Hi Bryan,
You said in an earlier post that the 5Kg limit was not a random choice.
You are absolutely correct in this.
5kg is/was the FAI's max for their definition for a 'model aeroplane' .
It's used for comps, attempts, records etc for all aircraft types.

I say 'is/was' because in some classes the rules have 'evolved' in recent years.
In F4C the weight rules are at variance with the 5Kg definition.

Also in F4C electric models are weighed without batteries !!!!!. (at WC's )

There are two discussions in this thread; Weight limits as an absolute and; The 'fuel' issue between 'E' and 'IC'.
This is making for some confusion.

From the outside I would make the following observation ; To agree a solution you need to first agree as to the nature of the problem.

Brian