The following information was written by Bob Pearce to the Ragwing online information group. Various paragraphs were edited for sentence structure and clarity:

Any of Rogers wings that I have seen use the same 4414 airfoil with a slight undercamber. Pete Bowers used the 4400 airfoil but modified the lower cord to a flat line. I have flow ships with both and didn’t notice the difference. The flat lower cord is a little easier to cover. The 44 means series 4400. The 14 is the percentage of maximum depth to cord. The more common is a 12% at slightly less drag. His probable reason for the14% is to gain more depth in the spars.

Airfoil, airfoils, airfoils. Too often we attribute the speed and flying performance of an aircraft by the type of airfoil it has, not taking into consideration the many other factors of design entering into the picture. More often an aircraft has more or less speed than another because of that ever present enemy of speed – DRAG. While we praise or damn the airfoil in its place.

The J3 Cub is used as a classic example of slow high drag airfoils because of the ship’s relatively slow cruse speed, while acknowledging it has a high take of performance and load carrying ability. We also cite the airfoil used by the old 65 Taylorcrafts for its good turn of speed. We do not take into consideration the Cubs very poor streamlining with its rudimentary cowling and very dirty landing gear and its relatively high cabin area providing more ground clearance for the wing.

Conversely we have the well cowled T-Craft with its very low and otherwise cramped cockpit, its very clean landing gear and smaller empenage and say it is all due to airfoil.

In between lies the Aeronca Champ. About the same size as the Cub but with cleaner cowling and landing gear. We say it’s airfoil must be better than the Cubs but not as good as the smaller, cleaner T-Craft. And then their is the Aeronca Chief with the same wing as the Champ but said to be slightly faster.

Let’s examine the 3 different airfoils used on Cub, T-Craft and Champ. Lift over drag speaks to the efficiency of the airfoil. Lift co-efficient is the lift factor at the highest angle of attack before the wing begins to stall.

U. S. A. 35B…..J3 cub and many other Piper models…..L/D…..(Ratio of lift to drag) 20.8
CL……(Lift co-efficient) 1.7 (highest)
The USA 35B Has a moderate stall profile and the best L/D comes at an angle of attack of 0 degrees

NACA 4412….Aeronca Champ and Chief, Luscombe. (and Volksplane)…..L/D……22
CL……1.65
The 4412 has a well rounded stall profile providing ample stall warning and a gradual stall entry. The best L/D comes at about -1 degree.

NACA 23012 Taylorcraft BC12D Interstate Cadet ……. L/D…..22
CL…..1.6
The NACA 23012 has a good lift over drag profile and the wing to fuselage angle is best set at about 4 degrees. The CL comes at 1.6 and then plunges abruptly to 1.3 indicating a very sharp breaking stall.

With the NACA 23012 Wingtips should be washed out slightly to prevent a sudden loss of lift at the tips along with complete loss of ailerons. For those interested in an aerobatic machine the airfoil flies quite well inverted and it sharp stall facilitates snap rolls. Also the center of lift on the wing moves very little with changes in speed meaning less elevator trim is required.

As you can see there is little to choose from the three with regard to drag and lift co-efficient. If all are equipped with the same engine, differences in speed will be mostly due to the weight and the drag profile of the individual aircraft. As may be guessed the J3 Cub with its rudimentary cowling and high drag landing gear is the slowest of the airplanes listed. The light clean and relatively small T-Craft the fastest along with the clean Luscombe 8E.

Here are some examples of a few light aircraft, their empty weight, cruise and stall speeds. Top speeds 10% to 15% higher:

T-Craft…Weight about 650/700lb. Cruise 91mph. Stall 39mph……23012 airfoil…..Span about 35′
J3 Cub….Weight about 650lb. Cruise 75mph. Stall 38mph……USA 35B airfoil….span about 35′
PA15….Weight about 600 lb.. Cruise 90mph. Stall 45 mph. USA 35B airfoil….span about 30′
Aeronca Chief….Weight about 800 lb…Cruise 90 mph..NACA 4412 airfoil…Stall 42.5 mph…..Span about 35′.
The above have a wing cord of about 5′ and a wing area of around 175 sq. ft…..Aspect ratio (ratio of span to cord) 7.00…. The PA15 150 sq. ft….Aspect ratio 6.00
Luscombe 8E…. about 675 lb….Airfoil NACA 4412…..Cruse 100 mph….Stall 42.5 mph. Span about 35′…Wing Cord 4′…Area 140 sq. ft…..Aspect ratio….8.75……The Luscombe with its high aspect ratio wing takes off and climbs very well and has a good turn of speed…..

Conclusion…….The 3 different airfoil types of the above aircraft aircraft is not an important factor in their speed. Most important are frontal areal and streamlining or a lack thereof….While it is often assumed that the 35B airfoil is ‘slow’ this is not really the case and Piper has used it on most of its earlier ships and it is written that it is effective up to speeds of about 135 mph. The 23012 although good in most respects has a very sharp stall point which must be taken into consideration……The airfoil I think best suited to small low power aircraft is the NACA 4412 and it is the one that I have used for most of the planes I have built.

If I wanted a small, lightweight ship to give the best possible performance I would use the slightly thicker 4415 airfoil and an aspect ratio of about nine…..I would use this thicker foil to provide more spar depth for the longer narrower cord wing…….For maximum performance I would provide it with Fowler type flaps and spoilers. The Fowler flaps for max take off lift and the spoilers to dump lift on landing……..old uncle bob

Additional information from outside sources –

According to the designer of the Skypup the airfoil outside of the center section is the 43018. The same airfoil was used on the Skypups predecessor the Blue Light Special.

As for the 23012, Don Stack House is quoted on http://www.djaerotech.com/dj_askjd/dj_questions/blunt_wing.html
as saying the following “It is very possible to design a wing with an airfoil that is known to have truly wicked stall characteristics by itself, and yet have an airplane with very benign stall behavior. For example, the very popular ( in full scale light aircraft) NACA 23012 has truly awful stall characteristics. (For those of you trying to follow along in the book, it’s page 498 in Abbott & Von Doenhoff’s “Theory of Wing Sections”.) It’s painful to look at its rather bizarre Cl vs. alpha plot (that’s lift coefficient vs. angle of attack). Almost no rounding off at the top just before the stall (indicative of little or no stall warning before the actual stall break), with a precipitous massive drop in the lift coefficient right at the stall, so abrupt that the plot shows a vertical dotted line for that part of the curve. The tiny amount of lift coefficient that’s still left after that initial drop continues to decline steeply at angles above the stall. This is truly an airfoil with malevolence in its heart. BTW, it also has a reasonably blunt leading edge, although I doubt that sharpening it would help. Yet, many airplanes use this airfoil, some with rather abrupt stall characteristics, and others with very gentle stall characteristics. ”
—————————————————-
Also in light of the differences between the speeds of a Cub, Taylorcraft, and Champ, it’s good to know how big a difference drag may have on airframe components. This is especially important for the Ragwing Sport Parasol I’m building.