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CapnOz

Ballast Fuel Explaination

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I would really like to fully understand the purpose, usage, concept , and logic behind the use of Ballast Fuel.... that would go above and beyond what is explained in the manuals.Perhaps you could eloborate on how and why a pilot would want or need to use it as it pertains to adding it in the FMC during preflight planning.Thank you.Capn' Oz

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Peter, getting the full concept on ballastfuel in just a forum message is impossible. I did a RW md-11 weight$balance training and the subject easily takes half a day. In general one could say the MD-11 is not always easy to balance or distribute the load in such a way that the the CG stays in the allowable range at all stages of the flight. Various factors contribute, one being the tailengine which is a lot of weight added to the tail. This has it its greatest effect when the aircraft is empty and explains why e.g. freighter cannot fly empty. In my RW job we were even prohibited from parking an freighter empty on the ground without putting some weight in the front. There are many pictures of tailtipped md-11's on the net where during (un)loading the loadmaster did not follow the strict procedures on the MD-11. However you will notice that there is lot more aircraft in front of the wing compared to aft of the wing. Somewhere on the wing there is the balancing point where the centre of the downward forces (Centre of gravity) will need to be aligned with the centre of the upward forces ( centre of lift). Having much more weight (be it cargo or passengers) in front of the wing will make the aircraft (very) noseheavy. The disbalance in length between the loading area in front and aft of the wing is such that it will even cancel out the weight of the tailengine. Large amounts of fuel in centre tank will also make the aircraft also quite noseheavy. Combining the extra payloadweight in front of the wing and/or the centretank fuel may cause you having to load ballast fuel the tailtank to balance the aircraft. Especially on freighters this may happen. This ballast fuel will bring the CG aft. Ballast fuel could also be required in the centretank on empty freighters to bring the COG forward to compensate for the weight of the tailengine.Paxaircraft are not so much affected as they have much more equipment weight (seats/galleys etc) in front of the wing compared to aft and can therefore fly empty, unlike the freighters. When loaded the weight of pax doesn't add up that much compared to freight. An freighter takes max around 90 tons of cargo whilst 250 pax would weigh 25 tons affecting the COG far less. Provided the ratio between the weight of the bags in the aft belly and the cargo in the forward belly is not too much off a pax aircraft is far less likely to have weight&balance problems unless you have large quantities of fuel in the centretank.Hope this helps/ b rdgs - Dick

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How would you setup the ballast fuel in an empty passenger aircraft for a short empty positioning flight?For example a flight of lets say around 10,000kg trip fuel, I would want to load around 20,000kg fuel however this leads to a ZFW CG of 32.9 and a TOW CG of 37.1 with normal fuel loading which is obviously well beyond the aft limit.In fact the load manager suggests that in this empty configuration 59,500kg fuel is the minimum to load to keep the CG in limit, but surely I can use the ballast fuel function to keep the CG in limit with less fuel than this (perhaps using centre tank ballast), rather than take 80,000kg fuel for a 10,000kg trip?If so how would I do it?ThanksAndy

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