G-Force, Jerk, and Passing Out In A Centrifuge

G-Force, Jerk, and Passing Out In A Centrifuge


– This is the Royal Air Force
training centrifuge at Farnborough. And the team here are
going to push me as far as they’re allowed
to push a civilian. – The centrifuge has been here since 1955. The device was originally installed
for research purposes, although these days it’s used for training
as much as it is for research. What it does is recreate the forces
that you feel in an aircraft. For our routine pilot training, the
first time pilots go on the centrifuge, we expect them to get up to 5g
without a g-suit, and then up to 7g
with an anti-g-suit. – Now I’m not taking a
significant risk here. I’m healthy, I’ve pulled a few gs before. And the human body can take this. And the reason we know that
is because in the 1950s, the US Air Force used rocket sleds
to push volunteers to incredible speeds. But that rocket-powered acceleration
wasn’t the dangerous, or even the really
high-g part of the test. See, high-g acceleration takes a lot
of incredibly expensive rockets or a big ol’ centrifuge like this. But high-g deceleration? All you need for that is a wall. Or for something less destructive,
like the rocket sleds, you use scoops
dropped down into a water trough. USAF flight surgeon John Stapp, aboard the rocket sled
Sonic Wind Number One, holds the record for the
highest sustained g-force anyone has ever voluntarily endured, 25g for 1.1 seconds,
with a brief peak over 46g. And he was badly injured,
but he survived and he recovered and he
lived to the age of 89. The human body is an incredible thing particularly because
we didn’t evolve for this. – G-tolerance is something
that’s innate in all of us. Some of us have high G-tolerance.
Some of us have low G-tolerance. Over the years, people’s g-tolerance
doesn’t really adapt. Any shortfall in g-tolerance
has really got to be made up by physical exertion
and the g-straining manoeuvre. – What this centrifuge doesn’t have
is much jerk. And jerk is a technical term. In the same way that acceleration
is the rate of change of speed, jerk is the rate of change
of acceleration. And because it takes time to
spin up and spin down… Oh, here we go! Even though
the acceleration is high, the jerk here is relatively
low, about 1g per second. Jerk is the difference
between a rocket to space which might take a couple of minutes
to reach peak acceleration and a fighter jet, where manoeuvres might
change the G force acting on you in a fraction of a second. And it can go further than that. You can measure the rate of change of jerk
which is called snap or jounce. The two derivatives after that are called
crackle and pop but they’re not all that useful
in the real world. – As we increase the G
that Tom is exposed to, the blood’s going to be
pushed down into his feet, and he’s going to have to work really hard
to push that blood back up to feed oxygen to his brain
to keep him conscious. And in real life, we would be expecting
that person to be flying an aircraft whilst doing that. – I’m getting a little bit of grey-out. I can’t quite see. Agh. – We teach the anti-g straining manoeuvre
which composes of two separate parts. First of all, muscle tensing, so both the buttocks and legs
squeezing the blood vessels to try and get the blood
back up into the chest and the head. But also the second part
is a breathing manoeuvre which increases the strain in the chest directly increasing the blood pressure
to the great vessels in the chest and keeping him conscious. And when you lose
blood pressure to your head, you could even lose consciousness. And we term that g-induced
loss of consciousness or G-LOC. [gasping] – Blimey! I lost everything there. Wow. – G-LOC in itself is not dangerous. But the real point is when you G-LOC
you’re flying an aircraft. So if you’re not able
to fly that aircraft, I’m sure you can appreciate
that that is a real problem. – Because of John Stapp
and all the volunteers like him that rode the rocket sleds, there is a lot of research into acceleration on the human body. How many gs can be withstood
for minutes at a time? How many gs can be
withstood for brief moments? And how many can be withstood with
training that I clearly don’t have. Rocket scientists and
roller coaster designers use that data. But there’s not much research into jerk because how do you test it without
also testing acceleration? Over on the Starrship channel,
I am not passing out pulling gs with the
Blades aerobatic team(!) And as for this video, thank you so much to all the team at the
RAF Centre of Aviation Medicine, to the team at Qinetiq, and
to the team at Starrship.