Take the other piece sheet steel you made and roll it into a tube/gentle cone around your ducted fan unit. Secure this end in place with tape.
Take the other end of your sheet steel tube and put that into the cone coming out the back of your engine. Secure this end in place with tape. Then use a stapler as previously described to secure this end, Duct tape cannot take the temperature.
***Note, most of the pictures in this instructable were from my mark II jet engine hence the hole in the cone which shouldnt be there in this version, and the combustion chamber with no copper tube input. unfortunatly these are the only photos currently available but i will replace them asap.***