Frostmane Map and Some Ice Vanes · 1:40am Jul 20th, 2014
Due to a question that had me scratching my own head (Ow, forgot about the glue), I sat down and made a dang map for The Last Link today. It took far too long, but it was good to see everything laid out.
(I)s there also a omnidirectional antenna to pick up any signals that the plane isn
As you can see, it's sort-of color coded. Light green represents the airways between ranges, the... mauve-ish color (don't blame me, it's like what Jeppesen uses!) represents their approximate flight path. The black dots, of course, are towns, and their associated nav ranges. Blue is water, I figured you'd know that. But the little blue letters? That tells you which zone you're in, whether you'll hear Morse (Horse Code?) for A or N.
A plus: I figured out how to use vectors to make line art here! The rest of it is pretty crappy, though. Does anyone else remember OLD versions of Bryce making it easy to manipulate terrain? I've tried the new one and it's not that easy to work with. I'd been hoping to do a representation of the Fetlock valley, but it's been taking too much for too little result. Hmmm, bezier curves for a topo map might work...
Also, Adm. Biscuit mentioned ice protection for engines. I did post a pic of a small turbine whose inlet vanes were horribly iced- any chunks that go into the engine tear up the blades badly. Some jets used to have nozzles for alcohol to be sprayed into the intake to cut down on icing (and it burned, providing a little performance boost), but nowadays jets are designed with heated inlets- some exhaust is ducted up to the metal inlets and heats them from the inside. My plane actually does this too, and you can see the metal inlet that gets heated in this next photo:
Behind it you can see a flat plate before the back part of the inlet-- that flat plate is the ice vane. It's currently in the deployed position, and it forces the air and any dirt or ice to make a sharp turn before going up into the nacelle. The air makes the turn, but the dirt and ice have more inertia, and go straight, back to where there's a small duct that dumps them out the bottom of the nacelle. Now, I can't find the photo showing how it looks when it's open, but the ice vane folds up, and another flap covers the exhaust duct, and forces all the air to go up into the nacelle. We see a pretty good rise in power from this, since more air is being made available to the engine. Conversely, when we turn anti-icing on, we see a loss in power. Remember what I said about icing taking more and more power? At the same time, we LOSE some, so in some situations it can make you nervous.
Here's a bat I found on a post-flight. I call him Wile E. Batty. Poor guy.
Neat.
Yeah, that's a pretty good explanation for what's going on with the radio navigation.
In terms of real world flying, I'm assuming that these days regardless of whatever else you might have, GPS must be a pretty huge advantage, right? Or can it also have weather issues, just like the radio signals in the story? My layman's understanding is that radio waves have vastly different behavior patterns depending on what frequencies are being used, but I have no real idea what the means for the signals used for various applications.
I actually had my S-10 stall on the highway once from what could only have been carburetor icing. Of course, I had the advantage of coasting off to the side of the highway, letting it heat-soak for a couple of minutes, and then getting back on my way.
I didn't know about the divertor plates in the intake, but that makes a lot of sense. I've owned two trucks with heated throttle bases; is that something they do on airplanes as well?
2300708 Absolutely! All carbureted aircraft have some provision for preventing carb icing. Fuel-injected ones may as well, but I haven't flown a non-turbo FI aircraft, so I'm not sure.
Carb icing can occur with ambient temps up to about 70 or so- the temp drop, combined with the pressure drop due to the restriction of the carb cools the air considerably as well as causing water vapor to condense out.
The problem usually occurs when descending. During climb, you're pumping out max power, and in cruise you're still using 70% or higher- like running your car at 5000rpm all the time. But when you start to descend, the engine puts out less heat and the closed throttle plate increases the vaccuum considerably, causing a greater decrease in temperature, and the narrower opening is more easily blocked by ice.
Carb heat is usually taken from a cuff surrounding the exhaust manifold. It's like an old manual choke, you pull a cable, open a flap, and hot air goes in. When you use it, you see a definite power loss, because the hotter air is less dense, so less of it will fit in the cylinder. You'll also run rich, so you need to re-lean the engine (and remember to richen the mixture when reducing carb heat).
I have a lot of time in Piper Chieftains, which use a TIO-540-J2BD. J2BD is the airframe-specific model, 540 is the cubic inches, O stands for horizontally opposed, I for injected, T for turbocharged. One of the engines is L, for left- counterrotating props means one engine is slightly different. The TIO-540 uses a pressure carburetor, also called a Stromberg, and has a complicated system to compensate for altitude changes and keep manifold pressure the same. More importantly, compressed air from the turbo is running through the carb, so you can never, ever get carb icing. There IS an alternate air door, for in case the air inlet gets iced over or clogged with a bird, and that'll cut power because it's a less efficient air path.
It'll make 350hp, which doesn't sound like much for burning 36 gallons per hour, but on takeoff it'll crank out about 45in of manifold pressure. The turbo is as big as your head. Bigger, probably. On takeoff from short runways, we'd push it up to 30in and pause to let the turbos spool up. Remember how turbocharged cars used to give you nothing, nothing, then BAM you're breaking the wheels loose? Same thing here, they give you a righteous kick in the kidneys, better than pushing up the levers on 2200hp of Pratts.
God I miss flying those things...
2300647 GPS is an amazing tool. At the same time, it does have some limitations. Yes, it's radio-based, but it's a pretty high frequency. Furthermore, navigating by it isn't based on the signal itself, but on the data carried by it. GPS works by pseudoranging-- it's not quite triangulation, it's much more complicated. Pseudorange means it's measuring distance not directly, but by assuming a certain amount of time has passed.
Each satellite in the constellation broadcasts a stream of data, including which one it is, various orbital corrections, error-checking blocks, but the most important block of data is the timecode. Each satellite is synchronized, but because of the distances involved the synchronized signals will reach a GPS receiver at different times. We're talking speed of light here, so it's on the order of nanoseconds. The receiver has a database of where the satellites should be, combined with the correction data, and calculates where it is based on the time delay from various satellites.
And yet, we can get accuracy down to yards in an aircraft moving at 300mph with just the constellation. With only three satelllites in view and locked in, you can get a position over the ground. To get an altitude, you need a fourth. Aircraft GPS have a few extra systems.
One is called RAIM: Reciever Autonomous Integrity Monitoring. Basically, you need one extra satellite, and then the receiver can compare them all and discard the signal from a faulty one.
Another is WAAS, Wide Area Augmentation System.It uses a ground-based station to send out very precise corrections, and allows accuracy of a foot or less.
Now, vulnerability. GPS, being a radio signal, and a digital one at that, can be subject to signal degradation that wouldn't bother an analog system. If enough data gets lost, the signal is useless. This could happen from a coronal mass ejection, or something more nefarious, like a jamming signal. Theoretically it's possible to spoof a GPS system, but that takes an incredible level of technical know-how and equipment.
Your reciever is, like any other piece of electronic equipment, a potential weak point. I had a GPS unit once go haywire- somewhere, water was leaking in on it (and running down the front face) and it just kept adding approach after approach after approach, to the point I just turned the damn thing off and fell back on the single VOR that was left.
Personally, while I like GPS, I try not to get dependent on it- I've seen people become addicted to the moving map and be unable to navigate with paper charts and VOR stations, let alone concieve of how to use an ADF.
Oooo, that's really neat. I had a feeling that aircraft GPS was more complicated than the client on my phone, but like I said, layman, no idea what the differences might be.
This is fascinating, so here's another question, how does modern non-GPS radio navigation work? My high-school was in sight of what was always said to be one of the transmitting buildings (imagine a circular building with a peg sticking out of the top), and I've always wondered if that was true.
2301460 Well, the basics of the GPS chip on your phone are the same, except it isn't as accurate, usually doesn't have RAIM, but everything else works the same. If you have an Android, you can get apps like GPS Test and actually see the signal strength and where the satellites are in relation to you, etc
Modern radio nav hasn't changed in years and years, except it's possibly moving backwards. LORAN has been shut down- that was LOng RAnge Navigation, a long-distance, over-the-horizon network that was pretty accurate and used time-dependent technology a little like GPS uses. Many NDBs, Non Directional Beacons (AM radio) are being shut down and their approaches deleted because they cost money to maintain and GPS gives better accuracy, a move I oppose. I like having backups. NDBs are the navaid tracked by your ADF- Automatic Direction Finder, which has two antennas, a sense and loop, All it does is point to the beacon. You have to figure out winds, crab angle, etc. That means you have to point your nose slightly away from the navaid- you have to turn a little into the wind to track in on a certain radial, otherwise you keep sliding sideways and turning in and sliding and turning in and your instructor will yell at you and oh god why is this so hard who ever thought of.... ahem, sorry. ADF nav takes a little practice to get right because the instrument only tells you the very basic
The navaid you describe is indeed a VOR. Very High Frequency Omnidirectional Range. Inside that peg or cone is an antenna that sends out a pulse that sweeps 360 degrees 30 times a second, while a fixed pulse is sent out at the beginning of the sweep. The VOR receiver can be set to listen for a specific difference between the two based on the phase of the two pulses- you turn a dial to set which radial you want to navigate along, which sets the receiver for the proper time delay. When you are on that radial, a needle is centered. If you are to one side or the other, the needle swings to the side. But even better, it gives you qualitative information as you get close to the radial- the needle swings through about 10 degrees on either side, so if you're a little off, the needle is a little off. If you're far off, the needle is far off.
Here's a picture of the VOR that's on airport at DFW, the Maverick VOR (113.1, TTT). Because of all the stuff on the ground, they've raised it up about five stories and set up a metal grid to act as a ground plane to reduce interference. There are two other VORs in the DFW metro, the Ranger and Cowboy, that are similarly raised up.
static.panoramio.com/photos/large/4141054.jpg
Most VOR stations also have DME- Distance Measuring Equipment. It's sort of like radar in reverse: The aircraft's DME unit sends a signal to the station, and measures the time delay to receive a response. The delay can be computed to give a distance from the navaid, and can also be used to calculate speed and the time to get to the station. HOwever, DME is limited in that it can only tell you relative speed-- it's only accurate when you are heading towards or away from a station. If the station is off your wing, your speed will read near 0. In practice, it's 'close enough' when there's less than 30 degrees of difference between your bearing and a bearing direct to the station.
Some quick terminology
Course: Line over the ground
Bearing: Where you are GOING
Heading: Where you are POINTING
Drift: What happens when you hold a bearing, but wind pushes you off your course.
Wind Correction Angle: The difference between the bearing you need to fly, and the heading you need to hold to stay on that bearing.
Radial: Magnetic or True bearing from a point
Luna: NOOOOOOoooooo..... My poor dear little bat!
... Now my cloak will have a hole in it...