54 Nacelles/Pylons

TTP	B1-L3	ATA 54
Beech 90 Series	B2-L1	Nacelles/ pylons

The cowling encloses each powerplant and accessories  from  the  firewall forward. The

 cowling consists of four assemblies: the forward upper and lower cowlings and the aft upper 

and lower cowlings. Refer to the Hoisting procedures in the AMM and CMM.

Forward Upper Cowling

The upper forward engine nacelle panel is constructed using three stiffeners, an aft doubler, and nacelle skin to provide for strength and shape the nacelle around the engine. This forms a streamlined fairing across the upper part of the engine to improve aircraft performance by reducing drag. The upper forward nacelle is attached using a set of alignment studs and a hook and cam assembly that secures the upper forward cowling in place during operation.

Forward Lower Cowling

The lower part of the forward nacelle is formed using an air inlet lip, lip angle, and three frames with the skin attached to form the lower portion of the nacelle and inlet. The air inlet duct and oil cooler duct assemblies are part of the lower forward cowling assembly. The cowling assembly also streamlines the airflow around the lower part of the engine while providing support for the engine and oil cooler inlet ducts.

Aft Upper Cowling

The upper aft nacelle cowling is designed for ease of access to the accessory section and is hinged and can be removed if necessary to perform maintenance on the engine. The aft cowling is constructed from frames, seals, and skin to form a aerodynamic fairing to improve performance and reduce drag. An access door is provided to allow for access to service engine oil.

Aft Lower Cowling

The lower aft cowling utilizes frames, seals, and longerons to provide for the attachment of the skin to create the proper airflow under the engine. This cowling also provides for the support of the generator airflow inlet and ducting. It also supports the engine inertial anti-ice vanes, actuators, and forward/aft vane limit switches.

NACELLE

This is the structure which connects to the aft upper and lower cowling to complete the fairing across the upper and lower portions of the wing.

The nacelle forms the structure in which the nacelle fuel tank is mounted as well as the landing gear wheel well and supporting structure. The nacelle utilizes formers, longerons, and framing that provide the structure necessary for skin and fairing attachment. The nacelle skin incorporates access  panels  for  use  during  maintenance  of the various components. The nacelle  also provides the attachment structure for the firewall assembly. The firewall assembly is constructed from stiffeners, angles, and a firewall web to create a firewall between the engine and wing leading edge and nacelle tank. It also provides for engine mount fitting placement.

Mounts

 

Engine Mount Truss

The  engine  is  supported  by  a  welded  tubular truss of 4130 chrome molybdenum steel, which is bolted to the nacelle firewall at four attaching points. Various brackets are welded to the engine mount truss to attach the cowling and components adjacent to the engine.

 

Engine Mount Vibration Isolators

Four engine mount vibration isolators secure the engine to the engine mount truss and dampen engine vibration to the airframe structure.  Each  engine  mount  vibration  isolator is attached  to the engine by four bolts and is anchored to the engine mount truss with one bolt. Individual engine mount vibration isolators may be replaced without removing the engine from the engine mount truss, provided that the weight of the engine is adequately supported.

CAUTION: All engine mount vibration isolators on an engine must be of the same manufacture and type.

For overhaul of the engine mount vibration isolators, refer to the King Air Series Component Maintenance Manual.

 

Fireseals

The basic engine incorporates two fireseals, one forward and one aft of the compressor inlet. A heatshield, constructed of two semicircular sections and bolted to the forward engine fireshield, and a U-shaped baffle bolted to the engine mount truss seal the area between the cowling and the engine fireshields. Both the baffle and the heat-shield provide a mounting location and support for lines, controls, ducts, and electrical wiring.

 

Electrical Harness

The powerplant electrical harness distributes power to or from the starter-generator, fire detectors, and all engine electrical  accessories. The harness is connected to the nacelle firewall by three connectors: two on the left side and one on the right side. The harness is routed from the firewall forward through the baffle assembly and forward heatshield to the propeller electrical system on or adjacent to the RGB.

PTP  Beech 90 Series	B1	LOC
	B2