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Jackonicko
Topic Author
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Turboprops vs Turbofans.... and Propfans!

Sun Oct 30, 2022 9:03 am

How much more environmentally friendly is a modern turboprop than an equivalent sized turbofan-powered airliner in terms of environmental impact?

Roughly 30% lower fuel burn per passenger seat/mile?
Lower flying and less likely to contrail?
Lower flying and releasing emissions at a 'better' height?
A better 'neighbour' in terms of noise?

Is there an environmental argument for making greater use of turboprops for short haul?

How do the new generation of Open Rotor Fans/Unducted fans/Propfans compare?

Any thoughts?
What am I missing?
 
Avatar2go
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Re: Turboprops vs Turbofans.... and Propfans!

Sun Oct 30, 2022 10:05 am

Each propulsion type has a peak of efficiency at different airspeeds, and to a lesser degree, different altitudes. Moving faster through the air, or at lower altitude, generally means higher fuel consumption, regardless of technology.

Turboprops are most efficient at lower speeds, propfans (open rotor) at intermediate speeds, and turbofans at higher speeds. They likely will operate at increasing cruise altitude with airspeed, as well.

So the environmental answer is that one is not inherently superior to the other. It just depends on the desired cruising airspeed/altitude of the aircraft.

The market is determined by what passengers want. Faster transit times are generally favored by the market, which means turbofans dominate. With environmental awareness, that could change to propfans if passengers will accept lower speeds, longer transit times, generally smaller aircraft, and greater noise.

The same is possible with turboprops, but the changes would be even more significant, and the public has not embraced the concept of a mass return to that technology.
 
Jackonicko
Topic Author
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Re: Turboprops vs Turbofans.... and Propfans!

Sun Oct 30, 2022 11:55 am

Thanks, that's a good shout!

I wonder what the differences are in terms of fuel burn and CO2 emissions per seat/mile....
 
Avatar2go
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Re: Turboprops vs Turbofans.... and Propfans!

Sun Oct 30, 2022 1:42 pm

The fuel burns depend on the design of the aircraft and the operational conditions. So there isn't a clean, direct comparison. Airlines have very complex and detailed models to calculate the seat/mile numbers.

The best comparisons for propfans would be on a smaller airliner like the Boeing 717, which is close to the design required for a propfan. The savings in fuel, at lower speed, would be maybe in the range of 10% to 15%, under ideal conditions.

Most of that improvement comes from the increase in the fan diameter, which increases the area of the rotor disk. That allows the blade speed to be lower for the same thrust, which reduces losses.

The propfan gets around the fan diameter limitations inherent to turbofans, at the expense of greater noise and somewhat greater risk of a blade out, without the containment cowl.
 
ArcticFlyer
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Re: Turboprops vs Turbofans.... and Propfans!

Sun Oct 30, 2022 3:49 pm

Part of the turboprop vs. turbofan debate is controlled by what passengers want to fly in. Jets are seen as modern and safe while turboprops are seen as antiquated "puddle-jumpers" regardless of the fact that there is absolutely no data to back up these perceptions. Several years ago I flew for an RJ operator in the northeast and our shortest route was PHL-ABE (45 nm I think). On such a short flight there is absolutely no difference in flight time on a jet vs. a turboprop, but trip fuel and therefore cost will be much higher. The only reason we flew routes like that was because uninformed passengers want jets.

On a larger scale, note that PT and C5 were strictly turboprop operators as recently as 10 years ago but now they're both all-jet. I think QX is the only "regional" still flying turboprops (Q400s in their case) in the USA.
 
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77west
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Re: Turboprops vs Turbofans.... and Propfans!

Sun Oct 30, 2022 9:20 pm

ArcticFlyer wrote:
Part of the turboprop vs. turbofan debate is controlled by what passengers want to fly in. Jets are seen as modern and safe while turboprops are seen as antiquated "puddle-jumpers" regardless of the fact that there is absolutely no data to back up these perceptions. Several years ago I flew for an RJ operator in the northeast and our shortest route was PHL-ABE (45 nm I think). On such a short flight there is absolutely no difference in flight time on a jet vs. a turboprop, but trip fuel and therefore cost will be much higher. The only reason we flew routes like that was because uninformed passengers want jets.

On a larger scale, note that PT and C5 were strictly turboprop operators as recently as 10 years ago but now they're both all-jet. I think QX is the only "regional" still flying turboprops (Q400s in their case) in the USA.


I think this may depend on where in the world you are - here in NZ generally people have no issue with our ATR72 / Q300 operations. NZ's ATR72 are newer than many of their mainline jets.
 
kalvado
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Re: Turboprops vs Turbofans.... and Propfans!

Sun Oct 30, 2022 10:38 pm

As far as I remember, service ceiling is a significant factor. Dash-8 and ATR are limited below FL300, while RJ can go over FL400. As a result, there is a non-insignificant pool of cases when RJ can go above the weather, but turboprop has to go around the weather, burning more gas and subject payload to more turbulence
 
GalaxyFlyer
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Re: Turboprops vs Turbofans.... and Propfans!

Mon Oct 31, 2022 1:02 am

Very empty RJ above F400, certainly no CRJ.
 
kalvado
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Re: Turboprops vs Turbofans.... and Propfans!

Mon Oct 31, 2022 10:51 am

GalaxyFlyer wrote:
Very empty RJ above F400, certainly no CRJ.

WHat is the usual cruise of a turboprop? Service ceiling is an official number from the datasheet - easy to find, easy to verify...
 
ArcticFlyer
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Re: Turboprops vs Turbofans.... and Propfans!

Mon Oct 31, 2022 4:49 pm

GalaxyFlyer wrote:
Very empty RJ above F400, certainly no CRJ.

Very true, spoken from experience. Mid-high 20s was our typical domain; even 310 was a struggle. Did 370 once but that was on an empty repo flight so it really doesn't count.

kalvado wrote:
WHat is the usual cruise of a turboprop? Service ceiling is an official number from the datasheet - easy to find, easy to verify...

When I was flying the DHC-8 we typically cruised in the low 20s on flights longer than about an hour. Max certified altitude was FL250 but that was due to not having drop-down oxygen masks for the pax, not a performance limitation. I think it could have gone quite a bit higher but due to mach effects there really would have been no benefit in doing so; once we were above the mid-teens TAS pretty much stayed the same and fuel flow only improved marginally.
 
kalvado
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Re: Turboprops vs Turbofans.... and Propfans!

Mon Oct 31, 2022 5:27 pm

ArcticFlyer wrote:
GalaxyFlyer wrote:
Very empty RJ above F400, certainly no CRJ.

Very true, spoken from experience. Mid-high 20s was our typical domain; even 310 was a struggle. Did 370 once but that was on an empty repo flight so it really doesn't count.

kalvado wrote:
WHat is the usual cruise of a turboprop? Service ceiling is an official number from the datasheet - easy to find, easy to verify...

When I was flying the DHC-8 we typically cruised in the low 20s on flights longer than about an hour. Max certified altitude was FL250 but that was due to not having drop-down oxygen masks for the pax, not a performance limitation. I think it could have gone quite a bit higher but due to mach effects there really would have been no benefit in doing so; once we were above the mid-teens TAS pretty much stayed the same and fuel flow only improved marginally.

what about "above the weather" part - can you comment?
 
GalaxyFlyer
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Re: Turboprops vs Turbofans.... and Propfans!

Mon Oct 31, 2022 7:10 pm

I’ve always been skeptical about the “above the weather” idea. At F450, I’ve deviated around lots of weather, admittedly, at lower latitudes. I’ve had plenty of turbulence above F410, too. And the real weather issues are on departure and arrival, not cruise. Above F430, you can usually see a loss of headwind which is nice. OTOH, with the wind, climbing can reduce your ground speed tailwind decreases. Once, over Iran, Tehran had us descend for Pakistan ATC required us at F390 or below. Fuel was tight-ish with low viz st Delhi, we slowed to LRC about M.07 less than at F450. Tailwind increased, same arrival time & fuel.
 
CowAnon
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Re: Turboprops vs Turbofans.... and Propfans!

Mon Oct 31, 2022 10:05 pm

Jackonicko wrote:
How much more environmentally friendly is a modern turboprop than an equivalent sized turbofan-powered airliner in terms of environmental impact?

Roughly 30% lower fuel burn per passenger seat/mile?
Lower flying and less likely to contrail?
Lower flying and releasing emissions at a 'better' height?
A better 'neighbour' in terms of noise?

Is there an environmental argument for making greater use of turboprops for short haul?

How do the new generation of Open Rotor Fans/Unducted fans/Propfans compare?

Any thoughts?
What am I missing?

Turborprops and propfans can make use of variable pitch in their propellers to adjust for the different stages of flight. Turbofans are currently stuck with having fixed pitch in their fans, so they have to optimize the pitch mostly for cruise. This means that turboprops and propfans have a 30-40 percent advantage in specific fuel consumption (SFC) during takeoffs. So yes, a lot of the proposals for turboprops and propfans have been for short-haul airliners.

At cruise speed, propfans would have a 10-20 percent better SFC, and (IMO) would retain an SFC advantage up to Mach 0.85. I tried to go through the math on on the Emirates superjumbo thread awhile ago, since this topic is a little controversial on this forum: viewtopic.php?f=3&t=1475727&p=23478899#p23478899
 
ArcticFlyer
Posts: 110
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 01, 2022 2:57 am

kalvado wrote:
what about "above the weather" part - can you comment?

It all depends on where you're flying. In Alaska or Northern Canada the low 20s is plenty to get you above 99% of the bad weather even in the summer; I can remember only once in several years being faced with a line of thunderstorms (south of Fairbanks) that we couldn't outclimb and was dense enough to make it challenging to pick our way through. On the other hand, even FL370 is nowhere near high enough to get above the buildups I routinely see crossing the Great Plains during the summer months and we're usually too heavy to even make it to FL370 anyway.

Technically there is no reason a turboprop couldn't be designed to fly higher, in fact I think the Saab 2000 goes up into the low 30s. As evidenced by the type's meager sales (63 over 7 years of production), there simply isn't a large market for such an airplane. Turboprops will never be as fast as jets making them unsuitable for longer flights, while for shorter routes where they might make economic sense they suffer (at least in America) from passenger bias in favor of jets as I have stated in prior posts.
 
Nicoeddf
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Joined: Thu Jan 10, 2008 7:13 am

Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 01, 2022 10:58 am

GalaxyFlyer wrote:
Very empty RJ above F400, certainly no CRJ.


I have been doing 400 and 410 in the CR9 with reasonable loads (2:20h block times, 28 tons ZFW, about 33 tons TOW. No issue.
 
kalvado
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 01, 2022 12:46 pm

ArcticFlyer wrote:
kalvado wrote:
what about "above the weather" part - can you comment?

It all depends on where you're flying. In Alaska or Northern Canada the low 20s is plenty to get you above 99% of the bad weather even in the summer; I can remember only once in several years being faced with a line of thunderstorms (south of Fairbanks) that we couldn't outclimb and was dense enough to make it challenging to pick our way through. On the other hand, even FL370 is nowhere near high enough to get above the buildups I routinely see crossing the Great Plains during the summer months and we're usually too heavy to even make it to FL370 anyway.

Technically there is no reason a turboprop couldn't be designed to fly higher, in fact I think the Saab 2000 goes up into the low 30s. As evidenced by the type's meager sales (63 over 7 years of production), there simply isn't a large market for such an airplane. Turboprops will never be as fast as jets making them unsuitable for longer flights, while for shorter routes where they might make economic sense they suffer (at least in America) from passenger bias in favor of jets as I have stated in prior posts.

Honestly speaking, hard to buy "passengers don't want" argument when it is "passengers buy the cheapest" in all other cases, when something like Oasis, 1 sq ft lav and <30" pitch has to be justified. I suspect that if turboprop would actually offer a significant cost advantage, we would see some regional all-prop LCCs, at least for east coast or intra-CA, TX routes.
For me, nothing beside obvious more crew, more mechanics for a bigger and slower fleet comes to mind. Is there anything else to consider?
Once upon a time a gate agent was bragging about "poor reliability of these props, we may get all RJ next year" - but we were waiting for an old and tired Q200...
 
GalaxyFlyer
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 01, 2022 2:21 pm

Nicoeddf wrote:
GalaxyFlyer wrote:
Very empty RJ above F400, certainly no CRJ.


I have been doing 400 and 410 in the CR9 with reasonable loads (2:20h block times, 28 tons ZFW, about 33 tons TOW. No issue.


“No CRJ” was a blanket statement in error, huge difference in perf for the 700/900 than the the original 200. My brief experience was in the 850 corporate version, which was a dog, perhaps worse than the -200.
 
Nicoeddf
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 01, 2022 3:51 pm

GalaxyFlyer wrote:
Nicoeddf wrote:
GalaxyFlyer wrote:
Very empty RJ above F400, certainly no CRJ.


I have been doing 400 and 410 in the CR9 with reasonable loads (2:20h block times, 28 tons ZFW, about 33 tons TOW. No issue.


“No CRJ” was a blanket statement in error, huge difference in perf for the 700/900 than the the original 200. My brief experience was in the 850 corporate version, which was a dog, perhaps worse than the -200.


Oh yes. I hear no good things about the 200s altitude performance. I haven’t been flying it myself, though.
 
gloom
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 01, 2022 4:25 pm

kalvado wrote:
As far as I remember, service ceiling is a significant factor. Dash-8 and ATR are limited below FL300, while RJ can go over FL400.


Are you aware it's not a powerplant limit, but a general choice of aerodynamic efficiency vs payload vs range?
There are turboprops able to go way above F300. Dash8 and ATR are optimized for short hops.

Cheers,
Adam
 
kalvado
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 01, 2022 7:05 pm

gloom wrote:
kalvado wrote:
As far as I remember, service ceiling is a significant factor. Dash-8 and ATR are limited below FL300, while RJ can go over FL400.


Are you aware it's not a powerplant limit, but a general choice of aerodynamic efficiency vs payload vs range?
There are turboprops able to go way above F300. Dash8 and ATR are optimized for short hops.

Cheers,
Adam

Well, a bigger picture:
I am pretty sure that, should turboprop operation be actually cheaper than turbofan, we would see at least some "Fly green! Save the planet and pay less!" operations even with current types. There is definitely some cohort to bite on such approach, and NYC-CHI may be a reasonable range without good ground competition. Why it doesn't happen? Pax feeling it's an "old technology" should not be a real show-stopper IMHO. Altitude and weather is another possible explanation - but looks like people in the know are not buying that as well. Manufacturer also thought that getting higher service is not a good idea.... Any other reason?

And a bigger question is if it is feasible to run a operation like that today with today's Q400 and ATRs; or if any manufacture would develop and offer a family of larger turboprops how that would look like in a long run? In the ideal-most world?
What is reasonably achievable if someone has some loose change of couple $10Bs? Reasonable for, say, NYC-FL service with longer trip with "it's green!" slogan? How would operational economics look like? Would a FL450 ceiling be feasible and beneficial?

I hope I am just expanding the original question which started the discussion.
 
gloom
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 01, 2022 9:09 pm

kalvado wrote:
What is reasonably achievable if someone has some loose change of couple $10Bs? Reasonable for, say, NYC-FL service with longer trip with "it's green!" slogan? How would operational economics look like?


We have no platform to actually compare apples to apples. If/when Embraer delivers first turboprop based on EJets fuselage, we will know.
Based on how jets are developed (higher temp core, more bypass), it seems fuel advantage for turboprops will diminish over time.

Would a FL450 ceiling be feasible and beneficial?


Not likely.
Some advanced concepts (A400M, An70) are able to fly as high as high 300s (limited at F400 for A400M, F390 for An72), and I guess this is more or less what could be expected if someone built a "state of art" turboprop from scratch.
To be fair, it should be mentioned that props are slower than jets (props at around 0.7Ma, narrowbody jets usually around 0.78Ma), so higher jet speed could offset some (or all) of fuel advantage prop has, since burn is calculated and compared as "per hour" metrics.

Cheers,
Adam
 
744SPX
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Re: Turboprops vs Turbofans.... and Propfans!

Sat Nov 05, 2022 11:57 pm

The SAAB 2000 can fly at FL 310 and the TU-95 can fly at FL 450. The TU-96 was intended to fly at FL 550 (modified engines and slightly bigger wing)

Turboprops can definitely cruise faster than .7 mach, (A400M and An-70 cruise at .72 and they have big, draggy fuselages) but Embraer won't do it because it would kill the E2

The Tu-116 (Tu-95 executive transport version ) demonstrated a cruise speed of mach .76 for 4600 nmi (out and back) all at 35-40,000 ft with enough fuel left for another 1000 nmi:
-and this was in 1958. 64 years ago.

In 1960 the TU-114 demonstrated an average speed of 545 mph or mach .825 for 5000 KM while carrying a 55,000 lb payload.
-62 years ago.

In the 1980's NASA demonstrated with its ATP program that open rotor maintained double-digit efficiency over equivalent technology turbofans up to .90 mach

It's really all about the negative public perception of turboprops, and the industry has done absolutely nothing to address that.
 
strfyr51
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Re: Turboprops vs Turbofans.... and Propfans!

Mon Nov 07, 2022 11:07 pm

Jackonicko wrote:
How much more environmentally friendly is a modern turboprop than an equivalent sized turbofan-powered airliner in terms of environmental impact?

Roughly 30% lower fuel burn per passenger seat/mile?
Lower flying and less likely to contrail?
Lower flying and releasing emissions at a 'better' height?
A better 'neighbour' in terms of noise?

Is there an environmental argument for making greater use of turboprops for short haul?

How do the new generation of Open Rotor Fans/Unducted fans/Propfans compare?

Any thoughts?
What am I missing?

A turboprop is morev fuel efficient than and turbofan as a turbofan is nothing more than a straight jet powering a fan on the first stage not unlike a PT6 which powers a reduction gear and a Propellor in which the low speed compressor is powering the fanvor in the case of the GTF, It powers the fan turning at lower speed via a gearbox.
the GTF isn't much more than a "gussied up" PT6.
 
LucaDiMontanari
Posts: 102
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 08, 2022 3:00 pm

kalvado wrote:
Well, a bigger picture:
I am pretty sure that, should turboprop operation be actually cheaper than turbofan, we would see at least some "Fly green! Save the planet and pay less!" operations even with current types. There is definitely some cohort to bite on such approach, and NYC-CHI may be a reasonable range without good ground competition. Why it doesn't happen?


Short answer: total cost per passenger. The "props are cheaper than jets rule" only fits if we talk about similar sized planes, a CRJ700 to a Q400 for example. But one can't ever match a 150-180 seater (what a typical LCC would use) with a 70-seater, because you can spread especially the overhead costs over much more pax. Problem: we do not have any 150 seat turboprop nowadays, think of something like a Vickers Vanguard/Lockheed L-188/Bristol Britannia with two engines. If we had it, this would be a whole different story.

On a side note about the Saab 2000: in my oppinion the biggest issue with that plane is, that it was overdone and honestly a swedish tank (like Saab cars as well...). It has a roughly 1 ton higher empty weight than an ATR72, but with 20 pax less capacity. And almost the fuel burn of a Q400. So not an actually efficient design.
 
GalaxyFlyer
Posts: 10296
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Re: Turboprops vs Turbofans.... and Propfans!

Tue Nov 08, 2022 6:02 pm

Yes, even the price be dammed NASCAR teams couldn’t make the SAAB 2000 work.

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