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One Engine Cruise  
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Posted (1 year 3 months 2 weeks 2 days 22 hours ago) and read 5217 times:

Idea is to reduce drag (the same as my previous topic    )

More than 90% commercial airplanes are twin engines because of efficiency not only fuel but also maintenance and purchase cost.

Two engines, like todays aircraft would be used for TO, LDG and Climb. When the plane reaches crusing altitude, one engine stops and folds into the fuselage. Engines should be placed in tail like MD-11, 727, DC-10 not like 737 pr A320

The cruising engine would be more powerfull than comparable engine on classic 2 engine aircraft, because only one engine would have power the aircraft.

I also have one question: if you place engines in the tail, do you get drag reduction (because jet exhaust goes into wake of the plane), or is it better to place them under wing?

Your thoughts?

46 replies: All unread, showing first 25:
 
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17016 posts, RR: 67
Reply 1, posted (1 year 3 months 2 weeks 2 days 22 hours ago) and read 5211 times:

Quoting cobra27 (Thread starter):
Two engines, like todays aircraft would be used for TO, LDG and Climb. When the plane reaches crusing altitude, one engine stops and folds into the fuselage

Any savings would be eaten by the extra weight and complexity of this solution.

Quoting cobra27 (Thread starter):
I also have one question: if you place engines in the tail, do you get drag reduction (because jet exhaust goes into wake of the plane), or is it better to place them under wing?

Advantages and disadvantages. Disadvantages prevail. The exhaust mixing with the wake is not an issue in any case.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently onlinemandala499 From Indonesia, joined Aug 2001, 6839 posts, RR: 75
Reply 2, posted (1 year 3 months 2 weeks 2 days 21 hours ago) and read 5199 times:

1. Maintenance:
That retraction and extension mechanism is going to be a nightmare to do, add weight, complexities, hence: more maintenance costs from that system.

2. Engine wear and tear:
The remaining engine would have its life used up pretty quickly... and that engine would run at higher cruise settings, adding to the wear and tear.

3. Waste of space:
Where are you going to put the engine when folded? Into space that would otherwise be usable for revenue generation purposes.

Add 1, 2 and 3... the savings go up in smoke pretty quickly.

A less complex method have been used in the past, that is to use booster engines for take off. The Trident had some versions with a 4th jet used for take off only... well... they don't use that method anymore for a reason. Some of the Antonov-2* series also had that additional jet option to augment the turboprops... the P-3 Orions had those too. Once more powerful engines became available (with the benefits of lower maintenance & fuel for lower thrust use), the augmented engines quickly became history.

There is a reason why those methods aren't used anymore.

Have you seen the single engine cruise performance tables of modern day twins? Lose an engine, you'll end up cruising at lower altitude and at higher power... and negates any fuel savings gained from shutting that engine down.

---
On the off note, it is probably going to be lighter to put an aerodynamic cone extension/retraction capability for such a system instead of retracting the whole engine into the fuselage... and if the system fails, take out hydraulic/pneumatic power, releases the locks, and the cone slides back leaving the engine intake open like in normal operations.

And the only airplanes I know that regularly shut down engines in-flight are the RAF Nimrods (thanks to the in-wing engines), where for low-level patrol speeds, they shut 2 engines down and fly on the remaining 2... and when they want to go back to base, they relight the 2 engines and go back to base on 4 engines.

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 3, posted (1 year 3 months 2 weeks 2 days 20 hours ago) and read 5147 times:

Quoting mandala499 (Reply 2):
The remaining engine would have its life used up pretty quickly... and that engine would run at higher cruise settings, adding to the wear and tear.
Quoting mandala499 (Reply 2):

Have you seen the single engine cruise performance tables of modern day twins? Lose an engine, you'll end up cruising at lower altitude and at higher power... and negates any fuel savings gained from shutting that engine down.

It would be a more powerful engine, so there wouldn't be high cruise setting. Bigger turbofans have lower specific fuel consumption (SFC) Altough the number of cycles on a helper engine would be lower, thats for sure

Quoting Starlionblue (Reply 1):

Any savings would be eaten by the extra weight and complexity of this solution.
Quoting mandala499 (Reply 2):
That retraction and extension mechanism is going to be a nightmare to do, add weight, complexities, hence: more maintenance costs from that system.

it would only be small increase in weight, and not more complex, a folding mechanism a nightmare, why? Compared to hydraulics and piping in the engines?

Quoting Starlionblue (Reply 1):
Advantages and disadvantages. Disadvantages prevail. The exhaust mixing with the wake is not an issue in any case.

Some howitzer shell have a much more range when they use gas at the end to reduce drag.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17016 posts, RR: 67
Reply 4, posted (1 year 3 months 2 weeks 2 days 20 hours ago) and read 5133 times:

Quoting cobra27 (Reply 3):
Quoting Starlionblue (Reply 1):
Advantages and disadvantages. Disadvantages prevail. The exhaust mixing with the wake is not an issue in any case.

Some howitzer shell have a much more range when they use gas at the end to reduce drag.

Apples and oranges. Howitzer shells are not self propelled.

Quoting cobra27 (Reply 3):
t would only be small increase in weight, and not more complex, a folding mechanism a nightmare, why? Compared to hydraulics and piping in the engines?

Way more complex.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinemmo From Qatar, joined Apr 2013, 66 posts, RR: 0
Reply 5, posted (1 year 3 months 2 weeks 2 days 20 hours ago) and read 5131 times:

Quoting cobra27 (Thread starter):
Your thoughts?

1) What would you do in case of an engine failure in cruise? I can picture it now, an aircraft descending with no engine running, no cabin pressure somewhat out of control. Having the one "helper" engine would not solve any problems. It would have large enough to sustain flight on one engine.

2) Twin engine ops are there for a reason.

3) Can't see it because of the complexity and redundancy that would be needed in the setup.

4) Are you taking two engines on the centerline? Otherwise you will have drag from the asymmetrical thrust and resultant rudder required for coordinated flight.

Just some quick thoughts.



If we weren't all crazy we would all go insane
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 6, posted (1 year 3 months 2 weeks 2 days 18 hours ago) and read 5062 times:

Close to centerline, like 727.
And 2 engines would there be for redundancy

Quoting Starlionblue (Reply 4):
Apples and oranges. Howitzer shells are not self propelled.

Some have gas at the end to reduce drag.
My point if engine in wing reduce drag, or is it the same as under the wing


User currently offlinemmo From Qatar, joined Apr 2013, 66 posts, RR: 0
Reply 7, posted (1 year 3 months 2 weeks 2 days 18 hours ago) and read 5048 times:

Quoting cobra27 (Reply 6):
Close to centerline, like 727.
And 2 engines would there be for redundancy

Then I have to ask, why not just have two engines to begin with? Much simpler and easier.

Close to centerline will mean adverse yaw which means rudder which means increased drag. Again, why not just two engines as it exists not?



If we weren't all crazy we would all go insane
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 8, posted (1 year 3 months 2 weeks 2 days 16 hours ago) and read 4952 times:

That is the reason that most airplane are 2-engine and not four engine.

Somehow I think a single engine would reduce fuel consumption and increase range of the aircraft. On longer flights you burn fuel just to carry the fuel, not short hops.

I think 767/787/A330 would be ideally suited.

Two engines compared to one engine has more frontal area


User currently onlinemandala499 From Indonesia, joined Aug 2001, 6839 posts, RR: 75
Reply 9, posted (1 year 3 months 2 weeks 2 days 15 hours ago) and read 4926 times:

Quoting cobra27 (Reply 3):
It would be a more powerful engine, so there wouldn't be high cruise setting. Bigger turbofans have lower specific fuel consumption (SFC) Altough the number of cycles on a helper engine would be lower, thats for sure

I dunno if this is bad news... but...
2x 30,000lbs engines at cruise will burn about 2.5 tons an hour using current technology... hauling 70 tons of aircraft.
2x 60,000lbs engines at cruise will burn about 5 tons an hour using current technology... hauling about 140 tons of aircraft...
sure, looks good for your argument... But... lose one engine on that widebody, you'll have to go down 15,000ft from your cruise altitude, burn 5.5 tons of fuel an hour, and go 80 knots slower.
The sad truth is, 2 engines will burn less than one the same engine taking the burden of 2 engines.
Besides, look at it again... 2x30,000lbs burns 2.5 tons an hour... so what happens if you replace those two engines with 1x60,000lbs engine at cruise... you'd still burn 2.5 tons, but now have extra weight to carry (you still got that one other 60,000lbs engine folded somewhere remember), you'd end up burning MORE than 2.5 tons.

And those numbers are from actual performance numbers, not some SFC number...

Quoting cobra27 (Reply 3):
it would only be small increase in weight, and not more complex, a folding mechanism a nightmare, why? Compared to hydraulics and piping in the engines?

1. Engines are not light... they are certainly heavier than landing gears... now see how much work goes into the landing gear, how beefed up the thing is... etc etc etc...
2. The mounts retracting and extending, the whole mechanism has to be able to support the engine thrust pulling the aircraft along... certainly gotta have to be way beefier than landing gears...
3. Plumbing? Bleeds? Electricals? Hydraulics? etc etc...

Quoting cobra27 (Reply 6):
Close to centerline, like 727.
And 2 engines would there be for redundancy

Close to centerline? Like 727? OK, how are you going to do it?
1. High Bypass turbofans need clean airflow coming into the fan... put it near the body and you'd start having aerodynamic challenges... otherwise, throw out the fuel economy.
2. Mounting hi-bypass engines on the tail is a LOT more complex than low-bypass... that's why we don't see widebody twins with tailmounted engines. The DC-10 and MD-11 was a structural nightmare. The Tristar, well, the center engine can't behave as reactive as the wing engines due to the S-duct...
3. How are you going to fold an efficient high bypass engine into a smaller than the usual cross section part of the plane?

Are you going to put the engines left and right of the rear body, and then fold one in during cruise? Will you have the option of folding either of the two engines, or just one side gets folded in? And then there's lateral structural loads on the vertical fin when cruising with one engine folded... and then... trim drag...

How do you keep the aircraft flying pressurized and with electrical and hydraulic power should that cruise engine decide to go and have an uncontained engine failure or just simply... fail...?
How long would it take to flip out the other engine and start it up?
What are you going to use to start that engine up?
Bleed? Well, where's the source going to come from? The failed engine? Won't work...
Electrical? Well main AC power would lose it's main source... DC will drain the battery too... and RAT will only generate enough for critical systems (and HYD too).
APU?    Is the airplane in the APU starting envelope or not? Will the APU at that altitude be able to generate Bleed and ELEC or only one of the two? Not all APUs today can start at 35,000ft and provide Bleed and ELEC at that altitude.

And then... after all that... the other engine that you now want to start, is out of it's starting envelope... so you have to drift down to its starting envelope altitude and speed before starting it and restore power, elec, bleed, etc...

Drifting down... consumes the battery power too... will you have battery power by the time you enter the starting envelope?

Quoting cobra27 (Reply 6):
My point if engine in wing reduce drag, or is it the same as under the wing

Engines IN wing has less drag than engines under wing.
Engines IN wing is structurally more complex than engines under wing.
Engines IN wing has critical systems and structure damage risk when the engine goes kaboom or catches fire, than engines under wing.

Quoting cobra27 (Reply 8):
Somehow I think a single engine would reduce fuel consumption and increase range of the aircraft. On longer flights you burn fuel just to carry the fuel, not short hops.

But as you see above... for the same weight, having 1 bigger engine instead of 2 smaller engines, burns more for the same engine technology generation.



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 10, posted (1 year 3 months 2 weeks 2 days 12 hours ago) and read 4840 times:

Wow what a long reply!

Quoting mandala499 (Reply 9):
2x 30,000lbs engines at cruise will burn about 2.5 tons an hour using current technology... hauling 70 tons of aircraft.
2x 60,000lbs engines at cruise will burn about 5 tons an hour using current technology... hauling about 140 tons of aircraft...

Off the topic, but
numbers of fuel burn seem a little low esecially if you take for example A320 which has less powerful engine and runs at nearly maxi weight. I think 3 tonnes at that weight would be more appropriate.

Anyway it is just a discussion, I didn't consider all the possibilities.
Engine failure would be probably the biggest obstacle. More powerful APU would solve the electrics and pressurisation

But to show what was my point:
747 or A380 could do perfectly well or better with 3 engines in cruise

I am not proposing building a single engine airliner, just one engine for cruise


User currently offlinemmo From Qatar, joined Apr 2013, 66 posts, RR: 0
Reply 11, posted (1 year 3 months 2 weeks 2 days 12 hours ago) and read 4822 times:

Quoting cobra27 (Reply 10):
More powerful APU would solve the electrics and pressurisation

I know of no APU that can supply bleed air for pressurization and complete electrics at altitude. In addition to bleed air for pressurization, you will need bleed for engine start.

I feel as if this keeps coming back to the same issues, which you seem to just gloss over.

Quoting cobra27 (Reply 10):
I am not proposing building a single engine airliner, just one engine for cruise

In reality you are!



If we weren't all crazy we would all go insane
User currently offlineViscount724 From Switzerland, joined Oct 2006, 25117 posts, RR: 22
Reply 12, posted (1 year 3 months 2 weeks 2 days 11 hours ago) and read 4811 times:

I can't see any certification authority ever certifying an airliner designed to carry a few hundred passengers that could potentially become a glider if the one operating engine failed.

User currently onlinemandala499 From Indonesia, joined Aug 2001, 6839 posts, RR: 75
Reply 13, posted (1 year 3 months 2 weeks 2 days 11 hours ago) and read 4795 times:

Quoting cobra27 (Reply 10):
I think 3 tonnes at that weight would be more appropriate.

3 tons for a 1 hour flight yes, but we're talking about cruise fuel burn, not trip burn. An A320 at 70tons landing weight flying for 375NM will burn about 3tons for the trip at 0.78mach cruise... which takes 1Hr02mins.

Those numbers I picked are from operational performance manuals for A320 with CFM56-5B engines for the narrowbody, and 767-300 (PW4060) for the widebody.

Quoting cobra27 (Reply 10):
Anyway it is just a discussion, I didn't consider all the possibilities.

I know   
But I did those numbers just to give a little dose of reality to the idea...

One major obstacle to your idea would be certification of redundant system requirements... You can kiss ETOPS goodbye with your idea, not only because of the "single active engine and the other stowed", but also due to requirements for requiring 2 separate generators from 2 powerplant sources to be online on the ETOPS portion of the flight, plus numerous other redundancy requirements... usually dependent on having 2 engines for the electrics and hydraulics. So your idea unfortunately will not be allowed for flying more than 60mins from a suitable airport.



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineRoseflyer From United States of America, joined Feb 2004, 9592 posts, RR: 52
Reply 14, posted (1 year 3 months 2 weeks 2 days 10 hours ago) and read 4757 times:

Quoting cobra27 (Thread starter):

The cruising engine would be more powerfull than comparable engine on classic 2 engine aircraft, because only one engine would have power the aircraft.

Airplanes cruise at about 80-90% N1. At altitude the amount of thrust available is only 30-40% of what is available in denser air near the ground. If a twin engine airplane loses an engine in cruise, it usually drifts down 10,000ft or so (depends on airplane) due to its inability to remain in level cruise in the thin air above 30,000ft. In order to be able to cruise at conventional altitudes, you are going to have to drastically increase the size of your one primary engine. Your second backup engine won’t be able to shrink because the plane has to be able to take off if you lose your primary engine. All that one engine cruise did is forced you to put a larger engine on the airplane and probably made fuel burn worse.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 15, posted (1 year 3 months 2 weeks 1 day 22 hours ago) and read 4545 times:

Quoting Roseflyer (Reply 14):
Airplanes cruise at about 80-90% N1. At altitude the amount of thrust available is only 30-40% of what is available in denser air near the ground. If a twin engine airplane loses an engine in cruise, it usually drifts down 10,000ft or so (depends on airplane) due to its inability to remain in level cruise in the thin air above 30,000ft. In order to be able to cruise at conventional altitudes, you are going to have to drastically increase the size of your one primary engine


I think 757 engine size would work on A320 size platform.

I think that if you have optimal engine specially designed for cruise (not overbuilt), you got lower consumption.

[Edited 2013-05-08 03:09:41]

User currently offlineRoseflyer From United States of America, joined Feb 2004, 9592 posts, RR: 52
Reply 16, posted (1 year 3 months 2 weeks 1 day 17 hours ago) and read 4445 times:

Quoting cobra27 (Reply 15):


I think 757 engine size would work on A320 size platform.

I think that if you have optimal engine specially designed for cruise (not overbuilt), you got lower consumption.

It's an interesting concept, but one engine working harder is not necessarily better. For example, in a L1011, if the center engine was shutdown in cruise, overall fuel burn goes up. And I don't think a retractable engine is possible.

Also, engines are already optimized for cruise.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 17, posted (1 year 3 months 2 weeks 1 day 15 hours ago) and read 4382 times:

Quoting Roseflyer (Reply 16):
t's an interesting concept, but one engine working harder is not necessarily better. For example, in a L1011, if the center engine was shutdown in cruise, overall fuel burn goes up. And I don't think a retractable engine is possible.

Also, engines are already optimized for cruise.

Yes because not working engine has the highest drag, because it has a hole, it has real bad aerodynamics.

Engines aren't optimized for cruise. They have to provide take off thrust which is around 4 times higher than cruise thrust


User currently offlineKC135Hydraulics From United States of America, joined Nov 2012, 298 posts, RR: 0
Reply 18, posted (1 year 3 months 2 weeks 1 day 14 hours ago) and read 4352 times:

Quoting cobra27 (Reply 17):
Yes because not working engine has the highest drag, because it has a hole, it has real bad aerodynamics.

Engines aren't optimized for cruise. They have to provide take off thrust which is around 4 times higher than cruise thrust

People here have already demonstrated numerous reasons why this concept is not economically feasible but you continue to argue the point despite it, so why even bother asking for our thoughts? Move forward with your concept and we'll see how far it gets. I'm sure if it was a viable plan it would have already been attempted


User currently offlineRoseflyer From United States of America, joined Feb 2004, 9592 posts, RR: 52
Reply 19, posted (1 year 3 months 2 weeks 1 day 13 hours ago) and read 4349 times:

Cobra,

I appreciate you coming up with clever ideas to reduce drag. Innovation is a great thing, but I don't think you are on the wright track.

One thing that Boeing has played around with in the past and has a lot of opportunity to reduce drag is to replace the horizontal stabilizer with a lifting canard. With a canard, you can have the canard and wing both producing positive lift during climb and cruise. With a tail mounted horizontal stabilizer, the elevator creating downward lift relative to the wing, which requires the main wing to get even more lift during climb and nose up attitudes. If you put a canard in the front with the elevators forward of the wing, both lifting surfaces are positive and induced drag drops dramatically. A lifting-canard generates an upload, in contrast to a conventional aft-tail which generates negative lift that must be counteracted by extra lift on the main wing. As the canard lift appears to increase the overall lift capability of the aircraft, this may appear to unambiguously favor the canard layout.

The problem with a canard is stall recovery and stability. The downwash has a negative effect on the main wing as well. These problems can be solved. A lifting canard configuration is inherently unstable unlike a rear stabilizer which is inherently stable, so you have to over come this with the control system. With the latest fly by wire software, commercial airplanes are moving away from being inherently stable throughout their entire flight envelope. The canard also has to be designed to stall before the main wing as well, which requires some creative engineering. In general it is really hard to do, but possible and would greatly reduce induced drag. I think it is a much better idea than retractable engines, vertical stabilizers or other control surfaces.

Quoting cobra27 (Reply 17):

Yes because not working engine has the highest drag, because it has a hole, it has real bad aerodynamics.

Engines aren't optimized for cruise. They have to provide take off thrust which is around 4 times higher than cruise thrust

It sounds like you have an underlying assumption that airplanes have excess power at altitude and aren't optimized for cruise. In reality they don't have excess power. They may take 4 times more power at takeoff, but that's also because the denser air and slower speed allows much more thrust. At altitude an engine is only capable of about 30-40% of the thrust that it is on the ground. At cruise engines are running at 80-90% of available power. If you push the engine harder, then you are going to tear it up and require more frequent overhauls.

Your one engine idea either requires a much larger engine (75% more powerful), which is going to add a lot of weight and kill any efficiency gains or forces an airplane to cruise in the 20,000ft range with the turboprops which is not ideal cruising altitude for drag.

[Edited 2013-05-08 11:55:08]


If you have never designed an airplane part before, let the real designers do the work!
User currently onlineoly720man From United Kingdom, joined May 2004, 6697 posts, RR: 11
Reply 20, posted (1 year 3 months 2 weeks 1 day 10 hours ago) and read 4259 times:

Quoting cobra27 (Reply 17):
Engines aren't optimized for cruise.

They are optimized for cruise (just like the wings are optimized for cruise). That's what they spend 80% of their life doing. What that means is the performance is less efficient at take off it doesn't mean they can't achieve take off thrust.



wheat and dairy can screw up your brain
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 21, posted (1 year 3 months 2 weeks 23 hours ago) and read 4126 times:

I had something different in mind.

Bigger fan that has fewer and more aerodynamic blades. Possibly geared turbofan. I think slower rotating fan has advantages
And that engines exhaust that exits in the wake of the plane (in the tail).


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17016 posts, RR: 67
Reply 22, posted (1 year 3 months 2 weeks 23 hours ago) and read 4126 times:

Quoting cobra27 (Thread starter):
I also have one question: if you place engines in the tail, do you get drag reduction (because jet exhaust goes into wake of the plane), or is it better to place them under wing?
Quoting cobra27 (Reply 21):
And that engines exhaust that exits in the wake of the plane (in the tail).

What's up with the perceived need to put the exhaust in the wake of the plane?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSlcpilot From United States of America, joined Aug 2003, 582 posts, RR: 2
Reply 23, posted (1 year 3 months 2 weeks 19 hours ago) and read 4059 times:

This has been an interesting thread with most replies being in the "con" area. There are two examples; however, that suggest the idea might not be as outlandish as many suggest.

It is my understanding Boeing considered a thrusting APU for the 777-200LR in early iterations. Now this obviously didn't happen for engineering/economic reasons, but it was studied enough to make it into the public domain. Most of
us here aren't privy as to how close that trade off study was.

Another non-121 solution that involved an engine being shutdown was the Voyager flight in 1986. While I agree, single engine Part 121 turbine flight is unlikely now, who is to say a 3 engine solution defaulting to 2 engine cruise won't ever work? Most would agree the Voyager was very optimized for efficient flight, which is what we're all after, right?

Thoughts?

SLCPilot



I don't like to be fueled by anger, I don't like to be fooled by lust...
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 24, posted (1 year 3 months 2 weeks 18 hours ago) and read 4048 times:

Quoting Starlionblue (Reply 22):
What's up with the perceived need to put the exhaust in the wake of the plane?

In the wake of wings, but that seems impossible. The wake of the body more likely.
Like cyclists in peloton . The driver behind gets up 40 % less drag, am not sure but front driver also benefits from it but not as much.

Quoting Slcpilot (Reply 23):
who is to say a 3 engine solution defaulting to 2 engine cruise won't ever work?

naysayers


User currently offline26point2 From United States of America, joined Mar 2010, 820 posts, RR: 0
Reply 25, posted (1 year 3 months 2 weeks 17 hours ago) and read 4134 times:

A folding vertical stab with attached engine sounds like a mechanical nightmare.

Here's mine.....we know fuel can be close to half the total weight of a long range airliner at takeoff. Huge amounts of fuel are used to lift more fuel. Why not takeoff with minimum fuel and incorporate mid-air refueling? This could allow the use of smaller and more efficient engines saving even more fuel.

Edit: spelling

[Edited 2013-05-09 07:49:33]

User currently offline7BOEING7 From United States of America, joined Oct 2012, 1537 posts, RR: 8
Reply 26, posted (1 year 3 months 2 weeks 16 hours ago) and read 4117 times:

Quoting mandala499 (Reply 2):
the P-3 Orions had those too

Actually the P-2 Neptune which had 2 recips was equipped with 2 jets, the P-3 had 4 turboprops and didn't need the jets.

Quoting mmo (Reply 11):
Quoting cobra27 (Reply 10):More powerful APU would solve the electrics and pressurisation
I know of no APU that can supply bleed air for pressurization and complete electrics at altitude.

  

Quoting mmo (Reply 11):
In addition to bleed air for pressurization, you will need bleed for engine start.

Inflight starts do not use the APU if there is sufficient airspeed for a windmill start which is normally the case.

Quoting cobra27 (Reply 10):
But to show what was my point:
747 or A380 could do perfectly well or better with 3 engines in cruise

If they wanted to fly at a lower less efficient altitude. One of the airplanes that flies this way is the P-3 Orion which will "loiter" with either #1 or #4 or both shutdown. However when they do this they are interested in staying airborne longer not getting from A to B -- they are at a very low airspeed and a much lower altitude. This is an efficiency that works with a turboprop but not a pure jet.


User currently onlinemandala499 From Indonesia, joined Aug 2001, 6839 posts, RR: 75
Reply 27, posted (1 year 3 months 2 weeks 15 hours ago) and read 4134 times:

Quoting cobra27 (Reply 15):
I think 757 engine size would work on A320 size platform.

Good luck to that. The A320 engines are physically capable of producing 33,000lbs at take off (and used as such on the A321), the 757 engines are 40,000lbs take off thrust range...
So how and where are you going to fold that engine into again?

Quoting cobra27 (Reply 15):
I think that if you have optimal engine specially designed for cruise (not overbuilt), you got lower consumption.

On the efficiency front, the primary criteria IS cruise efficiency. On the power front, the primary criteria is take off thrust.

Quoting cobra27 (Reply 17):
Engines aren't optimized for cruise. They have to provide take off thrust which is around 4 times higher than cruise thrust
Quoting 7BOEING7 (Reply 26):
Actually the P-2 Neptune which had 2 recips was equipped with 2 jets, the P-3 had 4 turboprops and didn't need the jets.

D'oh! Silly me! Yes! the Neptune! Why I typed P-3 I dunno!

Quoting 7BOEING7 (Reply 26):
One of the airplanes that flies this way is the P-3 Orion which will "loiter" with either #1 or #4 or both shutdown.

That makes it the Nimrod and P-3 then...

Quoting 7BOEING7 (Reply 26):
Inflight starts do not use the APU if there is sufficient airspeed for a windmill start which is normally the case.

If you're outside the windmilling in-flight start envelope, then you'd need either a motor start or a bleed start...



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 28, posted (1 year 3 months 2 weeks 14 hours ago) and read 4118 times:

Quoting mandala499 (Reply 27):
Good luck to that. The A320 engines are physically capable of producing 33,000lbs at take off (and used as such on the A321), the 757 engines are 40,000lbs take off thrust range...
So how and where are you going to fold that engine into again?

I didn't know they are so powerful, real Hulks.

Quoting 26point2 (Reply 25):
Here's mine.....we know fuel can be close to half the total weight of a long range airliner at takeoff. Huge amounts of fuel are used to lift more fuel. Why not takeoff with minimum fuel and incorporate mid-air refueling? This could allow the use of smaller and more efficient engines saving even more fuel.

It has been discussed a lot. Also a fuel stop uses less fuel than lets sen 8000nm trip. But the hole process of inflight refuelling is kind dangerous


User currently offlinemmo From Qatar, joined Apr 2013, 66 posts, RR: 0
Reply 29, posted (1 year 3 months 2 weeks 13 hours ago) and read 4086 times:

Quoting 7BOEING7 (Reply 26):
Inflight starts do not use the APU if there is sufficient airspeed for a windmill start which is normally the case.

Really???? Then perhaps you could tell me why both Boeing and Airbus have that applicable section in their QRHs?

I guess the reference to APU bleed is something to be disregarded...................

Please note the qualifier you have written ....IF



If we weren't all crazy we would all go insane
User currently offline7BOEING7 From United States of America, joined Oct 2012, 1537 posts, RR: 8
Reply 30, posted (1 year 3 months 2 weeks 12 hours ago) and read 4045 times:

Quoting mmo (Reply 29):
Quoting 7BOEING7 (Reply 26):Inflight starts do not use the APU if there is sufficient airspeed for a windmill start which is normally the case.

Really???? Then perhaps you could tell me why both Boeing and Airbus have that applicable section in their QRHs?

I guess the reference to APU bleed is something to be disregarded...................

Please note the qualifier you have written ....IF

Chill out.

Since you can dispatch with an inoperative APU and the 747 APU can't be started in flight, I was just pointing out that in flight if you needed to relight the engine you always had the ability to due a windmill start. That's why there's an "IF" there. In fact faced with an in flight start requirement (very unlikely these days) most crews would already have the airspeed required for a windmill start or would accelerate to get it rather than wait to descend to a much lower altitude when the APU finally becomes available for a cross bleed start. The times an in flight start has been accomplished through either method are rare and generally have something to do with a volcano.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17016 posts, RR: 67
Reply 31, posted (1 year 3 months 2 weeks 9 hours ago) and read 3984 times:

Quoting 26point2 (Reply 25):
Here's mine.....we know fuel can be close to half the total weight of a long range airliner at takeoff. Huge amounts of fuel are used to lift more fuel. Why not takeoff with minimum fuel and incorporate mid-air refueling? This could allow the use of smaller and more efficient engines saving even more fuel.

As mentioned above, it has been discussed at length on this forum. In flight refueling is expensive (gotta send up that other plane) and risky.

Quoting cobra27 (Reply 24):
Quoting Starlionblue (Reply 22):
What's up with the perceived need to put the exhaust in the wake of the plane?

In the wake of wings, but that seems impossible. The wake of the body more likely.
Like cyclists in peloton . The driver behind gets up 40 % less drag, am not sure but front driver also benefits from it but not as much.

Sorry but I still don't understand what you are trying to say. Do you mean that an engine in the tail is less draggy because of some sort of interaction with the exhaust?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMir From United States of America, joined Jan 2004, 21556 posts, RR: 55
Reply 32, posted (1 year 3 months 2 weeks 7 hours ago) and read 3946 times:

Quoting cobra27 (Reply 24):
Like cyclists in peloton . The driver behind gets up 40 % less drag, am not sure but front driver also benefits from it but not as much.

That's why people have talked about formation flights, but that wouldn't help a single airplane. An airplane's exhaust is going to be caught up in its wake anyway, since the wake is at least as wide as the wingspan.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 33, posted (1 year 3 months 2 weeks 7 hours ago) and read 3941 times:

You'll have a friend in keesje in this one, who is a fan of a thrusting APU as a third engine. That no manufacturer has gone with that idea tells you something.

User currently onlinemandala499 From Indonesia, joined Aug 2001, 6839 posts, RR: 75
Reply 34, posted (1 year 3 months 2 weeks 5 hours ago) and read 3914 times:

Quoting mmo (Reply 29):
Really???? Then perhaps you could tell me why both Boeing and Airbus have that applicable section in their QRHs?

I guess the reference to APU bleed is something to be disregarded...................

Please note the qualifier you have written ....IF

For 777 & 787 (GE & RR): The QRH does also say for dual ENG fail (which would be applicable in this topic's discussion), "IF" APU available, then start it... However since the 777 APU cannot supply bleed below FL220 (and for 787 doesn't use bleed air start), I guess they put APU start in DUAL ENG FAIL checklist for ELEC needs. For both 777 & 787, GE needs 270KIAS prior to windmill start, and RR needs 250KIAS).

For 320/330/340, in the DUAL ENG FAIL (Fuel Remaning), the APU is stated "WHEN BELOW FL250, APU (if operative...START)".

At high altitudes, yes, Bleed for start is to be disregarded.

And for Cobra27... The inflight start can take longer than 2 minutes per engine...

Quoting cobra27 (Reply 24):
naysayers

Not naysayers, but economics. We didn't have Tristars, DC-10s, MD-11s, Tridents, 727s and Tu154s shutting down the middle engines in cruise...(yea yea yea, we know about the "draggy hole"). The nearest to this is the Super 727, with the bigger 1&3 engines, keeping the #2 original engine and used more as a boost engine... (but even that's not shut down in flight AFAIK).

Quoting cobra27 (Reply 24):
In the wake of wings, but that seems impossible. The wake of the body more likely.
Like cyclists in peloton . The driver behind gets up 40 % less drag, am not sure but front driver also benefits from it but not as much.

In the wake of the wing is not impossible... have an in-wing engine.   
You want the engine intake or exhaust in the wake ?
For efficient operations, you want the engine intake not in the wake of anything... the exhaust don't really matter.
With your idea of having only 1 engine running and the other is folded in... you want the engine to be in clean airflow to reduce risks of compressor stalls and surges (which leads to engine failures).



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlinePihero From France, joined Jan 2005, 4402 posts, RR: 76
Reply 35, posted (1 year 3 months 1 week 6 days 23 hours ago) and read 3836 times:

Quoting Roseflyer (Reply 19):
I don't think you are on the wright track.

  

I love it ! You made my day !

To be serious again, the **only** airliner I know wich could and did shut an engine down in flight was the HS Trident 3.

[Edited 2013-05-10 02:20:22]


Contrail designer
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 36, posted (1 year 3 months 1 week 6 days 23 hours ago) and read 3834 times:

Quoting Starlionblue (Reply 31):
Sorry but I still don't understand what you are trying to say. Do you mean that an engine in the tail is less draggy because of some sort of interaction with the exhaust?
Quoting mandala499 (Reply 34):
In the wake of the wing is not impossible... have an in-wing engine.
You want the engine intake or exhaust in the wake ?
For efficient operations, you want the engine intake not in the wake of anything... the exhaust don't really matter.
With your idea of having only 1 engine running and the other is folded in... you want the engine to be in clean airflow to reduce risks of compressor stalls and surges (which leads to engine failures).

You have a point. I looked at show Blended Wing Body design, and there were no inwing engine like B-2 bomber


User currently onlineoly720man From United Kingdom, joined May 2004, 6697 posts, RR: 11
Reply 37, posted (1 year 3 months 1 week 6 days 18 hours ago) and read 3748 times:

Quoting cobra27 (Reply 36):
and there were no inwing engine like B-2 bomber

Commercial aircraft don't need low observability.

Having buried engines means a compromised inlet flow which isn't good for performance efficiency.



wheat and dairy can screw up your brain
User currently onlinemandala499 From Indonesia, joined Aug 2001, 6839 posts, RR: 75
Reply 38, posted (1 year 3 months 1 week 6 days 16 hours ago) and read 3718 times:

Quoting Pihero (Reply 35):
To be serious again, the **only** airliner I know wich could and did shut an engine down in flight was the HS Trident 3.

You mean it took off on 3.5 engines, climbed on 3 and cruised on 2 engines?   



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 39, posted (1 year 3 months 1 week 6 days 14 hours ago) and read 3665 times:

Quoting oly720man (Reply 37):
Having buried engines means a compromised inlet flow which isn't good for performance efficiency.

Like Lockheed Tristar middle engine? As oposed to MD-11 engine?


User currently onlineoly720man From United Kingdom, joined May 2004, 6697 posts, RR: 11
Reply 40, posted (1 year 3 months 1 week 6 days 10 hours ago) and read 3598 times:

Quoting cobra27 (Reply 39):
Like Lockheed Tristar middle engine? As oposed to MD-11 engine?

No, like in a B2, though the S bend on the Tristar, B727 and Trident is less good for the engine performance than a straight duct.



wheat and dairy can screw up your brain
User currently offlinewingscrubber From UK - England, joined Sep 2001, 848 posts, RR: 0
Reply 41, posted (1 year 3 months 1 week 2 days 23 hours ago) and read 3120 times:

A lot of negative in this thread! This concept is achievable, but the motivation and benefit for doing so is the question.

I think the best example of auxiliary engines shut-down in flight is the B-36 peacemaker, which augmented the props with 4 turbojets, but the only reason for doing so was the limited turbine technology available at the time, together with the range requirements of the aircraft. The turbojets of the era were too thirsty to achieve the required range, but the props alone weren't powerful enough to allow the aircraft to take off, so it had to carry spare engines, but they were not retractable and dangled in the slipstream causing a drag penalty for the remainder of the flight.
http://en.wikipedia.org/wiki/Convair_B-36

But the golden example of a drag-reducing retractable jet engine has to be this-
http://www.gizmag.com/bonusjet-glide...h-jet-engine/16017/picture/119190/
But this is clearly for a niche application, with a very small jet   Achieving the same thing with an RB211 on an airliner would be a bit more challenging, and the drag penalty reduction wouldn't be worth carrying the weight, might as well just use the engine rather than tuck it away.

Airliners with JATO installed is a worthy concept though, no?  http://www.youtube.com/watch?v=97rSobuKBxI



Resident TechOps Troll
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 42, posted (1 year 3 months 1 week 2 days 23 hours ago) and read 3113 times:

Cost ineffective
Added weight
Complex mechanism
Assymetry chances.



Think of the brighter side!
User currently offlinePihero From France, joined Jan 2005, 4402 posts, RR: 76
Reply 43, posted (1 year 3 months 1 week 2 days 20 hours ago) and read 3103 times:

Quoting wingscrubber (Reply 41):
Airliners with JATO installed is a worthy concept though, no?

... or a runway built like a huge conveyor belt      



Contrail designer
User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 44, posted (1 year 3 months 1 week 2 days 13 hours ago) and read 2994 times:

Quoting wingscrubber (Reply 41):
This concept is achievable, but the motivation and benefit for doing so is the question.

Well if it is not double digit improvement it is not worth doing it.


User currently offline7BOEING7 From United States of America, joined Oct 2012, 1537 posts, RR: 8
Reply 45, posted (1 year 3 months 1 week 2 days 12 hours ago) and read 2997 times:

Quoting wingscrubber (Reply 41):
Airliners with JATO installed is a worthy concept though, no?

The option was available on 727's for Mexicana Airlines out of hot/high Mexico City way back when.

http://www.youtube.com/watch?v=G7LErwBNobU


User currently offlinecobra27 From Slovenia, joined May 2001, 1011 posts, RR: 0
Reply 46, posted (1 year 3 months 1 week 15 hours ago) and read 2767 times:

Quoting HAWK21M (Reply 42):
Cost ineffective - Yeah really?
Added weight-yes but considering you burn less fuel, the takoff weight should be lower for the same distance, otherwise is not god doing it
Complex mechanism- maybe you don't need a foldable engine, just a aerodynamic fitting over inlet
Assymetry chances.

Small assimetry like 2 engines in tail don't produce so much assimetry


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