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JC_YYZ

Falcon 50 Climb Speed + AOA

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I am really liking the updates that are happening with the Falcon 50. Each time I see an update in my inbox, I can't wait to download it and see what has been improved. Great work.

I have a question about the climb speed and I am sure that I am doing doing something wrong.

On take off, once I am gear up and stable, when I turn on AP, I typically dial in a VS of about 1500 FPM by doing the following:

Dial in Altitude (let's say FL120 for the sake of this example), press ALT SEL, then VS, then dial in +1500. The plane begins the climb. I usually bring the throttles back at this point to maybe 80% N1 and let the plane climb. However, the plane slowly begins to lose speed and the AOA slowly moves from the green, to yellow (activating the auto slats) and then red. I turn off AP, push the nose down, recover from the stall, back to 250kts and rinse and repeat. With the same result. For some reason, I cannot get the plane to climb without stalling.

I am wondering if I am missing something? I have checked trim, mach trim is on, flaps are clean, gear is up, but the plane just doesn't want to climb. Last night I managed to get to FL110 after almost 20 minutes at about 500 fpm with two stalls. Engines at TO/GA power.

One other weird behaviour last night is that I had FL110 selected on the AP altitude, the plane climbed to about 3,600 feet, ALT SEL changed to CAP, then ALT and the plane leveled off as if it was at FL110. As well, the AOA meter stayed just inside the green the entire time. I feel like the plane is dragging through mud when trying to climb and all the videos I see on YT have people happily climbing at 2000 FPM with no issue.

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Sounds like something is corrupted in your installation. Especially if the altitude suddenly captured thousands of feet below your preselected altitude.

In my installation, the aircraft has power to spare - in fact at higher power settings, it will easily climb at 4000 FPM+ at lower altitudes if not heavily loaded.

You didn’t mention what sim version you have, but in general, might be best to completely uninstall it using the Windows Control Panel. Then, re-boot your computer to insure that any existing Falcon files are purged from memory, then reinstall.

Also, loading a default aircraft before loading the Falcon might be advisable.

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15 minutes ago, JRBarrett said:

Sounds like something is corrupted in your installation. Especially if the altitude suddenly captured thousands of feet below your preselected altitude.

In my installation, the aircraft has power to spare - in fact at higher power settings, it will easily climb at 4000 FPM+ at lower altitudes if not heavily loaded.

You didn’t mention what sim version you have, but in general, might be best to completely uninstall it using the Windows Control Panel. Then, re-boot your computer to insure that any existing Falcon files are purged from memory, then reinstall.

Also, loading a default aircraft before loading the Falcon might be advisable.

I will give that a try. I am using P3D 4.4, but when installing the Falcon 50, I have repeatedly used the WCP Add/Remove feature but I haven't rebooted between installs. Also, I failed to mention I am using the F1 GTN750, so I am not sure if that has any effect (although last night out of CYYZ I was just using HDG mode and didn't actually have a flight plan in the system).

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JC,

That's perfectly normal.  

VS mode seeks to maintain the commanded rate of climb regardless of airspeed.  The ability to maintain that climb rests in three parts, lift, drag, and thrust. It is thrust in excess of drag that makes any airplane climb (or accelerate).  You can momentarily make an airplane climb by increasing lift, by increasing angle of attack.  That's what you saw when the AoA gauge moved from green, yellow, to red.  The AoA gauge provides a percentage of total lift capability of the airplane.  When the gauge reads 1.0, the wing is generating 100% of its total capable lift. Any further increase in AoA will stall the wing.

As AoA and lift increases, so does drag -- induced drag to be specific, which is a natural byproduct of lift. In some cases, induced drag generated by high AoA cannot be overcome by the thrust available. The airplane decelerates and loses lift, which is one part AoA and one part speed of the air over the wings. The only way to compensate for the loss of lift due to speed decrease is to increase AoA, which creates more drag further decelerating the speed, further reducing lift from the speed of the air over the wings, which requires further AoA increases until the critical AoA (AoA = 1.0 on the stall indicator) is reached.  Any further AoA increases the airplane stalls.  Any further speed decrease, the airplane loses altitude.  It's that simple. 

Trying to climb in VS mode only makes matters worse. The airplane's autopilot is just not trying to maintain altitude, it's trying to make the airplane climb at the commanded rate, which in your example is 1500 FPM.  If there is enough thrust, that's fine.  If not, then speed will decay.  AoA must increase to add additional lift, not only to maintain altitude but increase the altitude at a rate of 1500 FPM.  That just makes the whole process happen that much faster. 

Climbing at 80% N1 is likely the cause of your issue at low altitude. See what Flysimwhere provides for N1 charts and make sure you set climb N1, especially for an extended climb.  If memory is correct, the DA50 has TFM 731-3 engines.  I flew those engines with the Westwind.  You can use a climb ITT of 860C and not exceed a climb N1 speed, at least in the Westwind. That should be ballpark for the DA50 with these engines.  However, keep in mind as you climb in altitude, thrust decreases.  At the high flight levels, the whole process can happen again.  That's climbing in VS at high altitudes is frowned upon, even though common practice for pax comfort.  Wrong priorities in my view.

The FAA provides guidance to real pilots on this subject here:

https://www.faa.gov/other_visit/aviation_industry/airline_operators/training/

Presentation: Appendix 3-E, High Altitude Operations — All Jets (VLJs to Large Swept-Wing Turbofans) (PDF) To view presenter notes, mouse-over the text annotation in top left corner of the slide

The consequence of climbing in VS mode at high altitude can be seen in the Pinnacle Airlines Flight 3701 accident report.  Improper use of VS mode at high altitudes allowing the airspeed to decay was cited as a contributing factor:

Rich Boll

Wichita, KS

 

 

Edited by richjb2

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40 minutes ago, richjb2 said:

JC,

That's perfectly normal.  

VS mode seeks to maintain the commanded rate of climb regardless of airspeed.  The ability to maintain that climb rests in three parts, lift, drag, and thrust. It is thrust in excess of drag that makes any airplane climb (or accelerate).  You can momentarily make an airplane climb by increasing lift, by increasing angle of attack.  That's what you saw when the AoA gauge moved from green, yellow, to red.  The AoA gauge provides a percentage of total lift capability of the airplane.  When the gauge reads 1.0, the wing is generating 100% of its total capable lift. Any further increase in AoA will stall the wing.

As AoA and lift increases, so does drag -- induced drag to be specific, which is a natural byproduct of lift. In some cases, induced drag generated by high AoA cannot be overcome by the thrust available. The airplane decelerates and loses lift, which is one part AoA and one part speed of the air over the wings. The only way to compensate for the loss of lift due to speed decrease is to increase AoA, which creates more drag further decelerating the speed, further reducing lift from the speed of the air over the wings, which requires further AoA increases until the critical AoA (AoA = 1.0 on the stall indicator) is reached.  Any further AoA increases the airplane stalls.  Any further speed decrease, the airplane loses altitude.  It's that simple. 

Trying to climb in VS mode only makes matters worse. The airplane's autopilot is just not trying to maintain altitude, it's trying to make the airplane climb at the commanded rate, which in your example is 1500 FPM.  If there is enough thrust, that's fine.  If not, then speed will decay.  AoA must increase to add additional lift, not only to maintain altitude but increase the altitude at a rate of 1500 FPM.  That just makes the whole process happen that much faster. 

Climbing at 80% N1 is likely the cause of your issue at low altitude. See what Flysimwhere provides for N1 charts and make sure you set climb N1, especially for an extended climb.  If memory is correct, the DA50 has TFM 731-3 engines.  I flew those engines with the Westwind.  You can use a climb ITT of 860C and not exceed a climb N1 speed, at least in the Westwind. That should be ballpark for the DA50 with these engines.  However, keep in mind as you climb in altitude, thrust decreases.  At the high flight levels, the whole process can happen again.  That's climbing in VS at high altitudes is frowned upon, even though common practice for pax comfort.  Wrong priorities in my view.

The FAA provides guidance to real pilots on this subject here:

https://www.faa.gov/other_visit/aviation_industry/airline_operators/training/

Presentation: Appendix 3-E, High Altitude Operations — All Jets (VLJs to Large Swept-Wing Turbofans) (PDF) To view presenter notes, mouse-over the text annotation in top left corner of the slide

The consequence of climbing in VS mode at high altitude can be seen in the Pinnacle Airlines Flight 3701 accident report.  Improper use of VS mode at high altitudes allowing the airspeed to decay was cited as a contributing factor:

Rich Boll

Wichita, KS

 

 

This is an amazing explanation. I always thought (assumed) that it was SOP to dial in a VS and let the plane do its thing - instead of understanding correlation between the plane trying to maintain a climb performance request (from me, the pilot) and the decay of speed to maintain the desired climb.

I so appreciate the time you took to type this out and explain it. Many thanks.

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1 hour ago, JRBarrett said:

Sounds like something is corrupted in your installation. Especially if the altitude suddenly captured thousands of feet below your preselected altitude.

In my installation, the aircraft has power to spare - in fact at higher power settings, it will easily climb at 4000 FPM+ at lower altitudes if not heavily loaded.

You didn’t mention what sim version you have, but in general, might be best to completely uninstall it using the Windows Control Panel. Then, re-boot your computer to insure that any existing Falcon files are purged from memory, then reinstall.

Also, loading a default aircraft before loading the Falcon might be advisable.

I'm gonna have to AGREE with this assessment.  This FA50 is a "rocket " and can perform many climb outs (unless heavy loaded) at + 3000 fpm. Every flight I've flown has required pulling back on the throttles to avoid speeding under 10,000 ft. I'm not sure what's causing your stall issues JC but why not try "hand flying" up to at least 10,000 then once you're stable at 250 kts and on your desired heading, flip on the AP ( I use HDG and VS) ... this has worked very well for me with no problems.

 

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46 minutes ago, JC_YYZ said:

This is an amazing explanation. I always thought (assumed) that it was SOP to dial in a VS and let the plane do its thing - instead of understanding correlation between the plane trying to maintain a climb performance request (from me, the pilot) and the decay of speed to maintain the desired climb.

I so appreciate the time you took to type this out and explain it. Many thanks.

In a climb, it is far safer to use IAS mode. Accelerate to 250 knots initially and click on IAS on the autopilot. Now, the aircraft will use pitch to control airspeed. IAS will not let your aircraft pitch up into a stall, but V/S definitely can if you are not careful. Your rate of climb will be controlled by the amount of power in IAS mode.

Above 10,000 feet you can disengage the autopilot and accelerate to a higher speed, (or use CWS mode), then re-engage IAS.

V/S Mode is primarily used in descent.

However, in your initial post, the symptoms to seem to point to a corrupt installation - especially when your altitude capture engaged unexpectedly at too low an altitude.

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5 minutes ago, JRBarrett said:

In a climb, it is far safer to use IAS mode. Accelerate to 250 knots initially and click on IAS on the autopilot. Now, the aircraft will use pitch to control airspeed. IAS will not let your aircraft pitch up into a stall, but V/S definitely can if you are not careful. Your rate of climb will be controlled by the amount of power in IAS mode.

Above 10,000 feet you can disengage the autopilot and accelerate to a higher speed, (or use CWS mode), then re-engage IAS.

V/S Mode is primarily used in descent.

However, in your initial post, the symptoms to seem to point to a corrupt installation - especially when your altitude capture engaged unexpectedly at too low an altitude.

The altitude capture was definitely a mystery. I took screen shots to make sure I had them in case everyone thought I was going crazy. While I am an amateur sim pilot at best, I know enough to know that the behaviour was odd and wasn't something I had overlooked.

I will uninstall and restart when I get home tonight and then re-install the 1.7b installation. I will also select a default plane before loading into the Falcon.

I am a fan of regional and biz jets, so I am excited to tour around with this bird.

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