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De Havilland Canada DHC-6 Twin Otter: Difference between revisions
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Added systems overview, WIP
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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> == | |||
{{WIP}} | |||
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, directional gyro, lighting, auto-feather | |||
* Fuel: Supplies engines with fuel from two fuel tanks | |||
* Hydraulic: Operates flaps, nose wheel steering, and wheel brakes | |||
* [[FGproperties/Systems/Pitot|Pitot]]: Supplies airspeed indicators with dynamic pressure | |||
* Pneumatic/Bleed Air: Operates heating and de-icing system and intake deflectors | |||
* [[FGproperties/Systems/static|Static]]: Supplies airspeed indicators, altimeters and vertical speed indicators with static pressure | |||
* [[Aircraft systems#Vacuum|Vacuum]]: Drives gyros for artifical horizon and directional gyro/heading indicator | |||
Pleas note that as of July 2016 not all of these systems are implemented! | |||
=== Electrical system === | |||
The electrical system is fed by an 40 ampere-hour battery and two engine-driven generators (which operate as starter-motors when starting the engine). It is primarily a 28 volt, direct current (DC) system, but some components need alternating current (AC) to work. | |||
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 | |||
# Right 28V DC bus: Is driven by right engine's generator. It feeds the propeller overspeed governor, crossfeed fuel valvesecondary 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. | |||
# 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. | |||
# Battery/External Power bus: Is controlled by the EXTERNAL/BATTERY selector switch. When EXTERNAL is selected, it isolates the battery and connects the external power unit to the left and right bus. BATTERY will connect the battery to the left and right bus when generators are not running or the generator voltage is lower than the battery voltage. If the generator voltage is highter than the battery voltage it connects the left and right bus to the respective generator. When swithced off, the whole electrical system gets disconnected. | |||
# 26V AC bus: Torque presure, fuel flow, and oil pressure gauges, | |||
# 115V AC bus: Fuel quantity gauges, vacuum pumps for gyros (artifical horizon and directional gyro | |||
The two AC buses are fed from one of the two static inverters. The No.1 inverter receives power from the Left 28V DC bus (and hence from the left generator), and the No.2 inverter receives power from the right 28V DC bus (and hence from the right generator). The inverters are selected alternatively by the inverter switch located on the overhead panel. | |||
=== Fuel system === | |||
The Twin Otter's fuel systems consists of two fuel tanks, two primary fuel boost pumps, two secondary boost pumps, a crossfeed valve, gauges for fuel quantity and fuel flow, and a few caution lights. | |||
The fuel tanks are located beneath the cabin floor and arranged in tandem. While the forward tank has a capacity of 1235 lbs the rear tank can contain up to 1341 lbs of fuel. With the engines mounted significantly above the fuel tanks the engines cannot bes supplied with fuel by gravity and hence the system has to rely completely on the fuel pumps. In normal operation (i.e. when the fuel tank selector is set to NORM) the foward tank feeds the right engine and the rear tank feeds the left engine. | |||
However when the tank selector is set to BOTH ON FWD or BOTH ON AFT the boost pumps on the non-selected tank are deactivated and both boost pumps on the selected tank are activated which overwrites the boost pump switches. | |||
The cross-feed valve is powered by the right DC bus, i.e. to work properly it needs either the battery connected or the right generator to be online. | |||
If the primary boost pump fails, the secondary boost pump will automatically activate and the BOOST PUMP 1 FWD/AFT PRESSURE will light up. However the secondary boost pumps can be activated manually through the STANDBY BOOST PUMP EMER switches. | |||
The FUEL LOW LEVEL caution lights will illuminate when the forward tank contains less than 75 lbs resp. the rear tank contains less than 110 lbs of fuel. | |||
For the Twin Otter we have a refuelling system whereby you can easily refuel your Twin Otter or drain the tanks. To activate the fuel system, click on one of the fuel caps located on the left side of the fuselage or go to "Menu" -> "DHC-6" -> "Options" -> "Ground Services" -> "Fuel Truck controls". | |||
=== 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 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. | |||
=== Pitot system === | |||
A working pitot system is very essential for safe flight, although it is connected to only one instrument: The airspeed indicator (ASI). But if the ASI fails you have no opportunity to know your airspeed and you end up very likely in a stall or even a crash. | |||
The Twin Otter has two indepentently working pitot systems. The left pitot system feeds the pilot's ASI and the right pitot system feeds the copilot's ASI with dynamic pressure. | |||
The two pitot tubes are located on the side of the fuselage in front of the pilot's (resp. copilot's) door. Make sure you removed the pitot tube covers from the pitot tubes prior to the flight or your ASI won't indicate your airspeed but act similar to an altimeter as in this case only static pressure is provided. | |||
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. | |||
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