AS311 Test 2 Practice

What is the Definition of Bypass Ratio

Ratio of lbs of air per second through bypass compared with lbs of air that goes through core.

Acceleration due to gravity

32.2 ft/sec

what would you have to add to the Fn Formula to get the net thrust for a turbofan or a turboprop

F=Mx DV and F= A x DP

What can be entered into the Fn formula to make it gross thrust?

V1 = 0

Why is there net thrust formula for a turboshaft engine?

They do not make thrust

What are the four factors that pilots must pay attention to that directly affect thrust?

Engine RPM, aircraft airspeed, ambient temperature and pressure altitude

Of the four factors above which two can be directly controlled by the pilot

aircraft airspeed and engine rpm

If all other factors remain the same but the airplane goes faster, what would happen to engine thrust if v1 losses were the only factor that changed.

Engine thrust decreases

In a diverging intake duct, as the airplane gets close to Mach1 what happens to engine thrust due only to RAM effects.

Engine thrust increases

Taking into account all airspeed effects, what is the minimum mach must you be flying in order to get a significant amount of extra thrust due to the forward speed of the aircraft?

0.6

What happens to thrust due to all airspeed effects above Mach 1.0

Exponential increase

Why do turboprop airplanes and turbine helicopters not get much increase in engine power due to Ram effect?

They operate at lower subsonic speed.

Thrust vs engine rpm what happens to thrust as the engine rpm goes from 90% to 100%

Large change in thrust 20% increase

There is a direct linear relationship between engine thrust @e engine RPM

F

Assuming all other factors remain constant why does engine thrust increase in colder air temperatures

Higher molecules per cubic inch pulled into engine.

Assuming all other factors remain constant ( including if temperature remained constant) why does engine thrust decrease in higher pressure altitudes

Less molecules per cubic inch, net thrust decreases

In the above graph, why does the slope get steeper after 36000 feet

Temperature does not change after 36000 feet. More thrust lost at faster rate

Why do transport category jet airplanes typically not fly above 40000 feet

Loss thrust and more fuel used

Jet airplanes are typically overpowered at sea level temperatures and pressures. What would it take for a jet airplane to have the capability to easily climb and cruise at 51000

Overpowered like a MF

How high is the troporpause on a standard day

56000 ft

In degrees C, what is the standard atmospheric temperature at 66k 42k 36k and sealevel

-56 -56 -56 15

On a standard atmospheric day, the isotherm goes from

36000 feet to 66000 feet

What is the speed of sound int he atmosphere at sea level standard temperature

KEAS 662 KTAS 662

at 42000 Mach 1.0 574 kts, what is KEAS at this speed

287

What is the only factor that affects mach in the earth’s atmosphere?

Temperature

Drag is directly related to what airspeed

equivalent airspeed

What is the FAA speed limit below 10000 feet?

250kts IAS

What happens to the boiling temperature of water as it is exposed to lower pressures (higher pressure alts)

boiling temp decreases

At what alt on a standard day is the armstrong line

64000 ft

What would happen to the liquid water in a human who was flying in an aircraft if they had no pressure suit were flying higher than the armstrong line and the airplane depressurized

It would expand like crazy

Why does it save fuel to fly turbofan powered airplanes at high alts such as 36000 feet

Drag directly related to EAS

At high alt low EAS= high TAS

low EAS = low drag for high TAS

What is the definition of Thermal efficiency?

TE= THR/FF

What are the two factors that improve thermal efficiency

Higher Combustion temp

Higher Combustion pressure

What is the relationship between Thermal Efficiency and TSFC

Inversely Proportional TE = THR/FF

Define Propulsive Efficiency

Ability to convert thrust to airspeed

What is the formula for Propulsive Efficiency?

TAS/V2

In General, what engine has highest propulsive efficiency

Turboprop

What is the major characteristic of the Brayton cycle?

Constant pressure (across the combustion chamber) cycle

What is Bernoulli’s Theorem?

Closed energy system - no addition / subtracting

total energy is the same at any point

In what two sections of a jet engine does Bernoulli’s Theorem apply?

intake and exhaust

What happens to the speed of sound in KTAS when the air temperature rises?

Increases

If a jet airplane is at cruise alt and curist airspeed and maintaining a constant speed and alt how can the forward speed of the airplane be higher mach number than the veolcity of gases coming out of the engine core?

Temp and exhaust is high

Mach 1 at very high true airspeed

Exhaust is low mach but very high true airspeed

What are the three purposes of a turbine engine intake duct

Controls the angle pressure velocity of air going into compressor

Who designs a turbine engine intake duct?

airframe Manufacturer

What are the three basic kinds of inlet ducts?

low speed

high subsonic

super sonic

What shape is a low subsonic inlet duct

Bellmouth inlet

How much increase in pressure can be attributed to the use of a bell mouth inlet?

Does not increase pressure of air

What is the purpose of a bell mouth inlet

Greatest amount of airflow smooth airflow

High subsonic inlet duts are designed for airplanes flying at what speeds

mach 0.6 - 0.9

What shape are inlet ducts that are designed for high subsonic cruise?

Divergent duct

What happens to the velocity and pressure as air flows through a divergent intake duct?

Velocity down Pressure Up

What is the compression ratio of a well designed inlet duct that is used on a turbine engine that cruises at high subsonic speed

1.5:1

Why do turbofans and fast turboprops use slightly divergent inlet ducts

Adds to total pressure entering compressor

Why does the air entering the compressor section of a supersonic engine need to be subsonic and the air entering the intake is going supersonic

reduce velocity increase Pressure

What compression ratio can a supersonic intake duct have when it is going at mach 3.0

40:1

Why are blow in doors used on a few turbine engines?

Engine needs alot of air without making intake bigger.

Why are particle separators used during some helicopter operations

To keep engine from sucking in dust.

What are the three purposes of the compressor section

increase pressure

increase molecules per cubic inch

provide bleed air

What capability of a turbine engine is improved because of greater molecules per cubic inch air going into combustion section

tsfc down

What capability of a turbine engine is improved because of greater molecules per cubic inch air going into the combustion section?

Thrust Up

What is the negative byproduct when air pressure is increased

Temperatures Up

What two components make up a single stage of a centrifugal compressor?

Diffuser Impeller

What happens to the velocity and pressure as the air goes through a centrifugal compressor?

Impeller V Up P up Diffuser V Down P Up