General ATPL technical / 737-800 737 MAX

Question 1

How does a jet engine work?

Answer 1

Air is forced into the intake where it is compressed, this causes a temperature rise. Fuel is added and combustion takes place, increasing the volume. The expanding gasses exit to the rear of the engine through the exhaust nozzle creating a propulsive force.

Question 2

Why does a wing stall?

Answer 2

Airflow over the upper wing surface separates when the critical angle of attack is reached or exceeded.

Question 3

Does the N1 compressor produce thrust?

Answer 3

On a high bypass engine it does. Some of the intake air (70% on modern high bypass) is accelerated by the N1 compressor and bypasses the core.

Question 4

What type of engines on 737-800?

Answer 4

CFM56-7

Question 5

What is the approximate bypass ratio of the CFM56-7?

Answer 5

5:1 (varies slightly with engine variant)

Question 6

What engines does the B737 MAX have?

Answer 6

CFM LEAP-1B

Question 7

What is the compression ratio of the CFM LEAP-1B

Answer 7

9:1

Question 8

What is N1, N2, EGT, EPR?

Answer 8

N1 - Low pressure compressor spool or fan
N2 - High pressure compressor
EGT - exhaust gas temp (turbine temp)
EPR - Engine pressure ratio of inlet to jet pipe

Question 9

Why do aircraft have leading edge devices?

Answer 9

To increase wing’s chord and/or camber, which increases the coefficient of lift and reduces stall speed.

Question 10

What are fusible plugs? Where are they located? How do they work? Why do we have them?

Answer 10

They are in the aircraft wheels. If the tyres overheat the fusible plug will blow - deflating the tyre. They work by using a metal plug that has a type of metal that will melt at a predetermined temperature.
They offer protection from tyre blowout.

Question 11

Briefly explain what coffin corner is.

Answer 11

Aircraft has climbed to an altitude where speed differential between the onset of low speed stall buffet and the onset of high speed Mach buffet approaches zero.
At worst case any change in speed or banking aircraft will cause a stall.

Question 12

Why do we measure speed as a Mach number?

Answer 12

Mach number is speed relative to speed of sound.
If we get too close to the speed of sound we can get supersonic flow over the wing which will cause mach buffet which can cause structural failure of the aircraft.