Having problems with DC-8-62 Autopilot VOR Mode

[biggiraffe]

Hello,

I use FS2004 on a Windows 10 machine.

Recently, I downloaded the DC-8-62 along with the -62/63 control panel.  I find that this panel's autopilot has trouble tracking a VOR in cruise flight, diverging from the proper course rather than converging on it.

For example, I fly the aircraft to the middle of the VOR radial about 100 miles out from the VOR, needle centered, nose pointing toward the VOR.  Then I set the autopilot to "VOR".  The aircraft goes into an immediate right turn (always goes to the right first) until the needle is no longer centered.  It continues in this direction as the needle continues farther off center, and then the left wing dips slowly, and the aircraft begins a left turn back the VOR radial.  As the needle gets closer to center, the wing is still dipping farther into a left turn and we pass through the radial with the nose 20 or 30 degrees left of the desired course.  Eventually, the machine realizes it has flown through the course and the wings slowly return to level, aircraft still speeding way off course, and begins a right turn back to the radial.  If ATC doesn't call with course instructions this cycle, it will after we fly back off the right side of the radial.

I do not have this problem on the DC-8-50 (except possible very close to the VOR station, but that is true of all airplanes).  Do I have a setting wrong in the DC-8-62 that might be causing this autopilot behavior?

Thank you,
Kurt

[aerofoto - HJG Admin]

There shouldn't be any problem/s (obviously).

None have been reported at least.

And what we offer for the DC-8's are by no means new files.

The last panel file updates for the DC-8 DUPER 62/62 were released during 2007 (for the standard version) .... and during 2010 (for the INS version and which was actually released at this particular time)

The last gauges/core files updates for the DC-8 panels (for all DC-8 panels) were released during 2018 .... when a gyro stabilized WX radar was included.

The last DC-8 SUPER 62 (and 62-F) base pack updates were released during 2016 .... all DC-8 base packs were updated at this time.

No changes/alterations have been applied by us to anything since these times.


Need to know "specifically" which DC-8 SUPER 62 or DC-8 SUPER 62F base pack version you're using.

Also need to know which DC-8 SUPER 62/63 panel version you're using .... The standard or INS version ?


Other than the above and for starters all I can comment is as follows ....


1. Unless you've modified or added something (not suggesting you've done so .... I'm merely commenting only ) to the AP section of your DC-8 AIRCRAFT.CFG file, or have a corrupted file, you shouldn't be experiencing problems/difficulties at all.

2. It's advisable to intercept any VOR "as soon as possible and as close as possible" to it. 100 DME is a long way down the track. The further away from the VOR one tries intercept and capture its beam then the less stable the intercept is .... this is common in FS. I'm usually on the VOR beam within 40 DME of departure and don't experience any difficulties .... and most VOR's (with the exception of a few) are good for up to 194 DME.

3. It's advisable to intercept any VOR at a less than 30* axis. The greater or more acute any angle/axis of intercept then the longer it takes for the simulation to eventually stabilize in accordance with the VOR capture. I generally intercept at no more than a 10* to 15* axis .... and don't experience any difficulties.

4. It's normal for the simulation (any simulation .... not just these DC-8's) to gently weave left, then right, by several degrees and in reducing increments, for a couple of minutes or so upon capturing any VOR. Again .... the extent to which the simulation weaves can be greatly reduced by minimizing the angle/axis of the VOR intercept/capture.

5. Make sure the AP is actually fully engaged and is not set to YD .... before engaging any of the AP modes. When/if the AP is disengaged it'll default to its "YAW DAMPER" detent .... and it won't be possible to capture any VOR.

6. Make sure the AP "TURN" knob is cantered.

7. Make sure the AP Model Selector switch is actually set to its "VOR/LOC" detente .... or it won't be possible to capture any VOR either.

8. Check that you're actually working with the NAV1 Radio .... and it is tuned to the correct frequency.


I'm sure you know and practice #5 through #8 .... but had to comment

Given the absence of any known/general problem/s though I wouldn't mind betting the cause of your problem is possibly #2 .... trying to intercept, and capture, the VOR when you're already quite a very long distance from it .... and which will/can cause what you've described.

I don't think WINDOWS 10 will have any bearing on this issues, but, can't guarantee it won't.

Get back to us please with regard to the "specific" files you're using


Mark C
AKL/NZ

[aerofoto - HJG Admin]

There's times I wish I could make a video .... and right now's one of them

I've just had a look at this .... to satisfy my own curiosity

For my test I used our standard DC-8 SUPER 62 (JT3D-3B) base pack with the standard DC-8 SUPER 62/63 panel.

Files I have/use are the same as those currently available here .... save for the 3D model which is that for our developing project but which can't impose any influence upon panel performance.

Departure was KSEA RWY 34R. The NAV system was set to the KSEA VOR 116.80 .... and its 156* radial. This required a long climbing 114* left turn toward a 146* heading after TO and CU .... in order to be able to intercept, and capture, the 156* VOR radial using AP HDG Mode initially.

To cut a long an otherwise unnecessarily boring story short ....

The simulation performed flawlessly.

Acquiring a heading of 146* .... the KSEA VOR 156* radial was intercepted. Once the indicator bar, within HSI, was almost aligned within 1 or 2 degrees of the selected the 156* VOR course .... and by now about 20 DME from the VOR .... I used AP HDG Mode to adjust the simulation onto a heading of 156* .... then .... I engaged AP VOR/LOC Mode. The simulation captured the selected course .... no problem/s at all .... and with "minimal very long and slow weaving left and and right" before stabilizing on the selected 156* radial and by around 33 DME from the VOR.

Sorry .... I can't replicate your problem using this particular DC-8 SUPER 62/63 panel

Mark C
AKL/NZ

[aerofoto - HJG Admin]

Just now performed the same test again .... but this time using the DC-8 SUPER 62H (P&W JT3D-7) base pack and with the DC-8 SUPER 62/63 INS panel.

Precisely the same NAV data was set up .... and the very same flight performed .... only this time I made a long climbing 114* right turn after TO and CU to a heading of 170* in order to intercept, and capture, the 156* KSEA VOR radial.

The VOR intercept was performed in exactly the same manner as described per my previous test .... and the simulation performed fine/exactly in accordance with my procedure/s as previously reported.

So far as I'm concerned both DC-8 SUPER 62/63 panels are OK.

Still need to know precisely which DC-8 SUPER 62 base pack you're using though. We offer 4 different weight and engine configurations for these .... 2 of which I've checked per these tests and which I confirm to be faultless.

Unless there's a WIN 10 related issue (I "doubt it" though) I again suspect the cause of your problem might be trying to intercept and capture the VOR radial "way too far" down the track .... 100 DME (or more) is a very long way down the track to become established on any VOR. As I said within my first reply .... it's always best to try'n get established on the VOR at the earliest possible stage .... precisely as I also described.

ALSO .... the AP's in each of our DC-8 panels, and those for CV880's and CV990's too are identical and operate in precisely the same manner.

Mark C
AKL/NZ

[biggiraffe]

Hello,

(Sorry about my delay being back; had some things come up.)

I downloaded the DC-8-62 Base Pack Ver 54. The panel is the non-INS.

The reason I intersected the VOR so far out is because I was in South America and flying away from the previous VOR, and actually the two did not overlap. But I've also had the problem flying outbound on the VOR and end up have the airplane fly Heading and I just adjust per the needle indication. I don't know why I have more trouble with the -62 than the -50, but I'll do some testing and note the specific VOR station and such, and try with both airplanes.

(I haven't noticed the problem in the 880, which I also enjoy flying. Oh, and I also use the DC-8-10 and it's been doing fine.)

Thanks, I'll do some comparisons in a more scientific way and get back.

Best regards,
Kurt

[aerofoto - HJG Admin]

I'll perform another test later on today (just to further satisfy myself) .... and this time using the standard DC-8 SUPER 62 base pack with the DC-8-SUPER 62/62 panel. My first check of yesterday's was composed of this same base pack but using the standard DC-8 SUPER 62 panel.

I don't expect the results to be any different though .... because all of our DC-8 AP's are identical, function identically, and use the same NAV parameters too .... so .... there should be no variation in the AP performance among any of the DC-8 simulations we offer.

"Unless there's some form WIN 10 interaction going on in your particular case" .... I simply "CANNOT" replicate the issue your experiencing.

As I mentioned yesterday .... getting established on the VOR course, at the earliest stage after departure, or whenever transitioning from one VOR to another, is recommended. Intercepting any VOR 100 DME (or more) further down the track can .... "in FS" .... result in course tracking instability with an excessive degree of weaving/hunting for the selected course before eventually stabilizing on it .... if at all.

As I also mentioned yesterday .... whenever intercepting a VOR (in FS) a degree of "minor" weaving (left and right) over the selected course, but in decreasing increments, and before stabilizing on the selected course after a few minutes, is "perfectly normal FS behavior" .... but .... during both of yesterday's checks I was actually surprised how "VERY MINOR" this was. In my case the simulation "did not" drift more than a couple of degrees over the selected course (either way) before stabilizing on it after a few minutes. No massive drift/deviation or course hunting was experienced .... "at all". I do feel the VOR course stability I'm experiencing is a probably the result of the technique I employ/recommend though.

Once again .... my recommended technique is to use AP HDG Mode to align the simulation/HSI course indication within 1* or 2* of the selected VOR course .... then once almost perfectly aligned with the selected course engage AP VOR/LOC Mode. Any drift/deviation/course hunting should not exceed a couple of degrees, and not persist for more than a few minutes, and in decreasing increments, before stabilizing on the selected VOR course.

Mark C
AKL/NZ

[aerofoto - HJG Admin]

WELL .... I've just completed that check .... the 3rd one I've performed in less than the past 24 hours

Again using our DC-8 SUPER 62/63 AP NAV features .... BUT .... I simply "CANNOT" replicate any major issue/s at all.

AP HDG Mode was again used to align the simulation with the selected VOR beam. Then once within 1* to 2* of this AP VOR/LOC mode was engaged. The simulation drifted "a few minor degrees" over the selected course (both left and right) as it captured the VOR beam .... then "very acceptably settled onto the beam" without any apparent issues at all. This time I flew the simulation all the way up to cruising altitude .... which I didn't do yesterday. It settled nicely into the cruise, still on the VOR course, and at 31,000 FT .... and I let it fly on like this for well over 100 DME and at MACH 0.82. The simulation remained more-or-less right on the selected beam .... with very little, if any, drift evident at at all .... and whatever drift was evident was almost totally insignificant.

A professional DC-8 FE we used have here (John D), some years ago, told us these aircraft, like B707's too, and unlike advanced modern aircraft of today, never sat precisely on the selected radial (my understanding is VOR NAV is only good for up to 200 miles anyway .... 194 DME at the maximum in FS) and this had to be watched .... with any drift constantly noted and compensated for. Apparently such was quite normal for late 1950's/early 1960's technology .... like the DC-8's represent .... or so I've been told. What I've observed over 3 checks, of both of our DC-8 SUPER 62/63 panels, and 2 of our 4 DC-8 SUPER 62 base packs .... is perfectly in accordance with this.

Sorry .... I just "CANNOT" replicate the issue, you say, you're experiencing, but again, suggest/ask you to try'n implement my procedural recommendations.

I can't really do anything more .... and don't really have any further advice to be able to offer

Mark C
AKL/NZ

[biggiraffe]

Good Evening!

I've done some checking between the -50 and the -62. It appears my problem isn't so much related to the autopilot as my interpretation of the different HSI that the -62 has. To me, the needle appeared to be slightly right when the radial was centered. Therefore, I would align the needle the way I thought it should be, then set the autopilot to VOR, and it would immediately seek to center that needle. I watched it awhile and saw how I should be reading "centered".

There are surely some other pilot errors I've been making, so I'll continue to watch closely what I'm doing.

Thank you for checking things out so thoroughly, all the time you put in on test flying. I think your DC-8's are WAY cool, by the way.

Best regards,
Kurt

[aerofoto - HJG Admin]

the needle appeared to be slightly right when the radial was centered

That sort of observation's not at all uncommon in FS.

Sometimes the alignment can appear with a slight left or right axis.

And it's also not entirely abnormal to observe a fraction of "extremely long and slow" drift response .... both left and right (not more than a degree or so though) a couple of times only and throughout the entire 194 FME duration of alignment with any particular VOR course too. In fact such drift is "so mild/minor" it may even go totally unnoticed .... it seems to be just a simple FS quirk associated with some HSI gauges .... in so far as I've observed this at least.

So long as the simulation's basically "aligned with the selected VOR course" .... and is following that course .... is all you really need to really concern yourself about "in FS".

Once a VOR course is set within the HSI .... and once the simulation is established on that selected VOR course .... never try straightening the simulations course by readjusting the VOR indicator or course setting (unless you've set a wrong Course to start with). Instead switch back to AP HDG mode, then, acquire the correct course using HDG, and then, re-engage AP VOR/LOC as normal) otherwise you'll end up experiencing "quite wide axis of drift as the simulation then tries to intercept and acquire the new/adjusted VOR course.

Reading what you've just replied it seems, to me, this's highly likely to have been the cause of your issues all along

STILL .... I think we've got it sorted for you now and in doing so I hope other parties might learn from this thread accordingly

Mark C
AKL/NZ

[aerofoto - HJG Admin]

I've moved the "CV990" related content of this thread to the "CONVAIR SUPPORT" forum page.

These details are now all located within a/the new "HAVING PROBLEMS WITH CV990 AUTOPILOT VOR MODE" ....
tonymadgehjg.proboards.com/thread/10094/having-problems-cv990-autopilot-mode

Although both issues are similar (and extremely minor) .... the CV990 commentary is better located within the "CONVAIR" page.

Mark C
AKL/NZ