DOC AIRBUS | AMM A320FAPU MOUNTS - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The APU is positioned in the tailcone structure by 7 suspension rods. These are attached to one bracket each on the roof of the APU compartment between FR80 and FR83. Three vibration isolators, installed between the suspension rods and the APU, reduce the transmission of vibration and shocks from the APU to the aircraft structure and vice versa. Brackets attach the vibration isolators to the APU.
The entire suspension system is designed to withstand all vibration, shocks, inertia and air loads within the defined operational limits.
All components of the suspension system are fireproof with the exception of the vibration isolator elastomer components.
** ON A/C NOT FOR ALL The APU is positioned in the tailcone structure by 7 suspension rods. These are attached to one bracket each on the roof of the APU compartment between FR80 and FR83. Three vibration isolators, installed between the suspension rods and the APU, reduce the transmission of vibration and shocks from the APU to the aircraft structure and vice versa. Brackets attach the vibration isolators to the APU.
The entire suspension system is designed to withstand all vibration, shocks, inertia and air loads within the defined operational limits.
All components of the suspension system are fireproof with the exception of the vibration isolator elastomer components.
2. Component Location
** ON A/C NOT FOR ALL 
APU Suspension System - Component Location| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C NOT FOR ALL | |||||
| 4035KM | VIBRATION ISOLAT0R - FWD L | 316AR | 315 | 49-12-51 | |
| 4045KM | VIBRATION ISOLAT0R - FWD R | 315AL | 316 | 49-12-52 | |
| 4055KM | VIBRATION ISOLAT0R - FWD R | 315AL | 316 | 49-12-53 | |
| 4065KM | BRACKET - APU MOUNT FWD L | 315AL | 315 | 49-10-00 | |
| 4075KM | BRACKET - APU MOUNT FWD R | 315AL | 316 | 49-10-00 | |
| 4085KM | BRACKET - APU MOUNT AFT | 315AL | 316 | 49-10-00 | |
A. Suspension System Capabilities
- The suspension system is designed 'fail-safe' with respect to the failure of any one of the 7 suspension rods or their respective structure attachment bracket or vibration isolator housing lug or clevis.
- The left forward vibration isolator is supported by 3 suspension rods (2 lug/clevis and one eyebolt/clevis joints) and is thus fixed in space. The right forward vibration isolator is supported by 2 rods (one lug/clevis and one eyebolt/clevis joint) such, that movement in the y-direction is possible. The aft mount is designed similarly, but allowing movement in the x-direction. This design approach permits production and installation tolerances in the APU as well as the suspension system to be washed out.
- The metallic components of the 3 APU mounts (one each vibration isolator and APU attachment bracket) are designed 'safe-life'.
- All other APU system interfaces are flexible to permit translational movement and rotational displacement of the APU in all directions. The actual APU movement occurring during APU and/or A/C-operation is much lower than the design limits. Only negligible loads are therefore transferred through these interfaces.
- All components of the suspension system are made of CRES with the exception of the tailcone structure brackets, which are made of titanium, and the elastomer component, which is made of a silicon elastomer compound.
- In case of fire in the APU compartment, the design of the vibration isolator core member and housing does not allow separation of these parts if the elastomer component is damaged or destroyed. Although the function of the vibration isolators will then be lost, the APU will settle only slightly.
B. Maintenance
The entire suspension system is classified "ON CONDITION". Therefore, no regular maintenance tasks need to be carried out.
The entire suspension system is classified "ON CONDITION". Therefore, no regular maintenance tasks need to be carried out.
A. Suspension Rods
7 suspension rods of pre-adjusted and secured length support and position the APU. Their interfaces to the tailcone structure bracket clevises are designed as eye-bolts, thus allowing only axial loads to be transmitted.
At the lower end they interface with the vibration isolators. On 4 suspension rods, these interfaces are designed as lug (on vibration isolator) and clevis (on suspension rod), thus completely fixing the APU in position and transmitting axial and torsional loads. The remaining 3 interfaces are of identical design as the upper 7 interfaces.
7 suspension rods of pre-adjusted and secured length support and position the APU. Their interfaces to the tailcone structure bracket clevises are designed as eye-bolts, thus allowing only axial loads to be transmitted.
At the lower end they interface with the vibration isolators. On 4 suspension rods, these interfaces are designed as lug (on vibration isolator) and clevis (on suspension rod), thus completely fixing the APU in position and transmitting axial and torsional loads. The remaining 3 interfaces are of identical design as the upper 7 interfaces.
B. Vibration Isolators
The function of the vibration isolators 4035KM, 4045KM and 4055KM is to mechanically isolate the APU from the A/C-structure in order to minimize the two-way transmission of vibration and shocks. Their main components are:
The function of the vibration isolators 4035KM, 4045KM and 4055KM is to mechanically isolate the APU from the A/C-structure in order to minimize the two-way transmission of vibration and shocks. Their main components are:
- a housing with lugs and clevises for the attachment of the suspension rods,
- an elastomer component within the housing to act as a mechanical isolator and
- a core member to provide a conical interface with the APU attachment bracket.
C. APU Attachment Brackets
These brackets 4065KM, 4075KM and 4085KM are attached on the APU and provide a single point conical interface with the vibration isolator core member. Their design also assures the 6-degree nose-down APU installation position.
These brackets 4065KM, 4075KM and 4085KM are attached on the APU and provide a single point conical interface with the vibration isolator core member. Their design also assures the 6-degree nose-down APU installation position.
D. Electrical Bonding
On both forward mounts, electrical bonding between the APU body and the tailcone structure is achieved by a bonding lead between the APU attachment bracket and the lower end of the most forward suspension rod body. At the upper end of the rod body, a bonding lead connects the rod to a bonding bracket on the tailcone structure.
The other 5 suspension rods are connected identically to the tailcone structure.
On both forward mounts, electrical bonding between the APU body and the tailcone structure is achieved by a bonding lead between the APU attachment bracket and the lower end of the most forward suspension rod body. At the upper end of the rod body, a bonding lead connects the rod to a bonding bracket on the tailcone structure.
The other 5 suspension rods are connected identically to the tailcone structure.