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alaskan9974
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Will single engine designs be viable in the future?

Mon Jan 30, 2017 11:27 pm

As the reliability and efficiency of engines allowed aircraft to go from quads, to twins, in the future will engine design allow for a single engine commercial jetliner?

I can see drag and weight savings by streamlining aircraft and engine designs, but regulations and public opinion may be the barrier? As well as losing efficiency of current fueling to the low slung engines.
 
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TWA772LR
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Re: Will single engine designs be viable in the future?

Mon Jan 30, 2017 11:36 pm

No. Not for aircraft holding more than 19 pax. All it takes is one flight over the ocean to have a flame out for it to end up in the drink and the worldwide fleet of that type grounded indefinitely. Plus, imagine how big a GE90 is. You'd need an engine more than twice that size to power a 777-sized aircraft. Then you face another critical question, where to put the engine? How would you handle an engine out on take off, much less in flight?

Regulators barely allowed ETOPS in the 80s, and I'd imagine the public wouldn't want to go near that thing.

There are plenty of Cessna Caravans and Pilatus PC-12s flying around however, all one-engine birds.
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Flow2706
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Re: Will single engine designs be viable in the future?

Tue Jan 31, 2017 12:34 am

Not going to happen. An engine failure in this type of aeroplane would probably be classified as a catastrophic failure condition, so the probability of this failure must be below 1x10^-9 (for catastrophic). ETOPS regulations require engine reliability to be better than 0,02 engine shutdowns per 1000 engine operation hours (for 180min maximum diversion time) - i.e. 2X10^-5. While actual engine performance is much better than the requirement it is still at least one order of magnitude away from the requirement...
 
26point2
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Re: Will single engine designs be viable in the future?

Tue Jan 31, 2017 12:38 am

Modern airliners require, for certification, redundant systems. In the Part 23 transport I fly there are 2 and often 3 redundant components for any given system. Anything that has only one, such as APU, isn't needed for flight. Engine reliability might improve but it will never be 100%. Would YOU fly in a single engined aircraft across the North Atlantic? I thought not.
 
kabq737
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Re: Will single engine designs be viable in the future?

Tue Jan 31, 2017 5:02 am

26point2 wrote:
Modern airliners require, for certification, redundant systems. In the Part 23 transport I fly there are 2 and often 3 redundant components for any given system. Anything that has only one, such as APU, isn't needed for flight. Engine reliability might improve but it will never be 100%. Would YOU fly in a single engined aircraft across the North Atlantic? I thought not.

Although I personally wouldn't do it people fly Cessna single engine aircraft over the North Atlantic. It can be done. I think it's unreasonable to say it couldn't happen on airliners. I am by no means saying it will be soon or even in our lifetimes but someday we will engineer an engine suitable for single engine airliners. Who knows by that time we could have much better modes of transportation. Either way I think the technology for a single engine airliner is on the way.
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PhilBy
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Re: Will single engine designs be viable in the future?

Tue Jan 31, 2017 10:14 am

OK as long as it's flight-path remains within glide distance of an alternative runway in the event of single engine failure.
 
CXfirst
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Re: Will single engine designs be viable in the future?

Tue Jan 31, 2017 11:25 am

Flow2706 wrote:
Not going to happen. An engine failure in this type of aeroplane would probably be classified as a catastrophic failure condition, so the probability of this failure must be below 1x10^-9 (for catastrophic). ETOPS regulations require engine reliability to be better than 0,02 engine shutdowns per 1000 engine operation hours (for 180min maximum diversion time) - i.e. 2X10^-5. While actual engine performance is much better than the requirement it is still at least one order of magnitude away from the requirement...


If we can get engine failure rates down to below 1x10^-9, then yes, one engine operations won't be a problem (it won't be any more likely than a double engine failure for instance). However, this is an incredibly low failure rate, not just twice as safe as engines are now, but much much more. Every one redundancy drops probability of catastrophe significantly. Now, if they can add in other means of redundancy, that would slightly reduce how reliable it needs to be (perhaps a design with an absolutely massive glide range).

Furthermore, the amount of flight testing and certifying needed in order to prove this reliability will not be cost effective. It will be years of testing, and one bad result would be a massive set back.

-CXfirst
 
mxaxai
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Re: Will single engine designs be viable in the future?

Tue Jan 31, 2017 11:34 am

26point2 wrote:
Modern airliners require, for certification, redundant systems. In the Part 23 transport I fly there are 2 and often 3 redundant components for any given system. Anything that has only one, such as APU, isn't needed for flight. Engine reliability might improve but it will never be 100%. Would YOU fly in a single engined aircraft across the North Atlantic? I thought not.

I'm sure you'll agree that very few airliners carry a spare set of wings or gear. Especially wings are designed in a way to never fail under any expectable circumstances. So I suppose you could create a single engined airliner as long as your engine never fails, or, in terms of probability, a likelyhood of exactly one engine failure in 10^9 flights. Even though engines have become far more reliable, they are still shut down on a daily basis for many reasons. Additionally, jet engines are very complex machinery that is notoriously hard to create failure proof.
 
blacksoviet
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Re: Will single engine designs be viable in the future?

Wed Feb 01, 2017 12:49 am

What if you took a MD-10, replaced the #2 engine with a GE90, and removed the #1 and #3 engines? Assuming the engine could reach 100% reliability, would this be feasible?
 
Flighty
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Re: Will single engine designs be viable in the future?

Wed Feb 01, 2017 4:08 pm

blacksoviet wrote:
What if you took a MD-10, replaced the #2 engine with a GE90, and removed the #1 and #3 engines? Assuming the engine could reach 100% reliability, would this be feasible?


That sounds like the PA-47 PiperJet!

Image
 
blacksoviet
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Re: Will single engine designs be viable in the future?

Wed Feb 01, 2017 8:32 pm

Flighty wrote:
blacksoviet wrote:
What if you took a MD-10, replaced the #2 engine with a GE90, and removed the #1 and #3 engines? Assuming the engine could reach 100% reliability, would this be feasible?


That sounds like the PA-47 PiperJet!

Image

That looks scary.
 
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7BOEING7
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Re: Will single engine designs be viable in the future?

Wed Feb 01, 2017 11:51 pm

Sometime well after we lose the copilot.
 
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richcam427
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Re: Will single engine designs be viable in the future?

Thu Feb 02, 2017 7:20 am

As far as single engines are concerned, I'd be much more concerned about engine failure on takeoff than I would be about engine failure in cruise over the ocean.
 
WIederling
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Re: Will single engine designs be viable in the future?

Thu Feb 02, 2017 12:51 pm

blacksoviet wrote:
Flighty wrote:
That sounds like the PA-47 PiperJet!

That looks scary.


compared to a reciprocating engine the turbine is quite a bit more reliable.
you get a single engine plane with near twin (recip.) mot reliability.

GA twins seem to have issues with one engine out conditions. ( actually the "amateur" pilots seem to have .. )

Then there is this twin turbines working on single prop shaft concept around.
No idea what kind of reliability can be expected there.
Murphy is an optimist
 
Calder
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Re: Will single engine designs be viable in the future?

Thu Feb 02, 2017 1:51 pm

WIederling wrote:
blacksoviet wrote:
Flighty wrote:
That sounds like the PA-47 PiperJet!

That looks scary.


compared to a reciprocating engine the turbine is quite a bit more reliable.
you get a single engine plane with near twin (recip.) mot reliability.

GA twins seem to have issues with one engine out conditions. ( actually the "amateur" pilots seem to have .. )

Then there is this twin turbines working on single prop shaft concept around.
No idea what kind of reliability can be expected there.


I always thought the Piperjet was pretty ugly, although that of course is a matter of taste.

There have been a couple of aircraft that attempt to join the output of two engines into some kind of transfer case and one output shaft to a propeller.

The Lear Fan comes to mind.

Image

Supposedly it was to have a cruise of 280kts at FL400, and a max speed of ~370kts at FL250 pulling power from two PT6B-35F engines churning out roughly 650shp a piece.
C. T.
 
planewasted
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Re: Will single engine designs be viable in the future?

Thu Feb 02, 2017 2:27 pm

A valveless pulse jet can be made without moving parts, maybe the reliability can be made good enough? Huge problem with noise and low efficiency though.
Ramjets and scramjets can also be made without moving parts. But they need to go supersonic in order to work decently.
 
WIederling
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Re: Will single engine designs be viable in the future?

Thu Feb 02, 2017 3:26 pm

Calder wrote:
The Lear Fan comes to mind.

I seem to remember a two turbo shaft single prop tractor design
for a single pilot transport airplane sized well above the Caravan.

No luck refinding that on short notice.
Murphy is an optimist
 
RunningRidges
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Re: Will single engine designs be viable in the future?

Thu Feb 02, 2017 7:44 pm

Can't imagine that you'll ever see a large single engined conventional jet. However reliable you make it from a mechanical point of view, there's always going to be to high a risk from birdstrike / other FOD. What's more likely is a distributed electric propulsion system with one large gas turbine generating power for a large number of small electric motors. That way you get the efficiency of a large single engine with the power redundancy of multiple propulsion units
 
Flighty
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Re: Will single engine designs be viable in the future?

Fri Feb 03, 2017 3:12 pm

RunningRidges wrote:
Can't imagine that you'll ever see a large single engined conventional jet. However reliable you make it from a mechanical point of view, there's always going to be to high a risk from birdstrike / other FOD. What's more likely is a distributed electric propulsion system with one large gas turbine generating power for a large number of small electric motors. That way you get the efficiency of a large single engine with the power redundancy of multiple propulsion units


Great point. I still think it is reliable enough for GA, or Corporate, largely because of lower acquisition and maintenance costs. That matters more than fuel efficiency or that last "ultimate" layer of safety, for most of those customers. Of course, if you have the money for a late-model twinjet and 2 professional pilots to fly it, you can afford the ultimate level of safety. For mere mortals, we can't, so single jet is a worthwhile concept to talk about.

Airlines care more about fuel efficiency, by virtue of running 10 hours per day. So single engine could attract them there. And they also need ultimate safety. So maybe not. Although I have ridden on Cessna 208 Caravan single turboprop airliners before.
 
LightningZ71
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Re: Will single engine designs be viable in the future?

Fri Feb 03, 2017 8:49 pm

I have to think that you will never see any large commercial turbofan powered airliners that are allowed to do long, isolated ocean crossings. My reasoning is based more on how large, complex and expensive such an engine would have to be. Just off the top of my head, it would need the following:

At least 50% more thrust than a single engine from an equivalent twin jet (though double isn't really needed IMHO).

Two completely redundant fueling systems for the engine.

Two completely redundant oiling systems.

Two completely redundant generators

Two completely redundant digital engine control modules

Redundant anti icing systems

Redundant engine performance sensors

Fan and turbine blades that are stronger and heavier than current standards

A heavier casing to contain a failure of said blades

The list goes on.

When it is all said and done, the engine will be essentially as expensive as two smaller engines, just as massive, have a similar total surface area, and likely have to be off the plane twice as often for inspections.

Twins work well, provide the needed efficiency and redundancy, and have a largely superb record at the moment. I see no reason for the airliners to want singles, or for jet makers to further shoot themselves in the foot with respect to volume by persuing one single as an alternative.

I'm also not sold that a single would be any more efficient either.
 
frmrCapCadet
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Re: Will single engine designs be viable in the future?

Fri Feb 03, 2017 9:05 pm

People in Boeing country already fly single engine all of the time. Hour after hour we see these flights taking off and flying north out of our city.

http://www.kenmoreair.com/

The question begs the answer. How large a plane, how many passengers, and how long over water, and how far from an alternative airstrip. My suspicion is that as engines improve we will see the metrics up-gauging for a long time.
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ZKNCI
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Re: Will single engine designs be viable in the future?

Fri Feb 03, 2017 9:42 pm

WIederling wrote:
Calder wrote:
The Lear Fan comes to mind.

I seem to remember a two turbo shaft single prop tractor design
for a single pilot transport airplane sized well above the Caravan.

No luck refinding that on short notice.


Are you thinking of the Ayres LM200 Loadmaster?
https://aviationdoctor.files.wordpress. ... .jpg?w=603

Soloy also did the Pathfinder 21, a stretched C208 with two PT6s geared together.
Going a bit bigger and older, the Heinkel 177 had two DB605s per prop, and an unenviable engine fire record.
 
WIederling
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Re: Will single engine designs be viable in the future?

Sat Feb 04, 2017 9:13 am

ZKNCI wrote:
Are you thinking of the Ayres LM200 Loadmaster?
https://aviationdoctor.files.wordpress. ... .jpg?w=603

Yes, thank you!
Soloy also did the Pathfinder 21, a stretched C208 with two PT6s geared together.
Going a bit bigger and older, the Heinkel 177 had two DB605s per prop, and an unenviable engine fire record.

There were a wide range of "Kraftei" power unit devices around. ( and the high powered ones had geared together twin engine arrangements.)

Interesting to read the article on Wikipedia on "large aircraft engines".
What the author there misses is that the German engines were all held back by problems caused by unavailable high strength / high temp alloys.
( which on the other hand lead to early German jet engines having all the materials coping features of later designs like bleed air cooled turbine blades.)
Murphy is an optimist
 
chimborazo
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Re: Will single engine designs be viable in the future?

Sat Feb 04, 2017 1:38 pm

Jets generally have a much higher stalling speed than GA aircraft or the Caravan etc. The likelihood of walking away from a forced landing in a 1000kg GA aeroplane is actually quite high- if flown properly (and not over particularly rugged terrain for example) to touch down at the stall. In a 50,000kg jet at over 100Kn there is a huge amount of energy to dissipate so in general terms it should be less likely to have a "nice" forced landing because the availability of suitable places to put it down rapidly diminishes.
 
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Balerit
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Re: Will single engine designs be viable in the future?

Sat Feb 04, 2017 3:46 pm

Image
Licensed Aircraft Maintenance Engineer (retired).
 
benbeny
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Re: Will single engine designs be viable in the future?

Sat Feb 04, 2017 4:07 pm

I don't think that gonna happen. Just imagine how public perceives single engine for TATL.
Although we have single engined fighters flying for decades with very high requirements (high G load, rapid acceleration/deceleration, high temperature margin), fighters tend to fly far less than commercial jets, so chance for a failure to happen per given time is lower. Fighters have ejection seats, a luxury we mortals don't have.
I think you need to put high output APU to power hydraulics, pneumatics and electrics in an event of engine failure, which can simply be done cheaply by adding one more engine for redundancy instead of developing new high capability APU...
 
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flyingturtle
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Re: Will single engine designs be viable in the future?

Sat Feb 04, 2017 7:17 pm

mxaxai wrote:
in terms of probability, a likelyhood of exactly one engine failure in 10^9 flights


Isn't the cut-off defined as "less than one failure leading to a catastrophic outcome in 10^9 flight hours"? Or is it flights?

(Anyway, that makes aircraft, from an engineering point of view, much safer than any nuclear power plant. 100 years of uninterrupted operation are are only 10^5.9 hours.)


David
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7BOEING7
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Re: Will single engine designs be viable in the future?

Sat Feb 04, 2017 9:34 pm

benbeny wrote:
I
I think you need to put high output APU to power hydraulics, pneumatics and electrics in an event of engine failure, which can simply be done cheaply by adding one more engine for redundancy instead of developing new high capability APU...


A RAT (Ram Air Turbine) can handle the hydraulics and electronics needed to get you controllably to the ground/water. The only thing you need the pneumatics for is pressurization but without an engine you're descending anyway so you can probably get by without that -- cabin altitude rate of increase would be minimal with the pack(s) off and the aircraft would have a fair descent rate.
 
chornedsnorkack
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Re: Will single engine designs be viable in the future?

Tue Feb 07, 2017 11:23 am

chimborazo wrote:
Jets generally have a much higher stalling speed than GA aircraft or the Caravan etc. The likelihood of walking away from a forced landing in a 1000kg GA aeroplane is actually quite high- if flown properly (and not over particularly rugged terrain for example) to touch down at the stall. In a 50,000kg jet at over 100Kn there is a huge amount of energy to dissipate so in general terms it should be less likely to have a "nice" forced landing because the availability of suitable places to put it down rapidly diminishes.


Yes - so a jetliner designed to be safe for outlanding is likely to be inefficient.
Note that this does not rule out a turboprop designed for outlanding.
A widely popular commercial single engine plane is An-2. How do the reliability records of An-2s with piston engines compare against An-2s with turbopropellers?
 
WIederling
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Re: Will single engine designs be viable in the future?

Tue Feb 07, 2017 1:10 pm

chornedsnorkack wrote:
A widely popular commercial single engine plane is An-2. How do the reliability records of An-2s with piston engines compare against An-2s with turbopropellers?


difficult to tell. not many An-3 around ~35 ? ( versus 18,000 An-2 :-)
Murphy is an optimist
 
benbeny
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Re: Will single engine designs be viable in the future?

Tue Feb 07, 2017 3:22 pm

WIederling wrote:
chornedsnorkack wrote:
A widely popular commercial single engine plane is An-2. How do the reliability records of An-2s with piston engines compare against An-2s with turbopropellers?


difficult to tell. not many An-3 around ~35 ? ( versus 18,000 An-2 :-)

Ah, the mighty R-1820, a design dated from 1920s and still in production today as ASz-62 :old:

IMHO, TBO number itself says a lot about engine reliability
 
chornedsnorkack
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Re: Will single engine designs be viable in the future?

Tue Feb 07, 2017 6:57 pm

Also, how different, technically, are turbopropeller engines from turboshaft engines?
 
WIederling
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Re: Will single engine designs be viable in the future?

Tue Feb 07, 2017 7:51 pm

benbeny wrote:
Ah, the mighty R-1820, a design dated from 1920s and still in production today as ASz-62 :old:

IMHO, TBO number itself says a lot about engine reliability


Pedigree is slightly more convoluted:
https://en.wikipedia.org/wiki/Shvetsov_ ... vetsov.jpg
Murphy is an optimist
 
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DocLightning
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Re: Will single engine designs be viable in the future?

Sat Feb 11, 2017 6:29 pm

"The engine will never fail. Even if you throw rocks or large turkeys into it. Even if there is a critical manufacturing flaw. Even if it runs out of oil."

If you can satisfy that, then sure.
-Doc Lightning-

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