# Equations for determining MOI's?

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Hello all. Am looking for assistance in determining MOI characteristics for the .cfg file. What formulas or equations are used to help determine these numbers. The formulas in the SDK don't appear to be correct, especially when running the numbers on the stock aircraft, so I'm wondering if they're correct. I've done well in algebra in the past, so I'm certain that I'm using the equations correctly. Can anyone shed some new light on the subject for me?KevinBoise, Idaho

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Hi Ron, Thanks for your detailed answer. It's much appreciated.In plugging in some of the numbers tonight, I found that my 757 (Mike Stone's model) collapsed its landing gear upon loading into FS.Here are the numbers I came up with using the formulas above:Weight of the aircraft was determined by adding weight of, empty weight, 128730 + fuel weight, 77187 + payload weight (10,00 less than maximum) 39083 = 245,000 lbs. total weight. Maximum gross weight is 255,000 lbs.To obtain my numbers for MOI, I did the math as follows:For Roll; (245000/32.2^2)*(.246*124.833/2)^2=55708.746For Pitch; (245000/32.2^2)*(.382*155.25/2)^2=207770.695For Yaw; (245000/32.2^2)*(.456*140.0415/2)^2=240900.412This is what I came up with and obviously I'm doing something wrong here. Perhaps you can help me. Thanks again for your help...Kevin

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>Hi Ron, >>Thanks for your detailed answer. It's much appreciated. >>In plugging in some of the numbers tonight, I found that my >757 (Mike Stone's model) collapsed its landing gear upon >loading into FS. Hmm. Unless the MoI's make an AC unstable on the ground, the LG shouldn't collapse. >Here are the numbers I came up with using the formulas >above: >>Weight of the aircraft was determined by adding weight of, >empty weight, 128730 + fuel weight, 77187 + payload weight >(10,00 less than maximum) 39083 = 245,000 lbs. total weight. > Maximum gross weight is 255,000 lbs. >>To obtain my numbers for MOI, I did the math as follows: >>For Roll; (245000/32.2^2)*(.246*124.833/2)^2=55708.746 >For Pitch; (245000/32.2^2)*(.382*155.25/2)^2=207770.695 >For Yaw; (245000/32.2^2)*(.456*140.0415/2)^2=240900.412 >>This is what I came up with and obviously I'm doing >something wrong here. Perhaps you can help me. >Kevin I showed g = 32.2 ft/sec^2. (ft/sec^2) is the units for the conversion. Just use (245000/32.2) above. I brought up CFSCalc and for a 'Jet Airliner 2 eng wing' it shows '6,690,216' sl-ft^2 for Pitch MoI. When I multiply your Pitch value above by 32.2 to take out the extra division by 32.2 I get '6,690,194'. Virtually the same as CFSCalc gives. HOWEVER, use "128730", your empty AC weight, in the equations. The fuel and payload are added automatically in flight. Incidently, if the form of an AC stays constant, Weight increases with l^3. While MoI's incrase with l^5. Where 'l' is a length measurement, such as span. Double wing span, fuselage length and diameter and weight increases by 2^3 = 8X. While MoI's increase by 32X. Especially useful when one is modifying the total size of an AC by some small factor. At least as a check.Ron

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Thanks again Ron for your help. The corrections worked and have provided numbers which I feel help the realism in flight for the 757.Kevin

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