The Rockwell/MBB X-31 Alternate History

[YouCantbeCirrus]

Hello everyone, I have been researching supermaneuverable aircraft recently and the Rockwell-Messerschmitt-Bölkow-Blohm X-31 (MBB X-31 from here) has always fascinated me as it was demonstrated to be the most maneuverable modern fighter aircraft for years and still might be the most maneuverable even to this day.

The aircraft resembles the Eurofighter Typhoon so much (which makes sense as MBB is part of the Eurofighter conglomerate to this day) that I had imagined an alternate universe where the Typhoon had run into technical problems and due to cost and better performance the X-31 was the plane put into production as the modern shared Air Superiority fighter of Europe.

So here’s a short story of what I think might’ve happened in a world where the west would have an aircraft fully equal or better that the SU-27 in supermaneuvrability.

Tell me what you think and if this was a likely chain of events in this alternate universe!



An Alternate Universe: The Derecho is Chosen

It is late 1988 and the program known as the British Aerospace EAP is in turmoil. The West German government is in a tight spot financially as is thinking of withdrawing from the collaborative project with the British to develop the next generation of air superiority fighter. With cost being put more on the burden of the government of Germany many of the politicians are wanting to withdraw from the project entirely.

Due to the pressure from the German procurement office the BWB, alternate ways of funding the project where sought out. The idea of expanding the partners in the program was the main way the current countries believed would help with funding. As such, several other major Western countries where approached for a stake in the now establish Future European Fighter Program (FEFP) conglomerate. With a major need for new fighters to replace their SAAB Drakens and the interim Viggens in service, Sweden agreed to a 20% stake in funding of the project for an agreed 50 aircraft with a possibility of more. Due to them now having a larger stake in the conglomeration, they pushed for the adoption of the aircraft also in development by MBB, which would become the Rockwell-MBB X-31, due to its use of the well-known GE F404 then in licensed production there by Volvo Aero.

The X-31 was being jointly developed by Rockwell International and MBB and the first prototype was to fly the next year in 1989. Even early aerodynamic testing of smaller models such as the earlier Rockwell SNAKE had shown the maneuverability of the aircraft and Sweden where anxious to have another aircraft that was supermaneuverable to replace the Draken.

Due to this and then push from other governments the EAP fighter was abandoned and the X-31, now known as the FF-89 (Future Fighter of 1989) was pushed into the main development stage. With its first flight on July 8th, 1989 the proceeding test flights showed the aircraft was not only supermaneuverable but could possibly be the most maneuverable aircraft in the west.

Throughout 1990 into 1991, several iterations of the FF-89 allowed the aircraft to mature, and the off-the-shelf parts of the X-31's original design allowed development to proceed very quickly. The main snag was the control software for the plane allowing it to fly without its vertical tail in the event of a hit by enemy fire, and it was shown that with its advanced thrust vectoring the FF-89 could indeed fly without the vertical tail altogether; although it was kept for ease of flight training.

On November 14th, 1991 the project was accepted in production by the newly reunified Germany, the UK, Sweden, Spain and Italy as the Unifighter Derecho.

Production began the next year, with the first delivery going to the German fighter wing Taktisches Luftwaffengeschwader 71 "Richthofen" on September 27th.

 

[sferrin]

An X-31 with an F414 EPE would be a sight to behold.

 

[YouCantbeCirrus]

An X-31 with an F414 EPE would be a sight to behold.

Indeed it would; imagine the crazy acrobatics the airframe could do with an even more powerful engine.

 

[Archibald]

I can't see Sweden throwing the Gripen under a bus: it flew in 1988-89 (and crashed soon thereafter)

But the X-31 as basis for a cut-down Typhoon, via Germany - now that would be something.
In fact the X-31 WAS, very much, Germany dream of a single-engine Typhoon: the one they tried to impose their partners after reunification and 1991. Not sure Great Britain agree, because Tornado ADV replacement and GIUK gap - although Cold War is over, after all.
But Jaguars need a successor, and it would be perfect for that. Also Harriers if STOL enough, with vectored thrust... and who knows, perhaps a naval variant later, for the Q.E carriers.

Italy and Spain may agree, however: F-104, Mirage III, F1, were single engine types.

Mind you, it would sold far better than both Typhoon and Rafale OTL: single engine types are more affordable. In passing, that may encourage Dassault not screwing the 2000-5mk.2 after the last Greek airframe in 2007.

In fact that X-31 (F-31 ??!!) could achieve "the hold up of the Century" and sneak right between "late F-16s" and "early F-35 onslaught " (still 15 years in the future: the 2010's)

And you say "F414" and I say "EJ200 salvaged from the Typhoon". They are the same size and weight, EJ200 may have better T/W.

Such aircraft could play havoc with early F-35 history, pre-2001: from the JAST / CALF days of 1994 to Lockheed victory.

 

[uk 75]

A German/US fighter might have been needed if the Cold War had continued after the coup against Gorbachev.
Fears that the Luftwaffe F4 and the NATO F16 could not match the Mig 29 led to a rapid decision to order the F32, a Sidewinder/Amraam equipped version of the XF31.
Israel was the first foreign customer, needing a fighter to challenge Syrian Mig 29s.
The F32 soon replaced F16s in NATO and Israeli squadrons, freeing them up for the strike role. Japan and South Korea joined the list of F32 customers.
With the EAF Eurofighter programme dead, Italy chose the F32, Spain ordered more F18s. The RAF still wanted a twin engine aircraft. The Rafale filled the gap and British Aerospace found itself told to work with Dassault. The name "Squall" was initially given by BAe but the RAF chose "Tempest".

 

[sferrin]

A German/US fighter might have been needed if the Cold War had continued after the coup against Gorbachev.
Fears that the Luftwaffe F4 and the NATO F16 could not match the Mig 29 led to a rapid decision to order the F32, a Sidewinder/Amraam equipped version of the XF31.
Israel was the first foreign customer, needing a fighter to challenge Syrian Mig 29s.
The F32 soon replaced F16s in NATO and Israeli squadrons, freeing them up for the strike role. Japan and South Korea joined the list of F32 customers.
With the EAF Eurofighter programme dead, Italy chose the F32, Spain ordered more F18s. The RAF still wanted a twin engine aircraft. The Rafale filled the gap and British Aerospace found itself told to work with Dassault. The name "Squall" was initially given by BAe but the RAF chose "Tempest".

Based on the strict adherence to the previous designation system I'd fully expect it to be called the "F-31".

 

[YouCantbeCirrus]

I can't see Sweden throwing the Gripen under a bus: it flew in 1988-89 (and crashed soon thereafter)

But the X-31 as basis for a cut-down Typhoon, via Germany - now that would be something.
In fact the X-31 WAS, very much, Germany dream of a single-engine Typhoon: the one they tried to impose their partners after reunification and 1991. Not sure Great Britain agree, because Tornado ADV replacement and GIUK gap - although Cold War is over, after all.
But Jaguars need a successor, and it would be perfect for that. Also Harriers if STOL enough, with vectored thrust... and who knows, perhaps a naval variant later, for the Q.E carriers.

Italy and Spain may agree, however: F-104, Mirage III, F1, were single engine types.

Mind you, it would sold far better than both Typhoon and Rafale OTL: single engine types are more affordable. In passing, that may encourage Dassault not screwing the 2000-5mk.2 after the last Greek airframe in 2007.

In fact that X-31 (F-31 ??!!) could achieve "the hold up of the Century" and sneak right between "late F-16s" and "early F-35 onslaught " (still 15 years in the future: the 2010's)

And you say "F414" and I say "EJ200 salvaged from the Typhoon". They are the same size and weight, EJ200 may have better T/W.

Such aircraft could play havoc with early F-35 history, pre-2001: from the JAST / CALF days of 1994 to Lockheed victory.

You're correct about the Gripen, it was already in development at that same time frame but mostly to replace the Draken as far as my reading says. I could foresee them sharing the Swedish Air Force's stable however, the Gripen as possibly more like the F-15 and the F-31 as you call it the F-16 in US service. That is to say one plays the all-weather strike aircraft and the other more a pure light air superiority fighter. I did omit the mention of the Gripen from the writeup but my omission was not saying it would not happen.

I mostly included Sweden as the leverage to this idea because they had already been wanting to replace most of their aging aircraft at the time and through the sharing of the F404 engine with the X-31 it would be an easy transition to a production plane logistically speaking.

I could see the possible aircraft the X-31 would become being very much like the F-16 in every regard: a cheaper(er) air superiority and (through the F414 upgrade) possible multi-role plane. I suspect in UK service a Naval variant would be very attractive and fulfil the same area of small Naval fighter that the Harrier fills in their fleet.

I also like your idea of possibly taking the EJ200 off the ERP project as "salvaging" it for the F-31! I could see the UK being the sole user of it however, seeing as how they would be rather displeased about the ending of the ERP program.

 

[red admiral]

I think the main issue is that what actually is a production version of the X-31? Basically it's tiny and cobbled together from bits of existing aeroplanes. Its much worse than the F-16 in every regard apart from the ability to post stall manoeuvre.... Which has what combat value? Manouvre in the round is much more than post stall nose pointing - and the HMS and HOBS missile was a much cheaper way of getting the same effect

I think a push for cheaper Eurofighter leads to Gripen/P.106 rather than X-31. There was a massive push in Germany for BVR at this time

 

[YouCantbeCirrus]

I think the main issue is that what actually is a production version of the X-31? Basically it's tiny and cobbled together from bits of existing aeroplanes. Its much worse than the F-16 in every regard apart from the ability to post stall manoeuvre.... Which has what combat value? Manouvre in the round is much more than post stall nose pointing - and the HMS and HOBS missile was a much cheaper way of getting the same effect

I think a push for cheaper Eurofighter leads to Gripen/P.106 rather than X-31. There was a massive push in Germany for BVR at this time

One of the main reasons I thought this scenario might play out is precisely because it was made of various parts of other aircraft. That lowered its R&D time (in actual development and in this scenario) which also lowered its cost.
The biggest thing this aircraft would have over the F-16 would be cost and parts availability because of its engine and the borrowed parts. The GE 404/414 is used on many more aircraft than the F110 which has really only been used on three airframes (F-14,-15 and -16) which again lowers its cost.
Also yes the Viper outperforms the X-31 if you compare the modern F-16C/D Block 50/52 but if you look at the stats of the X-31 vs say an early F-16A they are almost identical with the X-31 being smaller in every dimension with a bit better Thrust/weight ratio as well.
So I'd say that if the X-31 had close to 50 years of development like the F-16 has it'd be an excellent aircraft. Because remember even the Viper was supposed to "just" be a light air superiority fighter.

 

[zen]

Some development of the X-31 isn't going to hold much attraction to the UK. Especially if it's a German exit from ACA/EFA.

EAP was pushed through by the UK.

But critically in choosing P.110 development with European partners that became Eurofighter, UK abandoned P.1216.

Arguably if the Germans walk and the rest of effort collapses. The UK will either continue development or shift over to P.1216.

 

[Excalibur66]

After being flown in the Paris Air Show in June 1995, the X-31 Enhanced Fighter Maneuverability Technology Demonstrator Aircraft is off-loaded from a C-5 transport after the ferry flight back to Edwards. 1995 NASA

 

[DWG]

The problem with this scenario is the X-31 is the complete tactical antithesis of the Eurofighter, and to a degree the Gripen. X-31 was designed to investigate post-stall manouvering in the WVR arena. Eurofighter was designed to explicitly avoid entering the WVR arena (because the Operational Research guys showed WVR fighting was a recipe for an Archer up your jetpipe, however good your aircraft was). Gripen was also intended to exploit the BVR fight, in its case by utilising datalink. To bring X-31 up to meet the Eurofighter requirements you have to junk the airframe and start over, it's just not big enough to carry ECR-90, Pirate, the defensive ECM system, 6x AIM-120, 2x ASRAAM/IRIS and a couple of big drop-tanks.

WRT engines, a big attraction for the Eurofighter partners was RB199 and EJ200 are fit compatible, they don't just fit in the same space, they have exactly the same mounting points, because Eurofighter was intended to be RB199 powered for the first 50 aircraft (IIRC, and ultimately it ended up being one because EJ200 was ready in time), and three of the users were already RB.199 operators (and Spain, the F404 operator, was apparently perfectly happy to go RB/EJ). So you have to provide a justification for overriding that driver. And by the time X-31 was tumbling around the skies over Paris, Enosa (IIRC) was showing a growth EJ230 with thrust-vectoring.

 

[uk 75]

As I suggested above, the Mig 29 overmatching F4s and F16s in a Cold War continuing into the 90s might have made a rapid introduction of a hastily modified F31 attractive.
Without that the Eurofighter is pretty much set.

 

[lordroel]

Hello everyone, I have been researching supermaneuverable aircraft recently and the Rockwell-Messerschmitt-Bölkow-Blohm X-31 (MBB X-31 from here) has always fascinated me as it was demonstrated to be the most maneuverable modern fighter aircraft for years and still might be the most maneuverable even to this day.

So if the Germans go that route, how much change is that the British will go the route of the British Aerospace EAP.

 

[red admiral]

If we're more keeping to the original X-31 then we're looking at a day-only battlefield fighter with gun+SRAAMs. Which is a definite concept but not one that actively been pursued recently. If we're looking at that role I think I prefer SABA like P.123x for even higher manouevrability and greater persistence. The low speed tight radius turns and high power/weight make an interesting comparison with X-31 - basically going post stall just makes you an excellent target.

 

[mr5oa]

Another craft I made the display model master pattern for before the first flight, and just today found this>

View: https://youtu.be/SRA_tKCWc0E

 

[DWG]

If we're more keeping to the original X-31 then we're looking at a day-only battlefield fighter with gun+SRAAMs. Which is a definite concept but not one that actively been pursued recently. If we're looking at that role I think I prefer SABA like P.123x for even higher manouevrability and greater persistence. The low speed tight radius turns and high power/weight make an interesting comparison with X-31 - basically going post stall just makes you an excellent target.

I forget which one of the SABA concepts it was had turreted AAMs making turn-radius irrelevant, no matter how tight you turned, it still had you in its engagement envelope.

 

[DWG]

As I suggested above, the Mig 29 overmatching F4s and F16s in a Cold War continuing into the 90s might have made a rapid introduction of a hastily modified F31 attractive.

At that point the F-16A/Bs are becoming F-16A/B MLUs, those not outright replace by F-16C/Ds, while the Phantoms are being reworked as ICE/Phantom 2000/Kurnass, which leaves the MiG-29 hoping it can survive the AIM-120s on the way in to get to the point at which its AA-11 Archers and HMS offer it an advantage. But equally the Western fighters are set to get AIM-9X/ASRAAM/IRIS, so even that advantage is severely reduced.

I think the only AF planning to keep Phantoms in un-upgraded form into the 2000s was the RAF, and they already had Skyflash vice Sparrow, and were due to be replaced by Eurofighter. In the event the four squadrons all decommissioned before re-equipping happened.

 

[DWG]

The other thing to consider with this alternate history is workshare. The original Eurofighter workshare split was BAe 37.42%, DASA 29.03%, Aeritalia 19.52%, and CASA 14.03%. While EJ200 workshare was RR 33%, MBB 33%, Fiat 21%, Sener 13%. Any change to the project has to preserve this split, because industrial benefits are a substantial part of why everyone signed up. We had to make concessions on workshare to give Germany a larger split of workshare than justified by planned purchases just to keep them on board.

Equally a major part of Germany's discontent was Volker Ruehe's ambition to become next in line for the Chancellorship. The single-engined Eurofighter was basically a one-man-band being driven by Ruehe. Eurofighter was unpopular in Germany, but completely altering the design was basically his baby. A complete replacement has to meet the same challenge the single-engined Eurofighter did(n't). It has to generate a significantly lowered project cost (so Volker Ruehe could ride that all the way to becoming Bundeskanzler), and it had to do it without compromising requirements too much, while preserving the workshare split. That's very difficult to do with a half-American design with no radar, ECM or weapons system.

Also intimately bound up in the workshare split were various promised roles. MBB was Flight Controls Lead, but only because it was politically important to MBB/Germany. Based on capability Marconi should have been FCS lead (and in the event did have to take over joint leadership), and BAe should have been airframe lead. If the UK was going to give up FCS lead to keep the Germans happy, then BAe had to be airframe lead, that couldn't be compromised. This is a major problem for an X-31 based substitution.

 

[sferrin]

I think the main issue is that what actually is a production version of the X-31? Basically it's tiny and cobbled together from bits of existing aeroplanes. Its much worse than the F-16 in every regard apart from the ability to post stall manoeuvre.... Which has what combat value? Manouvre in the round is much more than post stall nose pointing - and the HMS and HOBS missile was a much cheaper way of getting the same effect

As I recall, it's kill ratio against the Hornet was 32 to zero.

 

[DWG]

As I recall, it's kill ratio against the Hornet was 32 to zero.

But those were deliberate WVR combats - which is perfectly reasonable because that's what they were researching. Against an F/A-18 deliberately exploiting its BVR capability I suspect the ratio would be reversed.

 

[sferrin]

As I recall, it's kill ratio against the Hornet was 32 to zero.

But those were deliberate WVR combats - which is perfectly reasonable because that's what they were researching. Against an F/A-18 deliberately exploiting its BVR capability I suspect the ratio would be reversed.

Why wouldn't a hypothetical F-31 have BVR? Even the F-20, with it's APG-67 was going to have it.

 

[DWG]

As I recall, it's kill ratio against the Hornet was 32 to zero.

But those were deliberate WVR combats - which is perfectly reasonable because that's what they were researching. Against an F/A-18 deliberately exploiting its BVR capability I suspect the ratio would be reversed.

Why wouldn't a hypothetical F-31 have BVR? Even the F-20, with it's APG-67 was going to have it.

Oh, almost certainly. But by this point you've junked the X-31 and started over, in which case you're facing almost full development costs for a new fighter, and the rationale for using it as a cheap Eurofighter replacement disappears.

 

[sferrin]

As I recall, it's kill ratio against the Hornet was 32 to zero.

But those were deliberate WVR combats - which is perfectly reasonable because that's what they were researching. Against an F/A-18 deliberately exploiting its BVR capability I suspect the ratio would be reversed.

Why wouldn't a hypothetical F-31 have BVR? Even the F-20, with it's APG-67 was going to have it.

Oh, almost certainly. But by this point you've junked the X-31 and started over, in which case you're facing almost full development costs for a new fighter, and the rationale for using it as a cheap Eurofighter replacement disappears.

How do you figure? The F-20 was meant to be cheap. So is the Taiwanese F-CK-1 and it's also got BVR.

 

[BLACK_MAMBA]

I don't see a lot of the arguments in this group for X-31. X - eXperimental. It wasn't designed to replicate a prototype but was cobbled together out of various bits to keep the cost down. Any further development would at most use the same basic concept and be a full clean sheet design.

The X-31 didn't have any of the avionics required by a modern fighter (and why should it) but just thinking we'll take the same bits, cobble them together and throw a radar and some ECM in there and expect the same outcome is highly flawed.

At best an alternative history using the X-31 is a concept continuation of a single engine TVC aircraft. The rest is a start from scratch if you want to build a workable fighter.

 

[red admiral]

As I recall, it's kill ratio against the Hornet was 32 to zero.

Not quite when you look across all the trials. X-31 did better in neutral/offensive starts below ~200kts when it could immediately use the post stall regime. In all other cases it had a negative exchange ratio against F-18.

Hence you add the post stall / TVC on top of your other aircraft characteristics rather than instead of.

 

[Hood]

A fighter X-31 was kicked around at the time, but the late 80s/early 90s were the heyday of post stall/TVC. This seemed to be the future.
If you look at all the early ATF concept art they proved a very poor indication of what the ideal fighter for the year 2000 would actually be. Likewise the post stall/TVC generation looked like being the hottest thing to deal with the MiG-29-type fighters during the 2000s but instead the F-22 came along and everyone wanted supercruise stealth instead and have ever since. There was no chance of JSF being a super X-31-equese fighter, instead it was a mini-me F-22.
For everything else, everyone just kept tarting up the 70s and 80s 4th generation fighters and they still remain in production today and thrust vectoring has never more than a niche capability for a handful of types (usually Russian). The Typhoon by its timing straddled the WVR/BVR camps.
Maybe the 7th Gen fighter will be something mould-breaking but for now the stealth aspects dominates all fighter airframe design.

 

[kcran567]

Would an upgraded Mig-29 with thrust vectoring (OVT) compete fairly well against the x-31 in that alternate history timeline?

 

[publiusr]

Sometimes I wish stealth had never been invented-or you could have birds up there without ugly sawtooth tails. And microchips in everything! Ugh...

 

[F-2]

As I recall, it's kill ratio against the Hornet was 32 to zero.

Not quite when you look across all the trials. X-31 did better in neutral/offensive starts below ~200kts when it could immediately use the post stall regime. In all other cases it had a negative exchange ratio against F-18.

Hence you add the post stall / TVC on top of your other aircraft characteristics rather than instead of.

Not only that I think it was a pre F404-epe hornet, I also recall it not holding up so well against vipers and eagles. However the X-31 was set to be the test bed for the Ej200 with its TVC nozzle. This ended up not happening but an Ej200 powered X-31 is plausible.

 

[helmutkohl]

the X-31 looks pretty small.. does it have enough fuel capacity for a decent range and payload? assuming it makes it to production

 

[apparition13]

Source: https://tvd.im/aviation/1707-rockwell-mbb-x-31-efm.html

Length: 43.34 ft (13.21 m)
Width/Span: 23.79 ft (7.25 m)
Height: 14.60 ft (4.45 m)
Empty Weight: 11,409 lb (5,175 kg)
MTOW: 15,939 lb (7,230 kg)

It's a bit larger and heavier than an A-4 skyhawk, with around the same fuel load if most of the extra MTOW is fuel. I would guess range would be about the same as that of Singapore's Super-Skyhawk, which also has an F404 engine. Although I don't know whether there is any range difference.

A consideration on the suitability of the X-31 though, it tops out at around M1.3. I suspect it would be easier and faster to add the X-31's TVC paddles to a Gripen than turn the X-31 into a combat aircraft.

 

[F-2]

Source: https://tvd.im/aviation/1707-rockwell-mbb-x-31-efm.html

Length: 43.34 ft (13.21 m)
Width/Span: 23.79 ft (7.25 m)
Height: 14.60 ft (4.45 m)
Empty Weight: 11,409 lb (5,175 kg)
MTOW: 15,939 lb (7,230 kg)

It's a bit larger and heavier than an A-4 skyhawk, with around the same fuel load if most of the extra MTOW is fuel. I would guess range would be about the same as that of Singapore's Super-Skyhawk, which also has an F404 engine. Although I don't know whether there is any range difference.

A consideration on the suitability of the X-31 though, it tops out at around M1.3. I suspect it would be easier and faster to add the X-31's TVC paddles to a Gripen than turn the X-31 into a combat aircraft.

I don’t think the combat version would have paddles, they lose thrust. Their cheap and great for a research aircraft but not for a combat plane.

Would an F404 powered X-31 offer any benefit over a F404 powered A-4 besides post stall?

 

[apparition13]

It's transonic and has a greater than unity thrust to weight ratio, but the ST Skyhawk has a non-afterburning engine. An A-4 with an afterburning F404 - I don't know, though I think the canards would make a difference.

As for the paddles, if you're developing an F404 with TVC nozzles, again it would be easier to install it in a Gripen than build an operational X-31 around the engine. It's really the thrust vectoring that matters, not the airframe so much. The F-16 VISTA and F-18 HARV demonstrated similar capabilities with TVC. Build TV versions of any modern engines and all the 4 and 4+ gen aircraft could perform like an X-31.

 

[F-2]

Mach 0.8 and 15,000 ft
From “

The evaluation of several agility metrics for fighter aircraft usingoptimal trajectory analysis”​

 

[Fighterreaper97]

Has the aircraft design been started on yet?

 

[Maro.Kyo]

Another craft I made the display model master pattern for before the first flight, and just today found this>

View: https://youtu.be/SRA_tKCWc0E

One thing to note about the title of that video; X-31 is not called the "quasi-tailless" thrust vector jet. "Quasi-Tailless" was the name of the flight regime it flew in which it was manipulated to fly in a pseudo-tailless situation, the control surfaces acting to destabilize the aircraft while the TVC try to counter act and stabilize the aircraft.