Originally Posted by
olandese_volante
Are the wheel brakes applied before or during gear up, or are the wheels just allowed to spin down?
Being in intimate company with four or six rapidly revolving wheels would no doubt further increase the risk of a fatal outcome.
http://www.pprune.org/tech-log/414827-b747-400-heavy-vibration-after-take-off.html#post5697623
On the 744 when the gear is selected up the gear doors open. When the gear doors are open a hydraulic sequence valve positioned by the right hand doors ports hydraulics to an actuator (de-spin actuator) which actuates the alternate brake metering valve in the r/h wheel well which is meant to stop the wheels spinning before the gear is swung into the wheel bay. The braking pressure on retraction is sufficient to stop the wheels turning within a revolution.