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:
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.