29 May 2008

Wings and prayers and prayers and wings...

For those that do not know, I have a crashed airplane in my hangar right now, waiting to be sold to a junk dealer.

If you have followed the local news for Grand Rapids Michigan today, you would know that there was an incident involving a medical helicopter on the hospital roof.

I would be willing to guess that there have been an increase in aviation prayers emanating from West Michigan this past month.

That and it's probably not a good time to talk to my wife about resuming flight school...

I was just in the hangar again today, and I just had to walk around the wrecked airplane again. It's probably a weekly occurance for me, just to walk around the wreckage and marvel at the design, and how it operated during the crash. It really is fascinating how aircraft are designed.

Obviously, they're not designed primarily for getting into crashes, but like race cars, there is a fair amount of consideration in the design allowing for the stresses of a crash.

As I walk around the aircraft, I see things that I didn't see before. I can see that the propeller blades are all bent backwards, meaning that the propeller was spinning when the aircraft hit the ground. But two of them are bent more than the third, telling me that the engine was not producing power at the time of impact.

The huge, gaping hole in the side of the aircraft is from the wing ripping off and tearing a hole in it. I then look at the wing itself, and see where impacted a tree. You can see from the way the metal is ripped that it probably stayed in the tree, and that's why it ripped off the rest of the aircraft. It must have been a pretty formidable tree too, because the damage to the wing is probably two feet across.

I can see that both landing gear are bent outwards, indicating that the plane hit with a fair amount of force. Landing gear are designed to absorb much of the impact of a normal landing, and then some, so for them to be bent out is something rather impressive.

I can also see a buckle in the airframe directly forward of the tail, telling me that when the airplane hit, the weight of the tail actually bent the body of the airplane.

I look towards the front of the airplane, and I can see where the nose gear was. It collapsed in the crash, and that's why the propeller blades are bent. I can also see that the metal framework that holds the front of the airplane together and holds the engine in place is bent as well.

I can see that the cargo pods slung underneath the airplane are crushed, and full of grass and mud. The mud is quite far up the body of the airplane, telling me that wherever it came down, the ground was pretty soft, soft enough that a car or truck probably would have gotten stuck.

This aircraft experienced a massive amount of force when it hit, that much is obvious.

When we take all these clues and put them together, the crash becomes more and more violent than might be suggested otherwise. It was a brutal, metal-twisting, ground-plowing, whiplash-inducing moment.

But small details tell me that this pilot, and this airplane, both performed flawlessly considering the circumstances.

For instance, in emergency training classes, pilots are taught, somewhat counterintuitively, that in the event of a crash landing, you aim for obstacles. Not how you would think though. This does not mean aim right at the biggest tree you see in front of you. The idea is that if you can aim the aircraft to hit some obstacles, then the energy will be dissipated into the obstacle, and not into you, or the passengers. For example, if you can manage to rip a wing off the airframe, that will slow you down enough that the ultimate impact will be less traumatic. Studies have shown that in the event of a serious crash landing, if the aircraft comes to a complete stop in less than seven feet, then the forces exerted on any humans in the aircraft will be so great as to cause usually fatal internal injuries.

But if the pilot can dissipate that energy over a longer stretch of ground, then the crash will most likely be survivable. This pilot hit a tree right dead center in the middle of the wing, and ripped it off the rest of the airplane. That means that a lot of energy was absorbed by the wing and the tree, and not the pilot.

Another small detail about the airplane is the seats. Aviation seats in most aircraft are designed to absorb some of the force of the impact in the event of a crash landing. The idea is the same, the dissipation of energy before it gets translated into the human occupant. In this particular aircraft, the seats are designed with a curved, "C" shape support bar. In the event of a crash landing, this support bar, with the rest of the seat structure, will collapse slightly, absorbing the energy so that the pilot's spine doesn't have to.

Here's the awesome part: The seats weren't damaged.

That means that the pilot was skilled enough to pick a spot that would give him a relatively safe landing, taking all these factors into account, and it also means that the aircraft's design allowed the energy of the crash to be absorbed by key parts of the airframe, instead of the cockpit area, and by extension, the pilot. All this heap of crumpled metal means that the force of the impact was dissipated in ways that were not ultimately harmful to the human occupant.

I was talking to a mechanic that was helping with the investigation, and he said that the pilot didn't even have a sore spot or bruise from his shoulder harness.

That is impressive.


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