Goals:
- Intro to ADFs.
- Intro to VORs.
- IR maneuvers (including stalls).
- Crosswind landings -- WOO!
Flight:
JEPII-12 and 13 are solo work.
Preflight, check. We talked about basic operations of the VOR (which senses a VOR or VORTAC) and ADF (which senses an NDB). We talked briefly about low-level wind shear. We talked about how in the utility category W&B envelope the maneuvering speed is closer to the stalling speed. I dialed in the Harcum (HCM) VOR on nav2 and FAF's NDB on the ADF.
We started off toward 31 -- the first time for 31, I think, since my solos a month ago. We talked a little on the way down there and I was thinking about VORs and after pulling to a stop at the runway hold-short line to finish our conversation, I announced that we were departing. The second I got off the mike, Chuck said, "After the run-up, right?"
Holy freakin' crap. Where was my brain? Did I leave it in the car??!?!?!! I was mortified with myself and could feel my face grow exceptionally hot. I pulled out the checklist -- checklist, checklist, checklist! -- and went through it. Luckily, everything else on the flight went much better than this goof up.
We went up and headed back toward the river and almost immediately went under the foggles and stayed there for a while. We played with the ADF and VOR under the hood for a while. Harcum was generally NNW of us and first we dialed it in to find the general heading, and then we dialed in a ENE radial and continued NNW until we intercepted it. We flew along it and crossed over the VOR, noticing the increased sensitivity of the indicator at such close range, and then the cone of confusion, then the switch from "to" to "from".
We swung around and tracked back to it, crossed it, and then looked at the reverse sensing behavior of having the opposite radial dialed in for the direction of travel relative to the VOR.
Still under the foggles, I slowed for slow-flight maneuvers. Holding altitude using pitch and power and still trying to stay slow, I did some left and right turns. Then it was time for a few power-off stalls followed by a few power-on stalls. Next I did left and right steep turns, and then finally the foggles came off. Another steep turn in each direction and it was back to the airport for 4 landings in 7-10 kt crosswinds.
Discussion:
- Automatic Direction Finder (ADF): The ADF is an old technology that picks up low-frequency transmissions from non-directional beacons (NDBs). It can also function as an AM radio receiver, which is neat because (1) you can listen to the radio and (2) if you know where the station's transmission is coming from, you can use it as a navaid.
It basically works like this: The NDB sends out a signal in all directions. You tune its frequency in on the ADF. If you turn the volume up, you can listen for its Morse code, which is how you verify that you're tuned to the right signal. When you're in range, the ADF bearing indicator comes alive. What the indicator tells you is where the beacon is relative to your location.
The indicator itself can be a little confusing, because beneath the indicator needle is a movable heading card. One approach to using this indicator is to just leave 0 degrees at the top, regardless of what your actual heading is; your direction of travel is always "up" on the indicator. This is good because it brings home the fact that this is all relative information and it seems to me it would prevent misinterpretation of the info it's giving; I'll call this relative bearing. So if you look at the indicator, and you're going up toward 0, and the ADF needle is pointing to 350, that means the NDB is 10 degrees left of your current track. In reality, if you're on a heading of 140 and you wanted to go to the NDB, you'd point over to 130.
The other approach, which I'll call absolute bearing, is to use the movable heading to dial in your actual heading and then the needle will point to the heading you'd need to fly to go to the NDB. So if you're on a heading of 140 and you dialed 140 into the ADF bearing indicator, it would then be pointing to 130, the heading that would take you to the NDB.
The main thing I don't like about the second approach is the possibility for error in headings. The directional gyro will precess, and if you haven't remembered to set it recently or it was set incorrectly, then why would you want to propagate that error into another instrument? If you're using it for a relative bearing, then it doesn't matter what your DG actually says; you're going to change that reading by a certain absolute delta, and while the resulting heading will have the same error as the original heading, you'll be in sync with the navaid.
And how do you know if you're in sync with the navaid? Well, if it says the NDB is 10 degrees to your left, and you redirect yourself to the left by 10 degrees, the ADF needle should then be pointing straight up, meaning the NDB is directly in front of you. Pretty simple. Kinda like a magnet -- the arrowhead is drawn to the ADF, and you follow the arrowhead.
The ADF/NDB system has quite a few limitations. Distance, weather, terrain, occasional random 40-degree errors, ... I don't know all the details here yet, but I know enough to know I'm thankful for GPS! Homing and correcting for wind deviations are for another time... - VHF Omnidirectional Range (VOR): The VOR is a newer yet still old technology that eliminates lots of the problems with ADFs/NDBs. For one, it's a VHF signal, so it's stronger and less susceptible to distortion and noise.
The VOR has two rotating signals, one that goes "slowly" and one that goes "quickly." The quick one, the differential, sends out a little blip on each 1-degree section. The slow one, the reference, sends out an omnidirectional blip every time the quick one gets to 360. The VOR indicator in the plane digests that signal by noting the time between receiving the reference and the differential signals and therefore it knows which radial its on.
So what's this radial thing? There are 360 radials eminating from a VOR, one on each whole degree. They're numbered according to the direction relative to north (north = 360 = 0). The radials are also vectors, always eminating from the VOR. If you're on a heading taking you to a VOR, you're actually flying the radial coming out the other side since that's the radial that's in the same direction as your travel.
Let's say we're traveling east to west on a calm day with a VOR directly in our path. We're flying a heading of 270. The VOR has two radials on our path; 270, going out the far side to the west, and 090, coming out the near side toward the east. If we want to dial in the VOR for use in navigation, we'd dial 270 using the "bug" (the OBS, omnibearing selector) and when within 10 degrees left or right of that radial, the needle comes alive. In this example, we'd expect that needle to immediately be centered since we're flying right along that radial.
As we get closer to the VOR, the indicator becomes more sensitive. When we're 10 miles away, being 100 feet to the left or right of the actual signal source doesn't make much of a difference. But when you're 1/4 mile away that 100 feet is a much larger error, so the closer you get, the more deviation the needle will display. Those numbers are just to illustrate the point and shouldn't be taken as real guides for how it works. When you get right over the source, the indicator doesn't really know what to tell you, kinda like how a magnetic compass at the north pole doesn't know where to point.
As we cross over the VOR and move away to the west, the needle will have decreasing sensitivity and will stabilize. Also when we pass the VOR the indicator will switch its "to" flag over to the "from" flag. When we dialed in the 270, the indicator sensed that the VOR site was still in front of us and activated the "to" flag -- this is solely based on the fact that, if you drew crosshairs over the VOR with one axis on our selected radial and the other axis perpendicular, our position is on a radial in the semi-circle opposite from the selected radial. Once we passed it, we were on the same semi-circle as the radial so the indicator activated the "from" flag. That matches our travel and all is well.
Suppose on our east to west travel that the VOR was not directly in our path, but instead was 30 degrees off to the right of our "starting" position and we really want to fly over it heading northwest. In this case, we know we want eventually to be traveling on its 315 radial, so we dial that into the VOR. As we fly along and get closer to the intersection of our 270 heading and the bugged heading of 315, the VOR needle will come "off the wall." The VOR needle isn't magical and doesn't know that the VOR is to the right of the plane; it does not have that spatial awareness. What it does know is that (a) we're currently on some given radial of that VOR (say, 122 -- if we turned to 122+180=302 we'd be going straight to the VOR) and (b) we've dialed in to go to the VOR on 315. If we were on the 135 radial (the opposite of what we have dialed in), our needle would be centered because we'd be going roughly towards the VOR (we're SE of the VOR, heading W); alternately, if we redialed the OBS to 302, the needle would be centered since that's the radial that would take us directly to it from our current position.
But we're actually on 122. In order to intercept the 315, we need to go further to the "left" -- in a north-up sense, we know we're to the right of the VOR, on a radial that is to the right of our target radial. The needle tells us this by sticking to the left wall. Since we're already traveling west, we can keep that heading and just wait. When we get close to that intersection, the needle begins to move closer to the upright position. At 125, specifically, it comes to life. For every two degrees closer to the target radial we go, the needle gets one dot closer to center. When it's straight up and down, we're smack on the radial.
Now that we're on the radial, what? We're still pointed west as we cross over the 315 radial. We want to go to the VOR, and the indicator is telling us that the heading of 315 will take us directly to the VOR, so we have to change our travel heading to 315 (a right turn, in this case).
What if we don't change our heading, but instead keep trucking right along at 270? Approaching the selected radial, the needle was coming from left to center. Right on the radial, the needle was centered. As we pass the radial, the needle deflects to the right.
Reverse sensing. What we've seen so far is that when the VOR needle is to one side, that means you need to turn in the direction of the needle's deflection to get to the radial that you've dialed in with the OBS. Reverse sensing means you have the opposite radial dialed in, and so the indicator will give you "backwards" directions.
When we're flying east to west on a heading of 270, we dial in the 270 radial and the indicator says we're going to the VOR (the one that's right in our path). If we had dialed in the 090 radial, it would be the opposite vector of our flight path, and so the flag would show up as from. I think this means that, in the second example, if we dialed in 135 for our VOR that's 30 degrees to the right of our "starting" point, the indicator would show from with a right needle deflection. That only makes smile-and-nod sense to me right now, but I think that's how it's supposed to work. - Crosswind landings: The big secret to crosswind landings? Constant corrections. I can do that. On the first landing, I did my usual crab into the wind and just made sure to straighten out a moment before touching down. On the second one I tried wing low, and found myself constantly adjusting the bank – analyzing the situation for effectiveness was difficult since the wind was kinda punchy, and of course the 31 swamp monster… On the third one I leveled the wings a few feet over the runway and the wind pushed us off to the left of centerline (not close to the grass, though), so I learned about that effect and on the fourth aligned with the right side of the runway and it worked out just fine.
It’s just constant corrections. Especially getting down to tree level, then past it to the runway environment where the wind is different than it was 30-50’ higher. The slip part will take some refinement, but it’s nowhere near as intimidating as it was a month ago.
Self-Assessment: New things to work on as the old ones get polished up.
- Flying
- Preflight: Good.
- Taxiing: Good.
- Normal takeoff: Good.
- Short-field takeoff: Needs practice; maybe it was just the winds today and the aileron corrections but 388 seemed to stick to the ground more, but not once did I actually get off the ground at Vx.
- Soft-field takeoff: Needs practice.
- Maintaining airspeed: Good.
- Stalls: Okay.
- Slow flight (VR and IR): Good.
- Maintain attitude, altitude, heading by instruments: Good.
- Change attitude, altitude, heading by instruments: Acceptable.
- Recover attitude, altitude, heading by instruments: Acceptable.
- Forced landing: Good, need more practice.
- Forward slip:: Dunno, needs more practice.
- Pattern: Good.
- Normal landing: Improved.
- Crosswind landing: Improved, ha ha ha ha ha.
- Short-field landing: Okay, needs more practice.
- Soft-field landing: Not sure... need to establish the goals and then I can assess it!
- Directional control after landing: Better.
- Radio calls: Good.
- Navigating
- ADF: Okay for an intro, needs practice.
- VOR: Okay for an intro, needs practice.
Next: I've got the plane at 11 am on Monday, which will be either solo or lesson depending on weather.
- More landings of different types.
- Practicing everything.
Hours logged total: 22.1
Instrument hours logged this lesson: 0.5
Instrument Hours logged total: 1.3
Take-offs and landings this flight: 4
Take-offs and landings total: 62
PIC hours total:: 3.2
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