Regan Brown
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 located beneath the cabin floor and are arranged in tandem in the fuselage. The forward tank has a capacity of 1235 lbs, while the rear tank can hold up to 1341 lbs of fuel. The engines are mounted above the fuel tanks, requiring the system to rely on fuel pumps rather than gravity. The fuel tank filler ports are located on the left side of the fuselage, with only one port for each tank.
| Characteristics | Values |
|---|---|
| Number of fuel tanks | 2 |
| Location of fuel tanks | Beneath the cabin floor |
| Fuel tank arrangement | In tandem |
| Capacity of the forward tank | 1235 lbs |
| Capacity of the rear/aft tank | 1341 lbs |
| Fuel tank filler port location | On the left side of the fuselage |
| Fuel selector selections | Both Fwd, Norm, Both Aft |
| Fuel boost pumps | 2 primary and 2 secondary |
| Fuel gauge indication | AC powered |
| Backup for fuel gauge indication | DC power from the low fuel indication lighting system |
| Power for fuel flow indicators | 400-cycle, 26-volt AC bus |
| Fuel low level caution light activation for forward tank | <75 lbs of fuel remaining |
| Fuel low level caution light activation for aft tank | <110 lbs of fuel remaining |
| Power source for fuel low level caution lights | Left and right DC bus through 5-amp circuit breakers |
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What You'll Learn
The Twin Otter has two fuel tanks, located beneath the cabin floor
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 located beneath the cabin floor and are arranged in tandem, with the forward tank having a capacity of 1235 lbs and the rear tank able to contain up to 1341 lbs of fuel.
The engines of the Twin Otter are mounted significantly above the fuel tanks, which means that the system relies entirely on the fuel pumps to supply fuel to the engines. In normal operation, when the fuel tank selector is set to "NORM", the forward 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.
The Twin Otter's fuel system also includes a collector cell, which stays full until the feeder cells are empty. The collector cell 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. Each tank has four fuel drains on the belly of the aircraft, with one fuel drain in each collector cell and one at the lowest part of the fuel transfer manifold.
The fuel low-level caution lights illuminate when the forward tank contains less than 75 lbs of usable fuel, and the rear tank contains less than 110 lbs. The quantity gauge is the primary source for indicating low fuel, and a float switch is connected to a caution light on the main annunciator panel.
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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 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 located beneath the cabin floor and are arranged in tandem, with the forward tank holding 1235 lbs of fuel and the rear tank holding 1341 lbs. The engines are mounted significantly above the fuel tanks, so the system relies entirely on the fuel pumps to operate.
The forward tank's low fuel caution light will illuminate when there is less than 75 lbs of usable fuel left, while the rear tank's caution light will turn on when there is less than 110 lbs left. The forward tank feeds the right engine, and the rear tank feeds the left engine during normal operation (when the fuel tank selector is set to NORM). However, when the tank selector is changed 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.
The Twin Otter's fuel tanks are an essential component of its complex system, ensuring the aircraft has the necessary fuel supply for its operations. The forward tank, with its capacity of 1235 lbs of fuel, plays a crucial role in powering the aircraft and enabling it to undertake its intended functions.
The fuel system of the Twin Otter is designed to supply fuel to the engines from the two tanks. The forward tank, with its substantial capacity, is responsible for powering the right engine during normal operation. The fuel boost pumps play a critical role in ensuring the fuel is effectively delivered to the engines, as the elevation of the engines above the tanks prevents gravity from being used for fuel transfer.
The caution lights in the fuel system are an important safety feature, alerting pilots to low fuel levels. With the forward tank's caution light activating at 75 lbs, it provides timely notification of the need to refuel or switch to an alternative fuel configuration. The fuel system's functionality, including the forward tank's capacity and associated mechanisms, contributes to the overall performance and operability of the Twin Otter 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 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 located beneath the cabin floor and are arranged in tandem, with the engines positioned above them. This setup means that the system relies entirely on the fuel pumps, as the fuel cannot be supplied to the engines by gravity.
The rear tank in the DHC-6 Twin Otter holds 1341 lbs of fuel, while the forward tank has a capacity of 1235 lbs. In normal operation, when the fuel tank selector is set to 'NORM', the forward tank feeds the right engine, and the rear tank feeds the left. The fuel low-level caution lights will illuminate when the forward tank contains less than 75 lbs of usable fuel, and when the rear tank contains less than 110 lbs.
The fuel tanks of the Twin Otter are mounted in tandem in the fuselage, and have pitching moments around the centre of gravity when the aircraft is climbing or descending. This movement causes the aft fuel tank to rotate and tilt, which, in turn, affects the pitching moments. To counteract this, flapper valves are used to equalise the fuel levels and maintain stability.
The rear tank's capacity of 1341 lbs of fuel allows for a significant amount of fuel to be stored, ensuring that the Twin Otter can undertake a range of operations without the constant need for refuelling. This fuel capacity, along with the aircraft's complex fuel system, contributes to the overall performance and functionality of the DHC-6 Twin Otter.
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The fuel system includes two primary and two secondary fuel boost pumps
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 and are arranged in tandem. The forward tank has a capacity of 1235 lbs, while the rear tank can hold up to 1341 lbs of fuel. Due to the engines being mounted significantly above the fuel tanks, the system relies entirely on fuel pumps to supply fuel to the engines. The fuel system includes two primary and two secondary fuel boost pumps, ensuring uninterrupted fuel supply to the engines.
The primary boost pumps, also known as the number 1 boost pumps, are crucial for normal operations. They are powered by the left and right DC buses, with the left DC bus powering the number 1 pumps and the right DC bus powering the standby pumps. In normal operation, when the fuel tank selector is set to "NORM", the forward tank feeds fuel to the right engine, while the rear tank supplies the left engine. The primary boost pumps play a vital role in ensuring a steady flow of fuel from the respective tanks to the engines.
The secondary boost pumps, also referred to as the number 2 boost pumps, serve as a backup system. If the primary boost pump fails or experiences a significant drop in output pressure, the secondary boost pump automatically activates. This redundancy ensures uninterrupted fuel supply to the engines. The secondary boost pumps can also be manually activated through the "STANDBY BOOST PUMP EMER" switches in the cockpit.
The boost pumps supply fuel through the collector cell to the fuel strainer, fuel flow transmitter, and the fuel emergency shutoff valves before it reaches the engine pumps. Each collector cell contains two boost pumps, ensuring redundancy within the cell itself. The collector cell plays a crucial role in minimising the impact of fuel transfer and maintaining a stable fuel supply during various flight attitudes.
The Twin Otter's fuel system also incorporates caution lights and indicators to monitor fuel levels and boost pump performance. For instance, the "FUEL LOW LEVEL" caution lights illuminate when the forward tank contains less than 75 lbs of fuel or the rear tank dips below 110 lbs. Additionally, a boost pump caution light alerts pilots to any issues with the boost pumps, such as a drop in pressure below the acceptable threshold.
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The fuel tank filler ports are located on the left side of the 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 located beneath the cabin floor and are mounted in tandem in the fuselage. The forward tank has a capacity of 1235 lbs, while the rear tank can hold up to 1341 lbs of fuel.
The fuel tank filler ports, which are used to activate the fuel system, are located on the left side of the fuselage. There is only one port for each tank. This is an important detail to note, as it is specific to the left side. The location of these filler ports is essential for operational purposes, ensuring that the aircraft can be refuelled efficiently and effectively.
The fuel tanks play a crucial role in the overall functionality of the Twin Otter aircraft. With the engines positioned significantly above the fuel tanks, the system relies entirely on the fuel pumps to supply fuel. This unique design, where the engines are higher than the fuel tanks, necessitates the use of fuel pumps to ensure a consistent and adequate flow of fuel during flight.
The fuel tank filler ports being on the left side of the fuselage is a defining characteristic of the Twin Otter's fuel system. This design choice has implications for the refuelling process, accessibility, and overall aircraft performance. It is a key detail that operators and maintenance personnel must be aware of to ensure the safe and efficient operation of this complex aircraft.
Understanding the location of the fuel tank filler ports is essential for the proper maintenance and operation of the Twin Otter. This knowledge ensures that ground crews and pilots can efficiently refuel the aircraft, and it underscores the importance of the fuel system in the overall functionality of this aircraft.
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Frequently asked questions
The fuel tanks are located beneath the cabin floor and are arranged in tandem.
A Twin Otter has two fuel tanks.
The forward tank can hold up to 1235 lbs of fuel.
