number of engines on planes
Was the much smaller Bae-146/RJ-70 Avro (60-75 passengers)designed with four engines because of an RAF requirement to transport Her Majesty the Queen over water, and having two engines created too much concern?
If this was the case, then lesser mortals are deemed an acceptable risk for the majority of newer aircraft which all, except for the MD-11 and A-340, Boeing 747, just plain economics?
The US FAA would call it cost/benefit ratio during the regulation, certification process.
If this was the case, then lesser mortals are deemed an acceptable risk for the majority of newer aircraft which all, except for the MD-11 and A-340, Boeing 747, just plain economics?
The US FAA would call it cost/benefit ratio during the regulation, certification process.
Engine availability is a major issue
Most designs must pick from a rather small range of suitable engines likely to be available in the design timeframe. Old engines are out--noise, specific fuel consumption, so the menu is shorter than you'd think.
Just imagine that an A380 design person had the bright idea of making it a twin. Other issues aside, the prospect of working over the engine manufacturers to design something so far outside their current range for a modest total units shipped would have stopped this thought promptly.
Though I don't know the history, I'd guess the BAe-146 choice of four engines was likely driven by engine availability, as its short range and other characteristics are firmly in a slot dominated by twins.
You'll notice that long-range aircraft are those more likely to have more engines. With the rule that takeoff must succeed with n-1 engines at the awkward moment implying higher engine count gives less engine weight, the weight benefit of more engines is more helpful at long range (review the Breguet range equation if this point seems obscure).
Just imagine that an A380 design person had the bright idea of making it a twin. Other issues aside, the prospect of working over the engine manufacturers to design something so far outside their current range for a modest total units shipped would have stopped this thought promptly.
Though I don't know the history, I'd guess the BAe-146 choice of four engines was likely driven by engine availability, as its short range and other characteristics are firmly in a slot dominated by twins.
You'll notice that long-range aircraft are those more likely to have more engines. With the rule that takeoff must succeed with n-1 engines at the awkward moment implying higher engine count gives less engine weight, the weight benefit of more engines is more helpful at long range (review the Breguet range equation if this point seems obscure).
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The B727 was originaly designed with 3 engines due to approach minimas at that time being more restrictive for 2 engne aircraft than 4. Boeing persaded the FAA to grant the same minima as a 4 engine aircraft for the 72.
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I think the basic driver on the number of engines on an aircraft is simply financial.
There are all kinds of arguments being put forward about safety, ETOPS, take-off parameters etc., but surely the aircraft manufacturer will provide an aircraft that can comply with the requirements at least cost and lowest running costs.
It is naturally possible to expand the argument in all sorts of directions but to cut to basics, two engines will cost less than four, they will be more efficient and therefore use less fuel.
Do you suppose that the Airbus A380 would have two engines if there were large enough power units available? I think it quite possible, if the Certification Specifications could be met.
There are all kinds of arguments being put forward about safety, ETOPS, take-off parameters etc., but surely the aircraft manufacturer will provide an aircraft that can comply with the requirements at least cost and lowest running costs.
It is naturally possible to expand the argument in all sorts of directions but to cut to basics, two engines will cost less than four, they will be more efficient and therefore use less fuel.
Do you suppose that the Airbus A380 would have two engines if there were large enough power units available? I think it quite possible, if the Certification Specifications could be met.
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The 146 has 4 due to limited availability at the time (late 70's/early 80's). It had to be quiet so the option of putting 2 JT8D's on it was not feasible and at the time there wasn't any other choice other than a tank engine.
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ICT_SLB
As far as my memory goes, the Trident IIE was like all the other Tridents in that it had 3 Speys. It did however have some help in the in hot weather by using water injection. It also had a fin fuel tank to give it more range. It didn't have the Boost Engine though.
The IIIB was the the one with the Boost Engine (the RB162) which was needed because the poor old Speys were flat rated to 15 degrees C and needed all the help they could get
As far as my memory goes, the Trident IIE was like all the other Tridents in that it had 3 Speys. It did however have some help in the in hot weather by using water injection. It also had a fin fuel tank to give it more range. It didn't have the Boost Engine though.
The IIIB was the the one with the Boost Engine (the RB162) which was needed because the poor old Speys were flat rated to 15 degrees C and needed all the help they could get
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747 or A380 as a BIIIIG twin?
I think it could be done - theoretically - with today's GE90-115 or the like.
But it wouldn't operate at anything like the TOGW of the current designs. It would be a short-range plane for hopping around Japan or the US E. Coast or Western Europe.
I think it could be done - theoretically - with today's GE90-115 or the like.
But it wouldn't operate at anything like the TOGW of the current designs. It would be a short-range plane for hopping around Japan or the US E. Coast or Western Europe.
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I heard it in the pub, and the pub was probably where the story began, but.......
Is there any truth in the story that, as 30,000 Lb thrust (or so) engines became available, Lufthansa investigated the possibility of re-engining their B727s with 2 X 30000 Lb engines with a totally new (Boeing built) Section 48 to match the entire assembly?
Or was it just another pub story?
Regards,
Old Smokey
Is there any truth in the story that, as 30,000 Lb thrust (or so) engines became available, Lufthansa investigated the possibility of re-engining their B727s with 2 X 30000 Lb engines with a totally new (Boeing built) Section 48 to match the entire assembly?
Or was it just another pub story?
Regards,
Old Smokey
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Lufthansa investigated the possibility of re-engining their B727s with 2 X 30000 Lb engines with a totally new (Boeing built) Section 48
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The 146 started life as the HS681 - a VSTOL airlifter that was intended to support the P1154 (Supersonic Harrier II) force. It was powered by twin Pegasus with the efflux (one each side of each Peggy) being entrained by the flaps. To get the same effect required 4 small conventional jets. Again engine power, as such, had little to do with the choice of number of engines.
Regarding the DC10 and L1011 I recall they grew out of an American Airlines requirement for a 250 seater that could operate non-stop across the USA off La Guardia's runways and AA envisaged a big twin. Both Douglas and Lockheed looked at future growth options and hedged their bets by going for 3 engines. Douglas did look into a twin version of the DC10 later but it was not economically viable and was dropped.
AA supposedly said some years later that the A300 was what they were after, the DC10 being too big, but it came along a few years too late although AA did eventually buy some A300-600's.
I can remember Boeing stating at a presentation back in the late 80's/early 90's that no-one would build a 3 engined aircraft again as it was not economical. In their opinion all new conventional designs would be either twin or quad. The MD11 was an exception as it was a derivative and could be cost justified. Airbus said more or less the same thing.
Brain Fade,
Yes, the A330 and A340 were designed as a common airframe. The system architecture is common and the wing aerodynamics are the same. They are built on a common assembly line and share a single serial number sequence ie. the first A330 was MSN 12 the previous 11 being A340\'s.
The A340 was supposed to be the long range model and A330 the intermediate range one however there became a demand for a longer range A330 so the A330-200 appeared.
AA supposedly said some years later that the A300 was what they were after, the DC10 being too big, but it came along a few years too late although AA did eventually buy some A300-600's.
I can remember Boeing stating at a presentation back in the late 80's/early 90's that no-one would build a 3 engined aircraft again as it was not economical. In their opinion all new conventional designs would be either twin or quad. The MD11 was an exception as it was a derivative and could be cost justified. Airbus said more or less the same thing.
Brain Fade,
Yes, the A330 and A340 were designed as a common airframe. The system architecture is common and the wing aerodynamics are the same. They are built on a common assembly line and share a single serial number sequence ie. the first A330 was MSN 12 the previous 11 being A340\'s.
The A340 was supposed to be the long range model and A330 the intermediate range one however there became a demand for a longer range A330 so the A330-200 appeared.
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Strangely enough the A300 (which Eastern leased and later bought) was not permitted to operate from LGA. Something obscure like tire loads in lowspeed taxi turning. Had EAL been able to operate the Bus into LGA their demise might not have been so quick.
