ATPL Systems and Aerodynamics Questions Flashcards
ATPL Systems and Aerodynamics study
- What area in the engine does not normally need anti-ice proctection?
- First stage of the compressor.
Anti-icing is typically not needed for the compressor blades since the h
- Which part of the engine produces the most dominant noise?
- fan and Turbine
Anti-icing is typically not needed for the compressor blades since the h
- What is the best fuel to air ratio?
- 1:15
- In a free turbine type engine (turbo prop) the free power turbine?
- Not connected to any other turbine shaft.
The Free turbine has its own shaft / spool connected to a reduction gear
- In flight engine bleed air for anti-icing to the wing leading edges in known icing conditions is?
- Used continuously.
- An aircraft with a TAS of 300 kts has a fuel burn of 3000kg/hr. The specific AIR RANGE as a ratio of distance travelled per tonne of fuel would be most correctly expressed as a ratio of?
- 100nm/Tonne
SAR = TAS / FF = 300 / 3000 = 0.1nm/kg x 1000kg/1 ton = 100nm/1000kg
- Reverse thrust is most useful on large transport turnbine aircraft and at?
- At high forward speed in the landing roll.
Reverse thrust is always deployed at the beginning of the landing roll w
- Regarding the specific gravity of jet fuel..?
- Calorific value does not effect SG.
SG varies with temperature for AVTUR (Jet Fuel) but not with Calorific (
- An advantage of an axial compressor in a gas turbine engine is?
- Axial Thrust.
Axial compressors provide a bigger pressure ruse and consumes more air.
- Reverse Thrust during the landing roll on a transport jet is most effective at:
- High Speed, High RPM.
If thrust reverse is used at low speed, hot or turbulent air can enter t
- In order to avoid aeration of the fuel lines in a jet transport aircraft, the fuel system incorporates what?
- Boost Pumps.
Boost Pumps prevent bubble accumulation by providing positive pressure d
- The RPM of a GAS turbine APU in a large jet transport aircraft is controlled by?
- Fuel (Governor) FCU.
The fuel generator provides constant speed for the APU.
- The angle of attack of compressor blades in a gas turbine engine depends primarily on?
- TAS, RPM and Compressor outles pressure.
- The correct procedure to follow in the event of a hot start to prevent torching in a gas turbine engine is to?
- Motor the engine with the fuel supply cut OFF.
Motoring the engine allows the engine to continuously rotate the turbine
- The thrust output of a turbojet powered aircraft is greatest?
- On the brakes on the runway at full thrust.
As forward speed increases, thrust decreases until the RAM RECOVERY poin
- In a large transport category aircraft, fuel moving around in the tanks can cause uncommanded attitude changes after pitching or rolling maneuvres. This is prevented by?
- Baffles in the fuel tanks.
Baffles are dividing partitions that limit the movement of fuel in the t
- The main reason for the combustion of fuel in a gas turbine engine is?
- To raise gas velocity.
Thrust can only be increased by either increases the ,ass of the air or
- Regarding the function of the reverse thrust system on a high bypass turbo fan engine?
- Blocker doors are used to divert the cold stream.
On turbofan engines, the reverse thrust is on the cold by-pass air only. Cold stream reversers often use blocker doors in the by-pass ducts to redirect air out through cascade vanes in the engine cowling.
Hot stream thrust reversers often use the clamshell design or bucket targets in which two doors swing into position to deflect the hot exhaust stream in a forwards direction.
- The purpose of air shroud on an atomizer type (duplex) fuel spray nozzle in the combustion chamber of a gas turbine engine is?
- To reduce carbon deposits around the nozzle tip and the nozzle.
Shrouds are just openings around the nozzle.
The function of variable inlet guide vanes in a gas turbine engine is?
- To prevent compressor blade stall when the engine is operating at low RPM.
These are located after the rotating compressor blades and adjusts the airflow to the correct angle of attack,
- EPR (engine presure ratio) is the ratio of?
- Engine Compressor inlet pressure to jet pipe pressure.
EPR is the ratio of the air entering and leaving the engine. Simply the ratio of the inlet and exhaust jet pipe.
- In passing through the turbine section of a pure turbojet engine?
- Gas pressure reduces, velocity increases and temprature decreases
Bernoulli’s principle: In the turbine section we can treat it as a converging duct that causes pressure and temperature to decrease and velocity to increase.
- The failure of the bleed vlave to close in a gas turbine engine after start will result in?
- An EGT rise.
Bleed valves are opened during start to prevent too much air entering the engine which causes stalling or surge. If after start the bleed air is still open, there will be less bypass air being exhausted and only the air from the engine core, which is last, is exhausted
- The “Ram Ratio” in a gas turbine engine is defined as the ratio of?
- Total pressure to static pressure at the air intake.
- On a turbojet powered aircraft, the front engine EPR probes are blocked. As the pilot advances the thrust lever to take-off EPR, the EPR gauge will?
- Over read and the thrust will be less.
Based on EPR reading gauge will think you have a lot of exhaust pressure therefore will over read and indicate more thrust than the actual thrust that is set. Are they static???
- If an aircraft generator CSD is disconnected in flight, the correct method for re-connection is?
- Mechanically on the ground.
CSD completely detaches itself, therefore can only be connected again manually,
- The by-pass ratio of a gas turbine engine is?
- The ratio of By-pass air to core air.
High by-pass means more air passing through the by-pass duct compared to the engine core (turbofan)
Low by-pass means less air is passing through the by-pass duct than the core (turbojet)
- Regarding RAM effects influence on thrust output?
- It results in a total recovery of thrust as aircraft forward speed increases.
Initially thrust decreases as forward speed increases until the ram effect recovers all the thrust again.
- For a constant RPM in a gas turbine engine, a decrease in air density will?
- Decreased fuel flow and decreased thrust.
Air that is less dense means power available for the engine. As air density decreases there is less resistance to the compressor rotating meaning less force required to turn it.
- The inlet duct of a jet engine at subsonic speeds is designed to convert?
- Kinetic energy to pressure energy
Air moving towards the engine (Kinetic) is gradually compressed by the compressor and increases its pressure and velocity.
- The two most critical factors in determining the in-flight re-light or restart of a turbojet engine are?
- Altitude and Airspeed
In order to restart a turbo jet engine the air must be compressed, meaning more pressure, Air speed provides an increase in pressure through ram air. Altitude is inversely proportional to pressure, the higher the altitude, the lower the pressure.
- Factors affecting VMCA, An A/C without negative torque sensing, propeller should be?
- Feathered
By feathering the propeller you reduce drag and prevents the propeller from rotating faster than the gear box (negative torque)
- Regarding the diffuser in the engine and its affect on air??
- Divergent duct, converts kinetic to pressure.
Diffusers are located after that last the compressor and serves as a divergent duct, increasing pressure.
- What makes the Propeller Feathered when the engine fails?
- TSS (Thrust Sensitive Signal) or auto feather system
This is a safety feature that automatically feathers the propeller during engine failure on take-off.
- What is a hung start characterized by?
- Low RPM and High EGT
Hung start occurs when during engine start, RPM fails to teach the normal or self-sustaining RPM. This might lead to an EGT Rise as well as causing a Hot Start. (revise starting issues)
- Factors affecting thrust
- Temperature
Aircraft thrust and performance are affected by RPM, Density, Altitude and Temperature.
- Where is the highest pressure found in a turbojet engine?
- Impeller to diffuser
The highest pressure is found at the final stages of the compressor right before the combustion chamber.
- What is the advantage of annular combustion chamber
- Better and efficient pressure and flame Propagation. Compact but not structural.
- Where is the highest velocity found in a gas turbine engine?
- exhaust area. nozzle
Propeller nozzles are used in high speed aircraft to further increase the velocity of the air.
- What is the purpose of combustion?
- Increase velocity and temperature
Combustion in a Gas Turbine Engine occurs in constant pressure and increases temperature and velocity.
- What is the importance of constant fuel flow to the combustion chamber?
- To prevent flame out
- Compared to turbojets, turbo fans have
- Lower thrust for a given mass of air
- How does the starter motor disengage from the engine
- The starter motor is automatically disengaged via the clutch once the engine reaches a self-sustaining speed.
- Which of the following occurs when you are already in a self-sustaining state?
- When the engine could accelerate without the assistance of the starter motor
Self-sustaining state is when 35-50% of the engine is accelerated without the assistance of the starter motor.
At 55-60% idle RPM, engine is in stabilized idle.
Stater motor turns the turbine
- You are taking off from a short runway at max take-off weight, the position of the bleed valves should be?
- OFF, to increase mass air flow
Operation of bleed valves reduces the performance of the engine as it uses some of the air that should have been part of the thrust produced.
- What is the effect of temperature rise on SG?
- Decreases
A higher temperature yields a lower SG.
- What happens to jet engine thrust when humidity increases?
- Slightly decrease
As humidity increases, there are less oxygen molecules to burn as it is less dense than dry air. A/C engines are built for cold and dry air.
- What is the most common ice protection used on modern turboprops? (props?)
- Thermal Electric
- What leads airflow to the turbine?
- Nozzle guide vanes
They direct air coming from the combustion chamber, whilst at the same time converting pressure to kinetic energy and increasing the air’s velocity.
- In heavy rain during takeoff, the combustion in a gas turbine engine will be?
- Low energy, high output
- What does NTS do?
- Increase blade angle when there is a sign of plant negative torque
Negative Torque Sensing System sends a signal to increase the blade angle whenever negative torque is going out of limit. A separate coupling serves as a back-up to the NTS when it disengages from the gear box from the engine, when negative torque exceeds a preset value.
- Which part of the APU is bled to start the engine?
- Exhaust
- Why is AVTUR safer when there is a spillage?
- High Flashpoint
- Which will give you less thrust on take-off?
- High density altitude
High density altitude implies a high ISA DEV which assumes from a higher OAT than standard ISA TEMP.
- Maximum L/D is X. If you want to climb at max angle of climb, what speed should you fly at?
X
The minimum drag speed = Best L/D Ratio, Max glide range, minimum fuel flow per hour or best endurance, max excess thrust or max angle of climb.
- You are flying “straight and level” and you want to achieve maximum range. You should fly at the minimum
- Drag/TAS
At a constant altitude, max range is achieved by flying at an AOA that yields min fuel per mile or best TAS/Drag Ratio.
- A Yaw Damper prevents
- Lateral static stability
Static lateral stability is the tendency of the down going wing to return back to its level condition by rolling to the opposite direction.
Dutch roll is characterized by strong lateral stability which is prevented with the use of a yaw damper.
- Subsonic flow through a divergent duct will experience
- Constant density, increase in pressure and a decrease in velocity
In subsonic flow of air through a divergent duct, density is constant, pressure increases and velocity decreases.
In supersonic flow, density decreases, pressure decreases and velocity increases.
- If the angle of attack is increased on a swept wing compared to an un-swept wing of similar area and aspect ratio the swept wing will produce?
- Less lift and more drag
Due to induced drag from span wise flow (tip vortices)
With the same amount of AOA, the lift is lesser for the swept wing.
As AOA increases, drag increases (induced drag)
- In comparison to an un-swept wing, a swept wing will have?
- Lower max CL at subsonic and transonic speeds
- In supersonic airflow, static pressure behind an expansion wave will
- Decrease relative to the pressure ahead of the wave
Air behind the expansion wave increases in velocity, therefore causing a decrease in the pressure behind the wave.
- In steady asymmetric flight in a twin-engine jet transport category aircraft, the crew elect to level the wings. The position of the balance ball in this situation will be?
- centered
Wings level method in asymmetric flight rudder only
- An increase in gross weight will cause the position of the total drag to move
- Up and right
As weight increases, drag increases as more thrust is required. With this, speed increases as well. Thus drag moves up and to the right.
- The deployment of spoilers will cause the position of the total drag curve to move
- up and left
Spoilers are used to destroy lift causing more drag, which increases the weight therefore decreases the speed.
- The extension of the landing gear will cause the position of the total drag curve to move
- Up and left
The landing gear is a large source of drag and thus there is a speed reduction required, decreasing the drag speed but increases the total drag.
- A B767 is in cruise with the stabilizer trim set correctly for a relatively forward CoG, the position of the elevator would be?
- Faired
The stabilizer trim moves, while the elevator moves opposite to it. Thus a Forward CoG moves the trim to an upward position to compensate for the nose down motion, while the elevator will move opposite.
As it is set correctly, elevator is now here.
- Concerning the characteristics of the airflow behind a normal shockwave?
- Pressure and temperature increase
Airflow behind a shockwave becomes subsonic causing a decrease in velocity, therefore giving a rise in pressure and temperature. Just as in a converging duct.
- A variable incidence tail plane with stabilizer trim as an alternative to a conventional elevator with trim
- Can produce excessively high control forces if out of trim
The stabilizer itself is a larger control surface than the elevator so flight maneuvers will produced great control force when out of trim.