The 787 Dreamliner: What Are the Differences Between a -8, -9 and -10?
To the casual observer, the only difference between the 787-8, -9 and -10 is just the name. They all have two engines, all have the same number of wheels and all have the same number of cabin doors. However, look a little closer and there are some significant differences. Some obvious to you, the passenger, and others only which we, your pilots, know about.
Why the Different Types?
Built for a purpose
Right from the very start of the 787 development program, Boeing had planned three variants of the 787 — the -3 (yes, you read that correctly), the -8 and the -9. The -8 was developed as the base model, with the -9 being a stretched version and the -3 being a shortened version.
At the time of its creation, Airbus and Boeing had backed themselves on two polar opposite business models.
Airbus, with the A380, predicted that future demand would be limited by airport capacity. As a result, its solution was to create a bigger aircraft on which airlines could fit more passengers and fly between major hubs. Why have two flights when you could fit all those passengers into one?
Conversely, Boeing imagined that customers would rather fly direct from their start to end points, without having to connect via a major hub. To fulfill this prediction, the 787 program was created.
The -8 was designed to succeed the 767, being of similar size but with a 20% greater fuel efficiency. In order to give airlines greater flexibility, the -9 was developed the same time with its planned delivery date a couple of years after the introduction of the -8.
Even though the -9 was by and large the same aircraft as the -8, a few changes had to be made to accommodate the differences between the two. Encouraged by interest from Emirates and Qantas, in 2005, Boeing started looking into further stretching the -9 to a 310-passenger variant, the -10. In 2013, Singapore Airlines became the launch customer for the -10, with an order of 30 aircraft.
More in common than not
The fact that the three types are so similar means that both pilots and cabin crew are able to fly all variants without any need of further training. With most airlines that operate all types, crew will change between the three regularly each month. Whilst this is not a major problem, is does require focus on the day to ensure that the crew are aware of on which type they are operating.
Size
The only real observable difference between the -8, -9 and -10 from the outside is the length. The -8 is 186 feet long. The -9 comes in 20 feet longer at 206 feet, and the -10 is 18 feet longer than the -9 at 224 feet. The increased length is created by adding fuselage sections either side of the wing. This increase in length creates space in the cabin for an extra 38 passengers from the -8 to the -9, and 20 passengers from the -9 to the -10.
As a result of the increase in length, the distance between nose wheel and the main landing gear on the -9 is 10 feet greater than that on the -8. It's even greater on the -10. For passengers seated in the cabin, this has no impact at all. However, for the pilots, it does. When taxiing around airports — especially those with very tight taxiways such as New York's JFK — we have to be particularly mindful of where the main gear is when we are turning.
In order to account for this, we make sure that we taxi 'deep' into corners before turning the tiller to start the turn. Quite often we will wait till the centerline of the taxiway is over our shoulder before starting the turn. This means that we regularly no longer see concrete in front of us — only grass as we start the turn. We just have to maintain faith in the geometry of the aircraft and the fact that the nose wheel is nearly 10 feet behind our seat position.
The increased length and wheel spacing on the -9 also means that the turning circle of the aircraft is increased. Some smaller airports require the aircraft to turn 180° on the runway either before take off or after landing. This is common in the airports of the Caribbean and the Greek islands.
In order to safely complete these turns, the -8 requires a pavement width of 138 feet whereas the -9 needs an extra 16 feet to accomplish the same task.
For more on how we taxi the aircraft on the ground, check out, Parking a 200-tonne airliner: How pilots move a plane around on the ground
Not a difference, but a very conscious similarity is the wingspan of the aircraft. Aircraft are categorized depending on their wingspan so that all involved with the operation know on which parking stands and taxiways the aircraft will fit. By keeping the wingspan the same, all variants of the 787 can be considered the same type.
Weight
Maximum Take Off Weight (MTOW)
The MTOW of the -8 is 502,500 lbs. This is the heaviest weight the aircraft can be when it starts its takeoff run. The -9, being 20 feet longer with 38 more passengers, is understandably heavier at 560,000 lbs. This is the same as the -10. As a result, the structure of the -9 and -10 have been strengthened to accommodate this increased weight.
Maximum Landing Weight (MLW)
As you might imagine, if there is a structural limit to how heavy an aircraft can be on takeoff, with the increased forces experienced on landing, the MLW is significantly lower.
On the -8, it is 380,000 lbs., and on the -9 it is 425,000 lbs. and the -10 is 445,000 lbs. This means that should we take off at our MTOW limit, we would have to use up over 55 tonnes of fuel on a -8 and 54 tonnes on a -9 before we can land again.
Another useful similarity between the three, though, is the ability to dump fuel. Should we be above our MLW and need to land sooner than planned, for a technical or passenger problem for example, we are able to quickly empty fuel from the tanks. This method gets the aircraft down to the MLW much quicker than just flying in circles to burn it off. This means that on the -10, with its greater MLW, it will take less time to dump fuel down to a level at which we can land.
Cargo
With the increased space in the passenger cabin on the -9 and -10 comes increased space below in the cargo holds. On widebody aircraft like the 787, your baggage is packed into containers, which are then loaded into the aircraft. This not only enables ground staff to locate exactly where your bag is on the aircraft, but it also enables them to load the aircraft in the most fuel-efficient manner possible.
The extra length of the -9 creates space for 8 more containers than on the -8. This can either be used for extra passenger baggage, or, as is more common, to carry more cargo.
Flaps
In the flight deck, there are very few indications to the pilots whether we are on a -8, -9 or -10. However, the easiest way to identify the variant (apart from the registration) is to look at the flap lever.
The -8 has seven selection options — Up, 1, 5, 15, 20, 25 and 30. For the most part, up to Flap 15 are takeoff settings. Flap 25 and 30 are used for most landings and Flap 20 is used for some non-normal landings, for example, in the case of a single-engine landing.
The -9 and -10 have the same options but also adds the options of Flap 10, 17 and 18. These are extra takeoff settings due to the increased weight range of both variants.
Pressurization System
During normal flight, the pressurization system keeps the cabin environment as if you were on the ground. However, should there be a problem with the pressurization system, there is the Alternate Ventilation System (AVS).
The AVS provides an alternative method of ventilation should both air conditioning packs be inoperative. On the -8, the system consists of a dedicated inlet duct on the outside of the aircraft, which allows fresh air from the outside to be delivered directly into the cabin.
By the time the -9 was developed, Boeing was able to make changes to the air conditioning system to enable it to do away with the extra duct and its dedicated pipework. Instead, the system uses the forward and aft outflow valves to reverse the flow of air, driving fresh external air into the cabin.
For an in-depth explanation of how aircraft maintain the cabin conditions, check out, How aircraft are designed to keep you comfortable at 37,000 feet.
Engines
The 787 has two engine options — the Rolls-Royce Trent 1000 and the General Electric GEnx. Even though the same engine can power all variants, those on the -9 are rated to a higher output thrust, giving the aircraft a greater range than the -8. The 787-10 is powered by the Trent 1000 TEN or the GEnx-1B engine.
Range
Part of the attraction of airlines to the -9 was its increased range. Whilst the -8 is capable of a very respectable 8,464 miles, the -9 is able to fly an extra 322 miles. Not a massive amount, but considering that could be with an extra 20 tonnes of payload, it opens up routes that were not possible on the -8. At 7,443 miles, the -10 actually has a shorter ranger than both the -8 and -9. However, due to its far greater capacity of passengers and freight, it means that airlines can utilize its performance on routes where there is more demand.
Landing Gear
Whilst the landing gear on all variants is much the same, the way in which they operate is slightly different.
On the -8, once the pilots are happy that the aircraft is climbing safely away from the runway, one of pilots moves the gear lever up to retract the gear. This may take several seconds to do but then sets in motion a chain of events.
First, the landing gear doors open. This creates the space to allow the gear assembly to retract into the aircraft. Once the gear is up, the doors then close, giving the aircraft its full aerodynamic shape. https://youtu.be/F4yqzKYiwXY
However, on the -9, there is a slight difference. To improve performance, one second after the aircraft has detected it is airborne and prior to a pilot selecting the gear up, the gear doors automatically open. If the pilot does not move the gear lever to UP within 30 seconds, the main gear doors return to the closed position. Due to the increased length of the -10, there is an increased risk of striking the tail on the runway, particular during takeoff. To reduce the chances of this happening, the main gear on the -10 is semilevered. This means that the aircraft can rotate over the aft wheels, not just the center of the of the landing gear assembly.
Autopilot
A very minor difference, which is only of note to the pilots, is the altitude down to which the autopilot can be used on certain approaches. Briefly put, if certain navigation accuracies are not met, the autopilot but be disconnected by 100 feet above the ground on a -8 and 135 feet on a -9. I'll be talking more about navigation accuracy and automatic approaches in future articles.
The 787-3
Finally, let's look at the 787-3. You may have never even heard of the 787-3, and you'd be forgiven if so. Designed for the Japanese short-haul market, the -3 never got off the ground. Figuratively and literally.
It was designed to be the same length as the -8 but with a smaller wingspan, enabling it to operate into smaller airports. It initially attracted 43 orders from All Nippon Airways (ANA) and Japan Airlines (JAL).
However, the development of the -8 suffered serious delays. To keep it on schedule for its promised April 2008 delivery date, the -9 was pushed back two years to 2012, both taking priority over the -3.
As the delays to the -8 and -9 program intensified, the -3 was pushed backed even further, with no completion date being confirmed. This open-ended delay influenced both ANA and JAL to convert their orders for -3 aircraft to deliveries of -8s instead.
With the -3 order book empty and no production time in sight, Boeing decided to scrap the -3 program in December 2010.
Bottom Line
The 787-8, 787-9 and 787-10 are nigh on the same aircraft. However, due to its increased size, Boeing had to make some adjustments to the -9 and subsequently the -10. A stronger airframe enables the -9 to carry the extra 20 tonnes the -9 can lift over the -8. More flap settings enable the -9 and -10 to optimize its takeoff performance and advances in technology enabled designers to upgrade the air conditioning system. The -10 is so long that a change to the landing gear was needed to ensure that the tail doesn't hit the runway on takeoff. From the pilot's perspective, they are all a delight to fly. The small changes between the types create very few problems, mainly just requiring more thought when taxiing around airports with tight taxiways and stands.
However, from the passenger perspective, there is very little to notice. Whether you're flying on a -8, -9 or -10, you're going to be enjoying the best cabin experience in the sky.