18 December 2015, © Leeham Co:Part of the discussion following last week’s article around quad or twin engine airliner designs was about engine efficiency and specifically around the engine’s thermal efficiency as a function of Pressure Ratio, PR.
I got the question, if an engine working at a higher pressure ratio was therefore working at a higher thermal efficiency. I knew enough on the subject to know I did not have a good answer without doing a bit of checking; jet engines are no simple contraptions.
I have previously written about turbofan efficiency in a Corner. The article was focused around propulsive efficiency. Now we will have a look at the other part of overall engine efficiency, the thermal efficiency or the efficiency of the core.
11 December 2015, ©. Leeham Co: The debate over two or four engines for long range aircraft is as old as the jet airliner. A number of myths have been pedaled over the years over the virtues of the one over the other. The myths have even been presented by airline CEOs as “facts that are known in the industry.”
Having done several in-depth comparisons of two-vs-four engined long range aircraft, we can’t find the patterns that these myths propel: that a quad is less efficient than a twin and should have higher maintenance costs. What we see is that it is all dependent on what one compares and to what technology generation the one or the other aircraft belong.
When we didn’t get the same results as the myths on a number of areas, we started to wonder what could have created the myths in the first place. Looking at what four engined airliners could have been the source of the rumours, we started to see a pattern. It was a pattern of apple-and-oranges being compared and wide ranging conclusions being drawn.
Here is what we found. Read more
04 December 2015, ©. Leeham Co: During the last two weeks I have been busy explaining how a mid-life long range aircraft is refurbished. The articles have been about how to prepare 10 year old Boeing 777-200ER and Airbus A340-300 for their second half of life.
One of the things that must be done is updating the part of the aircraft that meets the customer, the cabin. Most passengers don’t know much about the aircraft they are flying, but they can tell you if the seats were comfortable, if there was enough leg space and if the movies on the entertainment system were any good.
This means that if the cabin is brought up to a modern standard with lie-flat business seats, refreshed interior surfaces and textiles, and if there is a personal IFE unit with good content, the passenger will not reflect over that he flies an old aircraft.
Such refreshes cost a lot of money. Without changing all items in a 300 seat cabin, one is easily at between $5m-$10m for material and installation. One of the problems when wishing to keep existing seats, for economic reasons, is that it is virtually impossible to implement in-seat IFE to an existing seat. Luckily there are other solutions. Read more
27 November 2015, ©. Leeham Co: In an article yesterday, we looked at the economics of acquiring used aircraft for long range operations. We compare getting a second hand Boeing 777-200ER or Airbus A340-300 to operate as a long range complement to an existing network or to start a charter operation to destinations further away than previously possible.
The low fuel cost has made longer range destinations economical for a number of business models and the low capital cost and good conditions of these aircraft open new opportunities.
One of the things that must be considered in such analysis is the deterioration of the aircraft’s components. This will affect the aircraft’s performance in a marked way. In fact, an aircraft only has its factory advertised performance once in its life-time: at delivery.
Certain types of deterioration can be reset to zero by maintenance actions; others will not be reset completely by a visit to the maintenance shop. Let’s go through the different forms of deterioration that one normally caters for in performance calculations and how one go about to restore the aircraft’s operation as much as possible with scheduled maintenance.
20 November 2015, ©. Leeham Co: Emirates Airline CEO, Tim Clark, is quoted as having said “it takes them forever to get this thing up.” He was talking about the Airbus A350 production rate and his reasons for delaying Emirates’ decision on what to buy for the airlines medium range needs. Clark said Emirates wants more aircraft in operational use before they can evaluate the operational characteristics of the A350.
Emirates want to see at least 20 aircraft in operation and right now it is about seven to nine that fly every day. Actual deliveries stand at 10 with one month to go before the first anniversary when deliveries started (the first A350-900 was delivered to Qatar Airways on the 22 December 2014).
Looking at how many aircraft that are actually flying, one can agree with him. It seems actual production rate is more like one per month rather than the three to four a month that Airbus talked about at the first delivery ceremony.
So why is this? Is the production of A350 therefore in serious trouble? What is taking them so long? Has Emirates pointed to a weak part of the A350 program?
23 October 2015, ©. Leeham Co: In last week’s Corner, we went through how Airbus can offer an Ultra Long Haul (ULH) aircraft to Singapore Airlines by increasing the Maximum Take-Off Weight of its A350-900, increasing the tankage and lower the payload. There are a couple of other considerations when extending the range of an aircraft that we did not touch upon. For completeness, we go through them here.
When increasing the allowed weights (really, masses) of a certified airliner, there are a few things that need to be re-evaluated and perhaps modified. First of all, the airframe needs to withstand the higher loads caused by the higher weights. Secondly, the aircraft’s field performance will be affected by higher weights. Required take-off field length must stay within usable limits, as must landing performance.
If the increase in flying weights are significant, it will also require a check on what happens to the aircraft’s flight profile when fully loaded. A heavier aircraft will cruise at lower flight levels and the One Engine Inoperative (OEI) service ceiling will diminish.
We now go through these additional areas and evaluate their impact on overall aircraft performance in general and on an A350-900ULR in particular.
16 October 2015, ©. Leeham Co: Airbus announced this week how it made an Ultra Long Haul (ULH) aircraft out of the long haul A350-900. The resulting A350-900ULR (Ultra Long Range) enables Singapore Airlines to reopen the famous direct “Flight 21” to New York.
But Singapore’s press release also talks about US West coast destinations, the first being Los Angles. They released this picture:
Reading the many comments around how an aircraft like A350-900 can reach such longer range, it can be worth going through the basics on how different parameters affect range and what Airbus or any other OEM has to consider when they want to increase the range of an existing aircraft.
We will do that from a slightly different angle than normal. We will show how a pilot would think about how he can get an aircraft with more range. Pilots reason in a different way to design engineers. They are better served by thinking on the aircraft’s range performance as endurance, meaning how many hours can we stay aloft. This works better when one plans with the prevailing weather on the route.
We will now take it step-by-step and explain which parameters matters for the pilot and which do not and how he gets his ULH aircraft. Read more