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to 280 gallons, and find a weight of 1,876 pounds and a Moment/100 of 3,437. Our curiosity shows that the average Arm for this fuel is 183 inches. Entering 1,876 pounds for the Weight on line one is correct; using 3,437 for the Moment/100 is incorrect.
Why? Because that Moment is showing the increase in Moment that the first 280 gallons, added to an empty airplane, contributed to the airplane. Yet the 280 gallons we consumed during this flight are not those same gallons. To calculate the correct Moment to use, we must find how much the Moment decreased as we went from our starting fuel to our landing fuel. The Moment/100 of the initial 380 gallons is 4,700, and for the remaining 100 gallons is 1,196. The difference – the Moment/100 decrease that our 280 gallons of consumed fuel provided – is 3,504. This is the value that should go in the Mom/100 column on line 11. The average Arm for this fuel is 187 inches. Although the error caused by using a fuel arm that is four inches off is not huge, it definitely makes for a CG error that is noticeable.
Two thoughts about how to fight this tendency to use the wrong Moment figure on line 11 of Beech’s form: First, reread my discussion here and be certain you are using the difference between starting and ending fuel moments to enter on line 11. Second, avoid using this form!
A different and perhaps easier way to calculate the CG for your landing condition is to start from the Zero Fuel Weight condition that you have already calculated and add to it the Weight and the Moment of the remaining fuel on board at landing. The Moment figure can come straight out of the chart in Section six, since this fuel is the same as the chart shows: The fuel that remains sits at the same location as that much fuel does when added to an empty airplane.
“Hey, you out there in readership land! Yes, I am talking to you, Mr. Foreflight, and also to you, Mr. Fltplan. com! I presume you are doing this correctly and not providing slightly erroneous answers to my peeps, right? You are? Great! Thanks.” KA
About the Author: King Air expert Tom Clements has been flying and instructing in King Airs for over 43 years, and is the author of “The King Air Book.” He is a Gold Seal CFI and has over 23,000 total hours with more than 15,000 in King Airs. For information on ordering his book, go to www.flightreview.net. Tom is actively mentoring the instructors at King Air Academy in Phoenix.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at kblonigen@ cox.net.
JULY 2015
KING AIR MAGAZINE • 21