Crop Flow Control in a Longitudinal Axial Threshing Unit Using Fully Adjustable Guide Vanes: A Field Study in Winter Wheat Harvesting

In axial-flow combine harvesters, guide vanes direct crop material through the threshing and separation unit. The research object has the standard configuration of guide vane assembly; the six rear vanes are adjustable, while the two front vanes—located in the threshing zone—are fixed, which limits material flow control. In European conditions, where crop biomass is typically higher, improved control in the threshing area is essential to reduce losses and maintain grain quality. This study introduces a guide vane angle evaluation to combine performance and a modified guide vane system that enables all eight vanes to be adjusted simultaneously between 10–35°. Field tests were conducted using two identical combines (A and B) in the same winter wheat field, under identical operating conditions. Combine A was equipped with the modified system, while Combine B retained the original manufacturer configuration. Both machines operated at a rotor speed of 980 rpm and a concave clearance of 15 mm. Results showed that Combine A achieved higher throughput (23.78 kg s−1), lower broken grain (0.18%), and lower fuel consumption (0.84 L t−1) compared to Combine B (20.6 kg s−1, 0.61%, 0.99 L t−1, respectively); the separation and sieve losses were also reduced in Combine A. Analysis of the results demonstrated that full-range guide vane adjustability—including in the threshing zone—can improve crop flow, grain separation, and harvesting efficiency in high-yield conditions.