Airstart Unit

[Shinyoung Gedris]

TheRheinmetall eMSU allows for carbon-free engine starts and reduction in overall ground operation emissions. It is powered by lithium-ion battery packs that ensure maximum running time and minimal energy loss. The eMSU requires very low maintenance and is designed to thrive in harsh conditions. This fully electric air start unit requires no warm-up or cool-down phase. It is the greenest ASU solution on the market.

The only turbine-powered ASU on the market, the Rheinmetall MSU keeps commercial aircraft running on time. Designed to be reliable and versatile, the Rheinmetall MSU is powered by gas turbine engines that are unique in their class. Proven across the globe in any climate conditions, the MSU is also remarkably easy to operate and store with its compact size.

The air start cart is rarely used because it is so loud, and probably expensive to the operator. I imagine at least 95% of all starts are done on APU, which most airports will allow the crew to use up to 20-30 min before push back. Depends on location. If you have an APU you're going to use it.

I saw an airstart being used on N668US - one of Delta's 747-400s in Detroit last Wednesday. I had a two hour layover waiting for a flight home, and stopped into Leo's Coney Island restaurant for lunch. The restaurant is adjacent to gate A50, and the Queen was parked right outside, so I made sure to get a seat right by the window on the airside. The aircraft was loading for departure to Narita as flight 275.

Sure enough, after the doors were closed, and the airbridge retracted, the ramp crew disconnected the conditioned air hoses, but left the bleed air hose connected. They started engine 4 at the gate. They did not disconnect the bleed air supply hose, or the ground power connection until the engine had been running for about two minutes. They pushed back as usual, and I assume did a cross bleed start of the remaining engines (one at a time) once they were on the taxi line.

i also noticed that the ground crewman who disconnected the bleed air supply line, was wearing high temp firefighter-style gloves, as I imagine that the coupling at the end of the hose was extremely hot, even after the pneumatic supply from the cart had been shut off!

Here in the States, I don't think you're going to find much of that sort of restriction. That sort of thing is usually found in the EU, with the exception of perhaps SMO over here (which is essentially an EU airport with all of the over-regulation).

I'd also argue that the start cart is rarely used simply because APUs are usually not deferred, and it's a somewhat safer operation. The expensive part is definitely true, however, I think it's more on the fact that the units are expensive, and are usually operated by people who are prone to breaking them. I cannot tell you how many times I had to tell the rampies "turn it on, let it idle for a bit while you wait, bring it up to full power when the crew requests the start, let them start, and once they tell you to disconnect, bring it back to idle and continue to let it run while you disconnect it and tow it away. Again: leave it running while you tow it away so it can cool down." Sure enough, they'd go start one plane and then immediately turn the thing off, which kills oil circulation and causes parts to fuse up, meaning that the next plane that needed it didn't get one that worked. That maintenance bill, of course, will also be expensive. The units themselves are so expensive (and infrequently used) that the operator usually has only one of them, and maybe a second if it's a major hub. If it's an outstation, it's hit or miss, and if there is one, it's usually the airport operator or management company that owns it.

Start cart for engine starts is rare, and usually only if the APU (or APU bleed) is deferred for some reason. Similarly, APU to pack takeoffs are pretty rare, except for certain weight situations, or specific airports due to their elevations/temps. Depending on the plane, the start cart procedure can decrease ramp safety (compared to the APU start), because certain aircraft have the high pressure port right next to the engines. Additionally, on an aircraft like the CRJ700/900/1000, you need a ladder to get up to it, and certain ramp management companies cannot differentiate between actual safety and notional safety, putting their people in a bind. As an example, one ramp company specifically forbade using the belt loader as a platform to get up to the port, simply because it was "not what it was designed for." Climbing up a ladder single handed with a semi-pressurized hose, however, was definitely less safe, and not as stable, but was the required method because "that's what a ladder was designed for." One of the many things I've stored in the "if I ever have to write ramp procedures at some point in my life" manual.

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The TLD ASU-600-100-CUP and ASU-600-150-CUP Continuous Flow Aircraft Jet Engine Air Start Units (ASU) produce 100 & 150 PPM and up to 40 PSIG start air pressure to meet the needs of most regional jets and narrow body aircraft. The TLD ASU-600 Series Air Start Units can be configured as skid or trailer mounted units.

Basic components include an air-cooled rotary screw compressor, diesel engine, and the TLD air regulating system. Standard features include dual mode operation, automatic throttle rollback and an easy access canopy. These components and features combine to produce the most versatile and cost-efficient air start units available.

Compared to a gasoline (petrol) engine, a diesel engine has a very high compression ratio, an essential design feature, as it is the heat of compression that ignites the fuel. An electric starter with sufficient power to turn a large diesel engine would itself be so large as to be impractical so there is a need for an alternative system.

When starting the engine, compressed air is admitted to whichever cylinder has a piston just over top dead center, forcing it downward.[2] As the engine starts to turn, the air-start valve on the next cylinder in line opens to continue the rotation. After several rotations, fuel is injected into the cylinders, the engine starts running and the air is cut off.

To further complicate matters, a large engine is usually "blown over" first with zero fuel settings and the indicator cocks open, to prove that the engine is clear of any water build up and that everything is free to turn. After a successful blow ahead and a blow astern, the indicator cocks are closed on all the cylinders, and then the engine can be started on fuel. Significant complexity is added to the engine by using an air-start system, as the cylinder head must have an extra valve in each cylinder to admit the air in for starting, plus the required control systems. This added complexity and cost limits the use of air-starters to very large and expensive reciprocating engines.

Another method of air-starting an internal combustion engine is by using compressed air or gas to drive a fluid motor in place of an electric motor.[3] They can be used to start engines from 5 to 320 liters in size and if more starting power is necessary two or more motors can be used. Starters of this type are used in place of electric motors because of their lighter weight and higher reliability. They can also outlast an electric starter by a factor of three and are easier to rebuild. Engines operating in underground mining activities tend to operate on this type of starter system to reduce the risk of an electrical system igniting flammable material.

Not all air starters require lubrication. Turbine type air starters do not require air motor lubrication, although some turbine air starters do use an oil filled transmission that may require periodic inspections and maintenance.

Compressed air has been used to start gas turbine engines using air impingement starting (in which air is directed at the engine turbine blades through nozzles in the turbine casing, used on US Navy General Electric J79 engines). It is much more efficient to use an air turbine starter (ATS) which is usually mounted on an accessory gearbox.[5] An early axial compressor turbojet had an ATS located in the compressor nose cone (eg particular variants of the J79).

Air impingement starting was not used for US military aircraft after the F-4B, A-5A[6] and F-5 as the pneumatic energy requirement was several times greater than when using an air turbine starter. The gas turbine compressor required to start a J79 with impingement starting was sufficient to start two J79 engines simultaneously in a B-58 when using air turbine starters.[7]

An ATS has its own turbine and gears to change its low torque and high speed to low speed and high torque at the engine mounting pad. Further gears in the engine gearbox connect to the engine shaft (high pressure spool on multi-spool engines). Compressed air is sent to the ATS turbine from the aircraft auxiliary power unit ( bleed air from the gas generator or from a free-turbine load compressor, eg PW901 APU), from an already-running engine (bleed air) on a multi-engined aircraft or, for early jet aircraft, from an air compressor mounted on ground support equipment.

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