76 Engine Controls

-

 

TTP

B1-L3

ATA 76

Beech 90 Series

B2-L1

Engine Controls

ENGINE CONTROLS - DESCRIPTION AND OPERATION

1. General 

The engines incorporate a propeller reversing system comprising a single-acting, hydraulically operated propeller controlled by a propeller governor, and with overspeed governor back-up. The propeller governor combines the functions of a normal propeller governor (CSU), a reversing (Beta) valve and a power turbine governor (Nf) into a single unit. Note that terminology used in this section is of a general nature and may thus differ slightly from that used in specific airframe manufacturer’s manuals. Likewise, the percentages stated are generalized, and specific airframe installations may require different settings.

2. Description  

A. Propeller 

The engine is normally equipped with a three-bladed metal propeller (refer to Propeller Manufacturer’s Handbook), which is dowelled and bolted to the front face of the engine propeller shaft flange. The propeller assembly consists of a hollow steel spider hub which supports the propeller blades and also houses an internal oil pilot tube and the feather return springs. Movement of the propeller blades is controlled by a hydraulic piston mounted at the front of the propeller spider hub. The servo piston is connected by a link to the trailing edge of each blade root. Centrifugal counterweights on each blade and springs in the servo piston tend to drive the servo piston into the feather, or high pitch position. This tendency to movement is opposed by propeller governor oil pressure. The governor oil pressure is applied to the servo piston via passages in the governor body, an oil transfer tube to the oil transfer sleeve on the propeller shaft, then, via the hollow centerbore of the propeller shaft to the propeller hub. An increase in governor oil pressure moves the blades toward the low (fine) pitch position (increased rpm). Conversely, a decrease in governor oil pressure allows the blades to move toward high (coarse) pitch position (decreased rpm) under the influence of the feathering springs and blade centrifugal counterweights. 

The servo piston is also connected by three spring-loaded sliding rods to a feedback ring mounted at the rear of the propeller. Movement of the feedback ring is transmitted by a carbon block and propeller reversing lever to the Beta valve on the propeller governor. This movement is utilized to control propeller blade angle from the normal forward fine pitch stop through to the full reverse pitch position.

D. Starting Control Lever (Engines with Starting Control) (PT6A-27 and PT6A-28) 

The starting control lever in the cockpit is connected through airframe linkages to a lever on the starting control unit; this is connected to the FCU. 

E. Fuel Condition Lever (PT6A-21) 

The fuel condition lever in the cockpit is connected through airframe linkages to a lever on the fuel control unit; the lever controls the position of the FCU integral fuel cut-off valve. 

F. Power Control (Engine Power) Lever 

The power control lever in the cockpit is connected through airframe linkage to the cam assembly which is mounted in front of the FCU at the rear of the engine. The power control lever controls engine power through the full range; from maximum takeoff power through to full reverse. It also selects the propeller pitch (Beta control) from reverse selection up to the constant speed rpm as selected by the cockpit propeller control (propeller speed) lever. 

G. Reversing Linkage  

The cam assembly, mounted at the 2 o’clock position on Flange G of the accessory gearbox, provides scheduled control movements to the FCU and starting control, the Nf governor section of the propeller governor and the propeller system. The cam assembly consists of a cam follower lever, which is connected directly to the power control lever linkage by a grooved pin, and three cam-type levers. The FCU reversing actuating lever is free mounted on the grooved pin while the propeller control cam and FCU actuating levers are free mounted on a second flat head pin. The three levers and pins are mounted on the control lever mounting bracket which is bolted to flange G. The FCU actuating lever is spring-loaded toward idle and is connected through an adjustable interconnecting rod to the FCU control arm. In operation, movement of the power control lever moves the cam follower lever through the lever linkage. Movement of the cam follower lever causes the associated lever pin to contact the rear face of the FCU actuating lever and also slide in the slot of the propeller control cam. During normal propeller operation, from IDLE to TAKEOFF, the cam follower lever pin moves in the circumferential section of the cam slot, but imparts no motion to the propeller control cam.



PTP 

Beech 90 Series

B1

LOC

FOT


TS

B2


Comments

Post a Comment

Popular posts from this blog

29A Hydraulic Power-Monitoring and Indication

-
  TTP B1-L3 ATA 29A Beech 90 Series B2-L3 Hydraulic Power – Monitoring and indicating Hydraulic Fluid Low-Level Sensor A h ydraulic fluid l o w-l e v el sensor is on the motor end of the p o w e r pack. A HYD FLUID LO annu n - ciator illuminates w hen a l o w fluid e xists . Engine b leed ai r , r e gulated to 18 to 20 psi, is plumbed into the fill rese r v oir to pr e v ent c a vit a tion of the pump.          A y ell o w HYD FLUID LO annunciator on the glare shield illuminates w hen the h ydraulic fluid in the seconda r y rese r v oir becomes l o w . An   optical   sensing   unit   on   the   motor end of the p o w e r pack contains the light source, senso r ,   and   s witching   circuit r y   to   trigger   the fluid   l o w   annunciato r .   The ...
Read more

56 Windows

-
Image
TTP B1-L3 ATA 56 Beech 90 Series B2-L1 Windows The King Air for w ard windshields are fo r med from t w o-p l y glass in an int e g ral aluminum frame. The t w o glass plies are bonded t o gether with a center po l yvi n yl sheet that co n tains the fine wire heating g rids. The windshields are electrostatical l y  coated and cu r rent-production windshields are sur f ace sealed. All the side wind o ws are const r ucted from ac r ylic plastic. WINDSHIELDS   The electrical l y heated laminated glass windshield is subject to the g radual process of delamination due to the effect of chemical action and differentials of temperature and pressure incu r red during pressurized flights at v a r ying altitudes and under v a r ying w eather conditions. This delamination is not detrimental to the st r uctural int e g rity of the windshiel d , b ut ...
Read more