5 hours ago, Von Target said:

This last video also shows something that is missing in FSX and present in XP's 737 - secondary stalls ...

Hmmm? I tried the default B737 (both XP and FSX), and if pulling too much after the first stall, the stick shaker activates indicating the secondary stall, just like in the video.

Yes, of course a secondary stall is exactly the same as a "primary" stall - it is just called that way because it usually happens after the pilot recovers from the initial stall but then "pulls too much" to get the nose back up when airspeed is too slow - therefore going over the critical AOA again. X-Plane models the secondary stall just fine - exactly like the first (or primary one).

The creator of the airplane can determine (with airfoil maker) what the lift over AOA curve of the wing profile looks like. You can make it loose lift very abruptly (this would cause a strong wing-drop in even the slightest assymetrical flow condition), or more gradual.

Also be aware that the 737 has built-in aerodynamic features that assure the inner wing section stalling first, so that the nose will drop, and additional features that assure airflow staying attached over the ailerons. So you WILL have lateral control in a stalled 737 (at least a few good degrees over the critical AOA).

Jan

9 hours ago, Murmur said:

Hmmm? I tried the default B737 (both XP and FSX), and if pulling too much after the first stall, the stick shaker activates indicating the secondary stall, just like in the video.

Hmmm, maybe it's my memmory fading away.... It's been such a long time since I used that....

Anyway, I mean the easy entry into secondary stall, as in the video....

 

You are right, Von Target, it is indeed very easy to get a secondary stall. The first one usually happens in a one G (or close to) situation, when the pilot(s) do not pay attention to the airspeed. When the critical AOA is reached, the plane will stall and usually (this is a certification criterium) drop the nose. With aircraft that have a stall warning, this "nose drop" is usually done by the pilot in the recovery maneuver (before actually reaching stall AOA). Nowadays they teach "reduce AOA right away, altitude loss is secondary".

But eventually during the recovery maneuver you need to adjust the flight path of the now (rapidly?) descending aircraft, and that requires a lot of lift => higher AOA than you had initially - therefore it is easy to enter stall conditions again on the "pull out".

Example: A normally loaded 737 in clean config will probably stall at around 160 knots in level flight (1 G). If you want to pull out of the subsequent dive with 1.4G, you need at least 190kts to avoid stalling.

Cheers, Jan

Something that seems to be missing in most aircrafts (both FSX and XP) are dutch roll tendencies, making the Yaw Damper close to useless even in those aircrafts that have it.

With regard to FSX, dutch roll can be modeled modifying the relevant aerodynamic coefficients for airfiles (example: https://www.youtube.com/watch?v=GIBZ-x8r2mo ).

With regard to XP, some aircrafts experience a bit of dutch roll in the right conditions, but it is probably less than it should be due to the excessive directional stability (the same reason that likely contributes to poor ground handling in crosswind). So the upcoming flight model revisions of fuselage side forces should have an effect on that too.

 

Edited September 20, 20187 yr by Murmur

On 9/19/2018 at 5:52 AM, BIGSKY said:

[VIdeo]

That was a bloody great lecture!