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PAUL BUI: MMS stand for Metrological Measurement System.
It is an instrument that measures "in situ" data
"in situ" meaning right at the aircraft,
not far away, right at the skin.
Our primary data is static pressure,
static temperature,
three dimensional wind, which is horizontal wind
and vertical wind.
And from the wind, we can also have turbulence measurement.
[Radio chatter]
The challenge of wind measurement
is because you're flying at the same time
that you're trying to measure wind as if you're not flying.
Imagine you're driving your car
and there's some wind going on,
but you're moving with the car.
If you stick your head out,
it's you moving plus the real wind.
So the way to calculate the real wind is to
take whatever wind is blasting your head
and you subtract out the car motion.
So that's how we do it.
So you measure the air motion
with respect to the airplane
and then you measure the airplane motion
with respect to the ground.
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The instrument measures in real time at 300 Hz,
but the data that we send down is at 1 Hz
just for decision making and quick data look.
But we actually store the data in flight at a much higher rate.
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To measure they call it the ground speed,
which is the velocity with respect to the ground,
we use inertial navigation system.
I have this one right here, but this is a tactical grade.
It's not very good.
We also sample with the aircraft one.
This gray unit here, this is a ring laser INS.
It's navigational grade.
It's about almost 100 times more accurate
than the small one we have over there,
So those two units
would give you how fast you're going
with respect to the ground.
You know, it would give you north, south...
The other equation is how the air is moving
with respect to the aircraft, the fuselage.
And the way we do that is this probe here.
This is a pitot probe.
This little hole here, it senses...
It's like when you stick your head out of your car,
the blast of pressure.
So, if you're not moving,
this pressure is the same as non-moving pressure.
But if you're moving, this pressure is higher.
So this is called "total pressure".
That kind of tells you how fast you're going.
So the other thing you have to measure also is temperature.
And that's what this sensor is over here.
There's an element in here.
Some of the air goes through,
some would turn up and bend around.
And inside there are platinum wires...
temperature sensors.
The other place we sense the static pressure,
which is the pressure when the airplane is not moving,
is on the side of the aircraft.
So we have a static port over here
and we have one on the other side.
So that goes at the bottom of this airplane.
And these are pressure transducers.
It basically converts whatever pressure
into a signal.
This is a very special sensor,
it is temperature compensated.
The other component we need is
which direction the wind is coming from.
Because if you're moving along and the wind is coming that way,
you have to know it's coming from there
or from the top.
And we do that by these pressure hoses.
So, for example, if you fly along
and there's no lateral wind,
both of these pressures are the same,
But let's say that this side has
the wind coming this way.
This hole would have higher pressure than this one.
So we measured the difference between these two pressures.
And then we also have one up here
and one on top,
which is on that fuselage over there.
So the difference in those pressures
gives you the angle of the wind coming from.
So, for example,
these pressure sensors give you a signal,
the difference between those pressures.
So, if they are the same, you get zero volts.
So, if this side is higher, you get plus
or if this side is higher, you get minus somthing.
So all the signals come here and this is the data system.
But this is basically... It's all right here.
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Every airplane needs to know almost the same data,
but regular airplanes doesn't need to know
down to this precision that the scientists need.
Because if you a little wrong, the equation...
the calculation is off.
So it's a fundamental measurement
because a lot of other data depends on it.
Because it's a basic value
in a lot of other calculations.
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