  Interplanetary coronal mass ejections (ICMEs) are a significant feature of
the heliospheric environment and the primary cause of adverse space weather at
the Earth. ICME propagation, and the evolution of ICME magnetic field structure
during propagation, are still not fully understood. We analyze the magnetic
field structures of 18 ICME magnetic flux ropes observed by radially aligned
spacecraft in the inner heliosphere. Similarity in the underlying flux rope
structures is determined through the application of a simple technique that
maps the magnetic field profile from one spacecraft to the other. In many
cases, the flux ropes show very strong underlying similarities at the different
spacecraft. The mapping technique reveals similarities that are not readily
apparent in the unmapped data and is a useful tool when determining whether
magnetic field time series observed at different spacecraft are associated with
the same ICME. Lundquist fitting has been applied to the flux ropes and the
rope orientations have been determined; macroscale differences in the profiles
at the aligned spacecraft may be ascribed to differences in flux rope
orientation. Assuming that the same region of the ICME was observed by the
aligned spacecraft in each case, the fitting indicates some weak tendency for
the rope axes to reduce in inclination relative to the solar equatorial plane
and to align with the solar east-west direction with heliocentric distance.
