Wikipedia:Reference desk/Archives/Science/2017 April 16

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April 16

DC-3 mountain ops

2 questions: (1) When performing a short-field, hot-and-high takeoff in a DC-3 at (or above) MTOW with a 20-knot tailwind, what is the optimal flap setting? (2) With the optimal flap setting for takeoff, given the following parameters: aircraft weight = MTOW + 1360 lbs., field elevation = 8400 ft., OAT = 2°C, wind = direct tailwind at 20 kts. -- what's the minimum runway length needed? (Question inspired by FSX mission "Crucial Extraction" from Aerosoft's "Flight Tales 2: Adrenaline" mission pack.) 2601:646:8E01:7E0B:88C9:21D2:79C0:44A3 (talk) 01:28, 16 April 2017 (UTC)

Flaps or no flaps? When you're at high density altitude, this is a very important question! A few weeks ago, me and my copilot spent our evening watching Density Altitude: The Nine Deadly Sins, an hour-long seminar presented by David Hunter, former Principal Scientist for Human Performance at the Office of Aerospace Medicine, Federal Aviation Administration.

"Wrong flap setting" is "deadly sin #8" in Dr. Hunter's talk.

• "...There comes a density altitude above which the use of takeoff flaps actually increases ground roll."
• "Don't use short field flap settings for high density altitude takeoffs (unless the field is truly short.)
  • Short field flap settings offer a better angle, not rate of climb.
  • At the typically long high-elevation airports flaps will be a hindrance to reaching V_Y more quickly.

This is a long, and technical, presentation. It's not going to tell you, in direct fashion, whether to use flaps or not to use flaps. It's going to tax your brain for everything it knows about mountain flying, so that you can make the best decision (simulated or real) about what will keep your aircraft safest. At high DA, you're often pushing the edges of the performance envelope of your aircraft. Every optimization along one axis is met by a degradation in some other performance metric. Do you want a slower rate of climb with better angle? Or do you want better margin against the stall with a poor climb gradient and marginal terrain clearance? Would you really take off with a 20kt tail-wind, or would you rather fight with the terrain in the opposite direction? What you don't know will kill you. (This is why - in the real world - we would delay or cancel the flight, even if the departure is "urgent").

To actually answer the quantitative parts: you need real and reliable performance charts for your aircraft - and you need to know how to use 'em! Have you got an E6B? The E6B computer costs less than the computer flight simulator software you're using, and it tells you how to calculate DA; then, you just have to read the rest directly off of your aircraft's performance charts. And yes - the former director of FAA's Aviation Human Factors division recommends hand-calculation using the E6B and the Take-Off Computer. Doing the math by hand, with an analog computer, is slower and less accurate than using a powerful digital electronic software computer; but the analog computer is shown scientifically to help you make a better decision.

Nimur (talk) 06:19, 16 April 2017 (UTC)

Thanks! In this case, I'm not concerned with terrain clearance -- I'm only concerned with reaching flying speed before running out of runway. And there's something I forgot to tell you about the runway -- it's 4,154 feet long, theoretically asphalt, and sloping on a 3.8% grade -- would the plane be able to take off under these conditions? Also, a related question (you can call it #3): At a gross weight about 1360 lbs. over MTOW (as specified above), is it even remotely possible for a DC-3 to maintain 8500 feet on 1 engine? 2601:646:8E01:7E0B:4457:AEC3:D9F:5111 (talk) 06:41, 16 April 2017 (UTC)

I'm going to preface this by saying "never fly above max gross..." because that's what the textbooks and the rules say. But if this is a question of physics: it is possible to fly above max gross; it's just significantly less safe. Above max gross weight, normal operations like taxiing, climbing, and even turns and banks, may cause structural failure of the aircraft. If you carefully follow certain rules and procedures, you can do it, safe-and-legal, but it is absolutely not normal. In aviation, when we hear the words "not normal", it is typically bad thing.

Not everyone agrees; Flying Magazine called max gross a "myth"; but what do they know? They're a fun read an an interesting trade-magazine - not a canonical source of correct information about aeronautics. Try asking a flight instructor if you can fly over max! Extra points if you say, "but I read all about it on the internet..."

Throw in the added complexity of multi-engine aircraft, and things get really weird: which engine failed? Was it the critical engine? So, again - these sorts of things come from your aircraft's performance charts - and your DC-3 simulator probably doesn't have really great and accurate charts... so let's default to the safer answer and say "no, the DC-3 can't be safely operated in that fashion." Has anyone ever done it? Well, those aircraft went through the wars...

Nimur (talk) 07:07, 16 April 2017 (UTC)

Yes, this is a question of physics -- is it possible, under these conditions (disregarding the structural considerations), to take off from the airstrip in question, and then to maintain altitude on one engine (the portside engine, to be exact -- in this mission it's the starboard engine that gets shot out right after takeoff)? And yes, I'm fully aware of the possibility of structural failure above MTOW -- in fact, Amelia Earhart had learned about it the hard way on her first (aborted) world flight attempt. Oh, and just to put this question about overloaded flying to rest: If you get rid of the extra 1360 lbs. and just try to take off at MTOW (the other conditions being as described above), would it be possible to take off within the specified distance and then maintain altitude on one engine? (Yes, I figured out how to prevent overloads in this mission -- once you board as many refugees as you think you can take (21, in this case), just increase power until the copilot shouts "We're leaving, close the f**king door!" (yes, he actually says that), and then the refugees will stop boarding.) 2601:646:8E01:7E0B:4457:AEC3:D9F:5111 (talk) 08:19, 16 April 2017 (UTC)

Let's build up to this problem: have you done a take-off roll calculation at sea level? And how about at 8400 feet? Next, how does the tail-wind factor in? Next, how does the emergency-checklist read for a single engine failure on takeoff? And how would you adjust for all the extra factors during the emergency?

I sincerely hope you aren't operating your simu-airplane without an appropriate simu-performance-chart! Those calculations are not optional - they are a very important part of flying your airplane! You must have and use those perf charts. I don't fly the DC-3; I don't have its limitations and numbers on hand, but I can say this: every single element in your scenario is urgent enough to warrant choosing not to take off in the first place. In combination, you're asking for (simu-)fatalities. This is not how pilots make decisions. We have seen things, and done things, that make us want those 5x- and 10x- margins.

For example, yesterday I was at sea level at KMRY in a single-engine aircraft. Sea level, and a perfect 12-knot headwind, on a seven thousand foot runway. To save a few bucks driving around on the ground, I opted for - and was cleared for - an intersection takeoff, 28L at K. As I rolled on the runway, I checked and verified three thousand feet of useful runway ahead of me. My aircraft can get off in, say, 600 feet in normal conditions; and with a 12 knot headwind... well, I can estimate 400 feet. So I had only about eight times more runway than I needed. As I rolled on to the runway, with four thousand useful feet already behind me, and eight times more than I needed ahead of me, the thought flickered across my mind: do I "actually actually" have enough runway ahead of me? And a moment of regret - why didn't I just taxi all the way to the end? Of course we took off with no trouble; but that's the kind of safety margin that makes a real pilot twinge. Your simu-scenario added mountains, terrain, hostile antiaircraft fire, overloading, sloping runway, short field, ... I mean, can you add a fogbank, questionable fuel, and an airsick pilot to the scenario for us just to bring the certainty of disaster closer to 100%?

So when you construct a scenario - simulated or otherwise - where you know you don't have the performance you require, you are so far from safe that no reasonable pilot would choose to take off. It would be better to stay on the ground and take your chances with the unfriendly groundlings who shot out that engine.

Nimur (talk) 16:20, 16 April 2017 (UTC)

I bet this is why FSX is not allowed for real pilot training -- because many of the missions (especially the harder ones) encourage the taking of risks which no pilot should ever take in real life (the "Jet City" mission being the most egregious example -- if you fly over (and under!) Seattle like that in real life, your "reward" would be a revoked pilot license and jail time for public endangerment -- and that's if you survive, which is unlikely!) But to get back to the question, the takeoff run for the DC-3 at sea level is listed in the learning center -- it's 1600 feet on a hard-surface runway with no wind. 2601:646:8E01:7E0B:B80C:1577:D989:3256 (talk) 00:32, 17 April 2017 (UTC)

Hm, that take-off roll (1600 feet?) sounds a little short, but I don't have a flight manual for DC-3 to verify... you really need a perf chart for the airplane (simulated or otherwise). But based on your questions, what you really need to do is go back to the Airplane Flying Handbook, with special emphasis on chapters:

• Chapter 5: Takeoffs
• Chapter 12: Transition to Multiengine Airplanes
• Chapter 13: Transition to Tailwheel Airplanes
• Chapter 17: Emergency Procedures

...and the PHAK, with special emphasis on:

• Chapter 11: Performance

Nimur (talk) 23:40, 17 April 2017 (UTC)

BTW, just so you know, I actually made it off that field and stayed aloft on 1 engine, even with a full load of refugees (which put me 1300+ lbs. over MTOW, as well as made the plane dangerously tail-heavy) -- the key, as you said, was to keep the flaps all the way up.  ;-) (And I didn't crash during that mission -- rather, my computer did.) 2601:646:8E01:7E0B:7D48:3AB5:AF2B:A040 (talk) 01:01, 18 April 2017 (UTC)

Ah, simulators... even when they're legal, it's hard to take them seriously...

Get back to studying your performance-charts, airman!

Nimur (talk) 14:36, 18 April 2017 (UTC)

Project_engineering

Just read [1]. Why is t that in some projects, project engineer reports to the project manager whilst in other cases, they are level in the structure, each reporting to their team manager who in turn report to the same project director. — Preceding unsigned comment added by 82.132.239.231 (talk) 15:05, 16 April 2017 (UTC)

Because that's how they want to do it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:42, 16 April 2017 (UTC)

Exactly. See: The Vertical Structure Vs. the Horizontal Structure in an Organization for more info. Aspro (talk) 18:20, 16 April 2017 (UTC)

In the organization I worked for, it was because project managers and people managers had different responsibilities: project managers were active engineers, or at least devoted to technical issues, but would not be responsible for things like hiring, performance evaluation, and promotion, which were the responsibility of the "people managers". In a complicated project, a project manager might be organizing some of the activities of several engineers (usually each engineer would have a designated fraction of full time equivalent (FTE = 40hrs/week) dedicated to a project). The project managers might aid the "people managers" in evaluating the people working on his/her projects, but the final say in the evaluation resided with the "people managers". Projects often spread across organizational areas, so some engineers would report to the same "people manager" as the project manager, and some would report to different "people managers". (I wish I could recall the exact title of the people managers; I think they were simply called "managers", or perhaps "engineering managers" to differentiate them from production and maintenance supervisors.)--Wikimedes (talk) 19:06, 16 April 2017 (UTC)

Doesn't PRINCE2 work on the vertical structure? 2A02:C7D:B95F:F700:9D03:FD57:30DC:BF4F (talk) 21:02, 16 April 2017 (UTC)

Sexual differentiation delay

According to Live Science, despite inheriting an Y chromosome already during conception, the human male sexual differentiation begins only after about 60 days when testosterone kicks in. Why there's such a delay between inheriting the chromosome and male development? Brandmeister^talk 17:47, 16 April 2017 (UTC)

Well it's not going to happen when it's a ball of undifferentiated cells. Sagittarian Milky Way (talk) 18:50, 16 April 2017 (UTC)

That, and also remember that just because you have certain genes in you genome doesn't mean they are expressed immediately. 86.28.195.109 (talk) 07:47, 17 April 2017 (UTC)

• It's that way because it works. That's how evolution operates. Unless there is a definitely "better" way, the old way continues to be used. As to how this evolved, "ontogeny recapitulates phylogeny". -Arch dude (talk) 15:42, 17 April 2017 (UTC)

No, it doesn't. AndrewWTaylor (talk) 16:27, 17 April 2017 (UTC)

In a sense, sexual development begins even at a negative age. Looking up SRY, I see its expression begins prior to implantation of the embryo. [2] (I say this is a negative age because an IUD or other device to prevent its implantation is not an abortion, and because pregnancies are often timed from implantation) SRY is the most directly genetic part of a male sexual differentiation program, being on the Y chromosome and driving largely male appearance all by itself.

But your source is not wrong either: sexual development in the morphological sense starts at 60 days because neither a single cell nor a blastocyst has a place to hang a penis from (genital ridge). (Although, to be honest, it seems entirely possible that with just the right stain and a very good eye and a whole lot of human embryos you could spot some difference in morphology in the first few cells, some difference in the cytoskeleton that is simply not presently known... it's just probably not pole-shaped. ;) And of course you can look for Y chromosome and Barr body, but I think philosophically that isn't sexual differentiation because of unusual cases like Klinefelter's syndrome or a mutant SRY gene. That said cases like freemartinism show that sexual differentiation at the early stage is prone to change, much more than it is for transsexuals taking hormones later.) Wnt (talk) 12:23, 18 April 2017 (UTC)

Magnifying glasses/diopters

Cheap magnifiers with magnification 3.5x or above tend to have a short focal distance of ~12 cm or less which are not practical for many applications such as soldering. I've noticed that some purveyors of reading glasses refer to the diopter rating as magnification so I was wondering whether +7 diopter reading glasses might provide 3.5x magnification with a greater than usual focal distance (ideally 30-40 cm)? Alternatively it's possible to have glasses made online to a prescription - would they be able to do whatever magnification (5x?) with a long focal distance? --78.148.99.149 (talk) 18:57, 16 April 2017 (UTC)

Dioptre is defined as m⁻¹, which means that +7 dioptre lens has the focal distance of 1/7 m or about 14 cm. This does not seem very different from the mentioned 12 cm focal distance. Ruslik_Zero 19:38, 16 April 2017 (UTC)

See Magnifying glass#Magnification. The Diopter value of a lens equals the reciprocal of its focal length measured in metres. Its magnification is MP₀ = (0.25 m)Φ + 1, where Φ is the optical power in dioptres, when held close to the eye, or MP = (0.25 m)Φ when close to the object. These assume the viewer sees comfortably at 0.25 m from the eye, but an older person may not manage such a near point.

Single lens magnifiers are limited to 5× or so before significant distortion occurs. A modification that allows 10x to 20x magnification is the Coddington magnifier. The Loupe spectacles with lighting illustrated are useful in dentistry and electronic inspection. Blooteuth (talk) 20:00, 16 April 2017 (UTC)

Thanks. I've found dentistry ones at 3.5x with 420 mm focal distance but I think they would be overall worse than my current 2.5x lens with ~200 mm focal distance since now the subject is further away, undoing some other magnification (although it is at least more comfortable to use). What about https://www.alie xpress.com/item/BIJIA-Portable-Zoom-Mini-Fishing-Glasses-Telescope-10X-Magnifying-Loupe-Green-Film-Binoculars-For-Outdoor-Concert/32661281596.html these]]? They're 10x but it doesn't say their focal length. It says the exit pupil distance is 0.8 m but I can't figure a way to derive the focal length from that. They're intended for watching football so I'm guessing they won't focus on something as close as 400 mm. Broken link to circumvent stupid spam filter. I'm not trying to sell magnifiers. 78.148.99.149 (talk) 21:17, 16 April 2017 (UTC)

water temperature of the Columbia River

Where can I find the water temperature of the Columbia River plotted over the course of a year? (Any recent year is fine)

Anywhere along the river is fine, but if possible I'm specifically interested in the section around Portland, Oregon. ECS LIVA Z (talk) 20:41, 16 April 2017 (UTC)

The USGS has this sort of data on their National Water Information System web site. Constructing a query is a bit complicated, but this URL should give you water-temperature data for 2016 for the Columbia at Dodson. They also have data for a number of other points in Oregon and Washington if you prefer. --76.71.6.254 (talk) 02:30, 17 April 2017 (UTC)

That's perfect. Thank you so much!! ECS LIVA Z (talk) 08:22, 17 April 2017 (UTC)

Natural selection and attractiveness - related?

Is the human mating process and what people find attractive related to natural selection? I.e. Can it be said that people who are found to be attractive by more of the population, are more likely to successfully find a mate and reproduce? 2A02:C7D:B95F:F700:9D03:FD57:30DC:BF4F (talk) 21:01, 16 April 2017 (UTC)

See sexual selection. Sometimes, the interaction between natural selection and sexual selection can have interesting consequences. I remember that there is a type of bird with very long tail feathers. The long feathers are believed to be maladaptive in terms of natural selection, but they are still favored because of sexual selection. 50.4.236.254 (talk) 21:10, 16 April 2017 (UTC)

Are you thinking about the bird of paradise? 2601:646:8E01:7E0B:B80C:1577:D989:3256 (talk) 00:34, 17 April 2017 (UTC)

Or peafowl? --Jayron32 00:57, 17 April 2017 (UTC)

On the long run, sexual preference is itself subject to natural selection. So, sexual selection acts to prevent medium term drifts toward unfitness due to a temporary change in the natural environment. Count Iblis (talk) 00:35, 17 April 2017 (UTC)

Yes, sexual attractiveness translates into physical featness and as such successfull reproduction and mating. Large breasts and wide hips in women, for instance, contribute to successfull nursing and childbirth, respectively, while long legs were particularly important in prehistoric times, as it meant faster running speed. Brandmeister^talk 09:37, 17 April 2017 (UTC)

[Citation needed] on the assumption that finding large breasts more sexually attractive is a general human tendency. Physical_attractiveness#Breasts suggests it's a bit more complicated than that. Adrian J. Hunter^{(talk•contribs)} 01:38, 20 April 2017 (UTC)

So, in theory, shouldn't this mean that only the most attractive in society get partners? Yet in reality, almost all humans get a partner. What's happened here? 2A02:C7D:B8FC:9000:B8C7:87EC:A8:3648 (talk) 10:46, 17 April 2017 (UTC)

No, that's not entirely true. In general, the more attractive (whatever biology and evolution and whatnot have determined for that particular population is "attractive") tend to be more likely to find mates, but that doesn't mean that no lesser attractive individual ever finds a mate. Evolution works in trends and generalities over long periods of time, and is not deterministic on the individual level. --Jayron32 11:03, 17 April 2017 (UTC)

I'd add that since attractive women and men are more likely to get a partner fast, this forces other mate-seeking people to adapt their preferences and tastes. As the result, when a man, for instance, can't find a tall blonde girl with large breasts for some time (as it often happens), he would eventually adapt and pick an average girl next door. Brandmeister^talk 11:15, 17 April 2017 (UTC)

Especially if he doesn't find blondes very attractive in the first place. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:21, 17 April 2017 (UTC)

Please note the paucity or complete absence of references above. For example, in querying the assertion "large breasts contribute to successful nursing", the only reputable sources I found stated the opposite. Breastfeeding and Human Lactation, University of Kansas, latest edition 2014: "Breast size does not affect the ability to breastfeed" (page 158); "the amount of adipose tissue [i.e. fat] does not affect either the breast storage capacity or the milk production" (page 82). A summary page from Milk Genomics, titled "Do larger breasts make more milk?": "Research into breast size and milk production shows that milk supply is not dependent on breast size." This is a reference desk: please provide references. Carbon Caryatid (talk) 22:06, 18 April 2017 (UTC)

I found a source here ... alas, this paper has so many problems with it that I can't really say it proves anything. To begin with, the lucky doctor who somehow gets every patient asked to allow him to twice measure the circumference of each breast is, well, a plastic surgeon doing breast procedures, and so this is not exactly a representative sample. More troubling is the fact that while it finds that breasts of women who had children have less fluctuating asymmetry, that doesn't necessarily prove that they find mates more easily. That's because pregnancy has no small effect on breasts, so they might fill out more evenly due to the physiology rather than selection! But most relevant for this discussion is that Table 3 shows no significant relationship between breast size and number of children. That said ... it's a small study, and the number of children in modern society may be a poor indicator of reproductive success under historical circumstances. And I'm too lazy to figure out what the signs of the non-significant relationships in those statistics mean to see if they point in the 'right direction' for the hypothesis. Wnt (talk) 11:06, 19 April 2017 (UTC)

To answer your second question see Matching hypothesis which says "people are more likely to form and succeed in a committed relationship with someone who is equally socially desirable". It's not that less "atractive" people don't get to breed - they just find partners of a similar level of "attractiveness" to themselves. And how many children they then have is not related to how attractive they are considered to be. Richerman (talk) 23:40, 19 April 2017 (UTC)