Thread by @JonHawkes275

1/ A much requested 🧵 thread on the confused and misunderstood topic of Challenger 2/3’s engine and just how many horses are, or can be fit under the deck of these tanks. Short answer – there is no 1,500 hp uplift for CR2 or CR3.

2/ There *could* be a lift to 1,500 hp but there are major technical obstacles and there is no intent to do it. There is be a mid-ground to be found that is being looked at outside committed programmes.

3/ First establish the as-is: CR2 is fitted with the original 1998 powerpack consisting of a Perkins CV12-6A V-12 diesel engine and David Brown TN54E epicyclic transmission, plus a monster cooling system.

4/ Powerpacks are a remarkable piece of engineering (a full powerpack primer coming very soon on the blog), combining the engine, transmission and cooling system into an incredibly compact assembly that can be rapidly fitted and removed from the vehicle as a single piece.

5/ People don’t appreciate the importance and challenge of the powerpack. Most tanks are built around it as the core component. Not the gun, the armour, the optics – the powerpack. And it is monumentally hard to design and build these things.

6/ Up to a third of the cost of developing a blank slate tank is the pack.

More on the insane complexity and challenges of powerpacks in a blog primer soon, but just appreciate it is extraordinarily hard to do this successfully.

7/ Retrofitting packs with new components is worse still – you have to fit your new kit in the space of the old one, and the old one has a space EXACTLY the right size for it. The cost, risk and time can be huge to touch anything in there.

8/ On to the now: CR2 is transitioning to CR3 via an upgrade programme that will see 148 vehicles fitted with a range of kit, the centrepiece being an all-new turret with smoothbore L55A1 gun, fancy optics and loads of digital wonderment.

9/ However, the CR3 upgrade does not include an automotive component. That’s down to 2 reasons; (1) the intended scope of CR3, and (2) the HAAIP programme.

10/ (1) is the background of the CR3, which started as a light-touch obsolescence management effort called Challenger Life Extension Programme (LEP), intended to manage CR2 through to the replacement which was then planned to occur in the 2030s.

11/ As with all things Army procurement in the UK, LEP was previously the Capability Sustainment Programme (CSP) and itself rolled in earlier efforts including the Challenger Lethality Improvement Programme (CLIP). It has a history.

12/ Over time this effort crept in scope and scale, and then in 2016 contracts were awarded to BAE and Rheinmetall to produce digital concepts for about £27m each over 2 years.

13/ BAE did what was ordered, they produced an obsolescence managed platform with some good uplifts in capability. Called Black Night (representing enhanced night fighting), and shown with Iron Fist as a potential add-on, it was doing what was asked and a good bit of kit.

14/ Rheinmetall meanwhile took a punt, and offered both an obsolescence managed platform, but also a much deeper enhanced option with a completely new turret to allow the fitting of Rheinmetall’s smoothbore 120 gun and associated 2-part ammo storage.

15/ Normally these sorts of punts don’t work with UK, who are desperately cash strapped and tend to keep the relentless scope creep for periodic programme resets (a transparent jab at the decades long histories of Ajax and Boxer there), but somehow this one stuck and the…

16/ …programme established it as a formal two-option solution – LEP as planned, or LEP+. (LEP+ included the new smoothbore gun, which itself was a resurrection of CLIP from >12 years earlier. As I said, its a UK Army thing to just turn back the pages every few years.

17/ Ultimately LEP+ was preferred and with only one option on the table for it Rheinmetall won then RBSL happened and everyone was a winner.

Recognising radical changes the moniker Challenger 3 was taken up (it had been bouncing around for a while) and we have what we get today.

18/ However, the upgrade had no automotive component at all, because: (2) there was alongside original LEP a pan-fleet automotive obsolescence management programme called HAAIP (Heavy Armour Automotive Improvement Programme).

19/ HAAIP was looking at how to get a unified pack standard across all the CR2 variants in the fleet and roll in a few tweaks and upgrades for good measure.

20/ This includes new third gen hydrogas suspension from @Horstman_Group, new hydraulic track tensioners, improved electric cold start system (an intake manifold heater), tweaks to transmission components (more on this in a moment), new air intake filters, an an upgrade to the…

21/ …cooling system in the form of new radiators and fans.

It also, and this is where the rumour mill began, included ‘upgrades’ to the CV12-6A engine, rebuilding them with a number of changes that include common rail injection, which *can* allow an increase to power output.

22/ In 2019 Caterpillar, who are involved in the upgrade, spoke with @Janes Sean Connors about the upgrade, in which they mentioned the common rail injection would allow opportunity for an uplift to 1,500 hp in the future.

23/ This meant/means that the engine could be rated to produce 1,500 hp, but it is not going to do so. It would require further paid work to do so. It was not what was actually happening then, or now.

24/ Last week the Army’s ATDU (@ArmourLab) started a trial of their new TN-54 transmissions from David Brown Santasalo, which include a new torque converter that is now rated to 1,500 hp.

https://x.com/ArmourLab/status/1712429613870100639?s=20

25/ Don’t be distracted by this though, the reason is that this is the native capacity of that newly designed component, not because it was required by the customer for a power uplift on CR2/3.

26/ Old parts were obsolete (well, the supplier dropped out because UK volumes of <10/year were too low) so they needed a new one, and David Brown designed one. Modern design/materials means its rather good, and can handle 1,500 hp. That’s not the requirement though.

27/ So we have an engine that *could* be uprated to 1,500 hp and a transmission which can handle 1,500 hp – we are done then, the tank is getting 1,500 hp, say the commentators? No. Running an engine at 1,500 hp on a bench is not running an engine at 1,500 hp in a vehicle.

28/ Firstly, all of that requires lots more work and funding, and there isn’t any. But bigger than that, the elephant in the room is cooling.

29/ AFV powerpacks and particularly the transmissions are spectacularly hard to design successfully, look at Korea and Turkiye who have spent decades trying to match their German-sourced packs, and only now are they claiming success, which is yet to be robustly proven.

30/ The packs are very, very hard to design, and a big part of that is cooling.

The transmission is concurrently a gearbox (or gearboxes, in reality) as well as steering and braking all in one mess of cogs and engineering magiks. The heat generated is immense.

31/ Add to this a 1,200-1,500 hp engine running at high output and then bury it all in a very compact sealed compartment buried deep inside a metal box and you have an utter nightmare for keeping it cool.

32/ And this is CR2/CR3s problem.
There is no way to keep the pack sufficiently cool at 1,500 hp output levels, even with HAAIPs new cooling rads and fans.

33/ To do so would require a new and much larger cooling system, which is undesigned, unfunded and would require significant work on the rear of the vehicle, which is just about to go into the complex and prolonged CR3 upgrade cycle.

34/ As such it is not going to happen. By the time it could be looked at properly post-CR3 youll be in the 2030s and major rebuilds are too big, expensive & slow when a successor tank should be just around the corner, depending how Europe/US are doing by then.

35/ However there is an option 3 being looked at, which I initially heard as whispers a while back, then again at an AFV Power Systems conference a few weeks ago and have dug into around the network since – 1,350 hp.

36/ There have been some experiments and modelling to see what can CR3 handle without any further uplift, and the analysis suggests there is potential for 1,350 hp to be tolerable in the HAAIP configuration (remember, UK won’t accept having a CR2 and a CR3 pack, the whole point…

37/ …of HAAIP is a unified pack)
That would require some modest work, so it has to be funded, designed, and contracted out, but it would be relatively minimal and could be layered into the fleet maintenance plans as-is.

38/ But it is not being done without money and contracts, so at the moment CR3 remains a rather asthmatic 1,200 hp, ~72,000 kg tank, giving a power to weight as low as 15hp/t depending on armour and APS.

39/ 25hp/t is the min. target for good mobility by the way, which you coincidentally get if you push for best-in-class 1,800 hp outputs that some of the newer pack designs can offer. But that is a lot of risk & money for what started as an obsolescence management project.

40/ And thats that - 1,500 hp not impossible, but nor is it likely or realistic, but there is hope for CR3s power to weight metrics. Don't get me wrong, CR3 is a very tasty tank that will be great for UK, but the lack of pack upgrades was bad on CR2 TES, and hobbling on CR3. /end