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degt

Twin Otter X CDI and Attitude indicator innacuracy

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I recently bought the Twin Otter X for use on my Windows 7 Home Premium 64-bit system with FSX. I like it even though the manual kind of left me a bit disappointed, but well, it is not a PMDG. My PRODUCT.CFG says it is product version 120 (v1.20).

Anyway this post is because I have been flying the twotter and have noticed that on the PFD the CDI is very inacurate. I tune the VOR station usually on both NAV1 and NAV2 so that I have both DME indication as well as horizontal navigation indication.

I have noticed that when trying to navigate a VOR radial many times when the CDI is perfectly straight as IF you were right on the radial, it turns out you are not. I have had this cross-checked with the GPS panel and when the CDI needle showed I was right on the radial it turned out I was actually either some nm to the left or right. This makes it difficult to align properly if it is not accurate. In other words during the tests the CDI should have shown a deflection. I think if you are more than 5nm off the radial then it would show correctly on the CDI.

The other problem I have noticed is with the attitude indicator, particularly during climb phase. When I have the yoke pulled for climb the attitude indicator is almost level with the artificial horizon when it should have been showing 5 to 10 degrees (even more in some other tests I did) pitch up attitude. For descent however I noticed I can rely on it, if I push the yoke to pitch down the attitude indicator properly shows the 5-10 degree pitch down.

I will post any other findings in this forum. I certainly miss the -400 and Vista Liner variants but the twotter is definitely very nice to fly. Asymmetric thrust seems to be working fine (I never flew the real plane though).

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Hello degt,

Did you load the default Cessna first then whilst in the 2D panel load the Twin Otter.

Eh, nope :( is there a particular reason? is it an FSX limitation? perhaps a bug that was never patched? Will try next time and see how it goes.

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Hello degt,

Its resets all the FSX parameters.

Thanks. I tried as mentioned but the attitude only goes a little up unless I really am pitched up to the point of stalling.

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Hello degt,

Does look a lot like 45 degrees when on the 20

I also think the CDI may be lagging a bit. I have been doing some circuits around a VOR'ed airport (or with ILS) and it only begins to move towards the center when I am very near the radial so by the time the turn is completed I am off. Normally with other a/c When the CDI starts moving I initiate the turn to align to the radial. With this one the CDI is dead until near the very radial.

Other than that it is a lovely a/c to fly, the Bendix GPS super radio is still on the complex side (haven't learned all of it) but it is a fantastic oppty. to really practice IFR navigation without relying on a GPS.

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Hi Shaun

Still learning how to post, but as you can see, I have the same problem with the attitude indicator. Pity because it is a great plane to fly. Look forward to any suggestions for a fix.

Regards

Bob

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I've noticed the lazy ILS turn phenomenon in many situations, with several different stock aircraft in FSX. That's one of the first issues I notice when I transition from X-Plane 9.6 back to FSX. So it may not be so much an issue with the plane as with FSX and more particularly that particular ILS (Some are worse than others for airplanes not noticing the beam until it's right directly in line with it)

But I'll follow this thread and see if anyone has any ideas.

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I hope this issue is resolved, it is very difficult to properly rely on it for navigation because even when you are relatively far away the CDI is nearly at the center so it becomes difficult to see the CDI coming alive (moving towards the center) when you want to align to a radial.

Let's hope the attitude indicator lazyness is also addressed :-) I have been enjoying this aircraft very much, in fact I may be starting my own Twin Otter virtual airline soon! VA Pilots would be able to use either the freeware Twotter or buy from Aerosoft this excellent a/c.

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Hello Degt,

Marking them up as there may be a few others but they are on my list of things to report, let me know about your other finding in your other thread.

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Hi Shaun,

Any news regarding this bug? it is really a bummer that one cannot trust the CDI :( I figure it was not noticed before because most virtual pilots simply fly the GPS line rather than actually looking at their instruments for navigation.

According to information each notch to the left or right of the indicator represent a 5nm deviation from the radial. What I believe is happening here is that the factor applied by the Twotter X software to convert the actual flight path deviation (from the radial) to the VOR indicator's visual representation is just too small, therefore when a 5nm deviation is observed (as an example) and is converted to a pixel value (i.e. at a given zoom level 1 notch = 5 nm = 25 pixels) rather than computing 25 pixels, it converts to a value nearing 0 (say 3px) so that the CDI appears very close to the center line rather than at the notch.

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It's not just the CDI that is out of kilter, the heading bug is also erroneous, I added a small window with a digital readout of the actual headings and the apparent headings the bug was set to and there is a wide variety of variation in the readings depeding on the placement of the bug. Here are some images to demonstrate both the heading bug and the CDI needles differences with the digital readout of each.

The first image shows that at the current heading of the plane, 126 degrees, both are fairly accurate, it also shows the corresponding digital readouts for each item.

Note though that as the bug and needle are rotated, the discrepancy between the dial and the digital becomes marked.

Note that only at the setting of 270 degrees are both smack on accurate

01.jpg

02.jpg

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05.jpg

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11.jpg

12.jpg

13.jpg

Hopefully this may prove useful to sort it out.

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Speaking of the HDG bug I have noticed the following:

When you rotate the CRS knob the tooltip indicates the current course that is selected so as you turn you can see what the actual value is. If you rotate the HDG bug on the other hand you get some other number that does not correspond to the current setting of the heading bug.

I think some justice has to be done to this wonderful a/c :-) and have these issues addressed by a patch some time in the near future for the loyal customers :-) Someone told me before I bought it "It gets to you, after that you won't be able to leave it in the hangar" and that is true! it is just a pity it has these few odd quirks that limit its suitability for instrument training :(. I used to be the jet-kind until I got stuck with this LOL.

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Snave. Good point, yes gyro drift is enabled, but I made sure to reset it "D" before I made these screenshots, besides which, Gyro drift would not account for the variation seen here, why would it read accurately at 270 and be out by 11 degrees when set at 90? If gyro drift were at fault then the error would at least be constant around the dial. Equally it still does not explain the difference between the readouts of the CDI and HB at the same points.

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Hi,

About the attitude indicator problem. It would seem to be an issue of 3D elements used to draw the indicator. The instrument "plate" is on the background and the horizontal level bar is some distance front of the background. Therefore your eyepoint will affect the perceived attitude indicator reading. Try lowering eyepoint to same level as the attitude indicator and it will read correclty. This could be simply solved by implementing the "Pull for quick erect" button that would raise/lower the indicator bar so that it would read correctly in relation with you eyepoint. E.g. Carenado Mooney has that feature. Unfortunately it is not implemented on the twotter.

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Although there was an unoficcial "trial" fix to some of these issues, the official patch never came out. If I have to reinstall I really don't know how to bring my twotter to the current state :(

And I must say it is Aerosoft's fault that I am addicted :o to this beautiful aircraft hahahaha :D . I used to be a hardcore B738 sim flyer and was ripped out of my virtual cockpit to be recruited into the turboprop realm to pilot this aircraft. It has been about a year since I did any flight with a jet.

For that reason I hope the developers consider bringing out an update with the Viking Air -400 model (glass cockpit) of the Twotter.

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