So everything in the BLOODHOUND garden is rosy. Yes? 

Well, of course, yes. A new sense of urgency. A hard-eyed re-evaluation of all the different design elements in progress. Budgets pinned down, critical paths decided upon, tasks and time-scales allotted to team members who mostly look only slightly stunned. Everyone completely focused on their targets. Everything rosy, hunky-dory, oojah-cum-spiff. Yes?

Well, er – not entirely. Of course not. This is the real world.

In the past month or so there have been great strides forward and a new attitude which says; look guys, we need to move. And with the present global financial climate unable to make up its mind whether it’s an incoming Ice Age or an Elysian field – and especially with Britain and Europe leaning noticeably towards the Ice Age school of thought – BLOODHOUND now has to move on a smaller budget than an optimistic chap would actually like to have at his fingertips. And has to do it now.

So oojah-cum-spiff? Well, call it spiff-ish…

The truth is that an endeavour like a Land Speed Record attempt simply does not march to a conventional drum. If you’re creating a new rail bridge, egg whisk, supersonic fighter, electric fence to discourage your moggy from chasing mice in front of a combine harvester, you are – however innovative you’re trying to be – working from known precedents. With a Land Speed Record car the precedents are firstly a touch thin on the ground, and secondly not always very much more than pointers to what not to do. You wanna hit 1,000 mph on the surface of the planet? Buster, you’re out on your own, there. Blunt fact is, BLOODHOUND can never be totally oojah-cum-spiff until it passes through the measured mile at 1,000 mph, then turns round and does it again within the hour.

And right now, there are problems as well as triumphs. Of course there are. Ron Ayers, Chief Aerodynamicist, once said “The purpose of research is to find problems and solve them one by one until there are no more problems. Then you look for the problems you haven’t spotted yet…”

So of course there are problems. Wouldn’t be an adventure if there weren’t any problems. And of course problems come in all shapes and sizes. Some are simply “We haven’t quite finalised that, but we’re getting there”. Others are “We’re going to have to allow for a range of uncertainty on this”. And still others are, shall we say, ongoing, and likely to continue to ongo for a moment or two yet. Call them the “Yeah, well…” problems.

But BLOODHOUND’s problems differ from other companies’ problems in one particular way. If General Motors or British Aerospace stub their toe on a design pothole, you are not going to hear about it. They will all hop around on the un-stubbed foot looking at the sky and whistling innocently. Chances are the opposition in the shape of Ford and Boeing are going to know about it within approximately 18 seconds because all these corporations use shifty characters in long black cloaks with ‘Industrial Espionage’ stamped in very small letters on the back – but you and I won’t hear a peep. On the financial side, yes, because most of these things tend to eventually sidle through into the arcane world of share price movements. But on the engineering side – usually not a chirrup.

BLOODHOUND, however, is different. BLOODHOUND’s credo is to make these engineering problems available for all to see. They are not unsolvable – very far from it. But to varying degrees they are the problems of the moment. Some are technical – and these are mostly now looking more like issues to clear up rather than mountains to climb. And some are logistical. And some are a mixture of both. But they are all part of the history of BLOODHOUND, which is fascinating right now and will become ever more fascinating in the future. So pardon me if I talk about one particular element here – the EJ200 jet. Given time, hindsight will get to chew away at the corners of what it was really like now, in June 2010, trying to integrate a late-generation fighter engine into… a car.

Problems? Of course there are problems. So let us look at some of those problems with BLOODHOUND frankness. As I’ve said, they will be solved – but these are the problems which exist now. And these are typical of the problems which come in from all quarters if you insist on the insolence and progress of creating a 1,000 mph automobile…

 

The three jet S’s – surge, stopping, and starting

The EJ200 is a very state-of-the-art jet – which means its basic design only goes back two decades or so. That’s a pretty normal lead-time for a ‘collaborative’ military fighter. It gives successive politicians in the various ‘collaborating’ nations plenty of time to mess the project about in their own unique and amusing ways, sometimes creating such ever-moving goalposts as to cause valuable design engineers to re-evaluate their career options and become swimming pool attendants.

However, in spite of this political assistance the EJ200 is in fact a very, very good jet. But like all jets it was designed for a purpose – in this case powering the Eurofighter Typhoon. It was not designed for a Land Speed Record car. So whilst overall the design parameters match up very closely, there are inevitably some areas which have a certain tinge of okay-ish about them. The odd raised eyebrow.

The first but hopefully least issue is compressor stall (or in the extreme case, compressor surge). Basically the workings of a jet engine boil down to three processes – suck, squeeze and blow. On the EJ200 the sucking and squeezing is done by a three-stage low-pressure fan in front of a five-stage high-pressure compressor. The job of the whole compression system is to take the air delivered by the intake and present it as high-pressure airflow to the combustion chamber where fuel is pumped in and ignites. The now very high-pressure and high-temperature flow is blown rearwards past the turbines and hence out the back.

If the airflow breaks up for any reason in the compressor stage (compressor stall) there will be a loss of efficiency. In the worst case, if the flow breaks down completely, you’re left with a volume of high-pressure, high-temperature air inside the jet just ready and willing to blow back the way it came in – which is compressor surge.

So there can be a bang. In extreme cases flames shoot out of the front intake, which always tends to grab a pilot’s attention. One bang is by no means necessarily fatal to the engine – to over-simplify grossly, call it a jet clearing its throat. But if the stall persists and you get an intense series of bangs you can be fairly sure you are not exactly improving the engine’s chances of a long and happy life. Or in really severe cases even a life at all beyond the next, say, five seconds.

So what causes compressor surge? Well, one thing is FOD – foreign object damage to the compressor blades. A few Canada geese going through the intake will do that big time, for example. Another is angled airflow into the engine – the early Canberras, for example, had only to turn onto a runway a bit too briskly in a strong wind for one or both engines to stall or even flame out, which created little or no engine damage but a lot of bad-tempered aircrew.

Then intake shape has a big bearing on surge vulnerability. And associated with that is the rate at which you wish to accelerate both the jet and the aircraft itself. If you want to wind the jet up to full power or near as dammit with the aeroplane static – which of course you do for every take-off, particularly in a fighter – then you need a big air intake at the front to swallow the weight of air per second that the engine demands. But once you start moving you obviously get a ram-air effect in said intake which increases most markedly with speed. So then you don’t want such a big hole in the front because you get air flow ‘spillage’ around the sides of the intake, which can create a lot of drag – not something the Iceman and Mavericks of the future are looking for.

The solutions to this are many-fold and often highly complex. Which decodes as I don’t understand them all, having spent my personal flying life with engines which rumble in front of your feet rather than whistle behind your ass. You can have an intake with a variable-geometry cowl (as Eurofighter has), or you can have a smaller intake with auxiliary doors around it that get sucked open to let in more air at low or no forward speed. Plus, for supersonic engines, perhaps other moving devices which control the position of the shockwave in front of the intake. There are supersonic engines with fixed-geometry intakes, but it ain’t easy of achievement.

BLOODHOUND, needless to say, are trying for it.

Because, quite simply, BLOODHOUND could never afford the R & D for active airflow controls, this being the province of major aircraft manufacturers with fat government contracts and umpteen years to do the research. So BLOODHOUND has to create a static – what I think of as a ‘raw’ system – which will work anyway, despite the engine being designed for a very different installation. The team are designing-in scope to for auxiliary low-speed intakes, but would prefer to avoid the cost and complication if they can.

A problem? Well, not a fully-qualified card-carrying problem… but it’ll do until a problem comes along.

Obviously this is a completely unique engine installation. For example BLOODHOUND’s pre-intake supersonic shockwave is shaped by – of all things – the cockpit canopy. Perfectly valid, but not exactly conventional aircraft design. In fact BLOODHOUND’s intake system is being deliberately sized on the small side to minimise drag at full chat. So the spectre of compressor surge at lower speeds – especially stationary – does sort of undeniably hover in the wings.

However…

In these days of electronically-controlled jet engines you don’t get the really interesting bangs you used to get – or at least, not very often you don’t – because the engine is bristling with sensors which talk to the computer and the computer throttles the thing back whether you like it or not to keep it just below the compressor-stall region. This is called surge-protection. The net result is that you might get the odd burble of compressor stall because the computer is programmed for Eurofighter and not BLOODHOUND, but it almost certainly ain’t gonna bang big time.

Which, in a wonderful exposition of the grand irony that most mechanical devices can produce if they really put their minds to it, creates a sort of opposite-problem. There might be an onset of compressor stall at low forward speeds – but with the surge-protection operating, the chances are Andy Green won’t hear a compressor burble above all the cacophony the thing’s producing anyway. All he’ll know is that he’s got his foot down to max dry power, and the jet seems a bit sluggish because the computer is wagging its finger. Various instruments will tell the tale of course, and also record same for all to pore over with pursed lips and furrowed brows. But the first thing Andy will feel in the here and now is that he’s got his foot on the floor and the computer has over-ridden him and eased off the grunt a bit…

So what are the parameters?

Well, firstly you lash BLOODHOUND to something absolutely immovable such as the Parthenon or Greece’s national debt (or ours, come to that), and try winding the EJ200 up to full power. If it reaches full power statically then you’re probably – not certainly, but very probably – oojah-cum-spiff. If it doesn’t – or if surge-protection means it takes an inordinate time to wind up – then you have to run the car experimentally to find the speed at which the ram-air effect is sufficient to let you fully clog it without the computer getting the sulks. 60 mph, 160, wherever…

Called research, that. I think I’ll let Andy Green do that before I kidnap him on the eve of the big runs.

In point of fact BLOODHOUND does have some advantages on the surge front. Firstly you are not going to be pulling a 10 G pitch-up on the thing, which means you don’t have to worry about angled airflow because all your airflow is going to be linear to the engine axis. Secondly, there ain’t gonna be no MiG 29 on Andy’s tail, so there isn’t quite the urgency to pour all the coal on instantly. And thirdly because a big contributor to surge, especially at low rpm, is ancillary loads such as generators, hydraulic pumps, and for all I know gizmos for running the in-flight movie – and BLOODHOUND ain’t planning on none of those things. So there is a bit of an edge here and there…

Enough of an edge to counter the jet being in a different environment than it was designed for?

Probably. Maybe. And that’s why you have a test programme to find out…

 

A matter of distance

Should experimentation reveal that initial jet acceleration needs to be reined in a bit, that isn’t necessarily the end of the world. The Hakskeen Pan will accommodate a ten-mile run plus a half-mile over-run at each end. So Andy Green could use that as a nearly 10 percent extra run-up distance from the start, which would reduce the acceleration stress a tad.

Of course that’s all right at the start – but you don’t want to be compromising your over-run distance at the other end. That distance is like carrying a small .22 pistol in your pocket – you may never need it, but if the day ever comes when you do, you’ll wish it was a .44 Magnum. BLOODHOUND should never need that extra half-mile of stopping distance – but in the event of an embarrassment such as a brake-chute failure, that half-mile ain’t gonna be looking none too long from the perspective of one Wing Commander Andrew Green in the hot seat.

Hence a max-rate BLOODHOUND slow-down from 1,000 mph is going to be just a touch dramatic. First there is pure supersonic aerodynamic drag – which is going to be like running into a brick-built blancmange when Andy shuts the power off – almost immediately followed by barn-door airbrakes progressively opening to 60 deg, the braking parachute(s) chiming in at about 600 mph as well, and finally either wheel brakes or the wonderfully antediluvian Flintstone dirt-brake. (See From Outside the Box May 2010)

Not entirely a gentle process. Indeed a process fraught with maximum effort and having the odd considerable G spike in it for the good reason that, unlike acceleration, slowing down involves certain things happening a bit jerky-like, such as parachute deployment. Current figures suggest the maximum G-spike could be 3.3 G…

Which makes it a bit of a pity that the EJ200 is only rated for a max linear deceleration of – er – well, somewhat slightly less than that.

(Just to be clear to the dumbest homo sapiens reading this – to wit, myself – linear deceleration is nothing to do with engine rpm but all to do with the rotating mass of the engine core trying to move forwards under heavy braking).

So why that particular limit?

Good question. The answer is that all military power units, from electric toothbrushes to jet engines, have to be designed to fulfil the requirements of the customer – the military. So for the EJ200 the military demanded a minimum deceleration tolerance of x G. If the engine had been designed for aircraft carrier operation with catapult launches and arrester-gear landings the requirement might well have been twice x – but it wasn’t. It was designed for the Eurofighter. The Eurofighter has excellent short-field performance, yes - but if anybody has a bad hair day and tries putting it down on a carrier deck they are going to be risking a small case of wet feet. The EJ200 design comfortably made the deceleration minima the military spec laid down, and so the problem went away – or, indeed, was never really a problem in the first place.

Until BLOODHOUND came along. Then the problem came back again.

Part of the issue is why this deceleration limit on the engine is there. Is it for fear of compressor or turbine blade contact with the casing? Or is it to do with main bearing lubrication? Well, of course the BLOODHOUND team don’t know. So they ask the engine manufacturer…

Who doesn’t know either.

Now at first glance that sounds highly derogatory – but it doesn’t work like that. In fact the engine-maker is extremely cooperative and unfailingly helpful. No – the problem is pure logistics. Let me explain.

You design a jet engine to meet the specification laid down by your beloved customer, the military. Linear deceleration – slowing down on the runway – will be on the spec-list, most certainly. But when you’re at the drawing board it’s unlikely be a huge issue for the perfectly practical reason that by the time you’ve designed the engine to meet all its other requirements it’s already going to be well tough enough to walk through the deceleration parameters with ease. Which it duly does.

But then someone has to fill in a box on the Operational Limitations form – and we end up with the figure of x G.

So why x G?

Well, that’s the question. And of course the answer is certainly there in the Research and Development calculations. So all the engine manufacturer has to do is glance through the design records and find what was the limiting factor – structural loads, bearing lubrication, blade-casing contact, or whatever. Should be perfectly simple…

Except that – and I’m guessing here, but I’ll bet I’m not far out – there are probably 35,000 pages of calculus relating to the engine development. Which means that checking through them to find out exactly which of thousands of research threads contributed to the deceleration G limit is not going be a five minute or five day job, or anything remotely like it.

And all this for one single engine which is planned to exceed one parameter for less than 30 seconds.

Ah…

Well, nonetheless the manufacturer is working on it. So far it seems the issue will probably be tolerable and certainly won’t be unsolvable – but for right now the limitation is there. And the BLOODHOUND team are keeping a wary eye on it.

 

But if you can’t start it…

Then there’s the small matter of starting the jet.

I’ll try to explain this. All jet engines nowadays have a PTO – a Power Take-Off shaft which rotates at a percentage of engine rpm. This shaft drives a gearbox which in turn drives ancillaries – generators, hydraulic pumps, the thingy that operates the toilets, you name it. Also attached to this gearbox is a device called an ATS – an Air Turbine Starter. The ATS is a relatively small unit but does a Herculaneum job. Basically you shove compressed air into it – either from a ground start-cart or from the aircraft’s on-board APU (Auxiliary Power Unit) – so that it smoothly winds up, spinning the gearbox and hence the PTO shaft and thereby the engine itself until the main core is rotating fast enough to turn on the LP fuel and the ignition clackers to light the thing up. Nothing intrinsically difficult about that. right?

Well, er – no, not quite entirely right. There is just one tiny almost unnoticeable snag.

To wit, and not to put too fine a point on it, BLOODHOUND at this time does not happen to possess an EJ200 gearbox. It is not made by the engine manufacturer, but by another member of the Eurofighter consortium. BLOODHOUND thought they had one lined up, but for reasons I won’t bore you with it appears to have become un-lined just recently.

Aaah, again. Hmmm, even.

So I’d like to ask all BLOODHOUND enthusiasts to have a quick glance around the attic to make sure you’re not hoarding an EJ200 gearbox you’ve forgotten about…

I joke of course. Because (a) you won’t find such an article – or you won’t unless the car boot sales in your neck of the woods are a lot more esoteric than they are around here – and (b) if you do, you’re likely to receive rather serious visits from men in nice suits with MI5 stamped on the inside of their skulls. No – getting hold of an EJ200 gearbox is suddenly a problem.

Well, I very much doubt it will be a problem for long. BLOODHOUND will conjure up one somehow and from somewhere. And even if they don’t, James Painter, one of the newest members of the BLOODHOUND team, told me cheerfully: “We’ll design and make one ourselves. After all, we only need the starter. We don’t need all the other power take-offs…”

Oh, fine then.

Oojah-cum-spiff. If there weren’t any problems it wouldn’t be an adventure…

 

Postscript: the fourth jet S – which is for Storage

The EJ200 going into BLOODHOUND was not exactly manufactured last week. In fact it was one of the Eurofighter test programme engines, and as such has been in storage for some years. Of course the MoD don’t just trundle an EJ200 into some garage and padlock the door. No, the engine was most carefully inhibited – a far bigger job than it may sound – then sealed off and placed in some sort of storage facility which would probably make the main vault of the Bank of England look like a push-over.

But – storage is storage. So what actually happens when you come to de-inhibit the thing and try firing it up again?

Well, I can exclusively reveal today that the BLOODHOUND engine has very recently been started up on the maker’s test-bed and ran perfectly satisfactorily – just the way it did several years ago when it whined into life for the first time.

Always knew it would, of course. But nice to see it proved…