Path: utzoo!attcan!uunet!ncrlnk!ncrcae!hubcap!gatech!ncar!dinl!holroyd From: holroyd@dinl.uucp (kevin w. holroyd) Newsgroups: sci.space.shuttle Subject: Re: reasons for fuel dumping [was: Re: shuttle landing sites] Message-ID: <787@dinl.mmc.UUCP> Date: 15 Nov 88 16:52:39 GMT References: <1185@client2.dciem.dnd.ca> <786@dinl.mmc.UUCP> <1914@eos.UUCP> Reply-To: holroyd@dinl.UUCP (kevin w. holroyd) Organization: Martin Marietta I&CS, Denver CO. Lines: 43 In article <1914@eos.UUCP> steve@eos.UUCP (Steve Philipson) writes: >A jetliner carries a large percentage of its maximum weight in fuel. The >higher its weight, the higher its stall speed and landing speed. Dumping >most of its fuel would allow a jet to decrease its landing speed by about >20 to 30 knots (very approximate figure here). > > Reducing aircraft weight by dumping fuel has a few other important >effects. Reduced weight results in an immediate increase in climb performance. >This would be considered critical if there is terrain to climb over. Stall >speed is reduced, so if there are configuration problems (stuck flaps, slats, >etc.) a greater speed margin is available over stall speed. Lighter >weights also reduce the wheel braking power required to stop the aircraft. > > In most cases, the operating procedures are not set up to minimize >post-crash fires, but to eliminate crashes. Lower weights reduce the >demands placed on the flight crew and aircraft components, making a >successful emergecny landing (with no additional damage or fatalities) >much more likely. >-- > > Steve > (the certified flying fanatic) > steve@aurora.arc.nasa.gov Just to back up Steve, I checked with my buddies that fly the BIG IRON, and they confirmed that the reason they dump fuel is to reduce the approach speed. In light planes, part of the forced landing checklist includes shutting down fuel, electrical, and engine systems prior to touchdown. In the airliners, it turns out that they don't shut off the engines until after touchdown. At that point if the airplane is going to come apart, it is probably already happening. The major reason for fire is the fuel air explosion caused by the fuel dispersing at high velocity (due to the crash speed), being touched off by the engine ignition systems. At any rate, they dump fuel to reduce touchdown speed. Kevin W. Holroyd CFI Aspen Flying Club Denver CO.