Hi Matt

I would have guessed it was empirical. I thought maybe someone was actually engineering a model. That would be something new to all of us.

David and Kevin

Turbines excluded, I do not know of one kit, ARF or set of plans that is truly engineered. (There may be some, but, I am unaware of them.) Engineered to determine what the material qualities are, the bending moments, etc. Most are designed by guys empirically, with a little help from some general guidelines as to the proportions of surfaces, nose moment, tail moment, wing loading,etc.
Recommended engines on planes are more of a suggestion so that the buyer has some clue of what he is getting into.

It has been my experience that if you actually talk to someone who designed a plane, particularly about power plants, that they really have no idea what the limits of the design are. Most can tell stories of their kits being equipped with engines twice the recommended size. Is it safe? Who knows? Without a real analysis the only way to determine the limit is empirically.

Empirically is a nice way of saying 'determined through experience', heuristically, if you will.

Case in point. A .40 size plane. Is that a TT 40, an OS 40 LA, or a Jett or Nelson? Basically, giving a displacement is worthless in the determination of power, other than a guide to the wing loading.

How many other non-turbine planes are tested thoroughly enough to put a VNE on them? That might actually have some use. Don't hold your breathe though.

JR