C*: Yaw

Mon 01 April 2019
aileron Vertical stabilizer (Photo credit: Wikipedia)

This post is about yaw control. This is also the post for which I did not find many references.

Remember the yaw is the axis controlled by the rudder. The rudder acts as any foil, providing a force dependant of its angle of attack. This angle of attack is function of side slip angle (noted β) and the rudder's deflection.

Basically, the rudder command an effort on the stabilizer, inducing a rotation around the yaw axis. Note that the stabilizer also induce a force on this axis. The stabilizer's force tend reduce sideway slip. This momentum grows with speed.

On the way

The aircraft velocity is high, there is little risks to stall. The goal is to avoid extra drag due to going sideways. When the pilot's rudder is at neutral position, the aircraft must go straight ahead and the pilot should command the sideslip angle. When performing turns, pilot's input to neutral must result coordinated turns (rudder not in neutral position). Yaw control is also used for stabilisation purpose (e.g. yaw damping).

At low altitude

When really close to the ground, roll cannot be used to control airplane's trajectory. The bank angle is limited due to both the ground clearance and the low speed (when near stall, having wings not leveled is not wise). Thus, the rudder is used to control direction.

Normal law

Normal law is used in flight in normal condition. The A320 and the A380 does not act the same way.

  • the A320 adds pilots' input and flight-by-wire (FBW) orders [2]. The FBW system add orders so that with neutral pilot input, it handles yaw damping and coordinates turns
  • on the A380, the pilot's input commands sideslip angle.

Ground law

On the A380, the pilot control the yaw rate [1]. I found no evidence for the A320, thus I assume the FBW system adds no input.

Direct law

[1]source: A380 Briefing For Pilots, march 2006
[2]source: AAIB Bulletin: 8/2008 incident report

Category: aviation Tagged: C star Flight dynamics yaw

C*: pitch

Sun 07 September 2014

The axes is the most documented one. Maybe because it is the less easy to understand. Of course other post will consider the two other axes.

The complication arise when thinking of what can be controlled:

  • the plane's stability (called "assiette" in french) and therefore the pitch rate.
  • the angle …

Category: aviation Tagged: C star

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C*: flight control

Tue 02 September 2014

[caption id="" align="alignright" width="350"]F-8C Crusader digital fly-by-wire testbed C* testbed (Photo credit: Wikipedia)[/caption]

I begun a serie of post dedicated to fly-by-wire explanation. I focus on C* command law as it is the most documented one.  All posts from this serie will be available under the C* tag on this blog …

Category: aviation Tagged: C star Fly-by-wire

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C*: introduction

Fri 04 October 2013

Ceci est le premier billet d'une série d'un nombre encore indeterminé. Je me suis posé la question: "Comment ça marche les commandes de vol électriques?" J'ai rapidement compris deux ou trois trucs, je vais essayer d'en faire une synthèse en indiquant des pointeurs utiles (principalement des rapports du BEA).

Je …

Category: aviation Tagged: C star

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