A main-chain semiflexible polyether (TPB-10) has been studied in the nematic phase by small angle neutron scattering (SANS) and by neutron and X-ray diffraction. Principally, we have determined the polymer chain conformation by SANS for mixtures of deuterated and hydrogenous polymers, aligned using a strong magnetic field (4.2 T). In good agreement with previously reported results on nematic polyesters, our data are well fitted to a model of a cylinder in which the main chain forms one hairpin defect including two very confined and extended wires. Moreover, the X-ray diffraction patterns show that smectic C fluctuations occur in the low-temperature nematic range. Referring to the layer normal of the local S-C arrangement, the mesogens are tilted with respect to the field. Strikingly, the whole chains are also tilted with the same angle as the mesogenic units.