Will the forthcoming Gulfstream G600 really only have 6,200nm range?

[tuna hp]

I am very suspicious of Gulfstream's advertised claims regarding the maximum range of their upcoming G600 model. I feel that they are advertising misleadingly low range targets in order to trick their customers into buying the old G550 while their production line is still running. I think that when they eventually release their G600, it will probably have the same or similar range to the current G550. Right now they advertise the G550 as having 6,750nm max range while they say that their upcoming G600 will have only 6,200nm range.

I am coming to this conclusion based on the massive drop in range-per-pound-of-fuel that is inconsistent with other plane offerings, but is found in the advertised ranges of the upcoming G500 and G600, and also in comparing the efficiency of the G600 to other heavy gulfstreams and other competitive planes. Here is a chart of my findings:

http://i.imgur.com/ZV9cgJC.png

First I compared sets of heavy business jets with their "stablemates": airplanes that they were developed alongside, generally at the same exact time with the same fuselage, wing, systems, and technology, where the main difference is usually fuel capacity and sometimes a slightly longer fuselage. I considered the G500 and G600 to be stablemates, and the Bombardier G5000 and G6000, and for the purposes of this exercise I thought it was valid to compare the G650 and G650ER.

The first thing we see looking at the G500/600 is that the G600 uses 7.7% more fuel per mile. OK, if we knew nothing about other airplanes that might seem reasonable, the G600's cabin is a few feet longer and it carries 10,000 pounds more fuel, it might make sense that it has lower overall fuel efficiency on a max-distance trip. So that's the baseline.

Then we look at the other stablemate pairs: in one example we have the G650ER using 1.75% more fuel than the G650. Unlike the G500/600 pairing, both G650 models have the same exact fuselage length so the only difference is fuel capacity, and the G650ER only carries 4,000 lbs more fuel than its stablemate, so while a 1.75% increase in fuel burn rate might seem to be much lower than a 7.7% increase in fuel burn rate, maybe this is because its the same size plane with a much smaller increase in fuel capacity. In the other example of the Global 5000/6000, we see that the larger G6000 actually a 0.5% lower fuel burn rate than the shorter-range G5000. How is this possible? Maybe because a large percentage of fuel is consumed at takeoff, so less takeoff fuel is burned per mile travelled in the longer-legged G6000, making it more efficient for a max-distance flight. The difference between the G6000 and G5000 is very analogous to the G500 and G600- the G6000 is a short stretch of the G5000 with 6,000 lbs more fuel.

Neither of the other stablemate pair examples lends credibility to the idea that the G600 should burn 7.7% more fuel per mile than the G500. On the contrary, the other examples indicate that it shouldn't necessarily burn more fuel per mile at all, or if it does, maybe only up to 2% more.

Now looking at the overall comparison to the G600:
-the much older, longer ranged G550 burns 2% less fuel per mile
-the larger, older-engined, longer-ranged G650/ER burn only 1% to 3% more fuel per mile

How can it be that the 20 year old G550, that has the same exact MTOW as the G600, consumes only 2% less fuel per mile than the clean-sheet G600 with brand new clean sheet engines? How is that possible? Forgetting aerodynamics and wing performance, don't engines alone advance in efficiency at least 10% per decade? And shouldn't there be huge aerodynamic improvements as well?

The comparison to the G650/ER is even more damning because the G650 has the same speed as the G600: how can the significantly larger G650 with its old engines derives from the same engines as the G600, with the same speed and many of the same features, and with much greater range, only use 1% more fuel per mile? How does that make sense? I would think that between being larger and heavier and having much older engines, the G650 should burn more like 5% to 10% more fuel per mile than the G600.

Basically I think that Gulfstream is mildly defrauding their customers by tricking them into buying the old G550 model when some of them would rather wait for the G600 if they knew what the true range capacity was going to be.

[LGW Vulture]

Simples - tell Gulfstream you want to buy a new G600 and you will not even consider an "old" 550 version.

Then get them to guarantee 6,750nm range in the G600 contract. That will give you your answer pretty quickly to whether they are bull$hitting.

[Booglebox]

Hmm.
With the G500/G600, have they activated all the fuel tanks? Or, are they going to pull another -ER stunt and install a fuel pump to a tank that is already there for $1m, a year after EIS?...

[imriozer]

Hi tunahp

I get what you are saying but if you take a close look at the numbers you'll see that something with the g500 number just don't add up, it think something went wrong with the g500 numbers...

[tuna hp]

Hmm.
With the G500/G600, have they activated all the fuel tanks? Or, are they going to pull another -ER stunt and install a fuel pump to a tank that is already there for $1m, a year after EIS?...

Well regardless, even if the G600 only has its advertised fuel capacity of 38,760 lbs, that means that that it consumes 2% more fuel per mile than the 20 year old G550 even though the G600 has a clean sheet fuselage, clean sheet wings, clean sheet engines, upgraded systems, and about the same MTOW. It only achieves 1% less fuel burn than the G650 despite have a newer and smaller fuselage, newer and smaller wing, much newer clean sheet engines, the same speed performance, and 9% lower MTOW.

When I read articles about commercial airframers upgrading their models, like the A320 to the A320NEO, or the B737 Next Generation to the 737MAX, they talk about efficiency improvements and which improvements are attributable to aeordynamic improvements, weight loss, engine improvements, etc. In these examples it seems like when airframers re-engine an existing plane, they do it because the new clean sheet engines will deliver several percent overall efficiency improvement to the plane.

For example see this article here (http://www.boeing.com/features/2015/05/bca-leap-engine-05-15.page), where Boeing admits that it is the new clean sheet engines, not their own aerodynamic and design improvements, that will deliver the majority of a 14% efficiency improvement over the 737NG. This means that they expect the new engines alone to deliver more than 7% efficiency improvement to the overall plane.

Compare this to our case of the G600 vs the G650. The G650 has engines nearing 20 years from entry into service. The G600 has brand new engines. It has a newer and smaller wing, a newer and smaller fuselage, 9,000 lbs lower MTOW, and yet the G600 only saves 1% on fuel burn? That's ludicrous. It should be saving at least 5%-10% on fuel burn.

The comparison with the G550 is the same in my opinion, completely not believable, although its less clear cut because the G550 is so much older and slower. I still think the G600 should fare better in comparison, it will be a 20 year newer plane. Yes the G600 is a little bigger and faster, but a lot of technological improvements in aerodynamics, aerostructures, and engine technology happen in 20 years. The 737MAX is scheduled to come out 20 years after the 737NG, and its advertised as delivering a 20% efficiency improvement over the first NGs, and its not even a clean sheet design! The G600 is a clean sheet plane! And it gets 2% less efficiency than than the G550?!

[Propellerpilot]

If you break it down to very basic chemistry and physics, it is always a function of the limited chemical energy that the carbons in your fuel can actually produce by burning them in order to move an optimally designed mass of an aeroplane through the atmosphere - wheras the latter will also be limited but dependant on a far greater number of factors, which can be made more efficient or compromised - the more mass to be moved or the more drag (e.g. due to bigger cabin size and other luxuries that the passenger demands), the more carbons need to be burnt in the most efficient way, by developing turbine materials and engine aerodynamics, that can handle higher temperatures - but even then you will eventually hit peak efficiancy and the gain will become insignificant unless we start developing fuels, that can produce more energy per molecule than current jetfuel.

So what I am trying to get to, is that even though the G600 is said to be optimized with more efficiant engines and aerodynamics- they must have compromised somewhere else, for a hopefully justfied reason, resulting in the unexpected information in the tables you have posted.

[Booglebox]

You make a compelling point OP but smaller / lighter doesn't always mean less fuel burn over a given distance at a given speed. Think of a C152 vs a C172.

Do Gulfstream have a history of underestimating and then revising performance figures to maintain the backlog of their older products?

[tuna hp]

Do Gulfstream have a history of underestimating and then revising performance figures to maintain the backlog of their older products?

Kind of. With the G650/ER they originally said that it was going to have a 5,000nm M .90 range, but then after they launched they said, "oops it actually has a 6,000nm M.90 range". And then there was the fact that 1-2 years, after having marketed the G650 as "being about the same range as the G550 because we found that's what our customers want", they released the ER variant which just enables another fuel tank that already existed in the base model, good for 500nm of additional range.

[AZAV8R]

tuna - I think that your comparison is missing a few variables. The G550 has to fly slower (M .80) than the G600 to achieve that 6700nm. The G600 is pushing a significantly larger airframe through the air, at M .85 while still having a respectable range of 6200nm (as advertised). The G600 will achieve this having the same MGTOW as the G550. If flown at the same speeds you can bet that the ranges would be about the same. The G600 meets the desired goal of having the larger cabin that Gulfstream customers want, pushing that larger airframe through the air (requiring more power to achieve) with more efficient engines and 2500 pounds less fuel capacity than the G550...while doing so at much higher speeds.

The G450 and G550 are great airplanes. But Gulfstream customers wanted newer technology, more speed, more cabin, with greater efficiency. The new G500 and G600 are those airplanes. They will fit their niches well along side the G650/ER.

[imriozer]

Agree with AZAB

Make a comparison between the G500 and the G450, for the same fuel the G500 will take you 800 miles further at a higher speed and a bigger cabin, that's because of the new designed engines and wings...

[tuna hp]

Make a comparison between the G500 and the G450, for the same fuel the G500 will take you 800 miles further at a higher speed and a bigger cabin, that's because of the new designed engines and wings...

Doesn't G450 vs G500 prove my point? G500 has the bigger cabin and faster, carries a couple percent less fuel and yet manages 15% better fuel efficiency. The G550 is a newer plane with a much better wing than the G450, but the G600 should still be able to perform better relative to it. Instead of 2% worse efficiency, like I said I would expect a few percent better.

[AZAV8R]

Your logic is flawed with this tuna hp. The G600 is still more efficient than the G550, with the G600 having 2500 pounds less fuel capacity. At M.87 (HSC) the G550 has an advertised range of 6000 nm. At M.85 (LRC) the G600 has an advertised range of 6200 nm. If you bump the speed of the G600 to a matching M.87 the G600 will fly the same 6200 nm., on 2500 pounds less fuel. Again...the G600 is doing so pushing more mass through the air, on less fuel, going the same distance, at the same speed.

The G600 fits the desired customer niche. I buyers want more range, that's when they'll step up to the G650/ER.

[tuna hp]

Your logic is flawed with this tuna hp. The G600 is still more efficient than the G550, with the G600 having 2500 pounds less fuel capacity. At M.87 (HSC) the G550 has an advertised range of 6000 nm. At M.85 (LRC) the G600 has an advertised range of 6200 nm. If you bump the speed of the G600 to a matching M.87 the G600 will fly the same 6200 nm., on 2500 pounds less fuel. Again...the G600 is doing so pushing more mass through the air, on less fuel, going the same distance, at the same speed.

The G600 fits the desired customer niche. I buyers want more range, that's when they'll step up to the G650/ER.

Of course its more efficient than the G550, but not by nearly enough given the 20 year difference in entry date.

At least as far as cabin size and speed, G450:G500 as G550:G600. The G450 and G550 has the same cabin cross sections, and they represent a certain length without a crew rest and with a crew rest. The G500 and G600 have the same larger cross section and are slightly longer representations of not having and having a crew rest. G450 and G550 LRC is Mach 0.80. G500 and G600 LRC is EDIT: Mach 0.85. So what I'm saying is to some extent, comparing the G450 and G500 should be analogous to comparing the G550 and G600.

Well the G500 gets 17.5% more nm to the lb than the G450. The G600 supposedly gets 2% FEWER nm to the lb than the G550.

I mean I could be wrong but that would make the G600 the worst plane Gulfstream has built.

[AZAV8R]

https://upload.wikimedia.org/wikipedia/commons/3/3b/Paris_Tuileries_Garden_Facepalm_statue.jpg

[AZAV8R]

tuna hp- With respect, since you are unable to comprehend the differences of the G450/G550 and the G500/600 as it's been explained...M.90 is not LRC for the G500/600 btw...stay away from the G600. I'm sure that Gulfstream will be quite successful with the G600 from operators that understand its performance, economics, and cabin size advantages.

[stilton]

I think you have a valid point THP.


It sounds like Gulfstream is playing with the numbers again, just like they did with the -650.

[AZAV8R]

His point is not valid when his comparison is not apples to apples. The G550 WAS Gulfstream's long-range flagship based on a cabin that was developed over 55 years ago. The G650 is Gulfstream's NEW long-range flagship. The G500 and G600 fit niches that Gulfstream customers asked for.

The G600 wasn't developed to be a DIRECT replacement of the G550. Therefore trying to make a DIRECT comparison between the G550 and G600, as tuna hp is attempting to do, is not valid, and is why he won't be satisfied.

[G550plt]

I thought the G650 wasn't exactly the "trick" most think it was.. It
had a guaranteed fuel capacity in pounds regardless of fuel density..
This comes in handy when your in Asia.. From what I understand the
650ER trades this "extra space" that would be filled with the lower
density fuel (in Asia for example ) and allows more fuel to be loaded
when in higher density areas (N. Amer) ..

[Richard101]

Tuna I don't think you are taking proper account of the aircraft's increased speed and increased size

G600 @ M85 = 6200nm (38,760lbs max fuel ~ 6.25 lbs per nm)
G550 @ M87 = 6000nm (41,300lbs max fuel ~ 6.88 lbs per nm)

That to me makes the G600 approximately 10% more fuel efficient than the G550, while at the same time offering the passenger 10%+ increase in cabin volume.

[tuna hp]

Tuna I don't think you are taking proper account of the aircraft's increased speed and increased size

G600 @ M85 = 6200nm (38,760lbs max fuel ~ 6.25 lbs per nm)
G550 @ M87 = 6000nm (41,300lbs max fuel ~ 6.88 lbs per nm)

That to me makes the G600 approximately 10% more fuel efficient than the G550, while at the same time offering the passenger 10%+ increase in cabin volume.

Hmm that's exactly the sort of comparison I would make but come to the opposite conclusion. I don't think that as manufacturers implement higher long range and normal cruise speeds, they are doing so incurring the same drag penalties as they did at the same speeds in older models. I think that as their wings get more sophisticated and mitigate drag better, they are able to put off the incidence of transonic drag to higher speeds, and that's where they're getting their speed increases from. Commercial airliners and business jets have continuously gotten faster over the years (well at least since a long time ago when turbofans took over from jets and maybe they were slower). Newer models of widebody airliners have long-range-cruise speeds of mach 0.85-.86

So to allow the G600 at its long-range-cruise speed of M.85, which is the speed at which flying any slower doesn't increase range at all, to only have to compete against the G550 after its already incurring enough drag to cut over 10% of its range, is a very forgiving to the G600.

Basically I think that, yes, with a 20 year newer wing, 25 year newer engines, and all the other advances that have come over the decades, the G600 should be able to do better than fly a 10% larger cabin 10% more efficiently at the same speed. The 737MAX is coming out 20 years after the 737NG and its supposed to have a 20% efficiency increase, and its not even a clean sheet design.

But probably the most telling example is the add the G650 to your example.

G650 @ M85 = 7000nm (6.31 lbs/nm).

So G650, with 20 year old engines, a ~13% bigger cabin, and ~13% more range only uses 1% more fuel per mile than G600? Even when Boeing attributes 7-8% of the 20% efficiency increase between the first 737NG and the 737MAX to the re-engining?

If none of you think Gulfstream's numbers are sketchy than I'm sure I'm wrong, but the numbers don't make sense (or they make the G600 the worst plane Gulfstream has made), and whats more Gulfstream has a huge potential motive. They don't necessarily want customers to know if they are coming out with a pretty direct replacement for the G550 because they probably have commitments until X time to continue ordering parts and delivering planes and they want to keep the assembly line as busy as possible until then.

[Astra driver]

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.

[tuna hp]

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?

[Astra driver]

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.

[tommoutrie]

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..

[tuna hp]

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.

This is what I was getting at... the G600 is as much smaller than the G650 as the G550 is smaller than the G600. It also has less range and clean sheet engines... and yet delivers supposedly no more efficiency. Thanks for putting those numbers together.

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 considered that. Very possible. Although its not as if they are riding the same exact wing. G600 wingspan is 8' longer than the G500.