Round reserve?

[Andy9o8 0]

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It's like saying the ditch along the highway has a magnetic attraction for my car. No, it doesn't, but if I go long enough without steering, I'll certainly be in one ditch or another.

Well, then why are tornados attracted to trailer parks?
You can't explain that, can you?

[pchapman 261]

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Every square reserve that I have ever drop tested with a dummy has turned down-wind; bar none.

From an upwind jump run?
(In which case every turn is downwind.)

So then one then gets into whether the canopy has time to turn past downwind yet stops at that point. (Maybe yes from 3000', maybe no from 500'.).

So if one wanted the canopy to fly straight, one would just do a downwind jump run?

(One might also have to deal with issues of wind direction changing with altitude, but in many situations it wouldn't be large.)

Signed, skeptical but interested.

[JohnMitchell 14]

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Well, then why are tornados attracted to trailer parks?
You can't explain that, can you?

Elementary, Dear Watson. Everyone knows trailer parks suck.

[JerryBaumchen 1,048]

Hi Peter,

There was plenty of time for them to get stable in the downwind condition.

As for upwind jump run: A moot point, they open in the direction they open; see the attached photo. Not a lot of stability there.

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So if one wanted the canopy to fly straight, one would just do a downwind jump run?

(One might also have to deal with issues of wind direction changing with altitude, but in many situations it wouldn't be large.)

Signed, skeptical but interested.

So go out and do your own testing; then let us know what you find.

JerryBaumchen

[ryoder 1,384]

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What's a canopy transfer?

Main is out & open, fire the reserve and cutaway the main.

Or, if you are jumping a Crossbow piggyback, it may fire the reserve for you,
(That was how I did my transfer).

"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

[ufk22 32]

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Hi Peter,

There was plenty of time for them to get stable in the downwind condition.

As for upwind jump run: A moot point, they open in the direction they open; see the attached photo. Not a lot of stability there.

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So if one wanted the canopy to fly straight, one would just do a downwind jump run?

(One might also have to deal with issues of wind direction changing with altitude, but in many situations it wouldn't be large.)

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Please don't spoil this arguement with factual data.
Signed, skeptical but interested.

So go out and do your own testing; then let us know what you find.

JerryBaumchen

This is the paradox of skydiving. We do something very dangerous, expose ourselves to a totally unnecesary risk, and then spend our time trying to make it safer.

[mdrejhon 8]

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Hi Phree,
It has many years ago but the old memory says that it stopped on/about the windline.

This would not happen if wind was 100% laminar flow, no turbulence, with no wind layers.

However, even in fractional mph differences have a tendancy to shift some uncontrolled light-weight aircraft (gliders, parachutes, paper airplanes, something with sufficiently low momentum that can't resist the micro turbulence) gradually towards the downwind direction where they tend to approximately linger. Also if you fly through turbulence, while keeping your brakes stowed, there tends to be bigger turns off your present heading if you're flying upwind than if you're flying downwind. (I even notice tihs -- remember I still fly a Sabre 170 after 500 jumps so I notice turbulence more than most of you skydivers do.)

Someone explained there is turns in one direction when wind speed changes in one direction, and a turn in opposite direction when wind speed changes in opposite direction. It should cancel out!? NAH! In reality, higher-speed air typically has more instability/turbulence than slower-speed air. As a result, transition from slowspeed to unstabe highspeed air will cause a turn of a different degree, than the identical mirror reverse transition from the same unstable highspeed air to the same slowspeed air.
Rinse and repeat several times. Eventually, the difference leads to a downwind heading.

Still argue it shouldn't matter? HAH! There's something else too: Even if the micoturbulences are exactly the same for both cases, remember planeforms aren't the same shape from the front as from the rear. Sudden pressure changes in front of the wing behave differently from sudden pressure changes behind the wing. Pushes and pulls from changes in pressure (wind boundary layers) will have different effects from behind than from the front. Wind tunnel tests prove that. Only a Frisbee can fly forward and backwards with the same effect. Wings cannot. Blow a paper airplane from behind (sudden gust/turbulence from behind), the airplane behaves differently than if you blow the paper airplane from front (sudden gust/turbulence from front).

THEREFORE, due to the reasons above, wings turn a different angle when transitioning from a highspeed to slowspeed wind, THAN when transitioning from slowspeed to highspeed. And you know, the atmosphere is full of wind layers and turbulence, the atmosphere is not laminar flow.

One says they are an airplane pilot and don't notice? It's not a meaningful factor: Don't worry -- metal bird pilots typically don't notice this because their plane has a lot of mass and inertia. Our wing needs to be low wingload, like paper airplanes and parachutes, and are more easily affected by the above. Keep reading.

Eventually, all the forces average out to a preferred downwind direction for many kinds of planeforms/wingprofiles as it is the flightline of maximum stability for many planeforms in turbulent air.

Just toss a paper airplane into slight breezes, the paper airplane has a tendancy to turn downwind as it hits the transition layer of the breeze. Same damn thing with parachutes (though it takes time for the forces to build up as the turns are tinier with micro-tubulence and slow wind speed changes in wind layers, etc). We're never parachuting in laminar flow air (zero eddies, zero microturbulence, identical wind speed for the whole altitude, that never happens for the whole skydive), so our parachute will definitely turn as a result of the wind speed changes. Turns are noticed. But turn where? Well, apparently, it seems to be downwind on average.

Pilots flying metal birds won't notice, as the wingloading of these aren't usually often enough to turn dramatically. (And any dramatic uncommanded turns are often followed by a startled pilot correcting heading. Dramatic uncommanded turns in certain metal birds also tend to dive the airplane a little, which just increases the panic factor of the pilot.) Takes much longer for the forces to build. Most pilots aren't willing to let planes glide themselves uncommanded long enough with no autopilot keeping compass heading. Therefore, scientific data from airplane pilots are less valid than parachute dummy drops and paper airplane tests, in the perspective of the "unconscious skydiver" uncommanded parachute flight.

Comment about overshoot tendancies: During the turns caused by going through transition layers, it is presumed that some parachutes/planeforms will 'hunt' heading more than others as it goes through random transition layers. Especially if the weather is very very stable and/or there isn't much altitude, so the downwind heading with tend to 'hunt' a little off (i.e. 20 degrees left off downwind, 30 degrees right off downwind), overshooting back and fourth past the downwind heading. Yes, the planeform's apparently tendancy to randomly hunt for a heading might sometimes massively outweigh its tendancy to point downwind. Yes, the planeform can have a built-in left turn or right turn that overcomes the weak desire to turn downwind. Yes that happens. Yes, there's been at least one unconscious skydiver that didn't land downwind, because of all the above factors. But in all the cases, there's always a preferred heading of maximum stability (point of maximum resistance to turning when going through transition layers) that goes into the equation, and that's almost always downwind.

To maximize likelihood of downwind heading, you would appear to need: (1) low intertia, bigness, like a big parachute, (2) maximum time under parachute wihch means sufficient altitude (3) more wind-speed boundaries will accelerate the tendancy (4) totally uncommanded with no body shifts or arm/leg movements to cause mico-harness-turns (5) stable planeform that automatically returns to level flight that (6) nearly no built-in turn. No planeform is perfect, but built-in turn tendancy should be easily overcome by the turning forced by the wind-speed boundaries. Most well-trimmed well-maintained not-too-old student parachute seem to fall in this category. (7) more immune to other shifts like moving body, engine vibrations, that might distort other turn tendancies. (8) and you have a wing that does have a clear noticable have a tendancy to turn when it hits turbulence;
NOTE: You can get away with just having 'most' of the above factors, but the fewer bullets that match the criteria, the downwind tendancy gets weaker, and the wing's desire to 'drift' or 'hunt' for a heading becomes greater.

So it makes sense that many wings tend to turn downwind -- especialy confirmed to happen in dummy drops (this thread), confirmed to happen with unconscious skydivers (numerous other threads), and confirmed to happen with paper airplanes in a drafty/breezy room (try it yourself). And yes, I've gotten 90%+ marks in Physics, Math and Chemistry classes back in my day, and it still makes sense.

It'd be nice to see proper scientific testing on this, though.

[JerryBaumchen 1,048]

Hi Mark,

Interesting reading ( and, yes I read it all if somewhat long ).

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It'd be nice to see proper scientific testing on this, though.

What is your definition of 'scientific testing?'

Just curious really; so please do not take this in a negative sense.

JerryBaumchen
An old Mechanical Engineer who got lesser grades than you did; I think it had to do with something about chasing women & going to school at the same time.

[mdrejhon 8]

Tough one; defining scientific testing: Do we use the outdoors as a testing lab? Or do we reproduce the variable winds in a wind tunnel? For the former, we cannot control the winds. For the latter, we won't be able to produce all kinds of the same turbulence conditions and wind transition layers in a scientific wind tunnel.

Thus, I think dummy drop tests probably would have to be one of the most scientific, but a lot more data should be collected for future dummy drops (by any parachute manufacturer), and recording all the data.
-> Altitude, Canopy, Canopy size, Wingloading, etc (determine co-relation of these variables versus tendancy of preferred heading)

Weatherstation-style telemetry should be recorded from the dummy (compass heading, GPS position, dynamic G-forces caused by turbulence. The technology is simple nowadays -- even iPhones have GPS/accelerometer/compass capabilities already!)
-> Determine coorelation of heading changes that correspond with sudden changes in speed or turbulence (increased random G forces detected by accelerometer), etc.
-> Post-analysis can determine a bias towards a preferred heading. GPS tracking determines wind direction, and computer compass determines heading.
-> Determine whether more turbulence/more variable winds, causes more frequent tendancy towards preferred heading (i.e. downwind)
-> Determine how much 'heading hunting' occurs after the heading points downwind: Is there less heading changes during a downwind-pointing heading, than upwind-pointing heading? Telemetry analsys and a graph would show a pattern like a beacon, once enough data was collected in many test drops...

There's more data to record (for a proper scientific plan), but the above examples will likely be sufficient "to get started" making conclusions...

Test drop. Record data. Rinse and repeat. Enough times. Various sets of drops in different kinds of wind conditions.
(How many? That is up for debate. 10? 100? 500 times? Enough dummy drops to get ironclad data that's not coincidence.)

Graphs can then, thus be generated out of all the record data. The data would be scatter plotted or many different lines from many different test drops.
-> One example graph is parachute altitude (as it drifts down) along horizontal axis, and parachute heading "degrees off wind axis" along vertical axis ... This would in theory show a pattern whether it stabilized to a downwind heading as altitude decreased, showing all the data converging into compact data along the "0 degree" level.
-> Another example graph is.... Along one axis is "degrees off wind axis at landing" .... Along the other axis is data such as altitude or canopy size or variability level of winds that day, amount of turbulence (detect turbulence by using accelerometer data analysis). Scatter-plot the recorded data. Bam. See convincing pattern that co-relates with a specific variable (if any).
-> Many different kinds of graphs could be experimented with to gain easy-to-visualize insight to the recorded data.

For generating the graphs, an Excel macro or quick-and-dirty one-day .NET app could even be used to do this, as a programmer time cost-saving measure.

In *theory*, if the precision of the iPhone sensors are sufficient enough (to be determined) then a custom iPhone app, with only 5 to 10 days of good programmer time ($2500 to $5000 at a generous $500 per diem programmer time, and just use a quick-and-dirty Excel macro to generate the graphs), and a sacrifical iPhone can be embedded into the dummy, in an off-the-shelf waterproof Otterbox case surrounded by additional shock-absorbing foam. The iPhone must be more-or-less horizontal for the digital compass in the iPhone to work properly, and to maximize the quality of the accelerometer data (for post-analysis to detect turbulence conditions, with accurately-enough distinctive G-force telemetry from swinging harness versus wind changes versus turbulence.). The iPhone could even be used as a backup method to assist in recovery of a dummy becoming lost, because an iPhone can be remotely GPS-tracked too, either through additional off-the-shelf software, or as a feature built-in into the custom private iPhone app. (the special private "black box recorder" iPhone app would not be put into the app store, for competitive reasons) Or upon the parachute manufacturer's option, part of the algorithm could be open sourced to gain maximum trust in the scientific technique and to make sure data wasn't being fudged by anyone....

Ideally, instead of an iPhone, a more precision lab computer instrument would be better, but such telemetry recorders that support recording in-depth GPS/compass/accelerometer data might be expensive. Whereas an iPhone is an expendable $500 instrument and the custom software can be reloaded onto it. Parachute manufacturers doing dummy drops might have a limited budget to "slipstream" or "embed" scientific tests like these, into their regular normal parachute testing regimen. (hint, hint Aerodyne, PD, etc -- if you are reading this -- please feel free to steal my ideas from this thread) Heck, I'd do it (both the iPhone and ground analysis software) if I got two custom-made (Both with my Rainbow-circle-logo on underside) parachutes for free out of it -- or bribe a different skydiver to program this telemetry recorder app for a mass market GPS/compass/accelerometer equipped pocket device such as iPhone.

Note: Down-headingness is expected to happen more often with stable squares that have quick recovery characteristics (i.e. reserves), than ellipticals. So down-heading tendancy likely varies from canopy to canopy. Therefore, I recommend my enhanced telemetry-recorder idea be implemented next time one of the parachute manufacturers are testing a new reserve, since we are more interested in down-headingness in situations where it's likely to happen (i.e. reserves) since if a skydiver is ever unconscious under parachute, it's likely happening under a reserve.

Once a parachute manufacturer does this, how useful is the data? Hard to say, but it could lead to a study of survivability of downwind landings, and recommended reserve wingloading for survivability of an unconscious skydiver, etc. (especially if the dummy is equipped with G-force shock meters, as in a crash test dummy). Or optimization of brake stow position for maximum downwind survivability (tradeoff horizontal versus vertical speed etc). Or if co-relation of downheadingness is proven by the testing, then more accurate searching patterns for tracking a lost skydiver if we now know we should begin the searching downwind of the drop. Or other unexpected 'useful' uses of this data might occur.

[captain1976 0]

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What's a canopy transfer?

Main is out & open, fire the reserve and cutaway the main.

Or, if you are jumping a Crossbow piggyback, it may fire the reserve for you,
(That was how I did my transfer).

Only saw a canopy transfer once. The guy who did it mentioned it a few times that this is what he would do if he had a malfunction, explaining the forward speed of the main would allow for the reserve to inflate.

Sounded good back in 1982 and sure enough, this jumper did exactly what he said he would do. He experienced his first malfunction after 4500+ jumps, unfortunately the reserve went right up into his main and he was killed. His name was Jim Stoyas D-60.

You live more in the few minutes of skydiving than many people live in their lifetime

[captain1976 0]

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the square will assume down wind flight

Myth.

Fact. There are probably exceptions, but since I hang out, fly the airplanes and help at a parachute testing facility, I would put the figures in the high 90% range for an unassisted square with or without brakes to assume down wind flight.

You live more in the few minutes of skydiving than many people live in their lifetime

[mdrejhon 8]

Very, very minor two-word correction to an error I notice in my writing

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Pilots flying metal birds won't notice, as the wingloading of these aren't usually often enough to turn dramatically.

I meant, "Most pilots flying metal birds won't notice, as the wingloading of these aren't often light enough".

[airtwardo 6]

He experienced his first malfunction after 4500+ jumps, unfortunately the reserve went right up into his main and he was killed. His name was Jim Stoyas D-60.

[captain1976 0]

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He experienced his first malfunction after 4500+ jumps, unfortunately the reserve went right up into his main and he was killed. His name was Jim Stoyas D-60.

I knew Stoyas, major S&A competitor way back when.

I didn't realize that was how he died, I remember stories about playing with the malfunction WAY too long, seeing he was low and just firing the reserve...didn't know it was 'pre-planned'.

[JerryBaumchen 1,048]

Hi captain,

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unfortunately the reserve went right up into his main and he was killed.

Isn't this the same thing that killed the young Thacker kid at the Nationals one year?

I was not there but a good friend was and this is what he told me. Maybe rumor - maybe true.

Also, a fellow doing a demo at the Abottford Air Show back in the 60's got killed this way. He always said that he would never do a cutaway and he didn't.

JerryBaumchen

[captain1976 0]

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Hi captain,

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unfortunately the reserve went right up into his main and he was killed.

Isn't this the same thing that killed the young Thacker kid at the Nationals one year?

I was not there but a good friend was and this is what he told me. Maybe rumor - maybe true.

Also, a fellow doing a demo at the Abottford Air Show back in the 60's got killed this way. He always said that he would never do a cutaway and he didn't.

JerryBaumchen

Jerry,

Don't know about the others, but the theory sounded good at the time. Why cut away something and take a chance on the reserve not opening?

A shame the facts cost these people their lives.

You live more in the few minutes of skydiving than many people live in their lifetime