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De Havilland Canada DHC-6 Twin Otter: Difference between revisions
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== Systems overview<ref>[http://www.cram.com/flashcards/twin-otter-dhc6-300-1980260 Twin Otter flashcards on cram.com]</ref><ref>[http://www.aerosoft2.de/downloads/twotter/Manual-Twin-Otter-Extended-Vol2-Systems.pdf Systems manual of Aerosoft's Twin Otter Extended]</ref> == | == Systems overview<ref>[http://www.cram.com/flashcards/twin-otter-dhc6-300-1980260 Twin Otter flashcards on cram.com]</ref><ref>[http://www.aerosoft2.de/downloads/twotter/Manual-Twin-Otter-Extended-Vol2-Systems.pdf Systems manual of Aerosoft's Twin Otter Extended]</ref> == | ||
The Twin Otter is equipped with several [[Aircraft systems|systems]] which operate the aircraft's components: | The Twin Otter is equipped with several [[Aircraft systems|systems]] which operate the aircraft's components: | ||
* Electrical: Operates i. a. hydraulic pump, boost pumps, engine gauges, | * Electrical: Operates i. a. hydraulic pump, boost pumps, engine gauges, turn coordinator, lighting, auto-feather | ||
* Fuel: Supplies engines with fuel from two fuel tanks | * Fuel: Supplies engines with fuel from two fuel tanks | ||
* Hydraulic: Operates flaps, nose wheel steering, and wheel brakes | * Hydraulic: Operates flaps, nose wheel steering, and wheel brakes | ||
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There exist seven buses which provide electrical power to several components: | There exist seven buses which provide electrical power to several components: | ||
# Left 28V DC bus: Is driven by left engine's generator. It feeds the DC voltmeter, hydraulic pump, prop auto-feather system, fire detection system, primary boost pumps (forward and rear), "R GEN FAIL" caution light | # Left 28V DC bus: Is driven by left engine's generator. It feeds the DC voltmeter, hydraulic pump, prop auto-feather system, fire detection system, primary boost pumps (forward and rear), "R GEN FAIL" caution light | ||
# Right 28V DC bus: Is driven by right engine's generator. It feeds the propeller overspeed governor, crossfeed fuel | # Right 28V DC bus: Is driven by right engine's generator. It feeds the propeller overspeed governor, crossfeed fuel valve, secondary boost pumps (forward and rear), "L GEN FAIL" caution light | ||
# Aux battery bus: Uses a auxiliary 3.6 ampere-hour battery to support the starter motors when starting the engines. | # Aux battery bus: Uses a auxiliary 3.6 ampere-hour battery to support the starter motors when starting the engines. | ||
# Main battery bus: Is controlled by the Master Battery switch. When switched off, only the interior lights are provided with power. When MASTER is selected, it connects the electrical system to generators or battery or external power, depending on the EXTERNAL/BATTERY selector switch position. | # Main battery bus: Is controlled by the Master Battery switch. When switched off, only the interior lights are provided with power. When MASTER is selected, it connects the electrical system to generators or battery or external power, depending on the EXTERNAL/BATTERY selector switch position. | ||
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=== Hydraulic system === | === Hydraulic system === | ||
The Twin Otter has a quite simple hydraulic system which is mostly fully automated. Hydraulic pressure is provided by an electrical pump which gets it's power from the left electrical bus. Only a few components are operated hydraulically: Nose wheel steering, wheel brakes, and flaps. If the hydraulic system fails or is inactive, you can still move the flap lever or the nose wheel steering bar, but it won't have any effect on the nose wheel or flap setting. | The Twin Otter has a quite simple hydraulic system which is mostly fully automated. Hydraulic pressure is provided by an electrical pump which gets it's power from the left electrical bus. Only a few components are operated hydraulically: Nose wheel steering, wheel brakes, and flaps. | ||
If the hydraulic system fails or is inactive, you can still move the flap lever or the nose wheel steering bar, but it won't have any effect on the nose wheel or flap setting. | |||
The only manual control is a mechanic hand pump whih can be used as a backup in case of an failure of the electric pump. The hand pump is stowed behind the copilot's seat. | The only manual control is a mechanic hand pump whih can be used as a backup in case of an failure of the electric pump. The hand pump is stowed behind the copilot's seat. | ||
=== Pneumatic/Bleed air system === | |||
The very simple pneumatic system of the Twin Otter is only used to provide hot air for the heating and the de-icing system. | |||
Two switches labeled "BLEED AIR" on the overhead panel control the bleed air valve on the left (resp. right) engine. | |||
To get the pitot heat and the prop de-icing working, you have to switch on the bleed air switches. | |||
The intake deflectors are also extended pneumatically, but they don't need the bleed air switch to be activated. Instead they need GG RPM (also called "N2", or "Ng") to be higher than 80 percent. | |||
=== Pitot system === | === Pitot system === | ||
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If you notice some odd behaviour of the ASI in flight (e.g. accelerating in climb and decelerating in descent) this is a strong indication of a iced pitot tube. Switch on the pitot heat to prevent icing. | If you notice some odd behaviour of the ASI in flight (e.g. accelerating in climb and decelerating in descent) this is a strong indication of a iced pitot tube. Switch on the pitot heat to prevent icing. | ||
=== Static system === | |||
There are three instruments that work with static pressure: Airspeed indicator (ASI), altimeter (ALT), and vertical speed indicator (VSI). The Twin Otter has a total of four static ports which are located in front of the cockpit doors, two on each side. As they are not pointing into the airstream they are not in danger of icing. | |||
Now what happens in case of an failure of the pitot and/or the static system? | |||
{| class="wikitable" | |||
|- | |||
!Instrument | |||
!Static failure | |||
!Pitot failure | |||
!Both failure | |||
|- | |||
!VSI | |||
|fixed at 0 | |||
|normal indication | |||
|fixed at 0 | |||
|- | |||
!ALT | |||
|fixed at current value | |||
|normal indication | |||
|fixed at current value | |||
|- | |||
!ASI | |||
|Ascent: indicates too slow | |||
Descent: indicates too fast | |||
|Ascent: Indicates too fast | |||
Descent: Indicates too slow | |||
|fixed at current value | |||
|} | |||
=== Vacuum system === | |||
Each engine has a vacuum pump that drives the gyros for the attidude indicators and the directional gyros. | |||
The vacuum pump is powered by the gas generator (GG) of the respective engine. | |||
== Keyboard shortcuts == | == Keyboard shortcuts == | ||