I am designing an RC airplane. My goal weight is under 10 lbs so I'm designing parameters based off of a 10 lb weight to allow for some overshoot. I also would like the wingspan to be around 4.5 ft for convenience purposes. I want it to be a high endurance flyer so I'm using a wing loading of about 20-25 oz./ft2. The issue is based on these parameters I end up needing a huge chord length (assuming straight wing) and always have an aspect ratio of under 5, which seems way too low for an endurance plane. I was trying to explore ways to increase the aspect ratio without increasing the wingspan or wing loading and I found some interesting tandem wing airplanes. However, it seems like in terms of efficiency tandem wings have proven to be inferior. Does anyone have any suggestions on how I could design around these parameters? Or do I need to either increase wingspan or decrease weight? Thank you.
An "endurance plane" is best built like a glider. Nice long high aspect ratio wings.
For "convenience", do what the Navy does, use foldable or removable wingtip for storage.
Decreasing weight always helps, but G loading parameters and overall strength must also be considered.
From experience, a 5 foot × 8 inch wing with an Enya 40 (around 1 hp) turning a 10 × 6 prop weighing around 5 lbs fuelled:
Wing area: 5 ft × 0.67 ft = 3.35 ft$^2$
5 lbs ÷ 3.35 ft$^2$ × 16 oz/lbs = 24 oz/ft$^2$
So: 10 lbs × 16 oz/lbs × ft$^2$/24 oz = 6.7 ft$^2$
6.7 ft$^2$ × 144 inch$^2$/ft$^2$ = 965 inch$^2$
Essentially, an 8 foot × 10 inch wing (Aspect ratio around 10) would be a good place to start. 10 lbs with engine and fuel included is reasonable.
The glider-like Reaper comes in at around 10 lbs weight/Horsepower (1 HP = 0.746 kW). For your endurance aircraft, 1 kW may be sufficient for cruising, and you may be able to lift a bit more weight given sufficient runway.