Fundamentals of airliner performance, Part 5; Approach and landing

By Bjorn Fehrm

Dec. 2, 2015: The time has now come to cover descent and landing in our Leeham logo with Copyright message compactarticles around airliner performance. As many aspects of descent are similar to climb we will repeat a bit what we learned in Part 4:

  • For high speed operation the pilots fly on Mach as this gives him maximum information around possible effects on the aircraft when he is close to the high speed limit, the maximum Mach number. Beyond this the aircraft gets into supersonic effects like high speed buffeting or unsteady flight.
  • For operations under the cross over altitude for Mach 0.78 to 300 kts IAS the pilot flies on Indicated Air Speed (IAS) which gives him maximum information how the aircraft reacts should he go close to the aircraft’s lower speed limits.

Lets now start to go through the steps that our 737 MAX 8 performs after leaving its cruise altitude.

Read more

Happy Thanksgiving, 2014

Today we’re watching the Seattle Seahawks…Go Hawks!

We’re off until Monday.

Fundamentals of airliner performance, Part 4

By Bjorn Fehrm

Nov. 25, 2014: In our article series around the performance of a modern airliner we have now come to the climb after takeoff. Leeham logo with Copyright message compactWe started with cruise as this was simplest because the aircraft is flying in steady state, then we looked at the modern turbofan and how this is affected by both altitude and speed. We then examined how this affects the takeoff and today we continue with the climb after takeoff.

Before we start, let’s sum up a few points we need for today:

  • Drag is the one thing we always need to be aware of as this regulates how much excess power we have in different flight situations and therefore if we can stay on our altitude or climb.
  • Drag diminishes with altitude as the airs density diminishes and thereby our dominant drag component, air friction against our aircraft’s skin. This is the major component of the aircraft’s dominant drag, parasitic drag.
  • Our lift force is generated by forcing air downwards and this causes induced drag as this downwash cost energy to generate and maintain. Induced drag is mitigated by a wing with a large span.

Read more

Fundamentals of airliner performance, Part 3

By Bjorn Fehrm

In our first article about how to understand the performance of a modern airliner we defined the main forces that are acting on an aircraft flying in steady state cruise. In our clinic we use the ubiquitous Boeing 737 in its latest form, the 737 MAX 8, to illustrate our case. Leeham logo with Copyright message compactIn the second article we introduced the aircraft’s engines and understood how they function by pumping air backwards faster than the aircraft’s speed and therefore generating thrust as air is in fact quite heavy. We also looked at the influence of flight altitude on the performance of the aircraft.

In short we can conclude our findings so far:

  • For cruise lift is the same force size as weight, only opposite. To understand the cruise phase we can therefore focus on how much drag this lift force and the aircraft’s friction against the air create.
  • When we have this drag we also know the engine thrust and we can calculate the cruise fuel consumption from the engines fuel consumption per unit of thrust and hour.
  • We also found that it is beneficial to fly high as the airs density diminishes and with this the airs friction against our aircraft’s skin.
  • Our lift force is generated by forcing air downwards and this causes drag due to weight as this downwash cost energy to generate and maintain. The air resists being downwashed and slinks up on the side of the wing thus generating large vortice sheds which consumes energy. This drag we call induced drag or drag due to weight.
  • We diminish this re-circulation of the air by spreading our wings as wide as we can, in fact we get double reward for increases our span, it counts twice in induced drag reduction.
  • Our limit to fly high for our cruise is set by the increase in induced drag, we are seeking a flight level where we have a drag minimum when adding the diminishing friction drag and the increasing induced drag.
  • We also have a problem with climbing to a to high cruise flight level, our engines lose power both due to the thin air and due to the aircraft’s forward speed.
  • Finally there are supersonic phenomena which stop high cruise altitudes. As the air gets thinner the wings need to throw the air downwards with higher speed (increase wing canting or alfa angle). This means the air on the top side of the wing has to speed up and is therefore going deeper into supersonic flow on parts of the wings overside. This causes disturbances called buffeting when these supersonic areas grow to strong.

Having covered the most important aspects of cruise we will today look at takeoff, a subject with a lot of aspects. Read more

Zhuhai airshow: Airbus gains A320 MOU while regional A330 needs explaining

The Zhuhai airshow has not brought the expected slew of announcements from Western aircraft manufacturers. Boeing announced an order for 80 737 MAX Monday but this was characteristically from a leasing company across the Chinese see, SBMC Capital of Tokio.

Airbus on the other hand has not been able to move the much talked about A330 regional to order yet, despite announcing it in China last year and enticing with an announcement for a Chinese completion center for the aircraft before the show. Flightglobal reports that the A330 regional needs further explaining, Chinese carriers seems hesitant to buy what Boeing pitches as “obsolete technology” in a weight variant that only could fly local missions.

Airbus China president Eric Chen explains that the 200t variant is not constrained to Chinese mainland and can fly any missions that its range would allow. He also points out that the weight variant is just that, a de-papered weight version that can be upped to whatever take off weight the customer wishes at a later date by paperwork changes (and perhaps some additional galley equipment). As for technology level, an aircraft shall be valued for its contribution to a carriers business says Chen, not by which years it says on its airworthiness certificate.

The smaller A320 did not disappoint reports Aviation Week, Airbus CEO Fabrice Bregier could announce a Memorandum Of Understanding (MOU) for 100 A320 from state affiliated China Aircraft Leasing whereof 74 would be A320neo. The order, once confirmed, can help Chinese carriers with the aircraft demand for the 2016-2020 economic planning period. Chinese carriers have been slow to place the necessary early OEM orders for the period (needed due to the large backlogs), the lessor sees it can back-fill that demand when the carriers comes around to needing the aircraft.

Airbus also has explaining to do in other corners of the world, Emirates intend to start second round talks around A350 in the next months according to Reuters. The first round of 70 aircraft was cancelled after Emirates did not understand a specification change that Airbus undertook without consulting Emirates. This time Emirates will see the aircraft flying with neighbor Qatar Airways before agreeing to any specifications according to Emirates CEO Tim Clark.

Fundamentals of airliner performance, Part 2.

By Bjorn Fehrm

In our first article on how to understand the fundamentals that make up airliner performance we defined the main forces acting on an aircraft flying in steady state cruise. We used the ubiquitous Boeing 737 in its latest form, the 737 MAX 8, to illustrate the size of these forces. Leeham logo with Copyright message compact

Here a short recap of what we found and then some more fundamentals on aircraft’s performance, this time around the engines:

When flying steady state (Figure 1) we only need to find the aircraft’s drag force to have all important forces defined.

Lift with downforce

Figure 1. Elementary forces acting on an aircraft at cruise. Source: Leeham Co.

The lift force is given as equal to and opposite to the aircraft’s weight and the tail downforce that we need to add to this was small. We also presented the two classes of drag that we will talk about:

  1. Drag independent of lift or as we often call it drag due to size as almost all drag components here scale with the aircraft’s size.
  2. Drag due to lift or drag due to weight as we call it as this drag scales with weight when one flies in steady state conditions.

We could see that the aircraft’s flight through the air created a total drag force of 7900 lbf, Figure 2 ( lb with an f added as we prefer to write it as this is a force and not a measure of mass. Mass we denote with just lb or the metric units kg or tonne = 2205 lb).

Drag components

Figure 2. Drag of our 737 MAX 8 and how it divides between lift and non lift drag. Source: Leeham Co.

We also learned that if the drag is 7900 lbf then the engine thrust is opposite and equal. It is then 3950 lbf per engine when cruising at our mean cruise weight of 65 tonnes or 143.000 lb on our 1000 nm mission. Drag due to size consumes 63% of our thrust and drag due to weight 37%. Read more

Part 3: Boeing 757 replacement: 757 and Airbus A321neoLR versus clean sheet designs.

Subscription required.

By Bjorn Fehrm

Part 3 of 3


In Part 2 of our three-part 757 Replacement analysis, we took a close look at Airbus’ new 97 tonne take-off weight A321neo, revealed in a world exclusive by Leeham logo with Copyright message compactLeeham News and Comment October 21. We analyzed the A321neoLR’s capabilities and limitations when compared to Boeing 757-200W and we saw that it could do the international flights that the 757-200 does with about 25% better efficiency. In this final Part 3, we will now compare the 757 and A321neoLR against what can be Boeing’s reaction, a clean sheet New Single Aisle, NSA, or New Light Twin Aisle, (NLT). First the conclusions from Part 2:

  • When using the United Airlines-configured 757-200W international as benchmark, we came within seven seats of the 757 capacity for an A321neoLR. It covered the same range and had trip fuel costs that were 25% lower.
  • The per seat fuel costs gave a 22% higher efficiency, which was within 2% of Airbus own figures.
  • 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.

For Part 3 we can summarize:

  • A New Single Aisle (NSA) or New Light Twin (NLT) which would enter the market in 2025 would be sized at around 200 passengers with subsequent variants covering the 175-225 seat market, all numbers with OEM standard two-class seating. Figure 1 shows the fuselage cross sections we have used in our modelling of NSA and NLT to cover this market segment.

NSA and NLT cross sections

Figure 1. Fuselage cross sections of our models of NSA and NLT. Source: Leeham Co.

  • In order to cover the market segment of the 737, A320 and 757 it would have a range in excess of 4,100nm. We will use 4100nm for our modeling to maximize the comparative efficiency information.
  • Its efficiency would be higher than an A321neoLR, primarily due to better engines and a more modern wing.
  • The New Light Twin (NLT) wins on comfort and ground turn-around time but pays with a larger fuselage cross section due to the extra aisle. This causes more drag and structural weight, net effect is a reduction in efficiency of around 2.5%.

Read more

Odds and Ends: wrap-up from ISTAT Europe Conference; Airbus Group joins Aerion to create biz-jet.

The European 2014 ISTAT conference took place in Istanbul Monday and Tuesday. We have reported elsewhere on the presentations by Airbus and Boeing, here follows three interesting tidbits from the rest of the conference. We also comment on the surprising news that Airbus Group will join the US company Aerion to develop the worlds first supersonic biz-jet.

Airline and passenger growth: The  ISTAT conference had an inspiring keynote by the CEO of Turkish Airlines, Dr. Temel Kotil. It was all about phenomenal passenger growth.

Turkish Airlines uses its location between east and west for a development in the scale of the Gulf airlines, Turkish is thereby a good example of the doubling of passenger traffic over 15 years as presented by Airbus. From its privatization in 2004 it has gone from 12 million passengers per year to 60 million 2014, spanning 250 destinations with 260 aircraft.

Turkish Airlines feels it is ideally placed at the cross roads to Asia and Africa, both continents with very high growth. They therefore foresee continued growth to 120 million passengers by 2033. They are fortunate that the Turkish state has played its part in enabling such expansion, leasing land to a 3rd major airport in the Istanbul area. This will be necessary should the majority of these passenger streams pass Istanbul, then the area will beat London Heathrow’s present 70 million passengers, calling for additional infrastructure.

Wizz Air CFO Mike Powell: In a discussion over the future of airlines, the development in USA and Europe was compared. In the US the consolidation has led to 4 airlines handling 90% of the traffic, in Europe the numbers are 40 airlines covering the same extent of the market. Wizz Air CFO Mike Powell (fifth largest LCC in Europe after Vueling) predicts that airlines which does not deliver returns on their assets or state-owned airlines not being able to operate without subsidies would be victims of European consolidation. The local traffic will to a large degree be taken over by LCCs whereas long-haul will move to the large hubs and networks in Western Europe like Frankfurt, Amsterdam, Paris etc.

Powell also explained what drove Wizz Air to go from taking delivery of A320 to A321 from next year. Their LCC traffic is very price sensitive but not so frequency sensitive, if they go from an average frequency over their destinations of 5 flights per week to 4 they would normally only loose a couple of percent in traffic margin. Flying the same load factor with a 321 and at lower frequency gains them around 6-7% in cost i.e. going to the larger aircraft will gain them something like 4-5% in margin.

Airbus Group teams up with Aerion: Airbus Group has joined Aerion, the supersonic biz-jet company from Reno, to help them develop the world’s first business jet which can fly at speeds up to Mach 1.6. The aircraft, called AS2, will seat 8 persons in typical biz-jet comfort and has transatlantic range.

Aerion AS2 supersonic Biz-Jet

Aerion AS2 supersonic Biz-Jet

Read more

Half time 2014 for Boeing and Airbus

The major OEM’s have published their half time 2014 results and we can make an analysis of their half year results together with orders / deliveries and the state of their product lines. We compare Boeing and Airbus on the high end and in a follow up article Embraer and Bombardier on the low end. To make orders and deliveries comparable we include the month of July as the OEMs collected business to be announced at Farnborough mid July.

Boeing had a strong first half 2014. Boeing Commercial Airplanes (BCA) business is now past the initial problems on the 787 program and delivered 48 units January to June 2014 (8 per month) which is the same numbers as for the 777 program. The 737 is now at rate 40 per month with a first half total of 239 deliveries. The 747-8 is at rate 1 with only 6 deliveries and the 767 has stopped as a commercial program with only 1 delivery during the first half year. The commercial deliveries of 342 aircraft drove a 4% increase in company overall revenue and a 5% increase in earnings compared to first half 2013 (both non-GAAP i.e. the core business performance), this despite a Defense, Space and Security side which was down 5% on revenue and down 15% on earnings.

777-9X, 787-9 and 777-300ER in ANA colours

777-9X, 787-9 and 777-300ER in ANA colors

The troubled unit is Boeing Military Aircraft (BMA) which is struggling with its 767 tanker program (KC46A charged BMA with $187 million and BCA with $238 million due to increased development costs) and it is also fighting to not have its major military airplane program, the F18, stop 3 years from now from lack of orders. The military aircraft order drought contrasts with BCA where first half orders was 783 aircraft, mainly 737 but also 777X, where Emirates and Qatar confirmed their orders for 200 777X. Read more

Odds and Ends: Airbus regional A330, IAG orders and Bombardier reviewing options

Airbus A330 regional might get sales after all, Airbus is negotiating a large order with China against local off-sets (assembly or final configuration, the experts are divided) according to Wall Street Journal. We reference Ben Sandilands writeup of the story to avoid the WSJ paywall. As we were told at Farnborough by Airbus the A330 regional is a de-papered A330ceo with an adapted interior. It does not make sense to wait for a neo variant for this aircraft as the fuel costs are a less important factor on sub 5 hour missions. It will be interesting to see if some other market will pick up on this 200 tonne aircraft, to some extent it is back to the roots for the A330-300, it started off as a medium haul complement to the long haul A340-200 and -300 at 206t maximum take-off weight.

IAG has given Airbus a cheer up signal after the bad news around SkyMark. In their second quarter report call IAG CEO Willie Walsh declare their A380 as “fantastic aircraft when you can fill it”, they see 98% load factors on their most popular routes (e.g. LHR-LAX). IAG also announced better results in their Spanish daughter Iberia, consequently it is allowed to order 8 A330-200 (ceos as the neo comes to late) and convert 8 of IAGs A350-900 options to firm orders for their airline.  Right now IAG is satisfied with the 12 A380 they have on order for BA according to Walsh.

Bombardier is re-examining its options for the recently created Aerospace divisions according to FlightGlobal; they want to leverage the Aerostructures divisions capabilities more when Boeing and Airbus looks for further partners for their booming supply chains. They also need to guard their bets on Russia as partner to drive sales of Q400 and Cseries, given the mounting political problems between Russia and the west. This results in renewed activity in the China / Comac discussions, initially for cooperation on the after sales side in addition to the present fuselage deliveries, but come a worsened situation with Russia such talks could find new depth we think.