Big Pussycat Chapter 9 – Final Assembly and Flying

Final Assembly of Major Components
 
At this point you will have completed the wing, tailplane, fuselage, propeller assembly and landing gear.  It is time to put all these together and make an airplane.
 
Put a small drop of glue on the tops of the tailplane spars, just inside the pencil marks you made earlier to locate the fuselage.  Here I am using the point of a toothpick to apply the glue.  The glue should extend across the spar and be wide enough to extend across the 1/16″ fuselage spar.  You want just enough glue to wet the wood without big gobs of glue squeezing out when you put the parts together.
 
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Join the tailplane to the underside of the fuselage with the paper side down, so there is a wood to wood glue joint and the fins point up.  Use a block of wood to get the tailplane square to the fuselage and make sure the fuselage is within the pencil marks.
 
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The back of the sternpost and the back of the trailing edge spar should be in the same plane.  You will need a flat surface to which to glue the tailskid.  Hold the parts together until the glue sticks.  You can put the plane down on the flat building board with some 1/16″ wood under the nose, to space it up the same height as the thickness of the tailplane, and put a small weight, like your sanding block, on top of the rear end of the fuselage to hold it down while the glue dries.  Let the glue dry before handling it again.
 
Similarly spread glue on the wing spars inside the fuselage locating pencil marks.
 
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Place the wing on top of the fuselage over the opening so the wing spars rest directly on the longerons with the wing perpendicular to the fuselage and the fuselage centered between the locating marks.  Hold it in place until the glue sets. 
 
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You can put the plane down on the building board with small weights on the leading and trailing edges to hold them down until the glue dries.
 
If you plan to fly your Big Pussycat with the landing gear, you will need a tailskid to keep the tailplane from dragging on the floor.  Place a piece of 1/16″ x 1/8″ hard balsa over the tailskid on the plan and mark it to cut to length.
 
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Sand the end square across the narrow direction while maintaining the 45 degree angle of the cut.  This face must be flat to get a good, straight, strong joint.
 
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Round the bottom end of the tailskid.
 
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Apply glue to the round bottom that will contact the ground, to harden it.
 
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The finished tailskid.  You may compare yours to the plan.
 
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Apply glue to the straight face of the tailskid and…
 
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Stick it to the center of the back of the sternpost.  It will extend a little over the tailspar.  This is one place where a little extra glue is good.  After the glue dries, put a little more in the angle between the tailskid and the sternpost, forming a fillet of glue.  Let it dry thoroughly before allowing anything to touch it.
 
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Insert the motor peg into one of the plates.  This is a 1 5/8″ long piece cut from a round toothpick.  You can also use 1/16″ diameter aluminum tube.  It should be a snug friction fit in the hole.  If it won’t go in, lightly sand the peg or file the hole.  If it is too loose, apply glue around the hole to fill it in a bit.  If that does not work, try gluing tissue paper inside the hole.  Or see if you can find a slightly larger toothpick.
 
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Click HERE to see the post on this site “Making a Rubber Motor”.  Make a 20″ loop of 1/16″ rubber strip.  Make sure that the opening in the propeller hook is wide enough to admit the O-ring.
 
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Here we see the motor attached to the hook with an O-ring.
 
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Hold the airplane with the nose pointing straight up and insert the motor down into the fuselage until the end appears inside the window below the motor peg.
 
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Push the motor peg through the loop, out the other plate and center the motor and peg.
 
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You can hand wind some turns into the motor to shorten it until it pulls inside the fuselage.  Here I am using a 20″ loop of 1/16″ wide rubber strip for test flights.  The distance from the propeller hook to the motor peg is 10″, so the motor is twice that length.
 
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Fit the noseblock into the nose to check fit.  You may want to pencil mark one surface as the top to be sure you insert it the same way for each flight. 
 
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The fit is good.  It should go in with slight friction and not fall out when the motor goes slack.  Let the motor turn to check that there is no friction and nothing rubbing inside.  You can put a tiny drop of light machine oil on the prop shaft and washers.
 
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Squeeze the landing gear legs together slightly and slide the top into the slot under the fuselage.
 
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Check that the landing gear is properly fitted. 
 
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The wheels should be slightly ahead of the slot. 
 
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The payoff for all your work!  Your airplane is now ready to fly.  Put it in a safe place until you can get it to the Gym.
 
Winding the Motor, Trimming and Flying
 
The Big Pussycat motor takes a few thousand turns, more than you want to put in by hand.  You will use a winder.  Stretching the motor during winding allow more turns to be put in.  Commonly winders put in 10 or 15 turns per crank of the handle.  It is easiest to keep track of cranks if you count by tens, like this “One, two, three, four, five, six, seven, eight, nine, ONE, one, two, three, four, five, six, seven, eight, nine, TWO, one, two, three, four, five, six, seven, eight, nine, THREE, one, two, three, four, five, six, seven, eight, nine, FOUR, one, two, three, four, five, six, seven, eight, nine, FIVE.”  At this point you have fifty cranks in, five hundred turns on the 10:1 winder or seven hundred fifty turns on the 15:1 winder.  Start with about 70% of maximum winds to check that the plane flies well in a circle that will fit within the Gym. It should be turning left, climbing only slightly.  Watch how it comes down when the power runs out.  It should glide slowly to the floor.  If you built the plane according to the directions, it should fit within the usual basketball gym.  You may want to adjust the turn if you are in a smaller or larger space.  Make the necessary turn adjustments before increasing power. Turn adjustments are made by placing a shim between the nose block and the front of the fuselage, to point the propeller more to one side.  Thin shims may be made from something like postcard or business card paper.  Thicker shims may be made from 1/32″ balsa or 1/16″ balsa.  Place the shim on the right side to make the plane turn more tightly to the left.  Place the shim on the left side to open the circle.  Gradually add turns, going to 80% to check climb and 90% to see how closely the plane approaches the ceiling. If the plane hits the ceiling, back off half way to the last number of turns that did not hit the ceiling.  By going half way up and down you will eventually get as close to the ceiling as possible without hitting it.  This gradual increase will also break in the motor so it will take a few more turns.  Once you have a flight close to the ceiling, try another flight with the same number of turns, but measure the torque.  Check that the plane still gets close to the ceiling.  Next flight, wind the motor up as much farther as you dare than the last time, then back off winds until you reach the torque of the previous flight.  You will find that you will have more turns in the motor at the same torque.  This will allow you to get more time using that motor.  After a couple windups to near capacity the motor will become fatigued.  Let the motor rest over night before using it again. 

For best duration, the Big Pussycat is flown without landing gear, using the 1/16″ motor. For flying with the landing gear, use a slightly thicker motor for more power to lift he extra weight and overcome the drag.  

Record each flight in a notebook. You can write down the date and location, the name of the plane, the weight of the plane, the size and weight of the motor, the center of gravity location, the number of turns put in, the number of backwinds if any and any trim adjustments. Describe the flight pattern, diameter of circle, rate of climb, estimate how close it got to the ceiling. Record the flight time and the number of turns left on the motor upon landing. You may also want to record the torque at launch and landing. 

Big Pussycat Motors Turns Tables

Turns tables give a rough guide to how many turns to put into a motor.  Every batch of rubber is different.  Different winding conditions and techniques have different results.  With experience, you will develop a feel for how many turns to put into a rubber motor.

20″ Loop of 1/16″ 

1.6 Grams, 146.8 tpi

%Max, 10:1 Winder, 15:1 Winder, Notes 

100     293              196            Breaks motor 

 90      264              176           Check approach to ceiling 

 80      235              157          Check climb 

 70      206              137           Check trim, circle 

25″ Loop of 1/16″ 

2.1 Grams, 146.8 tpi 

%Max, 10:1 Winder, 15:1 Winder, Notes 

100      367             244             Breaks motor 

 90       330            220             Check approach to ceiling 

 80       294            196             Check climb 

 70       257            171             Check trim, circle

For flying with the landing gear, use a slightly thicker motor for more power to lift he extra weight and overcome the drag.  

20 1/2″” Loop of 3/32″ 

2.6 Grams, 119.9 tpi 

%Max, 10:1 Winder, 15:1 Winder, Notes 

100      245             163             Breaks motor 

 90       221            147             Check approach to ceiling 

 80       197            131             Check climb 

 70       172            115             Check trim, circle

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