bio15
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What Is The Starter Like?

Mon Jul 03, 2006 3:21 pm

I am aware of how an engine startup procedure works, but I'm not familiar with what is the starter. I have in mind that the APU or ground airsource will supply pneumatic pressure and therefore an air flow for spinning the engine compressor. But then, is the starter just a name for a valve that opens or closes to let this air be fed into the compressor stage, or is it something more sophisticated?


Alfredo
 
KAUSpilot
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RE: What Is The Starter Like?

Mon Jul 03, 2006 3:39 pm

More sophisiticated than that, at least in my aircraft.

The ATS (Air Turbine Starter) is installed in a dedicated engine accessory gearbox pad and consists basically of an air inlet, an impller turbine, a reduction gearset, a clutch, and an output shaft.

The ATS converts pneumatic energy into driving torque for engine gas generator spool acceleration up to the self-sustained speed during the starting cycle. The air exhaust from the turbine is discharged inot the engine nacelle compartment.

Basically, the starter converts air from the APU or airstart cart into mechanical energy for a rotating starter shaft....this shaft rotates the compressor section when the starter is engaged. After lightoff, the starter shaft is disengaged, allowing the engine to attain self-sustained idle.
 
n8076u
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RE: What Is The Starter Like?

Mon Jul 03, 2006 3:53 pm

Simply stated, the starter is powered by air. A "start valve" opens, allowing the bleed air to reach the starter, and the impeller inside the starter gets spun from that air (like a children's pinwheel when you blow on it). The starter is bolted to the engine's gearbox. The starter turns the engine through the gearbox. The whole setup works more or less like a starter in a car, except the starter is air powered rather than electrically powered. Another way to look at it is to compare the starter to an air drill that is powered by compressed air, as the pressurized air is converted to a mechanical spinning motion.

Okay, maybe that wasn't so simply stated.  Wink

Chris
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tepidhalibut
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RE: What Is The Starter Like?

Mon Jul 03, 2006 4:06 pm

...and I'll take a spin at explaining things.

When flying, the engine sucks in air, and a proportion goes through the core, when the turbine turns the compressor. A portion of that HP system torque is fed through a radial drive shaft, and rotates an accessory gearbox. On that gearbox are a number of units which use that rotational enery to power the hydraulics, pump fuel, produce electricty, etc.

When starting, things work in reverse.
- Compressor air is fed into a small turbine, which starts rotating.
- This drives the accessory gearbox, which starts pumping fuel.
- More importantly, the radial drive shaft now rotates the HP system.
- The HP system starts sucking air through the core.
- With sufficient airflow, fuel and sparkplugs, the engine lights and begins to accelerate.
- When the engine is running fast enough, and the combustor is self sustaining, the starter disengages and the pilot has to wake up.

HTH
 
Goldenshield
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RE: What Is The Starter Like?

Mon Jul 03, 2006 9:03 pm

Quoting Bio15 (Thread starter):
But then, is the starter just a name for a valve that opens or closes to let this air be fed into the compressor stage, or is it something more sophisticated?

On many smaller turbines (turboprops and many business jets,) the starter is an electric motor that doubles as a generator.
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G4Doc2004
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RE: What Is The Starter Like?

Tue Jul 04, 2006 1:09 am

Here is a good cross section view of an ATS, the air inlet being on the left.


Big version: Width: 350 Height: 341 File size: 38kb
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jarheadk5
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RE: What Is The Starter Like?

Tue Jul 04, 2006 3:15 am

There are also hydraulic starters - the GE T64 uses a 4000psi hydraulic motor to spin the gas generator up for starting, through the engine accessory gearbox. Once fuel is introduced and the gas generator is accelerating on it's own, the starter is depressurized and an over-running clutch prevents the engine from back-driving the starter.
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MissedApproach
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RE: What Is The Starter Like?

Tue Jul 04, 2006 8:00 am

Quoting JarheadK5 (Reply 6):
the GE T64 uses a 4000psi hydraulic motor

Okay, chicken or egg time. Assuming everything's been off over the weekend, where does the hydraulic pressure come from? Is it stored in an accumulator or does an electrically driven pump supply pressure?
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n8076u
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RE: What Is The Starter Like?

Tue Jul 04, 2006 8:19 am

Quoting MissedApproach (Reply 7):
Okay, chicken or egg time.

That seems to happen quite often around here.  Wink

And to further muddy the waters, the SR-71 had a V-8 powered "start cart" which was hooked up to the aircraft through a driveshaft setup.

The only thing absolute in aviation is there's always an exception to the rule.

Chris
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Dougloid
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RE: What Is The Starter Like?

Tue Jul 04, 2006 8:56 am

Quoting JarheadK5 (Reply 6):
There are also hydraulic starters - the GE T64 uses a 4000psi hydraulic motor to spin the gas generator up for starting, through the engine accessory gearbox. Once fuel is introduced and the gas generator is accelerating on it's own, the starter is depressurized and an over-running clutch prevents the engine from back-driving the starter.



Quoting N8076U (Reply 8):
And to further muddy the waters, the SR-71 had a V-8 powered "start cart" which was hooked up to the aircraft through a driveshaft setup.

Another variation on the famed 'donkey dick' rig of A4 fame. Don't forget some of the early ones used combustion starters too...I b'lieve the B57 Canberra was one. We had a big discussion about this here a while ago.

Let me see if I can still do this. Sound of a 331 starting.

Shkrrrrrrrrrrrrrrrrreeeeeeeeeeeeeeeeeeeeeeeeeeeeetiktiktiktiktiktikwhooooooooooosssssssssshhhhhhhhphoooooooooooooooo and you're at ground idle.


 Wink  Wink  Wink
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60Mech
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RE: What Is The Starter Like?

Tue Jul 04, 2006 9:30 am

For hydraulic starters, the charge is stored in an accumulator for long periods. The charge can leak out though. One of our helos has had accumulator problems (ie. won't hold a charge for very long) and we have replaced nearly every component in the system. Darn Sikorsky's.
 
bio15
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RE: What Is The Starter Like?

Tue Jul 04, 2006 9:52 am

Excellent answers everyone, it's perfectly clear thanks. It seemed a bit odd to me that the air would be ducted directly into the compressor.


Taking a look into G4Doc2004's image, the turbine impeller shaft goes through a gear reduction after which the rotation should be passed to the accesory gearbox. Does the accesory gearbox increase the starter's RPMs (decrease the engine's RPMs in other words)? This is to get an idea of what are the average starter impeller RPMs versus the actual RPMs delivered to the compressor after going through the starter assembly reduction gears, and the ones on the accesory gearbox. I'm guessing the starter is a fast spinner, right?


Alfredo
 
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RE: What Is The Starter Like?

Tue Jul 04, 2006 10:34 am

Quoting N8076U (Reply 8):
And to further muddy the waters

Me too... one of my professors who was a former B52 driver and commander of a major air wing always talks about the cartridge starts they used to do with the buffs. The way I understand it was that this explosive cartridge (not sure of the materials, etc.) was placed in front of the compressor at a specific spot and when the charge blew, it spun the engine enough to attain speed for a lightoff...
Any further, better, or completely different and much more accurate explanations are welcome... Smile

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n8076u
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RE: What Is The Starter Like?

Tue Jul 04, 2006 10:35 am

Quoting Dougloid (Reply 9):
'donkey dick rig'

I'll have to remember that for future discussions. Priceless...

Quoting Bio15 (Reply 11):
Does the accesory gearbox increase the starter's RPMs (decrease the engine's RPMs in other words)?

Again, there may be an exception to this, but on the stuff I've worked on (turbofans on commercial airliners), for every one revolution that the engine itself (n2 to be more accurate) turned, the gearbox accessories turned less than one revolution, exactly how much I could not say.

We had some old aircraft tugs that had air starters to get their turbocharged V-12 diesel engines going. The air was kept in a huge airtank in the bowels of the tug. So air-starters aren't just for airplanes.  Smile

Chris
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3DPlanes
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RE: What Is The Starter Like?

Tue Jul 04, 2006 11:35 am

Quoting CptSpeaking (Reply 12):
Any further, better, or completely different and much more accurate explanations are welcome...

As I understand it, the cartridges in the Buffs burned rather than fired. (No real first-hand experience, mind you.) IIRC, they generated gasses (and SMOKE!) which turned the starter.

I think the cartridges were more for the "Oh cr*p, the missiles are inbound!" kind of starts. The times when they didn't have the luxury of wheeling out a start-cart. I know the B-1s still have a big button the nose gear that could run the start-sequence for the engines during a scramble.

Now some of the older radials had cartridges that (I believe) actually fired - like a shotgun shell. I'm not quite square on how those worked though, as I can't imagine a single "bang" impulse spinning anything fast enough to turn 9 cylinders through a few compression cycles. Even with gearing.

Anybody with better gouge is welcome to expand my limited knowledge.   

[Edited 2006-07-04 04:38:26]
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n8076u
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RE: What Is The Starter Like?

Tue Jul 04, 2006 12:02 pm

Quoting 3DPlanes (Reply 14):
Now some of the older radials had cartridges that (I believe) actually fired

This is how they started the engine in the movie "Flight of the Phoenix" (the original one, haven't seen the new one). But I will leave it up to someone with cartridge-starting-a-radial experience to comment on whether that was a realistic interpretation or not.  Wink

Chris
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cptspeaking
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RE: What Is The Starter Like?

Tue Jul 04, 2006 12:45 pm

Quoting 3DPlanes (Reply 14):
I think the cartridges were more for the "Oh cr*p, the missiles are inbound!" kind of starts.

From what I remember from the general, you're right!

[Edit:sp]

[Edited 2006-07-04 05:46:16]
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jarheadk5
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RE: What Is The Starter Like?

Tue Jul 04, 2006 1:44 pm

Quoting MissedApproach (Reply 7):
Assuming everything's been off over the weekend, where does the hydraulic pressure come from? Is it stored in an accumulator or does an electrically driven pump supply pressure?

Haha... this is where things get convoluted in the 53.

The 4000psi hyd. pressure for main engine starting comes from the engine-start hydraulic pump, which takes 3000psi from the utility hydraulic system and boosts it to 4000psi. The engine-start pump is driven by the accessory gearbox (AGB), along with two generators, the utility hyd. pump, and the 2nd stage hyd. pump. The AGB is driven via a driveshaft from the main gearbox (MGB) when the engines are operating and the rotorhead is turning. When the rotorhead is NOT turning, the AGB is driven through another driveshaft by the auxiliary power plant (APP). The APP is a Solar T-62 turboshaft that puts out about 100+hp, and is started by yet another hydraulic starter motor. (This is true for the H-53's flown by the US Marines, US Navy, US Air Force, and JMSDF - I've heard it rumored that the German and Israeli 53's have installed electric starters and batteries for their APP's, but I don't know if it's true or not.)

Anyhoo, the APP's hydraulic starter is powered by either one or two accumulators (the 53E has two, the 53D, J, and M have one) that have a 1500psi nitrogen pre-charge behind a "floating" piston. The accumulators are then charged with hydraulic fluid to 3000psi; either via a hydraulic hand pump (which is one of the worst tasks on the 53, especially in the desert - takes a lot of effort to make 3000psi by hand...), from utility hyd. system pressure from operating the APP for at least 2 minutes, or connecting a hydraulic test stand (we called it a "Jenny", but most civilians know it as a "mule". Don't ask me why the difference in terminology - no one has ever given me a good reason) to the utility hyd. system and pressurizing it to 3000psi.

The APP MUST be operational to start the engines on an H-53 on the ground. There is no way to connect a Jenny/mule to only the engine-start hyd. system; there must be 3000psi in the utility hyd. system to feed the engine-start pump, and the engine-start pump must be spinning to make the 4000psi for main engine starting.



Any questions? There will be a test later... Big grin
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HAWK21M
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RE: What Is The Starter Like?

Tue Jul 04, 2006 6:15 pm



Pneumatically operated Turbine Driving a Gear driven Shaft,with Reduction Gears,to reduce speed & Increase Torque.Centrifugal Switch to provide Cutout at Particular speed.

Drives the Main Gear box to turn the Compressor.

Looking for a Sketch,Cant find one yet.
regds
MEL
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MissedApproach
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RE: What Is The Starter Like?

Wed Jul 05, 2006 7:04 am

Quoting JarheadK5 (Reply 17):
Haha... this is where things get convoluted in the 53.

 Confused You mean all that stuff actually works?! So basically it starts from an accumulator, which starts 20 other things, which start the engine. I'm going to take a wild guess & say no technicians were consulted during the design phase.
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jarheadk5
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RE: What Is The Starter Like?

Wed Jul 05, 2006 9:41 pm

Quoting MissedApproach (Reply 19):
You mean all that stuff actually works?!

Most of the time. And that was the condensed version - I didn't even get into start valves, dropout switches, supercharge valves, speed control lever microswitches...

There's plenty of reasons why the CH-53E has the highest maintenance man-hours per flight-hour figure in the USN/USMC fleet - this is one of 'em.

Quoting MissedApproach (Reply 19):
I'm going to take a wild guess & say no technicians were consulted during the design phase.

Well, you'd have to ask the engineers at Sikorsky during the '50s and '60s. But judging by other military aircraft designed and built during this general timeframe... NO, mechs/techs weren't asked for input during any part of the design phase. It's one of the issues we were beating on the Corps, Sikorsky, NAVAIR, basically anyone with design input to the CH-53X (now the CH-53K) - "While you're making these changes, can you make [insert crappy system here] better, or somehow eliminate it?" Hopefully they'll listen to the Fleet inputs, and change at least one or two of the worst systems...
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