Introduction to Aviation Systems
Sensors
Prepared* by
Dr. Hamid Alper Oral
Yildiz Technical University
Faculty of Applied Science
Department of Aviation Electronics
* DISCLAIMER These notes, most of which copied from other references. are for educational purposes only and they are not meant to gain any credit or profit.
Primary Autonomous Sensing Methods
• Air data
• Magnetic
• Inertial
• Radar sensors
Air data sensors –
Sensed Parameters Derived Data
• Barometric Altitude (ALT)
• Indicated Air Speed (IAS)
• Dynamic pressure • Vertical Speed (VS)
• Static pressure • Mach (M)
• Rate of change in pressure • Total Air Temperature (TAT)
• Temperature • Static Air Temperature (SAT)
• True Air Speed (TAS)
Air Data Probes/Sensors
Deriving Data
• Pt
• Ps
Vertical Speed Indicator
Mechanical
Altimeter
Diagram showing the face of the "three-pointer" sensitive aircraft
altimeter displaying an altitude of 10,180 ft (3,100 m) and a
pressure reading of about 29.92 inHg (1013 hPa).
Airstream
Direction
Detector
(ADD)
to detect
angle of
attack
https://youtu.be/xxYn1UeuzH4
Typical parameters provided by an ADC are:
Air Data Computer . Barometric correction.
. Barometric corrected altitude.
. Altitude rate.
. Pressure altitude.
. Computed airpeed.
. Mach number.
. True airspeed.
. Static air temperature.
. Total air temperature.
. Impact pressure.
. Total pressure.
. Static pressure.
. Indicated angle of attack.
. Overspeed warnings.
. Maximum operating speeds.
. Maintenance information.
Air Data Computer Reference speeds based upon IAS and M
Vstall = aircraft stall speed
Vrotation = aircraft rotation speed
Vgear extend = aircraft gear extension maximum
Vflaps extend = aircraft flaps extension maximum
Vmaximum operating = aircraft maximum operating speed
Mmaximum operating = aircraft maximum operating Mach number
Computed airspeed is the IAS corrected for static pressure errors.
CAS is the computed airspeed with further corrections applied for
non-linear/square law effects of the airspeed sensing module
EAS is achieved by modifying CAS to allow for the effects of
compressibility at the pitot probe, thereby obtaining corrected
airspeed for varying speeds and altitudes.
The most meaningful parameter relating to navigation is TAS. TAS
represents the true velocity of the aircraft in relation to the air mass
and in still air would be representative of the aircraft speed over
the ground (groundspeed).
Aviation Q-Codes
Reference: https://www.skybrary.aero/bookshelf/books/3298.pdf
Airbus data system
ADM: Air Data Module
Magnetic Sensing
Inertial Heading Indicator
Radio Magnetic Indicator
ADF: Automatic Direction Finder
VOR: Very high frequency Omni-
directional Range is a type of short-range
radio navigation system for aircraft,
enabling aircraft with a receiving unit to
determine its position and stay on course
by receiving radio signals transmitted by
a network of fixed ground radio beacons
Enables pilot, by adjusting HDG SEL knob, to set marker to a
1. Heading marker
desired heading reference.
Horizontal Situation Indicator
2. Course pointer Indicates selected course.
Indicates selected course is in the direction, within plus or
3. TO indicator
minus 90 degrees, of the course to the station.
Indicates bearing relative to a ground station (ADF-VOR), as
4. Bearing pointer number 1
determined by the HSI Display Control Panel.
Provides selected course readout (in degrees) to indicate
5. COURSE indicator
course pointer.
6. NAV warning flag Indicates loss of radio navigational signal.
7. GS flag Indicates loss or unreliable glideslope radio signal.
8. Glideslope deviation pointer Indicates aircraft position relative to glideslope centerline.
Indicates selected course is within plus or minus 90 degrees to
9. FROM pointer
the course from the station.
Manually adjusts, course pointer and COURSE readout, to set
10. CRS SEL knob
desired course or track for VOR and LOC.
11. Azimuth indicator Indicates aircraft heading.
Provides immediate indication of azimuth relative to desired
12. Aircraft symbol
course and course deviation.
Indicates aircraft deviation from desired VOR, LOC or FM
13. Course deviation bar
course or track.
14. HDG SEL knob Manually adjusts to selected desired aircraft heading.
Indicates loss of instrument power or directional gyro
15 HDG flag (warning)
information is invalid.
Indicates bearing relative to a ground radio station (ADF-VOR)
16. Bearing pointer number 2
as determined by the HSI Display Control Panel.
17 RANGE readout Indicate range to destination.
Magnetic Heading Reference System
Inertial Navigation
• Position Gyroscopes
https://youtu.be/hVsx4XWafXg
• Rate Gyroscopes
• Accelerometers
Position Gyroscope
Position Gyroscope
Attitude Indicator
Attitude Indicator
Attitude Indicator
Inertial Heading Indicator
Ring Laser Gyroscope
No rotating parts
Rate Gyro
https://youtu.be/a4iLtZPp_-8
Pendulous force feedback accelerometer .
principle of operation
• The device is fixed to the body
Accelerometers
structure whose acceleration is to
be taken (shown as the structure
at the right).
• As the structure and the
pendulous arm move, the pick-off
at the end of the pendulous arm
moves with respect to two
excitation coils.
• By sensing this movement, a
corrective current is applied to the
restoring coil that balances the
pick-off to the null position.
• As the restoring coil is balanced
between two permanent magnets
above and below, the resulting
current in the restoring coil is
proportional to the applied
acceleration
Inertial Navigation
Errors get worse by the time because of drifting. Hence correction is required.
Gimballed vs. Strap Down
Inertial Navigation
Gimbals provide a stable platform
Inertial Navigation
Gimbals provide a
stable platform
Radar Sensors
• Radar Altimeter
• Doppler Radar
• Weather Radar
Radar altimeter
compared to barometric altimeter
Stand-alone
Radar altimeter radar altimeter display
principles of operation
Radar Altimeter Frequency Modulation Technique
Doppler Radar
By checking the frequencies
proportional to the ground speed,
aircraft ground speed components in
three axes are calculated and INS
system readings are corrected.
It can provide data at low speeds
hence very useful for helicopter
applications.
Flying over smooth surfaces such as
water or snow create problems for
Doppler radar giving millpond effect.
Weather Radar
Principle of Operation
. Weather and map with a maximum range of 320 nm.
. Turbulence (TURB) mode out to 40 nm.
. Wind shear detection out to 5 nm.
Weather Radar
Schematic
