Turbine Flashcards
Mach Number
ratio of airspeed to speed of sound
High Speed Buffet
aircraft accelerates into transonic region (.75- mach 1.2), shock wave generated on wing travels aft, causes airflow separation, ultimately this disturbed air affects horizontal stabilizer causing HIGH SPEED BUFFET
Mach Tuck
wing center of pressure moves aft as its speed approaches the sound barrier.
Farther back it moves, greater pitch down moment generated by wing –> airspeed continues to climb increaseing effects of shock wave and mach tuck
Critical Mach Number
speed at which airflow over any portion of upper wing surface becomes supersonic
(NOT A LIMITATION but simply the speed at which shock wave develops over the wing)
Limiting Mach Number
highest speed before aircraft becomes noticeably uncontrollable
Maximum operating speed
Mmo - max speed relative to speed of sound - displayed by barber pole
Pole adjusts for density & altitude
Coffin Corner
Stall speed increases as function of altitude
Mmo decreased with altitude
The two speeds converge at specified altitude creating the coffin corner
any increase leads to high speed buffet
decrease in speed results in stall buffet
Vne v. Mmo
Vne is structural limitation
Mmo is aerodynamic limitation
Buffet Margins
airspeed range between stall buffet and high speed buffet
Improve buffet margins - restrict aircraft altitude by weight
Swept Wing Pros & Cons
Pros:
- increase Critical Mach - allows for faster flight
- Less sensitive to turbulence
- Increase lateral stability
Cons:
- Produce less lift - issue at low airspeeds - addressed by use of LEDs & Trailing Edge Flaps
- Tendency to stall tip first - addressed with aerodynamic twist in wings - wing tip lower AOA than root
- Predisposition towards dutch roll
How does Swept Wing produce less drag?
Delays peak effects of drag to higher airspeeds
How? Reduce component of air that flows directly aft or “chordwise”
Creates Spanwise Flow - lower velocity than chordwise flow - increases critical Mach number allowing for faster flight
Dutch Roll
tendency of an aircraft to roll when it yaws
Sideslip (uncoordinated) - change wing effective wingspan - greater wing span = more lift - causes a roll - more lift means more drag on high wing - yaw towards that wing
Yaw dampers - auto rudder inputs to counteract yaw
Winglets
restricting airflow around wing tips - improve effective span of wing and therefore lift
Without winglets - air tends to flow from underwing high pressure to top wing low pressure - results in downwash –> increased drag & reduced lift
Tailets
vertical surface mounted on horizontal stabilizer
additional directional stability (especially on T-tail aircraft at low airspeeds and high AOA when airflow may be blocked by wing)
Vortex Generators
create small vortices that direct airflow to prevent airflow separation (at low and high speeds)
Can be mounted on wings, tail, elevator, engine pylon, fuselage
Vortilons
mounted on underside of wing by ailerons
basically large vortex generators designed to control turbulent airflow
Mmo indications
barber pole (adjusts with altitude) aural overspeed warning - often called the clacker
AC v. DC Power
AC Current flow changes current can travel farther Less expensive & lighter weight often drive high draw items
DC
linear electrical current - constistant power delivery
general use items
some instruments require DC Power
AC to DC TRU
DC to AC Inverter
more consistent voltage
Turbofan
Turbojet core with shrouded fan at front of engine
more fuel efficient, quieter
Fan - moderate acceleration to large volume of air
Highspeed/altitude advtanges of jet
Lowspeed/altitude advantages of prop
High Bypass
5:1 ration
80% of thrust from bypass at low altitudes
Normal Start
Start switch - ON
Engine turning- drawn through compressor section where compressed
Enter combustion chamber
10-12% N1 - fuel introduced & igniters light off
Rpm accelerates & stabilizes at normal idle speed
Hot Start
Temps exceed limitations during start
too much fuel too early OR insufficient airflow
Cut off fuel supply, continue motoring
Hung Start
light off occurs but engine stabilizes (hangs) at low rpms
insufficient airflow, inefficient compressions, low starter rpms
N1
low pressure compressor speed
N2
high pressure compressor speed
EPR
Engine pressure ration- ration of exhaust to intake pressure
EGT
Exhaust Gas Temperature
main engine temp guage
TOT
Turbine Outlet Temp
ITT
Interstate Turbine Temp
measured between compressor and power turbines
TIT
Turbine Inlet Temp
Igniters
spark plug like devices - light fire during starting
used during takeoff, landing, cruise in heavy precip
Starter/Generator
spins engine for starting
once light off - electric motor reverts to generator
Pneumatic Starter/ air turbine starter
low-pressure air motor
uses air from APU or GPU or other engine to spin starter turbine
Bleed Air
tapped from engine compressor section
used for pressurixation, AC, anti-ice
Compressor Stall
rotor blades fail to pass air smoothly
no longer able to force air through engine front to rear
high pressure air escapes from front & rear
occur in axial flow compressor
Inverter
convert DC to AC
AC Power
alternating current
used in larger jets to save weight and power loss due to long lengths of wiring
TRU - Transformer Rectifier Unit
convert AC to DC
Circuit breaker
automatically opens electrical circuit when an excess of current occurs
APU
Auxiliary Power Unit
small gas turbine engine
supplemental source of electrical power
Hydraulic Accumulator
stores hydraulic pressure
Piston Cylinder - pressurized one side with nitrogen, the other side with hydraulic pressure
Flight Control Terminology
Primary - elevator, ailerons, rudder
Secondary - trim tabs
Auxiliary - wing flaps, LEDs, slats, spoilers, speed brakes
Balanced Field Length
rwy needed to accelerate to V1 & stop if engine failure before V1
OR continue takeoff climb to 35 AGL if failure happens after V1
V1
Decision speed - to fly or not to fly after engine failure
