X-Bleed Start

[ericinexile]

Did a little experiment today flying along in the snow listening to Maykop Radio (That "Free Flight" song is still my favorite). I wanted to see it that little "Ice Detected" light on the Aft Panel worked with Engine A/I off. It didn't but that's not what I'm writing about. Fortunately, I only lost one engine. After getting the A/I on I tried to start that engine but without luck. I tried for 10 minutes all the way to Krasnodar before I realized that there is no cross-bleed start feature on this thing. Is Kamov nuts!? They really intended for the pilot to crank the APU so that he can attempt to restart an engine? Or am I falling into the trap of thinking like an airline pilot and assuming that all turbine engines use bleed air for starting and other services?

 

Smokin' Hole

[geogob]

I also wondered about the in-flight engine restart procedure.

 

This diagram speaks for itself

 

• Right engine impingement starter.
  
• Right engine TV3-117VMA.
  
• Main gearbox.
  
• Left engine TV3-117VMA.
  
• Left engine impingement starter.
  
• Intermediate gearbox.
  
• APU.
  
• APU bleed air pipeline.
  
• Right generator.
  
• Turbine drive.
  
• Left generator.
  
• Input drive shaft.
  

source: http://www.digitalcombatsimulator.com/index.php?lang=en&end_pos=1630

[RvETito]

Kamov are not nuts. How do you expect an airflow if 150km/h (speed you should maintain with OEI) will be able to drive a compressor with such a small diameter? If you'd have looked to the manual you would know that there is no other way to start an engine except bleed air from the APU. Cemmercial airliner are another story, forst they have high bypass ratio turbofans with huge fans and along with the much higher speed this is enough to drive the engine on autoratation to RPM enough for ignition.

 

And what do you mean by croos bleed? Bleed from the other engine?

[GGTharos]

That is what he meant. Personally I think in an OEI condition - in a helicopter - taxing your one still working engine like that is not a good idea

 

Also not all aircraft have it either - AFAIK, an F-15C doesn't sport cross-bleed air for cranking a stopped engine mid-flight. You have to get the plane up to proper windmill rpm speed (about 400kts IIRC), then you'll get ignition, much like Tito said.

Edited January 16, 2009 by GGTharos

[geogob]

So you have to start the APU, crank the stopped engine, start the engine, shut the APU off, or something along those lines?

[RvETito]

If you suffer engine flameout due to icing it is highly unlikely to start it either way. The ice will still be there.

[Aser]

Well there is another way... for the rest of the helicopters without APU it's the STARTER-GENERATOR.

 

Regards

Aser

 

Kamov are not nuts. How do you expect an airflow if 150km/h (speed you should maintain with OEI) will be able to drive a compressor with such a small diameter? If you'd have looked to the manual you would know that there is no other way to start an engine except bleed air from the APU. Cemmercial airliner are another story, forst they have high bypass ratio turbofans with huge fans and along with the much higher speed this is enough to drive the engine on autoratation to RPM enough for ignition.

 

And what do you mean by croos bleed? Bleed from the other engine?

[gear_monkey]

No aircraft I have flown or have heard of allows cross-bleed or cross-generator starts while airborne (maybe some 4 engine aircraft I'm not familiar with).

 

The bleed loss from the operating engine would be huge and could never be certified or insured that way. It would cause a power loss in the operating engine that would make single-engine operations near impossible.

 

As for cross-gen starts, because you have lost the generator powered by the dead engine, you are already putting a heavy load on the remaining generator. By trying to add a start cycle you would greatly overload the operating generator and cause it to fail or at least be taken off line by the GCU.

 

In apu powered aircraft, you always start the apu during an engine failure and use it for its generator source and bleed air for the engine relight attempt.

 

For non-apu powered aircraft, you only are allowed to use the main battery for the engine restart attempt.

[Frederf]

So you have to start the APU, crank the stopped engine, start the engine, shut the APU off, or something along those lines?

 

Not only that but you have to reduce the throttle to low idle in order for the starting engine to start so that means less power overall (now that I think of it I could have lowered only the off-engine's throttle but I didn't know the key). It's a lot to do in not so much time while falling!

[tutmeister]

And with a high density altitude, impossible, as you'll over-torque your good engine and end up with a DEF. Better to land on and try a cross-bleed if you are going to try one anyway...

[ericinexile]

Kamov are not nuts. How do you expect an airflow if 150km/h (speed you should maintain with OEI) will be able to drive a compressor with such a small diameter? If you'd have looked to the manual you would know that there is no other way to start an engine except bleed air from the APU.

 

X-Bleed starts and Windmill starts are two different things. All jets have a Airstart envelope in which, with enough speed, no starter assist is needed. But that's not what I'm talking about. I'm talking about a way to quickly get an engine started. Cranking the APU first doesn't seem very quick to me but, oh well, that's the way it is.

 

No aircraft I have flown or have heard of allows cross-bleed or cross-generator starts while airborne...

 

Well we're flying in two different worlds because every jet airplane I've flown with bleed driven starters do allow for in-flight cross-bleed starts. In Airplanes of that size the thrust decrease from bleed use is fairly insignificant for the short period the cross-bleed is open.

 

Smokin' Hole

[ericinexile]

...Also not all aircraft have it either - AFAIK, an F-15C doesn't sport cross-bleed air for cranking a stopped engine mid-flight. You have to get the plane up to proper windmill rpm speed (about 400kts IIRC), then you'll get ignition, much like Tito said.

 

True. But an F-15 or practically any other twin-engine fighter gets along just fine on one engine--The fight is certainly over but getting back home is no sweat. The Ka50 on the other hand, even with everything jettisoned will struggle at 130-150 kph. It'll still get you home (or to a soft spot) but you'll be puckering the whole way. I just thought a helicopter pilot would like a quick re-light if possible and prudent. Throw the APU into the mix and it's a 7-step process for any hope of a relight.

 

Sorry, Tito, I know nothing about helicopters and less about Kamov but intuitively to me, its nuts.

 

Smokin' Hole

[geogob]

All jets have a Airstart envelope in which, with enough speed, no starter assist is needed.

 

I'm pretty sure windmill starts are not possible in Black Shark. Airflow through the turbine is not enough to make it turn and the compressor turbine and power turbine are not coupled. I do not know if it's an accurate representation (but I really doubt you get enough wind speed to start a turboshaft engine anyways), but it doesn't work in the simulator...

 

The key to remember is that, although it's a turbine, it's not a jet engine or a turbofan engine.

[RvETito]

If a turboshaft engine has a pneumatic starting the only way to spool it up in the air is using the APU. For the TV3-117 (on the Ka-50) to initiate an airstart the gas-generator RPM should be less than 7% otherwise you gonna break the starter's driveshaft. Croos bleed is impossible because of the large airflow needed to crank the starter, if you take that air from the only operating engine which is already running at take-off power you simply gonna kill it. This is how it is with helicopters.

[ericinexile]

If a turboshaft engine has a pneumatic starting the only way to spool it up in the air is using the APU. For the TV3-117 (on the Ka-50) to initiate an airstart the gas-generator RPM should be less than 7% otherwise you gonna break the starter's driveshaft. Croos bleed is impossible because of the large airflow needed to crank the starter, if you take that air from the only operating engine which is already running at take-off power you simply gonna kill it. This is how it is with helicopters.

 

Ok. Thanks. I'll keep the APU running.

[ericinexile]

I'm pretty sure windmill starts are not possible in Black Shark. Airflow through the turbine is not enough to make it turn and the compressor turbine and power turbine are not coupled. I do not know if it's an accurate representation (but I really doubt you get enough wind speed to start a turboshaft engine anyways), but it doesn't work in the simulator...

 

The key to remember is that, although it's a turbine, it's not a jet engine or a turbofan engine.

 

Thanks but you didn't read the whole post.

[arneh]

Croos bleed is impossible because of the large airflow needed to crank the starter, if you take that air from the only operating engine which is already running at take-off power you simply gonna kill it. This is how it is with helicopters.

 

For what it's worth, the Apache is capable of starting the second engine with bleed air from the first engine. Though that's not normally how it's done and I doubt it can be done in flight (maybe AlphaOneSix knows more precicly). From the AH-64A flight manual, section 2.30.2:

 

2.30.3 Engine Start Using Engine Bleed Air Source.

When the No. 1 engine is operating and it is

necessary to start the No. 2 engine, bleed air may be used

from the No. 1 engine compressor under certain circum-

stances. This technique is not normally used; however, it

is fully automatic, and provides an alternative starting ca-

pability if the SDC shaft fails or if the SDC throttle valve or

surge valve clogs

Edited January 17, 2009 by arneh

[AlphaOneSix]

Yeah the AH-64A has a shaft driven compressor (SDC) attached to the accessory gearbox (also mounts the hydraulic pumps and the CA generators) which provides compressed air for engine starts. If it breaks, there is an automatic valve that will allow the #1 engine to start the #2 engine. You cannot start the #1 engine using the #2 engine. There is also an external air receptacle under the #1 engine nacelle for using an external air source.

 

I should note that in all my years working on the AH-64A, I never once saw, or even heard of anyone ever using the #1 engine to start the #2 engine. In my experience, if an engine fails, it is best to leave it off until you land and fix it. Personally, I would never, ever try to restart an engine in flight. I'd just fly back to base on one engine. It (the Ka-50) is perfectly capable of flying just fine with only one engine, provided you dump your external stores.

[bradmick]

There was a recent article in Army Aviation where a CW3 actually performed a Cross Bleed start due to his APU recieving damage. He got the aircraft up and running, took off and went to take care of more bad guys. I've also been demonstrated ONE Cross Bleed start in my training, and I can definately say it's my least preferred method of starting an engine, the amount of power you have to pull to make it happen makes the aircraft WAY to squirely for my tastes.

 

Brad

[RvETito]

That's correct, only in some exceptions you would try midair start of an engine. Usualy it gets shut down for a good reason- fire, vibrations, icing etc. It's forbidden to even try start it, no to mention operate it.

 

Don't know about Ka-50 but one of the Ka-32's I used to work on had a receptacle port for ground pneumatic power thus making possible engines start without the APU.

[Frederf]

In the Altitude mission I had an engine fail, started APU, dropped both engines down to low idle throttle, started the failed engine, got it going, and then brought the throttles back up and then it happened again! and I restarted it again then it cut out for the 3rd time I think and i landed down the mountain. It was nuts to be doing all that while losing altitude.

[RvETito]

All you gotta do is turn on the engines' ice protection :D

[IvanK]

What does Black Shark use for its Engine icing model ? Do you need to be in visible moisture with low OAT or is it just based on a simple temperature model.

 

i.e. if Temp <xx then Engine icing will occur

[Shepski]

For jet airliners, cross bleed starts on the ground are used on aircraft without a working APU... start #1 engine with an external air source then start #2 using cross bleed.

 

There would never be an occasion to require a cross bleed start while airborne... you would always use a windmill start.

 

_________________________________

 

The icing model is temp only... the team are working on a temp/visible moisture model for the future.

Edited January 17, 2009 by Shepski

[ericinexile]

For jet airliners, cross bleed starts on the ground are used on aircraft without a working APU... start #1 engine with an external air source then start #2 using cross bleed.

 

There would never be an occasion to require a cross bleed start while airborne... you would always use a windmill start.

 

What airline do you fly for Shep? I'm looking at my Continental Airlines 737 manual (Sec. 2.7 pp 25-29) and it has flight envelopes for both windmill and x-bleed starts. Depending on 737 version and altitude, windmill starts require somewhere between 275-300 kias. This is roughly true for every airliner, Douglas, Airbus, Boeing, and Embraer that I have flown.

 

It's not true for helicopters, I get it.

 

Smokin' Hole