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MEM425F11_HW6.soln - Problem 3 With the tail in place the...

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MEM 425: Aircraft Performance & Design Home work #6 - solution (due 11/03/11) Problem 1 : The zero moment coefficient, when the lift is zero for a wing body model is -0.003 (longitudinally unbalanced) Location of ac w : This could be obtained from . Note; The locations are given as fractions of chord length. This yields Converting the given data to non-dimensional coefficients as above, results in . (negative static margin statically unstable aircraft) The ac location then, is Problem 2: where is the new location of the cg in fractions of chord length, ie, . Hence, The moment about the cg is 383.26 Nm . Note: We do not need the location of the aero-center to solve this problem.
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Unformatted text preview: Problem 3: With the tail in place, the appropriate equation to use would be . Use to obtain a w = 0.09 deg-1 and = -0.2. (You compute the moment.) The slope of the C m-α curve is = -0.039 deg-1 . The aircraft is stable. For static balancing, we need to be positive. With . Hence, this a/c is statically unbalanced. See if the tail can be fixed to make this a/c balanced. We need to pick i t so that is positive, resulting in Fot i t close to this value, the trim α will be close to zero – you may not like it....
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