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DME Readouts and AP trim


ricfishner

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Hi,

I'm enjoying this wonderful twotter for a few days already. Thanks to Aerosoft for this immersive addon!

But I'm still struggling with a few issues. I also installed the update to 1.01 today, but still I see some odd behaviour regarding the DME and vertical trim while the autopliot is engaged.

For the DME:

I see the strange +1 nm for the distance to NAV2 VOR has been fixed with the update. But still the estimated time to the VOR seems to be off. If I set a course in the GPS to a certain VOR and also dial in that VOR in NAV2, the distance shown on the GPS and the DME match. But the estimated time on the DME is always much shorter than shown on the GPS. I can post a screenshot later to clarify a bit more.

Trim and AP:

This has been adressed in a sidenote in another post on the Forum already, but still like to point to it again so it doesn't get lost ;) and maybe the answer is easy:

Whenever I engage the Autopilot the aircraft starts automatic trimming immediately, although I haven't touched the "ALT Hold" button. It seems to try to hold a certain climb rate. I see the "trim in Motion" indicator and the "trim up" / "trim down" lights on the AP device flashing all the time. Any manual trim action is counteracted by the Autopilot, so it is not possible to e.g. hold a selected heading (HDG engaged) and manually set the trim of the aircraft. Still not sure, is this a bug or is this a Close to reality rendition of the AP (and it just works different from what I expect)? The manual doesn't point out any special quirks of the AP in this regards..

Anybody else seeing these issues?

Kind regards,
Ric

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I noticed that same thing not being able to use manual trim even with ALT button off; as soon as I disengage the A/P then the manual trim is operable. I expected I would be able to use HDG hold with ALT off and be able to trim for descent etc. I will be watching for this answer too if this is a quirk of this A/P or something else?

Thanks

Jerry

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  • Aerosoft

Hi,

I'm enjoying this wonderful twotter for a few days already. Thanks to Aerosoft for this immersive addon!

But I'm still struggling with a few issues. I also installed the update to 1.01 today, but still I see some odd behaviour regarding the DME and vertical trim while the autopliot is engaged.

For the DME:

I see the strange +1 nm for the distance to NAV2 VOR has been fixed with the update. But still the estimated time to the VOR seems to be off. If I set a course in the GPS to a certain VOR and also dial in that VOR in NAV2, the distance shown on the GPS and the DME match. But the estimated time on the DME is always much shorter than shown on the GPS. I can post a screenshot later to clarify a bit more.

Trim and AP:

This has been adressed in a sidenote in another post on the Forum already, but still like to point to it again so it doesn't get lost ;) and maybe the answer is easy:

Whenever I engage the Autopilot the aircraft starts automatic trimming immediately, although I haven't touched the "ALT Hold" button. It seems to try to hold a certain climb rate. I see the "trim in Motion" indicator and the "trim up" / "trim down" lights on the AP device flashing all the time. Any manual trim action is counteracted by the Autopilot, so it is not possible to e.g. hold a selected heading (HDG engaged) and manually set the trim of the aircraft. Still not sure, is this a bug or is this a Close to reality rendition of the AP (and it just works different from what I expect)? The manual doesn't point out any special quirks of the AP in this regards..

Anybody else seeing these issues?

Kind regards,

Ric

The DME uses IAS and heading and GPS ground speed and ground track if I am correct could, that be the cause? And of course ETA is a calculation and it would be unrealistic is two different ways to calculate it would be identical. For both things we use standard FSX data btw.

We can not find anything wrong with the AP, as far as we now know (and as far as our real pilots inform us) this is how it works. We will check it one more time.

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Exactly. DME has no factoring for wind, (it's simple IAS/Slant Range). GPS does factor ground speed.

This is neither Twotter-specific nor new. In fact the DME is covered in the Learning Center, as is the GPS

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Most autopilots will default to Pitch Hold when switched on. Manual control of pitch with the autopilot engaged

is an "FSX feature" that most real world autopilots do not have. Instead of manually trimming, use the pitch rocker

switch to accomplish the same thing, when the autopilot is engaged.

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  • Deputy Sheriffs

DME doesn't "know" IAS (indicated airspeed) at all. It simply computes the change in slant range from the aircraft to the station over time to arrive at a speed (e.g., if the slant range changes by 2.0 nautical miles in 60 seconds, it will display a speed of 120 knots. There may well be DME displays out there that have the speed labeled as "ground speed," but that's not correct. It's not really the same as ground speed unless you're tracking directly to or from the ground station, and even then, it's a close approximation. Certainly better though than the other methods besides GPS. Again, the slant range factor keeps it from being equal to ground speed unless you're a ways from the station and at a realtively low altitude (due to the slant range getting closer and closer to the ground distance. Flying a DME arc, the speed zeros out.

As was pointed out, GPS on the other hand does calculate an accurate ground speed.

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Hi,

thanx for the replies!

I do know that DME and the GPS use different data inputs and that DME has different readings if you circle around a DME or fly by it etc. Just due to the facts mentioned. So I did not expect GPS and DME to exactly match, but also not to be that off if I'm flying a straight line to a VOR/DME on the GPS and have the same VOR dialed in NAV2 for DME read out.

Please have a look at the following situation:

I just left LESB to ferry some stuff for a friends move to Barcelona :) I'm flying the leg LESBN - BCN (VOR/DME 116,70 Mhz), which is also the VOR selected in NAV2, distance hence shown on DME. The distance on DME and GPS kinda match, as well as the airspeed (still keeping in mind, it is calculated differently). It's just the difference in ETA that throws me off... but let's just look at the DME and forget about the GPS. How am I able to make this 88,7 nm in 20 min, flying at a speed of 144 knots?

Hm.. wait. Can't upload the screenshot ("attach file"), it says I'm not permitted. How can I upload? Is it because it's bmp format?

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Most autopilots will default to Pitch Hold when switched on. Manual control of pitch with the autopilot engaged

is an "FSX feature" that most real world autopilots do not have. Instead of manually trimming, use the pitch rocker

switch to accomplish the same thing, when the autopilot is engaged.

Many autopilots have this feature. It's called ControlWheelSteering on Boeing or TouchControlSteering on Bombardier for example, and is a dedicated AP mode. On older Boeings like the 707, or 727 / 731 / 732, depending on the used AP system, you also could just engage the lateral navigation by AP and handfly the vertical part (using the ELEVator DISConnect switch). So it's much more common as you would anticipate ;)

On the Twotter Yoke there is also a button titled CWS btw.. anyone knows what this would do IRL?

Anyway, the autopilot will maintain the attitude you had upon activation, unless another mode like IAS or ALT is used. The pitch attitude may be changed using the standard FSX commands for AP up / AP down.

I already posted this issue in the thread I opened, but as it is closed now i will report here as it refers to the same system. I often have the following situation:

*Descend to a target altitude with a rate of around 1500fpm, ALT ALRT (ALT intercept) armed.The AP is not disconnected at any time.

*It also happens on approach in APPR mode with MDA leveloff armed.

*200ft above the selected altitude the AP mode ALT comes on, at the same time the aircraft pitches up hard and gains around 500-1000ft of altitude, with the AP constantly trying to trim down.

*if airspeed had been sufficient, the aircraft levels off and slowly floats down to the target altitude, this time catching and maintaining it correctly. The AP mode ALT is active all the time.

*if airspeed had not been sufficient, the aircraft stalls if no intervention is made.

At the moment I tend not to use the level-off modes ALT ALRT or MDA, as they frequently ruin my approaches or vertical profile planning.

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Ahhhh! Thanks to the hints and tips I found here on the forum I was able to figure out the AP issue. The rocker switch in the middle of the yoke and the AP Alert function of the FD was what I was missing.. And I have to say: Nice!! Really like it, the AP not being like the default ones!

This bird keeps impressing me over and over again! Luv it! Thank you Aerosoft for this great and challenging addon!

Hm.. but still don't trust the DME though.. :glare_s: but I'm patient it will be clarified, I'm sure!

Ric

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Hm.. but still don't trust the DME though.. :glare_s: but I'm patient it will be clarified, I'm sure!

Ric

I repeat, the DME ETA has a bug in the code -see my other post- which is still present in 1.01.

As it it a tiny bug, I'm sure it will be fixed in the next update.

Tom

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Hi Tom,

that's what I meant. I'm sure with Aerosoft they will have a look into it and come up with a fix if that's what needs to done. Therefore I keep patient :)

Ric

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