RE: 1/2a Stick
I have a good mate-Dave Hipperson (no not the Australian one!) who was a top FFer in his day (he's since dropped out of modelling in favour of photography!) who designed a rather nice -and very competitive FF duration model called the T-34 (after the Russian tank-simple, effective, cheap to build, reliable etc etc)- three sizes have been published over the years-the original for .19-.21, a 1/2A one and a 1.5cc diesel version. They look the same-but all are different-they are not the same design scaled up or down- but have subtle differences in moment arms, wing or tailplane aspect ratios etc-because he had enough experience to know that a simple scale up or down would not deliver the performance and reliability he wanted in that particular size (I'm sure wing loading and flying speed would also have been factors influencing his design considerations)-yet if you look at them you would say 'oh thats a 75% or 60% T-34'. Its not just R/C models you have to watch for pitfalls in scaling..........
Going the other way-are you familiar with the 'Simplex' vintage design?-the original was designed by Paul Plecan in 1941 and intended to be very cheap to build and fly. It was 60" span. [still popular for vintage R/C in NZ today] 'Aeromodeller' published a 2/3 scaled down version in the mid 1980s which proved VERY popular for vintage FF in several countries-especially NZ and the UK. [I know you have a different vintage cutoff date in Australia] A few people here though it would be a good candidate for the vintage 020 replica class-which has a 36" wingspan limit (so you'd only need to shrink the 40" one to 90%)-not much.......BUT when you fit an 020 to a 36" Simplex, (on its normal 4-1/2" prop) you end up with about 1/4" of the prop tip extending outside the nose-and that won't fly much! So direct scaling down can trap you just as much as scaling up..... [as it was those 36" models flew quite well on a DC Dart .5cc-producing about the same power as a TD 020 at half the revs-but happily turning a 7" prop!] Somewhere in Aeromodeller in the late 80s or early 90s is a shot of another mate of mine, Hec Sapwell flying one of those 36" slightly scaled down Simplexes at one of the Old Warden vintage days
This is of course a situation (vintage) where the rules allow you to scale up or down to your heart's content-but you can't alter model proportions or structure in the process.
ChrisM
'ffkiwi'