Wheels Up

[PAXboy]

When the undercarriage is commanded up, are the wheels automatically braked prior to retraction?

One imagines that damage could occur in some wheel bays, although I know that the 737 does not have bay doors.

Thanks.

[tomcs]

I can only speak for small prop planes...but usually the pilot taps the brakes and stops the wheels spinning before retracting them into the bays or whereever they go....I'm sure someone will tell u for the big iron..

Hope that helps

Tom

[tinyrice]

Yes. The brakes are automatically aplpied on all modern jet airliners when the gear is selected up.

[Willit Run]

Most large planes have a auto brakeing system when the gear is retracted(main gear) and the nose gear usually have a snubber that the nose wheels rub on when they get in the well to slow them down. If i remember correctly, and if I don't I'm sure someone will correct me, the main gear gets around 500 to 1000 PSI to the brake system when the gear is retracted to stop rotation.

[FlyingForFun]

I seem to remember reading somewhere - probably here, in fact! - that this is as much to do with the gyroscopic precession of the wheel as they are moved to the Up position as it is to do with preventing damage to the wheel bay. Someone confirm this? Or did I just dream it?

FFF
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[knobbygb]

Gyroscopic procession sounds like it could be a problem on the main gear - what sort of forces would be produced, on, say, a 777 with six heavy wheels, all trying to twist the gear leg (to the left?) on retraction if they were still spinning at approx take-off speed? Not sure of the mass or radius of the wheels or radius of the arc of gear movement so can't work this out but it must be 'quite big'. Any mathematicians fancy working it out?

Also, peter B, I think you're right about the nose gear being 'stubbed' in the wheel bay. Recently sat up front on a 747-400 and was almost right above the nose gear on retraction. You could clearly hear the wheels spinning down for 3 or 4 seconds after they entered the wheel bay. Made me wonder just how close they were to the bottom of my seat! Didn't fancy a 'rubber enema' if a tyre just happened to burst. Is the floor strenghened here, I wonder?

[PAXboy]

Many thanks for the info that confirmed my thoughts. As to the 744 nose wheels potentially busting their house, one would hope that there would be a nice fat freight container between then and you in Row 2 or 3!