Will the forthcoming Gulfstream G600 really only have 6,200nm range?
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Tuna,
It may well come to pass that your suspicions about the G600 having greater range than currently advertised are true. However, I think that your assumptions about the G600 only being marginally more efficient than the G550 are incorrect.
In order to get an "Apples to apples" comparison I used the trip planning charts from the G550 POH to compare with Gulfstreams projected performance numbers for the G600, namely 6,200 nm trip, Mach 0.85, ISA standard day conditions, zero wind and NBAA fuel reserves, (Typically around 2,500 lbs for these aircraft. Not practical I know, but we want an equal comparison)
Here are the results from the charts
G550,
trip fuel burned = 40,400 lbs (which leaves us with only 900 lb reserve!)
(typically these planes burn 4% extra per hour for every extra pound carried, so, for comparison purposes to carry an additional 1,600 reserve you would burn an additional 832 lbs; .04 x 13 x 1,600. Which would make the total trip fuel burned, if it were possible, 41,232lbs, I'll leave it up to you to decide which figure you prefer to use, 40,400 or 41,232.
G600,
Trip fuel burned assuming 2,500 NBAA reserve = 38,760 - 2,500 = 36,260lbs
So, extrapolating from those numbers we can see that that the G600 with its much wider cabin is 13.7% more efficient (41,232/36,260) than the G550.
If you prefer to use the 40,400 fuel burn number for the G550 with its scary 900 lb reserve you still get 11.4% more efficient.
By the way, the BR725 engines used on the G650 are not a a 20 year old design, but in fact use a completely different 1st Stage Fan and many different internal components from the original BR710 design, enabling it to produce 16,900 lbs of thrust vs 14,750lbs in the original 710, a 14.57% improvement, with roughly equivalent fuel burn numbers.
For another comparison, the G650 I currently fly burns about the same amount of fuel flying at Mach 0.9 vs a G3 flying at Mach 0.8 and this is in an aircraft with a significantly wider fuselage and that has an approximately 40% greater MTOW.
It may well come to pass that your suspicions about the G600 having greater range than currently advertised are true. However, I think that your assumptions about the G600 only being marginally more efficient than the G550 are incorrect.
In order to get an "Apples to apples" comparison I used the trip planning charts from the G550 POH to compare with Gulfstreams projected performance numbers for the G600, namely 6,200 nm trip, Mach 0.85, ISA standard day conditions, zero wind and NBAA fuel reserves, (Typically around 2,500 lbs for these aircraft. Not practical I know, but we want an equal comparison)
Here are the results from the charts
G550,
trip fuel burned = 40,400 lbs (which leaves us with only 900 lb reserve!)
(typically these planes burn 4% extra per hour for every extra pound carried, so, for comparison purposes to carry an additional 1,600 reserve you would burn an additional 832 lbs; .04 x 13 x 1,600. Which would make the total trip fuel burned, if it were possible, 41,232lbs, I'll leave it up to you to decide which figure you prefer to use, 40,400 or 41,232.
G600,
Trip fuel burned assuming 2,500 NBAA reserve = 38,760 - 2,500 = 36,260lbs
So, extrapolating from those numbers we can see that that the G600 with its much wider cabin is 13.7% more efficient (41,232/36,260) than the G550.
If you prefer to use the 40,400 fuel burn number for the G550 with its scary 900 lb reserve you still get 11.4% more efficient.
By the way, the BR725 engines used on the G650 are not a a 20 year old design, but in fact use a completely different 1st Stage Fan and many different internal components from the original BR710 design, enabling it to produce 16,900 lbs of thrust vs 14,750lbs in the original 710, a 14.57% improvement, with roughly equivalent fuel burn numbers.
For another comparison, the G650 I currently fly burns about the same amount of fuel flying at Mach 0.9 vs a G3 flying at Mach 0.8 and this is in an aircraft with a significantly wider fuselage and that has an approximately 40% greater MTOW.
Last edited by Astra driver; 28th Aug 2015 at 19:10.
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Wow great insight, thanks for posting the figures, they are so hard to come by freely on the internet.
Like I said, I don't believe that comparing the two aircraft at the same speed is a more 'apples to apples comparison' than comparing them at their respective long-range-cruise speeds. The G550 burns the additional fuel at mach .85 because its design isn't handling high speed drag as well as the G600/650.
Are you a car enthusiast and/or do you ever watch the BBC series Top Gear? They once did an entertaining segment where they "proved that a BMW M3 is more fuel efficient than the Toyota Prius". And they did prove it, the catch was in how they compared them: the Prius was driven as fast as possible around a race track, and the M3 merely had to keep up. Lo and behold, the Prius being driven as fast as it could used much more fuel than the M3 keeping up, which wasn't coming close to using all of its available power. The M3 was designed to drive at those speeds (or faster), the Prius wasn't.
Similarly, engineers' understanding of aerodynamics wasn't as good back when the G-V was developed as it is today. They can design a plane that can fly faster while incurring less drag. And we see this in seeing that long-range-cruise speeds (which correct me if I'm wrong, are defined as "the fastest speed the plane can fly where flying any slower would be no more efficient") on new models increasing. Commercial airliners have followed the same trend in long-range-cruise speed increases.
But you are a professional Gulfstream pilot and your employer is an early adopter of high end Gulfstream products, so I am sure that you are much more keyed-in to whatever they are doing than I am.
It just doesn't make sense to me, how unfavorably it seems to compare to its own stablemate G500 or even the older G550. The most damning comparison of all is probably against your own ride, the G650, where you can have your "apples to apples same speed" comparison and the smaller, lighter, shorter ranged G600 hardly saves any fuel. In fact, I think it would be interesting to do your "apples to apples comparison at the same speed AND range" and see how much fuel the G650 uses to fly 6,200nm @M0.85. Would the G650 actually use LESS fuel than the G600?
Like I said, I don't believe that comparing the two aircraft at the same speed is a more 'apples to apples comparison' than comparing them at their respective long-range-cruise speeds. The G550 burns the additional fuel at mach .85 because its design isn't handling high speed drag as well as the G600/650.
Are you a car enthusiast and/or do you ever watch the BBC series Top Gear? They once did an entertaining segment where they "proved that a BMW M3 is more fuel efficient than the Toyota Prius". And they did prove it, the catch was in how they compared them: the Prius was driven as fast as possible around a race track, and the M3 merely had to keep up. Lo and behold, the Prius being driven as fast as it could used much more fuel than the M3 keeping up, which wasn't coming close to using all of its available power. The M3 was designed to drive at those speeds (or faster), the Prius wasn't.
Similarly, engineers' understanding of aerodynamics wasn't as good back when the G-V was developed as it is today. They can design a plane that can fly faster while incurring less drag. And we see this in seeing that long-range-cruise speeds (which correct me if I'm wrong, are defined as "the fastest speed the plane can fly where flying any slower would be no more efficient") on new models increasing. Commercial airliners have followed the same trend in long-range-cruise speed increases.
But you are a professional Gulfstream pilot and your employer is an early adopter of high end Gulfstream products, so I am sure that you are much more keyed-in to whatever they are doing than I am.
It just doesn't make sense to me, how unfavorably it seems to compare to its own stablemate G500 or even the older G550. The most damning comparison of all is probably against your own ride, the G650, where you can have your "apples to apples same speed" comparison and the smaller, lighter, shorter ranged G600 hardly saves any fuel. In fact, I think it would be interesting to do your "apples to apples comparison at the same speed AND range" and see how much fuel the G650 uses to fly 6,200nm @M0.85. Would the G650 actually use LESS fuel than the G600?
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Tuna,
I ran the same scenario for the 650 (M.85, 6,200nm, ISA, NBAA reserves, etc) and I get about 35,500 lb trip fuel burn,
Which is about 760lbs LESS than the 600's projected numbers.
It could be that Gulfstream is being conservative with its performance estimates, which they typically are, or it could be that the G600 being essentially a "stretched" version of the G500 is just having to carry too much fuel weight than is optimal for its wing and engine design.
I do personally feel that the the G600 is a tad underpowered compared to its stablemates; a quick review of Gross weight to thrust ratios clearly shows this.
And yes I did see the Top Gear M3 episode. Being a long time M3 driver myself I love to tell Prius drivers that an M3 can actually be more efficient than their car.
I ran the same scenario for the 650 (M.85, 6,200nm, ISA, NBAA reserves, etc) and I get about 35,500 lb trip fuel burn,
Which is about 760lbs LESS than the 600's projected numbers.
It could be that Gulfstream is being conservative with its performance estimates, which they typically are, or it could be that the G600 being essentially a "stretched" version of the G500 is just having to carry too much fuel weight than is optimal for its wing and engine design.
I do personally feel that the the G600 is a tad underpowered compared to its stablemates; a quick review of Gross weight to thrust ratios clearly shows this.
And yes I did see the Top Gear M3 episode. Being a long time M3 driver myself I love to tell Prius drivers that an M3 can actually be more efficient than their car.
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simply dividing the total fuel the aircraft can carry by the stated range doesn't give you lbs/nm. Your figures show that the Global 5000, for instance, uses more fuel per nautical mile than the 6000. But I don't plan flights which run out of fuel on landing - once you take off sensible reserves the situation reverses. Global 6000 uses 7.09 per nm, Global 5000 uses 7.06 on a max range trip.
who cares... I only ever fly from Geneva to Prague anyway...
ignore this, just noticed that someone cleverer than me has already said it..
who cares... I only ever fly from Geneva to Prague anyway...
ignore this, just noticed that someone cleverer than me has already said it..
Last edited by tommoutrie; 9th Sep 2015 at 10:12. Reason: I am a dillon that hasn't read the whole thread..
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I ran the same scenario for the 650 (M.85, 6,200nm, ISA, NBAA reserves, etc) and I get about 35,500 lb trip fuel burn,
Which is about 760lbs LESS than the 600's projected numbers.
Which is about 760lbs LESS than the 600's projected numbers.
it could be that the G600 being essentially a "stretched" version of the G500 is just having to carry too much fuel weight than is optimal for its wing and engine design
