The Ugly Stik airfoil

For decades Phil Kraft’s Das Ugly Stik has been the standard by which sport planes are measured.  It’s common knowledge that the original Das Ugly Stik has been copied dozens of times by various designers and kit manufacturers.  Even if the new design is intended to look completely unlike a Stik, the airfoil, moments, wing and tail area, and general layout will result in a new plane that flies well.

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Phil Kraft’s Das Ugly Stik as published in RCM

A less well known fact is that this sort of mimicry is how Phil Kraft designed the Das Ugly Stik in the first place.  A few years before the debut of Phil Kraft’s Das Ugly Stik, RC Modeler magazine published a design by Don Mathes called the Digester.  Mathes needed a test plane for his new digital radio, so he built a digital tester, which led to the name Digester.  It’s a big plane with a big wing and three channels of control.  A look at the airfoil reveals that Phil Kraft simply started with a Digester wing and added ailerons, and decided to scallop the trailing edges for laughs.

Digester by Don Mathes

Digester by Don Mathes

50 years and dozens of Ugly Stik copies later, some of the original specifications have become less well known to the modeling community.  Several Stik designs have been built with symmetrical airfoils or thinner profiles, or in some cases both.  I thought it would be interesting to show how the original Das Ugly Stik airfoil compares to two very popular clones.  For the following illustration I started with a Stik rib, copied it, flipped the copy, and superimposed the two images to show the asymmetry of the airfoil.  The ribs from the first two planes are roughly the same size, but the Sweet Stick rib was scaled to 130% to make it the same size as the other two.

stikribcomp

As you can see, contrary to popular belief, the Das Ugly Stik airfoil is not symmetrical or even almost symmetrical.  The Great Planes airfoil remained fairly true to the source, but Midwest pretty much abandoned the basic design of the original Stik.  The airfoil is almost symmetrical.

Maybe this is useless information, or maybe you want to build your own plane starting with the basic parameters of the Ugly Stik.  In any case, I thought it was interesting.