High altitude slammers (?)

[crapflinger2000 1]

Hey... got a question... I have always accepted the common wisdom that if you pull high (i.e. 10K AGL) AT TERMINAL, you will get slammed... I guess the theory is:

thinner air = higher fall rate = greater deceleration = ouchy

But part of me has always thought, "But shouldn't the theory be:

thinner air = higher fall rate = greater deceleration, BUT this would be offset by the deceleration taking longer (since there is less air "stuff" hitting the deploying canopy than at a lower alt) = not much difference in perceived opening shock...."

I guess my question is, why doesn't the lessened "wind resistance" make the opening longer and softer in the same manner that it makes you fall faster...

The more I think about it, it really doesn't seem like there should be an appreciable diff at all. I would expect measurable (i.e. perceived) differences if you were taking a terminal opening at like 25K, but pulling only 7K or so higher than normal doesn't seem like it would make a diff.... that is , assuming that the "conventional" wisdom is correct...

probably it's one of those "X increases by the cube of Z while Y increases by the square of Z" things....

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What would Vic Mackey do?

[BlueEyedMonster 0]

I am gonna agree with you theoretically. However, I have not pulled at high altitude after reaching terminal velocity; so I cannot say based on experience.

[mikkey 0]

When I received my current canopy (new) - I did a couple of jumps from 14 K opening at around 8 K to play with the canopy. I did not notice a harder then normal opening at all....

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When people look like ants - pull. When ants look like people - pray.

[masher 1]

I've done that several times. Out a 12, dump at 8, out at 12 dump at 10, out at 10 dump at 8.

I didn't get slammed, and I jump a Sabre.

.

You would probably notice it if you went out at 20 and dumped at 18, but I'm just hypothosising here...

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Arching is overrated - Marlies

[narcimund 0]

Consider the extreme case: opening at light speed in a vaccuum. Think about it.

First Class Citizen Twice Over

[lazerq3 0]

Same here... out @ 11000 dumped at 8000 and we are 4500 msl at the hanger so thats 12000 msl and had NO problems!!

jason

Freedom of speech includes volume

[billvon 3,111]

>thinner air = higher fall rate = greater deceleration, BUT this would
> be offset by the deceleration taking longer (since there is less
>air "stuff" hitting the deploying canopy than at a lower alt) = not
>much difference in perceived opening shock...."

You are partially correct, but one does not cancel out the other. When you are a high altitude, you decelerate to a faster speed after your canopy is open (i.e. 15mph vertical instead of 10mph) but that doesn't come close to canceling out the increase in vertical speed before the pull (i.e. 135 vs 115 mph.) The amount of time it takes is about the same, but you are decelerating a lot more in that time. There also seems to be an additional effect, a reduction in the effectiveness in the reefing system (the slider.) I don't quite understand that since a lot of the forces should scale as the air gets thinner.

A friend of mine tested HAHO systems for the military, and they would regularly destroy MT1X's by deploying them at terminal at 30,000 feet. They ended up using a tandem-like drouge system to slow the system to 'normal' freefall speeds (i.e. 110 or so) and that solved the problem.