How are the aerospace engineering departments at IIT Bombay, IIT Kharagpur, IIT Kanpur and IIT Madras?

Aerospace Engineering can be further divided into four parts 

• Aerodynamics - An extension of fluid mechanics 
• Structures - All about mechanics of materials
• Propulsion - A good base in aerodynamics will help you 
• Controls and dynamics - Mainly used for navigation 

Apart from this there is a lot of Math involved in the curriculum.

The aerospace engineering branches of all the institutes you mentioned give an edge to each other and are equally good. The choice should be based on personal preference, accessibility, campus life, academics, extracurricular activities and placements.

IIT Kharagpur: Pros

• Massive and surreal campus 
• Less academic burden
• Good faculty pool with experienced professors that are easier approachable.
• Companies like Airbus, GE, Honeywell, Altair, Rolls Royce, etc come for placements in the core sector.
• Some of the students go for higher studies in foreign universities like Purdue, Texas A&M, University of Texas, Austin, etc
• IIT KGP offers the Boeing Project wherein a team of 5 fabricates all parts of an Unmanned Aerial Vehicle (UAV). On clearing the selection procedure, you will also be offered a scholarship of about 10k per month for an entire year.
• I am not gonna mention any of the institutional activities (clubs, societies, fests etc.)because I reckon the scenario will be pretty much the same in all the aforementioned colleges.

IIT Kharagpur: Cons 

• It’s not easily accessible to students from Western and Southern States.
• Kharagpur is a town and lacks many amenities apart from its large railway station.
• Mess food is not good at all
• The huge campus delays the time taken to reach the academic area.
• The core companies only select the best students and a major portion of the batch has to go for non-core placements.
• Aerospace Engineering in India has very few job prospects though we expect the scenario to improve a bit 
• You can also apply for off-campus placements at DRDO or ISRO.

Judging a branch solely on the basis of placements is misleading. Yet, most students end up with decent jobs. The best part is that the course curriculum of aerospace engineering is intriguing and keeps you hooked.