Originally Posted by 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.
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.