pchapman

Here's one little thing that I don't think has been mentioned yet: If you have done 6 AFF jumps, depending on re-do's, you may be getting up close to what was Level 6, the unstable exit. No need to worry about that big transition from in the airplane to normal freefall. Forget the perfect exit, perfect presentation to the wind, leg kicks, and so on. Just tumble on out and sort it out afterwards. It is a bit of shock therapy and doesn't exercise one's actual stable exit technique, but can lead to it being less stressful because you're proving to your mind that falling out of an airplane isn't as big a deal as it was screaming at you! (DZ's will vary of course in exactly how they brief the unstable exit.)

Well, unlike Sgt. Nicholas Alkemade (and a few others) he was a bit of a wuss in that he did have the advantage of a parachute on his back. That's ok since he wasn't over deep drifted snow and pine trees. But yeah, still pretty good bit of luck. There are some other pretty amazing tales out there. At 50,000' one has about 11% of sea level pressure. Not quite space but not good for breathing. It would be interesting to figure out what kind of freefall time Siebold might have had. Some part might be faster if still strapped in to a seat or other wreckage. People have managed to survive ultra low pressures. E.g., "For example, in 1965 a technician inside a vacuum chamber at Johnson Space Center in Houston accidentally depressurized his space suit by disrupting a hose. After 12 to 15 seconds he lost consciousness. He regained it at 27 seconds, after his suit was repressurized to about half that of sea level." But once past a minute and a half, or maybe 3 minutes, who knows, things get very iffy. (Ref: Scientific American http://www.scientificamerican.com/article/survival-in-space-unprotected-possible/ ) Still when you wake up it may take some time to become usefully aware and able to take action. I seem to recall the record for highest intentional civilian skydive without oxygen was de Gayardon at 41,700'.

I'll guess he just got lucky to not have been physically injured much in the breakup, and to wake up sufficiently in time once there was more oxygen in the air. Explosive decompression and low temperatures wouldn't have been fun but not fatal. There certainly can be some time of confusion after unconsciousness due to lack of oxygen. And unlike the article there are no ejection seats. He probably had a mask on in the aircraft - there are FAA regs in case of depressurization at very high altitudes, although it clearly wouldn't help if the main supply were gone, a bailout bottle were manually activated, or the mask stripped off during the breakup. Although the breakup was at Mach 1, the Equivalent Airspeed would have been "only" about 250 kts if at around 50,000', which brings the forces down.

To add to that, there are packing tools that use Cypres cord Spectra line with less friction. The newer pull up cords tend to be a softer material and perhaps not as abrasive as the old Type III binding tape ones. Still, "sawing" a closing loop with a pullup cord can damage it quickly. And some people go for a closing loop out of heavier material than the usual type IIA (dashed diagonal lines on it), although that shouldn't change using good technique.

Cool. Perfect container for that -- with a quite flexible top flap so that flap could be retained, and it even has velcro at the top corners, to hold things closed around the risers. Hey, a Racer's (or Chaser's...) reserve container is derived from a belly mount design, so you're just reversing the process for the main!

It's funny how they're either used by newbies who can afford only the oldest, cheapest junk short of F-111 ... or by wingsuit jumpers, among whom I've heard a rave -- with perhaps a little exaggeration -- about how it is the best wingsuit canopy ever. (Glad I kept my old Sabre 1 135! With a pocket.)

+1 Engineers and technical types can get pretty pissed off with press briefings or releases full of platitudes and vagaries. Plenty of "explosions" of aerospace vehicles are indeed actually a more complex series of events involving aerodynamic disintegrations etc. If something looks like it exploded, does that mean it exploded? A big difference between the engineering and common use of a term. At least for the Space Shuttle Challenger, the official announcer did say, "obviously a major malfunction".

Since you've mentioned it twice now I think I'll suggest something different: It is incorrect to imply that it slows down because it jumps out at 120 mph. Once the pilot chute catches clean air, with its relatively low mass and high drag, and only dragging out a loose bridle, yes indeed it will decelerate very quickly. A spring loaded pilot chute can easily have a drag of at 150 lbs at terminal, and have a weight of around 1 lb (plus only light bridle to accelerate too). So once it clears some burble it will have a very high initial deceleration. (150 G in our idealized case of 150 lbs vs. 1 lb) That deceleration will fall off very quickly as the speed falls off, and of course a pilot chute will have some small terminal velocity on its own. (They don't float like Wile E. Coyote if dropped off a cliff) So it won't travel too far before having to accelerate the d bag out of the container. So yes a pilot chute will, compared to the speeds of skydivers, "almost come to a stop" due to its very high drag to mass ratio but won't "stop for a short duration" due to having the speed cancelled by springing out.

The latest seems to be that the tail booms started to rotate up early. http://www.avweb.com/avwebflash/news/NTSB-SpaceShip-Twos-Tail-Boom-Deployed-Early223043-1.html http://www.avweb.com/avwebflash/news/SpaceShipTwo-NTSB-Probe-Structural-Failure-A-Possibility223040-1.html I had hoped their systems would be good enough to avoid an uncommanded change of a basic aircraft configuration! But it at least starts to confirm the suspicion that it was hard to find anything related to the engine that 'exploded' enough to flip the aircraft.

There was a 1994 bulletin to inspect Swift Pluses for too-wide bartacks, as one had been found with ones wide enough to miss the fingertrapped line inside. That was for the line cascades. Other than that the canopies were fine. Although they often had fairly wide bartacks, any actually bad canopies were probably weeded out years ago. (Still, always good to check that some ancient bulletin wasn't overlooked...)

The Daily Mail has a good set of photos: http://www.dailymail.co.uk/news/article-2816224/Virgin-Galactic-SpaceShipTwo-exploded-45-000ft-One-pilot-dead-critical-Richard-Branson-s-500m-space-tourism-plane-blows-testing-new-fuel-California-desert.html Musings of an occasional engineer & pilot (me): From looking at a photo of the fuselage upside down on the ground (and comparing to others of the intact aircraft), it looks like the aircraft pretty much broke apart along the line of the wingtip hinges, the large wing flaps, and the bulkhead between oxidizer tank and rocket assembly. That's all sort of along the same line. Anyway, one of the long range photos from the ground makes it look like one or both of the tails has just come off and it looks like the aircraft has rotated 180. (The plume of smoke starts at the blunt upstream end of the object, and it looks like one can see a wing, backwards, projecting from the plume) But there's another similar picture out there, taken slightly before, with the aircraft also looking to be backwards, a bit of flame at the upstream end, and debris like both tails basically separating at the same time. ** I could be completely mistaken about the 'swapping ends' and missing alternative scenarios -- it is hard to tell from fuzzy photos ** And then some ground shots seem to show an at least largely intact black carbon fibre oxidizer tank within the fuselage -- so it wasn't as if all the oxidizer went up at once. Initial thoughts would have been that the problem was an explosion in the nitrous oxide system. I really don't know the mechanisms involved, but wikipedia suggests a couple. If the tank didn't explode, then it was in the piping aft of that, or the solid fuel part of the rocket itself, with the oxidizer pumped into the solid fuel area contributing. Hybrid rockets are known for being tempermental for combustion stability. (Although rockets in general tend to take a lot of engineering for that.) If both tails came off simultaneously, then it wasn't a case of a whole tail coming off either on its own or from an explosion, leading to loss of stability. Instead, given the photos and eyewitness testimony of a 'sudden puff', it sounds like something caused the vehicle to swap ends very quickly, and then both tails failed in structural overload once completely turned around. Would losing a smaller part of a tail be enough to cause such a fast loss of nose direction? -- Rather than a slower loss of control, dive, and then structural breakup. The cause of a partial tail loss could come either from an explosion or just structural failure. Would an explosion in the rocket be enough to push the craft off course enough to actually flip it (at what must be a decent dynamic pressure)? Seems surprising too. But an explosion could cause structural failure and some sort of jack knifing, with the still burning rocket pushing at an angle to flip the aircraft. Who knows. I guess one pilot wasn't incapacitated totally from any high g rotation or tumble. Perhaps it settled down into a relatively stable fall like a slow flat spin, and one pilot was eventually able to get out the escape hatch. Hope he at least does OK. Wonder who his rigger is too!

The Google translation to English, messy but usable: https://translate.google.com/translate?sl=no&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fnlf.no%2Fsites%2Fdefault%2Ffiles%2Ffallskjerm%2Fdokument%2Fso_2014-03_chernis_pilotskjermer_0.pdf&edit-text= One has to go to the original PDF for the photos.

Either way works, just a different frame of reference, earth vs. jumper

Amusement park ride? Maybe too scary and locked into it for too long. Pendulator? Rope jumps? Nice idea but hard to set up. Go to a local park, push some little kids away, and monopolize the swing? Maybe that would work, although you might want a slightly longer low G feeling than even the biggest swing can provide. I agree with the others about jump ship speed: One will get more downward acceleration with a slower jumpship. Also, I get the feeling that one may tend to notice a falling feeling less, the more other sensations add to the experience -- wind noise, wind pressure against the body. I certainly do remember "the falling feeling" a little bit when I started jumping, but it is hard to notice now. One acclimatizes. Some jumps later I could still feel it a little more if I did some sort of exit that felt unusual to me, like a back to wind 'ride the slide'. Distraction may help avoid the feeling -- like on exit looking up at the airplane and focusing on it and the face of anyone in the door. In addition to just toughing it out, you can of course work on learning to calm yourself before the jump by mental reasoning. I'm not sure of all the mental tricks but one can be reassured that the feeling (a) doesn't cause physical injury, (b) lasts only a few seconds, (c) mostly disappears from notice after habituation, and (d) plenty of other students have also lived through being super scared during their progression. Doctors must come across people who get terrified of needles or the sight of blood? Do they get told, with a bit of a snicker, to just tough it out?

You are right, I brain gapped, the reference value is indeed "S", the AREA not length, when talking about the drag coefficient for a 3-D object. (Length is appropriate when doing 2-D airfoil analysis.) Luckily you misspoke the first time around about the file size so now the whole file is here in two parts!

An interesting old study, which could demonstrate some general trends, although I wouldn't believe every single number. After all, one wonders how they get 0 lbs drag for some pilot chutes at 30 mph. Also, their Cd drag coefficient numbers jump around for each pilot chute, while it should probably stay about the same for each chute, no matter the speed within those that interest us. I believe they made a mistake in their Cd calculation. Their Cd formulas use the Area of the pilot chute rather than the Diameter. The drag and drag coefficient formulas always use a reference length, like the span of an airplane wing, or diameter of a round parachute. So although I didn't run the numbers, I'd say just ignore their actual Cd numbers, and don't put too much emphasis on low speed drag numbers. But perhaps the drag levels measured at higher speeds like 120 mph are reasonably accurate. The Vector II pilot chute came out as the lowest drag one tested. However it was designed with by far the strongest spring (thicker and more turns), back in an era when a lot of pilot chutes were decidedly wimpy.

========== reviving a 4 year old thread ========= The video link in Bill Booth's original post is no longer valid. I asked UPT to post the video again so they kindly did: "Meshless pilot chute explanation" https://www.youtube.com/watch?v=_yPshlycEJI&list=UUlRzGBH3ZaWMBGeIoHNXZFg It is good to see UPT explain their design choices for the pilot chute. While they show video with some great launches, Vector II pilot chutes can still get caught in the burble. A few youtube videos demonstrate this: -- a test jump I filmed of a jumper in student gear with a spring loaded main pilot chute https://www.youtube.com/watch?v=GF3wpTqdbEU -- a friend with a PFF (AFF) student where the pilot chute fails for a couple seconds to pull the main bag out: https://www.youtube.com/watch?v=_F1zOVlXpl4 (A reserve deployment would probably do better on average, as the much longer bridle allows a burbled PC of any type to bounce around and float further from the jumper, without having the risk being 'yanked back' by an extended but short bridle.) -- a 3+ second burbled pilot chute on an AFF jump, I think from Johannesburg: https://www.youtube.com/watch?v=6es6OCXhyyo So even if it can be argued that the Vector II PC might escape better from the edges of the burble, and perhaps on average deploy a little sooner, they certainly can still get tumbled around in the burble, with their extra fabric and more balanced fabric doing little when in the middle of it. And then when fully inflated, the shape ends up being a lot lower drag than other pilot chutes. UPT goes for meshless, many go for 50/50, and a couple rigs like Infinity and Wings have something in between. Despite all the arguments I don't think we have a clear winner among all the pros and cons to each design.

Leaving aside the more common stuff, the few unusual planes I've jumped from are: de Havilland Dash 8 Blanik glider (sitting out on the wing leading edge) Short Sherpa (Not mentioned yet but not that unusual as at least one has been on the jump circuit in recent years.) C-180 on floats (Climb rate sucked, but you could line your four-way up on a float and step off..)

Not sure about that main vs. reserve issue but the container does perhaps look as you described. I'm also wondering about the drogue deployment method up in minimal atmosphere / low dynamic pressure. Somewhere I saw it mentioned that they used special equipment or technique for that. The drogue bridle does look odd in the brief moment one can see it in the official video, as if it has a rigid tube lower section designed in some way to keep it away from any jumper entanglement. ....Aha, I found where I saw it: it was in the very short report on an aviation news site, avweb.com : "His technical team also designed a carbon-fiber device that prevented Eustace from becoming entangled in his parachute should he not be stabilized when he deployed the parachute." So could the drogue in tube not be trailed normally after opening? On the 'real' jump did they jettison the drogue after deployment with a cutter? Or did they cut the drogue first and have some sort "main in freebag in reserve pack tray"? Each option has various additional implications. ======== EDIT: Avweb also has a longer second article at http://www.avweb.com/avwebflash/news/Record-Skydive-New-Suit-Pioneered-Six-Person-Capsule-Planned222978-1.html which mentions, "The pilot chute device, called Sabre, reduces the risk of pilot chute entanglement, which nearly killed Joe Kittinger during one of his Project Excelsior jumps in 1960."

As the NY Times article stated, "He performed two slow backflips before a small parachute righted him."

It isn't just a rumour... but the information is pretty hard to find and they don't seem to advertise it much. Cutters are good to 14.5 years... but from its own manufacture date which might be older than the Cypres it is attached to. (I just looked at a my stock of expired Cypres 1's, and saw cutter dates of 4, 8, and 10 months older than the main units.) Pretty much only helps if someone local has a Cypres fire and you want to get them back in the air quicker and have a recently expired Cypres lying about. (Cypres 1 manual says nothing about 4 year checks on cutters separately, but the Cypres 2 manual does, but the attached document doesn't mention it. So one can argue about whether a 13 year old cutter than hasn't had a "12 year check" would be legal. I doubt few would worry until the actual 14.5 year point is hit.) In a quick google search I can't find where I got the Airtec document so I'll just attach it. Would be nice to have an original source to confirm. [Edit: Koppel obviously found another Airtec info source]

Perhaps we could agree that anemometers largely read TAS within reasonable limits of air density. For our purposes, we can ignore what issues there might be in using an anemometer on a re-entering Space Chuttle. (I get the impression that the idealized anemometer with zero mass or torque would be free of density effects but I'm not sure if that would eliminate all error or only some of it.) That was a nice find of a scientific article, with updated information at a level of measurement detail not found in the 1933 paper. On the one hand the new paper shows that air density has an effect: However the effects are small. They did their calibrations based on the calculated speed being equal to a constant times the anemometer rotation rate, plus a fixed offset constant. V=Af+B That linear constant "A", its rate of change with density changes could be either positive or negative depending on the model tested. And the data was pretty messy with a lot of scatter in the graphs, with different results from different studies. I took a sample graph, the one at the top left of p14 of the pdf, and used the linear formula they came up with. If that can be extrapolated to much higher density changes than they tested, the factor "A" would change from about .0512 at sea level to .0474 at half atmospheric density (or about 18,000') Ok, that's about an 8% change, or error from TAS. That's not negligible. But meanwhile IAS will have changed by 30% (root 2 = .707). But as I said, other anemometers may have very different changes in their constants (and even whether the number rises or falls with increasing altitude), so there's no consistent way of determining density altitude effects without, say, calibrating a particular anemometer in variable density conditions. But thanks for pointing out some of the lower level effects of air density on anemometer output. (The paper does mention the effects exist for both vane and cup type anemometers, but focuses on cup type ones. The implication is that vane types ones are similarly only lightly affected by density, but that's open to further investigation). So as to whether an anemometer basically measures IAS or TAS, it is still very much closer to TAS -- even if they can't quite approach the ideal. What you will be able to do is to see how consistent your own data is. If you do a high hop and pop and record a given airspeed with brakes off at 10,000', do you get nearly the same readings down at 2,000'? Does the speed decrease as you go down, roughly in line with the density increase, or does it stay nearly constant like an IAS?

Negative, Ghost Rider! But your questioning did get me to try to get a definitive answer. Check out NACA (predecessor to NASA) Report 420 from 1933 on airspeed measurement. It's out on the web. Relevant excerpts are in the attachment. It notes that an anemometer will read true airspeed and not indicated airspeed, which is why it is not particularly suitable for aircraft speed measurement. (This is for normal style anemometers which attempt to have a bearing of negligible friction. If it were a wind turbine with torque resistance, then it would act more like a set of airfoils and vary measured speed with air density -- showing IAS.) This is a subtle thing about anemometer airspeed measurement which isn't obvious at first glance!

Doesn't an anemometer style airspeed indicator give a True airspeed (changing with altitude) rather than an Indicated airspeed (constant with altitude)? Because they deal with the linear amount of air flowing through instead of just the pressure. Can't be sure offhand but I thought that was the thing to remember with them, if using for flight test purposes. Then the Altitrack would be used in TAS mode not SAS. (adjusted to 3000' with I guess an ISA assumed temperature). Then both sets of numbers would need to be converted to ISA conditions so you can compare tests down low vs. up high (and on different days) on an equal basis. Ideally one would have the anemometer on a trailing bomb (as they say in the flight test world) but I always just held one way out to the side and up a little, as far from my body and torso as possible, to minimize errors due to increased velocity around a blockage (one's body).

As others are getting at, it seems like the main lift webs may be a little long. Making sure the leg straps are extra snug may help but there's a limit. Chest strap positions on rigs do vary a bit. If tightening the chest strap a lot helps, maybe that's effectively shortening everything by creating more of an "X" shape rather than "H" shape -- when looking at the harness from the front of the jumper. Plus generally holding your body in tighter, so one may be 'slumping' less within the harness on opening. So who knows, lateral length and yoke size can all be involved too. I think by trying to cover all the points I pretty much just said, 'who knows, it could be anything' -- there's some sort of harness fit issue. A looser harness (despite the extra tight chest strap) might allow you to unintentionally load one leg strap more than the other on opening, not as symmetrically as desired. Still, line twists are a bit of a surprise as you would be at a low wing loading at ~113 jumps. Your profile says Sabre2 150 at a low 0.83 wing load.