- Oct 18, 2003
- Saline Michigan
I will point out the importance of optimizing systems vs optimizing components. If it doesn't make a better airplane, you have made a worse airplane with the efforts.That's why I'm interested in the planetary; I'm pretty sure it's lighter than a stiff system, and it should be significantly cheaper, with mostly off the shelf parts.
While the planetary gearset may look lighter than the stiff system gears, it requires some other hardware to work. The soft element is not trivial, requiring structure and significant spring mass. If it has elastomeric springs, they can be bulky, particularly if they are to see low enough loading for survival and to stay cool enough for long life. Then there is the issue that a two mass isolator has poor isolation with one mass much larger than the other. The engine has much smaller inertia than the prop, and the isolation performance (f/fn ratio) improves with added inertia at the engine side. Yeah, you could further reduce spring rate but your spring mass (and associated hardware on both prop side and engine side) will go up with the stored energy which goes up rapidly with reduced rates. Ross at SDS has talked about the benefits of added flywheel inertia on his bird. Optimal weight should be pursued in the design space because WEIGHT IS THE ENEMY.