Author Topic: Will scramjet planes ever take off?  (Read 15857 times)

Offline mlorrey

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Re: Will scramjet planes ever take off?
« Reply #20 on: 11/15/2009 12:02 AM »
I'm pretty sure you're wrong.  The engines weren't the limiting factor on the SR-71.  Around Mach 3.6 - 3.7, the airframe would start to fail; that's why it never went faster than that.

The SR-71 is limited by both engine and structural temperature to about Mach 3.6.  If it was just temp, it could dash to engine speed limit.

And next time I design a missile, I will remember I can just use a ramjet as long as I am moving.   This will save a lot on the large solid to get the engine up to start speed.

If not a shockwave to compress the air in a ramjet, what does the compression?

Danny Deger

At subsonic speeds, you are still piling up a pressure front at the head of the vehicle, but a ramjet expands the air once past the inlet to slow it down. A ramjet will normally have a compression ramp or spike at the inlet but notice that the inlet cross sectional area is significantly less than the combustion chamber cross secion. This ensures a) that combustion gasses won't want to go back out the intake, and b) once past mach 1, the combustion chamber airflow will remain subsonic while the vehicle is supersonic.
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Offline mlorrey

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Re: Will scramjet planes ever take off?
« Reply #21 on: 11/15/2009 12:07 AM »
I'm pretty sure you're wrong.  The engines weren't the limiting factor on the SR-71.  Around Mach 3.6 - 3.7, the airframe would start to fail; that's why it never went faster than that.

Yes that was my understanding as well, from pilots who flew them. By mach 3.5 the engines were pretty much on pure ramjet mode and could continue to accelerate if you didn't throttle them down.

Recall that when subsonic and refuelling, the aircraft's skin shrinks in size opening leaks in the tanks. Likewise, at top speed the skin is fully expanded and has the airframe in compression. Any more heating of the skin and panels would literally pop their rivets and peel off.
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Offline mlorrey

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Re: Will scramjet planes ever take off?
« Reply #22 on: 11/15/2009 12:11 AM »
So why nasa cancelled the RTA study http://gltrs.grc.nasa.gov/reports/2005/TM-2005-213803.pdf (it also should  be used for darpa's falcon project and funded under air force's Histed program). and instead darpa chose to use the vulcan configuration ( cvc/pde embodied with existing turbofan such as the p&w f119 ), pluse i have never seen a turbofan that could get you to mach 4 speeds even  the blackbird engine the J58 could 'only' get you to mach 3.2  and that with a ramjet bypass system, currect me if i am wrong :).

NASA has never let practicality be a factor in making cancellation decisions on anything. For many years their raison d'etre was not to colonize space, but to spend as much money as possible 'advancing the state of the art' but never actually doing much of anything with that state of the art.
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Offline Jim

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Re: Will scramjet planes ever take off?
« Reply #23 on: 11/15/2009 01:33 AM »
For many years their raison d'etre was not to colonize space,

Since when is that NASA's charter?
« Last Edit: 11/15/2009 01:33 AM by Jim »

Offline Jim

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Re: Will scramjet planes ever take off?
« Reply #24 on: 11/15/2009 01:35 AM »
I'm pretty sure you're wrong.  The engines weren't the limiting factor on the SR-71.  Around Mach 3.6 - 3.7, the airframe would start to fail; that's why it never went faster than that.

Yes that was my understanding as well, from pilots who flew them. By mach 3.5 the engines were pretty much on pure ramjet mode and could continue to accelerate if you didn't throttle them down.



It was the engines and EGT was the limiting factor.

Offline mlorrey

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Re: Will scramjet planes ever take off?
« Reply #25 on: 11/15/2009 01:41 AM »
For many years their raison d'etre was not to colonize space,

Since when is that NASA's charter?

Thats the question the Augustine Commission is asking: is it or is it not the mission of NASA to lead in the goal of colonizing the moon, mars, and other locations in space? If it is not the goal, then the Augustine Commission finds no reason for NASA to pursue the Ares program.
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Offline Jim

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Re: Will scramjet planes ever take off?
« Reply #26 on: 11/15/2009 01:44 AM »

Thats the question the Augustine Commission is asking: is it or is it not the mission of NASA to lead in the goal of colonizing the moon, mars, and other locations in space? If it is not the goal, then the Augustine Commission finds no reason for NASA to pursue the Ares program.

No. Exploration and colonization are two different things
« Last Edit: 11/15/2009 01:44 AM by Jim »

Offline mlorrey

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Re: Will scramjet planes ever take off?
« Reply #27 on: 11/15/2009 03:23 AM »

Thats the question the Augustine Commission is asking: is it or is it not the mission of NASA to lead in the goal of colonizing the moon, mars, and other locations in space? If it is not the goal, then the Augustine Commission finds no reason for NASA to pursue the Ares program.

No. Exploration and colonization are two different things

http://www.thespacereview.com/article/1483/1
Greason addressed—and rejected—some of the common justifications for human spaceflight, ranging from science to international cooperation to technology spinoffs. Humans can be far more effective in scientific work than robots, he noted as one example, “but that doesn’t mean you can justify the space program based on the science that it does” since other fields of research can give you “more science than the buck”.

“The trap with all of these justifications is that it’s not enough to say that if we spend money on space then we get these benefits,” he said. “If you’re justifying spending money on space because of this benefit or that benefit, you have to look not at the alternative of not doing it, you have to look at the opportunity cost: what else could you have spent that money on, and could you have gotten benefits out of that, too.”

All these things are benefits that you get as part of having a human spaceflight program, but what, then, is the key justification for it? “I knew that the reason why we go to space is because we’re going to live there someday,” he said. “We are opening a new frontier for humanity, we are creating new places and making them accessible for us. This is what the future is about.”

Greason said he was “stunned” that the rest of the committee agreed with him. “I never imagined that nine other people who are aerospace greybeards not only knew that but were willing to say that.”

And then, in a line that generated an impromptu round of applause from the Boston audience: “It’s time for the real justification for human spaceflight to come out of the closet.”

and to ensure you dont try to claim thats not in the Augustine report, voila:

"These more tangible benefits exist within a larger context. Exploration provides an opportunity to demonstrate space leadership while deeply engaging international partners; to inspire the next generation of scientists and engineers; and to shape human perceptions of our place in the universe. The Committee concluded that the ultimate goal of human exploration is to chart a path for human expansion into the solar system. This is an ambitious goal, but one worthy of U.S. leadership in concert with a broad range of international partners."
http://www.ostp.gov/galleries/press_release_files/Augustineforweb.pdf
« Last Edit: 11/15/2009 03:24 AM by mlorrey »
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Offline savuporo

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Re: Will scramjet planes ever take off?
« Reply #28 on: 11/15/2009 04:44 AM »

The holy grail is you catch an early morning flight, have your meeting, and get home at a decent hour.

That requires a short stay at the airport,
Stop right there. You can improve the flight times to silly hours, but if you have to be at airport 2 hours before, and it takes 1 hour to get out, adding an hour both to get there and back, minutes you will shave off the actual flight time will be irrelevant.

Orion - the first and only manned not-too-deep-space craft

Offline madscientist197

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Re: Will scramjet planes ever take off?
« Reply #29 on: 11/15/2009 07:22 AM »
Yes, but there are plenty of other places in the world which aren't quite so paranoid about airport security. It's essentially impossible to stop anyone with sufficient intellegence and determination (admittedly airport security does seem to have caught a fair number lacking the first ;) ).

If you can afford to fly on an ultra-expensive supersonic plane and the point of difference is that it takes less time out of your day then the carrier is going to go out of their way to intigate fast, efficient airport security. It is possible; I just think that for most (particularly budget oriented carriers) it doesn't make economic sense. You have to wait in queues because it is cheaper than using more advanced screening technology and having more personnel. For example, if people are going to be doing international travel extremely regularly it might make sense to do one-off detailed background checks in lieu of interrogating the person every time they cross the border. There would still need to be ID verification and baggage scans, but it might not require any human interaction -- just put your baggage in an scanning device and put your eye up to the retinal imager.
« Last Edit: 11/15/2009 07:25 AM by madscientist197 »
John

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Re: Will scramjet planes ever take off?
« Reply #30 on: 11/15/2009 12:21 PM »

The holy grail is you catch an early morning flight, have your meeting, and get home at a decent hour.

That requires a short stay at the airport,
Stop right there. You can improve the flight times to silly hours, but if you have to be at airport 2 hours before, and it takes 1 hour to get out, adding an hour both to get there and back, minutes you will shave off the actual flight time will be irrelevant.
That's why high speed rail has its value of survival: minimal waiting time at the terminal compared with jets

Offline Danny Dot

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Re: Will scramjet planes ever take off?
« Reply #31 on: 11/15/2009 03:35 PM »
On wait time at airports.  It would go much faster if they just gave everyone a knife and had us board.   And I pitty the fool that tries to light their shoes next time. 

There is no way anyone is going to take control of another plane.  People don't like to be Kamikazed into buildings on a beautiful fall day.

Serious though.  There is a good point that there is a point of diminishing returns on decreasing airline travel time due to all the time spent on the ground. 

Danny Deger
Danny Deger

Offline mlorrey

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Re: Will scramjet planes ever take off?
« Reply #32 on: 11/15/2009 04:16 PM »
On wait time at airports.  It would go much faster if they just gave everyone a knife and had us board.   And I pitty the fool that tries to light their shoes next time. 

There is no way anyone is going to take control of another plane.  People don't like to be Kamikazed into buildings on a beautiful fall day.

Serious though.  There is a good point that there is a point of diminishing returns on decreasing airline travel time due to all the time spent on the ground.

Well, that depends. You are going to spend all that time on the ground anyways no matter how long your flight is. If all you need to do is fly Boston to DC, I agree its a complete waste of time to go ballistic/hypersonic.

If your destination is a five hour flight away, to do a three hour business meeting, going ballistic is the difference between making it home for dinner that day to be with your kids or getting home at dinner the NEXT day. If you are someone who is a CEO/CFO/CTO/Rock Star/Supersurgeon/Power Lawyer who effectively makes $10,000 an hour, then an $50,000 ticket on a ballistic/hypersonic shuttle is a cost effective use of resources.
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Offline William Barton

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Re: Will scramjet planes ever take off?
« Reply #33 on: 11/15/2009 04:28 PM »
There's little need for commercial travelers to get anywhere on Earth any faster than they already can.

Maybe there's little "need", but there's plenty of "want" to get there faster. India from the West coast takes something like 30 hours. Lot of people would pay more to get there a lot faster.


You're talking about the difference between a commercial fleet airliner (which is what Concorde was supposed to be) and a private charter. I don't know what the prospects are for the Aerion Supersonic Business Jet coming to market and succeeding, but obviously somebody thinks there's enough "want" to sell them. Maybe we'll see.

Offline William Barton

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Re: Will scramjet planes ever take off?
« Reply #34 on: 11/15/2009 04:31 PM »
Concorde was profitable for the for the airline (british airways) for most of it's life but was unprofitable for the company that made it. Mainly due to the 70s spike in oil costs drying up orders and the US restriction on supersonic overflights.

I used to live under the flight path and the booms never bothered me, in fact I barely heard them.

Shame really.


I was working on a seismic survey near Dulles Airport in the late 1970s (to predict bedrock blasting requirements for new sewer installation). Concorde's engine noise didn't bother me, but it bothered the heck out of our geophones! My understanding is, Concorde only went supersonic over the open sea, so unless you lived on a boat, you wouldn't have heard the booms from closeby.

Offline mlorrey

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Re: Will scramjet planes ever take off?
« Reply #35 on: 11/15/2009 04:37 PM »
There's little need for commercial travelers to get anywhere on Earth any faster than they already can.

Maybe there's little "need", but there's plenty of "want" to get there faster. India from the West coast takes something like 30 hours. Lot of people would pay more to get there a lot faster.


You're talking about the difference between a commercial fleet airliner (which is what Concorde was supposed to be) and a private charter. I don't know what the prospects are for the Aerion Supersonic Business Jet coming to market and succeeding, but obviously somebody thinks there's enough "want" to sell them. Maybe we'll see.

There are at any given time, depending on the economy between 800-1200 billionaires in the world these days. Such folks would use a ballistic/hypersonic vehicle on a regular basis.

There are approximately 320,000 multimillionaires in the world in 2009. All of these are potential passengers at least once, along with family members. The top 20% are in the hundreds of millions of dollars range that makes flights several times a year economically smart if they are working rich.
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Offline William Barton

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Re: Will scramjet planes ever take off?
« Reply #36 on: 11/15/2009 04:53 PM »
There's little need for commercial travelers to get anywhere on Earth any faster than they already can.

Maybe there's little "need", but there's plenty of "want" to get there faster. India from the West coast takes something like 30 hours. Lot of people would pay more to get there a lot faster.


You're talking about the difference between a commercial fleet airliner (which is what Concorde was supposed to be) and a private charter. I don't know what the prospects are for the Aerion Supersonic Business Jet coming to market and succeeding, but obviously somebody thinks there's enough "want" to sell them. Maybe we'll see.

There are at any given time, depending on the economy between 800-1200 billionaires in the world these days. Such folks would use a ballistic/hypersonic vehicle on a regular basis.

There are approximately 320,000 multimillionaires in the world in 2009. All of these are potential passengers at least once, along with family members. The top 20% are in the hundreds of millions of dollars range that makes flights several times a year economically smart if they are working rich.

It's the same reasoning that leads some to predict sales of "space yachts." The question is, how often do these people really need to travel on business? If I were that rich, would I risk my neck on a ballistic transport, or would I send 50 flunkies economy class? What kind of business does Bill Gates do that requires his personal presense? (Of course, I am someone who doesn't enjoy travel at all. If it weren't for rdp, I'd be in a different line of work.)

Offline mlorrey

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Re: Will scramjet planes ever take off?
« Reply #37 on: 11/15/2009 10:04 PM »

There are at any given time, depending on the economy between 800-1200 billionaires in the world these days. Such folks would use a ballistic/hypersonic vehicle on a regular basis.

There are approximately 320,000 multimillionaires in the world in 2009. All of these are potential passengers at least once, along with family members. The top 20% are in the hundreds of millions of dollars range that makes flights several times a year economically smart if they are working rich.

It's the same reasoning that leads some to predict sales of "space yachts." The question is, how often do these people really need to travel on business? If I were that rich, would I risk my neck on a ballistic transport, or would I send 50 flunkies economy class? What kind of business does Bill Gates do that requires his personal presense? (Of course, I am someone who doesn't enjoy travel at all. If it weren't for rdp, I'd be in a different line of work.)

There are executives today who own retired supersonic fighter jets, partly for the fun, partly because they can get places faster to do business. Note you dont have to wait two hours at the airport if you own your own plane.

I doubt many private SS2's will be sold, but I can believe whatever XCOR builds after the Lynx would sell well, depending on its range. My own concept X-106 could be easily used suborbitally without the tow, launching from an airfield with the rocket engine to get the ramjet going, then turning the rocket off til you reach high speed, then use it again to boost ballistically. Wing loading on reentry is only 14 lb/sqft, so you can glide it like a Cessna 172, with less drag.

Larry Ellison is IMHO an excellent candidate for such a vehicle. He is notorious for flying his GIV into San Jose late at night to get home the same day, picks up a lot of fines for the late landings, which he pays without reservation. I think he'd pay very handsomely to get home earlier.
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Offline RanulfC

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Re: Will scramjet planes ever take off?
« Reply #38 on: 11/20/2009 04:18 PM »
On the history of the scramjet; they have been theoretically studied since soon after the first person though up the ramjet :)

It has always been "assumed" (yes I used that delibratly :) ) that ramjet engines would have issues with having to shock hypersonic (Mach-5+) incoming air down to subsonic speeds for combustion so that speeds above Mach-5 would need an engine capable of supersonic combustion. Hence SCRamJet or Supersonic Combustion Ramjet :)

Also "assumed" was that there was ONLY one fuel that could be used for supersonic combustion and that was Liquid Hydrogen.

Research into scramjets therefor had to 'wait' on the availability of LH2, then began to get it to burn (and produce thrust) at supersonic speeds.

Meanwhile research and testing along with actual real-world operations of ramjet engines showed they did NOT have an issue with hypersonic speeds and could be operated up to the limits of the matrerial strength of the engine. (Nothing "official" mind you but there is data around that indicates Mach-8 has been done at least in testing with a "standard" subsonic combustion ramjet)

Meanwhile OTHER research showed that you could actually get hydrocarbon fuels to ignite, burn and produce thrust in scramjets without resorting to overly long and 'drag-producting' ducts.
With the advent (though theoretically mentioned and studied as far back as the early '50s) of the "Inward Turning Inlet" (a good website for explaining the concept and other rocket or air breathing concepts is here:
http://books.google.com/books?id=7WStVFhkmwUC&pg=PA136&lpg=PA136&dq=inward+turning+inlet&source=bl&ots=HMntCFaOaf&sig=7MbTIlvCfOOM4VLwign9B1tfpsM&hl=en&ei=eMcGS5WdAYvysgPUg6jACQ&sa=X&oi=book_result&ct=result&resnum=9&ved=0CCsQ6AEwCA#v=onepage&q=inward%20turning%20inlet&f=false
for both ramjet and scramjet use especially the newest designs which reduces the need for heavy movable ramps systems.

An example of a simple inward turning inlet is here:
http://www.mae.virginia.edu/HyV/flighttesting.htm

Imagine a "C" turned open-side down, now it narrows down from the front towards the middle of the vehicle till it comes to the combustion section. The open 'slot' along it's length helps allow the engine to 'spill' excess pressure and achieve more effcient combustion in the combustion section. The "nozzle" area expand back out to take maximum advantage of altitude adjustment and thrust.

Now does ANY of this mean that scramjets will ever be actually PRACTICAL? I've not a clue, but my personal opinion is that they probably won't. Simply because they fill a 'niche' in propulsion that only really works at hypersonic speeds which require much more robust airframe to stand the terrific heating such speeds generate.

For travel such as has been discussed getting OUT of the atmosphere for most of the flight is MUCH easier on the airframe and in practice easier to do with skip-glide trajectories rather than having scramjets.
By 'skipping' out of the reasonable atmosphere (between 150,000ft to 200,000ft or more) the vehicle experiances much lower heat loads and can effectivly radiate the majority of that heat away in between 'skips' while maintaing 'speed' by using thrust when inside the effective atmosphere.

The skip-glide is NOT a "rollercoaster" ride of sharp up and downs but a low frequency 'gentle' motion with times between reaching appoge and the paragee of each 'skip' being on average around 10 minutes. By using a form of 'ramjet' propulsion known as "external burning" (where fuel is injected between vehicle shockware and the vehicle hull itself and combusted using the lower surface and shockwave interface as a 'virtual' ramjet) vehicle drag can be lowered dramitically and much less fuel is used than would be the case if the vehicle remained plowing through the atmosphere.

Technically I suppose "external burning" IS a scramjet of a type since the fuel would burn at supersonic speeds but by using the vehicle underside as intake, combustor, and expansion ramp combustion is much easier to achieve and the fuel has plenty of time to combust fully.

Randy
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