Musang From United Kingdom, joined Apr 2001, 797 posts, RR: 7 Reply 3, posted (12 years 2 months 1 day 1 hour ago) and read 1164 times:
Never operated L1011s but I know what you mean from years of hanging around ramps as a despatcher and pilot!
The start process is the same as just about any other turbine engine; the core section is spun to a certain RPM, the fuel is introduced, then ignited. The "Boom" you speak of is simply the fuel suddenly burning. The same process can be heard on any other engine if you're in the right place.
Large fans like RB-211 have correspondingly heavy rotating machinery, which takes more time to spin up than, say, a tiny 146 engine, which is why it takes so long and keeps you in suspense.
Some turbines are started by electric starter motors, some by forcing compressed air through the engine from the APU or an external Air Start cart. If its air started, the hissing of the escaping air often masks the sound of ignition.
Anyone know whether the RB-211 is air or electric start?
The characteristic start behavior of the L1011's RB-211s is therefore due to the exact timing of fuel on, followed by ignition, which results in more fuel being in the back of the engine than the ignitors can immediately deal with, bearing in mind the slow rotation at that time. Interesting that RR powered 747s don't make the same sound. Or put out the same smoke.
The sound must be simply the acoustics of the cowling and the hot section exhaust design.
But I repeat, I've no history with the type or its engine, just thought I'd offer the above until an RB-211 mechanic provides the expert answer!
Others with interesting start noise are BAC-111s and Tu-154s!
Charliecossie From Germany, joined Oct 2001, 478 posts, RR: 10 Reply 4, posted (12 years 2 months 1 day ago) and read 1158 times:
The 747/RR does make smoke!
The 211 is a 3 spool engine so has a lot more metal to get rotating than a CF6/JT9. Starting is slower because of this. Standard procedure when starting a 742/RR at BA is to use both ignitors but the Tristar only uses one ignitor. That's why the Tripe makes more smoke (usually). The 747 sounds the same as a Tristar (same inlet and exhaust).
The 1-11 makes such a strange noise because it doesn't have a starter as such. The CSD is driven (by air) which then turns the engine.
CPH-R From Denmark, joined May 2001, 5870 posts, RR: 3 Reply 6, posted (12 years 2 months 22 hours ago) and read 1137 times:
I can only agree on the 744's making smoke too.. Of course, this being in the right conditions. I once had a couple of hours to kill in Seoul Kimpo (during winter) and everytime the 744's started their engine, smoke was everywhere.
Charliecossie From Germany, joined Oct 2001, 478 posts, RR: 10 Reply 11, posted (12 years 1 month 3 weeks 6 days 13 hours ago) and read 1005 times:
I'm only a fixer so can't detail the precise reasons.
The later engines must be more efficient at starting - they're quite happy to start on one ignitor, for example.
The combustion chamber doesn't fall to bits either.
Finally, the FAFC is able to control starting fuel flow rather better.
That's my story and I'm sticking to it.
GIven the right conditions, though, and the G/H can do a pretty good impression of a 22B.
TimT From United States of America, joined Jun 2001, 168 posts, RR: 0 Reply 12, posted (12 years 1 month 3 weeks 4 days 11 hours ago) and read 984 times:
Ok, here's the thing. The RR on the L-1011 is started with compressed air either from the APU or a start cart. Starter is attached directly to the main gearbox forward side, right. Always. Engine is turned to about 20% N2 with the ignitor(s) armed, fuel is introduced and when it lights off you can get a boom, thump, woooff, or whatever else you could call it. The smoke is produced by oil. The RR uses labryinth seals that are held in place by bleed air into the bearing cavity. As the air pressure decays, (loose fit, long time shut down,etc.,) the seal ring can come "unstuck" from it's mating surface and leak into the cavity. I've seen totally dry RB's dump a quart out of the front bearing just by moving the fan (N1). If the oil gets to the combustion chamber or behind the turbine it's going to burn and presto-- white smoke.
TimT From United States of America, joined Jun 2001, 168 posts, RR: 0 Reply 15, posted (12 years 1 month 3 weeks 2 days 4 hours ago) and read 902 times:
The RB211 is a rather funny animal. The L-1011 version of that engine is totally (IMHO!) distinctive. I've never seen or heard another RR engine, including the BA747's (RR powered) moan and groan like the L-10. The CO 757's are powered with RB211-535C or E versions. Practically the same engine, I suspect the thrust rating is different, and they may have a different bearing cavity seal in them.
Not to start a flame war, but not all of the L-10's smoke on start either. One carrier we tested engines for would absolutely not accept an engine that smoked- startup or shutdown.