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Old 06-12-2019, 08:52 AM   #1
NeMoGas
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Default SAS engage on/off

So I have noticed when I turn all SAS channels off there seems to be no difference in flight characteristics vs all SAS channels on. However I did notice that if I put the autopilot engage switch below the SAS channel switches on, it seems to change the characteristics.

This is with all the autopilot settings turned to off. It seems to damp the roll and also the pitch. I looked in the manual and the NATOPS, but it mentions nothing about this switch needing to be on for SAS to function.

So the question is, is this a bug or am I missing something here?

Last edited by NeMoGas; 06-12-2019 at 09:16 AM.
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Old 06-12-2019, 10:18 AM   #2
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I think I may have found my issue. It seems as if the F14 automatically trims itself out when the autopilot engage switch is turned on. Even with alt and heading hold off on the autopilot control panel.
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Old 06-12-2019, 12:25 PM   #3
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When the autopilot engage switch is on the aircraft is in a sort of 'stick steering' mode. It's very useful. Not sure what the limits are though.

When you press the HOTAS autopilot button the autopilot reference light to the left of the ADI\TV display goes out and the aircraft follows the mode you set on the panel.
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Old 06-12-2019, 01:00 PM   #4
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with the Autopilot engages switch on, the jet goes into a kind of attitude hold mode. The limits are something like 60 deg nose up / nose down and same the same for angle of bank (could be wrong, as I am not looking at the documentation right now).
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Old 06-12-2019, 01:20 PM   #5
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I discovered this as well from NATOPS. Just using engage switch puts the autopilot in an attitude hold state. Puzzling is it functions still after pilot stick input in contrary when a HDG or ALT mode is selected, the AP will disengage those modes and a pinky switch press is needed to reengage.

As far as the SAS goes, I’ve noticed there is a difference when I fly it. The controls are super sensitive almost where I find it difficult to control, especially the roll SAS. Also, if that’s the case then why would you disengage it for the fence-in? I can understand more control authority, but if you can’t control it very well then what’s the point?


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Old 06-12-2019, 01:47 PM   #6
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Quote:
Originally Posted by Eagle7907 View Post
Also, if that’s the case then why would you disengage it for the fence-in? I can understand more control authority, but if you can’t control it very well then what’s the point?

I heard that it becomes important at the edge of the flight envelope, e.g. very high AoA. In this regime, it can lead to unintended behaviour...
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Old 06-12-2019, 02:12 PM   #7
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Default SAS engage on/off

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Originally Posted by Moafuleum View Post
I heard that it becomes important at the edge of the flight envelope, e.g. very high AoA. In this regime, it can lead to unintended behaviour...


Hmmm... that seems backwards to me. Even NATOPS says “all SAS switches should remain on in flight”.

Even under Flight Characteristics chapter for Roll SAS says....

“High AOA handling qualities are significantly improved by keeping ROLL SAS ON.”

Interestingly enough....

“Pitch SAS increases damping of the longitudinal, short- period dynamic response, but the aircraft can be operated safely throughout the flight envelope without it.”

Makes me wonder if turning the pitch SAS off is what was really intended and not roll SAS?

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Last edited by Eagle7907; 06-12-2019 at 02:51 PM.
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Old 06-12-2019, 03:16 PM   #8
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Not all NATOPS are equal, and for aircraft with multiple variants in service it should tell you which airframes are applicable to that volume. Are you perhaps reading the NATOPS for B model Tomcats with the Digital Flight Control System (DFCS) update?
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Old 06-12-2019, 03:24 PM   #9
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Quote:
Originally Posted by Eagle7907 View Post
Hmmm... that seems backwards to me. Even NATOPS says “all SAS switches should remain on in flight”.

Even under Flight Characteristics chapter for Roll SAS says....

“High AOA handling qualities are significantly improved by keeping ROLL SAS ON.”

Interestingly enough....

“Pitch SAS increases damping of the longitudinal, short- period dynamic response, but the aircraft can be operated safely throughout the flight envelope without it.”

Makes me wonder if turning the pitch SAS off is what was really intended and not roll SAS?

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Your NATOPS is for a DFCS equipped jet. It was standard procedure to turn off roll SAS for high AOA flight since the SAS does not function properly in the AOA range where roll reversal occurs.

This is pretty standard for SAS equipped fighters like the F-4 phantom as well. Since most swept wing jets experience high AOA roll reversal the SAS functions become counterproductive at high AOA.

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Old 06-12-2019, 07:52 PM   #10
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Thanks for the info guys.
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