Joined: Apr 28, 2005 Posts: 3632 Location: West shore Lake Eire, MI, USA
Posted: Thu Apr 03, 2008 11:57 pm Post subject: Airline question for AP
AP, I understand that the industry world wide switched from four engines to three as an efficiency measure, then switched down to two engines when the FAA amended the rules to allow it to happen.
How many three engine airliners remain in service with major airlines world wide? I am not talking about the outfits with a half dozen aircraft, I mean companies like Champion that had its entire fleet made up of 727 trijets.
Also has anyone looked at the feasability of producing or at least testing monojet airliners? Something like a DC-10 with a single tail engine should in theory be more fuel efficient than a twin jet like the A-320 simply on reduced drag, if for no other reason. _________________ Oxygen: - An intensely habit-forming accumulative toxic substance. As little
as one breath is known to produce a life-long addiction to the gas, which addiction invariably ends in death.--Isaac Asimov
Joined: Apr 05, 2005 Posts: 2464 Location: South of Atlanta
Posted: Fri Apr 04, 2008 1:06 am Post subject: Re: Airline question for AP
Three engine jets in major airline fleets?
Hmmm, not many at all really. Most of the DC-10/MD-11 series aircraft are now plying cargo routes. A few smaller charter type outfits are still operating the L-1011 and DC-10's. The four engine aircraft have remained as some sort of marketing/safety issue and can be as efficient as the larger two engined aircraft.
The 727 is being phased out rapidly in almost all but a cargo capacity. Fedex still has a bunch of them, but probably not for long. I think some of the issue why you dont see more new three engine designs these days is a complication and safety issue. With an engine in the tail you have some obvious issues which you dont have with all wing mounted powerplants. Soiux City Iowa and United are a case study in that. Their DC-10 shed a fan blade and lost all hydraulics to the tail. With wing mounted pod engines its rare for a failure to cause catastrophic damage to systems.
Personally I would not want to fly a long distance on a single engined aircraft. I doubt the FAA, or ICAO will ever go there for obvious reasons.
Joined: Apr 28, 2005 Posts: 3632 Location: West shore Lake Eire, MI, USA
Posted: Fri Apr 04, 2008 4:33 pm Post subject: Re: Airline question for AP
AirlinePilot wrote:
Three engine jets in major airline fleets?
Hmmm, not many at all really. Most of the DC-10/MD-11 series aircraft are now plying cargo routes. A few smaller charter type outfits are still operating the L-1011 and DC-10's. The four engine aircraft have remained as some sort of marketing/safety issue and can be as efficient as the larger two engined aircraft.
The 727 is being phased out rapidly in almost all but a cargo capacity. Fedex still has a bunch of them, but probably not for long. I think some of the issue why you dont see more new three engine designs these days is a complication and safety issue. With an engine in the tail you have some obvious issues which you dont have with all wing mounted powerplants. Soiux City Iowa and United are a case study in that. Their DC-10 shed a fan blade and lost all hydraulics to the tail. With wing mounted pod engines its rare for a failure to cause catastrophic damage to systems.
Personally I would not want to fly a long distance on a single engined aircraft. I doubt the FAA, or ICAO will ever go there for obvious reasons.
Well I would want to see a good track record of safety before I flew on a mono-jet for any long distance, but in terms of efficiency it would offer some pretty significant advantages. I have read that one of the cargo carriers had refitted a number of 727's with new larger wing engines while retaining the tail engine as orriginally installed. I don't remember which one it was so I can't look it up again. How well does a tri-jet fly on a single engine anyhow, is it better or worse than a twin jet with one engine out?
As for wing pods, doesn't a DC-9 use two tail pods instead? Does that pose some sort of added danger in a turbine failure scenario that I am unaware of? Engines now are so much better than they were even twenty years ago that it seems catastrophic failures are exceedingly rare events. _________________ Oxygen: - An intensely habit-forming accumulative toxic substance. As little
as one breath is known to produce a life-long addiction to the gas, which addiction invariably ends in death.--Isaac Asimov
Joined: Aug 03, 2006 Posts: 4267 Location: Graceland
Posted: Fri Apr 04, 2008 4:44 pm Post subject: Re: Airline question for AP
Tanada wrote:
AirlinePilot wrote:
Three engine jets in major airline fleets?
Hmmm, not many at all really. Most of the DC-10/MD-11 series aircraft are now plying cargo routes. A few smaller charter type outfits are still operating the L-1011 and DC-10's. The four engine aircraft have remained as some sort of marketing/safety issue and can be as efficient as the larger two engined aircraft.
The 727 is being phased out rapidly in almost all but a cargo capacity. Fedex still has a bunch of them, but probably not for long. I think some of the issue why you dont see more new three engine designs these days is a complication and safety issue. With an engine in the tail you have some obvious issues which you dont have with all wing mounted powerplants. Soiux City Iowa and United are a case study in that. Their DC-10 shed a fan blade and lost all hydraulics to the tail. With wing mounted pod engines its rare for a failure to cause catastrophic damage to systems.
Personally I would not want to fly a long distance on a single engined aircraft. I doubt the FAA, or ICAO will ever go there for obvious reasons.
Well I would want to see a good track record of safety before I flew on a mono-jet for any long distance, but in terms of efficiency it would offer some pretty significant advantages. I have read that one of the cargo carriers had refitted a number of 727's with new larger wing engines while retaining the tail engine as orriginally installed. I don't remember which one it was so I can't look it up again. How well does a tri-jet fly on a single engine anyhow, is it better or worse than a twin jet with one engine out?
As for wing pods, doesn't a DC-9 use two tail pods instead? Does that pose some sort of added danger in a turbine failure scenario that I am unaware of? Engines now are so much better than they were even twenty years ago that it seems catastrophic failures are exceedingly rare events.
I know almost nothing about planes, but a common sense question that occurs to me is whether the risk of catastrophic engine failure due to objects being sucked in can ever be completely eliminated. If not, then how could a single engine plan ever be viable (unless you sent all the passengers to jump school first)?
In a single rear engine model, it seems that the risk of debris from the plane itself would be higher than for wing mounted engines. Thus, it seems like there would be a design-based increased probability of catastrophic failure in a single engine rear mounted engine over the same engine mounted on the wing.
I am assuming that single rear engine aircraft (like some fighters, I suppose) are not flown nearly as much as commercial aircraft and thus the single engine risk is not as big an issue. _________________
Joined: Dec 02, 2005 Posts: 6388 Location: Oil-addicted Southern Californucopia
Posted: Fri Apr 04, 2008 4:56 pm Post subject: Re: Airline question for AP
Redundancy is good. No redundancy when 300 lives are at risk is not good. _________________ "Thank you for attending the oil age. We're going to scrape what we can out of these tar pits in Alberta and then shut down the machines and turn out the lights. Goodnight." - seldom_seen
Joined: Apr 28, 2005 Posts: 3632 Location: West shore Lake Eire, MI, USA
Posted: Fri Apr 04, 2008 5:36 pm Post subject: Re: Airline question for AP
BigTex wrote:
I know almost nothing about planes, but a common sense question that occurs to me is whether the risk of catastrophic engine failure due to objects being sucked in can ever be completely eliminated. If not, then how could a single engine plan ever be viable (unless you sent all the passengers to jump school first)?
In a single rear engine model, it seems that the risk of debris from the plane itself would be higher than for wing mounted engines. Thus, it seems like there would be a design-based increased probability of catastrophic failure in a single engine rear mounted engine over the same engine mounted on the wing.
I am assuming that single rear engine aircraft (like some fighters, I suppose) are not flown nearly as much as commercial aircraft and thus the single engine risk is not as big an issue.
While it is true that intake of a foreign object can not be 100% avoided and is a major source of turbine failure. When you are talking about a modern turbofan with bypass like is used on most passenger aircraft there are a number of things to keep in mind. One is, the engine intakes tend to be very large as do the blades on the first stage of the compressor. While flying through a flock of birds is never a good idea modern engines are tested before certification to survive injesting large flying birds like geese. The engine needs a complete overhaul and might suffer serious damage, but most of the time can continue to produce power until an emergency landing is made.
When you are talking about ingesting metalic debris, well odds are you are going to have a very bad day when that happens.
For short term flights, say up to 90 miutes, a no power landing is bad but not an automatic high fatality event. Even the Sioux City crash landing AP referred to above was not a 100% fatality situation and that was with no hydraulics and very poor manuverabillity. If you are talking about a damaged engine the crew will be declaring an emergency and landing at the nearest suitible airport. If you are talking about an engine totally out then you are relying on backup systems to provide the hydraulics and you are in a really big glider with a poor ratio. In that situation you are talking about setting down on the first available spot, hopefully something like the Bonneville salt flats but more likely a highway or such where you are praying and hoping all the way to touchdown and through rollout. The Space Shuttle lands that way every trip, but it was designed specifically to do so and has a large group of people planning every landing in great detail. The Monojet would be a whole different kind of glider.
As for single engine military aircraft, planes like the A-6 flew day in and day out for decades before they were retired in the mid 1990's. Military aircraft however have ejection seats and trained crews who know how to use them, that isn't practicle for a passenger jet. The concept is to make the plane lighter and more fuel efficient, with a trade off in the form of less safety.
On the other hand there have been quite a number of single engine civilian craft since the beginning of aviation, they just never caught on for passenger planes.
By the way, there is no reason that a single engine civilian airliner would have to have the engine in the tail, though that is the most common concept. You could also mount it on a fuselage pod like the DC-9 uses forward on the aircraft top, above the wing with a high wing design, or you could mount it in a 'stinger' which would protrude behind the tail where a catastrophic failure would throw debris completely away from the aircraft itself.
Imagine that wing shape with a single engine mounted in a pod centered over where the wing and the fuselage meet.
It would be no more vulnerable to debris than a wing mounted pod.
Or picture a Gulfstream 550 or 650 with a single tail engine and a passenger capacity of 20. _________________ Oxygen: - An intensely habit-forming accumulative toxic substance. As little
as one breath is known to produce a life-long addiction to the gas, which addiction invariably ends in death.--Isaac Asimov
Joined: Apr 28, 2005 Posts: 3632 Location: West shore Lake Eire, MI, USA
Posted: Fri Apr 04, 2008 5:47 pm Post subject: Re: Airline question for AP
BigTex wrote:
Zardoz wrote:
Redundancy is good. No redundancy when 300 lives are at risk is not good.
Thus spake Zardoz.
From a strictly mercenary POV, redundency is redundant and expensive.
I am not saying mono-jet airliners are likely to hit the market any time soon, just exploring the feasabillity of a system more fuel efficient than the current twin engine configuration. _________________ Oxygen: - An intensely habit-forming accumulative toxic substance. As little
as one breath is known to produce a life-long addiction to the gas, which addiction invariably ends in death.--Isaac Asimov
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