What is the thing above the gun and why is it covered??? the one with the red cover on it??
These are called Auxiliary air intake doors and you can find one on each side…Besides main intake which is in nose ( you cant miss it ) , Mig-21/F-7P/PG has few other small air intakes in the fuselage that open/close at certain speeds or throttle settings…In the above pic ( click it to enlarge), you can see that Aux door is open…….When aircraft is on ground , the front and Aux intakes are protected with intake covers so any bird or FOD doesn’t go into the intake…that’s what those red covers are for…..they are removed during the pre-flight inspection by the ground –crew…
In the above pic, if you watch closely, try spotting another air intake…any success? Well it’s on the nose where aircrafts number is written…just see ahead of number 8…there is a square thing.... You will rarely find a pic where these intakes are open….They are hinged outwards from front and open against springs to allow air in the duct to spill overboard whenever supply exceeds demand. These normally operate at Mach numbers greater then 1.3 …
Front intakes are easy to design than the side or belly intakes….But then front intakes do have many technical and operational limitation too…Remember that jet engines are big suckers…Once you make the pilot sit in the path between intake and engine , you are choking the poor engine…so it needs aux intakes elsewhere in the fuselage to support it appetite…
The biggest operational limit for the front intakes is that you cannot house a powerful radar or electronic / avionics equipment ….Other than Mig-21, F-7 and SU-22, I cant recall any other fighter that is still operational and has a front intake. Or is there any ??
P.S ..Any Mod or Webby, can you please enlarge the F-7s pic, I tried making it bigger but all my science failed...