mmattockx:
I believe the goal was "cheap". The F3A could be called a lot of things, but cheap isn't one of them... Not at $600 per.
Agreed, and I understand that. But the difference between using a ZDZ 40 and a DA/DL 50 may (or may not) mean the difference between meeting the weight requirement or not, which again means the difference between having a model solely for practice (as was stated in the original post) or having a model that can actually be taken to a competition, if only as a back-up model. The extra few hundred dollars may be well invested, in my opinion.
cmoulder:
aerobob, do you still plan to try the 3W 28cc?
Some 10 years ago I scratch built a (comparatively slim) balsa model using the 3W 24cc engine. (This was the predecessor to the 28, I believe.)
The model weighed just under 5 kg, and flew OK with a 17X13 prop, however not really powerful enough for F3A in my opinion. I don't know much about the 28, but looking at 3W's specification, they say 2.75 Hp, recommended propellers 16x10, 18x8, 18x10, 20x8.
The ZDZ 40 F3A is specc'ed to 4 hp, recommended propeller ZDZ 20x12. (7000 rpm+ reported with ES Composites pipe and this propeller.)
There appears to be a significant difference in power.
(I do have the ZDZ 40, and will try this as soon as time allows in an own design model.)
Magne