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Leeham News and Analysis
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- Bjorn’s Corner: New engine development. Part 4. Propulsive efficiency April 19, 2024
Bjorn’s Corner: Efficient systems, Part 2
By Bjorn Fehrm
12 February 2016, ©. Leeham Co: Last week we looked at what could be done to the aircraft’s systems to increase the aircraft’s efficiency. But it does not stop with systems which can improve the aircrafts internal efficiency. Modern avionics and flight procedures can improve the efficiency of an airliner’s flight operation.
Ever since the Second World War, the navigation of civil airliners has been done by flying straight leg routes with the help of special ground-based radio beacons. The most elementary of these is the Non-Directional Beacon, NDB. It requires the pilot to read bearings to the beacon and is difficult to use.
A directional beacon called VOR, that went operational after WW2, changed the way that airliners could navigate (over large un-inhabited areas like the Atlantic or the Oceans, different low precision wide area navigation systems were used like LORAN). While the VOR was a big step forward, it still required navigation in straight leg routes between VORs, and this was not 100% efficient.
The development of powerful navigation computers (FMS) and the use of GPS is now changing this.
RNAV and RNP
The traditional route to land at an airport from an airway followed the capabilities of the VOR and NDB based navigation beacons complemented with a Distance Measurement Equipment, DME. An approach chart which shows a numbers of ways to reach Boeing Field, Seattle, from different airways is shown in Figure 1.
Figure 1. MS Flight Simulator Standard Arrival (STAR) chart for Boeing Field. Source: Jeppesen and Microsoft.
This is a Standard Arrival, STAR, chart which shows the different possible ways to land at the Boeing Field from the east (it is a chart used in Microsoft Flight Simulator, which is a copy of an old real chart from Jeppesen). The arrivals are called GLASR FOUR as this is the central navigation point made up of different VOR radials (directions) and their DME distances (for instance, go from PAINE on radial 075° and to 23+44=67nm and you are at GLASR).
As can be seen, the paths are made up of straight segments and from Northeast, coming in over CRANBROOK, one would have to fly in Zig-Zag to reach the point HETHR where one is finally Radar vectored to the runways.
It would, of course, be more efficient to be routed directly toward Boeing Field and then do a smooth decent to land on the runway. This requires that the navigation would be changed to not follow possible radial of VORs but be free to define more direct routes (there would still be predefined routes, same for all, but more direct and efficient).
With the help of the modern airliner’s navigation computer, the FMS (for Flight Management System), it is possible to let the computer continuously calculate the directions and distances to the VORs and DME (make fixes) so that the aircraft could fly such an optimized path.
It is much easier done if the GPS system is also brought in as a navigation aid. Today the modern FMS has the capability to use all the aircraft’s navigation receivers, including any GPS receivers, and enable so called area navigation or RNAV. The pilot follows a predefined more direct route on the displays that he has keyed into the FMS and the FMS does all the work of tuning in different VORs and DMEs or using GPS to calculate fixes so that the aircraft is on track.
For landings, it can then look like Figure 2, which is an example of a RNAV, or the even more precise RNP (Required Navigation Performance) approach, being performed by one the markets FMS systems, in this case, the one for Boeing’s 737 from GE Aviation.
Figure 2. GE Aviations 737 FMS doing a RNP approach instead of a classical VOR/DME approach. Source: GE Aviation video.
It’s obvious that a one circle optimized descent from cruise altitude directly to the runway threshold (or to a final landing with ILS) is more efficient than the classical step wise decent following the typical straight leg-turn-straight leg-turn approach.
RNAV and RNP (which is an enhanced RNAV with even more precision) are the future for air navigation. It requires powerful navigation computers (FMS) and a multitude of redundant GPS and VOR/DME receivers. The FMS manages it all so that one can fly a modern more direct and optimized route, saving fuel, emissions and as seen in the picture generate less noise over urban areas.
Bjorn:
I know this is off direct topic, but its come up a number of times.
Do you have any assessment of the manufacturing efficiency of what we would call the 3 competing airframe types as follows:
1. Boeing rolled fuselage in CFRP
2. Airbus Frame and Skin done in CFRP
3. Latest aluminum (Li Al etcf) but in the traditional frame and skin as used the previous 50 years or so
Boeing’s one-piece fuselage barrels must need very expensive tooling to make them, and a very large autoclave. That’s OK, but it needs a dedicated facility and they need a long order book to make that worth while. It is also very inflexible. If they’re not make 787 barrel sections they’re not making anything else either.
Airbus make their CF fuselages out of much smaller pieces. This has a lot of advantages – almost any decent existing CF subcontractor can make those, you can ramp up / wind down production really easily without anyone minding too much, you can easily change the design without big changes in the manufacturing facility, etc. They do then have to assemble them into fuselage barrels, and transport those to Toulouse, but then again Airbus are good at that kind of thing.
There’s other subtleties too. Airbus’s method gives them more freedom of design, which can have a dramatic impact on the development cost of the aircraft. For Boeing, wrapping tape around a barrel mold means they cannot do concave surfaces, and they cannot easily vary the thickness of material throughout the cross section.
The cost of the development phase is important. For things like aircraft and cars the development costs are a huge fraction of the whole programme lifetime costs. Fairly simple design choices are fundamental to success. After many years of doing nothing radical at all Boeing embraced a lot (too many, too easily?) of new ideas in 787, and are paying the price now. Airbus didn’t go mad in the A350, though they did go slightly bonkers with the A380.
I’ve no idea about Li-Al, though presumably it’s cut and assembled in the normal way. In which case it’s a no-brainer I’d have thought. There is one other difference I presume – it will still have a fatigue life. CF and other composites don’t have the same life problems (they have other problems).
This could be looked at two ways.
The first is that Airbus/Boeing are making CF aircraft that may never, ever wear out. They’ve set up expensive plants to build these things, and their success may spell doom in decades to come. Whereas a metal air frames will always, eventually, wear out and will have to be replaced. So as the manufacturer you’re always going to have repeat business eventually, meaning that you will get a good and efficient return on the investment in the factory.
The second is that customers will look at a metal air frame and be put off by the fatigue life thing, and will instead buy a CF airframe. Suddenly your manufacturing facility is underused – very inefficient.
I get the various aspects of it though in reality Airbus went the route they did because they had not invested in the ability to do what Boeing did. they have tried to make a bug a feature (I don’t have any problem with stand alone that it works and works well, I just do not like spin)
One statement was : if we damage a section we can just replace an entire panels and not the barrel.
Reality is you will repair the panel or barrel the way Boeing did with Ethiopian aircraft.
That does not mean Airbus approach does not work, they have done well with the A350. Its obviously viable.
However what is being missed is that assembly is a mixed bag situation.
For Boeing, they snap the things together as they get a complete structure on the line. It goes fast.
Airbus builds the structure up by hand and then ships it.
Airbus system would have more in common I think with aluminum frame and panel than the Boeing system .
Where does less labor and use of high tech vs more labor and current tech cross? Or does it?
So you get an efficiency of spun and a lot less hand work for the reinforcement circles (right name?) but its also costly material and as noted, the method of spinning and curing
What I am interested in is what is the balance of the 3 systems?
I believe Airbus made the A350 nose out of alumni as they could not get what was needed out of composites (its a pressurized portion of course)
That has some affect on maint but that is an operational aspect not construction .
Is Boeing system really unviable? Or was it all the other loadings of muck ups that are dogging it now?
Going forward the next new aircraft is going to have to go with one of those 3 system and I am curious on the assessment of the tradeoffs and if one is better than the other manufacture cost wise or its it a wash of various aspects>
I don’t think the longevity situation is an issue. Not a lot of aircraft get retired and those that do are broken up for valuable parts.
there is market growth (or we hope) and the systems get old and antiquated and at some point replacement is needed.
Current fuel prices of course slow things down.
Bjorn, do you know when airports will begin to use the TrueNav setup (or some equivalent) in real life?
Hi Rob,
the first airline that used RNP was Alaska Airlines and the reason was their operating area had challenging geography for bad weather landings but could not motivate the infrastructure investments of classical precision guidance systems. From Wikipedia:
In 1996, Alaska Airlines became the first airline in the world to utilize an RNP approach with its approach down the Gastineau Channel into Juneau, Alaska. Alaska Airlines Captain Steve Fulton and Captain Hal Anderson developed more than 30 RNP approaches for the airline’s Alaska operations. In 2005, Alaska Airlines became the first airline to utilize RNP approaches into Reagan National Airport to avoid congestion. In April 2009, Alaska Airlines became the first airline to gain approval from the FAA to validate their own RNP approaches. On 6 April 2010, Southwest Airlines converted to RNP.
Ak Airlines had a tragic accident going into Juneau back int he 1971.
They were always on the lookout for anything that helped that perilous approach (good weather or bad, its a dicey one)
Originally the FAA and came out with what came to be called CAPSTONE that was tested in the Yukon Kuskokwim (YK) delta area.
https://en.wikipedia.org/wiki/Capstone_Program
Ak Airlines made the push to include SE AK in that as that’s one of their prime operating areas with the worst issues (bad weather, airports located where you could etc, ie. you take what you get)
They also were first into HUD I believe.
Hi Bjorn,
Again, a nice description of the advances in the field. Thanks.
I would like to point out that while optimization of individual routes is a no-brainer, in a sky filled with hundreds of aircraft arriving at the same destination, coordinating the routes of all those aircraft in a timely and efficient manner, and avoiding collisions is a monumental task. This is where the difficulty lies and I am sure an optimum solution will be found eventually. The current system is simple and “idiot-proof” so to say and any replacement must have similar characteristics.
On another matter, may I try to persuade you and Scott to release your analysis on Boeing cost-cutting and its implications to outside the paywall? This may truly be a pivotal moment in the history of Boeing and Commercial Aviation, and it would be nice to know the true picture and not what Boeing wants us to see. Thanks.
Some of these ‘more efficient’ changes when done over urban areas can lead to unrest from those living below.
Firstly, some who might be used to planes flying at higher altitudes and a more dispersed track over them dont take to kindly to lower altitudes and a tighter concentration which a fully computer controlled approach will do.
The above circumstances occurred in my city when these changes were trialled.
The graphic of the flight path avoiding the urban area and flying over open country is almost never achieved.
One of the biggest benefits of being able to navigate at will must surely be taking advantage of the all-seeing Earth observation satellites we have so that weather can be avoided or exploited on long haul routes.
Planning and following a tortuous route that coincides with a convenient loop of jet stream can knock whole hours of a journey. I know they can’t pull it off every time by when they do it can be spectacular.
Not so much, its general in nature, they are high satellites, small navigation details (specific flight routes) are not there.
Local weather information is vastly better but coverage of course is spotty.
What’s slowing adoption of RNP?