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How to calculate CG for Engine Swap?

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dapug

Member
Joined
Jul 17, 2019
Messages
18
I'm evaluating what it would take to put a EP 912TSi engine in a plane designed for a 915iS. This means the proposed new engine is lighter, and I'd like to modify the engine mount (shift engine forward) to maintain the CG of the aircraft as specified by the manufacturer.

Original dry weight: 84.6kg/186lbs
New dry weight: 68.6kg/151.5lbs

Here is info from the datasheet of the plane I am evaluating:
(probably need to sign in to see)

Screen Shot 2019-10-24 at 9.51.00 AM.png

Questions:
  1. What other variables are needed in order to figure this out? (engine mounting point? etc)
  2. How far forward does the engine need to move to maintain CG? *
  3. How does one go about calculating it?
* I mentioned a 16kg/35lb lighter weight engine, but I realize there are other factors. For example, is there a difference in exhaust, piping, or cooler weight between the 912 and 915? Propeller difference? And if the engine moves forward, this means likely more mass/weight for the engine mount, and longer cowling to accommodate, etc. I can't get that exact right now, but would need to eventually. I first just need an idea of what I need to do in general, and whether this is feasible.
 
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