KFRG
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L1011/B747-737 Classic Question

Sun Apr 13, 2003 10:34 am

Hey guys,
I have a few questions. First, the famous L1011 engine start:

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I believe the excessive amount of smoke coming from the engine's is due to unburned gas, which collected in the burner cans? Is this correct. Is it typical of Rolls Royce engines?
#2. The exhaust cone section on early RB.211's on the L1011's appear to be extended compared to later versions. Was were the differences between the two, old and new? What was changed?
Old:
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New:
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#3. The inlets on the engine nacelle lip of early Classic 747's and 737's (Non-Adv models). What was their purpose. I know that these were phased out, but why? They can also be seen on early JT8D's on classic B737's.

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Thanks alot,
-Tom
 
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CCA
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RE: L1011/B747-737 Classic Question

Sun Apr 13, 2003 12:48 pm

#1 Yep, your right it's fuel, it happens to cold engines on cold days which is also discussed here, http://airliners.net/discussions/tech_ops/read.main/59393/

#2 The L1011 used to have core thrust reversers which were removed mainly due to weight. 747s used to have core reversers but were removed for the same reason.

#3 They are blow in doors they supply the inlet with more air when at high thrust, removed due to weight and maintenance costs like the core reversers, plus improvements in inlet efficiency.
P1 in A330, A340, A346, B742, B744, B748.
 
KFRG
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RE: L1011/B747-737 Classic Question

Mon Apr 14, 2003 11:39 am

Hey CCA,
Thanks for the explanations. Just to dig in a little deeper, how exactly did Core Reversers operate? What other a/c used them?

Thanks again,
-Tom
 
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CCA
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RE: L1011/B747-737 Classic Question

Mon Apr 14, 2003 1:41 pm

Core reversers were just small versions of the big ones with a similar set up, using blocker doors and cascade vanes.
I suppose it was more engine type rather than A/C, I know RR used them on the L1011 and P&W used them on the 747, but I must say I'm not sure about GE and the DC-10, a quick search found this which looks like it could be fitted with a core T/R.

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P1 in A330, A340, A346, B742, B744, B748.
 
OPNLguy
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RE: L1011/B747-737 Classic Question

Mon Apr 14, 2003 9:27 pm

RE: the 747/737 cowling doors, to add to what CCA said, the most common name for these things are "sucker" doors, and if you search for that term, I think you'll find at least 1 or 2 threads, although they may have been awhile ago.

On the 737s, these doors were on the 737-100s and the 737-200 "Basic" (non-advanced) aircraft. When Boeing upgraded to the 737-200 Advanced version on the production line, the sucker doors were history, as advances in cowling design made them unecessary. A similar situation existed on the 747s.
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VC-10
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RE: L1011/B747-737 Classic Question

Mon Apr 14, 2003 9:43 pm

 
broke
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RE: L1011/B747-737 Classic Question

Mon Apr 14, 2003 10:40 pm

The RB211-22B engine on the L-1011 has only primary orifices in its fuel nozzles; the fuel nozzles are the units that inject fuel into the annular combustion chamber. The orifices are sized to allow for proper atomization of the fuel during engine operation. In very cold weather, the fuel thickens and does not atomize very well during engine starts resulting in the cloud of fuel vapor coming out of the turbine.
In very very cold weather, ignition can occur so slowly that you could see, if you are in the correct place, gaps appear in the fuel vapor cloud at the (approximately) 5:00 and 7:00 positions. These are the locations of the igniters and these holes occur where fuel ignition has occurred. Slowly the holes will grow until ignition is occurring throughout the combuster.
Many other engines have primary and secondary orifices in the fuel nozzles. The secondary orifices are much smaller in diameter and are used during engine starting to properly atomize the fuel to allow for easy ignition, the primary fuel nozzles come into play when the engine is running.
There are several methods of allowing only the secondaries to feed fuel during a start; one such system uses a pressure sensitive fuel valve that will select either the secondary or the primary orifices.
Some L-1011 operators would use JP-4 fuel in the winter at alleviate that starting problem; an unintended result were fires (JP-4 is cut with gasoline) that destroyed some airplanes.
The RB211-22B was a nasty engine to start in cold weather and the fuel nozzles were only a part of the problem. Low pneumatic air pressure to the starter, deteriorated compressor blades and vanes, deteriorated turbine blades and vanes, and/or a malfunctioning fuel flow regulator (FFR) are some of the other problems that affected engine starting.
Cold weather starting of the RB211-22B bcame a black art with many theories and techniques used to get it running. Flame outs in bitter cold weather were not uncommon and the starters took a real beating; being used longer and more often that they were intended to get a balky engine up and running.
 
broke
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RE: L1011/B747-737 Classic Question

Mon Apr 14, 2003 10:49 pm

RB211-22B tail cones. The L-1011 originally came with a reverser system that included buckets or diverters on the exhaust of the core or hot stream as well as a fan reverser system. The hot stream reversers were very unreliable and were eventually removed (not nearly as easy as that, unfortunately). One result was a change in the tail cone and was called the 5 degree afterbody.
The L-1011 was not meeting its design drag coefficients and wind tunnel testing indicated that replacing the tail cone with one of a steeper angle would reduce drag and reduce the aircraft fuel burn.
First came the 10 degree afterbody and then the 15 degree afterbody, later a fairing was added between the fuselage and the inlet lip of the #2 engine. Delta used the fairing, Eastern did not.
The 15 degree afterbody became the standard, but noone that I know of was ever able to confirm an improvement in fuel burn attributed to the revised afterbodies.
 
OPNLguy
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RE: L1011/B747-737 Classic Question

Mon Apr 14, 2003 10:59 pm

ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
DC-10Tech
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RE: CCA

Tue Apr 15, 2003 12:45 am

"Core reversers were just small versions of the big ones with a similar set up, using blocker doors and cascade vanes.
I suppose it was more engine type rather than A/C, I know RR used them on the L1011 and P&W used them on the 747, but I must say I'm not sure about GE and the DC-10, a quick search found this which looks like it could be fitted with a core T/R."


You are correct, the turbine reversers were used on the DC-10 back in the day. I'm not sure why they were removed, but my guess would be that they caused premature stress fatigue to the turbine blade, caused performance problems, were costly to maintain, or just weren't needed. I've worked on a few older DC-10-10's that still had some of the turbine reverser indication system still installed.
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RE: L1011/B747-737 Classic Question

Tue Apr 15, 2003 5:41 am

As far as core reversers and fan reversers... the core reversers have been removed in all 747s that I know of, since the mid-1970s... at least I have not seen one 747 with operating core reversers... In any case, when reversing, most of the braking-reversing "action" came from the fan reversers anyway, little work was done by the core reversers... so, they were eventually deleted in the 747...
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