# Avionics MCQs – Helmet Mounted Displays

1 - Question

Which of the following is not true with respect to HMD (Helmet Mounted Display)?
a) The flight parameters are displayed in the visor of the helmet
b) HMD comprises of collimated display
c) Using HMD the pilot has a FOV (Field OF Vision) of 360° without moving his head
d) The flight parameters are displayed in the pilot’s line of sight
Explanation: The FOV of an HMD is 360° in the sense that the pilot can look around(by moving his head) in all direction and still view the flight parameters in his line of sight. If the pilot does not move his head the FOV the HMD provides ranges from35° to 50° depending upon the type of aircraft and its role.

2 - Question

Which one of the following is not an essential factor in integrating the HMD with the helmet?
a) Must not interfere with the oxygen mask
b) Protect eyes and head during high-speed ejection
c) Geometry of the cockpit
d) Overall minimum weight for comfort
Explanation: The geometry of the cockpit does not affect the HMD nor the helmet as the helmet is worn by the pilot and the FOV of the HMD moves with the pilot’s head. Some of the factors that are essential are the minimum weight for comfort while wearing the helmet for long flight hours and in high g maneuvers, crashworthiness of the helmet with HMD and communication systems integrated no interference with other objects in the cockpit such as oxygen mask as it is crucial at ejection at high speeds.

3 - Question

What is the weight the pilot will feel on his head while executing a 9g maneuver with an HMD helmet of weight 800g?
a) 7.2kg
b) 0.72kg
c) 70.06kg
d) 9kg
Explanation: 800grams = 0.8 kg, during a 9g turn the pilot will experience a gravitational force 9 times that of a normal person at Earth surface. The total weight felt by the pilot = 0.8 x 9 = 7.2kg. Typical HMD helmets weigh around 1kg and at 9g the weight felt by the pilot will be 9kg which is just acceptable.

4 - Question

Which does not affect the inertial forces felt by the pilot when accelerating or decelerating?
a) Positioning CG with the pivoting point of the head
b) Reduce the weight of the helmet
c) Keeping the head in the upright position
d) Reduce the moment of inertia about yaw and pitch axis
Explanation: Keeping the head always in an upright position is not an option for pilots since the pilot will lose situational awareness if he does so. The pilot will feel the inertial forces irrespective of his head position. By reducing the moment of inertia we can reduce the inertial torques experienced. Reducing weight and positioning the CG of the helmet with the pivoting point of head ensures that there are minimal out of balance moments.

5 - Question

What are the advantages of HMS (Helmet Mounted Sights) over HMD?
a) Display flight data in the pilot’s line of sight
b) Provide target locking capabilities by looking at the target
c) Provide a FOV of 360°
d) Provide enhanced vision by combining radar and FLIR
Explanation: A Helmet Mounted Sights in combination with a head tracker system provides effective means for the pilot to lock on to target. The pilot can look at the enemy aircraft and lock on to it. The relative position of the enemy is then calculated by the head position of the pilot and sent to missiles to engage the target. A typical seeker head needs to be pointed to within about 2° of the target to achieve an automatic lock on.

6 - Question

Monocular rivalry occurs due to the brain trying to concentrate on _________
a) two equal displays on both the eyes
b) two different displays on both the eyes
c) one eye with display and the other eye without display
d) both the outside world image and the displayed image in one eye
Explanation: Monocular rivalry occurs because the brain is trying to process different images from each eye and rivalry can occur between the eye with a display and the eye without a display. The effect is most significant when flying at night when one eye sees less light whereas the other eye sees more. To overcome this binocular system is used where both the eyes are presented with the flight parameters.

7 - Question

Why are IIT (Image Intensifier Tubes) used in HMD?
a) Clarity of outside world scene
b) Provide night vision capabilities
c) Terrain mapping
d) Compensation for parallax errors
Explanation: IIT is an image intensification device which complements the infrared viewing system by providing night vision. The image form the Image Intensifier Tube is a phosphor screen which emits green light in the centre of the visual band where the eye is most sensitive.

8 - Question

In what type of display is the image projected directly to the retina of the pilot?
a) Virtual reality display
b) Binocular HMD
c) God’s eye view display
d) Optical display
Explanation: Virtual reality displays are for future virtual cockpits where the image is directly projected onto the retina of the pilot by a raster scanned laser light beam. The current technology of implementing a virtual retinal display involves lasers, optical fibers and miniature vibrating mirrors for raster scanning the retina of the eye, together with coupling optics.

9 - Question

Which of the following does not provide a proper reason for not using HMD in civil aircraft?
a) No need of helmets in civil aircraft
b) Acoustic noise level in civil aircrafts is much lower
c) Situational awareness is needed in civil aircraft
d) An oxygen mask is required only in the case of cabin depressurization