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My engineering class uses model plane kits to build "frankenflyers" which use parts from multiple model planes to make one plane that will carry a maximum load (pennies). I was wondering what the best configuration would be. We have three wings and three bodies. I was thinking we should use a biplane for added lift, but I couldn't find much on dihedral wings being used on a biplane. Open to criticism and ideas.

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If your aircraft is meant to be a "free flight" model, meaning that it flies without any guidance from any pilot, then generous dihedral will help keep the wings level.

Even if your aircraft is meant to fly under radio control, so long as the mission is load-carrying rather than aerobatics, some dihedral will help ease the pilot workload. You may want to mix some rudder to your aileron channel to help it turn better, otherwise the dihedral will tend to create some resistance to aileron roll/turn inputs. If you don't have a rudder, don't use very much dihedral. If you have only a rudder and no ailerons, use lots of dihedral.

Many full-scale (piloted) biplanes do in fact have dihedral on one or both sets of wings. Most typically the lower wing has dihedral while the upper wing is straight, because that helps improve ground clearance of the lower wingtips, but in some cases both sets of wings have equal or nearly equal dihedral. (See for example this 3-view diagram of the "Bristol Fighter". The combination of a straight lower wing and a dihedral upper wing has never been used before, to the best of my knowledge-- here's your chance to be the first!

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  • $\begingroup$ Actually I think sometime in the 20's or 30's there was a biplane design, possibly British, possibly a torpedo bomber, that had dihedral only on the upper wings. I'll modify the answer and include a link if I (or someone else) come/s across a specific reference. $\endgroup$ – quiet flyer Feb 27 at 15:03
  • $\begingroup$ The Sopwith 1 1/2 Strutter had a straight lower wing and a mildly dihedral upper. It's probably been done again in the intervening hundred-plus years... $\endgroup$ – Zeiss Ikon Feb 27 at 17:49
  • $\begingroup$ Yes, probably so. $\endgroup$ – quiet flyer Feb 27 at 17:54
  • $\begingroup$ @ZeissIkon -- Yet in this particular case, when I hold a ruler up to this three-view, it doesn't seem to support your assertion-- en.wikipedia.org/wiki/Sopwith_1%C2%BD_Strutter#/media/… $\endgroup$ – quiet flyer Feb 27 at 17:58
  • $\begingroup$ Yep, you're correct. I was going by photos I found in a quick search, in which the lower wing does look flat. $\endgroup$ – Zeiss Ikon Feb 27 at 18:42
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If you mean that you have three fuselages and three wings to choose from, and you want to maximize the weight of the payload carried, and you may use more than one wing, then build a triplane. More wing means more lift!

As quietflyer answered, dihedral increases stability (as does sweepback, somewhat), and reduces aileron authority. But this is true for monoplanes and biplanes and triplanes and stranger things. That's why you couldn't find much written about this, because mono-vs-biplane and amount of dihedral don't interact much. Just space the wings about one chord apart for their full span.

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