REFLECTOR: Performance

[Scott Derrick]

  exhaust gas is minimal.  For #2, the plum has no way to transfer its drag
> back to the plane.  Picture the plume as a cylinder projecting into the
> airstream.  It is not connected to the plane in any way to slow it down, so
> #2 is out.  The boundary layer at the back of the plane is already well

I'm not sure this is correct. In fact I'm sure it not correct.  Air is a 
fluid and all fluids, in our environment, have a viscosity and shear 
strength. While I agree the viscosity of air is very low, isn't the 
shear stress of a fluid flow determined by the speed and pressure of the 
fluid?

The exhaust stream when not aligned with the air flow is just like a 
solid structure sticking out into the air stream.

It is bent for sure, but the first ?? inches acts like a solid but 
flexible pipe, thus inducing parasitic drag.

Its not like it becomes instantly disconnected right after it exists the 
pipe.  Some of the force of the wind pushing against the exhaust stream 
is transferred to pushing against the airplane.

Thats how fluid clutches and torque converters work right? There is 
friction within the flow, thats why fluid in a pipe flows faster in the 
center than along the walls, that friction, transfered through out the 
entire fluid stream is why you have a pressure drop at the end of a 
pipe. The more fluid you try to push through the pipe the higher the 
pressure drop.

I'm a computer engineer and not a mechanical fluid engineer. So I don;t 
know how much drag is transfered to the plane. Maybe the imparted drag 
is insignificant? Like the push of the exhaust compared to the push of 
the prop?  Maybe not?

But the exhaust plume is connected to the plane.

Scott