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, resulting in sweet sticks, sweet and low sticks, giant sticks, lite sticks, micro sticks and bipe sticks.  Some sport planes have been designed by starting with the moments, incidences, and areas of the Das Ugly Stik and making the shapes of the tail, wing tips and fuselage prettier.  This is a safe strategy, because such a plane would still fly pretty much like an Ugly Stik even if it isn’t ugly.


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.  In 1964 RC Modeler magazine published a design by Don Mathes called the Digester.  Mathes needed a test plane for his new digital radio.  The name Digester was short hand for Digital Radio Tester.  It’s a big plane with a big wing and three channels.  Looking at the airfoil and general layout of the Digester, it’s easy to conclude that Phil Kraft took it as inspiration, simplified the nose and tail, added ailerons, and scalloped the trailing edges for chuckles.  Phil did something right.  Although the Digester is mostly forgotten, the Stik is the most successful design in RC history.

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 copycats have been built with symmetrical airfoils or thinner profiles, or in some cases both.  A lot of folks think they remember the original having a symmetrical airfoil, but in fact the original airfoil was thick and semisymmetrical.

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.

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.  Another popular plane in today’s market is the Ultra Stik, which has a fully symmetrical airfoil.  Some folks say it flies better than the old fashioned Stik planes, but that’s to be expected because it’s pretty common for modern RC pilots to have a strong bias in favor of symmetrical airfoils because they allow you to easily perform inverted maneuvers without being a good pilot.

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