Interesting Questions Flashcards
Describe the drag curve and importance of Vimd
Vimd is the speed for max range due to minimum drag
What are winglets and how do they work?
Winglets are aerodynamic efficient surfaces located at the wing tips. They are designed to reduce induced drag. They dispense the spanwise airflow from the upper and lower surface often at different points, depending on the particular design, thus preventing the intermixing of these airflows that otherwise would create induced drag vortices.
What causes/are wing-tip vortices?
Wing-tip vortices are created by spanwise airflow over the upper and lower surfaces of a wing/aerofoil that meet at the wing tips as turbulence and therefore induce drag, especially on a swept wing.
If you were loading an aircraft to obtain maximum range, would you load it with a forward or aft center of gravity (forward or aft cargo hold)? An aft center of gravity position/hold
B
Aft C of G as this will allow a natural nose up pitching moment allowing the stabilizer to remain neutral reducing the need for downforce and reducing Induced Drag therefore increasing range
How does C 0f G effect VMCA?
Rear C of G = VMCA increases
Forward C of G = VMCA decreases
This is due to the moment arm from the C of G to the tailplane, shorter it will require more force, therefore a greater speed in order to overcome the turning moment
In the event of an engine failure during a crosswind which is the most favourable engine to fail?
DOWNWIND ENGINE
This is due to the crosswind compenent assisting the vertical stabilzer in correcting the yawing motion
What is SFC
Specific fuel consumption
Ratio of fuel burnt over engine thrust
What is the compression ratio of a Gas turbine engine?
Ratio of compressed air between the inlet and outlet of each compressor stage
What are the advantages of a wide cord fan engine?
Weight
Noise
Fuel
Thrust
Describle tripple spool fan engine?
N1 - Front turbofan (Compressor) - not restriced in size due it having its own turbine, allows increase bypass ratio (LP)
N2/3 - More efficiant as they can run at optimal performance due to each seciton having its own turbine
Higher engine thrust
Easier to start because you only need to start 1 spool
Easier maintenance as its in 3 seperate sections
Why do Jets fly as high as possible?
BEST SFC beacuse you fly at a constant MACH NO, so TAS and EAS reduce, drag is directly proportional to EAS and therefore reduces, increasing endurance leading to increased SFC
Turbine’s operate most efficiantly at high RPM 90-95% N1, this is not achievable at low altitudes due to increased air density which will over torque the engine
The higher the ALT the greater the TAS for a constant IAS therefore leading to greater RANGE
How does flying LRC increase range?
Fly at constant Mach No as altitude increases TAS decreases and therefore GS decreases and range decreases
By increasing the Mach No slightly the TAS/GS/Range will increase but this will have a negative effect on endurance
Why must EPR be set as quickly as possible?
Initial setting there will be a reduction in EPR due to lag, inlet Pressure increases and Exaust pressure remains constant
So Pilot is not chasing the RAM rise
Adequate aircract acceleration to achieve V1 and VR in the TORR (take off run required)
What are lines that run from Pole to Pole?
What is Departure?
Meridians - Lines of Longitude
Greenwich - Prime Meridian
Distance along a Paralell of Latitude other than the equator - D = change of Long x Co sin of lat
How Does INS work?
How does it find true North?
Measure’s your great circle track from the position of departure through the use of acclerometers, gyroscopes and a postion computer
By g
Describe GPS?
American satellite system for world navigation
24 minimum satellites
21 operational at one time
6 orbital planes 3-4 per plane at 55 degrees in 12 hours
4 satelites in range to obtain a fix - 3 for positon and 1 for altitude
5th satellite for RAIM
Calculates postion by time radio singals converted to a distance to obtain a fix
Disadvantages of GPS
US Military can downgrade system and accurracy
System errors - Receiver error
Clock Bias
Signal jamming
Satellite geometry
Ionispheric errors
How does a VOR work?
VHF omdi directional range
Transmits a VHF signal over 360 degrees which has an FM reference singal phases and AM varible phase signal which varies at a constant rate allowing a unique signal for each degree
108mhz-118mhz
What is an Isobar and Isotherm?
Lines of equal pressure
Lines of equal temperature
How are clouds formed?
Lifting action of air
Frontal
Orthographic (Hills/Mountains)
Convection
Turbulane
How is cloud base calculated?
temperature dewpoint spilt x 410
Different types of Fog?
Radiation - Convection terrestrail radiaiton
Advection - Advection warm air over cold surface
Frontal - Liftng
Describe formation of a thunderstorm?
When is lightening most likely to occur?
High Moisture content, Lifting action, Adiabatic cooling, Highly unstable air
Developing, Mature and dissapating stages
+10 to -10 and in mature stage of thunderstorm
Describr Upper Winds?
Jetstreams?
Wind direction wtih altitude?
Trade winds?
Caused by differential temperature at high altitude (Thermal Gradient)
Narrow bands of upper thermal winds
1500nm long, 200nm wide, 12000ft depth, greater than 60kts, CAT, speed is directly proportional to thermal gradient
Polar front Jetstream
Intertropical front Jetstream
Back in N.H and Veers in the S.H
Light winds blow from Subtropical High to Equatorical Low (ITCZ)
Why does a warm front move slower than a cold front?
Warm and cold front winds?
Cold air is more dense and pushes under warm air whereas warm air has to rise above the colder air
Warm Front - Wind Veer’s N.H backs in S.H
Cold Front - Wind Veer’s N.H Backs in S.H
Where do you find Windshear?
How do you detect windshear?
Microburst?
Below 3000ft, Frontal Passage, Microburst, Hills and moutains, approach over water, elevated threshold, Thunderstorms/CB clouds
Pilot reports, lydar, doppler shift, aircraft warning system associated with GPWS
Severe downgraughts and windshear found below mature CB, may not be associated with rain, last up to 10min, diameter 1-5nm, if encountered TOGO!!
Tropical Revolving Storms
Typhoon’s, hurricanes, cyclones
What is a Typhoo ?
Cyclonic Storm with gale force winds (above 34kts)
Formed along the ITCZ
Form over warm oceans and need at least 27 degrees
Die out over land
Do not form on Equator as there is no Coriolis force
Unstable air mass
Convective lifting through trade winds
Typhoon season is June-October
Monsoons
Seasonal change in wind direction
Basically a massive Land/Sea Breeze
Summer - April to September
Heavy rainfall, warm moist air blows from Southern eastern indian ocean
Blows from Ocean to Land
Winter - October -April
Blows from Land to Ocean
Hot and dry, less powerful, Himilaya mountains prevent wind and moisture reaching the coast
How is Windshear detected?
LLWAS - Low level wind shear detetion system
Aircrafts can be fitted with a system which uses AOA, airspeed and acceleration sensors to compare aircrafts actual performance to what it should be under in existing circumstances
Lydar - Unique to Hong Kong, Doppler Radar by laser light up to 12km away from the airport
If you increase weight what happens to descent?
The glide distance remains the same but an increase in weight leads to increase in lift required, leads to increase in ROD so you will get the faster
Increase weight - Start desent earlier to account for increase in ROD
Effect of C of G on stall
Forward C of G increase stall speed
Due to tailplane having a greater downforce action required to maintan S and L and therefore incease the amount of weight the tail has to support leading to higher indicated airspeed required to maintain the extra lift and INCREASING the stall speed
Factors Increase Tip Stalling?
Factors reducing tip stalling?
Power/slipstream on during stall re-engergising the boundary layer
Flaps increasing camber at the wing root
Swept wing aircrafts
REDUCE
Washout (incidence)
Change of aerofoil section (Camber)
Root Spoiler (disturbs airflow at root)
Why does swept wing aircraft still at a higher AOA
Low aspect ration leads to increased downwash which effectively reduces the apparant angle of attack and increases stall angle
Typers of flaps
Trailing Edge?
Leading Edge?
Double/Slotted Flap - Increase camber and re-engergize boundary layer
Fowler Flap - Slotted flap which increases camber, increases wing surface area and re-engergizes boundary layer
Leading edge
Slats - extend from top of wing, increase camber and slot re-engergizes wing
Drooping leading edge - The whole leading edge deploys and increases camber
Kreuger Flap - Deploys from underneath the wing…same theory as slats but The advantage is when retraced the leading edge radius is thinner and more aerodynamic for high speed flight
Factors that reduce Adverse Aileron Yaw
Control Balancing
- Frise Ailerons (hinged to the rear so small peice is deflected into airflow creating profile drag)
- Differential Ailerons (upgoing deflects more)
- Spoilers - Deploy on upgoing wing creating drag
Control Balancing
Horn Balance - small horn sticks out in airflow creating drag
Setback hinge
Tab balance (Piper 180 on elevator)
Varible Incidence Tailplane
Controlled by trim tab
By Auto pilot servo’s
Acts as a Mach Trimmer
Mfs
Local Mach No.
Mcrit
Mdet
Mmo
Mcdr
Free stream mach No of the aircraft throught the air
Mach no at a particular point on the wing
The critical Mach no is where the first evidence of supersonic flow is found
Detachment Mach no is where the bow wave attaches to the leading edge (compresibility)
Critical Drag rise is observed
Why does Cathay use the RB211 524HT engine
Reduced SFC by 2%
800lb weight saving per engine
Environmentally friendly
Take off climb segments
1 - 35ft (Screen Height) to gear up @ V2
2 - Gear up to 400ft @ V2 - 2.4% // 1.5%
3 - Acceleration segment - 400ft to flap retraction - Level V2+30 to V2+50
4- Level off height to 1500ft at constant V2+50
What is the Difference betweent the CFM 56 5C4 engine and the RR RB211 524HT
The CFM is a twin spook design where as the RB 211 is a tripple spool design
What happens to Brake Temperatures after wheel retraction
Brake temperatures decrease but tyre temperatures increase due to convection
TAT
SAT
Total air temperature
Static air temperature
Why does the 747 classic not have winglets
The structural requirements for adding winglets large enough to be worth it in the cruise are far to great to be economically feasible
What is the difference between an INS and an IRS?
An INS is a collection of components that together provide a system that is able to provide navigation computations and solutions. An IRS is different in that it is a single box that contains an Inertial Reference Unit [IRU] and a computer to produce reference information. This information is then provided to numerous other aircraft systems and displays.
What do you know about the Trans-Polar routes Cathay Pacific is pioneering?
The first commercial trans polar flight [from Toronto to Hong Kong] was operated on May 18th 2000 by a Cathay A340-300, with a flying time of 14hrs 59mins.
Cathay stands to benefit a great deal from the new routes as they dramatically reduce flight times [between 2 and 3 hrs], which make them more attractive to passengers [no stop over in Anchorage].
Some problems operating at high latitudes include:
Low fuel temperature [Jet A1 freezes at around -50ºc]
Communications are solely by HF [Satcom stops working around 85ºN]
Exposure to increased levels of cosmic radiation [magnetic field]
Iso Counter Radar
Weather detection, sends out pulses of radio waves which bounce back off precipitation
Larger flap setting, how does it affect take-off roll, screen height?
Larger flap settings will decrease the landing roll but reduce the climb gradient
The 3 laws of fly by wire
Normal - Hard Protection (Pilot cannot override)
Soft Protection - Pilot can override
Direct - Sidestick is used directly to determine position of the flight controls (No Autotrim)
Advantages of Free Turbine
Greater propeller range of operating speeds
Lighter
Less drag due to no shaft or gearbox
easier to shutdown, no excess heat trapped in the hot section
