lightsaber wrote:Please recall the GE9X will have variable cycle technology. There will be reduced turbine cooling at cruise, already in the LEAP engines.
RR already has this for the 97. I think also the Trent 1000-TEN.
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- kurtverbose
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Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
RR already has this for the 97. I think also the Trent 1000-TEN.
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- OldAeroGuy
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Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
zeke wrote:OldAeroGuy wrote:Just a few replies ago, you were arguing that takeoff TSFC was indicative of cruise TSFC. Are you now arguing that the TXWB will have an OPR improvement over takeoff and the GE9 won't?
No argument at all, I stated fact in your quote from GE the basis was “per-pounds-of-thrust basis‘, and the only thrust level they have advertised is takeoff thrust. GE made no reference to TSFC or cruise thrust like you did. Additionally you previously said the 10% was the improvement in cruise, and later you said the 10% improvement was for takeoff, the statements are contradictory.
Once again, you're putting words in my mouth. Please show me the place that I said the GE9 10% TSFC improvement vs the GE90 was for takeoff.
I gave an OPR comparison for takeoff. You indicated that the TXWB would have a top of climb OPR of "over 60" vs a takeoff OPR of 52 without acknowledging that the GE9 takeoff OPR of 60 would have similar increase at top of climb to "around 70".
Why not tell the whole story rather than only part of it?
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- OldAeroGuy
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Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
zeke wrote:OldAeroGuy wrote:I don't think that it's proven that the GE9 and the TXWB are about similar.
Of course not, only one of them is certified and in production.
The GE9 is scheduled for certification around the end of 2018 and is about to begin flight testing on a 744 test bed. Its performance is probably pretty well established.
You still can't conclude their TSFC performance is "similar".
Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
flipdewaf wrote:A351 779X
OWE 155 181
MTOW 308 351
Pax 366 414
Range 7950 7600
Pax weight36.6 41.4
MTOW-Pax 271.4 309.6
Fuel 116.4 128.6
Fuel per
pax 0.318 0.311
Fuel per
pax per
mile @max
range 4.00E-05 4.09E-05
Weights in tonnes and distance in nm.
if my numbers are wrong let me know which I should change and excel will be unbiased with the maths.
Fred
PS. sorry for the table being badly formatted, I really tried to get it right this time with a fixed width text editor and it didn't help.
The OEW of 779 really got my attention. It is too early for Boeing to release the official OEW of 779, so all what we have so far is predictions. I have to say, the 181t figure you used is the lowest I have seen. If Boeing manages to pull that off, then 779 would truly surpass all predictions.
All the other OEW figures I have seen is somewhere between 186t-188t (Again, they are only predictions, nothing more). Since GE9X is confirmed to be heavier than expected, and since most planes tend to be heavier than desired, I personally think 779 would end up with an OEW that is considerably higher than 181t. That would also change the fuel burn per pax that you calculated as well.
Heck, we don't even know the official OEW of 787-10 yet, I guess we are at least a couple of years away before hearing anything official from Boeing about 779 then
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lightsaber
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Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
kurtverbose wrote:lightsaber wrote:Please recall the GE9X will have variable cycle technology. There will be reduced turbine cooling at cruise, already in the LEAP engines.
RR already has this for the 97. I think also the Trent 1000-TEN.
Do you have a link? To my knowledge, the LEAP was the first variable cycle technology to hit the fleet. I would love to find out more.
Lightsaber
Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
OldAeroGuy wrote:You still can't conclude their TSFC performance is "similar".
Nor can you (or anyone for that matter) state it is better, nor can you state how the aircraft will perform once it is it starts to fly. On the other hand both the A350-1000 and the TXWB-97 are certified and flying. And they will improve again before the 778/9 enter service.
We do not know what conditions GE is making their claims under, takeoff or cruise. We do not know is they are saying TSFC or not.
We also do not know if their claims of 5% improved SFC, and OPR are related to cruise or takeoff.
It’s just marketing blurb, as they don’t actually know the TXWB performance.
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- kurtverbose
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Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
lightsaber wrote:kurtverbose wrote:lightsaber wrote:Please recall the GE9X will have variable cycle technology. There will be reduced turbine cooling at cruise, already in the LEAP engines.
RR already has this for the 97. I think also the Trent 1000-TEN.
Do you have a link? To my knowledge, the LEAP was the first variable cycle technology to hit the fleet. I would love to find out more.
Lightsaber
Sorry Lightsaber, I didn't have time to look up a link in my earlier response.
In any case, LEAP might well have been the first.
It's detailed in this link - http://aviationweek.com/caring-engines-today-and-future/perfect-ten
Unique to the TEN is its modulated air system which optimises the secondary air flow within the engine. Historically an engine’s secondary air system has had to be designed to cope with the most demanding point in the flight cycle (take-off) but of course that means the system has a larger air flow circulating during the rest of the flight regime than is really required. With the new modulating technology, the engine can regulate the amount of air it needs on demand and then when in cruise or idle, a novel valve arrangement uses air vortices (not moving parts) to regulate the amount of air flowing through the system and this helps further reduce fuel consumption.
Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
flidewaf wrote:Indeed, the trip fuel per pax for the 779 is ~2% lower than the A351 but then the A351 trip is 4.6% further...
Ah the format of your per-pax-mile thing threw me off. A couple things:
-You're going off published range figures, but Boeing and Airbus use different standards
-We have two published analyses that show 777-9 being more fuel-efficient. One is by Bjorn Fehrm at Leeham, who is no anti-Airbus guy. Do you have any reason to believe Bjorn is wrong? Any reason to think your apples-oranges comparison is better?
Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
Matt6461 wrote:flidewaf wrote:Indeed, the trip fuel per pax for the 779 is ~2% lower than the A351 but then the A351 trip is 4.6% further...
Ah the format of your per-pax-mile thing threw me off. A couple things:
-You're going off published range figures, but Boeing and Airbus use different standards
-We have two published analyses that show 777-9 being more fuel-efficient. One is by Bjorn Fehrm at Leeham, who is no anti-Airbus guy. Do you have any reason to believe Bjorn is wrong? Any reason to think your apples-oranges comparison is better?
JESUS!!! That's quite the accusatory tone toward someone who posted some numbers. I found some numbers online and used those to form a rudimentary comparison . I have the utmost respect for the work that Bjorn does and even more so for the transparent way In which he does it. The fact that my numbers disagreed with someone else's does not mean I think he is wrong, I think it probably means we have different sources and assumptions and to talk to someone interested in the technical side of this for the merit of the discussion would be nice rather than to have some trumped up lawyer who can scale factors thinking it's worth an engineering degree.
You always claim you want to learn more and you pointed out a valid point about the way the max range is calculated and I was going to ask about where those differences lie but actually you attack on my character has made me not want to engage in this thread any more. You have once again rubbed someone up the wrong way and made this thread 5hit.
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Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
flipdewaf wrote:Matt6461 wrote:flidewaf wrote:Indeed, the trip fuel per pax for the 779 is ~2% lower than the A351 but then the A351 trip is 4.6% further...
Ah the format of your per-pax-mile thing threw me off. A couple things:
-You're going off published range figures, but Boeing and Airbus use different standards
-We have two published analyses that show 777-9 being more fuel-efficient. One is by Bjorn Fehrm at Leeham, who is no anti-Airbus guy. Do you have any reason to believe Bjorn is wrong? Any reason to think your apples-oranges comparison is better?
JESUS!!! That's quite the accusatory tone toward someone who posted some numbers. I found some numbers online and used those to form a rudimentary comparison . I have the utmost respect for the work that Bjorn does and even more so for the transparent way In which he does it. The fact that my numbers disagreed with someone else's does not mean I think he is wrong, I think it probably means we have different sources and assumptions and to talk to someone interested in the technical side of this for the merit of the discussion would be nice rather than to have some trumped up lawyer who can scale factors thinking it's worth an engineering degree.
You always claim you want to learn more and you pointed out a valid point about the way the max range is calculated and I was going to ask about where those differences lie but actually you attack on my character has made me not want to engage in this thread any more. You have once again rubbed someone up the wrong way and made this thread 5hit.
You should learn about how to engage technical people in useful conversation rather than tripping them up, because that stinks!
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Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
flipdewaf wrote:JESUS!!! That's quite the accusatory tone toward someone who posted some numbers.
Ya know right before I posted that reply, I thought, "Is this going to come off the wrong way?" Seems it did but had no such intent. I meant my questions in a very simple way - like are you presenting these numbers as your final judgment, Bjorn notwithstanding, or as just another slice at the cake?
Sometimes I feel like I spend too much time hedging for tone, but this time the balance was off. Apologies.
...by way of explanation let me remind you again that I'm used to lawyer argumentation. We routinely confront each others' arguments and just take it for granted that even a blunt, unsparing attack on an argument isn't personal. I'll always believe that's the best norm for conversation but often forget it's not the normal norm.
Re: Honest Discussion. Which Plane is More Efficient.....The A351 or 779?
flipdewaf wrote:JESUS!!! That's quite the accusatory tone toward someone who posted some numbers. I found some numbers online and used those to form a rudimentary comparison . I have the utmost respect for the work that Bjorn does and even more so for the transparent way In which he does it. The fact that my numbers disagreed with someone else's does not mean I think he is wrong, I think it probably means we have different sources and assumptions and to talk to someone interested in the technical side of this for the merit of the discussion would be nice rather than to have some trumped up lawyer who can scale factors thinking it's worth an engineering degree.
It is good you have taken the time and effort to put the figures together. My personal way to deal with that poster is to put them on my ignore list in the control panel. Every post they make is collapsed so I don’t see them, it makes no difference to the thread, it actually improves it. Some people seem just to come on here to have arguments. They thrive on people responding to them.
Both types can carry 440 pax maximum, any reduction on that is due to “comfort”. At the design passenger range the A350-1000 is not fuel limited, it has less than full tanks. The A350-1000 and it’s engine will improve over the base certification level by the time of the 779 EIS.
Many of these comparisons are moot anyway, the 777-X is sold out for a few years, plus the years we have to wait for EIS. The aircraft that will be available is the A350-1000. The 2018 list price on the A350-1000 is 366.5 million, 777-300ER 361.5 million, 777-8 394.9 million, 777-9 425.8 million. Or to put it another way, based upon list rices for every 5 777-9s one buys, you can buy around 6 A350-1000s and have half a chance of getting delivery in a few years..
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