Ameer Randolph
The de Havilland Canada DHC-6 Twin Otter is a complex aircraft with a fuel system consisting 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 mounted in tandem in the fuselage, with the forward tank having a capacity of 1235 lbs and the rear tank holding up to 1341 lbs of fuel. Each fuel cell has two vents, with one located on the top left and the other on the top right. The collector cell, located in the centre of the aircraft, contains two boost pumps, a low-level float switch, a quick drain outlet, a fuel capacity probe, a level control valve, and a sump drain.
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What You'll Learn
The Twin Otter has two fuel tanks
The Twin Otter's fuel system is quite complex and consists of two primary and two secondary fuel boost pumps, a crossfeed valve, gauges for fuel quantity and fuel flow, and a few caution lights. Each fuel cell has two vents, one located on the top left and one on the top right. There are eight vents on the left side of the aircraft and eight on the right, each connected to its respective side's vent fitting on the under-surface of the wing. The fuel vents are not heated, so a wooden bullet-shaped fitting is mounted forward of the vent opening to prevent ice buildup.
The Twin Otter has excellent climb capabilities, even near sea level with full fuel tanks and passengers. The fuel tanks have a significant impact on the aircraft's climbing and descending performance due to their positioning and the resulting pitching moments around the centre of gravity. This can cause the aft fuel tank to rotate and tilt either up or down.
The collector cell, located in the centre of the aircraft, contains two boost pumps, a low-level float switch, a quick drain outlet, a fuel capacity probe, a level control valve, and a sump drain. The feeder cells only contain a fuel capacity probe.
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They are located beneath the cabin floor
The de Havilland Canada DHC-6 Twin Otter is a complex aircraft with a unique fuel system. The fuel tanks are located beneath the cabin floor, mounted in tandem in the fuselage. This positioning allows for pitching moments around the centre of gravity when the aircraft is climbing or descending.
The Twin Otter's fuel system consists of two fuel tanks, with the forward tank having a capacity of 1235 lbs and the rear tank capable of holding 1341 lbs of fuel. The tanks are equipped with flapper valves, which play a crucial role in maintaining fuel balance during flight. The valves ensure that fuel is fed to the collector tank, located in the centre of the aircraft, to minimise the effect of fuel transfer.
The collector cell contains essential components, including two boost pumps, a low-level float switch, a quick drain outlet, a fuel capacity probe, a level control valve, and a sump drain. These components work together to monitor and regulate the fuel supply. The boost pumps are particularly important, as they provide the necessary fuel pressure to supply the engines.
During flight, the fuel tanks experience dynamic conditions, with the aft fuel tank either rotating down and tilting aft or rotating up and tilting forward. This movement influences the pitching moments and gravity effects, which impact the overall performance of the aircraft during climb and descent.
The Twin Otter's fuel system also includes caution lights and gauges for fuel quantity and fuel flow. These indicators provide critical information to the pilots, ensuring they are aware of the fuel status at all times. Overall, the unique design and positioning of the fuel tanks beneath the cabin floor contribute to the Twin Otter's excellent climb rate and complex operational characteristics.
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The forward tank holds 1235 lbs of fuel
The de Havilland Canada DHC-6 Twin Otter is a complex aircraft with a unique fuel system. The fuel tanks are mounted in tandem in the fuselage, with a forward tank and an aft tank. The forward tank has a capacity of 1235 lbs of fuel, while the rear tank can hold up to 1341 lbs.
The Twin Otter's fuel system is quite intricate, featuring two primary and two secondary fuel boost pumps, a crossfeed valve, gauges for fuel quantity and flow, and caution lights. The engines are mounted significantly above the fuel tanks, so the system relies entirely on the boost pumps to supply fuel, rather than gravity.
The forward tank's low fuel caution light will illuminate when there is 75 lbs of usable fuel left, while the aft tank's caution light will turn on when there is 110 lbs of usable fuel remaining. These lights are powered by the left and right DC bus through 5-amp circuit breakers.
The fuel tanks play a crucial role in the Twin Otter's impressive climb rate, which can exceed 1500 fpm near sea level, even with full fuel tanks and passengers on board. The positioning of the tanks and the reliance on boost pumps contribute to the aircraft's overall performance and complexity.
Overall, the forward tank's capacity of 1235 lbs of fuel is an essential aspect of the Twin Otter's fuel system, impacting the aircraft's functionality, climb rate, and overall performance. The intricate design of the fuel system showcases the engineering considerations that went into the development of this complex aircraft.
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The rear tank holds 1341 lbs of fuel
The de Havilland Canada DHC-6 Twin Otter is a complex aircraft with a unique fuel system. The Twin Otter's fuel system 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 of the Twin Otter are mounted in tandem in the fuselage. This means that during the climb or descent of the aircraft, the aft fuel tank rotates either up and forward or down and backward.
The rear tank of the Twin Otter holds 1341 lbs of fuel, while the forward tank has a capacity of 1235 lbs. The difference in capacity between the two tanks is due to the positioning of the engines, which are mounted significantly above the fuel tanks. This means that the system relies completely on the fuel pumps, rather than gravity, to supply fuel to the engines.
The fuel selector on the Twin Otter has three positions: "Both Fwd," "Norm," and "Both Aft." The boost pumps have a nominal output of 450 pounds per hour and a pressure of 22 psi. When the fuel selector is positioned on crossfeed, both boost pumps turn on in the collector cell on the selected tank, while the boost pump on the non-selected tank automatically turns off.
The collector cell for the aft tank is Cell 5, which feeds the engines through two booster pumps and associated check valves. The booster pumps draw fuel from Cells 6, 7, and 8 into the collector cell. The low fuel caution light for the aft tank will illuminate when there is 110 lbs of usable fuel left, providing an important indication to the pilot.
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The tanks are filled via ports on the left fuselage
The de Havilland Canada DHC-6 Twin Otter is a complex aircraft with a fuel system consisting 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 filled via ports on the left fuselage, and the aircraft's climb rate is excellent, even near sea level with full fuel tanks.
The forward and aft fuel tanks are mounted in tandem in the fuselage, with the engines positioned significantly above them. This means that the engines cannot be supplied with fuel by gravity, so the system relies entirely on the fuel pumps. The forward tank has a capacity of 1235 lbs, while the rear tank can hold up to 1341 lbs of fuel.
Each fuel cell has two vents, one located on the top left and the other on the top right. These vents are connected to the left and right sides of the aircraft's exterior, with eight vents on each side. The fuel vents are not heated, but a wooden, bullet-shaped fitting mounted forward of the vent opening prevents ice buildup.
The fuel selector has three positions: "Both Fwd," "Norm," and "Both Aft." When the fuel selector is on "Norm," the boost pumps are automatically turned on in the collector cell on the selected tank, and the boost pump in the non-selected tank is turned off. The boost pumps have a nominal output of 450 pounds per hour and a pressure of 22 psi. The excess output from the boost pumps is used to transfer fuel to the collector cells in each tank through a motive flow valve, also known as an ejector or jet pump.
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Frequently asked questions
The Twin Otter's fuel system consists of two fuel tanks, with the forward tank having a capacity of 1235 lbs and the rear tank having a capacity of 1341 lbs. The fuel tanks are mounted in tandem in the fuselage.
A float switch connected to a caution light on the main annunciator panel indicates low fuel. The forward tank's low fuel caution light will illuminate when there is 75 lbs of usable fuel left, while the aft tank's light will turn on when there is 110 lbs of usable fuel left.
Each tank has a collector cell, with the forward tank's collector cell being Cell 4 and the aft tank's collector cell being Cell 5. The collector cells contain two boost pumps that help transfer fuel.
