A typical payload-range diagram looks like this:
There is aircraft range along the horizontal axis and payload carried along the vertical axis.
What are they used for?
As a Pilot
First and foremost a pilot can look at an aircraft’s payload range diagram and confirm that an aircraft is able to achieve a given mission, i.e. can fly a give combination of payload and range. Everything within the three lines is an achievable payload-range mission combination for a particular aircraft and everything outside is not. When flying close to the boundary pilots may have to pay close attention to make sure they really can fulfil the mission (see this slightly unusual example).
As an Airline
Comparing a payload-range diagram with the typical routes and passenger volumes an airline expects can help an airline in deciding if an aircraft is a good match.
For example the Airbus A330-300 and Boeing 787-9 are similar size aircraft with similar payload abilities, however the 787-9 has a better range and the A330-300 is probably somewhat cheaper. Comparing the payload-range diagrams with the the routes an airline operates would be a first step in determining which aircraft is suitable. If an airline wants to transport 40000kg 8000km (88 185lbs, 4970 miles/4320 nautical miles), both aircraft are suitable, but only the 787-9 can fly that payload to 10000km (6214 miles/5400 nautical miles).
As an Aircraft Manufacturer
Payload and range are two of the most important factors for airlines when choosing aircraft. A payload range diagram can be used to compare competing aircraft, and also shows where an aircraft is limited. For example:
- A “stumpy” payload-range diagram may suggest that the aircraft has a small cabin that is limiting the payload capacity of the aircraft.
- A payload range diagram with a large corner missing points to a low maximum take off weight, preventing the aircraft from flying with both payload and fuel at the same time.
- A “tall and thin” payload range diagram staying in the left side of the diagram suggests an aircraft strongly limited by its fuel capacity.
This can then influence the direction that upgrades or new variants of an aircraft take.
Why are they this Shape?
Payload-range diagrams are formed from three fundamental limits on the aircraft; the maximum payload, the maximum take-off weight and the fuel volume available. Drawing these three limits on a single diagram then shows what missions an aircraft can achieve:
Why these three factors shape the diagram in such a way is easier to understand if the other variable affecting range, the weight of fuel, is also included. A payload-fuel-range diagram looks like this:
Payload Limit (Area A)
Fuel can be added as needed to reach any range needed in this area, but payload cannot exceed the certified or physical maximum possible for the aircraft.
Maximum Take-Off Limit (Area B)
There is still space in the fuel tanks to add more fuel, but the maximum take-off weight of the aircraft has been reached. In order to fly further, some payload must be offloaded in order to allow more fuel to be loaded.
Fuel Volume Limit (Area C)
The aircraft fuel tanks are full, so the only way to fly further is to reduce the total weight of the aircraft by reducing the payload further. Due to the reduced total aircraft weight, the aircraft is then able to fly further, even with the same amount of fuel.
Footnotes
Note that although they are appear straight, the lines in Area B and Area C are not perfectly straight, since the relationship between fuel load and range is non-linear.