Sweek (oz9189)

About this Plan

Sweek. Radio control model for Class III competition and sport. For .60 power.

Quote: "ONCE upon a time there lived a designer of radio controlled aircraft who dreamed of designing the perfect airplane. Oh, it would be a thing of beauty. It would fly perfectly through all maneuvers and always bring its builder great glory in the contests.

Well, maybe it works that way in the fairy tales, but for me it has taken a period of seven years and four airplanes to come up with the airplane which each of its ancestors was designed to be. Like a lot of other modelers, I had grown a little weary of the sameness of all of the multi-stunt designs, low wing, stab on or about the thrust line, almost identical force arrangements on them all, and so forth.

When looking over the ships at any local flying site they are all the same, basically, except maybe the rudder or wing tips arc shaped a little differently. Sure, they do fly excellently, but why not try to improve even this and, at the same time, design a ship that has a different look, one that will stand out on the flight line because it is different? This is what I had set out to do, and, while none of the first three designs I produced was a bad airplane, none seemed to be exactly what I wanted.

It seemed to me that a good multi ship would have to have these features:

A. A steady pitch axis to keep it from hunting up or down.
B. It should roll about the thrust line, keeping the fuselage as a pivot, and not show any tendency to barrel roll. It should not change its headings or lose airspeed excessively during consecutive rolls.
C. It should enter spins easily and recover instantly with no overspie or ex-cessive corrections.
D. It should be fast, smooth and have a relatively light wing loading.
E. It should look good as well as fly.

Normally, at this point, the designer goes into a long dissertation relating to aerodynamic theory and gives complicated and wondrous reasons why his particular design is aerodynamically perfect for the job intended. I spent a period of seven years fiddling with this force arrangement off and on, with numerous kits and magazine plan ships in between, but always seemed to come back to my first love.

My first airplane was an 800-square-inch shoulder wing design, .45-powered on an 8-channel reed rig. It flew well but rolled much too slowly, and had too much trim change between high and low throttle.

The second ship was the first taper wing job, with a fast, smooth roll, but
unfortunately, it didn't last long because of the PIO factor (pilot-induced oscillations). A bad case of more-airplane-than-I-had-experience- to-fiy!

The third job was very close to the dream but still just wasn't quite right. It went through all the maneuvers well except spins. It had to be flown out, or it would take an extra 100 feet coming out. This resulted in a major rebuild job twice. This airplane was the only one to use strip ailerons and seemed to have more yaw in the rolls than the versions with conventional ailerons.

Since I had just acquired a new Kraft KP6-S which has a very small airborne package, I could finally put the wing where I felt it should be - in the center - because the receiver and servos required only a depth of one and three-quarters inches below the wing.

It's a sort of swept back kind of freak. So 'Sweek' is a shortened version of this description although it does sound like some sort of disease. Maybe it is a disease, but probably one any modeler who builds it will be glad he got.

Before drawing the Sweek, all the good and bad habits of the first three ships had been analyzed. The poor spin recovery I felt was the result of the stab riding in wing turbulence and becoming less effective. The dihedral in the Sweek stab is not just for looks, it cures this problem. Many modelers have been curious about this stab treatment and the only peculiarity I have found is that it takes more down elevator travel than up to bring about equal maneuvers. This is accomplished by raking the horns back 15 degrees.

Sweek will enter a true spin easily on command, the spin has fast rotation and recovery is automatic when controls are neutralized. The ailerons were made conventional and big, while throw has been held down, which results in a fast, smooth roll and almost no loss of air-speed. Sweek will roll from the limit of radio range in one direction to the op-posite extreme and maintain altitude and heading all the way. The ship has very good slow flight characteristics and aileron control is positive at all speeds. This is accomplished by using a 16% section at wing root and progressively tapering to a 20% section at the tip, causing the wing to stall from center out to the tips and holding aileron control to the bitter end.

Sweek uses a full symmetrical zip-zip airfoil for the simple reason that it flies very well, and it seems logical to me that an aircraft which is to fly equally well upright or inverted should be as near symmetrical in all respects as possible.

The ship is flown on a .60. While it is light enough to be flown with a good .35, it is my opinion that the more power the better. With speed and power to spare you have an adequate safety factor. I have seen many underpowered airplanes stagger around in a poor imitation of flight, or stall on takeoff, or not have the power to pull through maneuvers; but I've never seen a plane lost from too much power. You can always throttle back, you know..."

Supplementary file notes

Article pages, thanks to hlsat, JHatton.

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