Rotorcraft typically tend to exhibit considerably more noise and vibration than jet or even turbo prop aircraft. Rotorcraft are exposed to excessive forced-vibration from the aircraft rotor rotation (i.e. blade pass) as well as from transmission gear mesh. Sometimes the frequency of these forcing function events will coincide with resonances of the fuselage skin and frames/stringers, creating excessive noise and vibration.
To correct this, a detailed analysis of the forcing function and structural dynamics of the aircraft is required to develop effective countermeasure strategies.
A passive damping system will be ineffective if resonance response does not contribute to the unwanted noise and vibration. In the case of rotor blade-pass forced-vibration, the frequency content of the forcing function will tend to occur below resonance frequencies of the fuselage skin or fuselage structure. However, this may not be the case with forcing function emanating from transmission gear sets.
Because of this, DTI has determined the combination of a SODS + TVA Array to be a powerful noise and vibration attenuation methodology for rotorcraft applications.
DTI’s Stand-Off Damping System (SODS) technology can be beneficial in the stiffness region to contend with frequencies below structural resonances, since the Stand-Off Layer – due to its “box-like” construction – adds significant stiffness to the fuselage skin structure, which is being forced.
DTI’s TVA Array countermeasure consists of a large number of relatively small TVAs which are tuned to blade-pass frequency, transmission gear-mesh frequency or harmonics thereof. The TVA array is mounted to high-response fuselage skin panels and other fuselage structure.
DTI has enabled the TVA Array countermeasure via careful control over TVA elastomer formulation as well as TVA injection mold process. DTI TVAs require no hand-tuning; therefore, the TVA units can be produced in large quantities at affordable costs. Some applications utilize up to 135 TVAs in the array.
DTI’s combination of a SODS + TVA Array proved to be powerful noise and vibration solution for rotorcraft applications.
DTI also utilizes De-Coupled Mass (DCM) Acoustic Barrier Technology in cases where there is substantial forced-vibration (high-frequency gear-mesh) and/or resonance response.
In the rotorcraft application, this may involve application of the DCM to the rear surface of aircraft trim panels. Effectiveness will depend on the frequency content of the noise.