Descent

Descent

DESCENT

Concepts we are going to use:

What is the reason that provokes a descend?

It is easy to know, because it is completaly the opposite of the climb perfomances. 

To have a descend the powere required must be higher than power available ( Pr>Pa).

 

As you can see in that picture the angle of descent (a) is equal to  (Drag – Thrust)/Weight  (of course  we consider sen a = a)

a= (T-D)/W

The rate of descend (in the picture u)  :

u=(Pr-Pa)/W

  

  • Speed of minimum angle of descent : It is the speed which allows us the maximum distance at a given altitude.

          If we want to travel the maximun horizontal distance  during the glide, the angle of descent must be minimum. 

         To get that, the relation between  L/D must be maximum . We only reach that at a certain angle of attack called maximun fineze (Cl/Cd)max. This angle of attack it is a fixed value.

 

  • Speed of minimum rate of descent : Speed which allows us being the most time in the air

 

CONSIDERATIONS OF GLIDDING

Speed :  If we mantain another angle of attack besides the maximun fineze , the speed will  change, so we will not travel the most distance.

 

Weight : The weight has a contradictory effect on una hand the rate of descend increases, and the speed of minimun descend increases. So if we have 2 identical aircrafts, one heavier than the  other  gliding. The result is that both planes will land at the same point, but the heavier one arrives earlier.

Configuration : For travelling the highest horizontal distance, the drag must be the lowest. So it will be reached without flaps ( flap 0). 

Wind : The wind does not affect in the time that the airplane is in the air as it does not affect the drag, however it does affect the distance traveled with respect to the ground. If we had  tail wind decreases the angle of descent by increasing the distance of glide, reciprocally happen with the head wind.

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