Vfsg In Aircraft

[Boots Burnside]

Thisvideo shows a maintenance tip for proper installation of the Variable Frequency Starter Generator utilizing the spline alignment tool. This video is for reference only. Always use the approved aircraft or engine manuals, as well as proper safety equipment, when performing engine maintenance.

A constant speed drive (CSD) also known as a constant speed generator, is a type of transmission that takes an input shaft rotating at a wide range of speeds, delivering this power to an output shaft that rotates at a constant speed, despite the varying input. They are used to drive mechanisms, typically electrical generators, that require a constant input speed.

The term is most commonly applied to hydraulic transmissions found in the accessory drives of gas turbine engines, such as aircraft jet engines. On modern aircraft, the CSD is often combined with a generator into a single unit known as an integrated drive generator (IDG).

CSDs are mainly used on airliner and military aircraft jet engines to drive the alternating current (AC) electrical generator. In order to produce the proper voltage at a constant AC frequency, usually three-phase 115 VAC at 400 Hz, an alternator needs to spin at a constant specific speed (typically 6,000 RPM for air-cooled generators).[1] Since the jet engine gearbox speed varies from idle to full power, this creates the need for a constant speed drive (CSD). The CSD takes the variable speed output of the accessory drive gearbox and hydro-mechanically produces a constant output RPM.[2][3]

Different systems have been used to control the alternator speed. Modern designs are mostly hydrokinetic, but early designs often took advantage of the bleed air available from the engines. Some of these were mostly mechanically powered, with an air turbine to provide a vernier speed adjustment. Others were purely turbine-driven.[4]

On aircraft such as the Airbus A310, Airbus A320 family, Airbus A320neo, Airbus A330,[5] Airbus A330neo, Airbus A340,[6] Boeing 737 Next Generation, 747, 757, 767 and 777, an integrated drive generator (IDG) is used.[7] This unit is simply a CSD and an oil cooled generator inside the same case.[8] Troubleshooting is simplified as this unit is the line-replaceable electrical generation unit on the engine.

So the 787 engines have 2 VFSG each which are rated at 250 KW each which is 1000 KW -> 1 MW which is said to power a 2000 population town. Since the power is generated using the rotation of the engine, im assuming it does not always produce 1 MW , only at peak rotations?

What on earth in the plane sucks that much energy, I know the 787 is a more electric aircraft, but still how much power does it really take? If the total power output of the plane is 1.45 MW, I'm assuming the APU Gens are able to provide 0.45 MW in total to the airplane.

Load shedding always occurs during engine start, according to the FCOM of the B789. Both engines are allowed to start simultaneously. The B789 engines are started using both VFSGs of each engine, which are mechanically connected to the N2 shaft via the accessory gearbox. So, the VFSGs are using power instead of delivering during engine start. The APU cannot provide enough power to prevent load shedding.

If the engines are started using external power, at least two 90 kVA external power sources are required. Optimal start performance is achieved using 3 external power sources (2 on the left forward fuselage and 1 behind the left wing on the fuselage). If only 2 external power sources are used, significant load shedding can occur (e.g. First Officers displays blanks and even the audio control panel receive and trasmit selections may be lost).

In a modern twinjet airliners, if one engine-driven generator fails, load shedding is activate to protect the electrical system. What will normally be shedded is IFE and galley equipment (ovens, coffee makers, etc.). Should this happen, a checklist will direct flight crew to start the APU in order to establish normal power supply for all the equipment of the aircraft. If APU starts, the flight can continue normally. If APU is unable to start for some reason (flight could be dispatched with APU INOP, or APU generator INOP), then the crew will likely have to land at the nearest suitable airport, as the electrical reduncancy is lost.

So, in case 1 when generator fails and crew successfully starts APU, the IFE and galley equipment will not be powered for perhaps 5 minutes or so. No big deal to be honest. In case 2, where the APU is not available, the flight will have to divert to an airport, so no real need for ovens or IFE anyway.

Now, of course the manufacturers could design electrical systems that would handle this kind of failure, but the cost/benefit just doesn't support it. The generators would have to be more powerful, which would in turn lead to increased weight, wires would have to be thicker, other electrical elements would have to be designed to take the increased current/load, etc. All this, just so passengers could enjoy IFE and a hot meal during their short diversion to a nearby airfield.

Technically the VFSG are 250kVA (kilo VoltAmps). VoltAmps and Watts are only equal assuming a perfect power factor. The various systems are largely motors and controllers and do not have a particularly good power factor, so there is some losses there.

The generators are also used for starting the engines, so if a engine fails in flight the generators on the other side may be called upon to provide power to restart the opposite side while at the same time providing power to the dead engine's hydraulic system, the center system and all the loads above.

At the depths of the battery crisis in early 2013, Boeing said the 787 was performing better on reliability problems than the 777, citing slightly higher despatch reliability and slightly fewer technical error reports, called EE-1s, submitted to the US Federal Aviation Administration.

Not every airline has complained about 787 despatch reliability. Earlier this year, Boeing announced that one 787 customer had received an award for operating its first aircraft 100 days without recording a single delay related to an onboard technical problem.

For most other airlines, despatch reliability remains a sore point. Earlier this year, Boeing executives openly discussed a goal of reaching 99.5% fleet-wide despatch reliability by the second quarter of next year, matching the benchmark achieved by the 777-300ER.

One of the universally problematic parts for airlines has been the variable frequency starter/generators (VFSGs). There are two on each engine, and they represent one of the major innovations introduced by the 787. In all other commercial aircraft, functions such as cabin pressurisation and wing de-icing are powered by bleeding compressed air from the engine. To improve fuel efficiency, Boeing converted those systems to electric power. That required significantly more powerful engine-mounted generators, so Boeing introduced VFSGs on the 787 that each produce up to 250kVA of electricity.

It is an issue that Boeing acknowledges has been a long-term problem, and one that may still not be completely solved. So far, Boeing has rolled out three improved versions of the VFSG, with each upgrade requiring a reinstallation.

As each new version of the VFSG becomes available, airlines face another headache. The VFSGs deliver significantly more power than integrated drive generators on bleed-air systems, but they are also heavier.

Boeing provides tooling, such as slings, to help airline maintenance workers remove heavy equipment. Airlines also have taken more elaborate steps, such as pulling a 787 out of service for 10 days to fix various reliability issues, such as the VSFG, all at the same time. Air India reported to parliament that each aircraft in its fleet was grounded sequentially for a 10-day period between December 2013 and March 2014.

Other reliability problems have all but disappeared or are being addressed. Earlier this year, Boeing reported that electromechanical actuators for 787 spoilers were one of the two biggest reliability headaches, but the issue was resolved by a recent software update.

Hailemariam recalls early days when his pilots would push back from the gate, only to have to return after a spurious message appeared, warning of an inoperative control surface. Most of the time, there was no real issue, only a software bug.

A combination of hardware and software changes finally made the flight-control issues go away, Fleming says. But it also revealed what has become a familiar pattern. As soon as one major issue is retired, another glitch pops upthat was buried one level deeper in the system.

As for Boeing, it still has to work through at least next year to meet customer reliability targets on the 787-8. Meanwhile, it has the 787-10, three versions of the 737 Max and two versions of the 777X already in development. None employ the moon-shot level of risk that Boeing accepted with the 787-8, but that does not mean there will not be challenges.

Reporting and writing by Stephen Trimble in Addis Ababa, Seattle and Washington DC. Additional reporting by Greg Waldron in Tokyo, David Kaminski-Morrow in Palma de Mallorca, Oliver Clark in Warsaw and Firdaus Hashim in Singapore.

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An aircraft under the skin made up of different systems that allows manoeuvering, control, and operation . There are many systems such as; electrical, pneumatic, hydraulic, environmental control... Beside the main objectives to fly an aircraft with its lift producing engine(s) these systems also produces lift,drag, control and way for comfort.

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