IndianGuy
Posts: 3126
Joined: Fri Jul 07, 2000 3:14 pm

Do Landing Gears Have Any Anti-Lock System

Sun Jan 13, 2002 2:46 pm

My new car claims to have an *Anti-Lock system* even though it barely touches 140 kph on an expressway.

Just wondering, do Large jets like the 737/747 have any such system. I think they will definitely require it.
 
jsuen
Posts: 204
Joined: Tue Aug 14, 2001 2:36 pm

RE: Do Landing Gears Have Any Anti-Lock System

Sun Jan 13, 2002 2:59 pm

Just about all jets, even bizjets, have an antiskid system. They first appeared on the B-47 in 1946 and in commercial planes, the 707 in 1956. Failure of antiskid often results in blown tires. I believe the automotive version was derived from aircraft.

Theres an article here http://www.hydroaire.com/downloads/AntiskidTutorial.pdf
 
Contact_tower
Posts: 534
Joined: Mon Sep 17, 2001 4:05 am

RE: Do Landing Gears Have Any Anti-Lock System

Sun Jan 13, 2002 7:57 pm

The antskid skystem on airplanes was the inspiration for ABS brakes on cars. All jets today have this, they allso have a "autobrake" system to utilise the friction available better.  Smile
 
TechRep
Posts: 1877
Joined: Sun Jan 13, 2002 6:53 am

RE: Do Landing Gears Have Any Anti-Lock System

Sun Jan 13, 2002 11:49 pm

Yes you are correct Large Jets do have "ANTI-SKID" control. I can attempt to briefly explain it if you would like. Hydraulic systems (A,B and stand by) are employed on the B737. The braking for the B737 in normal mode is from "B" system and when "B" system is not available "A" system is used and is called alternate braking.

Pedal input is recieved from the cockpit transmitted by cable or electrically (dependind on aircraft) to a BMU (Brake Metering Unit), then to a shuttle valve, distrubuted to the anti-skid valves. The B737 100/300 has one normal anti-skid valve for each brake (4ea.) and one alternate for each gear leg (2ea.). Wheel speed is sensed through a wheel speed transducer installed in each axle (4ea). These are basically little DC motors that supply an output voltage to a Anti-skid control unit (ASCU). The anti-skid system has an on/off switch in the cockpit and typically a monitoring display for defective systems within the anti-skid system. Basically the anti-skid system (ASCU) over-rides the pilots metered pressure (brake pedals), by monitoring the wheel speed transducers for wheel lock/speed sensing to stop the aircraft with most efficency.

I hope this was helpful any more questions send me an e-mail.

TechRep
 
od-bwh
Posts: 312
Joined: Sun Jan 13, 2002 6:25 pm

RE: Do Landing Gears Have Any Anti-Lock System

Mon Jan 14, 2002 12:15 am

All of the above is right... ABS first appeard on aircraft, before being used on vehicles. LH posted an article in the late 90's in its onboard magazine. I wish you can find this article...
A300, A319, A320, A321, A332, A333, A343, A346, A388, B734, B738, B744, B772, B773, B788, F70, MD11, CRJ7, CRJ2, Q400
 
FDXmech
Posts: 3219
Joined: Sun Mar 19, 2000 9:48 pm

RE: Do Landing Gears Have Any Anti-Lock System

Mon Jan 14, 2002 12:33 am

Be careful interchanging the terms ABS with antiskid while talking about commercial jets.

While ABS on an automobile means "anti-lock brake system", on airplanes it is referring to the "auto brake system".

The auto brake system (ABS) on a jet automatically applies the brakes during landing (or rejected take-off), as opposed to the antiskid system which prevents the brakes from locking up.
You're only as good as your last departure.
 
Metwrench
Posts: 715
Joined: Fri Aug 17, 2001 11:25 am

RE: Do Landing Gears Have Any Anti-Lock System

Mon Jan 14, 2002 2:57 am

Good point FDX, I've been guilty of using incorrect acronyms myself.

This might be a good time to bring up the subject of "wheel speed spin up" (WASSUP).
 
ThirtyEcho
Posts: 1409
Joined: Tue Jan 01, 2002 1:21 am

RE: Do Landing Gears Have Any Anti-Lock System

Mon Jan 14, 2002 4:41 am

A friend owned an old Aston-Martin and it was one of the first production cars with anti-skid brakes. It seems that the manufacturer simply scaled down the DC-9 system and used that. My friend had to use brake fluid with a Mil-spec that required him to buy it from an airdcraft supply house.

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