Airliner question

Narwhal said:
Although it has been over 10 years since I flew it, I seem to remember that the EMB-145 did have a synchronization system through the engine FADECS even though the airplane didn't have autothrottle. If the thrust levers were matched to a relatively close angle by the pilot the system would tweak engine thrust to minimize any vibration.
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I doubt it, splitting the throttles like an old piston twin is often necessary just to get the N1s within a few tenths of each other. Also can't find anything in the systems manual about it.
 
luvflyin said:
Dang. Now things are turning in opposite directions. But it still looks like fuel being squirted into hot air is what causes the combustion.
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Nope, spark ignition for startup, then ignition is self-sustained by continuous flame like an old stove with a pilot light. The igniters are turned off after start, though the FADEC has an auto-relight feature and we also manually turn on the igniters in heavy rain.
 
dmspilot said:
Nope, spark ignition for startup, then ignition is self-sustained by continuous flame like an old stove with a pilot light. The igniters are turned off after start, though the FADEC has an auto-relight feature and we also manually turn on the igniters in heavy rain.
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Ok. Makes sense. My thinking on it went way back to like 8th grade science class.
 
Pinecone said:
Which turbojet engines have multiple shafts
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Pratt and Whitney 2038 is a two spool engine used on the 757.
Rolls Royce RB211 is a triple spool engine so…a solid shaft inside a hollow shaft inside another hollow shaft. Also a 757 engine.
GE CF6 on the 767 is a dual spool engine.
 
A 757 with RB211 engines has a noticeable pulsing frequency variation on takeoff, moreso than other aircraft and engine pairings.

 
Let'sgoflying! said:
I guess I should have followed my instincts and gone up, hammered on the cockpit door til they opened it and let me barge in and flip the sync switch which they obviously forgot. ("sheesh, do I have to fly this airplane for you?"
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Yes. No, it's not a big deal. Aeronautical engineers much smarter than you or I have looked at it and determined it is not worth whatever the cost would be to sync it.
 
dmspilot said:
I doubt it, splitting the throttles like an old piston twin is often necessary just to get the N1s within a few tenths of each other. Also can't find anything in the systems manual about it.
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Hmmm, I don't remember having to do that, even on the clapped out O.G. 145ER's which became EP's. Maybe I just repressed the memories from the lost decade that I spent in the taco jet, or maybe the engines got worse over time, but you're probably right. I did a few deadheads in row 18 and do remember those Allisons chugging out of sync quite a bit on takeoff though. Seems like they'd sync up pretty well without a big split after thrust reduction.
 
Thanks for the F-111 mention. A guy I knew in college lived in northern VT, his dad worked on radar systems for F-111s, I think flying out of Plattsburgh. These days folks in the Adirondacks sometimes have A-10s flying low and fast over them. In those days, it was sometimes F-111s. I kinda think the F-111s would be more of a "holy crap" moment. Probably a lot less endearing as a close air support plane, though.
 
luvflyin said:
Dang. Now things are turning in opposite directions. But it still looks like fuel being squirted into hot air is what causes the combustion.

https://www.google.com/search?clien...fan+engine#kpvalbx=_mQQeY_CXKtXE9AO3lrHwCg_23
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Nope. But you are squirting fuel into a fire, that lights the new fuel. Like squirting more lighter fluid into a BBQ that is still burning with flames.

To get a jet engine started, it uses ignitors (basically spark plugs).

In USAF UPT when you did your night formation flight, you would get up behind the other plane and they would hit the ignition buttons and you could see the ignitors sparking.
 
Busflyer said:
Pratt and Whitney 2038 is a two spool engine used on the 757.
Rolls Royce RB211 is a triple spool engine so…a solid shaft inside a hollow shaft inside another hollow shaft. Also a 757 engine.
GE CF6 on the 767 is a dual spool engine.
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Those are all turbo FAN engines. So at least 2 shafts.
 
Pinecone said:
Those are all turbo FAN engines. So at least 2 shafts.
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I wonder how long a true turbo jet was actually in use. Even the old JT-8 on the 727 was considered to be a turbofan. It had a 1:1 bypass ratio. I don’t think any airliner had a pure jet engine. Are you aware of any?
 
Tarheelpilot said:
I wonder how long a true turbo jet was actually in use. Even the old JT-8 on the 727 was considered to be a turbofan. It had a 1:1 bypass ratio. I don’t think any airliner had a pure jet engine. Are you aware of any?
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707 and DC-8 both originally had the JT3C turbojet, later versions had the JT3D turbofan (the JT3D was basically the JT3C with a small bypass added, a very cludged together engine but it was very popular)
Others include the de Havilland Comet, the Tupolev Tu-104, and the Sud Aviation Caravelle. Plus a whole host of early biz jets.
 
AKiss20 said:
707 and DC-8 both originally had the JT3C turbojet, later versions had the JT3D turbofan (the JT3D was basically the JT3C with a small bypass added, a very cludged together engine but it was very popular)
Others include the de Havilland Comet, the Tupolev Tu-104, and the Sud Aviation Caravelle. Plus a whole host of early biz jets.
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Interesting. Just read up on the J57. It a pure jet with two spools to handle the low speed compressor stalls. I bet it sipped fuel…
 
Tarheelpilot said:
Interesting. Just read up on the J57. It a pure jet with two spools to handle the low speed compressor stalls. I bet it sipped fuel…
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Yeah as I said, PW went to the two spool architecture to deal with matching related stability issues, GE stuck with single spool and introduced variable stators. The 727 and 737 both shipped with JT3D or JT8Ds from the get go as you said.
 
AKiss20 said:
Yeah as I said, PW went to the two spool architecture to deal with matching related stability issues, GE stuck with single spool and introduced variable stators. The 727 and 737 both shipped with JT3D or JT8Ds from the get go as you said.
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The LEAP geared engines are an interesting development path. They are very quiet and burn less fuel. I keep waiting for one to blow up. That gear box has to be impressive.
 
Tarheelpilot said:
The LEAP geared engines are an interesting development path. They are very quiet and burn less fuel. I keep waiting for one to blow up. That gear box has to be impressive.
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It’s actually the PW GTF (geared turbofan), not the CFM/GE LEAP engines with the gearbox but yeah it’s impressive they made the gearbox work on that scale. Geared turbofans aren’t a new idea, there was a biz jet engine back in the 70s (80s? Not quite sure) that had it but scaling it to take the power required for a 20-40K lbf thrust class engine was impressive. The GTF is very quiet due to its low fan pressure ratio/low speed fan and its low pressure turbine is much smaller than what you’d see on basically anything else of that class.
 
Pinecone said:
Those are all turbo FAN engines. So at least 2 shafts.
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GE produced two single spool turbofan engines, the CJ805-23 developed from the J79 for the Convair 990 and the CF700 from the J85 for Biz jets. They added a turbine stage to the turbine bolted to the rotor that had “bluckets”. Bluckets were a single piece that had a turbine bucket on the inner span and a fan blade on the outer span. Even had a marketing slogan “Aftfans are better” except they weren’t as Convair and GE lost a boatload of money.

Cheers
 
Seems to me that an imbalanced generator can produce an out-of-sync noise.
 
Pinecone said:
Nope. But you are squirting fuel into a fire, that lights the new fuel. Like squirting more lighter fluid into a BBQ that is still burning with flames.

To get a jet engine started, it uses ignitors (basically spark plugs).

In USAF UPT when you did your night formation flight, you would get up behind the other plane and they would hit the ignition buttons and you could see the ignitors sparking.
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How? Wouldn't you have to see through the exhaust and turbine to be able to see the igniters sparking?
 
This is a really fun thread for me. Lots of history & tech knowledge in this group.
 
AKiss20 said:
It’s actually the PW GTF (geared turbofan), not the CFM/GE LEAP engines with the gearbox but yeah it’s impressive they made the gearbox work on that scale. Geared turbofans aren’t a new idea, there was a biz jet engine back in the 70s (80s? Not quite sure) that had it but scaling it to take the power required for a 20-40K lbf thrust class engine was impressive. The GTF is very quiet due to its low fan pressure ratio/low speed fan and its low pressure turbine is much smaller than what you’d see on basically anything else of that class.
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Yes. You are correct. I misspoke. Was thinking about the geared P&W. Not the leap. Thumbs were faster than the brain
 
Tarheelpilot said:
I wonder how long a true turbo jet was actually in use. Even the old JT-8 on the 727 was considered to be a turbofan. It had a 1:1 bypass ratio. I don’t think any airliner had a pure jet engine. Are you aware of any?
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Comet, Comet4, Avro Jetliner

https://en.wikipedia.org/wiki/Avro_Canada_C102_Jetliner

EDIT: Can't believe I forgot the most famous of all - Concorde! Got to watch her takeoff twice from my home airport! Amazing sight and sound for sure!
 
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