Supercharging and Turbocharging

Question 1

Supercharger

Answer 1

A piston engine with an engine driven compressor
May be used to :
1. Boost the manifold pressure at sea level
2. Compensate for reduced density at altitude by maintaining the power available at sea level

Question 2

Measuring Power Output

Answer 2

In an engine with a CSU the pressure of the mixture in the manifold is a measure of the power output
Power can be monitored on the RPM and manifold pressure gauge

Question 3

Maintaining Power at Altitude

Answer 3

Pumps high pressure air into the inlet manifold using a compressor, allowing the engine to burn extra fuel and produce extra power
Allows engine to maintain power in the climb

Question 4

Rated Boost

Answer 4

The highest manifold pressure the engine can tolerate without the danger of detonation

Question 5

Ground Boosting

Answer 5

When manifold pressure can exceed 30 inches
Can tolerate a manifold pressure greater than normal sea level pressure without the risk of detonation and can boost the inlet manifold pressure above the normal sea level pressure
Engine develops more power at sea level and maintain better power output at altitude
MAP will progressively reduce in a climb, however it will reduce from a higher manifold pressure

Question 6

Altitude Boosting

Answer 6

To allow the engine to develop the power required at altitude the compressor is able to overboost the engine at sea level and damage it at sea level if full throttle is used
Open the throttle partially at sea level and continue to open it as you climb
At a point in the climb, the throttle will be fully open and max MAP will still be maintained, as you climb higher the MAP will then start to reduce

Question 7

Detonation Risks

Answer 7

As the supercharger compresses the mixture, the MAP increases and the temperature rises
If the manifold air pressure is too high (overboosted) the temperature limits may be exceeded and there is a risk of detonation
High manifold pressure and low RPM

Question 8

To Avoid Detonation

Answer 8

Use only approved power settings

Use correct leaning procedures

Question 9

The Compressor

Answer 9

Air enters at the centre of a rapidly rotating impeller
Inertia causes the air to be thrown outwards, accelerating in the process
It is slowed by passing through diffuser vanes and the kinetic energy is converted to pressure energy
The compressed air then enters the manifold

Question 10

PLANE = BHP

Answer 10

P = Power
L = Length of the stroke
A = Area of the piston
N = RPM
E = Number of cylinders

Question 11

Increasing the Power

Answer 11

Mixture
RPM
Manifold pressure

Question 12

Decreasing the Power

Answer 12

Manifold Pressure
RPM
Mixture

Question 13

Normally Aspirated Engines

Answer 13

Best manifold pressure = 29.92 inches of mercury (1013.25hpa) at sea level
As the aircraft climbs this will gradually decrease at approx 1hpa per 30ft

Question 14

Power Augmentation Process

Answer 14

Pushing more air into the engine

Question 15

Impellor

Answer 15

Works 6-12 times faster than the engine

Question 16

Rated Altitude

Answer 16

The maximum height at which manifold pressure can maintain 30 inches
Manifold pressure increases to rated altitude as the exhaust gases exit more easily as the density of the air decreases and can be higher than 30 inches

Question 17

Automatic Boost Controller

Answer 17

Controls the amount of air going into the cylinder
Ensures you don’t exceed 30 inches otherwise the cylinder may pop
Boost gauge = tells an increase in PSI according to 30 inches

Question 18

Types of Superchargers

Answer 18

Geared (internally driven)

Turbochargers (driven externally by exhaust gases)

Question 19

Geared Superchargers

Answer 19

The impeller is driven from the crankshaft via gears

A clutch arrangement enables them to operate at different speeds

Question 20

Speeds of Geared Superchargers

Answer 20

Single-speed
Two-speed
Variable speed

Question 21

Gear Ratios

Answer 21

Usually between 6:1 and 12:1 to give the required boost

It is important to make smooth RPM changes at avoid dramatic acceleration or deceleration of the impeller

Question 22

Single-Speed Superchargers

Answer 22

Have a high gear ratio (high impeller RPM) which provides optimum performance at high altitude but lower performance near sea level

Question 23

Two-Speed Superchargers

Answer 23

Have two optimum altitude ranges

Means you can change gears to gain a greater manifold pressure at higher altitude (a greater BHP for longer)

Question 24

Variable Speed Superchargers

Answer 24

Maintain an impeller speed close to optimum throughout the altitude range of the aircraft
Are more complex in design

Question 25

Turbocharger

Answer 25

Driven by the exhaust gases by placing a turbine in the exhaust system, which creates a better way to control the speed of the impeller
Exhaust gases drive the turbine and then exit to the exhaust pipe, the turbine controls how fast the compressor turns

Question 26

Waste Gate

Answer 26

Varies the amount of exhaust gas that drives the turbine

Either fixed or variable

Question 27

Open Waste Gate

Answer 27

All the exhaust gas goes overboard and the turbine ‘free-wheels’ with the engine working as if normally aspirated

Question 28

Closed Waste Gate

Answer 28

As the gate is closed, more exhaust gas is directed over the turbine, increasing the compressor speed and boosting the manifold pressure

Question 29

Advantage of Turbochargers

Answer 29

The compressor does nothing until the throttle butterfly is open
As the throttle is opened further, the waste gate closes and the turbine delivers power to the compressor

Question 30

Fixed Waste Gate

Answer 30

A fixed proportion of the exhaust gas goes to the turbine all the time
Overboosting is possible at low altitude
At no stage is all the gas available to drive the turbine so the boost is limited

Question 31

Variable Waste Gate

Answer 31

Movement is controlled by:

1. A pilot operated lever
2. Throttle operated
3. Automatic operation

Question 32

A Pilot Operated Lever Waste Gate

Answer 32

Allows you to adjust the wast gate manually

During the climb the pilot can gradually close the waste gate and maintain MAP

Question 33

Throttle Operated Waste Gate

Answer 33

The first portion of throttle movement opens the throttle butterfly
Once the throttle is fully open, any further movement of the throttle closes the waste gate and powers the turbine

Question 34

Automatic Operation Waste Gate

Answer 34

Controlled automatically to maintain MAP

Question 35

Waste Gate Control

Answer 35

Fully closed at critical height
Spring opens the waste gate
Oil pressure closes the waste gate
At higher altitude settings, the oil pressure increases, which closes the gate, as the oil aneroid capsule increases pushing the needle down stopping oil flow and creating a build up

Question 36

Density Controller

Answer 36

Takes into account pressure and temperature

Question 37

Advantages of Increased Manifold Pressure

Answer 37

Can carry more weight

Require less runway

Question 38

Full Throttle Height

Answer 38

The height at which a certain power is available with only full throttle

Question 39

Full Throttle Height In a Supercharged Engine

Answer 39

The altitude at which the rated boost is available at a certain RPM (any lower MAP setting will also have a higher full throttle height)

Question 40

Handling Techniques

Answer 40

Do not exceed rated boost - only use recommended MAP/RPM settings
Avoid sudden throttle movements
Avoid sudden shutdowns