rbavfan
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Re: Could an unpressurised passenger jet ever become competitive?

Sun Sep 08, 2019 8:30 pm

rjsampson wrote:
There's often a small exception to the rule...

While not a jet, a Part 121 Carrier called Cape Air placed 100 orders for a brand-new, unpressurized aircraft called the Tecnam P2012:

https://en.wikipedia.org/wiki/Tecnam_P2012_Traveller



Yes and that is for a short hop to smaller airports. Not really meant for mainline ops at some of the airports. Not the same market needs, irrelevant to the discussion as Cape Air uses them for under 20 passenger seat ops.
 
rbavfan
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Re: Could an unpressurised passenger jet ever become competitive?

Sun Sep 08, 2019 8:48 pm

RJMAZ wrote:
We will definitely see unpressurized airliners in a decade or two.

Electric propulsion will be the reason why. On a multiple hour flight it is worth the effort to climb up to 30,000ft. On a very short flight the benefit of flying high is not as great. As electric aircraft will be limited to ultra short haul they may as well save weight and fly low.

The noise issue of flying low will not be a problem for electric aircraft.

Also generating cabin pressure and cabin heat in an all electric aircraft might be an issue as there is no bleed air from a gas turbine.

I expect small general aviation airports close to city centres that have strict noise curfews to open up with electric aircraft. We can then have small point to point flights between tiny airports capturing a new market often served by cars and trains. These electric aircraft can also feed into large hubs to take conventional fueled aircraft for long flights.


You realize a large portion of the noise is from the prop, not the engine.
 
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atcsundevil
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Re: Could an unpressurised passenger jet ever become competitive?

Sun Sep 08, 2019 9:17 pm

SoCalPilot wrote:
atcsundevil wrote:
They certainly wouldn't be operating above FL600. Controlled airspace only extends to FL600 (in the US, anyway).

Not correct. The airspace above FL600 is Class E airspace which is controlled airspace.

Okay, I guess I should have specified that Class A only extends to FL600, but I wasn't trying to get bogged down with details. While the FAA has control authority and responsibility for services above FL600, it lacks the capability to do so. While it is technically controlled airspace, FAA controllers don't currently have the ability to provide navigation or separation services due to radar and VOR limitations (even though no one flies by VOR anymore). While I've never worked a flight above FL600, my understanding is the facilities that regularly do so simply clear an aircraft to operate above FL600 since separation services can no longer be provided. So yes, controlled, but sorta not.
 
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SEPilot
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Re: Could an unpressurised passenger jet ever become competitive?

Sun Sep 08, 2019 9:44 pm

Jets basically gain efficiency dramatically with higher altitude (until the air gets too thin) so it makes no sense to build one that is limited to 10,000 ft. Even on relatively short hops it uses less fuel to climb high and then descend than to stay low. Prop planes, yes. Electric planes make no sense with current technology; the energy density of all current and foreseeable batteries is so much lower than jet fuel that they cannot begin to be competitive. And charging time is prohibitive as well.
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VSMUT
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Re: Could an unpressurised passenger jet ever become competitive?

Sun Sep 08, 2019 10:30 pm

AirFiero wrote:
VSMUT wrote:
RJMAZ wrote:
We will definitely see unpressurized airliners in a decade or two.

Electric propulsion will be the reason why. On a multiple hour flight it is worth the effort to climb up to 30,000ft. On a very short flight the benefit of flying high is not as great. As electric aircraft will be limited to ultra short haul they may as well save weight and fly low.


This. Flying the ATR on really short island hopper routes, I've found it much faster to fly at around 6000 to 8000 ft. You waste a lot of time climbing, it is much faster to just level off and rush off towards the destination at Vmo. On a short 80 mile flight, I could do it in half the time it took the competitors' CRJs. I saved a lot of fuel too.


I’d like to see the cost of these flights versus longer routes flown at typical altitudes. I’d bet it’s higher (also meaning higher fares).

One thing that doesn’t seem to be taken into account in this discussion is that the physics of flight and air density doesn’t change with an electric aircraft. The engine efficiency might not matter, but the denser air at lower altitudes is still an issue. Even my single engine airplane gets much higher true airspeed in the mid-teens. And less air resistance means better fuel consumption. An electric motor still needs to use more power to overcome the denser air, which is still inefficient. Those short flights will eat up a lot more battery power.


I only fly the thing and note down all the details myself.

There are a few things to consider. It isn't all about cruise efficiency. Climbing up to those efficient altitudes costs a tremendous amount of energy, easily a few hundred kilos of fuel more than level flight.
Secondly, aircraft deprecite in value with flying time, run out of flying time and need to go in for checks based on, among other things, total flying time. Saving 10 to 20 minutes over the course of a working day adds up a lot in savings.
And finally, electric aircraft, like ATRs, will be underpowered. Flying these sorts of planes is all about energy management. You can either climb or go fast, not both. In the ATR 42, I will be more or less stuck at 160 knots during the climb. If I level off at 8000 ft, I can scoot along at almost 250 knots. At low level, the plane will accelerate to that speed in no time, while at high level it can take 10 minutes. Climbing from the ground to 8000 ft might only take 5 minutes, FL170 another 10 minutes on top of that! At low levels you don't have to mingle with jet traffic, so you get much better shortcuts.

Flying low is more efficient up to a certain point.
 
rbavfan
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Re: Could an unpressurised passenger jet ever become competitive?

Sun Sep 08, 2019 10:41 pm

tomcat wrote:
In today's world, the main benefit I'd see in flying unpressurized aircraft is that the security requirements for checked-in items might be relaxed. Shower gels and bottles of water might be allowed again on board. For short distance trips, we'd be back to a travel experience closer to the train experience, ie a more "hop-on, hop-off" kind of experience. It's not that unpressurized aircraft are not explosion-proof but they are more tolerant to limited energy explosions.


In today's world the ATR's leave from air side past TSA or equivelant so how do you segregate the un-pressurized passengers and the others at JFK, LHR, CDG?
 
remingtonbox
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Re: Could an unpressurised passenger jet ever become competitive?

Sun Sep 08, 2019 11:33 pm

CanesFan wrote:
The lack of pressurization would mean that it couldn't comfortably fly any of the jet climb/descent profiles either .


Its a pain in the ass for corporate piston twins also. I get told to fly jet profiles a lot and going into big airports and getting far behind the power curve of the airplane.
 
timeless159
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 2:07 am

I flew cargo for years in the Shorts 360. Sometimes in the teens with oxygen, sometimes below 10,000. I've never had the crap beat out of me so consistently by weather and turbulence as when I was limited to 10,000.

In the Shorts 360-300 MGTOW was 27,100 lbs and the empty weight was 17,000 lbs (without seats, galley or lav). The Dornier 328 has a MGTOW of 34,500 and an empty weight of 20,700. So yes a pressurized plane with a comparable payload was heavier, but the benefits of pressurization far outweigh that advantage.

An efficient decent profile for a jet leaving 10,000 ft is around 1500 fpm. Anything above 500 fpm can be painful to certain people. In the United States you can exceed 250 knots at 10,000ft, but going east requires an odd altitude and 9,000ft would limit you to 250 knots. So really you'd need to design a wing that was efficient at 250 knots. Now your true airspeed is around 300 kts instead 500 kts in a pressurized jet. And even though you can go to 10,000 ft without oxygen, some people can't handle it. I continted one flight in a CRJ that wouldn't pressurize (avionics ground cooling valve stuck open) and going to 10,000 ft made some people sick. The high cabin altitude seemed to compound the effects of airsickness, even on a smooth flight. It was not a happy or clean cabin. So really I'd never want to take passengers above an 8,000ft cabin altitude. So if you're limited to 8,000ft and 250 knots props are a better idea. If we ever see new 30-50 seat unpressurized passenger planes, they will probably be electric.
 
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SuseJ772
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 2:14 am

atcsundevil wrote:
dfwjim1 wrote:
On the opposite end of things will we ever see commercial airliners flying between 45,000 and say 70,000 feet on flights over 4 hours long?

They certainly wouldn't be operating above FL600. Controlled airspace only extends to FL600 (in the US, anyway). That said, I don't think that flying that high is terribly practical until there's a radical redesign in how aircraft are powered. Bizjets regularly cruise at FL430/450, but even the fanciest of Gulfstreams can only manage FL510 at the highest (at least that's the highest I've personally seen, and according to a Gulftest pilot, that's their max). At least for the foreseeable future, I think that FL410 will probably be as high as commercial aircraft will go. FL420 isn't a usable altitude, so FL430 is just beyond what most commercial aircraft can manage with current tech.

tropical wrote:
I suspect the answer is no, or it would have been done already. But as technology on composite materials and advanced aerodynamics gets better all the time, could we ever reach a point when an ultralight non-pressurised passenger jet flying low becomes more efficient than the current ones despite the increased drag?

I’d imagine the weight savings could be enormous from structural issues to oxygen supply etc, and maintenance checks and the lifetime cycle limit would also be so much better...

(Mods, feel free to move this to Tech though I fear it might be too dumb a question for that forum)

I just don't think there's any practical reason for it. Having an aircraft pressurized isn't a significant additional expense. Operationally, it would be extremely limiting, and rather unpopular in any sort of commercial application. Flying below 10,000ft means 250kts max, so even if they could manage higher speeds, they'd be limited unless they could climb higher than 10K. It also limits their ability to climb above weather, so precip and icing would have a significant impact. Operating at higher altitudes means they could simply climb above. Those limitations alone would be far more costly in the long term than carrying the additional weight and paying for additional maintenance to have the aircraft pressurized.


Why is FL42 unusable? Never heard that before and genuinely curious.
Currently at PIE, requesting FWA >> >>
 
timeless159
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 2:17 am

SuseJ772 wrote:
atcsundevil wrote:
dfwjim1 wrote:
On the opposite end of things will we ever see commercial airliners flying between 45,000 and say 70,000 feet on flights over 4 hours long?

They certainly wouldn't be operating above FL600. Controlled airspace only extends to FL600 (in the US, anyway). That said, I don't think that flying that high is terribly practical until there's a radical redesign in how aircraft are powered. Bizjets regularly cruise at FL430/450, but even the fanciest of Gulfstreams can only manage FL510 at the highest (at least that's the highest I've personally seen, and according to a Gulftest pilot, that's their max). At least for the foreseeable future, I think that FL410 will probably be as high as commercial aircraft will go. FL420 isn't a usable altitude, so FL430 is just beyond what most commercial aircraft can manage with current tech.

tropical wrote:
I suspect the answer is no, or it would have been done already. But as technology on composite materials and advanced aerodynamics gets better all the time, could we ever reach a point when an ultralight non-pressurised passenger jet flying low becomes more efficient than the current ones despite the increased drag?

I’d imagine the weight savings could be enormous from structural issues to oxygen supply etc, and maintenance checks and the lifetime cycle limit would also be so much better...

(Mods, feel free to move this to Tech though I fear it might be too dumb a question for that forum)

I just don't think there's any practical reason for it. Having an aircraft pressurized isn't a significant additional expense. Operationally, it would be extremely limiting, and rather unpopular in any sort of commercial application. Flying below 10,000ft means 250kts max, so even if they could manage higher speeds, they'd be limited unless they could climb higher than 10K. It also limits their ability to climb above weather, so precip and icing would have a significant impact. Operating at higher altitudes means they could simply climb above. Those limitations alone would be far more costly in the long term than carrying the additional weight and paying for additional maintenance to have the aircraft pressurized.


Why is FL42 unusable? Never heard that before and genuinely curious.


RVSM stops at FL410 so 2,000 ft separation above that.
 
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atcsundevil
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 2:33 am

timeless159 wrote:
SuseJ772 wrote:
Why is FL42 unusable? Never heard that before and genuinely curious.


RVSM stops at FL410 so 2,000 ft separation above that.

Yep. Practically speaking, any even altitude above FL410 isn't usable due to non RVSM. The best response I've heard a controller give to a pilot asking why FL420 was unusable was because the altimeters were low :lol: (for anyone who doesn't get that — FL180 becomes unusable for separation purposes when the altimeter drops below 29.92)

Technically FL420 can be used if it's within a block altitude FL410-FL430, but that's unusual. Bizjets will regularly ask for block altitudes in the 40s, but it would usually be mid to high 40s...or for the show-off G6 maintaining 490B510.
 
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 3:21 am

Or a Lear 45/75, Citation X, real light Global.
 
prebennorholm
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 4:12 am

timeless159 wrote:
An efficient decent profile for a jet leaving 10,000 ft is around 1500 fpm. Anything above 500 fpm can be painful to certain people….

.... And even though you can go to 10,000 ft without oxygen, some people can't handle it. I continted one flight in a CRJ that wouldn't pressurize (avionics ground cooling valve stuck open) and going to 10,000 ft made some people sick. The high cabin altitude seemed to compound the effects of airsickness, even on a smooth flight. It was not a happy or clean cabin. So really I'd never want to take passengers above an 8,000ft cabin altitude. So if you're limited to 8,000ft and 250 knots props are a better idea.

Back in the late 80'es Maersk Air put in two Shorts 360 on Danish domestic routes. Passengers got serious pain in the ears due to the decent / climb rates needed into and out of CPH.

It damaged the company seriously. People, who were used to pressurized DC-9, B737, F50, etc. avoided Maersk Air at any cost, and took car or train when there was no other substitute.

Even if those Shorts 360 never exceeded 10% of their fleet, and they were mostly used on only two certain routes, then you couldn't be sure not to be on a 360 until you saw the plane at the gate. Therefore the word was among at least frequent travelers: Avoid Maersk Air whenever possible.

It coincided with the period when Maersk Air went from being profitable to diving deeper and deeper into red ink. Not that it worried Mr. Moller seriously, but enough to make him donate the company to Sterling European Airways some years later.
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 10:34 am

RJMAZ wrote:
We will definitely see unpressurized airliners in a decade or two. Electric propulsion will be the reason why.


no way

you by far (!) underestimate the
- energy storage problem on a electric driven plane if the energy ist stored in batteries
- complexity of energy conversion of the fuel cells

in batteries there was a huge development during the last decades
and of cause there will be more development
but from what level on?
batteries are heavy
even if they can gain a 50% reduction in weight
its MUCH to heavy for the reality of flying
no broad impact here within our lifespan, maybe niches

in the development of fuell cells there have been invested multi billions in the last decades
there was nearly no gain in lifespan of the membrane and overall economics during that periode
if there would ever be a development ... to get the materials need for the membrane is very harmful to the environment
if there would be a large step towards this technology it would be a environment nightmare
no broad impact here within our lifespan, maybe niches
 
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 11:49 am

tropical wrote:
I suspect the answer is no, or it would have been done already. But as technology on composite materials and advanced aerodynamics gets better all the time, could we ever reach a point when an ultralight non-pressurised passenger jet flying low becomes more efficient than the current ones despite the increased drag?

I’d imagine the weight savings could be enormous from structural issues to oxygen supply etc, and maintenance checks and the lifetime cycle limit would also be so much better...

(Mods, feel free to move this to Tech though I fear it might be too dumb a question for that forum)



I guess this question holds more into itself than we see only looking in the past.

An aircraft without a pressured cabin can be much lighter, cheaper and better tailored to specific loads than a pressured one.

Looking at the success of new geared fans, it becomes possible to optimized a turbo fan for lower speeds than in the past, but avoid turboprop noise and special requirements.

Short flights (<500NM) that don't reach cruise height anyway, speed is less important, bigger capacity requirements (e.g. 200 seats) might create new requirements & engine design.
"Never mistake motion for action." Ernest Hemingway
 
clipperlondon
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Re: Could an unpressurised passenger jet ever become competitive?

Mon Sep 09, 2019 12:57 pm

RetiredNWA wrote:
Noshow wrote:
During the times of the Berlin Wall all allied jet aircraft within the Berlin air corridors -like Pan American's 727 or BEA's Tridents- flew at only 10.000 feet because of old customs from propeller aircraft used there after WW2. Everything was intended to keep the status quo going. So nothing got changed.
Flying so low you are flying in and not above the weather and while you don't need to pressurize the cabin the engines use more fuel. Back then many flights climbed over West Germany for the final miles to their destination in order to save some fuel.


That is not entirely correct. Air corridor altitudes changed in the late 70’s with the IGS operations.

Additionally, this topic is off the rails.


Just to nit pick. AFAIK, BEA used BAC 1-11s on the German corridor routes, as Deutsche BEA, and not Tridents.
 
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Re: Could an unpressurised passenger jet ever become competitive?

Tue Sep 10, 2019 3:22 am

asdf wrote:
RJMAZ wrote:
We will definitely see unpressurized airliners in a decade or two. Electric propulsion will be the reason why.


no way

you by far (!) underestimate the
- energy storage problem on a electric driven plane if the energy ist stored in batteries

I completely accept that a conventional fueled aircraft of the same weight will be able to fly 10 times further than a electric powered aircraft using the latest battery tech.

Most ATR and Q400 flights are taking off with a quarter tank of fuel as they are doing flights under 400nm.

Now the latest battery tech could easily produce a 200nm range ATR in a few years. In 10 years time the weight reduction and newer battery tech the range might hit 500nm. That is enough to cover the vast majority of the ATR flights.

Think of Hawaii doing island hops. Also London city airport to Paris–Le Bourget in the heart of Paris. A good example of an inner city airports that have strict curfews or can only be used for general aviation.
 
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lightsaber
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Re: Could an unpressurised passenger jet ever become competitive?

Tue Sep 10, 2019 3:32 am

RJMAZ wrote:
asdf wrote:
RJMAZ wrote:
We will definitely see unpressurized airliners in a decade or two. Electric propulsion will be the reason why.


no way

you by far (!) underestimate the
- energy storage problem on a electric driven plane if the energy ist stored in batteries

I completely accept that a conventional fueled aircraft of the same weight will be able to fly 10 times further than a electric powered aircraft using the latest battery tech.

Most ATR and Q400 flights are taking off with a quarter tank of fuel as they are doing flights under 400nm.

Now the latest battery tech could easily produce a 200nm range ATR in a few years. In 10 years time the weight reduction and newer battery tech the range might hit 500nm. That is enough to cover the vast majority of the ATR flights.

Think of Hawaii doing island hops. Also London city airport to Paris–Le Bourget in the heart of Paris. A good example of an inner city airports that have strict curfews or can only be used for general aviation.

Lithium sulfer probably will beat your estimate. I"m biased, my employer is fairly far along on that technology. I expect commercial service to be pressurized.

But the TSA killed too much short haul travel. An unpressurized jet is limited to low speed airspaces which is where turboprops thrive. That won't happen.

Lightsaber
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GalaxyFlyer
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Re: Could an unpressurised passenger jet ever become competitive?

Tue Sep 10, 2019 3:34 am

keesje wrote:
tropical wrote:
I suspect the answer is no, or it would have been done already. But as technology on composite materials and advanced aerodynamics gets better all the time, could we ever reach a point when an ultralight non-pressurised passenger jet flying low becomes more efficient than the current ones despite the increased drag?

I’d imagine the weight savings could be enormous from structural issues to oxygen supply etc, and maintenance checks and the lifetime cycle limit would also be so much better...

(Mods, feel free to move this to Tech though I fear it might be too dumb a question for that forum)



I guess this question holds more into itself than we see only looking in the past.

An aircraft without a pressured cabin can be much lighter, cheaper and better tailored to specific loads than a pressured one.



Looking at the success of new geared fans, it becomes possible to optimized a turbo fan for lower speeds than in the past, but avoid turboprop noise and special requirements.

Short flights (<500NM) that don't reach cruise height anyway, speed is less important, bigger capacity requirements (e.g. 200 seats) might create new requirements & engine design.


BDL-DCA is under 400nm, I’ve been to F390 many times on the route, bizjet and airliner. The most efficient climb profile is a parabolic curve.
 
XT6Wagon
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Re: Could an unpressurised passenger jet ever become competitive?

Tue Sep 10, 2019 4:08 am

Sure, but it would require a technology such that flying cars as seen in cyberpunk books and films becomes possible.

In effect changing wheeled bus to flying bus service.

However Its unlikely as even an infinite free power source would still have to deal with secondary effects produced by flight. Noise and heat being the big two I can think of. So maybe city to city service from dedicated depots , but nothing local as I'd not like to have transit bus noise replaced by helicopter/harrier noise.
 
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keesje
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Re: Could an unpressurised passenger jet ever become competitive?

Tue Sep 10, 2019 10:04 am

Let's not introduce irrelevant / unfeasible assumptions and base engine development on that.

I think it should be a more open requirements specification. If there is a (shuttle, LCC, intercity) requirements for 200 seats, or equivalent amount of parcels, for the 200-600NM segments, max range 1000NM. Noise shoudl be way lower than current generation aircraft, short runway performance / climb very important, such an aircraft would probably look very different from a A320. And have different engines.

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