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melushell

Maximum descent rate

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At sea level, about 80 MPH under an 86 @ 2.6:1 and a 74 @ 3.1:1. This is data that I gathered back in 2003 for an article in Skydiving Magazine where I demonstrated that an Expert CYPRES could be made to fire under canopy.

Around that time, a friend and I did a Mr. Bill on an FX 94 and, based on outside video and our knowledge of the altitude loss in the turn, we calculated around a 130 MPH descent rate on an aggressive spiral.

In Colorado (5500 AGL, usually around 7K density), I average around 90 MPH on most landings with a 92 and the 86, slightly faster on the 74. I have spiked my 99 at just over 100 MPH. These numbers are coming from a Flysight GPS.

I've heard claims of 106 MPH, which is what I would expect on a well-executed aggressive "competition" approach at these altitutdes.

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I think I remember that Jay did 105.14mph (47m/s) during the testjumps for the speedcypres. But I´m not 100% sure about it as it´s been quite a while... I think that information was on the Airtecwebsite, (cant find it at the moment) but I can ask em. I can also ask em what the fastest speed is they ever downloaded from their dataloggers. I was doing some jumps a couple of years ago for em (2008?) and pulled 101mph. That was at a loading of about 2.55 (if I remember correctly) by doing 450s, initiated from pretty high. (I´m burning the same or even more altitude for a 450 than many persons use for 630s). I dont know how fast I go today at loadings between 2.9 and 3.2. What I would be even more interested in, aint the vertical speed - but the true airspeed! As we dont go straight down but in spiral, the way is longer and the true speed HAS to be faster than the rate of descent. It would be of my interest to get more of those numbers as they likely exceed belly terminal. (And this also tells us that you can only go that fast in a tiny bodyposition.)

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106mph @ 3.8 on a flysight

Normal loadings say 2.4 or so probably around 75-80mph

Was talking with Ernesto the other day and he is getting around 30m/s descent rate on the 39 in normal fligh - so not sure what that is in mph
"Don't blame malice for what stupidity can explain."

"In our sleep, pain that cannot forget falls drop by drop upon the heart and in our despair, against our will comes wisdom" - Aeschylus

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Hey,

Just read your numbers on the PI and was curious if you guys have done much XRW with the canopy? As that speed is a nice fall rate for wingsuiters without the use of trims.

I am guessing the PI is like the petra with the faster roll rates though so a bit harder to manage with docks and unintended body roll?

Cheers
"Don't blame malice for what stupidity can explain."

"In our sleep, pain that cannot forget falls drop by drop upon the heart and in our despair, against our will comes wisdom" - Aeschylus

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cs_troyk

Just finished some jumps today on the VX74 @ 3.1:1, trying out the new JVX lineset. Sustained descents of 110mph measured by Flysight.



Can someone explain to me how, when terminal velocity for a belly flier is around 120mph, a vertical descent of almost the same speed is possible with a deployed canopy?

Even the wings on a camera jacket can slow the wearer more than that!
"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

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DocPop

***Just finished some jumps today on the VX74 @ 3.1:1, trying out the new JVX lineset. Sustained descents of 110mph measured by Flysight.



Can someone explain to me how, when terminal velocity for a belly flier is around 120mph, a vertical descent of almost the same speed is possible with a deployed canopy?

Even the wings on a camera jacket can slow the wearer more than that!

Someone that knows the physics of the system better can probably offer an actual explanation that makes sense, but I can at least describe what it feels like...

First off, I think the JVX lineset made a significant difference. As I said earlier in this thread, I was hitting around 80MPH on this same VX skin under the original lineset. A couple of points, though;
- the earlier tests were at a dropzone near sea level (200 ft MSL), and this latest jump was at a DZ at 5290 MSL, so my descent started from about 15K MSL
- I'm sure my technique has improved, plus I was going for maximum descent, and not necessarily simulating a high-rotation landing as in the prior tests.

I was wearing baggy shorts over some longjohns. I had done a couple freefall-terminal jumps earlier in the day and fallrate was about 125-130. I was jumping a removable slider, but left the dbag/pilotchute on the topskin (i.e., I think if I wore tighter clothes and went full-RDS, I could probably get another 5MPH - will try again soon).

There was "noticeable" G-force in the turn, and I was completing each full rotation in just over 2 seconds. But it actually felt like the G's built up more as I evened the input to the harness exiting the dive. In the future, I'll be jumping with more instrumentation so that I can get a true reading on the actual G's that are built up during the different phases of the flight.

The best layman's guess I can give as to why it's possible to hit these kinds of speeds with such a large surface area (i.e., the whole front nose of the canopy + the lines + the jumper) is that the canopy is producing an incredible amount of lift and the speedy rotations are converting that power into downward flight.

Regardless of whether that's a good explanation, it sure is fun!

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cs_troyk

******Just finished some jumps today on the VX74 @ 3.1:1, trying out the new JVX lineset. Sustained descents of 110mph measured by Flysight.



Can someone explain to me how, when terminal velocity for a belly flier is around 120mph, a vertical descent of almost the same speed is possible with a deployed canopy?

Even the wings on a camera jacket can slow the wearer more than that!

Someone that knows the physics of the system better can probably offer an actual explanation that makes sense, but I can at least describe what it feels like...

First off, I think the JVX lineset made a significant difference. As I said earlier in this thread, I was hitting around 80MPH on this same VX skin under the original lineset. A couple of points, though;
- the earlier tests were at a dropzone near sea level (200 ft MSL), and this latest jump was at a DZ at 5290 MSL, so my descent started from about 15K MSL
- I'm sure my technique has improved, plus I was going for maximum descent, and not necessarily simulating a high-rotation landing as in the prior tests.

I was wearing baggy shorts over some longjohns. I had done a couple freefall-terminal jumps earlier in the day and fallrate was about 125-130. I was jumping a removable slider, but left the dbag/pilotchute on the topskin (i.e., I think if I wore tighter clothes and went full-RDS, I could probably get another 5MPH - will try again soon).

There was "noticeable" G-force in the turn, and I was completing each full rotation in just over 2 seconds. But it actually felt like the G's built up more as I evened the input to the harness exiting the dive. In the future, I'll be jumping with more instrumentation so that I can get a true reading on the actual G's that are built up during the different phases of the flight.

The best layman's guess I can give as to why it's possible to hit these kinds of speeds with such a large surface area (i.e., the whole front nose of the canopy + the lines + the jumper) is that the canopy is producing an incredible amount of lift and the speedy rotations are converting that power into downward flight.

Regardless of whether that's a good explanation, it sure is fun!

Thanks, but that still doesn't ring true for me. Additional lift = additional drag so that should make things worse.

Any scientists care to have a go?
"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

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So I did a bit of calculation based on the GPS data from the jump...

In the dive, I was pulling a bit over 4.5 G's as I spiraled. The system, of course, was flying predominantly straight at the ground. I will be doing jumps with more instrumentation in the future to find what the exact attitude is.

My wingloading in a static glide is 3.1:1 on this canopy. 4.5 G's is producing an effective wingloading of about 14:1. My exit weight is 225 lbs, so the thrust being produced is similar to what would be experienced in full glide by a 1000 lb. payload (under a VX74). Imagine a Mr. Bill with 4 or 5 people. Clearly, this is enough to significantly overcome the drag vector.

When I'm able to jump with more sensors, it will be interesting to see if lift vector of the system is parallel to the ground, or whether it is actually past parallel and contributing to the downward acceleration.

All this is on a 2000 model VX with the dbag/pilotchute still attached to the topskin. I'm pretty certain that, given a more efficent wing (JVX or JPX, full sail) and full RDS, I'll be able to get close to a 130MPH descent rate.

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cs_troyk

When I'm able to jump with more sensors, it will be interesting to see if lift vector of the system is parallel to the ground, or whether it is actually past parallel and contributing to the downward acceleration.



That's a very interesting concept.
"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

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The way I understand it is that there is a pulling of forces between the jumper and the canopy itself. The canopy wants to generate lift away from the jumper while the weight suspended by it is pulled back to earth; almost essentially pulling the two apart from each other and that it is this tension which keeps the jumper from resuming true freefall and the canopy no longer flying.

Our bodies, basically, serve as the motor to drive our canopies. So what we have is a mass of weight suspended from an airfoil; in flight, gravity wants to pull our bodies back to the ground while the canopy itself wants to fly, creating tension on our lines. The canopy continues to 'try' and fly away from the jumper while the jumper 'tries' to pull away from the canopy.

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projectalarum

The way I understand it is that there is a pulling of forces between the jumper and the canopy itself. The canopy wants to generate lift away from the jumper while the weight suspended by it is pulled back to earth; almost essentially pulling the two apart from each other and that it is this tension which keeps the jumper from resuming true freefall and the canopy no longer flying.

Our bodies, basically, serve as the motor to drive our canopies. So what we have is a mass of weight suspended from an airfoil; in flight, gravity wants to pull our bodies back to the ground while the canopy itself wants to fly, creating tension on our lines. The canopy continues to 'try' and fly away from the jumper while the jumper 'tries' to pull away from the canopy.



I think I understand what you're saying, but to me you answered the question "Why is there tension in the lines?" rather than the one I asked; "How can a jumper with an open canopy approach any where near freefall terminal velocity, given all the extra drag?"

If, as was mentioned before, the pitch angle changed sufficiently that the lift vector of the canopy is angled below that of the horizontal (which I find unlikely, but I don't know that), then that might explain some force, additional to gravity, which could accelerate the system towards the ground.
"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

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Quote

How can a jumper with an open canopy approach any where near freefall terminal velocity, given all the extra drag?"





I may be wrong as i never studied but i believe the short answer is the 'G' forces experienced whilst rotating a mass at speed around a single point...the mass of the jumper essentially increases.

Practical demo lead fishing weight suspended on a length of cord.
Whilst suspended easy to hold etc.
Now take the end of the cord and rotate/swing above your head and the forces generated essentially cause the weight to want to part company with the cord or the cord to part company with you grip.
.CHOP WOOD COLLECT WATER.

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trigger

Quote

How can a jumper with an open canopy approach any where near freefall terminal velocity, given all the extra drag?"





I may be wrong as i never studied but i believe the short answer is the 'G' forces experienced whilst rotating a mass at speed around a single point...the mass of the jumper essentially increases.

Practical demo lead fishing weight suspended on a length of cord.
Whilst suspended easy to hold etc.
Now take the end of the cord and rotate/swing above your head and the forces generated essentially cause the weight to want to part company with the cord or the cord to part company with you grip.



No, I don't think so.

The mass of a given body is always constant. "Weight" can vary as it is the force exerted on a given mass by gravity.

Additionally, the centrifugal force you describe works against the canopy and I can't see how it would aid acceleration towards the ground.

Just my thoughts but that doesn't answer it for me.
"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

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Good conversation, though, and I am really interested about this.

I hope a CP competitor, canopy coach or canopy designer will chime in with an explanation.
"The ground does not care who you are. It will always be tougher than the human behind the controls."

~ CanuckInUSA

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