RE: Home made P - 82 mustang
Actually... the P-82 was only dimly related to the P-51. The fuselage of the P-82 is longeer and taller. the span of the wing outboard of the fuselage is considerbly arger than the same portion of a P-51 wing. The ruder and fin are larger... (its not 2 mustangs joined... its a compltely different airframe)
They simply BASED the design on something that had worked.
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Re the left engine... on some twins the left engine has as much as 9 deg LEFT thrust angle. (that same design would have 3 deg MORE right thrust on the right engine... 12 deg!) They found that downthrust can markedly reduce the requirement for side thrust on twins for single-engine stability. (it really does work... 1 deg downthrust can reduce side thrust required by 2 to 3 deg)
Get good 3-views of some twins... you will find almost all use both down and side thrust on both engines. I'll look for my book that has the info in the F-82... and other twins. Has good pictures showing thrust angles.