry more payload or carry the same payload over longer distances (or a combination of both).

    2. Increaseing MTOW and increasing MZFW require different structure reinforcement.
      Bending moment on the wings drives the MZFW. The lift bends wings upward and the weight of fuel contained in the wings bends wing downward. However, at MZFW there is no fuel in the wing, meaning only the lift applies to the wing and so bending moment is at maximum.

    3. Thanks for the technical clarification. I did not want to go into the technical details how to make these changes (and as I am not an aircraft engineer I have not the expertise to do it anyway) but only how it impacts the way the aircraft can be used.

  3. This is V V

    Why make it complicated?
    You have all the payload range diagrams you need here:

    See page 96 of the chapter 3 (performance) chart titled "3.2.12 PAYLOAD/RANGE FOR LONG-RANGE CRUISE"

    As far as the removal of the "dry bay" is concerned, please read carefully this article:

    The all-important engine installation is an evolution for the 737 and builds on the mounting design used for the 787. The installation moves the engine “a little forward and up,” says Teal. By cantilevering the engine out ahead of the wing, Boeing is avoiding the need for a dry bay above the engine, thereby preserving fuel volume. “It's not new technology, but we wanted a little more room under the nacelle,” says Teal. The bottom of the MAX nacelle will be 17 in. off the tarmac, 1 in. less than an NG's.

    1. Thanks for the link. I think meanwhile it became clear that there will be more tank volume - either thrue the elimination of the dry bay or thrue an extra tank.

  4. Dear aeroturbopower,
    I think with more fuel tank volume available, the slope of the line A-B remains unchanged and the line is shifted to the right. Consequently, the MTOW-limit line B-C is extended and point B comes further down.

    1. Point B coming down would mean that MTOW is reached with less payload - that would mean that MTOW was lowered with the additional fuel tank - this would be an unlikely scenario, I guess.

  5. What i mean can be seen here, second page:

  6. A very interesting post but what has happened to the graphics? All I see are exclamation marks in a triangle, this on 2 different computers