BAe Systems Nimrod MRA.4 (Nimrod 2000)

[Grey Havoc]

It was intended to be capable of carrying out either role, as well as other ones such as mine laying and maritime reconnaissance.

(h/t RyanCrierie)

 

[FighterJock]

One aspect not often talked about, in regards to the MRA.4, was its attack capability. The MRA.4 was fitted with pylons capable of carrying Storm Shadow cruise missiles, and JDAMs, turning it into a bomber, of sorts.

‘Almost a bomber’ – The Nimrod MRA4

Many people aren't aware that the scrapped Nimrod MRA4 was wired up to carry a range of ordnance including Storm Shadow cruise missiles and satellite guided bombs.

ukdefencejournal.org.uk

https://www.researchgate.net/publication/294825147_UK_chooses_BAE_Systems_to_provide_Nimrod_replacement

That is one of the reasons why I miss the Nimrod MRA.4 Wyvern, I liked the fact that the RAF were going to install the Storm Shadow and the JDAM, that is why I still miss the Nimrod after all those years after it was scrapped. I wonder is the P-8 ever going to be as capable as the Nimrod MRA.4 was going to be?

The P-8 is getting LRASM capability for c2027. The contract award also mentioned that 500lb to 2000lb JDAM, MALD, SDBII and Mines could be added as well. The BRU-55 rack is being integrated that will allow 2 x 1,000lb JDAM per pylon, that could also be used for JSOW. It wouldn't be a huge step at all to go from LRASM (which has land attack capability) to JASSM or JASSM-ER. There hasn't been a mention of Sidewinder though, which was originally on the list of weapons to be added to P-8.

Interestingly....Nimrod MRA.4 was definitely going to get Sidewinder, Paveway's, Harpoon, Stingray and Maverick. In reality I suspect if it had not been cancelled it would have entered service with ASRAAM, Paveway IV, Stingray and the remainder of the UK's Maverick stocks from the Harrier fleet. I suspect Brimstone would have been added at some point, perhaps when Maverick had reached end of life. As to Anti-Ship missiles I've no idea if the UK would have life extended Sea Eagle or Harpoon stocks if Nimrod hadn't been cancelled.

Oh and Nimrod MRA.4 was also originally going to get......AMRAAM....

Oh how I would have liked to have seen the Nimrod MRA.4 with the AIM-120 missile.

 

[TomS]

As it turned out only the RAF wanted such a fast ASW aircraft, everyone else went for props (Atlantique, Orion, Il38).

Not quite. The USN's Martin P6M Seamaster for example was killed off by the perceived need to pour money into covering rather large Polaris program cost overruns.

I think Seamaster was a nuclear highspeed bomber, not ASW. Admittedly the difference now is minimal, although I'd expect the 'backseaters' to have a view, as at least the seamaster gave everyone a bang seat.

Seamaster was nominally an offensive minelayer. The USN rationalized that as a "sea control" role, the idea being to mine Soviet naval bases and bottle up their subs and surface ships in the early stages of a conflict. But it was clearly designed around delivery of large nuclear weapons. The "minelaying" mission was pretty much a fig leaf to get around the directives limiting the USN to sea control, rather than strategic nuclear strike. It was never an ASW patrol aircraft.

 

[Grey Havoc]

While they did use the minelaying role to help obfuscate the Seamaster's nuclear strike role, the United States Navy treated the aircraft's mine warfare capabilities quite seriously as well. Memories were still fresh of the mauling the navy had received in the Korean War from sea mines, so being able to freely & rapidly deploy both conventional and atomic sea mines across whole theaters was rightly considered vital to help counter sortieing Eastern Block naval forces (including their own mine warfare forces!).

 

[TomS]

While they did use the minelaying role to help obfuscate the Seamaster's nuclear strike role, the United States Navy treated the aircraft's mine warfare capabilities quite seriously as well. Memories were still fresh of the mauling the navy had received in the Korean War from sea mines, so being able to freely & rapidly deploy both conventional and atomic sea mines across whole theaters was rightly considered vital to help counter sortieing Eastern Block naval forces (including their own mine warfare forces!).

Fair point. They were also very aware of the analysis in the US Strategic Bombing Survey, which showed how effective mine warfare had been in crippling Japanese coastwise shipping.

 

[Jason Dykstra (Wyvern)]

It was in the early requirements for Nimrod to perform bomber duties for internal security.

Yes it was, coming to think of it. The Shackletons were used to a great degree in conflicts in the Middle East, using bombs and strafing targets with the nose mounted guns. It makes sense, considering that that these aircraft were operating against insurgents, and could loiter for extended periods of time above their positions. It makes sense, although the pulling out of various colonies would make such a use rarity. It is a detail often forgotten about when talking about both the Shackleton and the Nimrod.

 

[CJGibson]

It's covered in Nimrod's Genesis.

Chris

 

[Jason Dykstra (Wyvern)]

Yes, that's were I first heard of the Shackleton and Nimrod's role as a bomber. It is a highly interesting, in depth book that is well worth a read, especially about the topic at hand.

 

[Foo Fighter]

On another tangent, was there ever any interest in a V bomber MRA? Lots of loiter ability there.


OK, found it.

 

[Jason Dykstra (Wyvern)]

Nimrod's Genesis features a project based off of the Vulcan, featuring a widened fuselage necessary to contain all the crew, equipment and weaponry. It was dismissed in favour of more conventional designs, and it was felt that the design would require too many modifications to make it worth it.

 

[JohnR]

Was the Vulcan proposal based on the fuselage of the Atlantic airline project? I've not got access to my copy of Nimrod Genesis at the moment.

 

[Hobbes]

no, it's a Vulcan with a larger spine. The Atlantic had a much larger fuselage. It's on the front page of Nimrod's Genesis:

 

[taildragger]

The Nimrod's wing-root engine placement may have mitigated the reliability benefit of having 4 of them:
- a single engine failure in a Nimrod would reduce available thrust by only 25% (vs 50% for the P-8) only if the engine failed in a way that didn't take out it's neighbor (inches away). Shrapnel containment is hard to guarantee.
- Engine failure on a Nimrod is also more likely to send debris into the fuselage than on a more modern configuration.
- I'd think that a Nimrod would be less likely than a P-8 to survive an engine hit by an IR-guided missile

 

[Zoo Tycoon]

Ah no, not really;- all blade detachment must not escape the engine case, which is key airworthiness cert requirements......if does go through the casing, then the aeroplane doesn’t fly. This is proven by analysis validated by test. A torching flame must not penetrate the engine casing. With the Tay we showed that if one of these occurred it wouldn’t make it past the bypass duct.

The only item permitted to pass through the engine casing is a section of the disc (one third). This has sufficient energy to go through anything. So certification requires analysis (known a particular risk analysis) to prove that a piece of debris of that size will not disable a flight critical system. This is a time consuming analysis conducted in three dimensions. It’s standard for all large aircraft whatever their engine arrangement. Disc failures are exceptional rare and thanks to this analysis airframe losses are fewer.

Even on a four engined aircraft such as a 747 the disc fragments can take out its neighbour. Yes the close spacing on Nimrod does mean the there’s a greater arc of coverage to its neighbour or fuselage, but equally real world experience shows disc failures generally depart with a downward trajectory. Statistically considering this event probability’s and the projected fleet flight hours its massively likely there would not have been a single incident of this nature.

One of the real issues with side by side engines is co-excitation whereby because the two engines have close coupled mounting structure, significant vibration from say a blade loss can resonate the other engine. This doesn’t cause the engine to fail but it dictate a precautionary engine change. So the problem is economic rather than safety.

A lot of missile vulnerability work done on the project with the general conclusion that Nimrod MRA4 survivability was a lot better than first expected. I don’t recall anything specific about the close engines spacing being a particular problem.

 

[CJGibson]

Ah no, not really;- all blade detachment must not escape the engine case, which is key airworthiness cert requirements......if does go through the casing, then the aeroplane doesn’t fly. This is proven by analysis validated by test.

True. Contagious failure was one of the 'drawbacks' of the VC10 but has anyone heard of such an event on a VC10? Or a Comet or Nimrod? B-52? B-47? I'd be interested.

As for IR SAMs - the MRA4 jetpipes are pretty long and as the Israelis showed with the Skyhawk, a long tailpipe can reduce the damage.

Chris

 

[CJGibson]

re; 4 vs 2 engines. The Air Staff demanded four engines in their MR types to allow the mission to continue if one engine failed. That's why the various Avro and Atlantique proposals for OR.350 and OR.357 had a Spey in the tail. Also, propellers were such old hat and would take ages to get up to the top end of the Norwegian Sea.

I believe ETOPS has pretty much proven the viability of twin fans over the sea.

Chris

 

[Zoo Tycoon]

I believe ETOPS has pretty much proven the viability of twin fans over the sea.

Chris

Twin ETOPS over the sea has been proven for a cruise at 30k feet, largely above the weather turbulence , above the moisture, above the salt, above the sea bids, generally at around one g and most importantly at a constant throttle setting. ETOPS is fundamentally a statistical driven process.

These conditions don’t reflect those specified for a typical day on an MRA4 or indeed MR2. The devil is always in the details and transients, in particular in engine power and g will make a real mess of statistics. Therefore Twin ETOPs is irrelevant for an RMPA performing its duties in a classical manner.

 

[Grey Havoc]

I believe ETOPS has pretty much proven the viability of twin fans over the sea.

Perhaps not so much of late, unfortunately!

 

[CJGibson]

I believe ETOPS has pretty much proven the viability of twin fans over the sea.

Chris

Twin ETOPS over the sea has been proven for a cruise of 30k feet, largely above the weather turbulence , above the moisture, above the salt, above the sea bids, generally at around one g and most importantly at a constant throttle setting. ETOPS is fundamentally a statistical driven process.

These conditions don’t reflect those specified for a typical day on an MRA4 or indeed MR2. The devil is always in the details and transients, in particular in engine power and g will make a real mess of statistics. Therefore Twin ETOPs is irrelevant for an RMPA performing its duties in a classical manner.

Aye, true, very true.

 

[Hobbes]

is that image part of a full top view of the MRA.4?

 

[CJGibson]

Yes, but a simplified diagram of what was changed.

Chris

 

[aim9xray]

True. Contagious failure was one of the 'drawbacks' of the VC10 but has anyone heard of such an event on a VC10? Or a Comet or Nimrod? B-52? B-47? I'd be interested.

Yes, B-52 in 1969. Cascading failure. Explosion in engine 5 after takeoff caused uncontrollable fire and separation of #3 engine pod containing engines 5 and 6. Damage rendered engines 7 and 8 running at extremely high power and non-responsive to any control input. Decision was made shut the engines down via fuel starvation (pumping fuel out of #4 fuel tank). Uneventful flaps-up landing was eventually made on four engines (all on left side).

The mishap was later covered in an Air Force Magazine in an article titled Incident at Wurtsmith. Scroll down to Page 56.

 

[CJGibson]

Thanks aim9Xray, I'll check it out.

Chris

 

[JohnR]

Here I go again; the beggar at the feast, ETOPS?

 

[Hobbes]

Extended Twin-engine Operations: a set of regulations that govern how far away from land you can operate a twin-engined airliner. Started out at ETOPS 60 (i.e. you had to be within 60 minutes' flying of an airfield at all times with a twin, which ruled out long overseas routes), these days you can fly transatlantic with some twin-engined aircraft.

 

[Yellow Palace]

In fact, there are 787s flying ETOPS-330 routes over the South Pacific, and the A350 XWB has an ETOPS-370 rating though I'm not sure if there any routes that need it yet.

 

[taildragger]

Ah no, not really;- all blade detachment must not escape the engine case, which is key airworthiness cert requirements......if does go through the casing, then the aeroplane doesn’t fly. This is proven by analysis validated by test. A torching flame must not penetrate the engine casing. With the Tay we showed that if one of these occurred it wouldn’t make it past the bypass duct.

The only item permitted to pass through the engine casing is a section of the disc (one third). This has sufficient energy to go through anything. So certification requires analysis (known a particular risk analysis) to prove that a piece of debris of that size will not disable a flight critical system. This is a time consuming analysis conducted in three dimensions. It’s standard for all large aircraft whatever their engine arrangement. Disc failures are exceptional rare and thanks to this analysis airframe losses are fewer.

Even on a four engined aircraft such as a 747 the disc fragments can take out its neighbour. Yes the close spacing on Nimrod does mean the there’s a greater arc of coverage to its neighbour or fuselage, but equally real world experience shows disc failures generally depart with a downward trajectory. Statistically considering this event probability’s and the projected fleet flight hours its massively likely there would not have been a single incident of this nature.

One of the real issues with side by side engines is co-excitation whereby because the two engines have close coupled mounting structure, significant vibration from say a blade loss can resonate the other engine. This doesn’t cause the engine to fail but it dictate a precautionary engine change. So the problem is economic rather than safety.

A lot of missile vulnerability work done on the project with the general conclusion that Nimrod MRA4 survivability was a lot better than first expected. I don’t recall anything specific about the close engines spacing being a particular problem.

I'm aware of the containment rules, but shrapnel does happen. The CFM-56, I believe, passed the same tests you mentioned but the only accidental death ever aboard a Southwest Airlines flight occurred in 2018 when one blew up and a fan blade penetrated the cabin and struck a passenger. Rare, but so are failures in general on modern engines - they were still part of the selection calculation.
Long tailpipes probably reduce the chance of engine damage from an IR missile hit, but a Nimrod in this situation still has a warhead detonating near the structural core of the airplane and, I think, a large fuel tank - the warhead detonating at the rear of a P-8's engine would be significantly further from the airframe. I know that a warhead doesn't necessarily detonate on impact, but the principal would apply regardless of where along it's path the detonation occurs.

 

[Zoo Tycoon]

In my experience, l’ve never seen an aircraft architecture choice based on or even influenced by an event that’s excluded by certification. Failures which breach certification are exceptionally rare;- you’ve got to have a foundation or you would never build anything above that.

The only missile vulnerability study I ever seen was MRA4 so can’t comment on others. I remember the general comment that the fail safe philosophy and critical system duplication/segregation embodied as part of normal civil certification was very effective at promoting/enhancing survival.

Missile fragments comes off the warheads in the multiple kilometres/second and were considered within the analysis, as unstoppable by any aircraft structure. The primary risk mitigation against the IR missile threat was decoy flares.

 

[kitnut617]

Just an observation -- having the engines further away from the fuselage didn't help the 737 that was shot down by the Iranians ----

 

[Fluff]

Extended Twin-engine Operations: a set of regulations that govern how far away from land you can operate a twin-engined airliner. Started out at ETOPS 60 (i.e. you had to be within 60 minutes' flying of an airfield at all times with a twin, which ruled out long overseas routes), these days you can fly transatlantic with some twin-engined aircraft.

You can do this for a passenger flight, but if you get an engine failure, your either close to the departure/arrival airport, or your at 30,000 feet, giving you some time and distance to play with. Now fly your twin engined MPA to mid atlantic and start loitering at 300 feet. Now you lose an engine. You have no speed and no height to play with, going to need to be on your toes.

 

[Hood]

What is the typical maximum altitude for sonobuoy ejection?
It seems the US tried 10,000ft ejection and achieved reasonable accuracy in the drop pattern: https://apps.dtic.mil/dtic/tr/fulltext/u2/a106692.pdf

I was thinking that with the decline in the use of MAD and sharper AESA radars, would a future MPA have to both descending and climbing and loitering at wavetop heights of old? Developments like MQ-9 Reaper with a self-contained ASW suite (https://www.secretprojects.co.uk/threads/universal-soldier-mq-9-reaper.36393/) might even allow a linked UAV to do all the low-level dirty work.

 

[robunos]

What is the typical maximum altitude for sonobuoy ejection?
It seems the US tried 10,000ft ejection and achieved reasonable accuracy in the drop pattern: https://apps.dtic.mil/dtic/tr/fulltext/u2/a106692.pdf

I was thinking that with the decline in the use of MAD and sharper AESA radars, would a future MPA have to both descending and climbing and loitering at wavetop heights of old? Developments like MQ-9 Reaper with a self-contained ASW suite (https://www.secretprojects.co.uk/threads/universal-soldier-mq-9-reaper.36393/) might even allow a linked UAV to do all the low-level dirty work.

I thought that was the way the P-8 was supposed to operate? Fly at medium altitude, and use a UAV to go low if necessary.

cheers,
Robin.

 

[Grey Havoc]

I thought that was the way the P-8 was supposed to operate? Fly at medium altitude, and use a UAV to go low if necessary.

That operational concept has sprung more than a few leaks...

 

[taildragger]

Just an observation -- having the engines further away from the fuselage didn't help the 737 that was shot down by the Iranians ----

I don't believe that the Iranian incident involved an IR-seeking missile and so the engine location wouldn't matter. Unless there's some sort of intelligence in the terminal guidance, I'd think that a radar-guided missile would head for the center of the return, not a tailpipe.

 

[DWG]

Started out at ETOPS 60 (i.e. you had to be within 60 minutes' flying of an airfield at all times with a twin, which ruled out long overseas routes),

Just for clarity, that's 60 minutes at single engine cruise speed.

Initially there was a lot of analysis of in-service engine reliability and certification at the individual airline level, but as the regulators got more confidence in it "ETOPS out of the box" - i.e. at entry into service - became a thing. eg https://www.flightglobal.com/cfm-goes-for-out-of-the-box-etops/12059.article

It was very much dependent on the significantly increased engine reliability that became apparent in the '90s.

Also known as Engines Turn Or Passengers Swim.

 

[Zoo Tycoon]

I'd think that a radar-guided missile would head for the center of the return, not a tailpipe.

Radar guided normal makes for the area of strongest signal, which is the pointy bits/sharp edges, that are within line of sight of the receiver. So if the target is approaching in front of the missile it’ll tend to zero into the nose or intakes. If it’s a beam approach, it’ll zero on the near wingtip or maybe an HTP tip. One reason why the aircraft manoeuvring worked well as an escape, is the bit the missile is zeroing on is constantly changing which destabilises the terminal approach. Of course I’m really talking of systems of a generation or so ago, the modern systems are much more clever.

 

[Grey Havoc]

There are imaging radar seekers I believe, but they are still pretty rare.

 

[Grey Havoc]

It was very much dependent on the significantly increased engine reliability that became apparent in the '90s.

Also known as Engines Turn Or Passengers Swim.

That humorous nickname has taken on something of a grimmer hue with the initially gradual downturn in engine reliability that began in the late 2000s/early 2010s. Not helped at all, to say the least, by the fact that since around the mid-1990s the spare parts market has being increasingly flooded with fake OEM aerospace parts mostly made in China.

 

[kitnut617]

Was the Vulcan proposal based on the fuselage of the Atlantic airline project? I've not got access to my copy of Nimrod Genesis at the moment.

The Atlantic's fuselage was as big as a 707's.

My project below

 

[kitnut617]

Just an observation -- having the engines further away from the fuselage didn't help the 737 that was shot down by the Iranians ----

I don't believe that the Iranian incident involved an IR-seeking missile and so the engine location wouldn't matter. Unless there's some sort of intelligence in the terminal guidance, I'd think that a radar-guided missile would head for the center of the return, not a tailpipe.

Thanks TD --