Wednesday, February 15, 2017

F-18 IRST Status

Infrared Search and Track (IRST) is one of the hot topics in aviation.  Supporters claim it greatly enhances the stealth of a fighter since it allows search and tracking via passive modes as opposed to active radar use.  It also allows detection of enemy aircraft that are radar stealth’ed and, thus, negates an enemy’s stealth advantage. 

The Navy has an IRST development program underway to equip the F-18E/F Hornet fleet with IRST as an effort to keep the non-stealthy F-18s relevant and combat effective in an age of stealth.

Following is a discussion of the F-18 IRST program as reported in the DOT&E 2016 Annual Report.

The F-18 IRST sensor will be mounted on the nose of a centerline fuel tank under the fuselage of the Hornet.  The current IRST21 unit is being developed by Boeing and Lockheed Martin and is descended from the F-14 IRST.  The Navy plans to procure 170 IRST units.  The current Block I will be fielded as test units and eventually upgraded to the future production Block II. 

Block I was originally scheduled to enter full rate production but the Navy decided to forego production in favor of the Block II version after a program review of the Block I test results.  This suggests that the Block I was deemed insufficiently successful to warrant production and, in typical Navy thinking, the unsuccessful Block I is bypassed in the hope that the non-existent Block II will somehow attain the success that the Block I did not.  There is nothing inherent wrong with this approach as long as we don’t commit to the Block II production before its capabilities are proven.  Too often, the Navy, faced with a failure, opts to incorporate undemonstrated “improvements” that exist only on paper and then immediately commit to production without waiting for demonstrated success.

The key development in the program thus far, Operational Assessment 2 (OA 2), took place in November 2015 when the IRST was tested under realistic combat conditions.  Unfortunately, the results were less than successful.

“The system … could not reliably detect and track targets well enough to support weapons employment in an environment that reflects realistic fighter employment and tactics.”

Immediately subsequent to this assessment, a program review was held.

“Assistant Secretary of the Navy (ASN) for Research, Development, and Acquisition (RDA) held an IRST program review on January 27, 2016, and in a September 8, 2016, Acquisition Decision Memorandum (ADM), ASN (RDA) approved a restructured program that foregoes full-rate production of Block I sensors and proceeds directly to development of the Block II system. The Block I system will not be fielded and IOT&E did not begin in 2016 as planned.

The Navy plans to hold the Block II Preliminary Design Review in May 2017 and begin IOT&E in 2020.”

As discussed, it is clear that the results of the assessment test and subsequent review indicated that the Block I IRST was not successful.  Unfortunately, instead of pausing until development could overcome whatever problems were seen, the Navy has opted to leap into Block II and has already scheduled production.

It is noteworthy that the Hornet-IRST-fuel tank combination has been approved for the full flight envelope as long as the fuel tank is empty.  Some restrictions have been placed on both launch and flight conditions with varying loads of fuel in the tank.

With the tank empty, the IRST becomes, in essence, a giant sensor the size, weight, and drag of a fuel tank!  If the tank can’t be used for fuel or only in partial load conditions, one has to wonder at the wisdom of placing the unit in a centerline fuel tank to begin with as opposed to a wing or nose mounted location.  On the other hand, DOT&E points out that the flight restrictions may not be significant.

“Given the rate at which fuel is consumed from the centerline fuel tank, these restrictions are effective for only a short period at the beginning of the mission profile and should not have an operational impact.”

The under-the-fuselage location also restricts the field of view of the sensor.  Obviously, it can’t see anything above the aircraft.  Thus, it’s only 50% effective to begin with, even if it worked perfectly for the lower field of view.

Reliability is also an issue.

“Demonstrated reliability is below what was expected at this point in the flight test program. As of the time of DOT&E’s OA 2 report, the cumulative Mean Time Between Operational Mission Failure (MTBOMF) was 4.1 hours; the reliability after incorporating known fixes was 19.5 hours. The MTBOMF requirement is 40 hours and the system was expected to have a projected reliability of 38 hours when entering IOT&E.”

DOT&E’s report concludes with this criticism of the Navy and admonishment to learn a lesson.

“Many of the Block I system’s difficulties with detection and tracking seen in OA 1 and OA 2 did not require flight testing to uncover them, but could have been discovered earlier via analysis and modeling and simulation. The Navy expects that the Block II configuration (which includes sensor and aircraft hardware and software), will provide improved capability. This assumption should be tested as early as possible, prior to major decisions …,”

Unfortunately, the Navy seems determined to ignore this lesson, having already scheduled Block II production.

Please don’t read this post as being against fielding an IRST.  ComNavOps believes that a fully functional IRST would be a relatively cheap and highly effective combat aid and is well worth pursuing.  Successful and functional IRST units apparently exist around the world and there is no reason to believe that the Navy and its manufacturing partners cannot produce a functional unit.  However, we need to go about this intelligently.

I would recommend that the Navy reconsider the under-the-fuselage location.  Perhaps there is a good reason why the unit can’t be wing or nose mounted but it would be worth some extraordinary effort to do so.  The actual sensor is small and should be able to be mounted in a more advantageous position.

I also recommend that the Navy stop making production plans for an unproven and, thus far, unsuccessful unit.  By all means, continue development but set production plans aside and remove that artificial deadline from consideration.  Take the time needed to field a fully functioning unit.


  1. Aviation Week write up yesterday on Boeing 'Block 3' Super Hornet proposal to compete with F-35C for funding curtesy of Trump. Block 3 changes from the 2013 Advanced Super Hornet, no internal IRST or weapons bay and no mention of the more powerful EPE version of the F414 engines. Block 3 retains the external IRST and conformal fuel tanks plus
    an advanced cockpit system with a large-area display , a new computer, Distributed Targeting Processor Network (DTPN), and a bigger data pipe Tactical Targeting Network Technology (TTNT) also used for the Growler and E-2D.

    Of note is the side swipe at the F-35 which uses the limited Link 16 for data transfer as it compromises its stealth, because Link 16 is not a low-probability-of-intercept waveform. The F-35 uses the stealthy Multifunction Advanced Data Link, MADL, line of sight nature and limited range restrict the scenarios where it is limited to connect four F-35 aircraft flight, no known plans of Navy to introduce MADL into fleet or how lack of it it interfaces with Navy's strategy of 'Distributed Lethality'.

  2. The IRST that they are basing this off of was first introduced onto the Tomcat in '90!!!! How on earth to they already not have a baseline of what it can do after 16 years in the fleet? It should have been relatively simple to know it does A well and B poorly so we modify it to do B better. AARRGGGH.

    The Navy seems concerned with the A2A threat; and justifiably so.

    What boggles my mind is why they don't try to make the SH's more A2A capable. Everything I've read on them is that they point their nose very well, but that they are underpowered and draggy so they don't regain energy very well at all.

    If you cancelled the upgrades on the A-C series, which by reports may not be able to be fixed at all due to poor corrosion, and buy new SH's with the EPE's, CFT's, a delete of the draggy weapons stations, and room in the nose for IRST you might get an 80% solution fairly quickly and with a more modest budget hit than trying to buy new and fix the old planes. Add the IRST after you get one to work up to snuff.

    Its not great, but it's something. But that's assuming they can make this all work. Given they can't get an IRST they should know all about to work properly I have my doubts that even a modest course of action can work for them.

    1. There's only so much you can do to make a Super Hornet better at air to air combat, except to design a new aircraft.

      It's like asking a pickup truck to go faster than a race car. You can maybe add a bigger engine, but that has other consequences too. Wing loading would go up. Same with the CFTs, and those would be a drawback in a dogfight.

      Widening the nose for IRST would lead to a more front heavy aircraft, unless you want to delete the radar. That would also limit the angle of attack.

      The problem is simple: The jack of all trades is the master of none.

    2. The vast opinion seems to be that the hornet is just a dump truck. That's not the case from what I've read.

      Some reading:

      This guy has flown both. He's mainly a Viper pilot. To him the viper, if it had AESA, has a decided advantage in BVR due to its power and its range. But it doesn't. The Hornet does.

      In WVR the viper still better but it's not like the Hornet is a sopwith camel. It's more maneuverable than the Viper which makes it dangerous, as more than one Viper pilot has confirmed. Its main failure is visibility (not much you can do) and power to regain energy (you can work on that).

      So with the Hornet, if you give it a decent ISTR, reduce the draggy bits (drop tanks and canted weapons stations), and give it like. 20% increase in power it becomes better.

      Add HOBS capable missiles and AMRAAM D or even meteor, both possible with existing kit, and it becomes something any opposing fighter pilot would have to take very seriously.

      Perfect? No, and I'd never argue that. But maybe, like an f-4f good enough in the short term. And it's do-able in our current budget situation. It would move the combat needle of our air wings in a realistic manner.

      Let's be real: we aren't going to buy Rafales. We aren't going to get a new plane to the fleet in anything under 8 years if we start now. But this is do-able now and gives us some capability.

    3. You know my stance on radar - they've historically had low Pk ratios, so I generally don't like using radar for air to air, just air to ground.

      But yes, if both sides did have a radar, Viper would have the upper hand.

      Keep in mind, if you can "reduce the draggy bits" of the F-18, you can do the same for the F-16.

      The F-18 was:
      - The loser of the YF-16 vs YF-17 competition
      - The YF-17 was taken and turned in to the F-18 at the cost of performance
      - The F-18 was made into the Super Hornet at the cost of even more performance

      That's just the cruel reality. It's a missile and bomb truck.

      Ultimately, a dedicated air to air aircraft is what is needed. Actually if it were made a priority, first flight could be done within 1 year. That's the kind of footing the US would have to be in a serious war - perhaps less.

      The Rafale, while superior is not perfect in this regard. The big problem with using European missiles is that it would take a lot of software work.

    4. "Keep in mind, if you can "reduce the draggy bits" of the F-18, you can do the same for the F-16. "

      100% true! But the F-16 isn't navalized. If there was a cheap path for making it navalized I'd be ducky with that.

      I used the F-16 because it *was* built as a dogfighter.

      The F-18 is an attack aircraft, but it *can* dogfight. Maybe not to the F-16 level, but people make it out to be like an A6 vs. an F-16. That's not the case. Its not an uber dogfighter. But it is what we have, and as I've stated more than one Viper pilot has said that they have to be careful dogfighting the Hornet because of its maneuverability. It's my opinion we can try to improve what we have in the short term and move the needle on the 'main battery of the fleet' or we stay where we are.

      "Ultimately, a dedicated air to air aircraft is what is needed. Actually if it were made a priority, first flight could be done within 1 year. That's the kind of footing the US would have to be in a serious war - perhaps less."

      I wish that were true, but I have extreme doubts in our current environment. Barring a war I just don't think it will happen. Defense contractors, congress, and the admirals will all get an oar in.

      Essentially Alt, I think we are in agreement (well, maybe not over the Radar thing :-) ) on one key point. The fleet needs a real, dedicated air superiority fighter. I'd love to get on board with that. I'd love to start now. But what do we do for the interim?

      Just IMHO.

    5. That's a big reason why a license of the Rafale might be the best option.

      - Proven design that can take off on aircraft carriers already
      - Acceptable (not great fuel fraction)

      But yes, in a war you'd desperately need it to be ready within a year because you need to be able to get good aircraft into product - FAST because if you don't, the enemy will.

  3. Keep in mind that the US is now years, perhaps decades behind the EUropean nations on IRST. In particular, QWIP IRST is widely used on the Eurocanards.

    The F-18's IRST is an F-14D derivative and I'd wager probably isn't nearly as advanced as the competition. Keep in mind that advancing computer semiconductor technology has been the main cause of advancements.

    A bit of reading:

    The Russians are developing their own QWIP IRST system, called the OLS-50.

    I think that the best way to do IRST is to mount it on the upper nose right below the front canopy, which is how the RUssians and Eurocanards do it.

    The problem with mounting it on a tank is that the tank becomes non-perishable. It cannot be used like a drop tank, which means that after it loses its fuel, it still must be carried. That adds weight and drag. That reduces range, speed, and would be a big disadvantage in a dogfight too.

    Might be better just to license PIRATE IRST or some other modern QWIP system.

    1. In principle I think that is a great idea, aulthough as far as I can tell the US would break its own fingers before signing a contract of non_US tech.

      The major problem is these is simply no room in the nose of the F18. The sensor "ball" is small yes, but the processor can take a similar amount of space to that of a AESA processor.

      If you loose the gun, that's about perfect :S

      I'm not sure anyone fancies going back to the F4 Phantom days though ?#


    2. This is just a packaging exercise. Other aircraft around the world have figured out how to do it. Surely we can, too. The Navy is exploring a Hornet Block III. This would be the perfect opportunity to do a little repackaging. Lugging around a centerline fuel tank just to be able to carry a IRST in the nose of the tank seems like the least desirable option! It's fine as a stopgap measure on existing Hornets but now's the chance to repackage.

    3. Re just a "packaging exercise". That is simplistic from my perspective. Yes, others may have done it "worldwide" but they ain't SuperHornets. There is only so much real estate on a fighter where every ounce counts as you know. There are aero-flutter, strength, cooling and power requirements etc. Putting it in a pod has its own, obvious drawbacks...etc etc. Some system already integrated and operational would have to go to make room. A fighter ain't a "flying truck" like a P-3, all varieties.. or an S-3 carrier type that could be easily modified.

      No doubt if it was made a PRIORITY a way would be found. IMO your attention on this system is like the Zumwalt folks forgetting about the Long range round shortage and concentrating on the .50 cals. If this system really extended BVR (V=eyeball) for air combat identification and really broke that barrier I would be all for it.

      COMNAV- reading those OT reports will make you go blind. ;-)


    4. b2, you're quite correct that I'm treating the IRST placement simplistically! Given the dimensions and layout of the aircraft, there may not be a viable way to locate the sensor in the nose or wing or wing root. My point was that with the Navy considering a Block III Hornet, now's the time to make a redesign, if it can be done.

      You also, correctly, note that the amount of effort that ought to be expended is dependent on the degree of benefit that can be gained. Here, I have no basis of experience on which to make a judgement. Is IRST the magic solution to stealth that proponents claim? I have no idea. Again, though, if there is a significant benefit to be had, now's the time to go for it. I note that other countries seem to have incorporated IRST and must see a value in it.

      Best I can do!

    5. "You also, correctly, note that the amount of effort that ought to be expended is dependent on the degree of benefit that can be gained."

      To me I think a big part of all of this is ROI. Can they make a Block III SH that is 'good enough', cheap enough, and easy enough to maintain that not only can the Navy fly it, but they can also train with it.

      To me, I have sticker shock at the F-35 and performance shock at its flight characteristics. Even if it's everything its supposed to be, its expensive to buy and expensive to fly.

      In my perfect world we make a dedicated striker, a dedicated air superiority plane, and a dedicated mission tanker.

      But given present reality I think its just as easy to say that we can save the purchase of a ladder for the planes because the pilots will just jump from the backs of their unicorns to get into the cockpit.

    6. Top of the nose is probably the best option.

      You want:
      - Full 180 degree view in front (which is why I oppose wing root)
      - Place that it's easy to get at to maintain
      - Doesn't add too much drag (which a fuel tank does and cannot be jettisoned)





      IRST on left, IFF system on right.

    7. SH always caries a CL-EFT. Mounting the IR sensor on it (vs. the lower fuselage) is because it's easier to move the system between aircraft. The increment 2 IR sensor has always been planned, but poor performance of Lockheed Martin's older sensor made moving forward with the upgrade necessary.

  4. The reason why it works is that most IR radiation is absorbed by the atmosphere. The exceptions are the 3-5 and 8-12 microns.

    Non-afterburning aircraft can be spotted in the 4 micron band, while afterburning can be spooted in the higher band. Keep in mind that blackbody radiation from warm objects starts at the 10 micron band and goes up to 15, which in turn makes it good for IRST.

    Thick clouds can degrade IRST, but they are rare above 30000 ft or so. Cirrus clouds don't have much effect on IRST performance.

    The other big 2 advantages are that:

    1. It's a passive sensor so the target doesn't know they are being spotted. With active sensors like radar, the detection range of radar warning receivers now detects longer than the radar range (kind of like why submarines rarely "go active" on sonar too).

    2. The other is that the sensor is not easily jammed, unlike radar. Flare is the only way and that lets the enemy know your position.

    There are a few lesser advantages:

    1. It weighs a lot less than a radar system. It still needs some specialized equipment - the QWIP sensor must be cooled to about <70k to work.

    2. It presents an image to the fighter aircraft. The reason why this is good is because that solves the friendly fire problems that radar has.

    The first IRST systems developed in the 1950s had a ton of problems and any radiation would generate a blip - something modern systems avoid.

    The Russians during the Cold War were able to detect an SR-71 at 100km, while the F-16 could be detected at 40km from the front or 60km from the rear.

    1. I understand the current IRST are accurate enough to provide targeting information.
      The Eurofighter version combines IRST with FLIR ( useful for ground targets or even landing aids)

  5. I disagree with your premise "non-stealthy F-18s relevant and combat effective in an age of stealth"

    The Russians haven't developed stealth to our degree but they have developed sensors to degrade or stealth advantage

    Stealth is like the technology of battleships. Good at first for its intended purpose but developments area making out almost irrelevant now

    Processing power and computers are changing AI which in turn makes stealth less valuable because of the ability to process information.

    Soon sensors will fuse several radars into a sensing suite where each had is detection advantages and disadvantages enhanced or dealt with by using AI to process all the information

    War is now the war of information. Those who stop the flow of it will have advantages not dreamt of yet. Stealth will be relegated to the dustbin of technology history soon

    1. Agree with this.

      Stealth is not an assured "I win" button.

      IRST and other countermeasures will come out. That's just physics.

  6. "The under-the-fuselage location also restricts the field of view of the sensor. Obviously, it can’t see anything above the aircraft. Thus, it’s only 50% effective to begin with, even if it worked perfectly for the lower field of view."

    Actually, Super Hornets cruise with a positive AOA (as most fixed wing planes). These few degrees + the degrees added by the geometry (it CAN loop forward & up by a few degrees) AND the forward field of view left and right of the nose should turn your "50%" into something more like "80%". Add a few course changes by 10° to the left and right of the intended course once in a while (this also helps the radar search) and we're rather at ~"90%".

    I actually think they could create a pod that combined a FLIR with chaff and flare dispenser and NGJ. Most combat aircraft simply lack internal volume for all that avionics stuff that's deemed necessary at least on offensive missions against top tier adversaries.

    1. Sure, by flying in continuous loops and rolls one can establish a full field of view. I'm referring to the instantaneous field of view.


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