JRN,

The engine, gear box and prop are off course balanced. But it's the nose structure that vibrates. Even the smallest vibrations (read: frequencies) can cause the destruction of a structure. Everything (buildings,bridges, engine compartments,...) have a certain frequency (at which it start to shake).
I saw once in a movie wind blowing across a big bridge at a certain speed. The frequency was the same as the own frequency (translated from dutch...). After a few minutes the bridge began jumping up and down and collapsed.

How about the Fieseler,


1. Adjusting the structure: making it stiffer increases the own frequency. It's necessary to have this above the highest achievable rpm. But it makes the plane heavier then it already is.

2. Changing certain rpm's:
2.1. Changing prop
2.2. Changing number of cells
2.3. Changing gear ratio

Or a combination.
As soon as i can i will finish my Fieseler. (after my new project)

And its true that the Fieseler is heavy. It was not intended to be used with an electric engine. But if i don't try it, i maybe regret it.

Bye,
Vincent