Today: Why Precision is Absolutely Crucial in Aerospace, Jan 02, 2017


Jan 2, 2017

Why Precision is Absolutely Crucial in Aerospace, Jan 02, 2017

Most people don’t give airplanes a second thought. But the reality is, they are an incredible combination of complex interlocking parts. What happens when one breaks?
Have you ever thought about how astonishing it is that humans can fly? Consider this for a moment. First, humans are clearly not designed to fly. We’re short, stocky, fleshy, and somewhat dense. We’re better equipped for lying on the couch. There’s a reason we couldn’t truly fly until 1903.

Second, think about airplanes. They’re usually made of metal, which is heavy and sinks. When you watch a giant, hulking 747 take off from an airport, it’s truly marvelous. How can such a massive hulk of metal get airborne? Is this magic? Is Harry Potter aboard?
Naturally, we take all this for granted. We’ve been flinging ourselves into the friendly skies for the last 100+ years, so the novelty has worn off a bit.
But the skies are not so friendly, and we should still be amazed at the power of flight. In the early days of flight, the odds of crashing were terribly high. The things that went up almost always came down in a frightening crash. Even now, planes go down, although it happens with much less frequency.
These crashes are a poignant reminder that:
  • If even the smallest thing goes wrong on a plane, things can go south really quickly.
  • Because of the science involved in flight, precision matters. A lot.
We’re going to take a look at some recent plane crashes, then dive into the science behind flight. Prepare to get a little bit morbid and a little bit nerdy. It will be fun.
The Crashes
Airline travel is pretty safe in the scheme of things. Compared to car wrecks, which happen all the time, planes go down much less frequently. In fact, 2015 was one of the safest years on record for air travel, with an estimated 1 in every 3.1 million commercial flights involved in an accident. The numbers are up a bit in 2016, with a total of 24 accidents and incidents.
As Steven Johnson says:
It is extraordinary how safe flying has become. You are now statistically more likely to be elected president of the United States in your lifetime than you are to die in a plane crash. What an amazing achievement as a society! But what we end up focusing on are the catastrophic failures that are incredibly rare
but happen every now and then.
And yet when a plane does crash, it can be devastating. Consider some of these recent crashes (all data and images from here).
On August 5, 2016, Emirates Flight 521 impacted the runway, lost an engine, and immediately caught fire. Thankfully, the plane was evacuated safely and there was only a single fatality.

On July 1, 2016, a Russian plane that was fighting a forest fire, went down in a wooded area, killing all 10 there were aboard.
On May 19, 2016, an EgyptAir Airbus carrying 66 people made an abrupt 90-degree turn, then a 360-degree spin to the right as it began to lose altitude. Finally, it crashed into the Mediterranean Sea, killing all that were aboard.
On May 19, 2016, a Flydubai flight aborted a landing and remained in a holding pattern at 15,000 feet. During a second landing attempt, the pilots lost control of the plane and then hit the runway at a high rate of speed, causing the plane to disintegrate. All 62 people aboard were killed.
The Causes of Plane Crashes
Due to the complexity of flight, planes crash for a variety of reasons. According to experts, the most common causes of crashes are:
  • Pilot error. Because planes are controlled by humans, there will always be a significant risk of error in flying. Currently, about 50% of all crashes are the result of human mistakes. Of course, there are numerous times when pilots save their planes, such as when Sully Sullenberger crash-landed in the Hudson River.
  • Mechanical Failure. Mechanical failure accounts for approximately 20% of all plane crashes. It’s true that this rate has fallen as planes have become safer, but this is still the cause of 1 out 5 planes going down. For example, in 1989, a disintegrating fan blade caused the number one engine in a 737-400 to lose power, eventually leading to a fatal crash.
  • Weather. Despite a plethora of tools designed to help pilots navigate challenging weather conditions, it still accounts for 10% of all flights going down. Challenging elements such as snow, fog, ice, and rain can cause pilots to lose visibility, which then triggers human error.
  • Sabotage. Approximately 10% of all crashes are the result of intentional damage from saboteurs. These tend to be the crashes that get the most media attention, such as the crashes of 9/11.
  • Other human error. Other human error, such as mistakes by air traffic control, maintenance engineers, or dispatchers accounts for all other plane crashes.
The Science of Flight
When we consider the science of flight, we should be amazed that flights don’t go down more regularly. Without going too in-depth on how planes remain airborne, let’s consider some of what’s involved.
The Power of Lift
Without lift, there is no flight. Several factors contribute to lift. Wings are shaped with a curved top and flat bottom, which makes a shape called an airfoil.
Image via Wikipedia
Lift happens when…
As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it. As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward…As air flows over the curved upper surface, its natural inclination is to move in a straight line, but the curve of the wing pulls it around and back down. For this reason, the air is effectively stretched out into a bigger volume—the same number of air molecules forced to occupy more space—and this is what lowers its pressure. For exactly the opposite reason, the pressure of the air under the wing increases: the advancing wing squashes the air molecules in front of it into a smaller space.
But it’s not just lift that causes the plane to rise. There’s also “downwash,” which is a result of the wings being tilted at an angle:
The angled wings push down both the accelerated airflow (from up above them) and the slower moving airflow (from beneath them), and this produces lift. Since the curved top of the airfoil deflects (pushes down) more air than the straighter bottom (in other words, alters the path of the incoming air much more dramatically), it produces significantly more lift.
Image via Wikipedia
But it gets more complicated than that. Consider, for a moment, these facts about the engine on the mammoth Boeing 777.
  • A single engine on the 777 puts out 111,000, the equivalent of 1,110 Mazda 2’s. The whole Titanic produced only 46,000 horsepower. The 777 has two engines, meaning the total output is 222,000 horsepower.
  • During takeoff, the engines are consuming 2 million cubic feet of air per minute. The Bugatti Veyron, one of the fastest cars in the world, consumes 45,000 cubic feet of air per minute when traveling at top speed.
  • A single engine costs $24 million dollars.
Or consider this. In a single Boeing 737, there are approximately 367,000 different parts, coming from hundreds of different suppliers.
Within commercial airplane engines, in general, jet fuel burns in the combustion chamber at around 2,000 degrees Celsius, requiring advanced cooling techniques since metal melts at around 1,300 degrees Celsius.
At full power, engine blades rotate at around 1,000 mph.
To ensure that planes will hold up under the extreme stress of flying, they are put through a series of rigorous stress tests. These stress tests include:
Static tests – To ensure that airplane wings can handle extreme loads, they are put through static tests, in which the wings receive loads up to 1.5 times what they will normally encounter while flying.
Before building a wing, engineers calculate the maximum load a wing can hold, as well as the maximum amount of stress at wing will encounter during any flight, based on the size of the plane, possible maneuvers, emergency situations, etc. Then the wings are pushed to approximately 150% of the maximum load limit to ensure that they don’t fail before then. Obviously, precise calculations are required to determine all these variables with preciseness.
Here is an example of the wings of a Boeing 777 being tested:
Ingestion tests – Because both birds and large volumes of water can cause significant damage to engines, the engines are given ingestion tests to ensure they can handle the impact.
The storied “chicken gun” is used to test whether the engines can handle the impact of a single, large bird. As noted:
“The chicken gun is designed to simulate high-speed bird impacts. It is named after its unusual ammunition: a whole, dead, standard-sized chicken, as would be used for cooking. This has been found to accurately simulate a large, live bird in flight. The test target is fixed in place on a test stand, and the cannon is used to fire the chicken into the engine, windshield, or other test structure.”
However, despite all the testing, if enough birds strike plane at once, the repeated impact will damage the engines. This was what caused Sully Sullenberger’s plane to go down in the Hudson.
Here’s a video of the famed chicken gun being used on an engine:
As Wired reported:
“The engines [of a Boeing 777] need to handle water, so GE will set up a hose and blast a running GEnx engine with 800 gallons of water per minute. When the test goes as planned, all that rain flies through the chamber and out back without diminishing thrust. That means it’ll easily handle the drizzle when flying out of O’Hare.”
The point in all this is simply that airplanes and flight are incredibly complex things composed of a massive amount of interlocking parts. The fact that 99% of all flights are successful is a tribute to how far we’ve come in airplane safety since 1903. When you consider all that goes into building a single engine part, and that planes are a combination of hundreds of thousands of different parts, it’s really quite astonishing that more plane crashes don’t happen.
If a single part, such as a bolt or mount fails, it can set off a chain of havoc. Small vibrations can lead to parts breaking which can then lead to entire sections of the plane shearing off. Again, it’s amazing how rarely this actually happens.
The Need for Precision
What’s abundantly clear from the above information is that absolute precision is needed when manufacturing aerospace parts. At Weldaloy, we keenly understand this reality since we manufacture aerospace parts. Few things matter more than exactness, hardness, precision, the ability to withstand temperatures, and the ability to make parts that match the aerospace engineer’s specifications. We must stay within these extremely small tolerances to ensure safety for all people in the air, on the land, or under any equipment with our parts in it.
Partnair Flight 394 crashed due to repairs made with unauthorized parts (to be clear, Weldaloy did not provide parts for this flight).
A broken mount on an auxiliary power unit caused it to vibrate, which in turn caused the tail section to vibrate. The bolts holding the tail to the plane were not authorized and were significantly weaker than normal. Eventually, the tail section disintegrated, causing the plane to crash. 55 people were killed.
The reality is, a single failure in any part of the plane can trigger a chain reaction with catastrophic results. Clearly, care and extreme precision are needed when building and maintaining airplanes.
It truly is a marvel that airplanes can fly. And it truly is a marvel that so many flights happen every year without an incident.
But plane crashes, unlike car crashes, tend to inflict damage on a much larger scale, resulting in many more injuries and deaths. In some ways, this shouldn’t surprise us. Planes travel at high speeds, are subjected extremes when they fly, and even a small error can have a catastrophic result.
But the good news is, safety continues to improve. We should expect crashes to get even less frequent than they already are as new methods are devised for building and testing aircraft.
Famous aviator Charles Lindbergh said:
I realized that If I had to choose, I would rather have birds than airplanes.
Maybe so, but we can’t fly on birds, and until we can, we’ll stick with airplanes.

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