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Comment Re:Beacons? (Score 4, Informative) 134

Already done. It's called Ground Based Augmentation System (GBAS).

There's also a system called WAAS, Wide Area Augmentation System, and others.

A short description (I know, TLDR...) is that ground-based transmitters broadcast an error signal - the difference between received data and the actual known surveyed position. Any properly-equipped receiver uses this signal to offset its GPS-measured position accordingly.

My Garmin GPS that I got back in 2005 used the WAAS system. It's been around for quite some time.

Comment Re:They have a use - heads up displays (Score 5, Informative) 171

Not so simple as transparent displays. I built a HUD for my car a few years ago, and proper optics are essential to the usefulness of a HUD. Essentially, you need lenses or curved mirrors or specially-tuned diffraction gratings to refocus the image some distance away - preferably many feet ahead of the car, so you don't need to refocus on the windshield.

Having information presented at the same depth distance as your windshield, but in the same general direction you're already looking for at-a-distance viewing, is distracting and hard for the eye/brain system to tolerate.

Here's a pretty good overview of HUD optics.

Comment Re:Data data everywhere and not a drop to think (Score 5, Informative) 366

I'm a flight test engineer that works on large (passenger-class) aircraft. We do tests related to this issue.

It actually has a lot to do with takeoff safety, ironically enough. If you lose an engine at high power, the airplane will try to yaw (turn left or right) because the engine(s) on the other side are still producing thrust. At lower speeds, with less aerodynamic forces, the rudder is not capable of keeping the airplane in a straight line. So there's a speed called "Vmcg" - "velocity minimum control ground" - below which you MUST pull back the power on the good engines to avoid going off the side of the runway (you're going to have to stop the takeoff). There's also a speed called Vmca, the airborne minimum control speed (you will start to yaw out of control).

So with less power on all the engines, there is less asymmetry possible in the event of a failure. With reduced takeoff thrust, you don't need as much rudder at any given airspeed, so your Vmcg and Vmca are both lower.

This is important for takeoff because if you have a lot of runway available, you can use it by taking longer to accelerate (by having lower thrust). As a consequence, your risk in the event of an engine failure is reduced - you won't head off into the grass if it happens on the ground, and you'll be assured of sufficient control authority if it happens in the air.

So when an airplane manufacturer builds the "takeoff performance charts", these Vmc speeds heavily factor into the takeoff planning.

Now, in this tail strike mishap, the lower weight caused the iPad to compute TOO LOW a speed. Lifting off too slow takes more nose-up (pitch) angle; lift goes up as a linear function of pitch angle; lift has to equal weight to go flying. Because of the reduced takeoff thrust, they were already planning to use most of the runway to accelerate - which put them into a corner; they were too slow to take off at the normal pitch angle, but were out of room to stop. So they pulled up until the airplane started flying - which means they pulled up high enough that the tail hit the ground (just barely in this case).

Comment Re:Obvious solution (Score 1) 172

Okay, so you can't shut down a SourceForge project page. How about simply uploading a final "release" that is essentially completely blank, and editing all the project information to make sure people know this? Can SF really reach out and pull back in external versions to replace the owner's edits?

There's more than one way to "shut down" an account, even if the website won't really delete it.

Comment Pick the right roof angle for solar (Score 1) 557

One thing that's impossible to change later: roof angle. I REALLY want solar, but I'll never get it, because my roof angle is exactly wrong for good solar coverage.

My ridgeline runs at a very bad angle for solar panels; although back of the house is more or less pointed south, it's just far enough off that getting good panel orientation requires large angled brackets, which decreases panel coverage by about half. I could probably double the energy fraction if I could turn the house by 30 deg.

Similarly, cutting some large trees down would help. But that screws with passive cooling. Tradeoffs...

The next house I build will definitely have orientation as a leading consideration for energy independence. It will absolutely affect my choice of location/lot, partly because decent curb appeal is important for resale value, and big solar panels on the street-facing roof are a turnoff for many buyers.

Comment Re:Future proofing (Score 4, Insightful) 557

I built my current house in 1998. Having built a house in 1994 and in just a few years been geek-frustrated with it, I did some things right the second time, and they've stood the test of time, mostly.

One, I set the entire house up as a star-configured system. No daisy-chained networks or wires. There's a central patch panel to which EVERYTHING runs. This makes debugging and tweaking far, far easier. I would absolutely do this again.

Two, I ran far more of everything than I needed at the time. That hasn't eliminated issues, but it decreased them significantly. Two Cat 5 cables, two three-conductor speaker cables, and two RG-6QS cables to every room, period. I'd do this again, but with the latest (and anticipated coming) technology.

Three, I built in an attic-to-crawlspace cable pipe. It turned out barely big enough for the four RG-6QS cables for two satellite dishes. Now with DirecTV's new combined LNBs, I'm back down to one cable and have plenty of spare room. Next time I'd put in a couple of 2" pipes instead of one 1" pipe; it would be no significant cost delta but add significant margin.

Thinking ahead, even though I have been okay for 17 years, I am still somewhat limited on expansion. I have since built on two extra rooms, and it's nearly impossible to add them to the star-configured patch panel. I am not sure I would try to do comprehensive room-to-room cable piping, because it takes a TON of piping and a very large network room to pull it off properly. Space is money when you're building a house.

What did I do WRONG?

For one, not enough photos of infrastructure before putting up the insulation and drywall. I took a ton of photos, but nearly every time I've looked at them for answering a question, I found I had somehow missed the precise shot I needed.

For another, too many places where messy infrastructure limited my options. Like cables and piping exactly where I found I wanted to add recessed lighting. I would be a lot more picky about directing the plumber and electrician where to run their stuff.

Also, I would pay more attention during design to the HVAC setup. It takes up a lot of volume, and tends to interfere with flexibility later. So I would do a better job of pre-thinking where it would go, and leave more built-in space for it.

Finally, I didn't give enough thought to house-to-street connectivity. It changes faster than my in-house systems. Every few years I have needed to have my yard dug up by the cable or telephone or electric or plumbing company. I wish there were a fairly large pipe running underneath my 150 foot driveway, through which all the necessary services could be routed and rearranged as necessary. Sort of a personal manhole thing.

Comment Re:misquote (Score 1) 117

Why not land in the desert?

Two very good reasons.

1) They have to use a lot more fuel to get back to said deserts (in the US, at least) than returning to somewhere on the Atlantic.

2) To get to any suitable desert, you have to overfly populated areas with a very, very large, very very explosive drone with very limited fuel reserves and control margins.

Comment When it's useful info, people listen and heed (Score 2) 406

Some years back I had the pleasure of flying Qantas, the Australian airline. Since we left from LAX, we were subjected to the American routine anyhow. Despite already being a seasoned traveler, I clearly remember elements of the brief - because it was entertaining, not formulaic, and loaded with real useful information. For example, even though I am an aerospace engineer with Aviation Physiology training in a high altitude chamber for government test flights, this tidbit was news to me:

If you see those silly yellow masks fall down in front of your face, you may be tempted to help little Johnny put on his mask first. Here's the problem: we're cruising at 35,000 feet today. If the plane loses cabin pressure, you'll have about 12 seconds of useful consciousness left. Now how useful do you think you'll be to little Johnny if he's sitting there with his mask on and mom and dad are both unconscious? So do us all a favor. Be selfish. Put your own mask on first. Then you'll have plenty of oxygen to help the people around you wake up again from their little unexpected nap, just in time to enjoy the rest of the emergency.

Wow. I never knew that. I've NEVER forgotten it. Oh, and thanks, I don't need to hear it five or six times a year again to remember it either... so that's why I'm not paying strict attention...

Comment Asymmetric eye prescriptions (Score 1) 550

I naturally have one 20-20 eye and one 20-200 eye (corrected with a single contact to 20-15), and I'm now 45 years old. When I asked about laser eye surgery maybe 10 years ago, my eye doctor said "NO. Don't do it. In a few years you'll appreciate that eye that's currently near-sighted." And I do. As I am slowly creeping up on the "arms too short" syndrome, I can still see closer with my nearsighted eye.

Comment Re:hacks against contactless? (Score 2) 146

My American family spent about a week in Canada and never once had our card merely swiped - every single terminal was a push-click chip-n-pin setup. They looked at us funny when we said nobody in America uses them yet. But it still worked with our non-chip cards. So apparently while all the terminals are chip-n-pin, they don'all have to ACT like it all the time.

Comment Won't they hit the ISS on a future orbit? (Score 4, Insightful) 52

Won't they circle back around and hit the ISS on a future orbit? I'm no rocket scientist, but I recall the idea that anything that departs from a given point in orbit will cross it again, and two objects leaving the same orbital point will both cross it again.

Maybe solar or atmospheric drag is enough to alter the cubesat orbits, and I know the ISS orbit is raised periodically, but since they were launched FROM the ISS by expelling them, instead of having a propulsive system, both the ISS and the cubesats left a single point in space and ought to converge there again.

I'd welcome an explantion from a real rocket scientist.

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