Why does the Indian BrahMos missile look like a MiG-21?

Well in order to answer the question, let us first consider this beautiful polish MiG-29 taking off.

What you see in the orange box is the left air inlet or air duct on the beauty, these are basically vents that sucks air in, to supply the engine with O2, oxygen. Oxygen in turn is used in combustion which ultimately provides thrust.

Now let us consider the riveting YF-23 a worthy rival to the mighty F-22.

The same principal follows here too, on an advance 5th generation fighter like YF-23, those large inlets are rather not a stealthy feature and in order to reduce the Radar cross-section (RCS) the designers would hated putting such big holes on either side of the fuselage, but we see them on every fighter, be it 3rd gen, 4th gen or 5th gen. Its on YF-23 on F-22 on J-20 or Rafale or the Su-30, you name it.

Why so ?!. Because it's imperative to the engine design we humans use. It's something designers just can't do away with even if they wanted to.

Now let have a look at a good old Mig-21

(Romanian Mig-21 manuvers during a simulated dog fight against USAF F-16)

Do you notice something ?! MiG-21 has no air intakes bellow its fuselage or on it's sides ! How come soviet designers get rid of those massive intakes in 1960s while designing it, something the designers of even F-22 couldn't achieve about 60 years later.

They actually placed the intakes right in the nose of the aircraft where usually the radar sits, as you can see in the above picture.

That's what makes the nose of the MiG-21 rather eccentric looking.

Now, let's talk about the Brahmos which is a supersonic antiship cruise missile. Brahmos uses a Ramjet Air-Breather engine as it's second stage and as the name suggests it too needs air for combustion which in turn exigences Air Ducts. Which fortutiously is rather based on the Mig-21 air ducts. And that's pretty much why MiG-21 and Brahmos look similar to an extent.

Hope I cleared the doubt.

Source : Souparna Das