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Hello Hans,

 

sorry for another thread, I just want to make sure that this is working as intended:

 

I was flying inbound to LOWS in FL160 and I was almost redlining the speedtape at about 320kts IAS. Upon reaching FL160 the autopilot commanded full trim deflection down but even then the aircraft was unable to maintain FL160 - it was climbing slightly at about 200-300fpm since full down deflection of the trim was not enough to maintain the flightlevel. Is this working as intended? After slowing down to about 310kts IAS full deflection was not needed anymore and the autopilot was able to maintain FL160.

 

liebe Grüße,

Alex

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That's probably a bit too fast. I believe even the real aircraft might run out of nose down trim authority at 320 knots at 16,000 feet. I'd recommend no faster than 300-305 knots IAS.

 

Jim Barrett

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Yes you control speed manually and you have to take in consideration tail winds and head winds. Operate the throttles manually it's a challenge but fun

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Well, I am pretty much familiar flying aircraft with manual throttle control - A2As Connie and PMDGs DC6 for example. Fact is, the aircraft was still within the envelope (below red tape) and the trim authority was not enough to maintain the flightlevel. I imagine that the real CRJ is not build this way ;)

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Shouldn't be a problem to maintain 16,000 and 320kts at all. I was at 10,000 in the real thing the other day, 310kts hand flying with about 1.8 trim setting.

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46 minutes ago, Frank Docter said:

Ofcourse this is not normal behaviour. Does this happen on every flight you make?

 

I imagine this will be the case. I will try again today or tomorrow.

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Yes, it seems to be happening every time; I just tried again.

 

https://youtu.be/xYXMh5cYW10

 

As you can see in the linked video, after passing 320kts IAS the trim approaches 0.0 and is unable to maintain the Flightlevel. Frankie mentioned something like 1.8 at 310kts, although I have to admit that the aircraft was almost empty. No PAX/Cargo and about 2.000 kg of fuel.

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That could be the issue... the light load might put you outside of the mass & balance envelope. Try adding a few hundred kilograms of cargo to the forward cargo compartment. If I remember correctly we had to do this to stay in limits when I did base training with just two pilots and a safety pilot in the first row. So that might be causing issues.

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1 hour ago, McChester said:

Frankie mentioned something like 1.8 at 310kts, although I have to admit that the aircraft was almost empty. No PAX/Cargo and about 2.000 kg of fuel

 

Can you try this empty with 17,500 pounds of fuel and no pax and no cargo.. send me the video? That was my fuel and load at takeoff

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With this load the CoG is at its very rear limit and can be flown but not maximum speed. I have not tested these extreme situation as the aircraft with a regular load /speed is indicating already low trim values. For example with a CoG of 28% (max is 33%) and 300 kts the trim is down to 1.6 on a real flight picture I have. So I clearly see a chance that with a CoG of 32% (empty aircraft and low fuel)  and 320 kts speed the actual aircraft would be out of trim capacity. I also remember that on ferry flights a minimum cargo weight in the front cargo hold is required. Maybe I find that somewhere again....

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FYI: Alexander (metzgergva) designed the flight dynamics of the CRJ. I will bother Mathijs to give him a developer tag so he is more "detectable" :D

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Just got home and tried it out... 320kts at 10,000ft empty cargo and pax.. 14.5 for fuel on board and trim was 1.7... Spot on! Good work guys

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Real Hawker 800 aircraft can run into this situation if the aircraft is lightly loaded, and the majority of the fuel has been burned off, such as would be the case at the end of a long trip. What will happen is that the aircraft will run out of nose-down trim at some point during the descent - typically below 18,000 feet. It's not necessarily an unsafe situation, but it will cause the autopilot to disconnect. The "cure" is to reduce airspeed, which will bring enough trim authority back to reconnect the autopilot.

 

Jim Barrett

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