How can business jets cruise so much faster than airliners in the transonic regime?
If you look at the cruise speed of many business jets, it will be somewhere in the Mach 0.90 to Mach 0.94 area. This is very fast and in theory would consume much more fuel than if they cruised at around Mach 0.85 which is around how fast most airliners cruise.
Business jets are built to save time for their passengers, who are often quite wealthy. Therefore, the design is based around favoring speed over efficiency.
Commercial airliners are built to make a profit for the airline, by moving passengers faster than the alternatives (cars, trains, and buses) and keeping a useful schedule with connections to other flights. Therefore, the design is based around favoring economy; saving money on fuel to maximize profit.
Many airliners can cruise faster, but at the expense of more fuel burned and tickets that are less affordable.
Many business jets can cruise slower and save money, but the important, wealthy passengers often wish to make the trip as fast as practical for their next business meeting (or tee-time).
cruise speed of many business jets... will be somewhere in the Mach 0.90 to Mach 0.94 area.
All of the Cessna Citation series of business jets have a maximum speed (in Mach) of 0.8.
All of the Dassault Falcon series of business jets have a maximum speed of 0.85 to 0.9 with a "long range" cruise speed of 0.8.
Bombardier lists 0.83 as the maximum Mach for its Challenger series.
So most of the current business jets actually fly at the same or even at a lower speed than any modern jetliner (Mach 0.85; 0.9 for the Dreamliner), no matter how rich or in how much of a hurry the VIP on board is (btw, this answer gives a very nice explanation about why Mach 0.85 is the sweet spot for jetliners).
That I know only the Citation X lists a higher maximum speed (Mach 0.93) together with the Gulfstream G650/G700/G800 (Mach 0.925). The former is anyway no more in production and the latter, according to Wikipedia, have a market share of some 13%. So those high Mach values are more of an exception than the rule: even the ultramodern Pilatus PC-24 and the HondaJet have a maximum speed comparable to all the other business jets. Yes, sure, the next generation of business jets is being advertised with incredible max speeds just slightly smaller than Mach 1 but then next to it there's printed a more plausible Mach 0.85 as cruise (real?) max speed, so this is more the marketing department at work and not physics.
How can business jets cruise so much faster than airliners in the transonic regime?
They don't. And they can't (again, except the Citation X or the Gulfstreams). To reduce transonic drag as much as possible, one or more of the following aerodynamic tricks has to be used:
In terms of speed, the real gain of a business jet is actually the much shorter "rest of the flight other than cruise" phase: no need to get to the airport two hours before the flight, no queue at the check-in, no queue at the gate, no queue for boarding and so on. This saves a couple of hours per flight. Plus, obviously, one can fly whenever and wherever wanted (and without any stinky fellow passengers).
By and large, long range airliners and long range business jets have very similar cruise speeds. A 747 and 787 both have a Maximum Operating Mach Number (Mmo) of 0.90 but typically use a maximum cruise speed of Mach 0.85 for their flight profiles and Mach 0.8 for long range economy cruise.
The biggest and fastest luxury business Jets these days e.g. Gulfstream’s G500/600/650/700/800 and Bombardier’s Global Express series all have an Mmo of 0.925, but use a high speed cruise of Mach 0.9 with an economy cruise of Mach 0.85. There has been very little efforts made on the part of these luxury bizjet companies to go faster than this. Even with Cessna raising the bar with its now defunct Gen II Citation X boasting an Mmo of 0.935, none of the other major bizjet players followed suit in the speed wars. The reasons I’m not clear on; it could be that M0.925 offers the best ability to wring out as much speed as possible while offering a reasonable safety envelope against Mach tuck or other undesirable high speed effects while maneuvering. All of the above listed aircraft have exceeded Mach 0.99 during flight testing.
Regional jets and intermediate range airliners have limited themselves of an Mmo of 0.8-0.82 or so with cruise speeds of Mach 0.75-0.8. That might seem slow, but consider this: a Mach 0.75 cruise (430 KTAS) is 83 knots slower than a G650 in high speed cruise at Mach 0.9 (516 KTAS). On a typical regional flight (ex. KLAX-KLAS), you will, at most have 12-15 mins in cruise prior to starting down on a STAR with its typical speed restrictions or those imposed by ATC. A Mach 0.9 cruise under these condition will, at best, shave about 2-3 mins off that flight; those gains could easily be lost if ATC requests you hold somewhere, how they sequence you for the approach, etc. Once below 30,000 ft they will typically restrict you to 280 KIAS or below, and even if they didn’t, you would probably maintain those slower speeds to fly the descent profile smoothly and get slowed up for the approach into the airport. Where the Mach 0.9 cruise can shine is long duration cruise. For a flight from KLAX to Narita Intl., Tokyo (~4,900 NM), the Gulfstream does it in 9.5 hours @ M0.9 vs a 787 at 10.05 hours @ M0.85, assuming calm winds. This saves approx 33 minutes on the trip.
Where business aircraft always beat airliners is in terms of passenger comfort and convenience. They are much more luxurious, quieter and with cabin pressures exceeding 10 psi, they definitely reduce fatigue during long-haul flights. The ability to schedule the flight whenever you need to and from whatever airport best suits your mission is another major factor. That alone can slash hours off your travel time, regardless of whether you made the trip at Mach 0.9 or not.
Business jets have more thrust relative to their mass for
The speed is just a welcome side effect of their ability to fly from smaller regional airports and to fly above most other traffic. The first two points are also favored by the lower wing loading of business jets, which, however, is rather detrimental to a higher airspeed. The combination of higher thrust loading and lower wing loading helps more than the high cruise speed to make travel times shorter:
To prove my point, here are some figures (data taken from the respective Wikipedia page):
| Type | static thrust | wing area | take-off mass | T/W | m/S |
|---|---|---|---|---|---|
| Learjet 35 | 2 x 15.6 kN | 23.53 m² | 8,300 kg | 0.383 | 353 kg/m² |
| Citation X | 2 × 31.28 kN | 48.96 m² | 16,601 kg | 0.384 | 339 kg/m² |
| Gulfstream G-550 | 2 x 68.4 kN | 105,63 m² | 41,050 kg | 0.34 | 389 kg/m² |
| Bombardier Global 5500 | 2 x 67,3 kN | 94.8 m² | 41,957 kg | 0.327 | 443 kg/m² |
| Boeing 747-400 | 4 x 276.2 kN | 541,2 m² | 396,893 kg | 0.284 | 733 kg/m² |
| Boeing 777-300 | 2 x 433 kN | 436.8 m² | 299,370 kg | 0.292 | 685 kg/m² |
| Airbus A340-600 | 4 x 249 kN | 439,4 m² | 368,000 kg | 0.276 | 837 kg/m² |
So their speed is indeed a consequence of the goal to make travel times as short as possible, but mostly indirectly. The largest time savings come from shorter travel times to and from the airport, followed by the ability to fly directly and at any time without waiting for a slot at a congested major airport. The high thrust gives business jets better short-field performance which allows them to fly from a much larger number of airfields and, since thrust is roughly proportional to air density, also allows them to fly in lower density air. The higher speed is just a side effect and helps to save a few minutes more.
Business jets are able to cruise at over 50,000 feet, above all but the very worst weather.
economical cruise speeds are considerably less
More in the Mach 0.80 to 0.085 range. But higher top speed sells.
Newer models, such as the Bombardier Global 8000, have been tested near or exceeding Mach 1, and can be flown at speeds of over Mach 0.9 to save time.
I think most answers so far seem to be missing a key point. We all agree that the point of business jets is speed in terms of A to B, but that is not what Mach measures. If you could do Mach .8 at sea level, you would be doing 609mph. At 40,000 ft, .8 is only 528mph (Mach .9 685mph at sea level, 594mph at 40,000ft). Having less parasitic drag means being able to go faster and being able to go higher means they are yet more efficient which means going further without stopping or going faster with the same fuel. Being able to go higher and faster means getting from A to B quicker which is why rich people pay over the odds to use them.
---Edit --- Looking at the comments, I clearly could have phrased that better.
An aircraft that 'can' do Mach .85 is by definition more aerodynamic that one that can only do .8, and an aircraft that can cruise at 45,000 ft can get better efficiency from its engines then one that can only cruise at 35,000ft (ie the same engine can go further or faster with the same fuel at 45,000ft then it can at 35,000ft), not to mention that at 45,000ft it can take a more direct path by being above the commercial traffic which also allows it to use its extra speed. Combine these and an aircraft that can go higher and faster will get from A to B in less time then the same aircraft going lower or slower.
Business jets are not sold just on their Mach numbers, but the combination of their speed and cruising height.
