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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.

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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.

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    $\begingroup$ Thank you for your response, I hadn't considered the possibility of folding the wings. $\endgroup$
    – Daniel Lader
    Commented Apr 9, 2023 at 15:32
  • $\begingroup$ What do you think about making a tandem wing aircraft? Am I correct in saying they are far less efficient? If so is the difference small enough at this scale that it may be worth the losses for the shortened wingspan? $\endgroup$
    – Daniel Lader
    Commented Apr 9, 2023 at 20:13
  • $\begingroup$ There are several discussions already on Av.SE about the pros & cons of tandem wings: search. One of these may have the details that will help your project. $\endgroup$
    – Ralph J
    Commented Apr 9, 2023 at 21:11
  • $\begingroup$ @DanielLader tandem wings, as in a biplane, especially if one wing was mounted in a parasol fashion, may be workable, but a monoplane will be more efficient and much gentler in roll. A fore and aft tandem wing, with potential interference issues, may not be the route best travelled. $\endgroup$
    – Robert DiGiovanni
    Commented Apr 9, 2023 at 22:01
  • $\begingroup$ this brings back memories, Enya Nr.3 glow plugs were the most durable $\endgroup$
    – user3535
    Commented Apr 10, 2023 at 8:26