Correct Answer : Intrusive probe
Explanation : All of the sensing probes, except for the flush mounted static probe, are intrusive because they disturb the local flow over the body of the aircraft. Thus they are also called intrusive probes.
Correct Answer : Static pressure
Explanation : static pressure is the pressure of the still air surrounding the aircraft body even when the aircraft is moving. It is measured using static ports placed along the aircraft skin.
Correct Answer : High angle of attack fighter aircraft
Explanation : When the angle of attack and the sideslip angle are under 10°, they do not affect the pressure measurements much. In applications such as high angle of attack fighters, special self-aligning pitot tubes are used to measure the stagnation pressure.
Correct Answer : Attitude indicator
Explanation : The instruments that use pitot-static probe are airspeed indicator, altitude indicator or the altimeter and the vertical speed indicator. The attitude indicator uses the gyro to measure the orientation of the aircraft.
Explanation : when the aircraft is stationary, the pressure sensed by the static port is the free stream air pressure and the stagnation pressure ports are zero. Since the aircraft is not moving stagnation pressure is zero and hence the difference between the two values is the static pressure.
Correct Answer : Pneumatic plumbing
Explanation : Pipes that carry the air pressure sensed from the pitot tube or the pitot-static tube to the air data computer and the various other flight instruments such as the airspeed indicator, altitude indicator and the vertical speed indicator is collectively referred to as pneumatic plumbing.
Correct Answer : Wind tunnel tests to find spots of body-flow interference
Explanation : Various wind tunnel tests are done to predict the optimum location for the static port so that the interference of the flow with the body is minimum. Since static defect is predictable, it can be corrected in the air-data computer.
Correct Answer : Static defect
Explanation : The pressure that is sensed via the pitot-static port will be different from the actual free stream pressure due to the interference from the skin, angle of attack and the sideslip angle. This difference is referred to as the static defect.
Correct Answer : Static temperature
Explanation : The outside air temperature is also called the static air temperature and is necessary for computing various parameters such as true airspeed, air density and for fire control aiming solutions.
Correct Answer : Stagnation temperature
Explanation : The temperature measured by the temperature probe on the exterior of a moving aircraft is called the stagnation temperature. It is always higher than the static temperature due to the heating effects of compressing air at higher speeds.
Correct Answer : Reduce time lag
Explanation : To avoid time lags in the temperature measurements, a leakage hole at the rear end of the probe allows for rapid exchange. For redundancy, multiple temperature probes are placed in different parts of the aircraft.
Correct Answer : Stall warning system
Explanation : When angle of attack sensors are installed on an aircraft they are usually apart of an independent stall warning or stall control system. Since such systems are flight critical, redundant sensors are usually installed.
Correct Answer : Angle of attack
Explanation : Angle of attack is the angle, in the normally vertical plane of symmetry of the aircraft, at which the relative wind meets an arbitrary longitudinal datum line on the fuselage. Angle of attack, is important as it corresponds to the amount of lift produced and the dangerous condition of stall.
Correct Answer : Greater than 1 Knot
Explaination : A 10°C error in the temperature will result in a true airspeed greater than 1 knot at a typical transport aircraft flight conditions.
Correct Answer : Isentropic compression
Explanation : The recovery factor of the probe corrects the original measured temperature readings for frictional heating in the skin, re-radiation from the aircraft to the flow, and nonisentropic compression of air. It is given by η and is measured empirically.
Correct Answer : Tip of vertical tail
Explanation : Probes may be mounted on the wing tips, vertical tail, forward fuselage or other areas where the local mach number is the same as the free stream mach number for all expected flight altitudes and speeds.
Correct Answer : Standard atmospheric model
Explanation : To determine the altitude from the measured static pressure, the standard atmospheric model has been established. The standard model gives the relation between a height and the properties of the atmosphere as the solution to a differential equation relating the difference in pressure.
Correct Answer : Pressure altitude
Explanation : The altitude at which the standard temperatures are used is called the pressure altitude. Pressure altitude is the altitude of the aircraft above sea level. It always takes it’s reference as sea level.
Explanation : Pressure altitude, as the name suggests, is the altitude derived from pressure measurements. It is measured from the static port of the pitot-static probe. The static pressure of air varies with altitude with approximately 101Kpa at sea level.
Correct Answer : Ground speed
Explanation : When you stand on the ground with a radar speed gun pointing at the aircraft, the speed measured is called the ground speed and is measured relative to the ground. True airspeed is measured relative to the wind.
Correct Answer : Trailing cone
Explanation : The most accurate value of static pressure is when the flow is least affected by the presence of the aircraft itself. In a trailing cone configuration, the probe is far behind the aircraft and is least affected by the flow.
Correct Answer : Ice formation
Explanation : Pitot-static tubes are generally placed with heating elements to stop the formation of ice in the orifice of the probe. Formation of ice on the probes causes erroneous readings and has lead to fatal air crashes.
Correct Answer : Stealth configuration
Explanation : Stealth planes, such as the B2 spirit stealth bomber, use retractable pitot tubes to maintain their stealth. When not in stealth mode they extend the probes for air data measurements.
Correct Answer : Thrust produced by the aircraft
Explanation : The mach number is computed from the corrected values of static and stagnation pressures. Mach number is comparatively easier to calculate than airspeed in supersonic speeds due to the compression shocks that form in the pitot tube.
Correct Answer : Vertical speed
Explanation : Air data computers usually provide an output identified as altitude rate which is an outgrowth of the early pneumatic vertical speed indicators which suffer from undesirable lags. Altitude rate combines accelerometer readings and pneumatic readings.
Correct Answer : Not the true altitude
Explanation : Pressure altitude is always referenced from the sea level. When flying over hilly areas, the actual altitude of the aircraft from the ground is definitely lesser than the pressure altitude, thus showing erroneous altitude readings.
Correct Answer : Mach number
Explanation : Mach number is used for programming stabilizer position for speed stability, defining high speed performance boundaries such as flutter onset, and for defining optimal cruise paths.
Correct Answer : Pressure ports
Explanation : A typical central air data computer is a box containing: the pressure transducers, associated excitation circuitry, and signal conditioning circuitry, the computer, and the output drivers that are compatible with interfacing subsystems.
Correct Answer : Non erasable ROM
Explanation : The air data equations are solved in the processor assembly, which contains the CPU, memory for the operational flight program which can be electrically erased or EEPROM, data storage memory( usually a volatile RAM), and non volatile RAM.
Correct Answer : Input processing
Explanation : Input processing usually involves A/D conversion and packing of discrete signals into logic words, plus implementation of special serial data interfaces.
Correct Answer : Software is flexible
Explanation : In centralized architecture, the software is not flexible. A minor change or update in one of the parts of the software requires the whole software to be written and checked again. Updating the software to the rapidly changing hardware is not possible.
Correct Answer : Better accuracy
Explanation : Accuracy is independent of the architecture used. The accuracy of a CADC is same as that of a distributed air data system but might suffer from lags occurring from long lengths of tubing.
Correct Answer : Distributed air data system
Explanation : With the advent of smaller and cheaper microprocessors, it became possible to pack them with probes and transducers. The result is a distributed air data system that replaces the CADC. A key feature is the packing of signal processing units with or adjacent to the probes.
Correct Answer : Primary radar
Explanation : Velocity from Doppler, inertial and GPS can be used as an approximation for velocity. It is possible for the radio controller on the ground to obtain the velocity of the rotorcraft but it is not possible for the pilot to get velocity data from primary radar.
Correct Answer : 40 knots
Explanation : The conventional pitot tube and the pressure transducer become ineffective as airspeed drops below 40 knots. At the lower speeds, impact pressure is equal to dynamic pressure q, and the sensitivity of this pressure to a change in velocity is minimal.
Correct Answer : Flush air data system
Explanation : Hypersonic vehicles used the concept of locating multiple pressure ports around an aircraft forebody to extract total pressure and flow direction. This type of configuration is referred to as the flush air data system and has been used at NASA Dryden research flights.
Correct Answer : 1 knot and below
Explanation : Test results show an accuracy of 1 knot or better at altitudes where the particle density is adequate. Aerosol densities and particle densities vary with altitude, time and volcanic eruptions.
Correct Answer : Laser velocimeter
Explanation : In a laser velocitimeter, optical sensors are located within the aircraft and look out through the flow into the free stream. They measure the Doppler shift from backscatter of naturally occurring aerosol particles in the free stream.
Correct Answer : Radio altimeter
Explanation : The principle of the probe is that the horizontal component of the induced flow velocity is a repeatable function of horizontal airspeed but varies with ground proximity. Hence, a radar altimeter is required to accommodate the ground effect.
Correct Answer : Due to difference in rotor down wash
Explanation : Static-source errors in helicopters tend to be difficult to compensate because of rotor downwash that differs significantly in and out of ground effect. Fixed wing aircraft do not compensate for static source errors in ground effect, and neither do helicopters.
Correct Answer : Rotating anemometer
Explanation : Rotating anemometer increases the magnitude of pressure change caused by the change in airspeed when the aircraft airspeed is near zero. They are used in low omni range airspeed systems for helicopters.
Correct Answer : Airspeed is measured in forward direction
Explanation : Rotating anemometer is like a pitot tube for helicopters to measure low velocities below 40 knots. In addition to obtaining improved sensitivity at low speeds, the rotating probe measures omnidirectional airspeed, including backward velocities.
Correct Answer : Frequency
Explanation : A vortex sensor measures vortices shed by fluid flow over a deliberately-inserted obstruction. The frequency of vortices is proportional to the airspeed. This method has been used in helicopters and in ground vehicle fire control systems.
Correct Answer : Swiveling pitot tube below rotor
Explanation : In the swiveling pitot tube below rotor system, a gimballed pitot tube containing vane arrangement that causes the tube to align with the airflow within the downwash field emanating from the rotor blades is used. Changes in the airflow field vector are correlated with changes in true airspeed.
Correct Answer : Time average of apparent vertical
Explanation : The simplest approach to the determination of the true vertical is to time-average the direction of the apparent vertical(vector sum of gravity and vehicle acceleration).
Correct Answer : Deviation is large
Explanation : The error caused in the vertical referencing can be rectified by introducing nonlinearities. One such method is the erection cutoff where the precession of the gyroscope is interrupted when a large deflection is sensed.
Correct Answer : Earth’s gravitational field
Explanation : The basic vertical reference in all forms of heading and attitude reference devices is the Earth’s gravitational field. The direction of Earth’s gravitational field can be sensed with great accuracy in stationary systems. However, when the platform moves, all the instruments indicate the vector sum vehicle acceleration and local gravity.
Correct Answer : Airborne magnetometer
Explanation : Aircraft have magnetic fields that add to the Earth’s field and are sensed by the airborne magnetometers. The induced error, called deviation, can be 10° or more.
Correct Answer : Magnetic pole migration
Explanation : Magvar has a diurnal change, a long term change due to the migration of magnetic poles, and random changes because of magnetic storms. The magnitude of the magnetic field changes about 0.5% per year.
Correct Answer : Dip angle
Explanation : The magnetic declination, also called the magnetic variation or magvar, is the angle between the horizontal component of B and true north. Navigators use ‘magvar’ in order not to confuse astronomical declination with magnetic declination.
Correct Answer : Maxwell
Explanation : The magnetic fields B are measured in Gauss and Tesla(104 Gauss). In geomagnetism, Units of “Gamma”(10-5 )are used.
Correct Answer : Use higher order leveling loop
Explanation : The stand off error depends upon the gravity sensors switch’s dead and gives poor acceleration errors. Significant improvement can be obtained in the averaging vertical reference by using a high order leveling loop.
Correct Answer : Standoff constant error
Explanation : A stand off constant error exists since the direction of the local vertical changes as a result of both the rotation of the Earth and the aircraft’s own motion around the Earth.
