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Cabin Alt/IAS hold/Flight Dynamics

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Shaun. View Drop Down
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    Posted: 01 Oct 2013 at 7:12pm
**Edited**

I had an issue with the cabin altitude, but it seems that I didn't engage the packs at the right time.


The IAS hold has some serious issues on descent, pulling 6,000 fpm. Also I find the aircraft underpowered and very difficult to control. 

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hifly View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hifly Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct 2013 at 10:19pm
Shaun, I have both these planes and have not encountered the problems you have described. For the 146 the IAS only works when changing altitude. The 146 AP is very different from others. Have you read the manual correctly?
 
As for the MD81/82 I have had no problem getting up to 29,000 ft and have found the handling very good. What yoke are you using?
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Shaun. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shaun. Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct 2013 at 10:24pm
Sorry, I did mean the 146-300 struggles to gain altitude.

I may not have changed the altitude bug prior to descent, I'll try that. Although it still should be a smooth initiation of descent with IAS, like with ascent.
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Lemmerp View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lemmerp Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 2013 at 3:04pm
Hey Guys
 
I have the same problem and I can't figure it out. I change my altitude bug and then when I engage the IAS, it also goes into a serious dive. It is my understanding that as my throttles are set to the cruise speed, when I engage IAS, it should stay level and only go into a smooth descent as a slowly lower the power or am I missing the picture here?
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Deltahotel View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deltahotel Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 2013 at 6:29pm
Yes the IAS hold function is far from accurate, but I have no idea how true to reality that is. You know it is done, or tries to be done, via pitch change through the elevators. I guess you have sussed the practical workaround for initiating a descent (or climb)... select IAS hold, retard throttles a teeny bit, hit the VS button as you approach your desired rate of descent, then use throttles to regulate your IAS. Annoyingly, I find controlling the speed by throttles is surprisingly sensitive ... keeps you awake though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lemmerp Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 2013 at 7:36am
That's what I'm doing, or at least trying to do. Again, not sure if I understand this incorrectly, but my understanding is when you reach your altitude, the aircraft maintains altitude and you have to control the speed via the throttles, obviously. But now logic tells me that because I'm controlling speed, if I were to keep my throttles the same, when I engage IAS, it should in theory stay in straight and level flight. Then decreasing the throttle gently, it should ease into a descent until I reach the 1800fpm at which stage I should engage the VS. But it doesn't. It just goes into a death dive.
 
With that said, I haven't tried this, but I will the weekend. If I disengage altitude hold, then decrease throttles to ease into descent and engage VS once I reach my 1800fpm, therefor bypassing the IAS hold step, would that not work? I'm going to try it and give feedback on this.
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Deltahotel View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deltahotel Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 2013 at 10:22am
Lemmerp I'm sure that would work fine - it may take a little longer to initiate the descent, or you could just give it a nudge with a touch of down trim after disengaging the ALT hold. Either way you will be playing the throttles for speed control in the descent. d
Dave H
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lemmerp Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 2013 at 10:28am
Playing with the throttles to control the speed is fine, part of flying, it's just to stop my virtual passengers from messing up my cabin and sparing my virtual ground crew from cleaning up the cabin just because of the nose dive it likes doing. LOL
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