PPRuNe Forums - View Single Post - Why heavier aircrafts take longer to slow down in the air?
Old 25th Nov 2012, 05:58
  #98 (permalink)  
mm43
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes on 0 Posts
I don't have an engineering degree, but have been interested in the points raised.

The OP's request related to two similar aircraft, one heavier than the other, and why the heavier aircraft took longer to slow down than the lighter one. Assuming that the initial speeds are the same, the mass of each aircraft along with the L/D ratio (associated with AoA) will become the variable. Discount the flight idle fuel usage and thrust which are equal for both aircraft, then we are essentially dealing with kinetic energy.

EK = ½mv²

The L/D ratio along with AOA will change in a similar (though different) fashion for both aircraft as they slow, so it can be assumed that the Mass and V² are the only real factors we are dealing with. SLOWING is the operate word, and it follows without too much argument that the aircraft with the higher mv² product will always take longer to slow than the lighter one.

My 3 year old grandson proved it to me when he set up two parallel lines of Thomas wooden railway and placed one engine and a carriage on one line, then one engine and a wagon loaded with sand on the other. He pushed them off together, and you know the answer - he observed it also.
mm43 is offline