DaVincisEnvy

Very interesting and creative work, and congrats on acceptance into your PhD program, Oli! Science is just a process of learning, and as such is never perfect. All we do -- all human scientific pursuits ever do -- is strive to minimize and improve upon the imperfections we discover so that we can peer deeper into the question each time. This study, at its core, seems to bring up the fascinating question of what it really means to experience stress. The results certainly point to a disconnect between stress as it is perceived by the mind and stress as it is experienced by the body. I'd love to see some future work address the question of where the disconnect between psychological stress and physiological stress occurs. For instance, meditation and breathing techniques have been shown to slow the heart rate and induce a sense of relaxation, but can such techniques affect cortisol levels, which this study indicates may be far more "hard wired"? Which stress markers correspond most closely to perceived/psychological stress? Which stress markers, if any, are physiologically "mandated" and uncoupled from the psychological response? I would be willing to bet that the experienced jumpers who self-reported lower stress levels probably had lower heart and respiratory rates, but I'm not so sure about pupil dilation or other chemical stress markers (e.g. those markers that are used in reliable lie detectors). Tons of fascinating opportunity for follow-up -- I hope you stick with this question, Oli, and keep us informed of your progress!!

Will do! It sounds like Airtight has a loyal following of fun jumpers, which is always a good sign :-) I'm going to give them a call this weekend.

Oops, yeah it looks like I swapped the locations of OSC and Skydive Tulsa when I posted. Thanks for catching that.

Hi, all. I'm looking for suggestions of a friendly, tandem and fun-jumper friendly DZ near Tulsa. My home DZ is in Florida, but I'll be in Tulsa for a wedding during July and want to get my brother a tandem jump as a college graduation gift (he lives in Tulsa). I'd love to jump with him, although with just shy of 200 jumps myself, I realize that may be a tough sell at a DZ that doesn't know me from Adam. The most recent posts on this topic have mentioned Skydive Airtight in Skiatook, but nothing newer than about 2005 has mentioned Skydive Tulsa in Cushing. Those are the two closest DZs and so are the ones I've looked at so far. Does anyone have new info/reviews about Skydive Tulsa? Has anyone jumped at both DZs and developed a preference for one over the other? And am I missing a nearby DZ that may be an even better fit? Many thanks in advance!!

Once. I was at a boogie and talking to some friends when, in my peripheral vision, I saw a body falling fast and low. About a second after I first noticed the jumper and when he was no more than a few seconds from impact, his reserved popped, followed an instant later by his main. He was in a stable belly-to-earth orientation and ended up with two out. Thankfully, the canopies played nicely together, and he landed a biplane a few seconds after deployment. After he landed, the jumper (an experienced older jumper) said he had trouble pulling his main and that he was "just about to go for his reserve" when he finally got it out right as the Cypres fired. It was scary low, but the jumper was in a good body position and the AAD worked as advertised. He was lucky, and he walked away.

I told my parents. After I got on the ground. At the time, I was 19 years old and spending the summer half a continent away, so my parents were simultaneously quite supportive of my independence and completely unable to do anything about it. To be fair, though, I started jumping off the roof of the garage at the age of 5 and had told them since the age of 10 that I was going to go skydiving, so while the timing may have been a bit of a surprise, the act itself definitely was not. Talk to your parents if you think they'll come around. If you think they'll never support it, consider whether taking up this sport is worth possibly damaging that relationship and how much damage it could cause. Your call.

That sounds a bit more in line with reality. A couple of years ago, after getting a ridiculously high life insurance premium quote when I disclosed my skydiving activities, I decided to crunch those numbers myself. Since the insurance company didn't care what type of motor vehicle I drove, I decided to compare the fatality risk associated with skydiving to that associated with another activity for which the fatality risk was considered so inconsequential as to be excluded from the life insurance premium calculation -- namely, riding a motorcycle. Using the skydiving data here: http://www.uspa.org/AboutSkydiving/SkydivingSafety/tabid/526/Default.aspx And the motorcycle safety data here: http://www-nrd.nhtsa.dot.gov/Pubs/810806.pdf You can calculate that, for 2006 (the most recent year for which data are available in both categories), the fatality risks are: per vehicle mile traveled on a motorcycle: 3.88E-7 per skydive: 1.03E-5 So, to accumulate the same risk associated with one skydive, you must ride your motorcycle (1.03E-5)/(3.88E-7) = 26.6 miles Since I live approximately that far from work, it would, statistically-speaking, be safer for me to skydive into work than to ride a motorcycle. When I called the insurance company back to share my findings with their actuaries, they were unsurprisingly uninterested.

Listen to what others have said re: getting good coaching and wearing proper gear, but if you are looking for some exercises to increase your flexibility, consider yoga. Bow, bridge, and upward facing dog are all fairly accessible back-bend poses that you can use to improve your spinal flexibility. Some info on yoga back-bends here: http://www.yogajournal.com/poses/finder/browse_categories/backbends That link has some instructions for the poses, but going to a certified yoga instructor would be best. And certainly speak to your doctor if you currently have or have in the past suffered any neck or back pain/injuries.

This whole situation has been characterized by bad behavior on both sides. The DZ management is not handling the situation with the mature, carefully considered, and legally rigorous strategy that would be most effective (yeah, I know that’s an understatement), and the airport authority board and city of St. Marys have been throwing out red herrings and engaging in legally-questionable actions. Security isn’t the real issue here, though. Base security personnel were annoyed and inconvenienced by the skydivers that landed on base. It meant additional paperwork. But a couple of guys “dropping in” to a residential area of base in the middle of the day looking like a couple of Power Rangers dressed up to crash Rainbow Brite’s birthday party don’t represent a genuine security risk. Air traffic overflies (the non-P50 portion of) Kings Bay daily. Jacksonville International Airport is located less than 30 miles south of the base, and traffic is regularly directed northward toward the St. Marys Municipal Airport and Kings Bay Naval Base. Any of those planes could “drop” something onto the base. A skydiver could infiltrate the base by exiting an aircraft that originally departed from any airport within several hundred miles of the base. All that shutting down the DZ and/or moving the St. Marys airport will do is reduce the chances of a very apologetic fun jumper landing on the wrong side of the unmarked fence. It won’t significantly reduce the risk of someone with true nefarious intent entering the base by air (fortunately, very well-trained and well-armed Marines are there to greet anyone who "drops by" in such a fashion). All this is to say: the skydivers landing on base recently was bad for Navy-drop zone relations and bad for PR, but security concerns are not the real reason that St. Marys is trying to shut down the drop zone.

Here are a couple of solo exits. A friend showed me how to do a gainer from a C182 this weekend -- super easy and fun. The gainer is smooooth and slow. Basically, you climb out on the step facing the back of the plane. Reach behind you and grab the strut with your left hand, and place your right hand on the back of the door. Then simply step/hop forward (while maintaining a vertical orientation), tilt your head back as far as you can, keep your feet symmetrical, and arch. This guy does it nicely: https://www.youtube.com/watch?v=YKD4qRbRknw Another fun one from a 182 is the backwards cannonball. Crouch on the step facing forward while holding onto the strut with one hand. When you're ready, let go of the strut, wrap both arms around your bent knees and lean backwards.

Most of mine have been pretty predictable, too, but here are a couple of the more unusual. Thumbs: A few days before I started grad school, I was invited to a department get-together at a prof's house. I brought a bottle of wine. No one else brought a cork screw. Undeterred, I decided to display my mad MacGyver skillz by opening the bottle of wine with my trusty pocket knife. I had almost dug all of the artificial cork out with the knife when the neck of the bottle shattered, and my hands slid right down the jagged edge. I sliced both of my thumbs down to the bone in almost identical places. Great first impression. Indestructible Gerber knife. Lip: On my first ski trip ever, I had a massive yard sale at about 30mph. Goggles gone, skis somehow still attached and planted vertically in the snow at a nearly impossible angle, contact lens lodged somewhere near the back of my eyeball. After a quick inventory determined that nothing was broken, I skied (gingerly) off the slope. I kept tasting blood, though. Once we got back to the car, I swished a bit of water to rinse away the metallic flavor, and red-tinged water started to dribble out of a tiny hole in the front of my bottom lip. Upon closer examination, the hole inside my mouth (entry wound) was about an inch long. Apparently, while using my face as a brake, my lower canine tooth punctured clean through my lip. If the hole had been centered just a centimeter to the left, I might have put a little diamond stud in it.

You are still experiencing 9.81m/s^2 (or "1G") of acceleration in freefall. That acceleration is responsible for your increase in vertical speed. If you experienced no vertical acceleration on a skydive, you would literally hover at altitude (i.e. your velocity would remain constant). Drag does not cause gravitational acceleration. The mass of the planet earth interacting with the mass of the skydiver through the force of gravity causes gravitational acceleration. Drag can only cause deceleration because it acts always to oppose the motion of an object. At terminal velocity, a skydiver experiences no net acceleration because the downward force of gravity is precisely balanced by the upward force of drag. You're absolutely right that falling at terminal velocity is not true free fall, although for a different reason than you stated earlier. The skydiving term "freefall" is actually different from the physics definition of "free fall". In pure free fall, there is no wind resistance (no drag), and the only force acting on an object is the force of gravity. The object therefore accelerates with a magnitude of F/m (where F is the force of gravity and m is the mass of the object) in the direction of the force of gravity. Near Earth's surface, the acceleration due to gravity is fairly constant and given by 9.81 m/s^2. Quoting Physics for Scientists and Engineers, Volume 1, 4th Ed., by Paul A Tipler, pg. 87: Very true, but I specifically emphasized in my analysis that it applies to a stable exit-to-freefall transition during which the skydiver maintains a belly-to-the-relative-wind (and therefore belly-in-the-direction-of-motion) orientation the entire time. We do not feel disorientation during such exits precisely because our orientation to our direction of travel does not change. However, during a funnel or other "fun" exit, we certainly do experience changes in orientation and certainly do feel it (or at least I do).

Freefall is not the absence of acceleration, gravitational or otherwise. Even astronauts in "freefall" orbit around the earth are experiencing an acceleration toward the earth. In fact, the force of gravity provides the centripetal acceleration necessary to keep the astronauts in orbit rather than flying off on a tangential path. True and already accounted for in the definition of the body's reference frame. Since the body's direction of travel (the vector portion of velocity) in its own reference frame is always "down" (as defined by the arrow out of the belly button) during a stable exit-to-freefall transition, there is no change in direction within the body's reference frame. Therefore, only changes in the speed (magnitude portion of velocity) contribute to acceleration.

A lot of confusion in this thread seems to come from a lack of definition of the frames of reference involved. From the frame of reference of the earth, a skydiver who exits an aircraft experiences an immediate vertical acceleration (due to the force of gravity) and an immediate horizontal deceleration (due to the drag force). Vertical acceleration continues until terminal velocity is reached and horizontal deceleration continues until the skydiver is moving with the same velocity as the horizontal wind. However, the human body does not experience sensation from the frame of reference of the earth. Rather, it experiences sensation (e.g. acceleration) relative to its own orientation. From the frame of reference of the human body exiting a turbine aircraft flying at 100mph (in a belly-to-relative-wind orientation) there is very little acceleration. Assume that, in the body's frame of reference, "down" is defined by an arrow extending out of the belly button and, if you remain stable, is always pointing into the relative wind. When you exit an aircraft and present to the relative wind, you have a "downward" (away from the belly) speed equal to the aircraft's horizontal speed. While on the hill, your body rotates relative to the reference frame of the earth, but not relative to the reference frame of the body. If you remain stable, "down" (defined by that arrow out of the belly button) remains in the direction of the relative wind. After a few seconds of stable freefall, your velocity is approximately 120mph "down". The net acceleration experienced in the frame of reference of the human body in a stable belly-to-relative-wind orientation is: [(terminal speed) - (horizontal speed of the aircraft)]/(time needed to accelerate to terminal speed) If you exit from a fast-flying aircraft, the difference in speed is minimal and, therefore, so is the acceleration in the body's reference frame. If you exit from a helo or balloon, the difference in speed is significant and, therefore, so is the acceleration.

Nah, just define your positive and negative directions of motion, then use trig to break your wind vector into downwind/upwind and crosswind components as applicable. If you define: 1) direction the canopy is flying = positive 2) then wind blowing in the direction the canopy is flying (flying with the wind) = also positive So ground speed = canopy airspeed + wind speed If you're flying into the wind, then the wind is blowing in the opposite direction that the canopy is flying, so: 1) direction the canopy is flying = positive 2) wind opposite the direction the canopy is flying = negative ground speed = canopy airspeed + (negative) wind speed Since adding a negative number is the same as subtracting that same number, the equation reduces to: ground speed = canopy airspeed - wind speed (for flying into the wind) The same equation works, you just have to define your positive and negative directions of motion. But you're right, when you start calculating ground speeds when flying crosswind, you'll have to do the vector math, and a calculator certainly helps with that...

Unless I'm missing something major here: You can think of your ground speed as having both a horizontal and a vertical component. 1) Ground speed = canopy's airspeed + wind speed Therefore: 2) Horizontal ground speed = horizontal airspeed + horizontal wind speed 3) Vertical ground speed = vertical airspeed + vertical wind speed Since the canopy's airspeed is constant in full flight (e.g. when you don't deform the airfoil by pulling on risers or toggles), the factor that causes your ground speed to change is the wind speed. Wind has an obvious horizontal component, but, unless you're caught in an updraft, downdraft, or turbulence, the vertical component is fairly negligible. Assuming, then, that vertical wind speed = 0, that last equation becomes: 3b) Vertical ground speed = vertical airspeed + 0 Your vertical ground speed is therefore determined by your canopy's vertical airspeed (a function of its flight characteristics at your wing loading), not by wind conditions. So, yes, you should just be able to clock your descent time from a given altitude and figure: Decent rate (i.e. speed) = (altitude)/(time to descend from that altitude)

Related question: If muscle memory is the reason that most people who find themselves in an unintentional low pull situation go straight for their main, would newbies (who have less muscle memory of going for their main and might tend to "think through" their EPs somewhat rather than instinctually reacting) be more likely to go for their reserve? Or is this unlikely to make a difference?

I don't know about other places, but at my home DZ, people who wanted to do the water training put their names on a list, and when that list got long enough (I think it was about 10 people for us), the DZ rented a pool and we did the training.

You think that a geopotential height increase of 200ft is a significant change in pressure? It's not. That represents a final/initial pressure ratio of ~0.993. That is easily achievable by simple daytime heating and cooling. And while homes are not air tight, any forced-air heating or cooling system can create temporary positive and negative pressures in the home relative to the outside air. An alti inside such a home and with a constant climate-controlled temperature would not read true (outside) atmospheric pressure. In homes that are designed for constant positive pressure, the buffering against outside pressure fluctuations can be even more pronounced. Conversely, an alti left out in a sunny spot that heats up to 10-20 degrees above the standard (2m above the ground, in the shade) temperature could indeed experience a slight decrease in pressure due to the formation of a micro-scale low pressure area. It's the same process that forms the vertical thermals that bounce us around under canopy as we cross paved and other dark land surfaces. Small changes (decreases, in this example) in pressure over a small area due to differential heating of the surface can create enough buoyancy to bounce you you right up to the pucker factor. And it can certainly deflect an altimeter needle by 200ft.

Unless the original poster lives in a air-sealed house, or used heavy fans during one of the readings, that does not matter for the air pressure. It matters for temperature. Higher temperature = lower density = lower air pressure. The reverse for colder temperatures is also true. In a quiescent weather pattern, the surface air pressure can certainly change by the amount described by the OP over a 4-6 hour period due to changes in temperature alone (typically decreasing during the afternoon as temperatures rise). Of course, the approach of a low pressure system could cause a similar (and more profound) change in surface air pressure. I asked whether his alti was inside or outside because inside, the temperature is rather constant, eliminating that variable as a cause for the observed decrease in pressure.

Weird. Well, unless a strong storm system was approaching your area, you might want to have it tested. Temperature changes and large-scale atmospheric pressure changes (e.g. approach of a strong low or high pressure system) are usually the only factors that will cause an altimeter to change on that time scale.

You wouldn't even need to have a low pressure system move toward your area to cause the air pressure to drop. Changes in temperature will do the same thing. Warm air is less dense than cold air, so if the temperature rose during that 4-6 hour time frame, your alti would sense the lower air pressure and would read a higher altitude (lower pressure). Was it outside or inside during this time period?

An alternative that I use is to land in the less crowded student or alternate (non-HP) landing areas. I load my canopy right at 1:1, so I'm often the first down in the student area. It's certainly not something to do at a new DZ without first talking to the S&TA or DZO like DocPop suggested, but it is a possible alternative to holding in brakes.

Thanks for the link! I appreciate the quantitative info (and a good reason to practice my German -- geez, I'm rusty...). I think I'll look into getting some custom earplugs made, since I can't find generic ones that fit my tiny ear canals. Here's a nice video about how clearing one's ears works: http://video.about.com/pediatrics/Ear-Pressure.htm A thought experiment: If you can clear your ears while wearing earplugs on the ride to altitude, doesn't that demonstrate that equalizing the pressure in your ears is possible while wearing earplugs? The only difference between the pressure change on the ride to altitude and in freefall is the rate of change. For those who wear earplugs in the plane, can you clear your ears by yawning, swallowing, etc (i.e. by not using your hands to plug your nose)? Is it more difficult with the earplugs in than without them? If it's no more difficult to equalize pressure with the earplugs than without on the ride to altitude, shouldn't the same be true in freefall? If it is more difficult with ear plugs in, that would indicate probable problems in freefall.

I have a full face helmet that I leave on during the entire ride to altitude (with the face shield up while in the plane). I've noticed that this provides a significant noise reduction, but does anyone know if the noise reduction provided by a full face helment is comparable to wearing ear plugs? (I'd just try the earplugs and do the experiment myself, but I have very small ear canals, and it's almost impossible for me to find earplugs that fit.)