Let me paint a scenario. You are part of the design team of a major aircraft manufacturer. You are attending a design symposium devoted to the latest mega-monster airliner. These meetings happen fairly regularly so that all the various disciplines can have a beer or six….. er, sorry, can be brought entirely up to speed on what everyone else is doing.

A Guru from aerodynamics speaks. Structural design speaks. Control systems speak. Pressurisation and air conditioning speak. None are exactly riveting. The whole project is 75% down the design road anyway, and you are thinking about lunch and wishing you could smoke a Lucky…..

And then Rocky from engineering steps to the podium.

“Hi Guys”, he says cheerfully. “We’re kinda thinking about a little-bitty change here. We’re thinking ‘bout putting two of the four engines above the wings instead of underneath ‘em….”

Stunned silence. Jaws agape: Then: “Hey man, we’ve always done it this way! – Ain’t ya got no sense of tradition? – Hey, this’d set the programme back five years…!”

Such is the reaction in a conventional big company team.

Today…

Today is a Design Meeting of a not-conventional team – BLOODHOUND. Brian Coombs, one of the Senior Mechanical Design Engineers, leans back in his chair and announces calmly; “We’re taking a look at swapping over the jet and the rocket – putting the rocket at the bottom and the jet on the top”.

The only jaw that drops is mine – which of course matters not a jot because I am known to one and all as a guy who is just around, and whose engineering expertise anyway begins and ends with remembering to put the undercarriage down. I am invited to such inner-circle meetings on the tacit understanding that I keep my ears open and mouth shut. So I do duly stop gaping and close the cake-hole.

The rest of the dozen or so around the table merely look…. well, interested.

Brian Coombs counts off the pro’s and con’s. Pro’s – reduced front axle load at high speed; much easier to mount the rear fin and winglets if the bl…. jolly rocket isn’t in the way; narrower underside of the car at the rear, which might help the rear-end uplift problem; more room for the parachute packs, and allowing the ‘chute anchors to be more or less on the C of G line; and making room for a cross-linkage which will simplify and safety-fy the airbrake system.

Con’s – the C of G will be higher; and there will be higher front axle loads at low speed. (Low speed being BLOODHOUND-speak for below about 300 mph – sort of parking-speed, really).

There ensues a certain amount of ear-scratching. Engines says that such a transmogrification would simplify the air intake for the EJ200 jet. Aerodynamics – Ron Ayers – says that the acoustic effects of a low-mounted rocket on the rear wheels should be investigated. Rockets – Daniel Jubb – speculates that the rocket exhaust that near the deck might gouge a furrow of a length and breadth to win every ploughing contest in the world for the next 100 years. (However it also so happens that he has a California university approaching him – him, Dan Jubb, who left school at 13 – asking to be allowed to embark on rocket-plume investigation, so maybe there’s a research avenue there….)

No-one even thinks to say, ‘Gawd, this is a helluva big change at this late stage’. I think it. But I am just a guy who is around.

In a conventional business organisation I’d probably be reporting ‘The initial research was approved’. In Richard Noble’s ‘flat’ organisation if a guy wants some research he talks it over with his peers and then it happens – and so it’s already happening. In my darker moments I have to confess that I am not a totally anointed convert to Richard’s Flat Organisation ethic – it seems to me to be flat with a certain number of lumps in it, converging on a Vesuvius-sized mountain in the middle called Richard himself. But in instances like this no person can deny it works. It has cut the crap. Completely.

And as far as my big-change-at-late-stage reaction goes, I corner Engineering Director John Piper after the meeting and put the thought to him with my customary tact and diplomacy.

John smiles his quiet Buddha smile and says simply; “This is not a big change”.

No? Oh….

This answer so takes the wind out of my sails that I don’t even think to say ‘Well, it’ll do until a big change comes along’. I am just left scratching my own ear and thinking there’s got to be a bit more to it than that. 

And so there is. We’ll come to it.

What is undeniable is that this man Brian Coombs has had what the team call a Cheese Before Bedtime moment.

If you eat cheese at bedtime, so goes the old saw, you will not be able to sleep. Your thoughts will vault far and wide, and indeed under the influence of a particularly virulent Stilton may cause you to leap from your bed at 4 a.m. crying; ‘Eureka!’  Which tends to wind up the Missus a treat.

In reality a BLOODHOUND engineer does not cry ‘Eureka!’  He or she is far more likely to be found staring into space for a while and then saying those ominous words; “Hey guys, I’ve got this idea….”

Well, meet Brian Coombs, who had this idea…..

This Coombs looks more like an instructor of an Outward Bound course than a scientist. Tall – well, maybe he isn’t excessively, but almost everybody looks tall to me – muscular, and not an ounce of fat on him. In his late thirties, he could star in an outdoor-type movie any day. (As, coincidentally, could his fellow Senior Mechanical Designer, Mark Chapman. These two are oppo’s in the quite literal sense, since their desks face each other and if either one of them gets the faraway-cheese look then the other can hardly fail to notice it in the odd moments when he raises his eyes from his own computer screen).

Brian Coombs is by hobby a mountaineer, although the only mountain he has time to climb these days is the mental cliff-face of BLOODHOUND. A man who was not a genius at school, but subsequently bulldozed his way into achievement in engineering academia by simply – well, bulldozing. Working hard. At one point he worked as a toolmaker by day and studied by night for the next engineering qualification. After education he went into various motorsport designing jobs, ending up as a Formula One transmission designer.

But he is his own man, this Coombs. F1 became boring – “You get pigeon-holed in a speciality” – so he made some slight life-changes. Like moving with his wife and small daughter to a little village in the west of Ireland because it was peaceful and because Irish schooling is better than English. Like turning freelance and commuting to jobs via Ryanair out of Cork. Like joining John Piper on the Dieselmax Land Speed Record team…..

Brian joined BLOODHOUND because here he wouldn’t be typecast into transmissions. Here was room for lateral thinking. Here he could sit back sometimes and chew the cheese for a while and then say: “Hey folks, I’ve got this idea….”

So – why did he get this idea?  And why – what looked like to me – so apparently late-on in the design process?
The answer is profoundly interesting. It is a story of how a flexible design team tackles an engineering progression into the complete and absolute unknown. An arena of dragons nobody – nobody – has ever entered before.

John Piper later explained it to me, with his finger exactly on the pulse. “This is the Concept Design Phase. This is when we come up with ideas, interrogate them, and make changes. It’s not only allowed – I expect it to happen. If it didn’t, we wouldn’t be creative. And if we aren’t creative, we go down the same paths as all the others. And no new records come from doing it the same…..”

At the beginning of time – BLOODHOUND-time, that is – aerodynamicist Ron Ayers and designer Glynne Bowsher began by designing the car’s fuselage and calculating the aerodynamic drag thereof at Mach 1.4, for the obvious reason that if you have a handle on the drag value then you know how much power you’re gonna need to overcome it. Unsurprisingly, the answer was – a lot. They considered twin jets – but not enough grunt. They considered twin – and even, briefly, triple – rockets – possibly enough grunt, but power delivery a tad on the sudden side of sanity. So they came up with an EJ200 jet plus a 16” diameter rocket. With the jet weighing 1,000 kg and the rocket less than half of that, the obvious solution was jet underneath and rocket on top, so as to keep the Centre of Gravity as low as possible. So far so good.

However, there is another Gremlin in the mix. Called stability. Clearly straight-line stability is essential, and clearly aerodynamics make an ever-increasing contribution to same as the speed rises.

But….

There is a second and very much associated plane of stability called dynamic – in other words, stability fore-and-aft, expressed in terms of axle loads. In an ideal world BLOODHOUND would have a 50 / 50 weight distribution between front and rear wheels from standstill right up to 1,000 mph and back down to stop. But the objective of going highly supersonic at a height of six inches is very far indeed from an ideal world, and several villains trip onto stage.

One of them is the immense high pressure build-ups behind supersonic shock waves. The team knew this would happen – but until various possible configurations had been laid down as CAD designs, and until those CAD designs had been through the maw of Computational Fluid Dynamics analysis, nobody really knew quite where they would happen. The hope was that the most vicious high-pressure bursts would take place behind the car – but as time went on the inquisitor which is CFD revealed that this was, sadly, not entirely the case, and that BLOODHOUND would be generating rear-end lift from transonic speeds onwards to a degree which was definitely not good for the health. Solutions – indeed, very elegant solutions – are now being found for this, but the problem may never to go away entirely.

Supersonic Sod’s Law

And then there is drag. A fundamental principle of Supersonic Sod’s Law is that almost all changes from the original sleek conception – such as the minor detail of adding rear wheels – tend to add drag. And more drag means you need more power. And so the rocket grew until it weighed 400 kg including casing, catalyst, and solid fuel.

Whacking out some 25,000 lbs of thrust very suddenly indeed. And with the centre-line of that thrust situated a whole metre above the C of G of the car.

Problem.

This problem is called rocking-couple, or pitching moment, and its action is obvious: if you have a massive kick in the ass that far above the C of G, not only does the whole assembly look a bit surprised and start going a lot faster very immediately, but it also wants to pitch nose-down. Big time. In fact it almost instantaneously increases the front axle load by well over a tonne – getting on towards a 50% rise – and decreases the rear axle load by the same amount.

Oh, and the BLOODHOUND run-profile calls for Andy Green to accelerate initially on the jet, then fire the rocket as the speed rises through 300 mph. So you’ve got this massive weight-shift occurring – WHAM – just as you’re passing through four-and-a-bit times the maximum UK national speed limit….

Not ideal. Not insuperable – but not ideal.

One way of tackling it is by (automatically) activating the winglets at rocket ignition to provide lift at the front and downforce at the back. This will work, but it does have its drawbacks. One is that if you’re creating that much lift – either up or down – it comes with a not insignificant penalty of aerodynamically induced drag. Another is that if the winglets are sufficiently big and powerful to do that at 300 mph they could become just a tad too much of a good thing at 1,000 mph – a tiny touch sensitive, or twitchy as one might say. Then there is the minor matter of what happens in the case of a winglet actuation failure – a many-million-to-one shot, but one that must be considered.

So – it can be done. But as research data comes in at an ever-increasing rate – of which more anon – there is a growing feeling within the team that it might be awfully nice if it didn’t have to be done. Or at least not so drastically.  And – especially – not all-of-a-sudden passing 300 mph. Engineering-wise it would be noticeably more cuddly if the winglets were aerodynamic trimmers rather than fairly major controls…..

Which is when Brian Coombs got stuck into the Stilton. Thinking laterally (or to be more literally accurate, vertically), he asked himself  “What if…. what if we swapped the rocket and jet over?”  On the face of it a silly question because with a 1,000kg jet you obviously you put the jet at the bottom and the rocket on top to keep the C of G as low as possible. Obviously…..

But now the rocket is 400 kg. Brian tapped the figures into his Centre of Gravity programme and found that with the jet on top the C of G did indeed rise upwards…..

By something like 45 mm.

About two inches. Almost negligible. Increase the rear wheel track by the same or a tad more and lateral stability is unchanged.

A tiny increase in drag for a massive increase in pitch stability, because now the rocket thrust-line would be kicking BLOODHOUND squarely in the ass – being very close to the C of G – rather than a metre above it.

But how? How could this miracle be? Well, in retrospect the facts are reasonably simple, as facts in retrospect so often are. Swap the jet and rocket over and you raise the jet 500 mm. At the same time, because the rocket is about half the diameter of the jet, you lower the rocket 800mm – and lo, the C of G comes out practically unchanged. That is the reality.

So Hosanna to Brian Coombs, who was the first to think of this – the first to look at the calculations with a revolutionary eye. The first to challenge rocket-over-jet, which – let us be honest – had become something of a design mindset. Oh, it would have been challenged anyway – but Brian was the first.

Problem solved. Buy Brian a curry, fill him up with Guinness. Yes?

Well, yes. Or at the very least yes-ish. Because this is not the end of the problem, by any means. You raise the jet up higher – and you get a similar down-pitch problem but in the lower speed range when you’re accelerating solely on the jet. Not good – but almost certainly the lesser of two evils, since with the jet you can at least control the thrust, whereas the rocket (which is anyway more powerful than the jet) just gives you an unceremonious wallop in the backside.

I don’t know. We shall see. It may not work out. Maybe the low-mounted rocket will churn up the desert something seriously horrible – or maybe it won’t. People are working on it – but I obviously don’t know.

But one thing I do know.

Since I started looking at BLOODHOUND ten months ago things have changed very, very much. Then there were a lot of ideas, some of which made it to CAD and then on to CFD analysis.

Now – things are much different.

I see the progression as a sort of inverted triangle. At the bottom point was Richard Noble snarling in the dark: ‘It can be done’. Then, further up the triangle, an embryo team determined to do it. Then, still further up the triangle, broader recourses, many, many more CAD records to form bases for further experimentation, hugely enhanced computing power, more inputs from Product Sponsors….

Now, research which a year ago would have taken four weeks can be processed in four days. It makes a difference – a big, big difference.

Which, quite simply, is the answer to my ‘why so late ‘ question. The problem was not so obvious before – but now it is. A rocket-jet swap-over would have meant a massive re-design ten months ago – but now it doesn’t. Major, yes – but given the research already in the can, not massive.

This, to use John Piper’s words, is what the ‘Concept Design Phase’ is about. At some point in the not-too-distant future the basic design will be ‘design freezed’ and the team will move on to the Detail Design stage. Once into that, any major change with its inevitable knock-on effects will be about as popular as a Jihad gunman crapping in the Vatican. As John Piper puts it; “That’s why we have to flush these ideas out now”.

So if you’re going to say; “Hey folks, I’ve got this idea…..”  now is the time to do it. Something of a last-chance saloon.

A slice of Stilton before you turn in, Brian…..