Turbulence: The Truth Options

[tucsondan]

I have a couple questions about turbulence. First, what exactly is turbulence and how does it make a plane shake? Does it travel through the engines or over the wings? Pilots always say there is nothing to worry about when hitting turbulence, but how can you say that when it feels like the plane is dropping and no one can stand up?

Thanks,

Daniel True

[The Airbuser]

I have a couple questions about turbulence. First, what exactly is turbulence and how does it make a plane shake? Does it travel through the engines or over the wings? Pilots always say there is nothing to worry about when hitting turbulence, but how can you say that when it feels like the plane is dropping and no one can stand up?

Thanks,

Daniel True

OK, I'll make a wild shoot here, since I screwed up yesterday...

Turbulence is movement of air molecules. Easy... Cooler temperature air descends, and warmer temperature air climbs. It makes the aircraft move because, since it is a movement it carries speed, and speed means pressure, pressure that is applied to the aircraft in the direction of the movement of the air molecules. So, no, it does not travel over the wings or the engines. It just applies pressure over the whole aircraft, whether it is upward or downward. And I think Clear Air Turbulence also moves horizontally i.e.:From the left or from the right of the aircraft...

Why pilots say there's nothing to worry about? 'Cause there's not. The airplane is just moving in other direction (i.e: vertically). The only thing that could go wrong in turbulence, is that if you don't fasten your seatbelt, and it's a messed up day, you could hit your head with whatever you have over your head. And you can't "stand up", again, since it is another pressure applied to the aircraft, it causes acceleration (downward or upward), just like in takeoff for example, and in some aircraft you feel unable to move because of the acceleration during rotation and initial climb.

Though, I believe, that there might be a problem, but it has to be a really strong turbulence... Maybe if the aircraft is shaking really hard, the flame could go out in a jet engine?

[Piltdown Man]

I'm not trying to be rude, but air is a three dimensional medium. As soon as you are above the surface, air can move in any direction it chooses. And it does. However, once one bit of air moves in a different direction to another you have a "sheer". It is these "sheers" which change the lift generated by the wings and the path the aircraft takes through the air. Let's call this "turbulence" Some of these sheers are small ones, where there is only a small change in speed and/or direction and you don't feel them and others are so massive that they can pull your wings off.

On the human side of things, we are blessed with amazingly sensitive balance organs and as a back-up, a high speed computer capable of accepting optical data. But unfortunately, we weren't designed to fly. We also have "hang-ups" about technology (generally through ignorance) and phsycologcal problems to do with "control". Bung all of this together and start moving the aircraft around a bit (like a few inches) and you will get reports from those affected who will state categorically that their aircraft dropped thousands of feet, etc. The media like stuff like this and publish it. This re-enforces people's perceptions about turbulence.

There is turbulence where it is so dangerous you don't want to be there. But because we have investigated enough accidents and incidents in the past, we now have a very good (bloody excellent to be honest) idea where not to go. And then there is "turbulence" so light you would let your granny go for a walk in the cabin. But the important thing to remember is we were designed for a static earth, not flight so we must make judgements accordingly.

Why do we say there is nothing to worry about? Well generally, when you have enough capacity (not doing very much work) and you have the time to speak to the passengers (speaking to passengers is about our lowest priority), there really is nothing to worry about. But we do understand that some people are worried about "bumps", so our hope is that we can reassure you - which obviously appears not to work!

But as a passing thought, have you ever wondered what turbulence is like for us? We hate it. It spills your tea, makes crosswords difficult to do and meals hard to eat. It also makes you work a bit harder (we fly because we don't like working for a living). So believe me, we do all we can to avoid it.

PM

[AIRCRAFT ENGINEE...]

OK - for the sake of the new person I'll try to explain it in simple terms.

Think of a stream of water pointing up and you pass your hand thru the stream. Your hand gets pushed up (you feel the pressure of the water on the palm side of your hand), water sprays on you (likely) and then your hand drops probably lower than what it was at first because you were holding pressure "down" to keep your arm from moving "up". That "up" and "down" movement is the functional equivalent of "turbulence".

Remember that aircraft are usually moving quite a bit faster than the air surrounding them. So the effect of flying into air that is moving in a different direction than you are is to force you to "move". Exactly where you "move" depends on a combination of things - how fast that "other" air is moving, what direction it is moving, how fast your aircraft is moving and in what direction - and HOW LONG YOU ARE IN THE MOVING AIR.

So, if the speed of the "other" air is relatively "fast" (lets say 100 kph - knots per hour) and you are moving at 500 kps, if it is coming at you from underneath (it's called an "updraft"), when you enter that moving air you WILL be forced up (at a relative angle of 20% - 5 feet forward forward for each foot up initially) and you will feel a "bump". In modern aircraft, the autopilot will adjust the flight path to compensate for the altitude change. Now, lets change the air movement direction quicly to "down" (downdraft) and you feel an "unbump" (you would raise up in the seat unless you were secured with the seatbelt). OK - now lets put bumps and unbumps together quicly (the amount of time you are in the moving air) and more or less shake the aircraft up and down "quickly" - that's turbulence - the quick movement.

(OK, this is simplified) Now, if you were in a balloon, you wouldn't notice it because you would be drifting along with the air - up, down, sideways and without the forward speed, you wouldn't notice the movement much unless you kept looking at the altimeter, but you would still be moving, just without the "bumps".

Because aircraft are DESIGNED to be flexible, the wings can move up and down in response to that air movement and a lot of the bumping is "damped" (reduced).

Don't worry about it, but when seated, keep your seatbelt loosely fastened.

[joecessna182]

Simply put, turbulence is caused air changing either speed or direction. As mentioned before, it is called sheer.

Two good terms to know are Chop and Turbulence.

Chop is pretty much like riding in a boat on a lake on a windy day when the water is CHOPPY. Get the correlation.

Turbulence is more abrubt and typically a little more upsetting. The nice part is, it doens't usually last too long, where as chop can hang around for a while.

Unless categorized as severe, turbulence, while uncomfortable, is not going to hurt the airplane when it is being flown properly.

I hope this keeps it simple, if not, what can I say. I guess I just used to it cause I do it everyday.