Flying Models Centerfold Plan - October 2010
The Big Pussycat
This cat may have a little roar, but you’ll still be chasing it
when it catches a thermal.
By Dick Baxter/Photos by Shirley A. Baxter
Want a sport model that flies well indoors or out? One you can build in three or four hours if you know what you are doing? Even a beginner can build the Big Pussycat in six or seven hours with just a little help (like a demo of assembling a full fuselage). If any of this is the case then the Big Pussycat is for you.
The stock Pussycat is a square airplane with “flat plate” airfoil and single surface, wrinkled paper covering. It is built almost entirely out of 1/16-inch square and 1/16x1/8-inch sticks. There are no ribs or former to cut out. Flight adjustments are “built in” and will work first time out for airplanes which are build accurately. Most experienced builders can do this easily but most beginners build in warps and skews which require some touching up to correct. I have used the (stock) Pussycat in 6th to 8th grade classrooms on and off for ten years. Most first time students now build the Starved Pussycat which is a stick model version of the Pussycat (same force setup), no built-up body). The stock Pussycat got a lot of publicity by being published in Model Builder in 1987 and getting very favorable mention as a sport model in Model Aviation. Consequently it became very popular with lots of stick and tissue sport flyers. I have received reports of lots of Pussycat sightings from Japan, Sweden, Yugoslavia, and all over the USA. It has been kitted by Lee’s Hobbies, Sunnyvale, CA. The Starved Pussycat is (bulk) kitted (15 in one box) by Peck Polymers, Santee, CA.
This model is a souped-up version of a beginner’s model I have used in 6th to 8th grade classrooms for the last 10 years. That airplane was called the Pussycat and has been very popular with a lot of experienced folk as a quick and easy sport airplane. The stock Pussycat was designed for easy construction and reliable flight. It flies well but is not an aerodynamic gem.
The Big Pussycat was designed as a follow-on project for “advanced” beginners (kids that have already built one or two models) and is much improved aerodynamically over the stock version. The improvements consist mostly of use of a cambered (sliced rib) and somewhat bigger wing. The fuselage is stretched a bit too for a longer motor base.
Big Pussycat will fly at least 30% longer than the stock machine. Be careful outdoors or you will lose it. It is slightly harder to build than the stock airplane because it introduces the beginner to making sliced ribs and requires him to shape a leading edge out of a strip of 1/8-inch square balsa. You can even sandpaper the structure prior to covering if you know how, but sanding is not necessary except to smooth out the bumps in the shaped leading edge. If you are a real beginner, don’t sand the structure, you will just break something and the lumps you remove are not worth the frustration.
Construction is super simple. All lines are straight, all surfaces are single surface covered (saves a lot of weight) and wrinkled paper is used to avoid warps. You can dope the wrinkled paper if you must, but do not water shrink it or you will have a pretzel instead of an airplane (I recommend no dope).
Avoid wet grass if you do not dope the model.Dew and damp grass are not usually a problem even without dope.
The family of flying Cats with the stock version at the top, the middle child—a jazzed-up stock with sliced ribs—and finally at the bottom the featured Big Pussycat that flies the best of all the Cats.
To “wrinkle” the tissue, precut pieces big enough to cover whatever, roll the stuff up into a little ball. Then unroll and smooth out as best you can with your hand on a flat surface. The result after installation is smooth on a large scale but has lots of tiny local kinks which give the surface a matte appearance and provide some slack to accommodate humidity driven tension changes in the paper. In other words, practically warp free. This does not look too swift but makes the model adjustments stable for months at a time.
The airplane uses a folded paper canopy (optional) to fair the wing into the fuselage. Leave it off if you want; I think it improves appearance and does not cost much weight. It probably lowers the drag a little too, but who knows for sure.
Be sure to cover the stab on the bottom as noted on the plan. If you do not, then the airplane will probably dive into the ground almost at your feet. Tests have shown that covering the stab on top instead of the bottom is equivalent to adding 4 degrees of down elevator trim. That’s an enormous
amount. If you do make this error you can fix it by adding a 1/8-inch up elevator shim between the leading edge of the stab and the bottom of the fuselage.
It helps to put a bushing into the Peck Polymers plastic prop to make the prop spin true without fussing with weird but minor bends in the prop shaft. Use a 1/4-inch length of 1/16 O.D. aluminum tube and drill the prop hub out to 1/16 I.D., then slip the bushing into the prop hub. You don’t need glue unless you make the bushing too long. You can skip this step if you want, but it is a quick way to avoid annoying prop wobble due to the small diameter prop shaft flopping around in the oversize prop shaft hole in the stock propeller.
The Big Pussycat framework is light and sturdy, a simple construction that would be a good third model for beginners. The first flight on this prototype flew eight minutes in a thermal its first day out.
Indoors, under a 20-foot ceiling, use a loop of 1/16-inch for the Big Pussycat. Outdoors, or under higher ceilings use 3/32 or even 1/8 rubber to climb high. I get over 60 seconds using 1/16 and over two minutes using 3/32 in the 180-foot ceiling Santa Ana blimp hangar. To get max performance with big motors, you will probably have to fine tune the downthrust and maybe use some side thrust to control high torque flight pattern. Outdoors, you can make a sort of dethermalizer by locking the freewheeler temporarily with a tiny lump or modeling clay. This messes up the glide L/D and trim and will save your airplane from weak thermals. Have fun!
Advice for real beginners
1. Use Duco Cement or Testor’s Green Label for structure. Use a 50:50 mix of white glue and water for tissue cement.
2. Color the plan structure patterns with (light colored) crayon or cover the plan with wax paper or Saran Wrap to discourage the structure from sticking to the plan where the glue squeezes out.
3. Build two identical body sides, separate them and install (⁷⁄₈ inch length) cross pieces where shown on the top view. Do not build a body top and bottom frames!
4. You can use a small Peck Polymers thrust button instead of the aluminum tube thrust bearing if you can find one. They work better but are rare in hobby shops.
5. Use a washer or bead bearing between the prop and nose block bearing, bend a 90-degree “freewheeler” latch at the front of the prop shaft to keep things from falling off.
6. Do a “preflight” inspection of your airplane before every flight to make sure you have not knocked anything out of line since last time. Reliable flight demands dimensional stability. You cannot expect to adjust the airplane for “good” flying unless the parts stay where you put them.
7. Do not expect your airplane to fly well without some check-out and adjustments. This model uses ballast (modeling clay works well) for pitch trim. Wing warps and fin warps correct for spiral dives and unsatisfactory flight circle diameters at low and medium power. You won’t need to do this if you build the airplane straight and true because turn and wing tip washout and downthrust are built in, but straight and true is harder than you think. If your airplane won’t fly right get expert advice from an experienced flier or read up on trimming. Most one, two, three... trimming recipes are oversimplified.
8. If you use really big (high torque) motors you will probably have to fine tune the power pattern with small changes in downthrust and sidethrust. A small change is usually just a ¹⁄₃₂ thick shim between the nose block and fuselage nose. Downthrust cures stalls at high power and sidethrust trims circle size at high power. Thrust adjustments don’t do much at low
torque, that is not wound up much.
9. Take care of low power (low torque) trim problems first, then cure high power trim problems with thrust adjustments without changing the low power trim setting.
Share the Big Pussycat plan for free with model clubs, schools and model building training groups.
This article originally appeared in the December 2006 Flying Models.