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Pitch/ lift Stability


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Gentlemen,

 

I'm not sure if this is the correct section to ask this question, but I have a question.

 

I notice the trim and negative lift stability in this aircraft is very pronounced.  I'll explain.

There doesn't seem to be a lot of 'positive' lift for the aircraft, even when the flaps are extended all the way. In fact, the more the flaps are extended the more the aircraft will pitch downwards,putting a heavy nose down attitude..thus,  needing a huge amount of trim compensation.   Is this how the aircraft should be (or is)? Or, is there an issue with my controllers? Or, ? 

 

The reason why I ask, is because this is the first aircraft ever to behave this way, of all the ones I have flown. Perhaps I'm doing something wrong, or maybe this is how the a/c should behave? I don't know. But, I would love to adjust lift- or have more lift-, when the wings are extended cause presently its seriously killing my experience.  (And, I'm not asking for a lift effect as the default F-22 that you could land it almost at 115 knots. lol )

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In the real aircraft there is a large pitch change during flap extension. The aircraft has an auto trim function that happens automatically when the flaps are moved between 0 and 20 to help with the pitch. The SFECU sends signal to the SSCU to control the auto trim during flap extension. 

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6 minutes ago, Ak47e6 said:

In the real aircraft there is a large pitch change during flap extension. The aircraft has an auto trim function that happens automatically when the flaps are moved between 0 and 20 to help with the pitch. The SFECU sends signal to the SSCU to control the auto trim during flap extension. 

 

Ahhh, ok. Well that explains it. Is the auto-trim something I can set-up myself on the CRJ, or adjusting it manually is the only option? 

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It's an automatic logic function built into the SSCU ( spoiler stabilizer control unit). In the real aircraft there is a pronounced nose down pitch moment during flap extension so if that's what is happening then I would say it's simulated correctly. 

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14 minutes ago, Ak47e6 said:

It's an automatic logic function built into the SSCU ( spoiler stabilizer control unit). In the real aircraft there is a pronounced nose down pitch moment during flap extension so if that's what is happening then I would say it's simulated correctly. 

 

Sure, I also believe it's simulated correctly. I am just surprised at the enormous amount of pitch down it does after the 20 settings to full flaps. I was hoping to see lift  (which will 'lift' the a/c during low speeds) when going full flaps for landing. However, I find myself having to adjust the trim excessively. And, again, as you mention, this could very well be the norm. But, man.... hmmmm I really don't want to mess with the parameters to adjust lift and trim.. I might end-up breaking something else, or causing the a/c to behave erratically. It's a beautiful aircraft and a  lot of work has been placed on it by Hans and Aerosoft. 

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As stated in real life there is also an enormous amount of pitch down when going from 20 to 45 so that is correct I would not change it. Irl it does require a substantial amount of retrimming once the flaps reach your desired setting. Remember that in transport category aircraft you are trimming for speed so every time you change speed you have to re trim. Also during flap movements the center of lift moves farther back which causes a larger distance between the center of lift and the center of gravity thus a nose down pitching moment. 

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Just from my side as the flight dynamics designer.

First, the CRJ has this feature that when settings flaps to 1-8-20, automatically trim is applied to reduce the flaps effect.

Secondly for 30 and 45 that auto-trim is not installed as the flaps are very low and primarily increase drag and pitch down effect. By speed bleeding off, you need to re-trim for the new speed.

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On 20.8.2017 at 0:00 AM, Johnny767 said:

 

Sure, I also believe it's simulated correctly. I am just surprised at the enormous amount of pitch down it does after the 20 settings to full flaps. I was hoping to see lift  (which will 'lift' the a/c during low speeds) when going full flaps for landing. However, I find myself having to adjust the trim excessively.

 

Basically, what you see is lift. Actually a lot of it. Even so much of it, that you have to point the nose below the horizon in order to keep your vertical speed on final approach.

The CRJ is rather different here compared with most other airlines. The CRJ actually requires a nose down attitude on final approach, compared with most other airliners which require a few degrees nose up attitude.

You may not be used to it since the CRJ is pretty much a one-of-a-kind jetliner with this behaviour. But it's entirely normal on this plane.

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On 8/21/2017 at 3:48 AM, Emanuel Hagen said:

 

Basically, what you see is lift. Actually a lot of it. Even so much of it, that you have to point the nose below the horizon in order to keep your vertical speed on final approach.

The CRJ is rather different here compared with most other airlines. The CRJ actually requires a nose down attitude on final approach, compared with most other airliners which require a few degrees nose up attitude.

You may not be used to it since the CRJ is pretty much a one-of-a-kind jetliner with this behaviour. But it's entirely normal on this plane.

 

Emanuel, thank you for your response. And, yes you are correct, it is a different kind of aircraft and it takes learning its new systems and behavior. I am learning it more and more and find myself enjoying this aircraft more than I thought.  

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