Transient convection has been investigated experimentally for the purpose of providing computational fluid dynamics (CFD) validation benchmark data. A specialized facility for validation benchmark experiments called the rotatable buoyancy tunnel (RoBuT) was used to acquire thermal and velocity measurements of flow over a smooth, vertical heated plate in air. The initial condition was forced convection downward with subsequent transition to mixed convection, ending with natural convection upward after a flow reversal. Data acquisition through the transient was repeated for ensemble-averaged results. With simple flow geometry, validation data were acquired at the benchmark level. All boundary conditions (BCs) were measured and their uncertainties quantified. Temperature profiles on all the four walls and the inlet were measured, as well as as-built test section geometry. Inlet velocity profiles and turbulence levels were quantified using particle image velocimetry (PIV). System response quantities (SRQs) were measured for comparison with CFD outputs and include velocity profiles, wall heat flux, and wall shear stress. Extra effort was invested in documenting and preserving the validation data. Details about the experimental facility, instrumentation, experimental procedure, materials, BCs, and SRQs are made available through this paper. The latter two are available for download while other details are included in this work.