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Inflight Engine Starts

CYKA From , joined Dec 1969, posts, RR:
Posted (10 years 9 months 1 week 3 days 21 hours ago) and read 831 times:

Would one need an APU running(providing the bleed) to re-start an engine in flight, or would the air passing through the N1 blades be enough?

10 replies: All unread, jump to last

FBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 8
Reply 1, posted (10 years 9 months 1 week 3 days 21 hours ago) and read 792 times:

The engine rotates due to the airflow and all you need is fuel and ignition to make it run.

Because of the rotating engine,applying APU air would cause a crash engagement between the starter and N2 spool.Very noisy,veeeeery expensive!

"Luck and superstition wins all the time"!

HAWK21M From India, joined Jan 2001, 30166 posts, RR: 61
Reply 2, posted (10 years 9 months 1 week 3 days 21 hours ago) and read 782 times:

The Rotor spool speed would be adequate.Only Fuel & Ignition need be supplied.
On B737 The Start Switch has a position "FLT" which performs the Inflight Start.Its similiar to a Grd Start Sw position except No bleed supplied to the Pneumatic starter.
regds.

Think of the brighter side!

JG From United States of America, joined Jun 2005, 0 posts, RR: 1
Reply 3, posted (10 years 9 months 1 week 3 days 18 hours ago) and read 771 times:

Not true FBU 4EVER!,

Sometimes fuel and ignition are not enough. Sufficient airflow is required to windmill start an engine inflight and the aircraft speed must be within the windmill start envelope for its respective altitude.

Airbus aircraft do have an inflight APU start assist when the speed is not withing the windmill start envelope. There is no "crash" engagement and it is neither noisy nor expensive.

JG

Klaus From Germany, joined Jul 2001, 20144 posts, RR: 57
Reply 4, posted (10 years 9 months 1 week 3 days 17 hours ago) and read 767 times:

BTW: The starter is a separate turbine unit on the main shaft? Bleed air is not blown to the "normal" turbine stages for starting?

Buff From Australia, joined Mar 2007, 0 posts, RR: 2
Reply 5, posted (10 years 9 months 1 week 3 days 16 hours ago) and read 763 times:

For a windmill start, airspeed on the B757 needs to be in excess of 300 knots IAS. Other jet engines would require a similar high IAS. For normal inflight starts (cross-bleed) the APU is not used - but the other engine is. The cross bleed goes through the same starter motor (a small air driven motor) on the engine to be started that is used on the ground.

In the unhappy event of a double engine flameout, one of the first actions is to start the APU, mostly for support services. You can be darned sure one of the "support" services I would use as soon as possible would be the bleed air to try and restart one of the engines if the windmill speed was insufficient!

Best Regards,

Buff

Twotterwrench From , joined Dec 1969, posts, RR:
Reply 6, posted (10 years 9 months 1 week 3 days 15 hours ago) and read 749 times:

Klaus - A pneumatic starter is a seperate unit, generally mounted on the accessory gearbox. Bleed air, from apu, or ground cart or from the other engine, is directed to the started and blows across vanes to provide rotation; very similar to a small turbine.

Oldman From United States of America, joined Sep 2006, 0 posts, RR: 0
Reply 7, posted (10 years 9 months 1 week 3 days 12 hours ago) and read 739 times:

One other item to ponder men. If a engine quits on today's jets there must be avery good reason for it. One must be extreemly cautious on attempting a re-lite. One example would be if a fuel line ruptured and it flamed out. Now, how would you know it was a fuel line and would you want to give it some hi energy ignition in that situation? Just food for thought. Me? I would surely let a "sleeping dog lie". Sorry, I may be drifting off the thread some. Regards, Oldman

Klaus From Germany, joined Jul 2001, 20144 posts, RR: 57
Reply 8, posted (10 years 9 months 1 week 3 days 12 hours ago) and read 736 times:

Twotterwrench: A pneumatic starter is a seperate unit, generally mounted on the accessory gearbox.

Thanks. I was wondering... Wink/being sarcastic

So the main turbine (probably the high pressure shaft?) is turned through conventional gears? Is it coupled to the starter only temporarily like with a car engine starter or is it connected permanently?

Twotterwrench From , joined Dec 1969, posts, RR:
Reply 9, posted (10 years 9 months 1 week 3 days 9 hours ago) and read 723 times:

klaus - the most typical example would be where the acc. gear box (AGB) is driven by a quill shaft which is a vertical shaft that picks-up rotation from the main shaft to turn all the components of the AGB. Vice versa, the starter turns the AGB which turns the quill shaft which turns the main shaft. The starter is designed to cut-out at a certain rotational speed so that as the engine comes up to operation speed, the starter doesn't turn into a hand grenade. Also, the shaft of most starters is designed to sheer off in the event that the starter seizes to prevent the starter from destroying the rest of the accessory gear box. This is a very simplified explanation, but I hope you get the picture. I am looking for a diagram of a quill shaft design and will post it if I can find one...