Constant cord wing for sloper?

[omega blood]

What is the best aspect ratio for a constant cord wing sloper? Not a flying wing mind you, a coventional airplane with about 4Ft. wing span.

[Ollie]

The "best" aspect ratio depends on a lot of things and their priorities. What are your intentions for low landing speed, light lift flying, high speed flying, high roll rate, type of wing construction, etc.?

The goodness of any design decision depends on how that decision affects the plane's ability to meet its intended use.

If high roll rate is the number one priority, then low aspect ratio is required. If low landing speed and light lift flying are high priorities then higher aspect ratio is called for. If high straight line speed is the objective, then moderate aspect ratio is appropriate. If tight turning ability and low lap time racing on a short course are the objective, then higher aspect ratio will improve performance. The exact numbers depend on wing area loading, wing spanloading, airfoil selection and how the various priorities are quantified. The design decision requires finding a balance betwen conflicting objectives based on their priorities.

In other words, the question of "best" can only be answered through engineering or a long evolution of trial and error like nature does it.

A program like PC Soar is a great tool for calculating the performance of various combinations of design decisions. With it, you can evolve a design in the direction you want to go at the rate of dozens of designs per hour instead of having to build and fly dozens of designs over years. See:
http://my.athenet.net/~atkron95/pcsoar.htm


You can come close to "best" by picking a plane that performs the way you like and copying its features.

Technology advances by the availability of better materials and better information. Therefore, the question of "best" can only be judged in the context of the technical information currently available on airfoils (for example) or the currently available materials (carbon fiber can have 20 time the strength to weight ratio of wood, for example). What is "best" now won't be "best" next month or maybe next year.

[omega blood]

Ollie, as always thanks for the help. I think I speak for all of us when I say you are a valuable member and source of information we can't do with out. Enough butt kissing back to my question.

I want to work on my foam cutting, glassing , and over all constuction skills before going back to my skymaster project. Any way I want to try building a folker E III. Simple and strait forward (I hope). I want to go for a scale look but that's not critical. I'm mainly looking for speed and acrobatics ( I love the high speed whoosh sound). I'm planing for a 4 ft. wing and possibly enlarging the tail srufaces.

[Ollie]

I suggest going with the scale aspect ratio. I would use a fairly thin symmetrical airfoil for two reasons. A thin airfoil will keep the weight of foam near the wing tips down, improving roll rate. A thin airfoil will be faster. Consider the S8020 airfoil. The lighter you can build the plane the better the all around performance will be if you also make provision for ballasting up for heavy lift conditions. Carbon spar caps with adequate shear webs may be necessary to take the wing bending loads of high speed maneuvers with balast.

[omega blood]

Cool thanks Ollie, I hope I can get started this week end.