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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.

Peter Mortensen
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user67740
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    Based on my rudimentary knowledge of these things, I feel like Mach .94 doesn't really make sense for anyone. Wouldn't that put it firmly in the trans-sonic flight scheme, where the plane would have to be built for supersonic flight anyway? And nudging it into supersonic territory would also be more efficient? – BlackThorn Feb 15 '23 at 16:35
  • @BlackThorn indeed. Each plane is built for a certain purpose. In most business and airliners speed is not one of them. But as answer stated, business jets try to save time and so are a little fast. So technically speed is one of its purposes but is not the #1 priority. – Deko Revinio Feb 15 '23 at 16:47
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    @BlackThorn The higher Mach number gives you bragging rights later at the golf course or the country club. Invaluable for some! – Peter Kämpf Feb 15 '23 at 17:35
  • @BlackThorn: Most jetliners are already well into the transonic regime at M0.85; bizjets are just somewhat further in than jetliners. – Vikki Feb 17 '23 at 22:38

6 Answers6

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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).

abelenky
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    Makes sense but how much useful time could actually be saved by going this much faster? – user67740 Feb 14 '23 at 18:57
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    @user67740, The time difference can be calculated, but the answer depends on how you define "useful". – Michael Hall Feb 14 '23 at 19:26
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    @MichaelHall when I was a bush pilot taking sport fishermen and wealthy Americans in to their summer hideaways in the NE corner of Lake Huron. I would often get tips, but generally only from middle class ppl from Southern Ontario and the US that I was taking into lodges etc. The wealthy customers I would take into their Georgian Bay "camps" (comfortable island cottages) were real tightwads, rarely tipped. I wouldn't be surprised at a lot of these ppl telling their corporate crews to cruise not much above min drag to to get max MPG lol. – John K Feb 15 '23 at 04:23
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    @user67740 my quick use of Google as a calculator tells me it would take Elon Musk an extra 1.6 hours to get back from World Cup in Qatar at mach 0.85 versus mach 0.94. How much does he value that time? – Michael Feb 15 '23 at 04:23
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    @user67740 there is also difference in how they are sold - if you want to sell a new business jet in 2023 you need it to be 'better' than the old one and one of the features they have collectively chosen to sell on is 'goes faster'. It does not have to make a lot of sense (witness various car fads over the years). – GremlinWranger Feb 15 '23 at 08:24
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    @JohnK I can anecdotally concur with your story. A old friend of mine owned a landscaping company. His clientele included swaths of people worth hundreds of millions of USD, as well as several handfuls of billionaires (I like that imagery, as it illustrates the money controls them, not the other way around). He said none of his clients are more miserable or such tightwads as those rich clients. He wisely elucidates *"the richer they are, they more miserable they are... they are just too stupid to know it"*. – End Anti-Semitic Hate Feb 15 '23 at 11:36
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    @Michael That is erroneously implying that one cannot work or sleep on a private jet. Given that the more Elon works, the less he sleeps, and the more he suffers (which, like most things about his narcissistic existence, he wants everyone to know). It's obvious that decreasing the throttle & taking long naps would be the smartest thing he could do. Actually, for that guy in particular, he and the world would likely benefit if he stopped working & dedicated his life to true philanthropy (instead of ridiculously claiming that Tesla & his other for-profit corporations are philanthropy). – End Anti-Semitic Hate Feb 15 '23 at 11:53
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    Comments are drifting toward socio-politic... I like that – sophit Feb 15 '23 at 12:23
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    Top F1 drivers earn more than 20 million per season each. That translates to 55000 per day, 2300 per hour, 38 per minute. Time is money fore these people, but more importantly, the faster speed translates to bragging rights. Speed is status. – Jpe61 Feb 15 '23 at 13:10
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    @RockPaperLz-MaskitorCasket unfortunately, they control us whether we like it or not - we can't simply decide to just ignore the stupid people who are miserable because of their own stupidity – user253751 Feb 15 '23 at 14:03
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    In many ways, this answer complements sophit's one: small and large passenger jets have similar maximum speeds, but their operators choose to fly them at different cruise speeds to suit differing objectives. – Toby Speight Feb 15 '23 at 14:13
  • @TobySpeight: I don't want to be pedantic but the present answer asserts that "the design is based around favoring speed over efficiency" while in my answer I demonstrate that (with a few exceptions) the opposite is actually true (or, even more precise, that speed and efficiency are both not true for business jets) – sophit Feb 15 '23 at 15:09
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    @abelenky the Concorde is the most extreme example of speed over efficiency in an airliner plane. Which at the end of the day, is one thing that caused its demise. – Deko Revinio Feb 15 '23 at 16:51
  • Interested to know how much fuel is saved when a typical business jet travels ~0.1 mach slower (0.94 -> 0.85). For, say, London to NY, we could then calculate the cost saving, and then divide it by the cost of the flight (as a percentage of the total flight cost, it might only save a few percent). – stevec Feb 15 '23 at 23:04
  • @John K You see this sort of thing in the service industry too. Middle class tend to be the best tippers since they've done jobs like retail, waiting tables, etc., so they know what it's like. Upper class tend to be tightwads there too! Lower class folks cannot really afford to eat out. – ackmondual Feb 16 '23 at 20:22
  • @Michael How much does (Musk) value that time? As much as we value our time when driving 75 Freedoms/hour instead of 65 Freedoms/hour. – RonJohn Feb 17 '23 at 05:17
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    Musk wouldn't fly at all, he'd use his teleporter. Oops! I've said too much! :-o – Grimm The Opiner Feb 17 '23 at 08:32
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    The other major time-saving element of private jets is that you don't have to deal with all that drudgery at the airport. The vast majority of time for taking a commercial flight is spent going through the security lines, waiting for hundreds of passengers to board, loading up the luggage, etc., and then again in reverse at your destination. With a private jet, you can just drive up to the plane and board immediately, and take off within minutes. The actual flying part of the trip doesn't have to be that much faster when you cut out all the waiting before and after. – Darrel Hoffman Feb 17 '23 at 14:26
  • @GrimmTheOpiner I only brought Musk up because it came out thanks to that guy on Twitter that tells the world where Elon Musk's plane goes that he his private jet went to the world cup. – Michael Feb 17 '23 at 22:34
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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:

  • the wing is swept of a couple of tens of degrees $\rightarrow$ many of those business jets (especially Citations and Falcons) have an almost straight wing for ease of manufacturing;
  • use of thin airfoils for the wing $\rightarrow$ according to this answer Cessna has used airfoils with a quite high 12 to 14% thickness; this gives higher max $C_l$ and fuel volume but at the expense of a higher drag;
  • area ruling $\rightarrow$ doesn't seem to have been implemented in any of those business jets and a straight wing definitely plays against it.

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).

sophit
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    Also worth noting that even 0.93 isn't really that much faster than most airliners designed for long-distance flight. The 747-400's MMO is 0.92, for example. 777-300ER is 0.89. It's more the narrowbody aircraft (designed primarily for relatively short flights) that have the lower MMOs (0.82 for 737 and A320, for example.) – reirab Feb 15 '23 at 17:34
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    @reirab: correct, that 0. something Mach more doesn't change anything for a flight of one hour, that's why many regional airplane are more efficient turboprops. – sophit Feb 15 '23 at 17:47
  • @psmears: thanks for the corrections, I'll never get the use of "the" – sophit Feb 15 '23 at 17:52
  • Yep, though that's more regional. All of the major airlines in the U.S. (including the regional airlines that operate under contract for the major carriers on short/thin routes) have stopped using them, for example, with Alaska (the airline, not the state) retiring their last Dash 8s this year. – reirab Feb 15 '23 at 17:56
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    Just being able to avoid a connection would be a huge time saver, probably more than all the other items you mentioned. – Mark Ransom Feb 15 '23 at 20:25
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    The logistics for boarding a private jet is VERY fast. After being cleared to enter the airport (very quick and basic clearance), you can literally drive up to the plane, board, and take off. They don't care about scanning your bags because if you blow yourself up, it's your own plane. – Nelson Feb 16 '23 at 02:03
  • I'm confused about some points in this answer, especially first and third bullet points near end. Which jets are meant by "all of those..."? Seems like nearly all the business jets I see have significantly swept wings. – quiet flyer Feb 17 '23 at 01:11
  • PS re one of your comments above-- usage of "the" is flexible, there was nothing wrong with your usage especially for non-formal (lists etc) writing-- just saying-- – quiet flyer Feb 17 '23 at 01:14
  • @quietflyer: yes right, I meant almost all of the Cessna and Dassault, I'll correct that part, thanks – sophit Feb 17 '23 at 07:07
  • Just wondering: Is there a large difference between "maximum speed" and "maximum speed over an eight hour period", for example? Like your engines, or your airplane, heating up at maximum speed? – gnasher729 Feb 17 '23 at 14:42
  • @gnasher729: There's definitely a difference since after eight hours of flight much of the fuel has been burned and the airplane is lighter $\rightarrow$ less lift $\rightarrow$ less drag. So the maximum speed actually changes continuously. – sophit Feb 17 '23 at 15:01
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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.

Romeo_4808N
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    … and the biggest time saver for business jet users is their ability to fly from smaller regional airports. Travel to and from the airport takes less time as does getting a slot when you need it. The faster flight speed is just some icing on the cake. – Peter Kämpf Feb 15 '23 at 17:40
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    Honestly, I'd say it's much more the ability to leave on whatever schedule from whatever airport (including ones without passenger terminals) and without dealing with security, baggage check, etc. than the passenger comfort in most cases. The passenger comfort on many biz jets isn't that great compared to a (far cheaper) business-class ticket on a major airline, where flat-bed seats are the standard nowadays for longer flights (and also some shorter ones, depending on route.) – reirab Feb 15 '23 at 17:41
  • Most commercial jets from after the 1950s (both jetliners and bizjets) lack a major tendency to mach-tuck at transonic speeds (this is how they're able to cruise at transonic speeds); first-generation Learjets do have such a tendency, but they're very much the exception. – Vikki Feb 17 '23 at 22:46
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Thrust-to-weight ratio

Business jets have more thrust relative to their mass for

  • better short field performance,
  • higher cruise ceiling, and
  • higher top speed compared to large passenger jets.

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:

  • Flying from many more airports means they can avoid the congestion of major hubs and the travel time to and from the airport will be much shorter for their passengers.
  • Flying higher allows them to take a direct route and frees them from the need to co-ordinate with scheduled traffic which would often incur holding times.

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.

Peter Kämpf
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  • For completeness I think it should be nice to consider the wing loading as well – sophit Feb 17 '23 at 15:02
  • @sophit Yes, lower wing loading is also a requirement for short field performance and high ceiling, but it is detrimental to high speed. The question is about high speed, so wing loading is not the right answer. – Peter Kämpf Feb 17 '23 at 18:59
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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.

Robert DiGiovanni
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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.

Paul Smith
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    Is this answer meaning to say, among other things, that business jet are not actually flying faster than airliners for the most part, they are just flying at higher altitude and therefore higher Mach for the same TAS? I can't quite tell. – quiet flyer Feb 17 '23 at 01:21
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    @quietflyer If that's what the answer says, it doesn't make sense - since above tropopause (36k feet), the temperature and therefore the speed of sound are constant. This means that a particular Mach no. always corresponds to a particular TAS; so an airliner flying at M0.8 at 36k feet travels at the same TAS as a corporate jet at M0.8 at 50k feet. – Aditya Sharma Feb 17 '23 at 06:26
  • "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" are you sure that the fuel consumption is lower at higher altitude? – sophit Feb 17 '23 at 15:11
  • @sophit - yes I am sure. Do you have any reason to doubt it? – Paul Smith Feb 17 '23 at 15:24
  • No reason to doubt, but I have in mind that higher than sone 36'000ft the fuel consumption remains more or less constant but maybe I'm just remembering it wrong. – sophit Feb 17 '23 at 15:58
  • @sophit - consumption is roughly constant but air density drops so the same thrust has less resistance to overcome, resulting in more efficient use of fuel. – Paul Smith Feb 17 '23 at 16:16
  • Ah, now I understand: is the drag that is less and not the engine's efficiency that is more. – sophit Feb 17 '23 at 16:21
  • @AdityaSharma: The altitude of the tropopause varies dramatically from below 30 kft to over 55 kft, depending on location. It is not always (or even usually) at 36 kft. Also, above the tropopause, the temperature rises with increasing altitude, rather than remaining constant. – Vikki Mar 17 '23 at 03:31