It is the intention of the BLOODHOUND Project to achieve many wondrous and awesome things. Many awesome things.

Progress in composite materials. Progress in ground-interaction aerodynamics. Progress in applied electronic solutions which would have been unimaginable a short decade ago. Huge progress in rocketry. Progress in acoustic vibration research. Progress in telemetry.

Progress – in particular – in sexing-up engineering as a career-option for young people in the education system.

Oh, nearly forgot – and setting a new Land Speed Record, hopefully raising it by over 30% in the process. 

When I use the words ‘sexing up’, Richard Noble looks at me sort of slant-wise and Andy Green assumes his deadpan expression, which he is rather good at. But I stick to my guns. For whatever reasons – and far be it from me to even hint that the ever-changing political leaderships of the education system had the foresight of a gerbil for at least two decades – engineering has drifted into becoming un-sexy. Slog through a difficult university degree and then spend a career in a white coat with poor pay doing things you can’t talk about – yeah, real attractive. That’s the perception. It ain’t necessarily so – in fact it very much ain’t so – but that’s the perception.

So BLOODHOUND sexes it up. Makes engineering what it really is, which is exciting. Hopefully goes some way to changing the image. If it does only that – and it aims to do much more –  BLOODHOUND will have done Great Britain a great service.

Bit of a pity, then, that there are two small grains of sand in the works which the entire engineering effort can do exactly nothing about. Or almost nothing.

The first grain is the human body.

And the second grain is the effect of G force upon same.

Now writers are often called upon to write about things they don’t know about. But G, I do know. In the course of 25 years of aerobatic displays it was a bullying daily companion – the sort of guy who feels compelled to slap you on the back every time you meet him with a force that threatens to drive your backbone out through your nose. I have overcome G, been punched in the gut by G, hit in the head by G, have received spinal injury from G, and had G creep out of a dark alley and sandbag me when I didn’t expect it. Oh yes, I know G…

Or at least, I thought I did. Let me come back to that.

First, a very quick guide to G force. Those of you who know perfectly well about G, feel free to yawn and scratch for the next couple of paragraphs.

The human organism was designed to run around on the surface of this planet on his or her own two feet at 1G – one gravity. It was not designed for anything else. Specifically, it was not designed to sit in an aeroplane and pull back hard on the stick so as to generate 6, 7, maybe even 10 times one gravity by courtesy of centrifugal force. With great respect to all the religions of the world, I sometimes have this whimsical vision of the Great Chief Designer in the Sky looking down on the human frame and saying “B – er, blow – me, I didn’t think they were going to do that with it…”

The fundamentals in aircraft are well known. Positive G – pulling back on the stick – presses you into your seat and makes your blood try to fall down your body and squirt out of your feet. Blood carries oxygen and sugar, and the brain very rapidly realises it’s being short-changed. Brain instantly sends a sharply worded memo to heart, and heart speeds up and the arteries open up, thus pumping more blood into the swede. This is either enough to solve the problem or it isn’t. If it isn’t – if the positive G load is too much – then first the eyes shut down (G black-out) shortly followed by the brain doing ditto, known as G Loss Of Consciousness (G-LOC). This is a considerable over-simplification and there are many more nuances – especially time exposure, which we’ll get to – but accept it as a broad-brush scenario.

Negative G, fairly obviously, operates the other way round. Push the stick forward and your weight comes off the seat and up into your harness. Push forward harder and you can rack up - 3 G, maybe - 6 G negative (- 3 being peanuts, - 6 being something you pay attention to). Negative G shoves the blood up into your head so it squeezes the brain (increases intra-cranial pressure), so the heart slows down and the arteries contract in an attempt to damn the flow.

There is a lot of legend attached to negative G – tales of vision ‘red-out’, blood vessels bursting in the eyes, etc. And well yes, you can get vessels pop in the whites of your eyes occasionally – which makes you look satisfyingly demonic for a few days, but is otherwise normally harmless and dissipates by itself. But I’ve never experienced ‘red-out’, and know of no other pilot who has. No – the main feeling associated with negative is that someone with a sense of humour has connected a high-pressure hose to your bonce and turned the tap on. Which makes negative G uncomfortable, but actually less dangerous than positive.

Except for one small thing. G-reversal.

If you’re flying along level at 1 G and you suddenly yank on + 8 G, that’s a G change of + 7. Which, if you’re used to it and tense your stomach muscles hard, the body can cope with. But if you push - 5 G and then suddenly reverse it and pull + 8, that’s a G change of + 13. And you’re asking the cardio-vascular system to switch from full negative G defence to full positive G defence in maybe two or three seconds…

At which point the body says “Ya gotta be kidding, Buster”, and promptly goes to sleep.

 

Between Heathrow and Westminster

So what has all this got to do with BLOODHOUND? The Design Team have just spent 3 years and more than £2 million trying to make sure, among other things, that the very last thing BLOODHOUND will be is a flying machine. So where do all the G problems come in?

The answer of course is during acceleration / deceleration. If BLOODHOUND had a 60 mile long dead-flat alkali desert playa run-track then accelerating and stopping could be a bit more leisurely – but there ain’t no such run-track anywhere on the planet at this time in history. The Hakskeen Pan provides 12 miles (10 miles with emergency over-runs of a mile each end). Which may sound a long way when you say it quickly – but in fact it isn’t. To give it perspective, it’s about the distance between Heathrow Airport and the Houses of Parliament in Westminster. Okay, put aside all the jokes about being lucky to average 10 miles an hour over the this particular 12 mile run-track – but the fact is that BLOODHOUND has to accelerate from 0 to 1,000 mph and then decelerate back to 0 again within the distance between Heathrow and Westminster. Preferably without demolishing the House of Commons in the process, however much the thought may have its passing attractions.

Let’s put that further into perspective. A serious record run takes 90 seconds or so – which is an AVERAGE speed of about 400 mph. Average. So if Andy Green pulled the trigger on BLOODHOUND at the instant an aeroplane doing 400 mph passed over Heathrow, he would accelerate to 1,000 mph and stop by the time that aircraft overflew Big Ben.

That is – going some. Think about it.

To do that, the acceleration has to be at about 2.5 G, followed almost immediately by deceleration of around 3 G.

And that is linear acceleration – not being shoved down into your seat and then up out of it, but heaved back into it for 40 seconds followed almost instantly at the apogee by being heaved forward into your straps for another 40 seconds.

All the same, doesn’t sound too bad at first glance. 2.5 G one way and 3 G the other? Nah…

The man on the Clapham Omnibus might pass out about halfway through the proceedings (which a recent journalist actually did, when Andy Green took him for a flight reproducing about half the G involved), but a 5.5 G change to a fighter pilot like A Green? Nah, peanuts. (Peanuts to me, too, who has spent more than half a working lifetime grappling with far more savage G reversals than that. I merely mention this, lest anybody should forget when Green mysteriously goes missing the day before the runs start and they’re looking for another driver…) So – peanuts G…?

Well, actually… not peanuts.

Let’s glance back at the way the G works. Answer within five seconds which way the G force is gonna go during acceleration. One, two, three – and the chances are you’ve already said positive G. Obvious, innit? Accelerating – positive G…

Er – wrong.

Think about it. You are in a reclining seating position – in fact not all that reclining in BLOODHOUND for reasons which will shortly become obvious – but nonetheless reclining. So the acceleration force is hitting you in the front. So which way does your blood slosh? Well, backwards…

Up to your head.

Which is negative G.

Now decelerate, with 3 linear G pulling the blood down into your feet.

Which is positive G.

This may be counter-intuitive but it’s obvious when you think about it – you accelerate under negative G, then immediately decelerate under positive G.

Now remember what I said. That the biggest problem with G is abruptly going from negative to positive…

Just like this.

Problem. And also remember I said that time-exposure to G is a big factor. And 40 seconds of negative followed by 40 seconds of positive is quite a long time exposure in one hit…

Problem again.

Not, in fact, insurmountable. But undoubtedly a problem.  A fit fighter jockey well-versed in the use of AGSMs – Anti G Straining Manoeuvres, largely meaning paying off your overdraft and breathing deeply and clenching stomach and leg muscles under positive G – should be able to take it. And indeed, should it prove to be worse than anyone – including Andy – thinks, then engineering does in fact have at least one relatively easy shot in its locker, despite what I said earlier, in the shape of G-trousers, should they become necessary. The normal operating systems for fighter G-suits are complex, expensive, weighty, and would take up space which BLOODHOUND could certainly use for other purposes. But a G-suit in BLOODHOUND doesn’t actually need all those systems – it’s just a one-time activation which could pick off, say, a pressurised nitrogen system to inflate the fashion accessory pretty simply. Make people’s brains ache, but with a team of genii on the job could be done in the field if it came to it.

So the G-reversal problem is not insuperable. But – especially coupled with noise, heat, and probably stupefying vibration – it sure ain’t going to make life any easier.

 

G the illusionist

And nor is the other effect of high linear G – somatogravic illusion.

Now ‘somatogravic’ may sound like something you’d order in a Chinese restaurant along with sleet flied lice. But in fact it’s to do with the balance organs in the human middle ear. These are three tiny semi-circular canals with liquid in them, which provide the brain with information on roll, pitch and yaw – nature’s own liquid-gyro instrument panel, if you like.

Only thing is, once again it was designed for a homo sapiens bouncing around on his two feet under a 1 G condition and maybe coshing the odd Brontosaurus on the head in his dedicated quest to invent the Big Mac. It was not designed to cope with multiples of G.

So when you throw minus 3 G at it under acceleration, the sensors in the canals – the otiliths – swing towards the back of the swede.  Which says to the Jurassic-designed brain, which ain’t never heard of no - 3 G: “Hey, sh – er, bother – I am falling over backwards!”

In other words, pitching up.

Which is a somatogravic illusion.

Which is well known to aviation medicine and has killed a considerable number of pilots. It says here.

What happens – it says here – is that the take-off obviously involves acceleration – it not being a particularly successful take-off if it doesn’t – but the pilot perceives the acceleration as a pitch-up because of the inner-ear sensory reaction. And after leaving the ground said pilot shoves forwards on the pole to cure same. Shoves forward enough indeed to impact the surface of the planet, which kind of ends all speculation. Especially – it says here – prevalent in aircraft carrier cat-shots – catapult launches – at night, when the aircraft is launching into a black void with no visual reference. (Although Andy Green, who has more experience of it than most people on the planet, personally finds it more menacing when launching off in a fast-jet into low cloud in daylight).

You will note there is a certain element of ‘It says here’ in the above. I am not sceptical in any way about the reality of somatogravic illusion. However fairy-tale it may sound to talk about the ‘reality’ of an ‘iIllusion’, it is quite certain that a number of pilots are no longer extant due to its affects. How many? Well, far be it from me to be sceptical, but I note three factors. One, that the pilots concerned were all highly trained and knew perfectly well to get on the instruments immediately and believe them and not their body impressions. Two, that there is an ever-so-slight tendency for aero-medicos to form a theory which becomes rather like an open box into which accident investigators can shove unsolved cases. And three, that the pilots involved are no longer around to discuss the matter. So what else might have gone wrong? I obviously can’t know, but…

Well, well. None of that changes the fact that somatogravic illusion definitely does exist. It is not just a confusing word. It is probably most often a black-or-white hole acceleration flying problem – but give it enough acceleration-deceleration on a blinding flat desert… and it’s a problem. The balance-impression fights with the eyesight input and the two come up with a compromise…

Said compromise means that during acceleration the desert appears to tilt upwards to about 70 degrees – so you seem to be driving up a 70 degree slope. Then when you decelerate you feel like you’re pointing down a cliff at about 80 degrees…

A compromise between eyesight and feeling? How much of a compromise? Well, that depends to an extent on who you are…

 

You won’t have experienced this…

Apart from high-performance pilots, this is almost completely an unknown phenomenon. On the deck, it is shared by perhaps 300 people in the world, most of them jet-car drag racers and five or six of them Land Speed Record holders at one time or another. All say the same thing happened to them. Accelerate – apparent pitch-up. Decelerate – particularly on decel with parachute braking, possibly worsened because it comes in jerks – apparent pitch-down.

Same for Richard Noble in Thrust2, and same for Andy Green in ThrustSSC.

Except that it wasn’t quite the same.

There was one big difference. Andy, with his fast-jet experience and very expensive and part-secretive training, was expecting it. Probably not to the extent it happened, but he was expecting it. Richard Noble, 14 years earlier in Thrust2, had never heard of somatogravic illusion. And Thrust2, which was light(ish), fairly draggy, and had a relatively large brake-chute did G rather well, especially on deceleration, when it could rack up 5. With a very upright seating posture the loading didn’t bother him too much bodily – but the somatogravic illusions worked just fine, and came gift-wrapped as a complete surprise. Under deceleration he felt as if he was driving down a cliff…

Which, if you’re trying to ignore the illusion – park it in a sort of think-about-it-later file – makes life just a tad difficult.

So for Richard Noble in 1983 – big issue. For Andy Green in 1997 – an issue, but only that. An issue.

“You feel your feet rising up over your head during accel. You feel you’re tipping backwards. But you know it only feels like that. Vision rules. Vision overcomes the illusion”.

Well… yeah. If A Green says that – then, well, yeah.

Except I may have a little idea about the power of the illusion, and what it takes to overcome it.

Illusions can be very disconcerting…

 

The day the pits tipped 40 degrees

Despite all my acquaintance with G I have never actually experienced somatogravic illusion in an aircraft. In my bank account – particularly in one of those decel phases which all aviation enterprises go through with tedious regularity – yes. But in an actual aeroplane, perhaps surprisingly, no. Probably because I’ve never had 20,000 lbs of afterburning thrust to kick in suddenly to produce prolonged and massive acceleration.

But I have experienced somatogravic’s sort of second cousin, somatogyral illusion (the ‘leans’) which also comes from the inner ear.

Against all odds this was not in an aircraft at all. And this really is against all odds. But I experienced it on a Vincent 1000 motorbike while practising for a 24 hour speed record on the Montlhery circuit in France 45 years ago. Montlhery was a banked speed-bowl with two short straights. And after about 30 minutes circulating at around 120 mph there came a lap when I swept down the banking into the pits straight…

And the pits straight was angled at some 40 degrees. Even now, 45 years later, I remember having the flash-thought that any second now some mechanic was going to slide down the slope on his bum right in front of me.

Illusion, of course.

But very powerful illusion. Very, very powerful.

I remember it seeming a massive effort to pull the bike upright – and then suddenly the world snapped back into place and I wasn’t making any effort at all. Very difficult to explain, that. But that was the way it took me.

Forget your computer illusion games. This was for real.

And it was weird. Just – weird.

So if my kidnap plot fails – very unlikely, but you have to allow for these things – then spare a thought for Andy Green when BLOODHOUND starts running. Massive noise, massive instrument-monitoring task, massive vibration, probably massive heat, massive bodily G effects.

And on top of all that, the Great Illusion…