Inefficiency from redirected thrust?

[_greg]

I am trying to figure out how much thrust would be lost in redirecting it.
I understand that that harrier jets redirect their thrust downwards to generate upward thrust but surely they lose some efficiency due to turbulence and friction inside the redirection duct.
My question is how much is lost? also, what is that loss dependent on? and finally are there any ways to engineer the redirection better so that less thrust is lost.
Thanks in advance for any help in this.

 

[berkeman]

I am trying to figure out how much thrust would be lost in redirecting it.
I understand that that harrier jets redirect their thrust downwards to generate upward thrust but surely they lose some efficiency due to turbulence and friction inside the redirection duct.
My question is how much is lost? also, what is that loss dependent on? and finally are there any ways to engineer the redirection better so that less thrust is lost.
Thanks in advance for any help in this.

I would think you could learn a lot by contrasting the older Harrier jet design with the newer F-35 STO/VOL design. Did they change the ducting mechanism for the newer F-35?