High Altitude Glider Project
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Intro Launch 5
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Glossary
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GPS |
Global Positioning System. This is a satellite-based navigation
system built by the US government in the late 80's, which is now
available for use by civilians the world over. A GPS receiver
provides position, altitude, time and velocity updates at a rate of once
per second. Accuracy is usually around 15m, although only about 100m
accuracy is guaranteed.
Russia has launched an equivalent system named GLONASS, and Europe is
planning a system of its own named Galileo. |
| Ground Speed |
Speed relative to the ground. This is one of the pieces of data provided
by the GPS. |
| Track |
Direction of motion relative to the ground, and/or path across the
ground. Provided by the GPS. |
| Heading |
Direction the aircraft is pointed in. This is provided by a
compass while in level flight, or for far more money yet stable output while
in a turn, a gyro-based heading indicator synced to a compass. |
| TAS |
True Air Speed. This is the speed relative to the airflow. For
example, while flying in zero wind, TAS will be equal to ground speed.
But if, say, an aircraft has a TAS of 40 knots, and is flying into a
headwind of 15 knots, ground speed will be only 25 knots.
TAS is
difficult to measure directly, and must be calculated from pressure
altitude and IAS. |
| IAS |
Indicated Air Speed. This is a measure of the pressure of the
airflow on the aircraft (the dynamic pressure). It is expressed as
the airspeed which would cause an equivalent airflow pressure at sea
level.
At high altitudes, TAS will be higher than IAS. But most flight characteristics of an aircraft will
generally be constant for the
same IAS, no matter what the altitude or TAS is. A Pitot
Tube is used to measure IAS. |
| Pitot Tube |
A small tube facing the airflow, often mounted on a wing or the nose,
which is used to measure IAS. |
| Pressure Altitude |
Altitude as given by a barometric altimeter, or in other words, altitude
based on the air pressure. Must be calibrated before flight with the sea
level pressure for a given day. |
| Static Port |
A small hole, usually next to the Pitot Tube, which is used to measure
barometric (ambient) air pressure. Can be used to obtain barometric altitude. |
| G loading |
Force supported by a structure, expressed in multiples of the normal load
from gravity while stationary. |
| Gyro |
A device that measures either orientation, or rate of rotation, in
pitch, roll, or yaw. These used to literally be heavy spinning
gyroscopes, but are now often tiny, cheap piezo-ceramic based devices
(of so-so stability), or very expensive laser-ring devices with
supernatural accuracy. |
| Inertial Nav |
Inertial Navigation is an extremely sophisticated navigation method that
works by sensing motion, and adding together all the motions that have
happened on a trip to arrive at current position.
It requires a set of X, Y, Z axis acceleration and rotation sensors,
which must be of extreme accuracy and stability for the method to work.
Lower-quality Inertial Navigation Systems can still be useful for
providing an "artificial horizon" reference, however. |
| Aileron |
A moveable surface on the trailing edge of an aircraft's wing, usually near
the tip, which can be moved to cause the aircraft to roll left or right. |
| Elevator |
A moveable surface on the horizontal part of the tail, which can be used
to pitch up or down. On the glider, it is mostly used to change the
airspeed. |
| Flaps |
Usually refers to moveable surfaces on the trailing edge of an
aircraft's wings, which can be put down to add both lift and drag.
This helps achieve a steep, easy to fly approach to an airfield, and a low landing speed.
Lowering flaps often causes strong pitch-trim changes. |
| Servo |
Moves the control surfaces. Has a small geared motor and a
position sensor. Easy to use, because the servo just receives a signal telling
it what position to take go to and it takes care of moving to and
staying at that position
by itself. |
| Yagi Antenna |
A radio antenna that is directional, so that most of the transmit and
receive strength is in a beam about 30 degrees on either side of the
antenna's end. Within that beam, the signal will be about 10x stronger. |
| Quickcam |
A cheap desktop digital camera designed to plug into your
computer's parallel port. Maximum resolution is about 320x240.
It's meant for indoor use, and has problems with bright sunlit days. |
| Dual-Redundant |
Two versions of a system are provided, in case one fails, with either
able to step in and fill the function. Sometimes performance is
lower without both items, but the function will at least still work with
one. |
| Fail-Safe |
If a system fails, it won't fail in a way that damages other systems or
creates a hazard. For example, a power board that won't catch fire
if there's a short, or an autopilot that won't dive the aircraft into
the ground trying to maintain a certain IAS if the pitot tube fails. |
| ELT |
Emergency Locator Transmitter. In people-carrying aircraft, this
means a little orange box that sends radio pings if you crash, so your
relatives will have something to bury (well, ideally so you can be rescued,
but that's less common).
In this case, it means a software feature whereby the aircraft transmits its position for several short periods each day, to
help in locating it if it lands or crashes away from the launch
site. |
| Expert System |
A very basic form of artificial intelligence which uses a decision tree
approach, to let something as obtuse as a computer make sensible
judgments. Works by having a person think through each possible
situation, how to tell whether it has occurred, and encode the best
action in that circumstance. |
Text and images © copyright 2002, Art Vanden Berg
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