View Full Version : Autothrottle, Autopilot, and other Nav questions
08-12-2008, 07:59 PM
Ok I'll get right to it, I appreciate any help available. These all pertain to the Learjet in FSX.
1) When I have my autopilot set to Nav to follow a radial on a vor, my learjet will turn to intercept the course, but overshoot it slightly. Then it will turn back to intercept the radial and again overshoot. This causes me to progress forward in a slight "S" pattern. What causes this and how can I fix it? I finally gave up and just switched the AP to HDG when the plane got close to the radial.
2) I sometimes have a hard time disengaging the autothrottle. I understand that the AT is independent of the rest of the AP system, so to completely disable autopilot, you have to turn off the AP Arm button AND the AT button. However, I did this on an ILS approach to ORD, and the plane still wouldn't respond to my throttle inputs (yoke inputs started working fine with the AP switch off). I TRIPLE confirmed that the SPD button light was off, I swear upon my life it was off, so why wouldn't the plane let me adjust speed? (I ended up overshooting the runway and hitting some houses on that one).
3) When you create a High Altitude Airways flight plan, IFR, through FSX's planner, how do you know when you're nearing an "intersection?" The planner puts together a flight plan with a few different VORs and intersections between them (the intersections are usually a point to adjust which radial on the VOR you're on). What I really need to know is how do I know when I've reached an intersection while traveling down a radial of a designated VOR? I'd like to know how to do this WITHOUT using the GPS (seems like cheating). The GPS has all the Intersections labeled for ease, but I'd rather know how to do it using the VOR instruments. FSX loads the flight plan data onto the kneeboard for reference. Is the information I need somewhere on that kneeboard?
4) Is this information that I could have obtained elsewhere? I really appreciate everyone's willingness to help, but I'm always striving to be self sufficient with my flight learning.
Thanks in advance for any input you can offer (especially throttle input[/badjoke])
08-12-2008, 08:01 PM
Thanks for posting these questions. The answers will help not only you but also a number of people who read this forum but don’t post. Now . . .
1 – The VOR mode of the autopilot in FS was badly coded. What works for me is to get within 1-2 degrees of the radial via heading hold, and only engage NAV mode once the aircraft is reasonably on course. Note, however, that the APP mode of the simulated autopilot has much better behavior. While you still can’t intercept the localizer at a 30 degree angle (which would be possible in the real world), the intercept angle doesn’t have to be as small as the 1-2 degrees required by NAV mode. Play with APP mode and you’ll see what I mean.
2 – Let’s see whether somebody else can answer this one. I cannot.
3 – Intersections are defined as the intersection of two radials of two different VORs. What I do is slide down the radial of the airway that I’m on (NAV1) and then wait for the NAV2 needle to center, with NAV2 being tuned to the frequency of the other VOR (the one that's defining the intersecting airway). So now the question becomes, How do you learn the frequency of that second VOR? I do it via the FAA high altitude charts, a full set costing about $35, available at www.sportys.com (http://www.sportys.com/), which is Sporty’s Pilot Shop. The same charts are available at slightly lower price from the NACO/FAA (National Aviation Charting Organization), but they won't put you on the mailing list for Sporty's most excellent catalog, which is ideal bathroom reading. :) It may be possible to do the same thing via the map mode display of FS. You certainly can get VOR frequencies that way but as I recall, map mode doesn’t give you the airway numbers, only lines depicting where the airways are. (If I’m wrong about this, somebody will correct me.)
4 – These are the kinds of questions that certainly have been asked and answered in various threads, but you would have to do an exhaustive search using Advanced Search, with search masks like …
chart airway vor frequency
and then see what the search comes up with. (No, I haven't tried this one. Try playing with things like this yourself because the forum search capability is very powerful once you get the hang of using it.)
There are obscure FAA publications you could download that would give you the information. While it wouldn't directly address the issue of VOR frequencies, one of the important publications available for download is the “Instrument Flying Handbook”. (I think that's the title, but it's been 40 years since I looked at it.)
Anyway, go out to http://www.faa.gov (http://www.faa.gov/) and poke around. You’ll find all kinds of useful stuff there including arrival, departure, instrument approach and airport diagrams for the airports in all 50 states that have published instrument procedures. (These are also NACO/FAA charts.)
Because of the hassle of identifying the required NAV2 frequencies, I usually take the easy way out and simply fly VOR to VOR, in which case the FS flight planner will list all the frequencies of interest.
There may be freeware or commercial flight planners that will produce this information, but somebody else will have to speak to that.
Again, thanks for asking these thought-provoking questions.
08-12-2008, 08:37 PM
Thanks for the prompt reply.
A follow up to your explanation of intersections. Do the charts you use tell you what radial to dial in for the nav2 VOR (not just the freq)? I imagine they'd have to tell you or your needle would never center or center too late/early while tracking the nav1 vor.
08-12-2008, 08:45 PM
The charts provide that information and more. The airways are clearly labelled, the defining radials are clearly numbered as to compass direction, and the VOR names and frequencies are clearly shown.
These high altitude charts (which show the Jet airways) are schematics with white backgrounds, very easy to read. In contrast the low altitude charts (which depict the Victor airways) are chock-a-block with sectional map type graphics.
08-12-2008, 09:29 PM
As Mike said, FS AP is badly coded for a VOR course change. The best thing you can do is disengage the VOR/LOC hold to either HDG HLD and make the course change with the OBS knob or manualy fly it around the turn to the outbound heading and ensure you are centered on the radial before re-engaging the VOR/LOC hold.
It's rediculous how the AP will wander around until it finally has the course centered. And forget about WCA. That takes forever if a stong crosswind is present. You'll be at the next NAVAID by the time FS figures it out. It's faster to set up the WCA manually after course interception before re-engaging the AP.
08-12-2008, 10:12 PM
You don't say what aircraft you are using, but here are a couple of thoughts:
I sometimes have a hard time disengaging the autothrottle. I understand that the AT is independent of the rest of the AP system, so to completely disable autopilot, you have to turn off the AP Arm button AND the AT button.
On some add-ons, you have to disconnect the AP using the AP Disconnect button on the yoke. Then, after turning off the AT, you will still have control. I don't why. I have just discovered this on the PMDG 747X, but haven't researched it yet to understand the logic. You could check to see if there is a better method of disengaging the AP on the aircraft you are using.
When you create a High Altitude Airways flight plan, IFR, through FSX's planner, how do you know when you're nearing an "intersection?"
I think another way this could be done is with DME, if you have it available on your aircraft. You would, of course, have to have made notes of all relevant distances before beginning your flight.
Is this information that I could have obtained elsewhere? I really appreciate everyone's willingness to help, but I'm always striving to be self sufficient with my flight learning.
Yep. Experience, but that can take longer than asking. ;) Like you, I try to teach myself as much as possible, but really, the forums are quite valuable as you can tap into others' experience when you wish.
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