The X-51a WaveRider flies...

[Downix]

What about intercontinental transport? I think that could be a real hit.

Oh, really? Intercontinental transport that needs a rocket booster will be a real hit? 

Commercial could use another jet engine for the initial acceleration to scramjet speed.

The deal killer for SSTs in the US was the damage from sonic booms (environmental impacts to livestock and public nuisance). Would a commercial scramjet HST have the same 'deal killer' issues?

Depends on if they operate exoatmospheric or not.  No air == no sonic booms.  Also we have had our knowledge of how to minimize sonic booms grow greatly these past few years.

[Arthur]

What about intercontinental transport? I think that could be a real hit.

Oh, really? Intercontinental transport that needs a rocket booster will be a real hit? 

Commercial could use another jet engine for the initial acceleration to scramjet speed.

The deal killer for SSTs in the US was the damage from sonic booms (environmental impacts to livestock and public nuisance). Would a commercial scramjet HST have the same 'deal killer' issues?

Depends on if they operate exoatmospheric or not.  No air == no sonic booms.  Also we have had our knowledge of how to minimize sonic booms grow greatly these past few years.

Exoatmospheric would be like a skip-bomber concept then?
I mean no air means no boom, but it also means no scramjet.

[mlorrey]

What about intercontinental transport? I think that could be a real hit.

Oh, really? Intercontinental transport that needs a rocket booster will be a real hit? 

Commercial could use another jet engine for the initial acceleration to scramjet speed.

The deal killer for SSTs in the US was the damage from sonic booms (environmental impacts to livestock and public nuisance). Would a commercial scramjet HST have the same 'deal killer' issues?

Anti-sonic-boom legislation did greatly limit the marketability of Concorde for overland routes, but the aircraft itself was greatly limited in its range that eliminated a lot of overseas routes. If you can build an SST with a 4500 mile range, it would have many times the number of useful routes as Concorde had.

[mlorrey]

What about intercontinental transport? I think that could be a real hit.

Oh, really? Intercontinental transport that needs a rocket booster will be a real hit? 

Commercial could use another jet engine for the initial acceleration to scramjet speed.

The deal killer for SSTs in the US was the damage from sonic booms (environmental impacts to livestock and public nuisance). Would a commercial scramjet HST have the same 'deal killer' issues?

Depends on if they operate exoatmospheric or not.  No air == no sonic booms.  Also we have had our knowledge of how to minimize sonic booms grow greatly these past few years.

Exoatmospheric would be like a skip-bomber concept then?
I mean no air means no boom, but it also means no scramjet.

It is possible to fly high enough that little to no sonic boom reaches the ground but still have air breathable by scramjets. In fact, they prefer it up there.

[Lee Jay]

It is possible to fly high enough that little to no sonic boom reaches the ground but still have air breathable by scramjets. In fact, they prefer it up there.

How high is that?  An 80,000 foot SR-71 hit me with a sonic boom that felt like it was going to shake loose some teeth.  I know these things could in theory go 200,000 feet or so, is that what you meant?

[sanman]

You felt the sonic boom from an SR-71 that was 80k feet above you, while you were standing on the ground?

But an SR-71 can only go Mach3 - you mean you can feel a Mach3 sonic boom that far below?

In that case, I'm sure that twice the altitude could eliminate the problem.

The point is to get spacelift-capable technologies into mass-market interaction. That's why space tourism has been an exciting possibility.

People will pay to reach the other side of the world at Mach5.
Then competition between multiple service providers will evolve the technology and bring down costs from there.

[kevin-rf]

New article with additional details:
 http://www.aviationnow.com/aw/generic/story_generic.jsp?channel=awst&id=news/awst/2010/05/31/AW_05_31_2010_p27-230271.xml&headline=X-51A%20Team%20Eyes%20Results%20Of%20Scramjet%20Flight

The X-51A began to accelerate, but slower than expected—up to 0.15g instead of the projected 0.22g. “We were seeing higher temperatures in the back of the engine bay, but have no idea why,” Brink says.

After reaching around Mach 5, the vehicle began to slow. When telemetry was lost, range safety officials decided to terminate the flight by destroying the vehicle.

[mlorrey]

It is possible to fly high enough that little to no sonic boom reaches the ground but still have air breathable by scramjets. In fact, they prefer it up there.

How high is that?  An 80,000 foot SR-71 hit me with a sonic boom that felt like it was going to shake loose some teeth.  I know these things could in theory go 200,000 feet or so, is that what you meant?

Firstly, I doubt you had any idea what the altitude was of the aircraft that made the sonic boom you heard, or what aircraft it was. The SR-71 generally only flies at high altitude when doing fast dashes over enemy territory, otherwise it flies at 35,000-50,000 ft. So unless you were in Cuba, Venezuela, Colombia, Vietnam, or North Korea (they haven't overflown mainland China or Russia in decades), it wasn't an SR-71 at 80k ft you heard.

Secondly, the SR-71 top altitude is 85,000 ft, at least that is what is publicly acknowledged. Given my own experience with published numbers, I would not be surprised if it could go 20-25% higher, but not much more without installation of some MIPCC equipment and some large LOX tankage.

That said, ramjet powered missiles have flown as high as 175,000 ft, but that was apogee after flameout at a lower altitude due to empty fuel tanks. According to charts I've seen, Mach 6 aircraft should find a comfortable cruising altitude at about 120,000-130,000, but with rapidly closing barriers to combustion from both atmospheric density and thermal issues without a transition to scram combustion. The subpar performance of the X-51 has me concerned about its capacity to actually achieve supersonic combustion.

However, such an aircraft should be capable of doing a boost zoom when at this altitude to get above the atmosphere and engage in some amount of skip gliding. The range possible by doing this greatly depends on the initial velocity at apogee, as you bleed both speed and altitude with each skip, so the next skip will always be lower and slower to maximize range.

[mlorrey]

WRT altitude and sonic booms, each aircraft has a different altitude at which its sonic boom is loudest. This is because the trailing shock wave always travels slightly faster than the leading shock wave, and eventually catches up with it at some distance from the aircraft, creating a reinforced wave that is known as an "N" wave.

For instance, the Shuttles peak shock wave is produced at about 50,000 ft with about 1.6 lbs/sqft of pressure, while the SR-71's peak N wave happens at higher altitude but peak pressure is only 0.9 lbs/sqft. This is because longer leaner fuselages have higher altitudes and lower peak pressures (wingspan has an impact as well).

Now, scramjets for the most part will likely produce very little sonic boom, because the design of scramjets is typically to use the fuselage as a compression structure feeding into the intake, and tends to also focus the underside portions of the shock wave to be swallowed by the scramjet engine. This means the primary downwards travellilng leading edge shock will be emitted by the lower leading edge of the intake, which will be likely less than ten meters from the trailing edge of the entire vehicle. For this reason the altitude at which the trailing shock catches up to this minor leading shock will be at a very low altitude, likely less than 25,000 ft, so that by the time the vehicle reaches supersonic speeds, it will be above this altitude and will thus produce little, if any, sonic boom at the ground once it is above this altitude.

[bad_astra]

GOX  injection into the intake at higher altitudes might make a scramjet very much part of a space launch vehicle, at least far enough to make a deployed upperstage more trivial than most. I don't think it would ever lead to a SSTO, but I would love to find I was wrong years from now.

Otherwise it does have spaceflight applications, just suborbital.

[mlorrey]

GOX  injection into the intake at higher altitudes might make a scramjet very much part of a space launch vehicle, at least far enough to make a deployed upperstage more trivial than most. I don't think it would ever lead to a SSTO, but I would love to find I was wrong years from now.

Otherwise it does have spaceflight applications, just suborbital.

Yeah I've thought about that, GOX injection is part of any MIPCC system anyways. At the least it allows a scramjet to operate at a much higher than normal altitude, and if you have enough variable geometry in the engine, you can close the intake and use it as a rocket engine itself. Thats what the strutjet is about anyways.

[DeanG1967]

You felt the sonic boom from an SR-71 that was 80k feet above you, while you were standing on the ground?

80K direct overflight of a SR-71 at Mach "x" and all you hear is a rumble (not really even a boom).  Your dentures had to have been lose or jarred due to some guy in a dark window tinted vehicle playing rap music really loud

[RanulfC]

According to the reports and studies I've read anything supersonic over 100,000ft the sonic boom disipates before it can reach the ground.

GOX injection per-se wasn't ever part of MIPCC, they used LOX injection to stabilize the combustion in the combustion chamber, but the LOX was/would have been injected into the intake to help cool and compress the incoming airstream.

As a note you need to keep in mind that the MIPCC system wasn't planned on being used for any type of "cruise" flight but instead was focused on "acceleration" flight profiles so they were more concerned with preventing combustion instabilities at high-AoA and rapidly changing altitude.

Randy

[mlorrey]

e to help cool and compress the incoming airstream.

As a note you need to keep in mind that the MIPCC system wasn't planned on being used for any type of "cruise" flight but instead was focused on "acceleration" flight profiles so they were more concerned with preventing combustion instabilities at high-AoA and rapidly changing altitude.

Randy

The only plane I've heard of thats used MIPCC was the F-4 Phantom II which used it as a cheat to beat the F-106's speed record, and that was flying level at altitude. What other vehicles have used it?

[DeanG1967]

e to help cool and compress the incoming airstream.

As a note you need to keep in mind that the MIPCC system wasn't planned on being used for any type of "cruise" flight but instead was focused on "acceleration" flight profiles so they were more concerned with preventing combustion instabilities at high-AoA and rapidly changing altitude.

Randy

The only plane I've heard of thats used MIPCC was the F-4 Phantom II which used it as a cheat to beat the F-106's speed record, and that was flying level at altitude. What other vehicles have used it?

Trying to figure out what "speed record" the F-4 beat the F-106 at? 

"On 15 December 1959 Maj Joseph Rogers flew F-106A serial number 56-0467 1,525.93 mph (2455.68 km/k) on a straight line course 11 miles long (18km) at an altitude of 40,000 ft (12192 m) setting a new single engine speed record of Mach 2.31.

Some history books show this accomplishment being set in serial number 56-0459, but due to engine compressor stall problems, which resulted in violent yaw oscillations the backup aircraft, 56-0467 was actually used to set the record.  This record run still stands today for a single engine aircraft.

Granted, the F-4 did get the overall speed record at 1606mph but needed 2 engines to do it.  The F-4 still couldn't climb like th Six. 

[mlorrey]

e to help cool and compress the incoming airstream.

As a note you need to keep in mind that the MIPCC system wasn't planned on being used for any type of "cruise" flight but instead was focused on "acceleration" flight profiles so they were more concerned with preventing combustion instabilities at high-AoA and rapidly changing altitude.

Randy

The only plane I've heard of thats used MIPCC was the F-4 Phantom II which used it as a cheat to beat the F-106's speed record, and that was flying level at altitude. What other vehicles have used it?

Trying to figure out what "speed record" the F-4 beat the F-106 at? 

"On 15 December 1959 Maj Joseph Rogers flew F-106A serial number 56-0467 1,525.93 mph (2455.68 km/k) on a straight line course 11 miles long (18km) at an altitude of 40,000 ft (12192 m) setting a new single engine speed record of Mach 2.31.

Some history books show this accomplishment being set in serial number 56-0459, but due to engine compressor stall problems, which resulted in violent yaw oscillations the backup aircraft, 56-0467 was actually used to set the record.  This record run still stands today for a single engine aircraft.

Granted, the F-4 did get the overall speed record at 1606mph but needed 2 engines to do it.  The F-4 still couldn't climb like th Six. 

Operation Skyburner: On 22 December 1961, a modified Phantom with water injection MIPCC set an absolute world record high altitude speed of 1,606.342 mph (2,585.086 km/h), beating the prior record set in 1959 by an F-106A of 1525mph.. On the second leg of the speed attempt, the Phantom exceeded 1700 mph.

[RanulfC]

e to help cool and compress the incoming airstream.

As a note you need to keep in mind that the MIPCC system wasn't planned on being used for any type of "cruise" flight but instead was focused on "acceleration" flight profiles so they were more concerned with preventing combustion instabilities at high-AoA and rapidly changing altitude.

Randy

The only plane I've heard of thats used MIPCC was the F-4 Phantom II which used it as a cheat to beat the F-106's speed record, and that was flying level at altitude. What other vehicles have used it?

RASCAL was to use it, they tested engines with various injected substances over the whole engine and flight regime, which is what I thought we were talking about.

Randy

[mlorrey]

e to help cool and compress the incoming airstream.

As a note you need to keep in mind that the MIPCC system wasn't planned on being used for any type of "cruise" flight but instead was focused on "acceleration" flight profiles so they were more concerned with preventing combustion instabilities at high-AoA and rapidly changing altitude.

Randy

The only plane I've heard of thats used MIPCC was the F-4 Phantom II which used it as a cheat to beat the F-106's speed record, and that was flying level at altitude. What other vehicles have used it?

RASCAL was to use it, they tested engines with various injected substances over the whole engine and flight regime, which is what I thought we were talking about.

Randy

I wasn't aware they even got to testing any hardware on that, it always seemed to me to be a paper study rigged to prove the impossibility of RLVs.

[RanulfC]

They did engine testing but the airframe proved harder and more expensive as they went along. Rather than proving RLVs were 'impossible' the program managed to show that even DARPA could fall for building a "mouse" to government specifications and ending up with an Elephant... A large White-One at that )

Too much got piled on the RASCAL program too fast, instead of a 'proof-of-concept' vehicle which is what DARPA had originally been aiming for the program morphed into an operational vehicle program (which DARPA doesn't tend to do) with pretty ambitious and far-reaching program goals, and operational requirments that ended up pushing the design away from being what it was intended to be.

In the end though a lot of groundwork got layed on MIPCC, flight trajectories, command and control systems and simulator process' for an RLV first stage that the Air Force is in part using to base their latest effort on.

Randy

[SimonDM]

Now, scramjets for the most part will likely produce very little sonic boom, because the design of scramjets is typically to use the fuselage as a compression structure feeding into the intake, and tends to also focus the underside portions of the shock wave to be swallowed by the scramjet engine. This means the primary downwards travellilng leading edge shock will be emitted by the lower leading edge of the intake, which will be likely less than ten meters from the trailing edge of the entire vehicle. For this reason the altitude at which the trailing shock catches up to this minor leading shock will be at a very low altitude, likely less than 25,000 ft, so that by the time the vehicle reaches supersonic speeds, it will be above this altitude and will thus produce little, if any, sonic boom at the ground once it is above this altitude.

Researchers found that sonic boom is mostly altitude independent (although 100.000 feet is often quoted as an altitude at which sonic boom becomes negligible) and dependent on lift (=weight) and length of the vehicle. Wave drag, strength of the shock wave and sonic boom are further three different things. A blunt body will for example generate a stronger shock wave and wave drag than a sharp body but a lower sonic boom.

Further, I really doubt this is anything but a military toy and research funding sinkhole. A rocket may have lousier ISP than a scramjet but can also operate with less drag (no air inlet) and operate in very thin atmosphere for part of its mission with virtually no drag at all, plus thrust to weight ratio of a rocket is much better and mass fraction too. I don't think it is straightforward that this scramjet thingy would perform better than a rocket on the same mission. If ground targets need to be hit, rockets offer the benefit they might go supersonic all the way down, imparting significant kinetic energy too. The inlet of a scramjet would work as a drag chute at anything significantly below its design speed, probably slowing the thing to subsonic at sea level.