MiG-31BM/Κ Interceptor/Attack aircraft: News

A supercruising engine would be the ideal match for the plane, technology should be available for it once izd. 30 is ready. I guess that would be rather used in the PAK-DP, but who knows.

I know it sounds crazy... but no.

Supercruising is useful for an air superiority fighter on combat air patrol, and it would actually also be useful for a bomber or strike aircraft because it would mean all aircraft interceptors would need to fly supersonically to chase it down which dramatically reduces their flight radius or demands constant inflight refuelling capacity.

An interceptor needs to get to its intercept point as quickly as it can... the difference between Mach 2.84 and Mach 1.8 super cruise might be the difference between shooting down 10 B-1Bs, or having to take on 10 B-1Bs plus the 220 cruise missiles they just launched...

Don't get me wrong... super cruise would be amazing for the Tu-160... normally it flys subsonic for 4,000km and then has a 1,000km dash in and back at supersonic speed, which gives it enough fuel to fly 4,000km back to base if there is one... so essentially a 10,000km flight range or 5,000km flight radius.

With super cruising at perhaps mach 1.8 or so then the dash becomes a little redundant and wasteful of fuel, but super cruising all the way means it gets done much much faster and most interceptors intercept range is halved when it comes to chasing you down. the Flight radius would probably expand to 8,000km, and the ground would be covered in half the time...

For an interceptor the best propulsion would be a combined bypass turbofan with a ramjet or scramjet...

Totally. They had the best conditions thinkable to keep their advantage, so decided it was best to squander them and just fill their pockets... and they can't blame Russians for that

But you know they will...

By now it seems to be just a very limited action to restore the life of the airframes. It is thinkable that they get beyond that, once they agree on the requirements for PAK-DP and can understand what role MiG-31 can play in reducing technological risk of the solutions to be implemented.

I would say they are repeating what they did with the Blackjack... the difference is that while they only had 16 odd Blackjacks available so they had to restart production, with the MiG-31 what they were short of was the hot sections of the engines... which are the bits that wear out. Building new hot section bits should allow existing engines to be brought back to service and use meaning all those MiGs in storage can be used if needed... together with upgrades and overhauls to existing models they should be able to spend extra time getting the MiG-41 to where it needs to be... the US is funding hypersonic weapons... so clearly a good focus for the MiG-41 is to deal with such threats and also potentially launch weapons and satellites out of the atmosphere...

The Mig-31s might refocus on an Anti AWACS mission as well as anti cruise missile and anti HALE and MALE roles...

They could be the inner layer... the inner ring defence, with the faster likely longer ranged MiG-41 being an outer layer of defence.

GarryB wrote:An interceptor needs to get to its intercept point as quickly as it can... the difference between Mach 2.84 and Mach 1.8 super cruise might be the difference between shooting down 10 B-1Bs, or having to take on 10 B-1Bs plus the 220 cruise missiles they just launched...

Who is talking about reducing speed of the plane?  

These are charactristics of the D-30F-6 engine:

Maximal thrust (H=0, M=0, t=15°C)                9500 kp (93,16 kN)
Full afterburner thrust (H=0, M=0)                15500 kp (152 kN)
Specific fuel consupmtion on maximal thrust 0,72 kg.kp-1.h-1
Specific fuel consumption with full afterburner 1,9 kg.kp-1.h-1
Maximal turbine inlet temperature                1387 °C
Air flow                                                150 kg.s-1
Pressure ratio on low pressure compressor 3
Pressure ratio on high pressure compressor 7,05
Overall pressure ratio                                21,15
Bypass ratio                                        0,57
Inlet diameter                                        1020 mm
Length                                                7040 mm
Dry mass                                                2416 kg
Maximal operation speed                        M=2,83

This is a huge engine with levels of thrust smaller products already reach (F119 indeed, AL-41F1 is close). It is even larger than the F135, which is not a supercruising engine and still produces ca. 128 kN mil. thrust and ca. 191 kN with AB. I don't think it is too risky to say that lower bypass or two stage VCE with today's technology could reach levels of thrust close to 150 kN in military settings. In fact the izd. 20 was tested on the MiG-25, supposedly 176 kN max thrust, I didn't manage to find dry thrust, but in any case it was an already designed supercruising engine with the right size, if you know what I mean...

Operation in afterburner has advantages at high altitudes because in mil settings the power of the turbine is being extracted at the same level while the thrust itself decreases with increasing altitude so in the end there is little left for propulsion. That creates an additional difficulty to reach AB thrust in mil settings, but even if it was not possible to cruise a 2.8 M but 2.3 or 2.5, it would be already a huge advantage in fuel consumption.

Look at the TSFC in dry vs. wet modes above, there is a 2.6 factor between them which would be translated almost directly into range. So you cannot fly 2.35 M to 700 km but to what, >1000 miles? And therefore allows to attack carriers even before they release long range missiles like AGM-158 JASSM-ER, or to substantially extend the range of Kinzhal attack missions too... it is a massive improvement, one that would put NATO again on their back foot, threatening their assets theatre-wide.

BTW another possible optimization of the MiG-31 could be to unify the K and BM versions, so it is not necessary to divert airframes from air defence to attack roles and vice-versa. Work on airframe + re-engining would make it possible, since the K got its radar removed and fuel increased due to the needs o the new mission, so a more powerful engine with lower fuel consumption is a big deal. They were not exaggerating when they said the modernization potential of the plane was far from exhausted...

For an interceptor the best propulsion would be a combined bypass turbofan with a ramjet or scramjet...

The YF-120 was modified in such way, since it was a VCE this was already implicitly possible in the original design. They said it could reach 4.1 M... which is shockingly similar to the speed announced for PAK-DP (4.2 M) and, to me, it makes clear what solutions the Russians are considering. Since izd. 20 was already done and probably izd. 30 is its continuation, an ABVCE based on it is only a logical following step...

The YF120 was also proposed as the basis for a more exotic engine, the Turbine-Based Combined Cycle (TBCC) engine that was to be used in demonstrator aircraft like the X-43B and future hypersonic aircraft. Specifically, the YF120 was to be the basis for the Revolutionary Turbine Accelerator (RTA-1). The variable cycle technology used in the YF120 would be extended to not only turn the engine into a turbojet but also into a ramjet. In that mode all airflow would bypass the core and be diverted into the afterburner-like "hyperburner" where it would be combusted like a ramjet. This proposed engine was to accelerate from 0 to Mach 4.1 (at 56,000 ft) in eight minutes.[11][12]

https://en.wikipedia.org/wiki/General_Electric_YF120



https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050196667.pdf
https://www.slideshare.net/PraveenPratapSingh2/variable-cycle-engine-ppt-65048391

But you know they will...    

Sure, since Maidan was Putin's fault, the dementia of US politicians must be his fault too!!  

I would say they are repeating what they did with the Blackjack... the difference is that while they only had 16 odd Blackjacks available so they had to restart production, with the MiG-31 what they were short of was the hot sections of the engines... which are the bits that wear out. Building new hot section bits should allow existing engines to be brought back to service and use meaning all those MiGs in storage can be used if needed... together with upgrades and overhauls to existing models they should be able to spend extra time getting the MiG-41 to where it needs to be... the US is funding hypersonic weapons... so clearly a good focus for the MiG-41 is to deal with such threats and also potentially launch weapons and satellites out of the atmosphere...

Exactly. New capabilities are needed no doubt, a very long range / very high speed performance on PAK-DP would benefit from a very big airframe capable of providing high performance weapons with additional launch energy, which is critical for operations against very high speed threats or in near space. That is not necessary for other roles the MiG-31 is covering now. The repair of the D-30F6 was already solved, and as said before, one of the main problems they found and that significantly delayed their capability to overhaul and airframes was de deviations from spec that they find in the planes. This forces them to rework the pieces before installing them, which is a very time consuming and very ineffective effort. With 3D printing they can tackle that problem much better.

https://www.ainonline.com/aviation-news/defense/2019-08-13/russia-relaunches-production-engine-cores-mig-31
https://zen.yandex.ru/media/id/5ddfbc8b9515ee00ac9e370a/3dprototip-dlia-miga-5dfb6c4e11691d00aeaac1e6

They could be the inner layer... the inner ring defence, with the faster likely longer ranged MiG-41 being an outer layer of defence.

That is a good idea, and one that is also reminiscent of the PAK-DA / Tu-160 case, with different performances that actually allow to think about parallel operation in complementary roles...

Who is talking about reducing speed of the plane?

I understand what you are saying... going 5th gen supercruise engine technology on the MiG-31s engines should increase performance, but I am thinking it would be much easier to look at redesigning the engine to operate as a ramjet at higher flight speeds like the engines on the SR-71 does.

It would be easier to engineer and also I think taking it further and making the engine of the MiG-41 into something similar but with a 5th gen super cruising engine with a scramjet mode for higher flight speeds would be a natural progression...

BTW another possible optimization of the MiG-31 could be to unify the K and BM versions, so it is not necessary to divert airframes from air defence to attack roles and vice-versa. Work on airframe + re-engining would make it possible, since the K got its radar removed and fuel increased due to the needs o the new mission, so a more powerful engine with lower fuel consumption is a big deal. They were not exaggerating when they said the modernization potential of the plane was far from exhausted...

Keeping the designs separate makes the performance of the K model better... it is lighter and simpler and likely cheaper, which makes it better for the role of launching Kinzhals... and possibly those Anti satellite missiles...

In that mode all airflow would bypass the core and be diverted into the afterburner-like "hyperburner" where it would be combusted like a ramjet. This proposed engine was to accelerate from 0 to Mach 4.1 (at 56,000 ft) in eight minutes.

That is basically what the jet engines of the SR-71 did... at top speed almost no air went through the turbojet engines... which were idling... most of the air went around the outside of the engine as a ramjet...

GarryB wrote:

Who is talking about reducing speed of the plane?

I understand what you are saying... going 5th gen supercruise engine technology on the MiG-31s engines should increase performance, but I am thinking it would be much easier to look at redesigning the engine to operate as a ramjet at higher flight speeds like the engines on the SR-71 does.

It would be easier to engineer and also I think taking it further and making the engine of the MiG-41 into something similar but with a 5th gen super cruising engine with a scramjet mode for higher flight speeds would be a natural progression...

For the MiG-31 the supercruising engine would keep the speed and reduce the consumption. I don't know what the airframe is ready to take in terms of dynamic pressure and temperatures, going beyond 3 M is pretty extreme. But why not. My point was that izd. 20 was already that very type of engine. I don't think they just destroyed the design documentation and I also doubt they don't realize the use it would have in the MiG-31, since they tested it precisely on the MiG-25. As said, by now the effort in the -31 simply means keeping it usable (BM modernization) and the airframes safe to fly for more years (newly announced project). Should they decide to go further, there are indeed interesting paths ahead...

BTW another possible optimization of the MiG-31 could be to unify the K and BM versions, so it is not necessary to divert airframes from air defence to attack roles and vice-versa. Work on airframe + re-engining would make it possible, since the K got its radar removed and fuel increased due to the needs o the new mission, so a more powerful engine with lower fuel consumption is a big deal. They were not exaggerating when they said the modernization potential of the plane was far from exhausted...

That is basically what the jet engines of the SR-71 did... at top speed almost no air went through the turbojet engines... which were idling... most of the air went around the outside of the engine as a ramjet...

Certainly, only new design and technology would allow to add 1 M to the speed. The J58 was a very exotic engine then, now VCEs are maturing and are going to turn into mainstream.

[/quote]

As said, by now the effort in the -31 simply means keeping it usable (BM modernization) and the airframes safe to fly for more years (newly announced project). Should they decide to go further, there are indeed interesting paths ahead...

My understanding is that it was the engines and the rotational speed capacity of their blades that limited flight speed to mach 2.84.

By running the engine as a ramjet and slowing the engine rpms down at high speed flight that speed limit is removed so then the speed limit is the heat limit and that high temperature aluminium and of course new ceramics and composites and titanium bits become more interesting.

It might be fairly easy to get it up to mach 3.2 or faster without much more effort, which would make it useful in designing the MiG-41 too.

It might be the case that the new engines for the MiG-41 allow the MiG-31 to fly slightly faster than it does with the upgrades but also massively improve range and acceleration etc etc, which means you could get commonality of engines there too eventually.

I would presume the shape of the MiG-41 will mean if flys faster than they could make the MiG-31 fly and likely with an internal payload so drag is not an issue with full weapons loads either for the 41.

Will remain an issue for the 31 of course.

GarryB wrote:My understanding is that it was the engines and the rotational speed capacity of their blades that limited flight speed to mach 2.84.

I thought it was the max TIT being reached. Ram effect + compressor would overheat the air at the entrance of the combustion chamber, the faster you fly, the hotter it gets.

By running the engine as a ramjet and slowing the engine rpms down at high speed flight that speed limit is removed so then the speed limit is the heat limit and that high temperature aluminium and of course new ceramics and composites and titanium bits become more interesting.

Sure, that removes the temperature limitation of the turbomachinery and you use (almost) only the afterburner section. I am not sure this saves fuel in any significant way though

It might be the case that the new engines for the MiG-41 allow the MiG-31 to fly slightly faster than it does with the upgrades but also massively improve range and acceleration etc etc, which means you could get commonality of engines there too eventually.

It could be the case, if they where VCE enabling the -31 to supercruise as argued above. If it is only a hypercombustor, then it would not necessarily help with range. Of course the technological difference would be substantial, it may provide much more thrust and a more efficient design in general. A change to a ramjet engine in general is considered necessary to go above 3 M, if the air vehicle itself is not designed for that, the advantage of using the same engine may not be justified.

It might be fairly easy to get it up to mach 3.2 or faster without much more effort, which would make it useful in designing the MiG-41 too.

+

I would presume the shape of the MiG-41 will mean if flys faster than they could make the MiG-31 fly and likely with an internal payload so drag is not an issue with full weapons loads either for the 41.

Why do you think they designed it for a speed higher than what they knew it would be operated at? That would mean to assume many compromises in other areas. For instance, the wing sweep is not very marked for a plane which is almost 3 M, but it provides more lift so, in the end the thing needs to take off and land too. Dynamic loads at those speeds are huge, temperature becomes a significant problem from 3 M onwards... maybe with new materials they manage to do that, I (personally) just think it was not designed to fly significantly faster than it does.

They should make a radar with 600-700km range and improve even more the r-37 to give it a range of 500km with why not a scramjet.

Irbis of su-35 already has 400km with 20kW against fighter size target. So they can make a radar with 700km range and 40kW against bombers. Mig-31 has more powerfull engines to power it.

The talk about what powerplant/engine should be powering MiG-31's, completely neglects FPI's successful efforts in creating test benchmarks in spin-detonating ramjets, and completely electric engines.

magnumcromagnon wrote:The talk about what powerplant/engine should be powering MiG-31's, completely neglects FPI's successful efforts in creating test benchmarks in spin-detonating ramjets, and completely electric engines.

I just think PDE is way too far in the future for an update to MiG-31 that should be done within next 10 years and not be massively expensive, as to electric engines... what would they offer here? We talk about levels of energy density that electric propulsion is nowhere close to reaching, and BTW how do you use them to create a highly supersonic gas flow that propels a Mach 3 plane?

I thought it was the max TIT being reached. Ram effect + compressor would overheat the air at the entrance of the combustion chamber, the faster you fly, the hotter it gets.

Alcohol injection cools the intake...

Sure, that removes the temperature limitation of the turbomachinery and you use (almost) only the afterburner section. I am not sure this saves fuel in any significant way though

It wouldn't need extra after burner, it just needs airflow bypassing the jet engine... so essentially you fly faster without dramatically increasing the fuel burn rate...

It could be the case, if they where VCE enabling the -31 to supercruise as argued above.

I have a problem with supercruise.

The value is flying at supersonic speed in dry thrust.

It really does not matter whether you have to use AB for a few seconds or even minutes to achieve supersonic flight, if you can continue in dry thrust the result is essentially the same, so I discount the US requirement to achieve supersonic speed without using AB because it is simply childish.

Being able to fly a supersonic speeds in dry thrust even if it can't super cruise is good enough in my opinion.

A change to a ramjet engine in general is considered necessary to go above 3 M, if the air vehicle itself is not designed for that, the advantage of using the same engine may not be justified.

The MiG-25 and MiG-31 were both intended to fly at Mach three as their intended target was originally the Valkyrie Mach 3 bomber and then the SR-71 mach 3.2 recon aircraft. In both cases the top speed was limited by their engine and in both cases it was engine blades overheating and being damaged and distorted... you could exceed Mach 2.84 but the engines would be trashed...

As such engines designed to operate at higher flight speeds should allow it to fly rather faster.

I am not suggesting more than Mach 3.5 or so...

Why do you think they designed it for a speed higher than what they knew it would be operated at?

As I just said above, these interceptors were intended to intercept mach 3 plus targets so any speed close to that would be of value... simply the faster the better... even against slower targets because you can intercept them further out.

They should make a radar with 600-700km range and improve even more the r-37 to give it a range of 500km with why not a scramjet.

Indeed right now they are working on a new replacement for the R-37M, the Item 810, which is described as having between three and 9 times more range than the R-37M depending on the launch profile... AFAIK it is a rocket powered missile.

GarryB wrote:Alcohol injection cools the intake...

I know about that trick in the MiG-25, does it apply to the MiG-31 too?

It wouldn't need extra after burner, it just needs airflow bypassing the jet engine... so essentially you fly faster without dramatically increasing the fuel burn rate...

You use the already existing afterburner but the air comes bypassing the core... I would need to check about what the fuel consumption would be in that regime, because maybe you are right. The compression is done by the speed itself so the combustion should be more efficient than conventional afterburner...

It really does not matter whether you have to use AB for a few seconds or even minutes to achieve supersonic flight, if you can continue in dry thrust the result is essentially the same, so I discount the US requirement to achieve supersonic speed without using AB because it is simply childish.

I would agree, in fact it makes sense to engage AB to go through the transonic region as fast as possible, no point in staying for a long time blocked in a region of specially high drag...

Being able to fly a supersonic speeds in dry thrust even if it can't super cruise is good enough in my opinion.

Where I agree with the US criteria (the original one) is that supercruising should not be >1 M but >1.5 M. There are and were many planes capable of flying faster than Mach 1 on mil power. 1.5 M sets  specially designed platforms apart. It is not the same to fly 1.1 M than 1.8 M... in the case of a very low drag platform like the MiG-31, maybe >2 M would be possible. And the flight altitude for platforms with such high wing load depends on flying very fast. Based on the diagram I already attached few days ago, MiG-25 with 28 t weight can fly at 15,000 m @ 1.5 M, 21,000 m @ 2.5 M.

I am not suggesting more than Mach 3.5 or so...

It is not unthinkable, but I don't know how much margin there may be.

Indeed right now they are working on a new replacement for the R-37M, the Item 810, which is described as having between three and 9 times more range than the R-37M depending on the launch profile... AFAIK it is a rocket powered missile.

Special for internal carriage, with 1.5 times more range from what I read. 360 sec. operation (ca. 500 km @ 5 M), 40 km altitude.

The DCS agreement, announced by Boeing on 28 July, lays the foundation for a wider USD4.5 billion modernisation programme for the Japan Air Self-Defense Force (JASDF) F-15J fleet into the Japanese Super Interceptor (JSI) configuration that was disclosed by the US government in October 2019.
https://www.janes.com/defence-news/news-detail/mhi-boeing-sign-dcs-agreement-to-upgrade-japanese-f-15j-fleet

https://www.ainonline.com/aviation-news/defense/2019-10-31/green-light-f-15-japanese-super-interceptor-upgrades

https://www.thedrive.com/the-war-zone/30726/japan-cleared-to-transform-98-of-its-f-15j-eagles-into-japanese-super-interceptors

https://nationalinterest.org/blog/buzz/%E2%80%9Cjapanese-super-interceptor%E2%80%9D-japan-could-get-%E2%80%98super%E2%80%99-f-15-92331

It would be interesting to compare it with the MiG-31BMs.

I know about that trick in the MiG-25, does it apply to the MiG-31 too?

I have always assumed so...

The compression is done by the speed itself so the combustion should be more efficient than conventional afterburner...

Just like the bypass air in a turbofan.

Turbofans in aircraft often offer more power than those in a turbojet because the bypass air is much more oxygen rich so more fuel can be added and burned efficiently and the higher through volume of air is also good for thrust.

It would be interesting to compare it with the MiG-31BMs.

It would require a complete redesign in shape and materials if it was to operate at the same flight speeds... I doubt that huge canopy could take more than 30 seconds at mach 2.5.

It would require a complete redesign in shape and materials if it was to operate at the same flight speeds...

true; what about radars, ECM, & weapons? They may also team up with F-18E/F/Gs to capitalize on their respective strengths & minimize weaknesses.
IMO Australia could also use upgraded F-15s which r better than F-18E/Fs she won't be using as deck fighters.
The MiG-31BMs r still going to be superior but the USAF, not to mention Canada, don't need such monsters- they have F-15/18/22s for interceptions.

This piece is about the PAK-DP but it deals also with the same topics we were discussing about MiG-31

http://www.aviationunion.ru/news_second.php?new=18338

Honored military pilot of Russia Vladimir Popov believes that the main task of the promising aircraft, as well as its predecessor, will be to patrol and defend the Northern territories of Russia.

"The designers have the possibility of deep modernization of the MiG-31 fighter at the expense of new engines," says Popov. — The interceptor will be able to fly at supersonic speed for a long time without an afterburner. It will barrage in economy mode at a high altitude in the waiting area. Such vehicles will help very quickly repel the attack of any means of air attack — cruise, ballistic or tactical missiles, drones and bombers."

The situation in the far north is unique in that there are no mountain ranges or hills to skirt between to sneak up, so targets will often be detected quite a distance out, so being able to efficiently cruise to an area to intercept crossing targets on their way to say St Petersburg or Moscow or other places would be very valuable... a weight reduction programme replacing heavy older parts with newer stronger lighter more heat resistant parts should improve performance quite dramatically without extensive costs... with the hot parts of the engines back in production they can bring most of the ones in storage out for upgrades and modifications to improve performance... with the MiG-31M they were able to design a new belly arrangement for 6 (of the currently used) missiles to be carried instead of four... perhaps a redesign could allow shallow weapon bays to be added to greatly increase capacity without a dramatic increase in drag.

The R-33s and R-37s already use the arm launchers to push them clear of the aircraft on launch to ensure clean separation at any speed, and experience with bomb bay operations at high supersonic speed will be needed for the MiG-41 anyway...

In the video, filmed from the cockpit, you can see footage of takeoff, climb, and flight in the stratosphere.

Why was there no Mig31BM in Syria for testing?

Mig-31BM2 Super Irbis-E wrote:Why was there no Mig31BM in Syria for testing?

What would they do there?

The filthy wahabbi goat-rapers don't have any aircraft that require high speed/altitude interception, and MiG-31s aren't exactly configured as bomb trucks for moving mud...

With the 2000km kinzhal they are in some way already in Syria, even if they are operated from Russia. Just like the Caspian flotilla with its Kalibr.

They could at least keep Israeli planes from bombing Syria &/ shoot down their CMs/PGMs.

- Escort operation on the airlift via Iran
- Practice operations over the Mediterranean
- test the aircraft in a hostile environment

Russia tests pretty much everything in Syria. Why not a Mig-31BM?

Not a 100% on this but were not a couple Mig-31's there right after the Su-24 was shot down? Don't believe they hung around long but thought there was a recorded visit.

The Syrians wanted to buy MiG-31s:
https://militarywatchmagazine.com/article/mig-31-foxhounds-over-damascus-how-syria-s-game-changing-arms-purchase-would-have-shaken-turkey-and-israel

Perhaps the reasons they weren't deployed r: it's not urgent, with adequate AD assets there now; persistent danger from missile attacks on bases; the need to keep them in Russia for exercises & intercepts of NATO aircraft.

They could at least keep Israeli planes from bombing Syria &/ shoot down their CMs/PGMs.

Russia is there to fight terrorists... getting into a fight with Israel would not be a good idea for Russia.

The MiG-31BM gets operational use every day and is one of the few Russian platforms that is doing what it is normally doing and will do... short of actually launching missiles of course.

Practise in a dust bowl against ISIS is not valuable experience for them.

Would like to say regarding the discussion with LMFS above about fitting new 5th gen engines to the MiG-31 to give it super cruising performance... 5th gen engines will be expensive and wont effect top speed... in fact in this case it might allow the plane to fly at mach 2 in super cruise but it probably wont be able to fly continuously at Mach 2.4, and for 20 minutes at mach 2.6 or 5 minutes at mach 2.84 like the previous models could. (I suspect with upgrades and improvements it can fly faster than this... these were cold war speed limits AFAIK.

On this forum there was a mention of a new western civilian aircraft that was supposed to super cruise using a ramjet... the design didn't use a brand new high tech 5th gen super engine.... it used a crusty but reliable old engine that wasn't particularly fuel efficient, but it was powerful.

The point was that the jet engine itself is used for low speed flight... take off and landing, but once airborne and at altitude it would change over to ramjet power and essentially run down the old engine to either idle or perhaps even totally shut down with no air flow going through it at all.

Once running as a ramjet the speeds the aircraft will be flying at will be much more fuel efficient than any jet engine because these supersonic speeds are at the edge of the performance of the engines. Ramjets are efficient up to about mach 5 or 6, so flying at mach 2 is actually fuel efficient and they would burn nothing like the fuel thrown at an after burner on a turbojet or turbofan to fly that fast.

It makes no sense to have a super advanced super modern jet engine if it is going to spend most of the flight in idle or even turned off with the thrust coming from a bypass ramjet.

It is more important for the engine used to be reliable and solid and powerful enough... and the current engine is that already.

It could still supercruise, but supercruise on a bypass ramjet arrangement.

The SR-71 had enormous range at mach 3.2 using ramjet propulsion most of the flight... at those sort of speeds it is the most efficient way to fly.