Sensitivity of aircraft stability with respect to the CG location I am working on the design of an aircraft (2 m long, wingspan = 3 m). The platform is longitudinally stable but it is very sensitive to the variation in CG location. For example,
1) CG_location = 100 mm from wing L.E, the static margin is about 15% of MAC.
2) CG_location = 105 mm from wing L.E, the static margin is about 8% of MAC.
3) CG_location = 110 mm from wing L.E, the static margin is about -1% of MAC. (Unstable: Cm vs Alpha curve slope becomes positive)

So, effectively while manufacturing the aircraft or while dropping the payload the CG of my aircraft should not vary more than 1 cm, otherwise it would become completely unstable. Taking into any manufacturing errors, the platform CG might not be exactly as expected and hence having such a small margin creates issues. 

How should I deal with this issue? Can I have any suggestions on how do decrease the sensitivity of the longitudinal stability to the CG location? Thanks in advance.
It sounds like it has a horizontal tail, so you basically need to increase the tail volume which will allow you to move forward CG limit forward, allowing you to move the median CG forward and expanding the overall range. So just make the horizontal tail a bit bigger.