From the current AMA Rulebook, CL General,
10. Profile Definition. The fuselage of a
profile model resembles that of a
conventional airplane in the side
(profile) view and appears as a thin flat
sheet in the plan (top) view. The engine
shall be completely exposed from the
mounting lugs to the cylinder head and
shall not have any type of fairing.
Additional reinforcements such as
plywood nose doublers and cheek cowls
on the opposite side of the engine (for
side mounted installations) are
permitted. Cheek cowls may extend
from the prop drive washer to a point 25
percent of the root chord back of the
leading edge at the root, and may be
faired in. In the case of an inverted or
upright engine installation, the engine
mounts may protrude from the fuselage
sides but may not be faired in.
(Underlining added.)
On the previous page, there's a chart of widths allowed by specific events. Can't copy that in, but its specs are:
1/2A Proto...........1/2" fuse width ......3/8" mx cheek cowl
Scale Racing.........5/8"......................? possibly as 1/2A Proto
Slow Combat.........3/4"......................3/4"
Carrier..................3/4"......................? possibly as Slow Combat
Slow Rat and.........3/4"......................? possibly as above
.. Rat Racing
These are most likely AMA "safety specs" local contests can't tinker with, for these events at an AMA Sanctioned meet, anyway.