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AGK: Systems 2 (Pneumatic Systems (Intro
Light AC use small ENGINE…
AGK: Systems 2
Pneumatic Systems
- Intro
- Light AC use small ENGINE DRIVEN PUMP pneu sys. for gyros. Twins 4 cabin heating & de-icing
- Large AC use ENGINE BLEED AIR 4 A/C, pressurisation & anti-ice
- Uses of pneumatics: gyros, heating/cooling, A/C, de-icing, CABIN PRESSURISATION, water tank and toilet pressurisation, inflating door seals,
- Uses cont.: Gas Turbine starter & Thrust reversers, pressurise hydraulic reservoirs, emergency back-up U/C, air-driven hydraulic pumps
- Light AC Pneumatic Sources
- Eng. Driven Vacuum pump via a quill shaft which shears if torque load excessive i.e. if pump seizes it doesn’t affect engine
- Twin Light AC Pneumatic Sources
- See schematic. Sys. Press ~3000psi
- Each eng has own compressor
- Moisture Separator/Extractor > Desiccator = remove water otherwise it'd freeze @ alt.
- Isolation valve: incase of emergency can switch to emergency system
- Can have pressure reduction valve for srvs that need it i.e. gear operation, pax door, nosewheel steering
- Large AC Engine Driven Compressor (EDC/Rootes Blower/ Blower)
- MASS FLOW CONTROLLER = provide fixed mass flow of air under all circumstances
- EDC (as opposed to a gas turbine) air comes from the EDC/Blower & works in conjunction with Spill valve & Mass Flow Controller
- Spill valve regulates air into Mass Flow Ctrller
- Learn schematic from notes
- Cabin compressor (Blower) -> Silencer-> Spill Valve -> Mass flow Ctrller ->Choke Heat Valve ->Pack Valve -> (only if being cooled) Cooling pack + Water Separator -> To Cabin
- EX: Choke valve used to raise temp of air if reqd
- Large AC w/ Gas Turbine Engine Bleed
- Source of air = Compressor stages of the HP compressor
- EX: In normal stages of flight our delivery comes from the LP Stages of the HP compressor (from the HIGHER Press stages) - may be taken from LP & HP if low RPM
- EX: Uses variable metering orifice to control amount of air to mass flow controller
- Fine tuning system stops it oscillating too much
- Engine Bleed Systems info
- Most common method 4 supplying charge air for A/Cond
- Hot bleed air pass thru Mass Flow Cntrllr
- THEN COOLED BY A/C PACKS
- See schematic
- EX: HP Shut off Valve (HPSOV/Crossflow Valve) is press. sensitive and pneumatically operated. Open when insufficient air from LP
- EX: HPSOV designed to OPEN SLOWLY but CLOSE QUICKLY i.e. in case of fumes u want quick close
- EX: OVERPRESSURE: USUALLY CAUSED BY FAILURE OF THE HP SHUT OFF VALVE
- EX: OVERHEAT: ACTION = CLOSE the bleed switch and THEN OPEN THE ISOLATION VALVE to make up for the lost system
- Cabin pressurisation
- Generally max of 8000ft
- Needs Mass Flow Controller(constant mass of air)->A/Cnd (dry air)
- EX: We control the pressure within the cabin by controlling how much we let out via OUTFLOW VALVES controlled via PRESSURE CONTROLLER
- EX: If Outflow valves failed closed we have SAFETY VALVE to stop OVEREXPANDING
- EX: If pressure outside is >inside (-ve press i.e. rapid descent) and we are not equalising enough we have INWARDS RELIEF VALVE to stop hull COLLAPSE
12 Anti-Ice, De-ice & Rain Protection
- Hoar frost, Clear Ice, Rime Ice
- **EX: We adopt CLEAR AC POLICY prior to T/O
**
- Effect of Ice Accretion
- ⬇️CL + ⬆️Stall Speed + ⬆️Drag + ⬆️Power Reqd + ⬆️weight
- Jammed controls
- Overread of thrust if intake sensors freeze
- EX!!Countering the effects of icing
- Avoid icing conditions
- ‘De-icing’ = where ice is allowed to accumulate prior to being removed
- EX: When will we switch the de-icing system on? A = When ice = 1.5cm && off when ice gone
- Anti-icing = where the object is to prevent any accumulation of ice?
- EX: When will we switch it on? A= B4 entering area where icing likely && off when icing not likely
- Ice Detection Devices - detect ice accretion
- EX: You must be able to inspect the AC by day and night so have lights
- Hot Rod: EX: Ice will build up 1st on the narrowest section & the smallest surface area. Aerofoil shaped w/ light for night + visible from flight deck.
- Vibrating (Rosemount): EX: Short cylindrical probe, 40khz. Ice ⬇️freq. = warning light
- EX: When will light go off…when u cancel it or switch on anti-ice
- Pressure: Smith press. detector = aneroid capsule connected to tube open to airflow. If sensor holes get clogged pressure in aneroid drops = ice warning caption
- Rotary
- Inferential: looks at if conditions INFER ice build up
- De-icing
- Mechanical: Pneumatic Boot
- Piston & Turboprops (De-icing(
- When Ice = 1.5cm we switch on. It cyclically inflates + deflates boots to remove the ice
- Too thin (<1.5cm) = ice flexs and doesn't break
- Too thick (>1.5cm) = ice too heavy for boots to break
- Fluid based Ice Protection
- Uses Isopropyl alcohol to de-ice
- May also be used for wind-screen
- For single curvature LE u pump into distribution panel
- For dble curvature LE u use a strip distributed sys.
- EX: With a weeping wing (fluid deicing) what is the purpose of a head compensating valve? A= It ensures the fluid goes to all parts of the system
- Thermal Anti-Ice Protection - ANTI-ICE
- All modern jets!!!
- Bleed air from compressor stage of the gas turbine and then blow it down a duct/ pipe (piccolo pipe) then into gaps in the LE including slats!!!
- EX: Thermal anti-icing protects whole of LE including slats but NOT KRUGER FLAPS or LE CAMBER FLAPS!!
- EX: When would you not employ thermal anti-icing? A = Not on T/O, Landing cos reduces thrust
- EX: When would you not switch it on? A = on ground cos melt wing cos no cold air passing over wing as u get in flight
- Turbo-prop Thermal Anti-Icing
- Same principle as above but turboprop doesn't have HP bleed air.
- Ram air passed over surface of heat exchanger which has exhaust hot air passing thu. Ram air is heated then used 4 thermal anti-ice
- Jet Engine Anti-Icing
- Same as above but EX: FBW allows us to RELAX the natural stability of the AC which means on modern AC SOMETIMES we will protect the tail…BUT ON MODERN transport AC we don’t have tail anti icing!!!
- Electrically heated elements for eng. nacelles
- EX: Propellor protection System
- Ice formation on a prop blade produces distortion to the aerofoil section causing
- Effects: Distorts aerofoil, Imbalance, Vibration, Efficiency loss
- Protection by EX!!: ANTI-ICING fluid system or EX!!:Electrical thermal DE-ICING system
- EX!!:Electrical thermal DE-ICING system
- Spinner anti-iced ALL TIME HOWEVER prop done cyclically thus collectively system = DE-ICING!!
- EX!! Anti-icing fluid system:
- Fluid pumped to slinger ring from supply tank > Slinger tubes distribute fluid to blades by centrifugal action (sometimes aided by rubber overshoes)
- Windscreen Ice Protection
- EX: DC controlled system via Temp Control unit with embedded sensor
- IF the controller was to fail, to avoid overheat. We have an overheat sensor that annunciates a warning and cuts the heating
- EX: What does it mean by over heat on screen? A: IT doesn't mean your screen has failed…it means that your controller has failed
- Windscreen Rain Repellent System
- EX: Purpose = make the drops coalesce so that they are big enough to be blown away
- EX: IT should NEVER EVER BE APPLIED TO A DRY SCREEN
- Windscreen Wipers
- Independent 2 speeds, may be electrical or hydraulically powered
- EX: They should not be operated on a dry windscreen
- EX: Windscreen heating sys. usually Cycle on/off to maintain a windscreen temperature between approximately 18 & 35deg
11 Pressurisation
- Why pressurise?: At hi altitude mass of O2 available is insufficient to sustain life = Hypoxia
10,000ft ur considerably affected so need to use O2
- Differential Pressue of pressurised areas of AC CAUSES HOOP STRESSES which structure must withstand
- Skin takes majority of load but frames designed to take hoop stresses
- Applied cyclically every time the AC is pressurised & de-pres. causing fatigue which could ultimately lead to structural failure
- Altitudes
- 15,000ft = Max cabin alt (emergency)
- 14.000ft Cabin O2 auto drops. Presented in HALF HUNG POSITION so pax can be on O2 by 15k
- 10,000ft = Max cabin Alt warning systems operate. Flight crew 02 via quick-don masks!!
- 8000ft Max cabin alt. (normal)
- EX: Pressurisation requirements
- Max diff press. = 9psi (jet 8-9, turbo prop 5) BUT use whatever is specific to AC!!
- Max -ve differential press. 1/2psi
- What is max RoC for pax comfort? 500fpm
- What is max RoD for pax comfort? 300fpm
- What is general AC max RoC/Rod ? 1800fpm
- Pressurised Areas = Cockpit and Fwd/Aft cabin + Fwd/Aft Cargo holds
- Unpressurised areas = U/C bays + Radome + Centre torque box etc...
- Pressurisation Operation
- AC Pack delivers air from the HP compressor. Cabin pressure controlled via PRESSURE CONTROLLERS using OUTFLOW VALVES
- Crew set cabin alt and RoC then AUTO. Max Diff Capsule in P.Controller c/f ambient press. w/ Cabin press. then this w/ setting us used to determine press. control in cabin.
- Outflow Valves: open/closed by P.Controller to control cabin press.
- Safety Valve: Press. release if cabin = 0.25 OVER MAX DIFF. Maintain cabin at 0.25 over
- Inlet relief valves: If outside press. > inside (i.e. rapid descent). Trip when diff is = 0.5-1psi
- Dump Valve: manual dump if needed
- EX: Typical Pressurisation Cycle
- Note: Cabin Alt rises in proportion to AC alt
- Outflow valves PREDOMINANTLY OPEN on ground.
- Set 'FLT' (After Start) = 0.1PSI = +ve press. to stop ingress & press. changes & press. lock doors
- Climb = RATE or PROPORTIONAL CONTROL = Cabin and AC press. in proportion
- Cruise = ISOBARIC CONTROL = maintain normal Diff P
- MAX DIFF P CONTROL = if we climb but cabin doesn't & we hit MAX DIFF P then P.Controller maintains MAX DIFF P = our AC ceiling alt.
- Descent = RATE or PROPORTIONAL CONTROL = Cabin and AC press. in proportion
- Set 'GRD' (Taxiing) = to remove 0.1PSI & release press. locks on doors etc
- Cabin Altitude Warnings
- 10,000ft : visual and aural CABIN ALT warning
- 13,850ft: AUTO FAIL light on the pressure controller panel
- 14,000ft pax oxygen masks automatically drops - into 1/2 HUNG positions - PAX OXY
- Ground Testing and checking
- Done initially + as per maint. schedule + After mods to hull/windscreen/door etc... + any malfunction
- EX: How many people do you need to do a ground pressurisation test? A = AT LEAST 2 possibly 3
- EX Q's
- EX: How do we control the pressure in the cabin? A = by the amount we let out via Outflow valves
- EX: In terms of pressurisation what indication on FD?
- Diff press. + Cabin Alt + Cabin VSI (Cabin Rate of Change aka Cabin Climb/Descent ind)
- EX: If the pipe to the gauges is blocked…which gauges affected? A = ALL OF THEM!!
- EX!!: You’re at hi alt in the cruise the cabin VSI is showing -200. The press. controller is serviceable and the pilot elects to do nothing. What will happen?
- A = The P.Controller senses max diff & opens outflow valves to keep it at max diff
- EX!!: You’re at hi alt in the cruise the cabin VSI is showing -200. The press. controller is unserviceable and the pilot elects to do nothing. What will happen?
- A = When we get to 0.25 above max diff the safety valves trip & keep the press. at max diff.
- EX: AnAC climbs from 1500' to 25000' then lands at 1000'. The Cabin altitude climes from 1500' to 4000' and lands at 1000'. Calc. the RoC and RoD of AC.
- A = RoC = 24,700fpm, RoD = 2400fpm
- Method = 1. KNOW Cabin RoC = 500fpm, RoD = 300fpm!!! 2. Determine Time to Climb for Cabin 3. Time to Climb same for AC so calc. AC RoC. 4. Do same for Descent using Cabin RoD of 300fpm
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13 Fuel Systems
- Purpose = supply engnes w/ sufficient fuel at given pressure under all operating conditions
- EX: Fuel tank types
- Integral
- Adv: Save weight, utilise space
- DisAdv: maintenance difficult
- Flexible/Bag (Rubberised fabric. Attached w/ chords or buttons)
- Adv: Easy to maintain, Self-Sealing
- Disadv: punctures
- Rigid/Drum/Fabricated (Alu tank fitted to AC after construction)
- EX: Disadv = adds significant weight
- Fuel Types
- Learn table!!
- Piston Eng Fuel: Low Flash pt, good lube, good anti-knock, wide temp range, non corrosive
- AVGAS:
- RGB FlashPt -47, FreezePt -60, SG 0.72
- 80 (Red) EX: Only used for lo compression ratio Older pistons. Could cause detonation otherwise
- 100(Green)
- 100LL (Blue)
- AVTUR - Colourless or Straw
- Jet A (US): FlashPt 38, FreezePt -40, SG 0.8
- Jet A1: FlashPt 38, FreezePt -47, SG 0.8
- FSII (Fuel system Icing Inhibitor) additives to bring the freezing/waxt pt down
- Jet B (AVTAG): FlashPt -23, FreezePt -60 - WIDE CUT fuel prohibited by EU-OPS
- EX: If fuel cloudy = Contaminated w/ water or cladosporium resinae - we have additives to get rid of it
- EX: Waxing = formation of waxy deposits or wax crystals in the fuel at lo temps
- Single Eng Gravity feed sys
- Use resistive (float) guages - VOLUME only = susceptible to temp/density changes
- EX: Only accurate in SnL unaccelerated flight
- Light AC Fuel System
- Collector/Feeder tank ensures fuel available to engine at all times when manouvering.
- Fuel stack pipe not at bottom so debris, sludge etc. avoided
- Water drains at lowest pt
- Uses float type resistive gauging = Inaccurate when AC changes attitude
- Booster pump ensures no cavitation…and back up for EDP
- Vapour lock avoided by pressurising fuel lines
- EX: We have a fuel imbalance. What can we do about it?
- Turn ON BOOSTER PUMP in 'fuller' tank > OPEN X FEED VALVE > OFF BOOSTER PUMP of receiving tank