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

[JackC1 0]

ianyapxw

No, the forward speed does not restrict acceleration.

In vector addition, there are two components, horizontal and vertical, and both components are independent. You would accelerate downwards as fast jumping out of an otter, 182 and baloon (assuming you have the same position)

That's close enough for most practical purposes but it's not quite right. When you have horizontal velocity into a relative wind, it does affect your vertical acceleration, not by much but it does. If you lobbed a bowling ball out of a balloon and an Otter from 5k, it would hit the dirt first from the balloon, by maybe 0.5s depending on the parameters.

The reason is that aerodynamic drag doesn't care whether you are going horizontally or vertically, it only works on the square of the total velocity. Hence drag term in the vertical component of the equations contains a horizontal velocity term and that horizontal speed will slow your vertical acceleration.

[Andy9o8 0]

All of you are wrong.

When you jump head-down, the relative wind enters the pores in your neck - it's how we breathe in freefall, after all - and exerts upward pressure on the blood vessels, forcing blood away from the head, toward the feet, thus (usually) maintaining equilibrium. Caution is indicated: it could increase the risk of orthostatic hypotension.

[erdnarob 1]

So many posts not answering the question here.
Just like belly flyers, headdowners have to reach a terminal velocity which is higher than belly flyers since less surface is opposed to the relative wind.
What one has to remember is that when reaching terminal velocity, the relative wind generates an aerodymical force equal but opposite to the total weight of the jumper, then opposite forces cancel each other. The result is zero force on the jumper. Therefore, there is no acceleration anymore. That means at that time you fall at constant velocity. The body of the jumper then is just like being at rest with no blood rush at all in the body.
During the acceleration phase (from exit to reaching terminal velocity) the maximum acceleration is one G just like belly flyer. And this maximum acceleration happens at the very beginning when the jumper exit the airplane. After that, due to the aerodynamical force, the acceleration decreases to become zero at terminal velocity.
Nothing to compare with jet fighters pilots who get acceleration as high as 7 G (7 times your weight)
I think in this thread, there is a confusion beween the effects of the speed and acceleration. A constant speed (like an airliner cruising at 35000 feet) has no force (on the body or else) involved and provided there are no turbulences, you are like at rest. A force is generated only when there is an acceleration (an increase or decrease of speed)
This is basic physics.

Learn from others mistakes, you will never live long enough to make them all.

[billvon 2,396]

>That means at that time you fall at constant velocity.

Agreed.

>The body of the jumper then is just like being at rest with no blood rush at all in
>the body.

It is just like being at rest - on your head. Your body's circulatory system then does its job and keeps the blood pressure in your head and feet under control.

>A constant speed (like an airliner cruising at 35000 feet) has no force (on the
>body or else)

If you are falling at a constant speed, and you weigh 180 lbs, then the force on you is exactly 180 lbs.

[manseman 0]

erdnarob

So many posts not answering the question here.

That's a healthy dose of irony right there ;)

From the first post:

Quote

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?

Clearly, there is more to this than high school physics.

[potatoman 0]

Probable answer: The guy in the tunnel has a full face helmet, so you don't see his face going reddish.

Who does a hand stand with a helmet?

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