Wikipedia:Reference desk/Archives/Science/2016 May 17

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May 17

Parachuting

What special precautions (if any) must be taken when parachuting into a heavily forested area? 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 01:49, 17 May 2016 (UTC)

https://en.wikipedia.org/wiki/D._B._Cooper68.48.241.158 (talk) 02:30, 17 May 2016 (UTC)

That should be avoided if at all possible. The parachutist is likely to get hung up in a tree and need rescuing, so communication equipment and GPS would be needed, and water to drink until the rescuers arrive. Diapers might be a good idea, too. StuRat (talk) 02:34, 17 May 2016 (UTC)

Also, try to avoid carrying large satchels of money, as D.B. Cooper did. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:44, 17 May 2016 (UTC)

I wonder if a specially designed parachute could be made that would allow the occupant to lower themself down on a rope to the ground. Depending on the height of the trees, it could be hundreds of feet down. Of course, there would still be the risk that they would hit a branch and be killed or incapacitated. StuRat (talk) 02:47, 17 May 2016 (UTC)

Aside from pre-planning as you're suggesting, the best advice would be, "When parachuting into a forest, try to avoid trees." ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:49, 17 May 2016 (UTC)

That might not be as silly as it sounds. Obviously, where you have complete tree cover, avoidance isn't possible. But if aiming for a clearing in the middle of forested area, a stunt parachute may help to steer it into the clearing. StuRat (talk) 15:17, 18 May 2016 (UTC)

For unintentional tree landings in sport parachuting, see the "Trees" subsection of 5-1F (General Recommendations / Skydiving Emergencies / Landing emergencies) of the USPA Skydiver's Information Manual. -- ToE 03:20, 17 May 2016 (UTC)

For paratroopers intentionally targeting forested areas, see Treejumping. -- ToE 03:31, 17 May 2016 (UTC)

For forestry personal, I would have expected us to have something under Fire jumper, but alas that link is currently red. see Smokejumper -- ToE 03:36, 17 May 2016 (UTC)

I created redirects from Fire jumper and Firejumper to Smokejumper. --Guy Macon (talk) 10:24, 17 May 2016 (UTC)

Here's a publication from the FAA that includes both regulatory and advisory details on parachute landing areas (e.g., information about mandatory rules and optional decisions): from their advisory circular database, Report DOT/FAA/AR-11/30, Criteria for Parachute Landing Areas on Airports. In their section on hazards, they describe trees, and recommend sizes of areas at specific distances from dense trees. There are a lot of useful diagrams. More complex operations need more obstacle-clearance. The publication also references several Army sources for paradrop operations; if you actually do decide to go parachuting, those field manuals are sort of the "canonical" source of math and equations. For example, the FAA cites FM 3.21 Pathfinder Operations for equations on landing drop zone sizes. Obviously, consult your dive-master or parachute jump coordinator for more specific, current, local information.

More good reading: Advisory Circular 105-2D, Sport Parachuting; this government publication advises about hazard and obstacle avoidance, and references several other publications of the U.S. Parachuting Association as further reading. For example, here's the Skydiver's Information Manual, a lengthy 270-page book that includes the BSRs (Basic Safety Requirements). These are advisory rules - the Government doesn't enforce them, but FAA encourages you to learn from a reputable instructor, especially one affiliated with USPA, and to adhere to their safety rules. Per Federal Aviation Regulations parts 91.15, 105.21, 105.23, and 105.25, the Government doesn't really care what happens to you if you fall out of an airplane - as long as the pilot takes "reasonable precaution," and provided that you don't land on an airport, a congested area, or special use airspace. You can land on those things too, provided that you carefully comply with the rules. But if you splat on a tree, that's sort of on you; or, rather, you are on it.

Part 105 of the Federal Aviation Regulations does specify actual federal laws that pertain to parachute operations ("skydiving").

Nimur (talk) 04:26, 17 May 2016 (UTC)

Thanks, all! ToE was especially helpful. Now, a follow-up question: Does Baseball Bugs's advice about large satchels of money also apply to carrying weapons and ammo? 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 11:29, 17 May 2016 (UTC)

Well, the more weight you carry the larger the parachute would need to be to support that weight. At some point it would no longer fit in a backpack, but then an alternative deployment system can be used. Alternatively, ammo and supplies can be sent down on their own parachute. Not so good when there's just one jumper, because if he doesn't find and retrieve his supplies he is in rough shape. But with many jumpers, they will find at least some of the supplies and ammo. I wonder if a timed system could then be used to lower the supplies and ammo on a line after they hit the trees. (Some would get hung up, but not all.) StuRat (talk) 13:39, 17 May 2016 (UTC)

Good -- that's just what I needed to know! 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 04:38, 18 May 2016 (UTC)

Maybe read through the U.S. Army's Airborne School description. The life of an airborne infantryman is not an easy one. Before they let you jump at all, you have to be pretty prepared. Before they let you do a tactical jump with full equipment, there are a handful of requirements, including completion of Basic Combat Training (described in detail at the Army recruiting page). Weapons, ammunition, and jumping out of airplanes are each uniquely dangerous; there's a lot of prerequisite training to prepare yourself physically and mentally.

Nimur (talk) 14:02, 17 May 2016 (UTC)

“have to be pretty prepared.” Brain washed more like it! Here on Wikipedia many editors take exception to 'fringe science' . This is a good example of a 'so called' intervention that has not under gone any – repeat- any scientific randomised trials. Read: Parachute approach to evidence based medicine. So it also needs hating as we don't give answers to anything remotely medical in nature.--Aspro (talk) 19:30, 18 May 2016 (UTC)

Nazi Luftwaffe parachute troops had it even tougher, hence carried less; see Fallschirmjäger#Uniforms_and_equipment Jim.henderson (talk) 22:59, 18 May 2016 (UTC)

This is a very strange "dig" to add to this specific question, I really can't figure out how it is at all relevant. It sounds like you've just been waiting for an opportunity to link this parachute paper you found somewhere. The fact is Randomized controlled trial are the gold standard, but of COURSE science recognizes that it is not always possible to test everything in a randomized controlled fashion. I know this article you linked is trying to be facetious but in my opinion it's crossing the line of disingenuous. Just because its not possible to test some things in a randomized fashion, does not mean we should accept a lower standard of evidence from other interventions that could be tested but haven't. you know there have even been medicines that were so effective that the trials were discontinued, since it was deemed unethical to not give the medicine to the placebo group. Vespine (talk) 23:16, 18 May 2016 (UTC)

The parachute paper is a famous piece of satire that was written by some highly-qualified medical researchers in order to present a point by way of a humorous counter-example. Deeply interested readers can research its authors for context on why they wrote it, and why the editors of a prestigious journal decided to publish it. From the "rapid responses" (electronic letters to the editors), you can get a quick feel for the spirit of the paper.

I really try not to use appeal-to-authority, but in this case... when you're the department head for a major research hospital, you're allowed to write a little bit of satire, even a piece as blunt as the parachute paper. I somewhat suspect that the contributor who reposted that journal paper here on the reference desk does not carry any equivalent such credential, so when he posts the same joke, the irony is completely lost.

In case any of our readers actually really don't understand, the paper is not advocating against the use of parachutes, nor is it making a sincere plea for any research related to parachute aeronautics of any kind. It is a paper whose thesis is a rhetorical question on the topic of how medical journals (and other peer-reviewed scientific journals) ought to set their editorial standards, as they pertain to the burden of proof.

Nimur (talk) 02:09, 19 May 2016 (UTC)

Wait a minute, how did we jump from parachuting to medical research all of a sudden??? 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 02:41, 19 May 2016 (UTC)

Another editor posted this comment. Nimur (talk) 03:25, 19 May 2016 (UTC)

@Aspro and Nimur: That paper fails to explain the main point of doing such a parachute study, which would be to have the FDA hand over many years of market exclusivity to the company doing it, including a likely patent term presuming the parachutes were tested with minor modifications. See colchicine, dihydroergotamine, evergreening etc. No one would do a study like this unless it meant an opportunity to monopolize parachute sales and raise the price 10,000% or more. Wnt (talk) 13:38, 21 May 2016 (UTC)

If you feel there's a need to continue this line of inquiry, let's move any further discussion of this topic-diversion into a new section-header. Nimur (talk) 18:31, 21 May 2016 (UTC)

Related:if you are reading historic or foreign sources, bear in mind that "forest" may not mean what you assume. Some have no trees, for example, and so would pose little difficulty to parachutists. From our article: "Although forest is a term of common parlance, there is no universally recognised precise definition, with more than 800 definitions of forest used around the world. Although a forest is usually defined by the presence of trees, under many definitions an area completely lacking trees may still be considered a forest if it grew trees in the past, will grow trees in the future, or was legally designated as a forest regardless of vegetation type."

Carbon Caryatid (talk) 10:00, 19 May 2016 (UTC)

References

bioengineering a space telescope lens

Could it be feasable or beneficial to develop a space telescope that incorporates biological material? For instance, using elecrowetting with synthetic electrolytes in order to create a superfluidic lens that can be spun in zero-G to generate a concave lense shape. Would this have an advantage over traditional designs (ie, self-repair in case of micrometeor strikes, curvature adjustability)?

119.171.79.241 (talk) 05:08, 17 May 2016 (UTC)

I'm not sure if it's me or you but I think you are mixing up some concepts which are not necessarily related. We have an article about Liquid mirror telescope which is directly related to what you are asking, but it does not seem like you need to involve biology, electrowetting or superfluidity. Unless you think somehow those factors would counteract the fact that I'm not sure simple spinning would stop the fluid from just floating off in zero G. Vespine (talk) 05:33, 17 May 2016 (UTC)

Aaand we also have this artcile Liquid mirror space telescope. Vespine (talk) 05:36, 17 May 2016 (UTC)

There is high energy radiation in space that even has an aging impact on tough construction materials. Any biological material would either have to be very tough in multiple senses or its simply put in a very wrong place. --Kharon (talk) 02:49, 18 May 2016 (UTC)

• Space telescopes need phenomenally precise lenses – the Hubble Space Telescope was very nearly ruined by just a 10 nanometer error in the mirror grinding stage – and I doubt you could get practically achieve that precision with biological growth (you'd basically need every cell to be in exactly the right place). A non-biological liquid mirror telescope is already adjustable and (since it's just liquid) largely self-repairing. Smurrayinchester 08:30, 18 May 2016 (UTC)

If you read that link more carefully, the 10 nm tolerance was fine, and the mirror met that tolerance. The problem was not the tolerance; it was the shape, which was off by more than 200 times the tolerance at the edge. --Trovatore (talk) 20:07, 18 May 2016 (UTC)

I read it as a cumulative error (a 10 nm misalignment that built up towards the edge of the mirror), but I could be misreading it. If anyone knows better, please fix the article. Smurrayinchester 08:42, 19 May 2016 (UTC)

Go/no go thread gauge

When you have a pair of Go/no go thread gauges, is the go male thread gauge supposed to screw freely into the go female thread gauge?

There are 4 possible combinations:

1. go male + go female

2. go male + no go female

3. no go male + go female

4. no go male + no go female

Which of the four is supposed to screw freely into the other? Johnson&Johnson&Son (talk) 06:35, 17 May 2016 (UTC)

Yes. A "go" is essentially the "correct" version of the thread, so a go male will fit into a go female (case 1). A "no go" is the other test, it is NOT SUPPOSED to fit into the go thread, so case 2 and 3 should fail, (NOT fit more than 3 turns). Whether it is possible for a no go to fit into a no go is undefined to the test and i am not familiar enough with it to say if there is a 'common' or 'standard' resolution, i.e. if they "usually" do fit or usually do not fit, but it does not matter to their actual purpose. Vespine (talk) 06:47, 17 May 2016 (UTC)

• No it's not supposed to screw anywhere! They're both precise and hardened. Screwing gauges together like this is a route to damaging them. Especially when people "store" them screwed together like this (avoid all contact on the gauging faces in storage anyway).

The "go" gauge is intended to fit a workably sized thread. So the male go gauge should fit the female go gauge. The other combinations should not fit. The no go / no go combination won't work because the male is oversize and the female undersized, so it won't fit by two tolerances, not just one.

Note that it's not practical to use this sort of simple go/no go gauging to detect a faulty undersized male thread, or an oversized female. It is rarely seen that a "must not fit" gauge is produced where "no go" is then correct behaviour (ie an undersized female gauge used for detecting undersized male threads). These are rare though, as they create endless confusion with unfamiliar operators. Andy Dingley (talk) 10:32, 17 May 2016 (UTC)

Thanks, you two. @Andy I know they're not supposed to be screwed against each other, but I need a way to check that I've been given properly tools and haven't been scammed, so this is a one-time emergency measure.

Since my go male + go female gauge won't screw into each other, there must be something wrong with at least one set of them. I called the seller about it for a replacement and he told me that they're designed not to fit into each other like that, since the male is "M27x0.75 6H" thread, and the female is a "M27x0.75 6g" thread and thus incompatible. Is this true？ How do I verify this? What he says does make sense, but then again he does have a financial incentive to mislead me. Johnson&Johnson&Son (talk) 11:01, 20 May 2016 (UTC)

This is a little more complicated - and why you REALLY don't screw gauges together (they will fit eventually, but you will certainly damage them).

The supplier is correct. The gauges should not fit. They are both correct.

The suffix is the "tolerance class". To provide a useful, practical fit between nuts and bolts it's usual to produce nuts a smidgen oversize and bolts a smidgen under. Which means of course that the gauges to match will have their tolerances the other way, making them harder to fit together. A lowercase class is undersize, an uppercase class is oversize. So the female ring gauge for the bolts will be a g, the male plug gauge for the nuts a H.

The letter used indicates the "deviation" of the nominal dimension (as an offset from the basic design figure), the number ("tolerance grade") is the range of permissible variation. In effect, the letter indicates the intended looseness of fit, the number the manufacturing precision needed. A H (or a h) have a range that just borders on the design dimension, a g / G is definitely slightly off. A pair of gauges of h/H will fit together (still not wise) but a practical set of gauges is g/H for "typical" threads. When a bolt is to be screwed into a long hole (so pitch mismatch becomes more critical) then g/G is used, meaning that the tapped hole has to be an even looser fit.

Tolerance class is sometimes given twice, in which case the first is about the pitch, the second about the diameter. These are usually something like "4g6g" where the deviation is the same but the tolerance grade differs.

There's also an issue where bolts are to be plated. They would commonly be specified to fit a g gauge after machining and must still fit a h gauge after plating (or an e and then g).

Use the gauges to gauge the product, not other gauges. Andy Dingley (talk) 00:47, 23 May 2016 (UTC)

Free gases

Are there any free gases floating about in the solar system between the planets?--178.106.99.31 (talk) 21:13, 17 May 2016 (UTC)

See Interplanetary medium. CodeTalker (talk) 21:16, 17 May 2016 (UTC)

(ec) sure, there is. See interplanetary medium. On the outskirts of the Solar System it transitions, via a heliopause region, into interstellar medium. All along, it's a mixture of dust, neutral and ionized gas, with varying composition. You may also want to read plasma (physics) article,. --Dr Dima (talk) 21:25, 17 May 2016 (UTC)

So are the gases differnt depending on which planet you are near?--178.106.99.31 (talk) 21:54, 17 May 2016 (UTC)

Yes. see Solar wind#Solar System effects. The solar wind interacts with the top layers of the planet's atmosphere, so that there is a persistent flux of matter from the planet's atmosphere into the interplanetary medium. The amount and composition of atmospheric material being stripped by the solar wind depends on the planet's mass, radius, orbit, atmosphere composition density and temperature profile, strength of the planet's magnetic field, and so on. Mars lost most of its atmosphere this way, while Venus, Earth, and the gas giants still have substantial atmospheres. I don't remember the Earth rate of atmospheric loss, but I'll add it here when I find it. --Dr Dima (talk) 22:57, 17 May 2016 (UTC)

Here you go: Atmospheric escape. You may also want to read Atmosphere of Earth#Evolution of Earth's atmosphere. --Dr Dima (talk) 22:59, 17 May 2016 (UTC)

"Gas" is a mass of elemental molecules and most common Gases build pairs among their Particles/Atoms (Hydrogen=H₂=two Hydrogen atoms,O₂). But Atoms are far to scattered in Space to refere to them as a mass of elements or even Molecule. Outer Space Vacuum is "space void of matter" and thus the complete opposite. There are just a few atoms per cubic meter and that is commonly refered to as "particles" per Volume of space. So there is no "Gas" in Space at all. --Kharon (talk) 22:59, 18 May 2016 (UTC)