The present work shows a method to verify if the new designed tail beam of an aircraft in composite material may be assembled without interferences and if its geometric specifications satisfy the functional requirements of the tail beam. The considered functional requirements are the trend of adhesive gaps at the interfaces between couples of components and the transmission of the drive motion from the main rotor to the tail rotor. The analyzed adhesive trends depend on tolerances assigned to the tail beam's components and on the constraints due to the assembly sequence. The applied tolerances have been considered to follow a Gaussian distribution. The assembly sequence and the assembly jigs have been designed by satisfying the assembly functional requirements. The distribution of the adhesive gaps has been estimated by means of Monte Carlo simulation. To ensure an efficient assembly, interference conditions and excessive gap variation must be avoided. A sensitivity analysis has carried out in order to identify dimensional and geometric tolerances that mostly affect the variance of the gap's distributions. Results of simulations show a percentage of interferences of about 21% along the between rib and skins. To reduce this percentage it is needed to decrease the position tolerance of the adopted TH. The front gap between rib and spar is extremely critical, since the dimensional tolerances applied to the thickness of the faced surfaces reduce this gap to 0. Therefore, it is needed to adopt a special jig able to recover the gap between the spar and the rib. The performances connected with the motion drive of the tail beam have been evaluated by means of three parameters: the parallelism between the adhesive planes of rib and spar, the perpendicularly between the axis of the rib and the plane of the rib, the offset of the tail beam. The obtained results show that the critical parameter is the parallelism between the adhesive planes of rib and spar whose percentage of non conformities is about 15%. This is due to the dimensional tolerance applied to the thickness of the rib. To reduce the value of this dimensional tolerance there are two ways: to change the nominal value of the thickness and the new value needs to be verified by means of a structural analysis of the component; to improve the capability of the manufacturing process in order to obtain parts with smaller tolerances (i.e. a better quality).
Tolerance analysis of an aircraft tail beam
Toleranzanalyse eines Hubschrauberheckträgers
2008
10 Seiten, 15 Bilder, 1 Tabelle, 13 Quellen
Aufsatz (Konferenz)
Englisch
SAE Technical Papers | 2021