Avionics MCQs – Helicopter, Optical and Hyper Sonic Air Data
1 - Question
Airspeed is not an essential quantity for rotorcrafts.
Explanation: Unlike fixed wing aircraft, where knowledge of airspeed is essential for safe flight, a helicopter’s airspeed is not an essential pilotage quality, except for certain engine failure conditions where hover capability is lost.
2 - Question
Which of the following cannot be used to obtain an approximate velocity?
b) Doppler radar system
c) Inertial navigation system
d) 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.
3 - Question
The conventional pitot tube cannot be used under______
a) 100 knots
b) 40 knots
c) 2 knots
d) 80 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.
4 - Question
Why is the static source errors compensated in helicopters?
a) Due to difference in rotor down wash
b) Not economical
c) Requires high computational power
d) Static source error does not matter
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.
5 - Question
Device that causes the magnitude of pressure to change when the aircraft speed nears zero are called ______
a) Airspeed indicator
b) Low speed indicators
c) Stall indicators
d) 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.
6 - Question
Which of the following is false with respect to rotating anemometer?
a) Used in low speeds
b) High sensitivity
c) Airspeed is measured in forward direction
d) Can be used within the rotor blade
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.
7 - Question
Airspeed measurements can be made by measuring the vortex’s _______
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.
8 - Question
Which of the following systems use a gimballed pitot tube?
a) Swiveling pitot tube below rotor
b) Omni directional pitot tube
c) Rotating anemometer
d) Rotating pitot tube
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.
9 - Question
What is required to accommodate for the ground effect in swiveling pitot tube below rotor system?
a) Secondary radar
d) 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.
10 - Question
What instrument measures the velocity by Doppler shift from backscatter of aerosol particles?
a) Rotating anemometer
b) Doppler radar
c) Laser velocimeter
d) Laser pitot tube
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.
11 - Question
What is the approximate accuracy of laser velocimeter?
a) 1 knot and below
b) 2.5 knots
c) 10 knots
d) 0.14 knots
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.
12 - Question
The configuration in which multiple pressure ports are located in the aircraft forebody is called as _____
a) Flush air data system
b) Redundant air data system
c) Multiple port system
d) Nose cone port 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.
13 - Question
Air data measurements in hypersonic flight provide primary flight control parameters.
Explanation: Air data measurements in hypersonic flight do not provide any primary flight control parameters. They usually support aerodynamic research to confirm structural loading and aero thermal models.