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Steve & Nancy Riffe
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Date:  4-20-2017
Number of Hours:  4.00
Manual Reference:  
Brief Description:  Measurements for cg

I remembered to bring plumb bobs etc to the hangar for the cg measurements today. I did forgot the charger for my camera, which died after the first 2 pics. I started with right side and hung 2 plumb bobs off the leading edge of the wing. I measured forward 70” and marked points on poster board I had taped to the floor. I measured between the plumb bobs and used the same reference to measure 2 points at the datum line, thus insuring that the datum line is parallel with the wing. I did this same thing for the left wing, then used a chalk line between the outer marks of the datum line. The string also hit the 2 inboard points exactly, so I’m confident that the 70” datum line is parallel to the wings. Instead of measuring back to the center of the axles, I dropped another bob across the center of the axle and measured back to the bob hanging off the wing. I used this measurement to compute the distance from the datum line to the axle. Next, I marked a center line between the gear on the bottom of the fuse and hung a bob there. I also hung a bob off of the tail wheel. I measured from the tail wheel bob thru the forward fuse bob to the datum line. I checked and re-checked all measurements at least 3 times and kept getting the same answer, so I believe I have good numbers for the cg computations. I used the sample form in the builder’s manual and filled it out with my data. I ran several scenarios of various fuel, passenger and baggage loading. At full gross weight, I can take 100 lbs of bags (probably run out of room, before running out of weight). The plane will also stay in cg with fuel burn—the fuel tank arm is very close to the cg, thus fuel usage affects the cg very little. Ok, satisfied with cg computations—moving on!
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Measuring distance between wing and axle

Measuring distance between wing and axle

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Datum line 70

Datum line 70" from wing

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W&B computations

W&B computations

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