pchapman

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Well, NASA (and others) have tested "lifting bodies" which do not in general exhibit typical stall characteristis as expected of a wing, and have very high AOA. So lift does not have to be "pre-stall" in order to (a) exist, and (b) be effective.

Oh yeah, neat aerodynamics. Although the aerodynamics are different, they remind me strongly of modern high wing loading parachutes: When one has a crappy glide ratio, diving for extra speed gives one the energy to create an effective flare and plane out long enough to gently ease down to a landing.

So the issue still remains, how to describe the type of aerodynamics that are "pre-stall" ... in terms of conventional aircraft wings, not lifting bodies or vortex flow low aspect ratio deltas or whatever.

The best I could come up with was 'attached flow aerodynamics'. Can you think of a good way to describe it to those not trained in aerodynamics, other than just saying 'like a normal wing when it is flying'?

All in all I see Gary's point, but I think his short post can be misinterpreted, and can seen to be too hard a criticism of Kallend's letter, which was also pretty short. (... for engineers, anyway.) Kallend's letter in turn doesn't invalidate what Ralph Glasser was trying to get at, even if Glasser didn't understand lift correctly. Kallend says what Glasser got wrong, not what he got right.

Point by point:

-- John Kallend is right about the definition of lift.

-- Yet the concept of Ralph Glasser's criticism of Atmonauti can be valid, given the over-enthusiastic claims of some Atmonauti supporters. Glasser didn't get the concept of lift right, but what he means is that skydivers aren't creating the kind of lift we normally think about from a flying airplane wing -- with lift that is from attached flow, or 'pre-stall' lift. That's to be distinguished from lift that is barn-door in nature, or from unattached flow (on the upper surface), or 'post-stall' lift. I'm not sure what to call it myself, even though it is such a fundamentally important concept in aerodynamics and aviation.

So IF some Atmonauti supporters keep talking about how their bodies are like wings and are truly flying, then Ralph's criticism may be valid. I have seen diagrams published for Atmonauti which also show a misunderstanding of the definitions of lift and drag.

-- Pressure differences between top and bottom have to be the source of lift, whether a wing or object is flying pre-stall or post-stall. If there were no differences, one couldn't create any lift. And de-arching couldn't provide a better track.

-- As for the implied issue of wings vs. barn doors, or deflection vs. pressure differences in Kallend's letter, that's an old debate of Newton vs. Bernoulli for how an airplane flies. The simple answer is that both are true and are part of the process of lifting an object aerodynamically: Pressure differences create the lift force, and when that lift pushes a flying object one way, the air gets deflected the other way.

-- Dearching has been shown to be very useful in providing a good track, so it does need to be taught.
One interpretation of Gary Peek's words indicates that he objects to that, but I think what he means is that he objects to suggesting that it helps due to providing extra attached-flow lift.

I'm not an expert on tracking, but it seems that the lift we skydivers make is basically all post-stall lift. As Glasser says, the body isn't very aerodynamic. Also, consider the angles: Even if a superb tracker were able to get a 1:1 glide, or nearly that good, a common "good tracking position" is only slightly head low vs. the horizon. So we might have a down 45 to 55 degree flight path combined with a body oriented down 15 degrees. This gives an angle of attack of 30 to 40 degrees.

Definitely post-stall lift at that high angle! (Even if one were talking about a wing, not a lumpy, ultra-low aspect ratio skydiver.)

As to whether one should be, say, 10 degrees dearched, vs. 5 degrees (or even 0 degrees dearch), that I'm not sure about. Certainly for inexperienced trackers, one has to emphasize dearching, otherwise they may retain some arch withought realizing it.

In the end do I agree with Gary Peek about his concerns about telling people to "make their body the shape of a wing"? I agree that people shouldn't learn that one is truly flying like a wing normally does (with attached flow lift). I'm strongly against that misconception. But the idea is still a useful basic analogy and training tip, even if it shouldn't be taken too far and used as an explanation of the physics involved.

From the posts by dorbie and jennr8r:

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There wouldn't be anything to notice if you fumble your bag when doing up your stows or when dropping it in the container and it somehow falls through your lines.

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I would put the bag behind the container while I arranged the risers in the channels. The unstowed lines were long enough to allow the bag to roll. I'd put the bag in the container and have my stepthrough.

These are interesting examples of how to give oneself a step through. I'd like to note that the pilot chute & bridle should normally be a clue that something is amiss, even when one can't tell whether the lines themselves have a subtle twist where they go into the line stows on the bag.

Even when the BAG has flipped through, the BRIDLE & PC haven't yet.

The exception is if one had the bag, bridle, and PC all together and fumbled them together into a flip through.

But in most cases during the packing process, the bridle and PC are laying stretched off somewhere away from the bag. (And if the bridle does cross the lines, it is sitting ontop of the lines.)

In this sort of normal case, when the bag does its somersault through the lines, the bridle will now be trapped underneath the lines (and/or bag) at some point. That's the clue. To get the bridle and PC to the normal spot, one will have to pull the full length of the bridle out from under the lines, to fully complete the step through. One should be thinking, "How did the bridle get under the lines? That's not how I pack; something's wrong."

(This addresses the step-throughs of the two posts quoted, not the step-through that billvon mentioned where a step-through exists before the pack job starts, but is not noticed.)

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The only method that's ever worked for me consistently is a purpose-built bag with a riser-keeper on the outside that both held the risers and the bag and prevented them from turning.

I've found commonly available plastic storage containers that worked great. (E.g., Rubbermaid 17 l / 4.5 US gal "Roughtote" bin)

If one gets the size just right, the bagged canopy fits in snugly without room to roll around. The risers are neatly laid out over one edge of the bin. The lid is flexible enough to snap on and stay in place with the risers over the lip, so that it traps the risers in place. Adding riser keepers, like billvon has done, would make it even more secure.

More people should mark their risers for left & right too. It's a real help when untangling or reconnecting a canopy yet takes so little time to do.

(I jump a rig in which I put a removable pillow system so I can swap between a couple canopies. With a full set of PC, bag, and risers for each canopy, I can swap quickly without repacking. Never made a mistake hooking up the canopies...yet.)

Packerboy provided some good air regs references.
I hope I can add something on summarizing some of the main concepts.

If you are doing a real demo in Canada, you need either the Canadian Exhibition Jump Rating, or the USPA Pro rating. Both are accepted. (Other parachute organization ratings may be accepted after special approval.)

By 'real demo' I mean those that require a Special Flight Operations Certificate (SFOC) because of a "built up area or open air assembly of persons" -- i.e., jumping over a town or an airshow crowd.

The air regs (CARs) require an SFOC not just for towns & crowds, but also when jumping in controlled airspace. (Both control zones and Class E airways.) Reading those air regs is misleading, as there is also an Exemption to the rules, that is harder to find in the online CARs. The Exemption applies to everyone, just that it's not permanently in the rules and gets renewed from time to time. The Exemption is quite reasonable, with some regs on broadcasting jumps on the radio, being in contact with ATC, having a transponder, things like that, depending on the class of airspace.

So that allows one to easily enough jump into a friends place etc through airways, without the whole SFOC approval procedure and demo rating requirement.

One uncertainty is the "open air assembly of persons". That's always been confusion and consternation here in Canada about it, whether for parachuting or general aviation. Mainly it is intended to make sure one has Transport Canada SFOC approval if one is parachuting or doing a flying demonstration in front of a crowd. Not being an expert at this, I just don't know what constitutes an "assembly of persons". Two buddies watching you jump? A private party of 100 people?

The rules say "over and into" such assemblies of persons. So one might get away with jumping 'off to the side' of such a crowd without going near them.

I remember years ago (before the 'new' CAR air regs of 1996) there would be 'non demo demos' where you didn't need an EJR because the landing area was huge with lots of outs and no crowd or city to one side. I'm not sure if Transport Canada still accepts that or not, given the above argument.

Transport Canada people seem very reasonable with SFOC's for demos. If you apply within the requested time, do your homework, and have the ratings, it seems to work out fine. The paperwork includes submitting picture or scale diagram of the site with landing area, outs, crowd line, etc. They also need a list of jumpers' names. (Perhaps it is the same in the States -- if one doesn't know who exactly will do the jump, submit a longer list of names and state that only some will actually jump.)

Staff instructions at Transport Canada and ATC say that parachuting is to be treated like any other aerial activity to be coordinated. So approval can't be withheld just because someone at ATC doesn't want to deal with both planes and skydivers.

For the SFOC there are a couple equipment regs like square reserves, and reserves packed withing 120 days. (A bit of a bizarre holdover from the old regs, as other than that we've gone to a 180 day cycle in Canada.)

[edit:] One thing I'm not sure about is insurance. I didn't see it in the regs, so it may just be an issue if the landowner or municipality requests it.

As for whether one needs to be a CSPA member: Those with EJR ratings need it of course, but a USPA Pro rating holder wouldn't seem to, unless insurance is an issue. Demo jump insurance is available through CSPA for members.

Background: I'm not a regular demo jumper so don't know all the details. I have jumped in and helped do the paperwork for a few demos.

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Just keep in mind that your canopy isn't (hopefully) flying at 5 feet altitude... How does your formula look like? It looks like it is very non-linear near ground

The heights I chose were arbitrary, but the 15 ft level corresponds very roughly to a canopy on landing, and the 5 ft level corresponds to where we feel the wind in our face when standing on the ground.

The formula uses height ratios and an exponent, so yes it is quite non linear:
v2 = v1 x (h2/h1)^n where v1 is the known reference wind speed at height h1 above ground, v2 is the speed at a second height h2, and n is an exponent based on testing. The exponent n varies between .1 for smooth ocean and .2 for tall crops & low woods.

I can't comment on how well the various formulae and statistics out there are regarded by those in fields dealing with wind measurements. This one appeared reasonable, and good enough for a rough image of the kind of wind speed changes a skydiver may deal with during landing approach. (Being downwind of a large obstacle is another matter.)

Just to touch on the wind gradient issue:
Various formulas (usually exponential) exist. As height goes up, wind speed increases rapidly at first, and then more slowly.

One reasonable formula, for example, results in the following numbers, over terrain that consists of high grass or low crops:

5 ft height ------ 18 mph
15 ft height ------ 22 mph
33 ft height ------ 25 mph
100 ft height ------ 31 mph
200 ft height ------ 35 mph
(The above would be for a weather report of 25 mph winds, since a standard measuring height is 33 ft.)

Real life of course will vary a lot! While the formula makes it all a gradual change, the overall change is significant -- the wind is about doubled a couple hundred feet up, compared to what one feels in one's face on the ground.

To add to the remark about Tiny's "reserve" being the one on the ground, there's also this story:

"When I asked her how many malfunctions she had using this rather unique deployment method, she quietly answered "27". When I then asked her what she used for a reserve, and she questioned, "What's a reserve?" I almost s**t. Then I realized that her malfunctions were most likely "Mae West" partial inversions, and that her large canopy combined with her light weight allowed her to walk away from all of them."

[Source: Bill Booth in
http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=283437;search_string=broadwick%20malfunctions%20how;#283437]

Where else but dropzone.com can one find Bill Booth writing, "I almost s**t"?...

I just don't worry about getting uncurrent over the Canadian winter. That's the way life is.

I'd rather just make sure that I've got the money saved up so that I can be nice and current when the summer comes. So for example, if I had the money and time for 100 jumps a season, I'm quite happy to do them all in a few summer months, rather than spread it out over 12 months.

A shorter period of intensive jumping may not be quite as good for safety at the start of the season (due to the long layoff), but it will be better for learning new skydiving skills and really getting everything "dialled in" during the season. This might be the better choice over the long term.

(That being said, I do jump in winter, jumping a little bit all season at the DZ I go to, which is closed only December and January.)

Otherwise my recommendations are common sense ones: Take it easy at the start of the year, take some time beforehand to look over one's gear, refresh one's memory on skydiving techniques & safety, review one's accomplishments & performance from the last year, that sort of thing.

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All but the 106, 113, and 281 were certified under TSO C23b.

Little correction for the record:
Most PD sizes were certified under C23c, Category B.
The 106, 113, and 281 are C23d.

C23c Cat B (254 lbs, 150 kts) is still a lot better than C23b with all its vagueness for the user...

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Get big and out fly them.

I will re-emphasize that point! For many areas of skydiving, body motions need to be subtle to avoid overcontrolling. When dealing with the mass and unintended control inputs of a tandem student, it can be useful to lunge out with arms and legs, grabbing as much air as possible. (Edit: To be precise, it's not just the force of air, but also distance from center of mass for greatest torque.)

Think about how agressively style jumpers grab air. A tandem instructor shouldn't just lie there in a boxman position, tilt their legs and upper body a little bit as for a conventional solo turn, and complain about how the student was turning them.

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Well, since it happened in Germany there's probably not much the FAA could do, but it's still ironically apropos.

Well, the US has gone into Germany before to enforce the rule of law. But what with the cost of Afghanistan & Iraq, the US treasury & armed forces might be stretched a bit thin. Now, back to the thread...

One may wish to distinguish between arrogance inside the sport, vs. that outside of it.

A skydiver might present themselves to the whuffo world arrogantly, because of that feeling of superiority over the apparently boring, timid, flightless masses. But at the same time that skydiver might be patiently working on their canopy and freefall skills, and feel humble within the sport.

It is still nice to feel good about the cool sport one is involved with, and be accepted by other skydivers, no matter what one's experience level is.

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The BASE community has a considerable amount of experience jumping gear with varying degrees of wetness.
Walt

When I recently searched the BASE forum I couldn't find anything on wet canopies, which surprised me given the detailed analysis that people try to do in BASE. But my search wasn't exhaustive, nor have I checked blincmagazine.

Bridge Day is one event where soaked canopies are commonly jumped without drying.

Perhaps a post in the BASE forum mentioning this thread might obtain some useful response?

The USPA also puts a whole bunch of their reports online. It's not just the fatalities, but many non-fatal incidents too. So there's a lot of interesting reading.

It's not clear from the web page how often it is updated or what date range is covered, but there should be plenty of new things to read if one checks it two or three times a year.

http://www.uspa.org/safety/incident.htm

That's cool that someone came up with a new rotating parachute!

As far as I had known, the idea had died with the old Barish Vortex Ring parachute, jumped back in the 1960s.

Even with a swivel, the payload will tend to rotate. Not good for a human but irrelevant to a jug of water.

While economical in terms of fabric & lines, one wonders about malfunction potential. It looks like a nightmare for partial inversion type of mals, which would then result in entanglements of all the rotating parts, as was supposedly experienced in the 60s. If only low value payloads are used, higher mal rates are acceptable. Overall delivery costs might still be minimized.

120 lbs at 22 fps at 1.5 lbs chute weight? Maybe someone has to jump a slightly enlarged version to beat the "smallest landed parachute" record... :)

But I didn't design or test it, so good for Atair if they've figured out how to make it work well.

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I don't guess you guys routinely do end-of-day formation RW loads, do you?

Yes, we do formation fun loads from time to time, and they are interesting for jumpers and pilots alike.

But some formations could indeed be flown tighter. The pilots don't get to practice formations enough, due to a combination of not getting formation loads organized as often as we'd like, having a large pool of pilots, and the inevitable yearly pilot turnover. (On busy weekends, the DZ typically runs 3 or 4 182's.)

Thought I'd mention an odd tandem technique that was used a couple times this past weekend at the DZ I jump at. It's no big deal but I'm curious to what degree anyone else has tried it.

The DZO experimented with doing a two C-182 formation load, with a videographer from the trailing plane diving to catch and video one of the tandem pairs from the lead plane. This was done so that both tandem students on the lead plane could get their own video.

We run modified C-182's that usually can take 5 jumpers, which allows two tandem pairs and one video, but not video for both. These customers insisted on being together in the airplane, as well as getting their own freefall video. We don't have hand cams.

The trail plane held the videographer going for the lead plane, plus two tandem pairs who weren't getting video.

That videographer had an interesting challenge to get to the tandem pair within the limited time available from 10,500' down to tandem pull altitude. On one formation load the video went well, while on the other there was too much separation between the aircraft on exit, so the videographer (despite his experience and freefly skills) was only able to get in close to the tandem for the last 5 or so seconds.

Trying this technique was controversial at the DZ, both for the time taken, and the notion of doing tandem flights with students. It took a long time to organize and brief, while the formation climb also takes longer. The whole experiment did significantly delay other jumps at the DZ on a busy day. I don't know whether the DZO will try it again some day, but I'm guessing even he will feel that on the balance, it just isn't worth the extra effort unless there were some very important reason to have two tandems getting video to be on the same load.

In reply to phoenixlpr who started all this, everything I've read about parachute testing suggests that weight does matter...although not as much as speed. Even without understanding all of the opening dynamics, this will be related to aerodynamic forces (e.g., dynamic pressure) increasing with the square of the speed.

>>> The rest of this post just looks at some numbers based on actual parachute testing. <<<

While phoenixlpr isn't inclined to believe anyone, let's look at the NAS 804 specs, which JerryBaumchen and mjosparky mentioned. To get to a 5000 lb peak force, one could have 150 mph and 660 lbs, or other combinations including 300 mph and 200 lbs.

The NAS 804 standard was based on a particular old round canopy, the C-9. It's not the same as a slider-reefed ram air, but some general trends should be similar.

Those numbers show that to keep the same load, when the speed was doubled, the weight didn't just get halved (a ratio of 1/2), which would be the case if weight and speed were equally weighted. Instead, the weight had to multiplied by a factor of 1/3.3 to compensate. So a change in speed has a substantially greater effect on peak opening force than does weight.

When comparing the rest of the NAS 804 tables for 3000lbs of force and 5000 lbs, it can be seen that forces nearly but don't quite rise as fast as the weight does. So doubling the weight won't quite double the force. (At least in some of the speed and weight range tested.)

As for speed, the tables show that forces rise much faster than does speed. But forces don't rise as quickly as the dynamic pressures (i.e., speed squared). So doubling the speed will increase force by much more than a factor of 2, but not by quite as much as a factor of 4. A canopy with a slider to control inflation should exhibit a smaller speed effect.

This is all based on one old type of parachute, but it still provides some feel for how opening forces can change with weight and speed.

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I always feel strange when I hear (read) people speaking or writing about "races".

It's fine if "race" may not be a strong taxonomic term and it isn't as important genetically as some think.

But... while the post may well be an accurate comment on a term being used in this discussion, I wanted to say that it doesn't really change the discussion so far. Race is still a convenient label, a first approximation or indirect measure of sometimes different cultural backgrounds. Nobody here is really suggesting any inherent genetic differences in regard to interest or ability in skydiving. ('white men can't jump/black men can't fall')

I bet it's just a "round chute" that's built in a square pattern. It's just the photo that makes it look like a wing.

The Soviets, for example, had a long history of building square shaped "rounds", to an extent greater than in the US. The square canopy's simple shape makes them less expensive to build than a round canopy with all its roughly triangular gores and reinforcement tapes circling tangentially around the canopy.

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just wondering if I decide to get this rig if I'll be the only person in the world with a MB handle.

One data point:
I know a short female jumper in my area who bought a new Vector III some years ago. It was built with a Martin-Baker handle to fit her.

Just as a quick comparison of prices, here are list prices from the latest Para-Gear catalogue. (I don't know how discounts might differ but list prices are a starting point.)

PD Reserve (up to 160 size)...............$ 1180
Aerodyne Smart (all)...........................$ 949
Precision R-Max (128, varies by size)....$1108

Icarus Reserve (up to 169 size)............$1385

More briefly for less common reserves, of roughly similar sizes:

Super Raven 135 $959
Strong Stellar 140 $1238
NAA Eagle 140 $1175
FCI Cricket 145 $1098

So the Icarus is top-of-the-line, at least in price...

Guess I'll chip in with minor night jump recollections.

A few weeks ago I did my first night jump in a decade. It helped everyone on the load that the landing area was so well lit -- not just a couple car headlights, but a long row of them, shining onto the landing area from the adjacent parking lot. That was handy since I was at three times the wing loading as on my earlier night jumps under a big F-111 canopy.

Actually the jump only occurred 40 - 45 minutes after official sunset, so there was some glow in the western sky although the ground was completely dark, and nobody had glowsticks. Yes "the limits were being pushed" with one last load of high priority tandems! (Let's not get into that issue.) One could still vaguely make out one's altimeter in the air. Some guys with Neptune altis were scratching their heads trying to remember how in the heck to access the backlight control, given that the screen was barely readable in the aircraft.

In freefall I did a little solo head-down practice -- using the lights of a foreign city on the other side of one of the Great Lakes as a heading reference.

One jumper started spinning on opening. It didn't help that he still had his dark goggles on, as those were his only pair with the aiming dot for doing tandem video. But he got himself out of the line twists, not having to jettison gear into the darkness. I guess he had his dose of excitement for the night (without even having to get out his BASE rig).

Conditions weren't ideal for swooping, given the difficulty in reading the altimeter, and the loss of peripheral vision cues with the lit landing area surrounded mainly by dark. But other than that, it was absolutely beautiful swooping, with zero wind and newly formed dew on the grass to slide it in on one's feet...

I was going to ask about those outrageous old BSBD shirts, but someone else started the thread first. I'd certainly buy a shirt or two!