Originally posted by YellowAircraft
I definitely agree that unless your plan is to stay in the small jets, don't invest 85% of the cost of a .91/fan combo into a smaller setup. The O.S. .46 is about $10-$30 cheaper than the O.S. .91, and the same is true for the Turbax v. Dynamax setups.
You forgot to mention that a .91-sized setup will have to carry twice as much fuel because it has twice the rate of fuel consumption. So, he'll need bigger gas tanks and a place to put them.
At a minimum, a model with a .91-sized power package (engine/fan/pipe) will be 2 Lbs. heavier than the same model running a .46-sized setup. This makes for a heavier model with the higher resultant stall speeds.
Even though you're running an engine that's twice the displacement and has twice the fuel consumption and weighs almost twice as much, you won't get twice the thrust out of it.
Running a .91-sized model has it's advantages, but it also has it's disadvantages. To be fair, both should be mentioned.
There ain't no such thing as a free lunch.
Dan