The British FB-23

Originally posted by ghost

What's this about a SCRAMJET? SCRAMJETS (Supersonic Combustion Ramjets) are for speeds in excess of Mach 8! Are you maybe thinking of a Ramjet. It was a dule cycle turboramjet that gave the SR-71 Blackbird it's amazing speed.

Tim

The notion of an FB-23 concept with scramjet propulsion was put forth in a discussion regarding advanced technologies for the interim/regional bomber concept by planners of the program. Whether it was a real and viable suggestion I do not know.

However, regarding scramjets and at what speed their propulsion method can take hold, it is closer to the M3-M4 range, that is the point where the shockwave has enough strength to create an area of subsonic flow at the entrance to the combustor. From that point the scramjet could theoretically power a vehicle to speeds in excess of M15.

kilcoo316 is quite right, another propulsion system would be needed to get the scramjet powered vehicle to speeds that could kick off the scramjet - and yes that would be expensive but would it be prohibitively expensive? That's anybody's guess...





[edit on 12-14-2005 by intelgurl]

Originally posted by intelgurl

However, regarding scramjets and at what speed their propulsion method can take hold, it is closer to the M3-M4 range, that is the point where the shockwave has enough strength to create an area of subsonic flow at the entrance to the combustor.

I thought the whole point of a scramjet was that the flow was supersonic throughout the engine, hence the name - Supersonic Combustion RAM Jet.

It is, the only point the flow may be at M=1 is immediately downstream the combustor - otherwise its all above sonic speeds.


And I said supersonic speeds earlier, I should have said hypersonic - speeds would need to be well in excess of Mach 1 I would guess.

Originally posted by Nacnud

Originally posted by intelgurl

However, regarding scramjets and at what speed their propulsion method can take hold, it is closer to the M3-M4 range, that is the point where the shockwave has enough strength to create an area of subsonic flow at the entrance to the combustor.

I thought the whole point of a scramjet was that the flow was supersonic throughout the engine, hence the name - Supersonic Combustion RAM Jet.

Nacnud, I knew someone would ask this...
You are right - However, there is a small exception to the rule.

First let's look at the Ramjet; where incoming supersonic airflow slows to subsonic speeds due to shockwaves created by putting backpressure in the engine. The fuel is injected into the subsonic airflow, it combusts, and the exhaust gases accelerate through a narrow choke, to supersonic speeds.

The Scramjet's airflow on the other hand remains supersonic during the combustion process and doesn't require a narrow choke, this provides the greatest performance over a wider range of supersonic/hypersonic speeds.

HOWEVER, the scramjet engines the US is experimenting with can function as both a ramjet and scramjet by seamlessly making the transition between the two methods, the ramjet mode handling slower speeds and the scramjet mode handling the higher speeds.

Therefore, If you have a dual propulsion aircraft, with both turbojet and scramjet, the turbojet would need to get the aircraft up to somewhere between M3 and M4 so that the scramjet can kick in - but in order for the scramjet to fire up at such "slow" speeds, it will need to be in the ramjet mode, which is to have the shockwave slowing the airflow into the engine to subsonic speeds. Then as the ramjet proceeds past M5 (approximately) the scramjet mode would take over.

Thanks, it didn't occur to me that a scramjet would still be called a scramjet even when working in a ramjet mode.

Originally posted by intelgurl

The notion of an FB-23 concept with scramjet propulsion was put forth in a discussion regarding advanced technologies for the interim/regional bomber concept by planners of the program. Whether it was a real and viable suggestion I do not know.

Intresting! I must have missed that. I know about the FB-23 concept, but I haven't seen the part about the scramjet before. Do you have any web sites where I can look into this a bit more? I'm an F-23 fan, and have been trying to fallow it since it first showed up as an ATF contender. I would really be greatful for any insight you would be willing to share with me.

However, regarding scramjets and at what speed their propulsion method can take hold, it is closer to the M3-M4 range, that is the point where the shockwave has enough strength to create an area of subsonic flow at the entrance to the combustor. From that point the scramjet could theoretically power a vehicle to speeds in excess of M15.

kilcoo316 is quite right, another propulsion system would be needed to get the scramjet powered vehicle to speeds that could kick off the scramjet - and yes that would be expensive but would it be prohibitively expensive? That's anybody's guess...

[edit on 12-14-2005 by intelgurl]

Mach 3 to Mach 4? No offence, but that speed sounds much too low! I have a video at home on the development of the A-12 and SR-71 Blackbird spyplanes. On the video, they have an interview with Kelly Johnson, in which he talk breifly about some of the technology that made the planes work. In the interview, Kelly said the Blackbird needed to get up to 1400 mph (Mach 2) before the engine would cycle into Ramjet mode.

If a normal RAM jet doesn't work untill it hits mach 2, how does a SCRAM jet work at Mach 3-4? Could you have confused Ramjets and Scramjets?

Can you please check that for me?

Tim

Originally posted by ghost

Mach 3 to Mach 4?

No offence, but that speed sounds much too low! I have a video at home on the development of the A-12 and SR-71 Blackbird spyplanes. On the video, they have an interview with Kelly Johnson, in which he talk breifly about some of the technology that made the planes work. In the interview, Kelly said the Blackbird needed to get up to 1400 mph (Mach 2) before the engine would cycle into Ramjet mode.

If a normal RAM jet doesn't work untill it hits mach 2, how does a SCRAM jet work at Mach 3-4? Could you have confused Ramjets and Scramjets?

Can you please check that for me?

Tim

It would depend on the design of course - what holds for one does not necessarily hold for another.

For instance, the shock cones on the Blackbird will result in shockwave structures (relative to flight mach number) unique to that design, whereas the waverider (SC)RAMJET will probably be totally different.

As for the dual RAMJET/SCRAMJET idea - damn I'm stupid for not thinking of that before! Great idea

Originally posted by ghost
If a normal RAM jet doesn't work untill it hits mach 2, how does a SCRAM jet work at Mach 3-4? Could you have confused Ramjets and Scramjets?

Can you please check that for me?

Tim

I think you misunderstood my last paragraph...

"Therefore, If you have a dual propulsion aircraft, with both turbojet and scramjet, the turbojet would need to get the aircraft up to somewhere between M3 and M4 so that the scramjet can kick in - but in order for the scramjet to fire up at such "slow" speeds, it will need to be in the ramjet mode, which is to have the shockwave slowing the airflow into the engine to subsonic speeds. Then as the ramjet proceeds past M5 (approximately) the scramjet mode would take over. "

The Scramjet is a dual-mode system, relying on yet a 3rd propulsion method (a turbofan in this hypothetical scenario) to get it up to speeds that would make the ramjet-mode of the scramjet kick in.

It is at M3-M4 where the turbofan leaves off and the Ramjet mode of the dual-mode Scramjet would take over, propelling the vehicle to approximately M5-M6.5 where the Scramjet mode would then take over. From that point the speeds could range from M10 to M15+.

I don't understand one thing Intergul, if the scramjet is a dual purpose engine that can function at low and high speeds why did they have to attach a rocket to the X-43A in order to get it to hypersonic speeds where the scramjet could work.

Link to Dryden NASA

[edit on 15-12-2005 by carcharodon]

Originally posted by carcharodon
I don't understand one thing Intergul, if the scramjet is a dual purpose engine that can function at low and high speeds why did they have to attach a rocket to the X-43A in order to get it to hypersonic speeds where the scramjet could work.

Link to Dryden NASA

[edit on 15-12-2005 by carcharodon]

I believe the X-43a was purely a scramjet built for speeds of mach 5 and excess of that, the Pegasus rocket needed to get it to that point first, lets keep in mind, the Falcon is only 5 feet long.

Shattered OUT...

Originally posted by carcharodon
I don't understand one thing Intergul, if the scramjet is a dual purpose engine that can function at low and high speeds why did they have to attach a rocket to the X-43A in order to get it to hypersonic speeds where the scramjet could work.
[edit on 15-12-2005 by carcharodon]

A ScramJet is NOT a dual Purpose engine. It does not work bellow Mach 4 or 5. Remember, a scramjet is a type of ramjet. Ramjets do not have compressor to take in air, they use the shock wave from supersonic air entering the inlet to compress the air.

How a Ramjet works!

The above link will explane the physics behind Ramjets, and SCRAMJETS. Hopefully, this will answer your questions better then I can.

Tim

Originally posted by ghost
A ScramJet is NOT a dual Purpose engine. It does not work bellow Mach 4 or 5. Remember, a scramjet is a type of ramjet. Ramjets do not have compressor to take in air, they use the shock wave from supersonic air entering the inlet to compress the air.

How a Ramjet works!

The above link will explane the physics behind Ramjets, and SCRAMJETS. Hopefully, this will answer your questions better then I can.

Tim

Wikipedia? While Wiki is a good informative source, it does not drill down into current applied development, the link you give is Pure theory and history - No applied research or current level of development.

The scramjets being developed by Pratt & Whitney for military application are dual mode. period.

Try reading this:
"Scramjets"; The Industrial Physicist

This article is also written by one of the guys on Pratt & Whitney's dual mode scramjet development team.

Edit:

Also since you like Wikipedia so much, check out their page on Scramjets... - the last paragraph of the "Theory" section as well as the "France-Russia" section deal with dual-mode scramjets.






[edit on 12-16-2005 by intelgurl]

Ghost... You sure got pwned... I agree with Intelgurl in this matter... Wikipedia is good... But some facts aren't all too reliable... I remember one of my threads, I took a lot of facts from that page... And Waynos had to correct me big time...

I can't remember that

The trouble with wikipedia is that it is composed of reader contributions. I have read many articles that I know to be littered with errors. I wondered why this could be until the day I clicked on a link and it said something to the effect of 'no information available - submit your article on this subject'.

If I wrote a piece saying the Lightning was fast because it was painted with an undercoat of pink paint beneath the silver, wikipedia would publish it

Well I suppose it is too much asked... it was my first "long" thread... about the F/A-18... It was someting about the F-4 and the F-5... can't really remember... First I tought that "WTF, the guys ruining my thread" But then I realized that knowledge is power... And, well you know the rest...

just wondering could I get a comparrison of the FB-23, FB-22, And X-44(tailless version of the FB-22)
Thank you

Originally posted by TristanBW9456
just wondering could I get a comparrison of the FB-23, FB-22, And X-44(tailless version of the FB-22)
Thank you

There's not enough data out on any of these aircraft to do anything more than speculate - therefore an actual comparison is not possible.

However regarding the X-44 Manta; it was one of 6 preliminary concepts for the bomber version of the F-22. (source)

It is unlikely that the tailess X-44 version will be the actual FB-22 (should the FB-22 actually be developed). Chances are it will still have the vertical stabilizers same as the F-22.
I could be wrong - time will tell.

Speculation:
The FB-23 would probably be faster and quite possibly stealthier and carry a greater payload than the FB-22. I say the latter because I am unaware of Lockheed saying whether they would increase the airframe size of the FB-22 significantly - and the artist renderings presented by Northrop show a larger airframe for the FB-23, possibly F-111 size.

The FB-22 benefits in both the development timeline and it's cost by already having the F-22 in production.

Personal Opinion:
Although I would love to see the FB-23 in production, I personally doubt that it will ever get the nod from Congress/USAF/GAO due to the reasons I just mentioned.

Integurl


why haven`t they refurbd any aadvarks yet? they are needed NOW!!

Thanks Intelgurl,

I'm going to catch up on my research before my next big technical post.

Tim

Originally posted by Harlequin
Integurl


why haven`t they refurbd any aadvarks yet? they are needed NOW!!

The last F-111 retired from the USAF was back in the late 90's and I think it was a tactical jamming unit. Supposedly it was retired to:
1. Consolidate airframes in order to simplify support structure
2. Release more money with which to acquire F-22's

Refurbish? I don't see it happening unfortunately. I'm assuming your are referring to the Aussie Air Force as far as needing refurb F-111's?

If I was a consultant I would reccomend the Super Hornet, or the Strike Eagle with Tanker & AWACS support for range & eyes.
Additionally, the bomber concept of the C-17 (mentioned in another recent thread here on ATS) could be loaded with cruise missiles, along with some kind of UAV strike aircraft from Northrop, Boeing, Dassault or BAE and I'd say you'd be able to deliver a nice package to any area of interest in your hemisphere.
I'm sure others have a differing opinion...