String Caps Diagram

A few days ago (this past Tuesday), Boeing had to once again delay the maiden flight of the much-anticipated Boeing 787 Dreamliner. It is no surprise that it has harmed the company’s public image stock price as well as had damaging effects on deals with Qantas and Virgin, for example.

According to the Wall Street Journal:

Despite the steadily increased use of carbon-fiber composite parts in airlines, Boeing Co.’s disclosure Tuesday of design troubles with its 787 Dreamliner highlights the engineering, manufacturing and maintenance issues still associated with such high-tech materials.

By indicating that “a relatively small number” of added internal structural supports are needed on some of the upper portions of both wings, the disclosure underscored a broader problem that the aerospace industry has recognized for a while: shortcomings in computer-design systems’ abilities to precisely predict behavior of certain composite parts as they bend and twist in flight. …

You can read more about Tuesday’s delay announcement here, via The New York Times.

To understand what’s really going on here, we turn to Flight Global’s blog, FlightBlogger, “Understanding the 787 structural reinforcement (Update1)“. It talks about the engineering design and the history of design problems that have hindered the completion of the Dreamliner.

Because of the need to go back into the detailed design phase for this fix, combined with the need to fabricate, install and test at component and at full scale levels, several sources with a direct familiarity to the situation estimate that the fix will take “months not weeks.” …

The issue centers around the wing-to-body join that mates the wing box (Mitsubishi/Section 12) and the center wing box (Fuji/Section 45/11). The center wing box is the combination of two pieces, the center wing tank (Section 11) and main landing gear wheel well (Section 45). The area of concern centers on the 18 points where Sections 11 and 12 meet.

Digging deeper, the 18 points in question on each side of the airplane (36 total) are located on the top panel of the center wing box and run port to starboard inside the structure of the center tank through to the other wing. These 18 ‘stringers’ inside the center wing box are matched by 17 stringers on the wing box, which serve to stiffen the wing skin. The wing box has 17 stringers, but a source indicates they are designated 2-18, hence the reference to the 18 points that need to be reinforced.

(Image from Flight Global.)

Runway Design Markings

In terms of design consideration, I had quoted from HowStuffWorks:

Main runways are usually oriented to line up with the prevailing wind patterns so that airplanes can take-off into the wind and land with it. Local and ground air traffic controllers determine which runways are used for take-off and which for landing, taking into account weather, wind and air-traffic conditions. In some airports, main runways cross each other, so the controllers have to pay even closer attention.

Let’s take second look at this …

Runway Sections

Runway Sections

The runway is technically the surface between the thresholds (see the above image). On either side of the runway are sections called blast pads, which function as emergency space to slowly stop planes that overrun the runway on a bad landing on an aborted take-off. They are also used to absorb the initial jet blast from large planes during take-off. Blast pads are marked with yellow chevrons and typically aren’t as strong as actual runways. This section isn’t used (for taxiing, take-off, or landing) except in an emergency.

In between the blast pad and the runway is the displaced threshold section which can be used for taxiing, take-off and landing rollouts, only. They cannot be used for the touchdown part of landings.

Runway Configurations

There are four basic configurations for runways. Of course, there are others, but those are just variations of the four. The single runway is the simplest of the four. Then we get the parallel runway of which there are four sub-types. Next there is the open-V runway, which have two sub-types. Finally, the most complex configuration is the intersecting runway, with three sub-types.

In the end, though, reasons for choosing one configuration over another is all about the prevailing winds, noise pollution, and local restrictions, among other. See the table below that summaries the different types:

Runway Design Markings and Runway Sections images are taken from here.

Check out these links for much more information on these runways:
http://en.wikipedia.org/wiki/Runway

http://virtualskies.arc.nasa.gov/design/tutorial/tutorial1.html

What’s a runway for? It is for airplanes to take off and land. That one’s easy. But what are they made of, and how do people know how to position them in an airport? Considering the frequency of take-offs and landings at any major airport, it’s important to know that people have thought of these things (for the most part) to keep everything flowing smoothly and safely.

Airport runways are carefully designed to make air travel as efficient and robust as possible.

Some Specifications

As for the specifications of an average runway, they can run from anywhere between 6000 feet to 10,000 feet (about two miles) long. Most of them are able to accomodate landings of aircraft that are less than 200,000 pounds, but others can take much more weight. A typical Boeing 747-400 is about 800,000 pounds upon take-off, but it can only land safely if it is less than about 700,000 pounds. (This explains why we sometimes hear of airplanes circling an airport for some time before landing; it needs to burn up fuel to lose weight in order to land.) Similar situations are apparent in all aircraft (albeit not necessarily those particular weights). And of course, under no circumstance can the maximum landing weight be higher than the maximum take-off weight.

As for the runway length, we would need to consider the density of the air. Remember that, at higher altitudes, the density of air is less, which decreases the amount of lift and thrust. Just know that an aircraft landing at a higher altitude would require a longer runway. And along the same lines of density, fluids (like air) are less dense at warmer temperatures. As such, an aircraft will require a longer runway in hotter or more humid conditions than in cooler, dryer ones.

Design Considerations

Main runways are usually oriented so that during take-offs and landings, the airplane is flying into the wind. Flying into the wind upon take off is a good thing because it allows for more airflow across the wings (see last week’s post on lift: “Lift Force From Aircraft Wings“) while using less runway length. But once we’re in the air, however, going against the wind can massively reduce our efficiency and increase our flight time. We’ll want to avoid this as best we can, but there isn’t a way to control wind speed in nature just yet.

From HowStuffWorks: “Main runways are usually oriented to line up with the prevailing wind patterns so that airplanes can take-off into the wind and land with it. Local and ground air traffic controllers determine which runways are used for take-off and which for landing, taking into account weather, wind and air-traffic conditions. In some airports, main runways cross each other, so the controllers have to pay even closer attention.”

Markings

Each runway is labeled with seemingly random combination of alphanumerics. But of course, nothing in engineering is random (hopefully). Following navigation and surveying convention, picture a north-south-west-east compass with angles broken down from 0 to 360 degrees. In this configuration, 0 and 360 are pointed north (not east, as we are wont to expect!). So, 90 degrees points east, 180 points south, and 270 points west.

At the end of each runway is a number that indicates the angle that the runway points to, rounded to the nearest 10-degrees, and then divided by 10. So, if an airplane were to land by flying west, the “right” end of that runway would show a big 27. The “left” would show the opposite, which would be a 9.

Isn’t that cool!?

That’s all for now. We’ll pick up on this next time, with runway configurations.

(Image from NASA.)