LESSON # 5

Question 1

Control of the fuel flow to the burners is by two main methods:

Answer 1

a. Manual control by the pilot.
b. Automatic adjustment of fuel flow to correct for basic engine requirements.

Question 2

Automatic adjustment of fuel flow to correct for basic engine
requirements:

Answer 2

(i) Changes in intake pressure.
(ii) Excessive fuel to air ratio during engine acceleration.
(iii) Additional controlling devices as determined by specific engine requirements.

Question 3

The flow of a fluid through an orifice (jet) depends on the area of the Orifice and the square root of the pressure drop across it.

Answer 3

Principle of Fuel Metering

Question 4

= Orifice Area x √Pressure Drop

Answer 4

Fuel Flow

Question 5

Fuel Flow =

Answer 5

Orifice Area x √Pressure Drop

Question 6

it is possible to vary fuel flow by changing orifice area or the pressure drop across the orifice.

Answer 6

True

Question 7

In a fuel system the (?) is variable and is in fact the throttle valve.

Answer 7

orifice

Question 8

In the flow control system the fuel flow required to give a selected RPM is selected by throttle area under the control of the pilot (?).

Answer 8

manual control

Question 9

Compensation for air density variation is superimposed on this selection
by the altitude sensing control unit (?) varying the pressure difference across the throttle valve.

Answer 9

pressure drop control unit

Question 10

The controlling principle of a flow control system is that a constant throttle
pressure drop is [?] irrespective of throttle area (position) for a given
height and speed.

Answer 10

maintained

Question 11

If however, height and speed change, then the [?] will
vary the pump output and fuel flow (thus throttle pressure drop)
by changing the pump output at constant throttle setting.

Answer 11

altitude sensing unit

Question 12

two types of variable orifice

Answer 12

1. Half-ball valve
2. Kinetic valve

Question 13

In [?], the method of control is to use servo fuel as a hydraulic fluid to vary fuel flow (eg. by varying pump swashplate angle).

Answer 13

hydro-mechanically operated flow control units (FCUs)

Question 14

The (?) of the servo fuel is varied by controlling the rate of flow out of an orifice at the end of the servo line;

Answer 14

pressure

Question 15

the (1) the outflow, the (?) will be servo pressure and vice versa.

Answer 15

1. higher
2. lower

Question 16

The function of the (?) is to provide surge-free acceleration during rapid throttle openings.

Answer 16

Acceleration Control Unit (ACU)

Question 17

two main types of hydromechanical ACU in service

Answer 17

1. FLOW TYPE ACU
2. DASHPOT TYPE ACU

Question 18

All the fuel from the pump passes through the unit, which compares
fuel flow with compressor outletpressure (P3), which is proportional to [?].

Answer 18

engine speed

Question 19

The fuel from the pump passes through an orifice containing a contoured
plunger; the pressure drop across the orifice is also sensed across a diaphragm.

Answer 19

FLOW TYPE ACU

Question 20

When the throttle is opened, the pump moves towards maximum stroke and fuel flow increases. The increased flow through the ACU orifice increases the pressure drop across it and the diaphragm moves to the right, raising the half ball valve and restricting pump stroke.

Answer 20

FLOW TYPE ACU

Question 21

The engine now speeds up in response to the limited over fuelling and P3
rises, compressing the capsule. The plunger servo pressure drops and the
plunger falls until arrested by the increased spring force. The orifice size
increases, pressure drop reduces and the diaphragm moves to the left, closing the half-ball valve and increasing fuel flow. Fuel flow willincrease in direct proportion to the increase in P3.

Answer 21

FLOW TYPE ACU

Question 22

In order to keep the acceleration line close to the surge line, it is necessary to control on “Split P3 air” (a mix of P3/P1) initially and then on full P3 at higher engine speeds. This is achieved by the[?].

Answer 22

air switch
(or P1/P3 switch)

Question 23

P3

Answer 23

compressor outlet pressure

Question 24

At (?), P3 passes through a plate valve to P1 and the control capsule is operated by reduced, or split P3 until P3 becomes large enough to close the plate valve and control is then on full P3.

Answer 24

low speeds

Question 25

The (?) uses two co-axially mounted throttle valves.

Answer 25

DASHPOT TYPE ACU

Question 26

The inner one is moved by the pilot and the outer (main) throttle valve will move but is controlled by a [?] which slows the valve movement down to limit the acceleration fuel flow.

Answer 26

dashpot

Question 27

When closing the throttle the pilot pushes (?) sleeves in together.

Answer 27

both