I've been doing a lot of RCU research over the last few months on airplanes in the 78" wingspan range. What has got me confused is the wide range of weight and power that I'm seeing. On one hand, you have a typical 2M pattern ship at 11 lb with 1.40 glow power. On the other hand, you have a 16 lb Extra ARF with 50cc power. Both airplanes have essentially equal wing area.

It's difficult for me to guide my own decisions when I see such a huge range. What's the best weight and power compromise for Scale Aerobatics in this size range?

If you go with one of the lighter engines and kits out there and do a few lightning mods, you can get close to a 3:1 thrust to weight ratio with a light wing loading (under 30 oz per sq ft).

example (31% CA Extra 300L, carbon gear, LIon batteries, ZDZ 80 single) just under 20 lbs with a 93" wingspan and over 50 lbs of thrust.

If you go with a heavier engine with a spring start and a heavy kit and add extra uneeded weight, you can get closer to a 1:1 thrust to weight ratio with a very heavy wingloading (around 40 oz/sq ft)

example 2 (73" Cap ARF, G-23 engine, heavy nicad batteries, tires, pilot, etc.) 16 lbs and real close to a 1:1 thrust to weight ratio.

If you do everything the "light" way and don't try to save on an engine or any other part, you can get a 78" plane around 12-14 lbs. mostly depending on whether you go gas or glow.

If you get closer to a 90" wingspan plane (84" or above), the decision to go gas is clear.

Hope this helps

John

I'm currently flying a 72" Sukhoi at 10.25 lb (25 oz/sf). Although this is fairly light compared to other models I've seen, it's far from the light loading I see with 30-40% aircraft. When I hear about guys with 78", 16 lb, 32 oz/sf Extras, it seems like those airplanes are too heavy. I realize a larger airplane can handle higher wing loading, but 32 oz/sf on a 78" model is not going to provide the floating like a leaf quality that the big ones have. Even my little Sukhoi would float better.

It seems like the 78" class of airplanes should weigh no more than 14lb for good handling.

Thoughts?