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Badly Phrased, Contradictory, Doubtful or Wrong Questions

 
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K.Haroon
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Joined: 11 Dec 2005
Posts: 1308

PostPosted: Fri Feb 03, 2012 4:31 am    Post subject: Badly Phrased, Contradictory, Doubtful or Wrong Questions Reply with quote

Arrow In a stressed skin aircraft, bending loads acting on the wings are taken by:

a) ribs and stringers
b) stringers and spars
c) spars and skin
d) spars and stringers

(b) marked correct whereas (b) and (d) are exactly the same.


Arrow Cabin air for aeroplanes is usually taken from:

a) the low pressure compressor
b) the second fan stage
c) the high pressure compressor
d) the high pressure compressor and from the low pressure compressor if necessary

(c) marked correct. Cabin air for modern airplanes is usually taken from the low pressure compressor and from the high pressure compressor if necessary (as also mentioned in other answers).


Arrow An aircraft in straight and level flight at a constant Cabin Altitude when the Crew notice the Cabin rate of climb indicator reads 200 ft/min. What will be the sequence of events?

a) Crew should begin a climb to regain Cabin Altitude
b) Cabin Altitude will increase to outside atmospheric pressure
c) Cabin Altitude will descend to, and continue beyond normal max-diff, at which point the safety valves will open
d) Cabin Altitude will increase to, and continue beyond normal max-diff, at which point thesafety-valves will open

(c) is marked correct. Only possible if cabin rate of climb shows -200 feet/min. The question does not show the minus sign.


Arrow In an air cycle machine:

a) the turbine increases the pressure of the air supply to the cabin
b) the turbine drives the compressor which provides pressurisation
c) the turbine drives the compressor of the machine which causes a higher temperature, and so increases the second heat exchanger efficiency
d) the temperature drop across the turbine is the main contributor to the cooling effect of the air cycle machine

(c) is marked correct, however even (d) is not incorrect.


Arrow The primary LP fuel pump is driven by:

a) Hydraulic pressure
b) Air pressure
c) The engine
d) The electrical system

(c) is marked correct, whereas (d) seems to be correct as that is the case on most transport aircraft. See the questions below to verify:


=> Low pressure fuel pumps are:

a) engine driven
b) electrically driven centrifugal pumps
c) driven by the accessory gear box
d) swash plate pumps with self governors

(b) Marked Correct.


=> On most transport aircraft, the low pressure pumps of the fuel system are:

a) electro-mechanical wobble pumps, with self-regulated pressure
b) mechanically driven by the engine's accessory gear box
c) removable only after the associated tank has been emptied
d) centrifugal pumps, driven by an electric motor

(d) Marked Correct

However some engines like Rolls Royce RTM322 run their LP and HP fuel pumps from the accessory gearbox (i.e. not electrically).


Arrow If a fuel tank having a capacitive contents gauging system is empty of fuel but has a quantity of water in it:

a) The gauge will show the mass of fuel equal to the same volume as the water
b) The gauge will show the volume of the water
c) The gauge will show the mass of the water
d) The gauge will show full

(c) marked correct but (d) is a possibility as well.

Since water has a co-efficient of capacitance much more than air and fuel, the gauging system will interpret it as high calorific value and show full scale deflection.

It will take in to account the quantity of water in the tank and compare the water/air capacitance relationship in the same way that it measures the fuel/air capacitance. I think as far as correct indications are concerned the gauge calibration will be be for fuel with a permittivity level of 2.1. The change in permittivity level for water at 80 will cause the gauge to over-read by as much as 8000%, so in my view it will read full.

Source: (http://www.atpforum.eu/showthread.php?p=51711#post51711)


Arrow A feeder fault on a direct current circuit results from a flux unbalance between the:

a) generator and the series winding turn
b) voltage coil and the series winding
c) voltage coil and the series winding turn
d) shunt exciter and the series winding turn

(c) marked correct whereas (b) is also the same. Not much difference.


Arrow The detection of a feeder fault on a direct current circuit results in:

1) automatic disconnection of the generator from the aircraft AC busbar
2) opening of generator field current relay
3) opening of the main relay of the generator breaker
4) opening of balancing circuit connecting two generators
5) lighting of an indicator lamp

The combination of correct statements marked is 1,2,3,4,5 whereas 1 seems to be incorrect because:

If it is a DC gen then any AC busbar would be powered by an inverter from the DC busbar, so item 1 would be wrong.


Arrow In an AC power generation system, the constant speed drive (CSD):

1) can be disconnected from the drive shaft
2) can be disconnected from the generator
3) is a hydro-mechanical system
4) is an electronic system
5) cannot be disconnected during the flight
6) can be disconnected during the flight

The combination regrouping all the correct statements is:

1, 3, 5 as marked in the database.

whereas it should have been 1, 3, 6 as mentioned in another question which is:

In a generator, the Constant Speed Drive (CSD):

1) May be disconnected from the engine shaft
2) May be disconnected from the generator
3) Is a hydro-mechanical system
4) Is an electronic system
5) May not be disconnected in flight
6) May be disconnected in flight


Arrow Q.1. It may be determined that an aircraft is not properly bonded if:

(a) There is heavy corrosion on the fuselage skin mountings
(b) Static noises can be heard on the radio <-- Marked Correct

Q.2. Incorrect bonding of the aircraft structure may cause:

a) Corrosion at skin joints
b) Static on the radio <-- Marked Correct


Q.3. How can you tell when bonding is incorrect?

a) Corrosion at skin joints <-- Marked Correct
b) Static on the radio

If the question satrts from "How can you tell?" then its the skin joints otherwise its all about the radios.


Arrow The stators of a 2-phase alternator are separated by:

60
90
120 <-- Marked Correct
180

It should be about 3-phase not 2.


Arrow A normally aspirated piston engined aeroplane climbs at constant manifold pressure and RPM. The power output:

a) Decreases due to lower back pressure
b) Increases due to lower back pressure
c) Decreases because of the lean mixture being used at higher altitudes
d) Decreases due to lower frictional losses

(c) marked correct whereas (b) seems to be correct.


Arrow In a four stroke engine, when the piston is at BDC at the end of the power stroke the position of the valves is:

a) Closed/Closed
b) Open/Open
c) Open/Closed
d) Closed/Open

The question does not mention the name of valves. However option (d) is marked correct, which suggests that vlaves under discussion are intake and exhaust, as also mentioned in another question.


Arrow Which of the following is the correct description of the position of the Fuel Strainer in a carburettor

a) Between the needle jet and the metering jet
b) Upstream of the needle valve
c) Between the metering jet and the discharge nozzle
d) Downstream of the discharge nozzle

(a) marked correct whereas (b) is correct, as also mentioned in another question, which is:

A fuel strainer when fitted to a carburettor will be positioned:

a) between the metering jet and the discharge nozzle
b) between the needle valve and the metering jet
c) upstream of the needle valve
d) downstream of the discharge nozzle

(c) marked correct


Arrow PRESSURE RECOVERY within the air intake means that:

a) As far as is possible, total head pressure is achieved at the compressor face
b) Total head pressure is achieved at the air intake
c) Pressure recovery is only applied to bleed valve-operating characteristics
d) Intake pressures are reduced

a) marked correct

Not sure about what is being asked. Whether its about the pressure recover which takes place at M0.4 or something else?


Arrow Q.1. Some emergency exits must be equipped with devices so as to help the occupants to get out and reach the ground if their threshold is at a height above the ground greater than:

a) 6 ft, aeroplane on the ground, one main gear or nose gear collapse

b) 6 ft, aeroplane on the ground, landing gear extended

(b) marked correct whereas both options are correct.

Regulations are stated in JAR OPs Subpart K 1-805. Stating that an aircraft must be fitted with devices to assist occupants exit the aircraft if the sill height (doorway) is greater than 1.83m (6ft) above the ground with the aircraft on its landing gear OR greater than 1.83m (6f) with one or more of the landing gear collapsed.

Q.2. An emergency exit assisted escape device must be fitted if the door sill height is above:

a) 6 ft with the aircraft on the landing gear with the nose wheel extended.

b) 6 ft with the aircraft on the landing gear with the nose wheel collapsed. <-- Marked Correct


Arrow The bimetal strip detectors of an engine fire detection system:

1) Are arranged in series
2) Are arranged in parallel
3) Open during a fire
4) Close during a fire

1 and 3 marked correct whereas 2 and 4 seems to be correct.


Arrow The fire extinguisher system for an engine is activated:

a) Immediately that a fire is sensed and is automatic
b) Is automatic but is delayed to allow pilot to take out appropriate actions
c) By the pilot as required
d) Once the engine has been shut down

(d) marked correct whereas (c) seems to be correct as mentioned in another question as under:

The engine fire extinguisher system is activated:

a) After the engine has been shut down
b) Automatically when a fire warning is sensed
c) By the pilot when required
d) Automatically after a time delay to allow the engine to stop

(c) Marked Correct.


Arrow A diluter demand oxygen regulator selected to 100%:

a) Delivers oxygen flow when inhaling.

b) Is only recommended for use with smoke in the cockpit.

a) Marked Correct whereas (b) also seems to be correct. In another version of this question (in some european database) the last part of the question "regulator selected to 100%" has been omitted which probably is a correction to this question. In that case (a) is the correct option.


Arrow What is therapeutic oxygen used for in a pressurised aircraft?

a) To protect flight and cabin crew against smoke and fumes
b) To protect certain passengers and carried only for those passengers
c) To provide medical assistance to passengers and crew
d) To protect passengers and crew against the effects of accidental depressurisation

(c) Marked Correct

We know about SUPPLEMENTAL OXYGEN...for use following depressurization...

There is also FIRST AID OXYGEN...which is there for passengers who, FOR PHYSIOLOGICAL REASONS, MAY REQUIRE AN UNDILUTED SUPPLY OF OXYGEN FOLLOWING DEPRESSURIZATION, FOR AT LEAST 2% OF PASSENGERS, FOR THE REMAINDER OF THE FLIGHT BETWEEN 8000FT AND 15000FT CABIN ALT.

JAR OPS offers no definition of THEAPEUTIC OXYGEN....I think the exam question means FIRST AID OXYGEN...

Source: (http://www.atpforum.eu/showthread.php?t=1232)


Arrow An aircraft, 340 nm from land and its one engine inoperative speed is 150 kts:

a) does not need life jackets or life rafts
b) must carry life jackets for each passenger only
c) must carry life rafts but life jackets are not necessary
d) must carry life jackets for each passenger and life rafts sufficient to carry all persons on board

(d) marked correct, but normal cruise speed is not given in the question which is required to calculate the need of life rafts. According to the rule for multi-engine a/c; life rafts are required when the distance is 120 minutes at cruising speed or 400 nautical miles, whichever is the less.

Another question gives complete details, as mentioned below:

A turbo prop aeroplane is performing an overwater flight, which takes it further than 340 NM away from an aerodrome where an emergency landing could be performed. Normal cruising speed is 180 kt. One engine out airspeed is 155 kt.

a) Life jackets must be available for all occupants <-- Marked Correct
b) Life jackets and rafts must be available for all occupants

a) Correct according to JAR-OPS 1.825
b) wrong because according to JAR-OPS 1.830, life-rafts are not required. [life rafts required after 180 x 2 = 360nm but the a/c is at 340 nm]


Arrow A smoke hood is a device covering:

a) The whole head and with an oxygen flow only on demand
b) The whole head and with a continuous oxygen flow
c) Only the nose and the mouth and with an oxygen/air mix
d) Only the nose and the mouth and with a continuous oxygen flow

(d) marked correct whereas (b) is correct as mentioned in another question:

Smoke hoods protect:

a) Full face and provide a continuous flow of oxygen <-- Marked Correct
b) Mouth and nose and provide a continuous flow of oxygen
c) Full face and provide oxygen on demand
d) Mouth and nose and provide oxygen on demand


Arrow What are the basic types/type of fuel injection system?

a) Direct fuel injection and indirect fuel injection
b) Direct fuel injection, indirect fuel injection and injection carburettor

(b) Marked correct whereas (a) seems to be correct. However not sure about this one.


Arrow Which of the following combinations correctly shows the systems controlled on a turbo prop aircraft? Prop lever/RPM lever:

a) TGT/RPM
b) RPM/TGT
c) Torque/TGT
d) RPM/blade angle

(c) Marked correct. However not sure about the TGT part.


Last edited by K.Haroon on Sun Sep 30, 2012 5:54 pm; edited 1 time in total
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jthomson



Joined: 30 Sep 2012
Posts: 2

PostPosted: Sun Sep 30, 2012 3:21 pm    Post subject: Divergent/convergent ducts and supersonic flow Reply with quote

Hi Harood, excellent site thank you very much for the time and effort you have put into it.

In the question above "A convergent-divergent duct located in a gas turbine exhaust unit" the answer stated on the JAA paper is correct.

You are right to say that flow accelerates in a convergent duct, and slows in a divergent duct. However, this only applies to subsonic flow. Above Mach 1, it actually works the other way around.

This is why the exhaust ducts to rockets and some very fast jets have a convergent-to-divergent section. The convergent part accelerates the flow to Mach 1 which should occur at the throat or narrowest part. Beyond this the supersonic flow passes through a divergent duct and continues to accelerate.

The reason, I believe, is that if you try to converge a flow beyond Mach 1, you get powerful shockwaves set up that cause so much drag there is no more acceleration of the flow.

More information on this effect is here: grc.nasa.gov/WWW/k-12/rocket/nozzle.html (add the www to the start).

Jeremy
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K.Haroon
Site Admin


Joined: 11 Dec 2005
Posts: 1308

PostPosted: Sun Sep 30, 2012 6:19 pm    Post subject: Reply with quote

Hi Jeremy, you are most welcome.

Thanks for the feedback. Got your point. I have moved the question to the following section "Questions on Gas Turbine Engines", with your explanation.

However can you pls send me the link again, the one you've sent isnt working. Can you pls also highlight why not a straight duct which should maintain speed instead of a divergent duct which has the tendency of slowing the speed? Is it because of inertia or what?

Regards
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jthomson



Joined: 30 Sep 2012
Posts: 2

PostPosted: Mon Oct 01, 2012 8:25 am    Post subject: Reply with quote

Hi Harood,

Let's try the link again - this time it should work if you take out the spaces (I think if I paste it complete will get removed):

http:// www .grc.nasa.gov/WWW/k-12/rocket/nozzle.html

As to why supersonic flow accelerates in a divergent duct, I'm afraid I don't have common-sense explanation.

But if you follow through the maths on the page I have linked above you basically arrive at:

change in velocity = - change in area * (1 - M^2)

where M is the Mach number. M^2 is supposed to mean M squared.

So for subsonic speeds, M < 1, the term in brackets is greater than one and you have the normal relationship where an increasing cross-sectional area gives a decreasing flow velocity.

But when M > 1 the term in brackets is negative, and the relationship is the other way around; an increasing area gives an increasing velocity.

This formula also explains why you need to use a 'compressibility correction' when working with speeds close to Mach 1. With small Mach numbers, M^2 is pretty insignificant, but as the Mach number approaches 1 the term M^2 rapidly becomes more larger, and the simple relationship between area and velocity becomes less and less linear.

If anyone has a digestible explanation of why this occurs I would like to hear it!

Jeremy
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K.Haroon
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Joined: 11 Dec 2005
Posts: 1308

PostPosted: Mon Oct 01, 2012 9:00 am    Post subject: Reply with quote

Hi Jeremy

Thanks. The link is working now and I have posted it here "Questions on Gas Turbine Engines".

Regards
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