A feature becoming more and more common in fighters these days is a helmet mounted sight/display. These allow the pilot to look at the target he is interested in and designate it or to have his attention cued to something courtesy of the helmet displays. The more complex helmets now coming in to service on the F-35 have access to distributed viewing systems around the aircraft so the pilot can actually look through the aircraft – just as well given how crappy the visibility is from the F-35 cockpit!
These helmets need to know exactly where they are all the time so they can align accurately with the other sensors on the aircraft. They also have to have the image generator for the pilot displays built in. Consequently, they appear a bit bulky compared to traditional helmets.
They still have to be kept light in weight since the pilot does not want a lot of weight on his or her head when pulling g or, even worse, ejecting. Therefore, the bulk is a space issue but less of a weight issue. Spotting the helmets is not too tricky. The accompanying shots give you a number of different pilot shots and you can see what they are all wearing. Some two seat jets only have the helmet mounted display for one occupant. Compare the normal helmets with the display helmets. The Typhoon’s helmet is very conspicuous with a load of bumps covering the positional sensors.