Look at the graph on the right hand side: Eurofighter Typhoon ? Wikipedia There is a steep drag rise at mach 1. More over the centre of gravity changes abruptly when you go from subsonic to supersonic. Completely different aerodynamics. As a result there will be no business jet above mach 1. You would need something like a Concorde and that is very expensive and the market is too small.
There is a 550 and a 767 currently, with a 650 and a 777 in the pipeline. We were trying to look beyond that.
Interesting graph. But at Concorde speeds, you seem to be OK again. If (in theory) you could resurrect a Concorde for private use, I think you are limited to main airports with long runways.
Control reversion happens on some shapes above supersonic speeds. Flight control surfaces have to be proven and tested for "normal" flight, and then be able to function at supersonic speeds as well. Then, these control surfaces must survive gauntlet and severe testing for safety, stress, flutter and control parameters. You cant just " go fast" and fly the air vehicle the same way. Heat. That is a whole different issue, which affects the materials and construction of the aircraft. Go really fast, some parts get really hot. Slow down and start to descend, the hot parts get really cold. What is they crack and fail prematurely? Leaks? Look at the famous fuel leaks from the SR71 due to heating and structural issues. A civilian aircraft MUST overcome all those factors, or it will never be a revenue generating product. I hope somebody gets to build one.
In the mach 2 region, you are still largely pushing the air aside to fly, creating a lot of drag and heavy fuel consumption at relatively low altitude. At mach 3+, you are in a lower drag region and are actually sort of surfing through thinner air at much higer altitude. Trouble is, the high mach two regime is about the max limit for aluminum airframes without resorting to exotic leading edges and some airframe elements because of airframe thermal limits. So realistically, Concorde was limited in how fast she could go without using costly (and then largely nonexistent) exotic materials, higher tech engines, and paying a heavy weight penalty. US manufacturers were looking at much larger aircraft flying higher and faster, but could not make the business case close, especially with the restrictions on supersonic land overflight. The Mig-25 had steel leading edges to get to mach 2.85 or so, and they just put bigger engines in them. We had a mach 3 F-108 design using B-70 technology levels, especially engines, but that one did not make it because of cost and technology risk and loss of support from SAC for having an escort for the B-70. SAMs put the final nail in the coffin in 1959, the same thing that killed the B-70.
Taz is correct. Supersonic flight goes into an entirely different regime. Getting there is a strenuous process and after you do get there , air flow and heat turns it into a different ball game. At transonic speeds the airflow goes nuts when it can't figure out what it wants to do and drag rises at a geometric rate. Then when you get above Mach 1 there is heat to deal with if you get fast enough, and material considerations, and a lot of power required. How are you going to feed the engines with air that is going into shock waves ? The Boeing SST did it with translating inlets that directed the shock into the inlets. Center of pressure travel and all sorts of funny things start to happen with the compressed air and the heat from friction plays bad games with anything that isn't steel or titanium. It ain't easy and it ain't cheap.
Don- SS2 launches at high altitude and high pitch attitude and is rocket powered. Rockets do not care about velocity, since they carry their own oxydizer, and do not care about airflow, only air density, which affects nozzle and plume size. SS2 reaches high mach and high altitude in a very steep climb, where the atmosphere is thin and, eventually, virtually non-existent. On recovery, the shuttlecock speed brake design cuts down on velocity and reenty heating, so only rudimentary thermal protection systems (TPS) are required. Range is less than 100 nm from launch position. Profile is very similar to that of the rocket powered X-15 (except for pitch attitude), which reached ~364,000' and mach 3.7 on one flight, but reached mach 4.5 on a lower altitude flight (~100,000'). Because of its low drag design, the X-15 required quite a bit more TPS and an inconel structure for high speed and reentry from really high altitude. Both require attitude control systems for exo-atmospheric flight where aerodynamic control surfaces have little to no effect.
You can build a supersonic private jet that can supercruise like the F-22 at altitudes up to FL 600, but the F-22 pilots use a pressure device in case cabin pressure fails and that allows for a quick descent to below FL500 so blood boiling does not occur. Probably not a good idea for a private jet to cruise above FL 500. Still very expensive and very high on fuel consumption, but it could be done. Bring a pile of money and use it mostly for trans-oceanic trips. Overland, she would be limited to below mach 0.92, where transonic effects begin affecting autopilots, flight instruments, etc. VFR on top above FL450 would offer some advantages for cruising and flying a direct great circle course without flying from radio aid/reporting point overland. Assuming she could get there subsonic.
That makes sense, but the thin atmosphere is why I thought going higher, like that, and faster, would be the way to go for transportation. I guess the issue is the weight and cost of the rocket, as the speed and range of the vehicle goes up? Above, say, 350,000 feet, do the sonic boom issues become less as well?
Cd is coefficient of drag, not absolute drag, therefore drag at mach 2 is much higher than at mach 1.
Don- Flight above about 120,000' is not practical because there is not enough atmosphere to generate lift or thrust without using a rocket. The lowest orbit possible, with reentry in about 12 hours because of drag, is ~85 nm or ~515,000', so you are getting up there at 350,000'. No sonic boom in atmosphere that thin.
Thank you all for your input. The 650 is all approved, the 777 is in early stages yet. Anything beyond that will have to wait a few years...
Don- With a rocket, you have to carry your own oxydizer. That is heavy and also makes for a larger vehicle. In general, rocket engines do not burn that long since they are very efficient at burning all their propellants. A mach 10 reusable launch vehicle only goes about 200 nautical miles and would weigh about 200-300 Klb. Rockets are good at accelerating, but not too good at cruising. Plus they tend to be very, very loud and it is difficult to quiet them down. To give you some idea of efficiency, a modern high bypass fanjet might have a specific impulse as high as 10,000 seconds. The best rocket engines get is around 460 seconds with liquid oxygen and liquid hydrogen.
Very true. When I was at Redstone pitching a turbojet (which wasn't a very efficient one at that) for a particular missile application the missile guys quickly calculated the specific impulse and got real happy because the turbojet was about an order of magnitude better than the solid fuel rocket they were trying to use at the time. The problem with air breathing stuff (low or no bypass engines that you need for high Mach) is that it's often hard to get enough static thrust from a simple small engine to get you thru the launch phase but then after you get to speed it gets a lot easier. With a high speed aircraft there is also very often the issue of subsonic drag rise. The faster you go with a turbojet or ramjet the more thrust you make. An engine sized for the high speed cruise mission isn't big enough to provide enough thrust in the high subsonic region to get through that. Some aircraft have had to do a shallow dive to get through Mach 1 and then accelerate to higher Mach and finish the climb to cruise speed, so engine sizing becomes important and can dictate how you fly the mission.
look at Reaction engines Limited and their SABRE hybrid jet-rocket engine. They're developing it right now, it will be air-breathing up to Mach 5. It's got a very neat precooling system they developed that resides in the intake.
