To improve the performance of a helicopter turboshaft engine requires optimising the energy yield of the different components, and more particularly controlling clearance between the tips of the high pressure turbine blades and the stator. Dimension-chain tools take into account the manufacturing dispersion of the parts and assembly defects. This ensures the interchangeability of the different components and guarantees that a turbine can carry out different service functions, as the turbine is modelled in infinitely rigid solids. However, this approach does not take thermomechanical effects into account. And yet, the different operating regimes of a helicopter engine make it indispensable that the effects caused by the thermodynamic cycle should be integrated. The aim of this article is to show how using dimension chain and thermomechanical tools can contribute to controlling clearances at the tip of a high pressure turbine blade.