Subtracting object MOI from assembly to get other parts MOI?

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SUMMARY

The discussion centers on calculating the moment of inertia (MOI) of a specific section of an assembly, such as an airplane's tail section, using known values from the entire assembly and other sections. It is established that one cannot simply subtract the MOIs of known sections to derive the MOI of an unknown section. Instead, the correct approach involves applying the parallel axis theorem and considering the mass distribution of the entire assembly to accurately compute the MOI of the tail section.

PREREQUISITES
  • Understanding of Moment of Inertia (MOI) concepts
  • Familiarity with the Parallel Axis Theorem
  • Knowledge of mass distribution in rigid bodies
  • Basic principles of mechanics and dynamics
NEXT STEPS
  • Study the Parallel Axis Theorem in detail
  • Learn about calculating MOI for composite bodies
  • Explore applications of MOI in real-world engineering problems
  • Review examples of MOI calculations in aerospace engineering
USEFUL FOR

Students in mechanical engineering, aerospace engineers, and anyone involved in structural analysis or dynamics of complex assemblies will benefit from this discussion.

Jweck002
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Homework Statement


It's been ages since I have done Moments of Inertia of complex objects! :( Can anyone help??
Say you have an assembly like an airplane and you want to just get the moment of inertia(MOI) of the tail section and you are given the Mass of whole plane,mass of tail section, moment of inertia of front section, and moment of whole plane(moments about each axis for both). Can you just subtract the MOIs of known sections to get the MOI of unknown sections? If not, how would you go about getting the unknown sections MOI from that info.

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Last edited:
Oh. Sorry I posted this question in wrong area. I don’t have a specific problem but wanted to know for future problems on exams and real world applications.
 

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