What happens to FA-18C FM when 243 knots are reached?

[joker62]

In the landing configuration (gear and flaps extended) exactly at 243 knots something changes in the FM. To better highlight this strange behavior, note controls indicator display and HUD. Reached 243 knots, WITHOUT applying any input to the flight controls there is a strange reaction of the plane: the nose rises and there is a little yaw movement.

 

Track. Clean config, left turn 12:00.52-54 ok, right turn 12.01:32-33 ok.

Landing config (gear dw + full flaps) left turn 12:02:34-36 (upper pitch input + left-right rudder input), right turn 12:03:03-05 and 12:03:29-32 (upper pitch input + left-right rudder input)

 

Can you clarify? Thanks.

FA-18C strange FM behavior.trk

[MadCat1381]

At about 240kts the FCS switches from landing to flight mode, if the flap switch is not already in Auto (at lower speed this is commanded by the flap switch). At that point the FCS tries to achieve a 1g flight condition when no control inputs are made. I think that that is, what cause the reaction of the plane.

[joker62]

Thanks for the reply. I'll read the manual deeper, I didn't remember this.

[Stubbies2003]

Another thing to verify is if you also see the flaps light turn yellow instead of the green for half or full. If you are seeing this at the same time it is the plane letting you know you are too fast for your flaps setting and the plane is ignoring the flaps position and is in auto.

[joker62]

Thank you very much for reply. I'll check about this.