When doing head-down, why don't skydivers/tunnel fliers get the blood to rush to their heads?

[el_chester 4]

It is quite obvious to me that the blood does not rush to the head of head-down fliers, because otherwise we would constantly have people fainting and this would be a comfort and safety issue.

However, when I was asked by a friend WHY this didn't happen, I could not really find a convincing explanation of the physics of it.

TUNNEL FLYING
How is being "on your head" in the tunnel different from being "on your head" in the room next to the tunnel, in terms of blood weight/acceleration. Why can the guy outside the tunnel only tolerate it for a short while and get a red head, while the guy flying in the tunnel doesn't experience the red head?

AIRPLANE JUMPS
During the acceleration phase of an airplane jump, one could say it's conditions similar to zero-g. However, once in terminal velocity, the blood from the body would still "rush down to the head", wouldn't it?

As stated above, clearly it is not the case that blood rushes to the head on head-down, but WHY?

Anyone who knows what they're talking about care to explain the physics of it?

--
Be careful giving advice. Wise men don't need it, and fools won't heed it.

[ianyapxw 0]

I can't comment about tunnel, but you realise an aeroplane jump is maybe 30s of freefall? I don't think people pass out that fast.

Also, I wonder whether the fact you're exercising (using your muscles) has anything to do with keeping the blood circulating to all parts of the body.

[el_chester 4]

Yeah, I know it's a limited time and probably too short to pass out, –but even if not passing out–, if one stands on one's head "on the ground", the discomfort is noticeable immediately, and I haven't heard of anyone feeling this while flying head down.

--
Be careful giving advice. Wise men don't need it, and fools won't heed it.

[ianyapxw 0]

Maybe it has to do with the fact that in a headstand you're supported by your head while flying head down you're supported by your legs

[Bufobufo 0]

I stand corrected if I'm wrong, but I think it might be the other way around, el_chester.

In freefall once you reach terminal you should feel about the same as if you were hanging upside down if you are doing a headdown. Should be even more obvious in the tunnel since you basicly are terminal from the moment you enter.

Can't it be the same thing as when you make a bad exit from the plane, and in the evening notice half your leg is blueish from scrapes etc;you are just to focused to notice?

[manseman 0]

For me, a headstand or handstand is much more taxing in every way than just hanging upside down. I'm guessing that's the difference and that flying hd is simply more like hanging from your knees than standing on your head/hands. Standing requires a lot of muscles to be activated.

[el_chester 4]

Bufobufo

I stand corrected if I'm wrong, but I think it might be the other way around, el_chester.

We are actually making the same point about "once at terminal".

Bufobufo

Can't it be the same thing as when you make a bad exit from the plane, and in the evening notice half your leg is blueish from scrapes etc;you are just to focused to notice?

I also thought about the focus thing… but not fully convinced by that theory. More inclined to go for the "relaxed" vs. "tense" explanation.

--
Be careful giving advice. Wise men don't need it, and fools won't heed it.

[Joellercoaster 6]

I reckon this is on the right track.

Headstanding, you are supporting your body on your neck muscles. Intuitively, it seems like this would make it harder for blood to flow back out of your head again.

Handstanding, less so, but it's still a lot of upper body muscles working hard.

Head down in the tunnel, your legs are doing more of the work. Your upper body is less tense, and blood can flow more easily through your neck.

This is easy to test though - go find a kids' playground, and hang upside down by your knees for a while. Then compare to standing on your hands, then your head.

Report back

--
"I'll tell you how all skydivers are judged, . They are judged by the laws of physics." - kkeenan

"You jump out, pull the string and either live or die. What's there to be good at?

[potatoman 0]

Now this is a good question.

I am interested in hearing an educated answer.

You have the right to your opinion, and I have the right to tell you how Fu***** stupid it is.
Davelepka - "This isn't an x-box, or a Chevy truck forum"
Whatever you do, don't listen to ChrisD.

[pchapman 261]

el_chester

It is quite obvious to me that the blood does not rush to the head of head-down fliers, because otherwise we would constantly have people fainting

Having blood rush to one's head doesn't make one faint. It might be uncomfortable and distracting but there's no fainting involved, which is normally about lack of blood flow. Adding multiple negative G's is tough, and aerobatic pilots have to acclimatize themselves to it, but negative G on its own doesn't cause fainting.

Kids can hang upside down from monkey bars in the playground, and they don't all faint and fall.

If one doesn't notice something in freefall it would be because one is really focused on other things -- just like there are times when one hardly notices the wind noise (or one's dirt alert...) in freefall.

The 'red head' comment is interesting. Don't know to what degree that applies. Just guessing, but possibly body movement in freefall or tunnel helps promote circulation and reducing blood pooling. And like manseman said, if one is doing a hand stand, especially if not used to doing it a lot, the high muscle tension may cause one to increase pressure in the head too, just when one should be relaxing as much as possible to avoid adding blood pressure at the head.

[mjosparky 3]

pchapman

***It is quite obvious to me that the blood does not rush to the head of head-down fliers, because otherwise we would constantly have people fainting

Having blood rush to one's head doesn't make one faint. It might be uncomfortable and distracting but there's no fainting involved, which is normally about lack of blood flow. Adding multiple negative G's is tough, and aerobatic pilots have to acclimatize themselves to it, but negative G on its own doesn't cause fainting.

Kids can hang upside down from monkey bars in the playground, and they don't all faint and fall.

If one doesn't notice something in freefall it would be because one is really focused on other things -- just like there are times when one hardly notices the wind noise (or one's dirt alert...) in freefall.

The 'red head' comment is interesting. Don't know to what degree that applies. Just guessing, but possibly body movement in freefall or tunnel helps promote circulation and reducing blood pooling. And like manseman said, if one is doing a hand stand, especially if not used to doing it a lot, the high muscle tension may cause one to increase pressure in the head too, just when one should be relaxing as much as possible to avoid adding blood pressure at the head.


If you start pulling heavy negative G’s you can go into what is called a redout This is where blood rushes to your head under pressure. It can cause retinal damage, stroke and may lead to loss of consciousness. G-LOC.

Sparky

http://en.wikipedia.org/wiki/Red_out

My idea of a fair fight is clubbing baby seals

[pchapman 261]

This post digresses from the -1g environment of head down skydiving so isn't relevant except to discuss negative G in general.

While I have no professional physiology training, I've been a little bit in touch with aerobatics and acceleration research for many years, so can debate this all day. So excuse me if I go a bit overboard in my response.

Yeah, that redout thing is a partial myth as far as I know, from the very early days of aerobatics. Even the minimal wikipedia article kind of says so, wondering if it is the lower eyelid moving up.

Aerobatic pilots just get used to the negative G's, working their way up. You can get bloodshot eyes. Never heard of strokes but who knows -- not normally a concern of aerobatic pilots but anything is possible. People die just lying in bed too. G-LOC is normally only from positive G. It is tougher to go from negative G to high positive G since the body is sensing high blood pressure and thus thru vagal nerve response lowers the heart rate, which isn't what you want if switching quickly to high G.

Certainly long duration negative g will be tougher on the body but nobody every does that.

I can also defer to Fundamentals of Aviation Medicine 2008:

Quote

During -Gz, intracerebral blood pressure increases.
Congestion of the face and a subjective sensation of eye
bulging occurs; this can become intensewith increasing -Gz.
There is upward movement of the abdominal contents and the work of breathing is increased. Inverted flight (-1 Gz)
can be unpleasant, but tolerable. Between -2 and -3 Gz,
there is severe facial congestion and occasional reddening
of vision. Most subjects can tolerate -3 Gz for 5 seconds,
although some can reach -5 Gz without injury (10,22).
The feeling of facial congestion becomes intense at -3 to
-4.5Gz. The restraints, which are supporting the entire mass
of the body, cause additional painful sensations. Competitive
aerobatic pilots describe sustaining up to -9Gz for very brief
durations.
Some of the adverse effects of -Gz derive from
increased arterial blood pressure in the head, especially
where it is unopposed. Within the skull, where increased
arterial pressures are balanced by increased pressures in the
surrounding cerebrospinal fluid, adverse effects are generally
not seen (23). Where increased pressures are unopposed,
injury can occur. Facial petechiae have been described by
competitive airshow pilots. Nose bleeds and subconjunctival
hemorrhage have been reported due to high -Gz.

[DeeBeeGee 0]

you know, i never noticed until today that there are no playgrounds in the square mile. lunchtime ruined.

[jumpwally 0]

Thats cuz skydivers breathe thru their skin,,all that air pushes on the corpusles......forcing blood to pump thru out.....

smile, be nice, enjoy life
FB # - 1083

[format 0]

jumpwally

Thats cuz skydivers breathe thru their skin

Yeah but is it a F-111 or ZP skin?

My vager is on focus. If you set your mind to it, you have no clue where is UP

What goes around, comes later.

[allons2m 0]

I’ll open by saying that I’m no physicist, but I know that free fall is zero gravity. Sounds odd when there is so much wind resistance, but whether you are at terminal or not, if you are in free-fall, you are in zero-g. This is stated in the equivalence principal of physics. Being in a state of zero gravity in free-fall, I would speculate that blood would flow even more freely than it does when we are on the ground.

“Counterintuitively, a uniform gravitational field does not by itself cause stress or strain, and a body in free fall in such an environment experiences no g-force acceleration and feels weightless. This is also termed zero-g.”

http://en.wikipedia.org/wiki/Weightlessness

and
http://en.wikipedia.org/wiki/Equivalence_principle

[Joellercoaster 6]

allons2m

whether you are at terminal or not, if you are in free-fall, you are in zero-g

No.

--
"I'll tell you how all skydivers are judged, . They are judged by the laws of physics." - kkeenan

"You jump out, pull the string and either live or die. What's there to be good at?

[StreetScooby 5]

Great question...

We are all engines of karma

[allons2m 0]

Joellercoaster

***whether you are at terminal or not, if you are in free-fall, you are in zero-g

No.

It’s unfortunate that your ignorance to the natural world impedes your ability to grasp such a concept. I find it amusing that you statement above starts with, intuitively; when clearly we are discussing a counter-intuitive concept. If you have value to add to this conversation please do. Otherwise, I suspect this will be my last engagement with a troll the likes of you.

[Pablo.Moreno 0]

because your blood is accelerating at the same speed as the your frame of reference hence your skin.
Now if it is either in the tunnel or in the sky your frame of reference and blood are both falling relative to the wind, but in the tunnel relative to everywhere else you are not moving and in the sky you are losing altitude.

Now when you are head down on the ground, your frame of reference isn't moving, but your blood is rushing to your head because of gravity.

Thats what pretty much I came up with. there is probably other people out there with a more specific way of explaining it.

[wmw999 2,121]

Having spent lots of happy time hanging upside down by my knees as a child, I can assure you it's not all that hard on you. It might have to do with which muscles are contracted (i.e. leg vs. arm and neck). Also, consider all the hanging tables that people have for back problems -- they wouldn't do that if it were uncomfortable.

Wendy P.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[pchapman 261]

allons2m

******whether you are at terminal or not, if you are in free-fall, you are in zero-g

No.

It’s unfortunate that your ignorance to the natural world impedes your ability to grasp such a concept. I find it amusing that you statement above starts with, intuitively; when clearly we are discussing a counter-intuitive concept. If you have value to add to this conversation please do. Otherwise, I suspect this will be my last engagement with a troll the likes of you.

Joellercoaster is correct: No.

(I'll emulate his succinct style this time and leave it at that.)

[allons2m 0]

pchapman

*********whether you are at terminal or not, if you are in free-fall, you are in zero-g

No.

It’s unfortunate that your ignorance to the natural world impedes your ability to grasp such a concept. I find it amusing that you statement above starts with, intuitively; when clearly we are discussing a counter-intuitive concept. If you have value to add to this conversation please do. Otherwise, I suspect this will be my last engagement with a troll the likes of you.

Joellercoaster is correct: No.

(I'll emulate his succinct style this time and leave it at that.)

I looked for some of the simplest examples to explain this concept. If you can't comprehend that free-fall = zero-g then I will stop trying.

http://www.sparknotes.com/testprep/books/sat2/physics/chapter11section4.rhtml

[DSE 3]

This explains it well and explains why pens don't float in elevators (the link you used specifically says a pen will float, when most any 10 year old will tell you this is not so).
This article specifically references freefall.
HTH.

[craddock 0]

Huh? Dude. That is a big NO.

If it was zero gravity why do we need parachutes? Why do we pull such a high g load on opening following a 1g freefall.

Zero Gravity? What is that? Where is that? Where can one find Zero Gravity?(far far far away) What is the gravitational pull on the Shuttle in orbit? It is less than on earth but not by much(10%) Sure the astronauts inside feel a micro g environment but anyhoo.

You have three posts and so if three people tell you NO, don't get so offended.

That spot isn't bad at all, the winds were strong and that was the issue! It was just on the downwind side.