Oh my, do RTFP, KenV!

I wrote 'vertical', not 'terminal' velocity.

:rolleyes:

BEagle, he also made the assumption that they had jumped with a sufficiently great altitude to reach TV before planned chute opening. And indeed the TV at altitude will be higher than the TV at chute opening height.

But at a lower height TV may not be achieved before chute opening but as you say, the VV may well be higher than planned.

It seems to be open season on KenV every day in this forum, doesn't it?

What interests me more are the arrangements to exfil the paratroopers after they land. Any information?

What interests me more are the arrangements to exfil the paratroopers after they land. Any information? - FODPlod

In the immortal words of the port lookout:

"On the beam a submarine
On the bow, another cow":D

Jack

Dearest Beagle. Please read what I wrote and not what others assumed I wrote.

I said that for a freefall/HALO jump, vertical velocity at canopy opening IS terminal velocity. I politely stated I was confused and politely asked for clarification.

I also said that for a static line jump, canopy opening, and thus vertical velocity, is determined by the length of the static line which is independent of any altimeter the jumper may be wearing. I politely stated I was confused and politely asked for clarification.

Thank for your F'ing reply, but it did nothing to clear up my confusion. So I politely ask once again, please clarify my confusion.

Which rather points up my confusion. If they delayed their opening, then they would be lower when they opened, which would reduce rather than increase their terminal velocity. So I state politely again, I'm confused and politely request clarification.

KenV - on this side of the pond we have a habit of understating things slightly more than you might be used to.

By "lower than intended" I should imagine BEagle meant "lower than ground level".

When descending by parachute, it's desirable to arrive at ground level with a sufficiently low vertical velocity to be able to absorb the impact with one's legs. In this case, the parachutists in question arrived at ground level "with a higher vertical velocity than planned."

Does that help?

1. The plan was to freefall.

2. Then to open the canopy at a certain altitude.

3. At the planned altitude the parachutists would have been at a certain velocity, but not at terminal velocity.

4. If altimeter temperature error correction hadn't been applied in such cold weather, the actual altitude would be lower than planned.

5. Hence the vertical velocity would have been higher than planned.

6. The parachutes would have taken longer to reduce the vertical velocity to the normal parachute descent rate.

7. A combination of lower level and higher vertical speed when the parachutes were deployed might therefore have proved fatal.

Did anyone else not understand that line of thought from my original post?

As an example, if it was ISA-45 and they'd planned to pull at 500 ft, their actual altitude would have been only 380 ft and depending on the height at which they'd exited, they could have fallen 120 ft further than planned, perhaps accelerating beyond the capability of the parachute to develop fully?

BEAGLE:
Then I am more confused. It takes about 15 seconds for a human body to reach terminal velocity. Less if they are encumbered with heavy equipment like weapons. I've never encountered a military freefall jump where the freefall was planned for less than 15 seconds. In my experience, such a short freefall would be pointless and a static line jump would be preferable. And if it was planned for less than 15 seconds, they'd use a stop watch, not an altimeter to determine their opening point. Brits (or whoever did this jump) must have very different tactics or procedures than the American tactics/procedures I'm familiar with. That explains things. Thanks for the clarification.

Pasta clearly did not. He offered an entirely different explanation.

If it's the incident I'm thinking of, one parachutist deployed too low; two failed to deploy at all.

Neither were they military parachutists.....:rolleyes:

Ken,

How does the persons weight (with heavy equipment), alter the time it takes to reach terminal velocity? Perhaps there is a new form of gravity I'm not aware of.

These were sport jumpers?!! And they planned a jump with a freefall that never reached terminal velocity? And that was done at such low altitude that opening just a very few seconds late would result in their death? Not even smoke jumpers do that, and they arguably take the greatest risks of any jumpers. Before I was confused and your previous reply cleared that up. My confusion was caused by a difference of procedure. But now I'm incredulous. I've never encountered sport jumpers that planned such jumps. Never. I must live a very sheltered life.

Dearest O-P,

Cross sectional density is the primary driver of an object's terminal velocity. Putting heavy equipment on a human body makes the human body more dense which "alters the time it takes to reach terminal velocity". Reducing the cross section (like going straight head down vs spread eagled) also "alters the time it takes to reach terminal velocity." If gravity alone were at work as you suggest (like perhaps on the moon) you would be correct that neither mass nor density would have such an effect. But then there would be no terminal velocity at all and the max velocity from a free fall would be the escape velocity.

Ken,

I beg to differ. Two objects with identical Cd and frontal area, but with differing mass, will fall at exactly the same rate.

So a human being of mass 100 kg and that same human being of mass 300 kg will have the same terminal velocity? Ummm, no.

Terminal velocity is reached when the drag force equals the mass force. It is a very simple balancing equation.

If the Cd and frontal area are identical, their drag is identical and the resulting drag force will be identical for any given speed. Since one object is heavier, the mass force of one object will be greater than the other. Since they have identical drag force, the heavier object must have higher terminal velocity. It is very simple and basic math.

Nearly 100 paratroopers? A submarine? That's surprising. An ice breaker was used in other instances:
I'd be very interested in reading the source of your information, please?

I'd be very interested in reading the source of your information, please?

My apologies, FODPlod - I was of course having a bit of fun in the spirit of "Ice Station Zebra", and hence the:D

Jack

Cor. What a lot I've learned.

Terminal velocity
Cd
Mass
Drag Force
Cross Sectional Density

Everyday is a school day.

The biggest thing I've learned though

Russian Paratroopers to Land on Drifting Arctic Ice

All of them are F'ing barmy.

I hope the RAF paras are ok

RAF parachute instructors collided mid air during training jump - Mirror Online