My new plane with flight surfaces made from 9 foam plates. If it looks like aSierra Nevada Special, that is because that is what it is, but with three wing panels instead of two. Best way to get the span and dihedral without a complicated V bevel joint at the wing saddle.
The limitation was making parts from the 6 diameter flat disk in the center of the 9 foam plate. The foam wing panels are 3 1/16 x 5 3/16. Dihedral gore is 1/32 deep at 1 1/4 from leading edge. This produces 1 1/2 dihedral at the tip. Maximum camber is 1/4, also at 1 1/4, no incidence. Camber is formed by creasing along six lines spaced 1/4 apart. Tailplane is 5 3/4 span, 1 3/4 tip chord, 2 1/4 root chord. Fin is 2 3/8 span, 1 1/2 tip chord and 2 root chord, with creased 1/4 wide rudder panel. The 47.4 square inch wing area is asking for a 7 to 10 diameter prop. I used a 7 Peck-Polymers plastic prop, Midwest bearing and shaft. Standard right handed pigtail rear hook made from a straight pin. Stick is 1/8 x 1/4 x 16 with 1/8 square nose block. Tailplane taper is 3/16 in 2 1/4. It weighs 10.3 grams empty. Motor shown is a 14 loop of 1/8, which is good for test flights. This will get it up in the air and run out of turns high enough up that turning circle and descent rate can be checked. Some right thrust will be required under power, right rudder for right descent. Test flights will tell me what motor cross section to use when I go to a double length, thinner motor for maximum turns and longest flight.
This would be a good plane for the forthcomingFoam Plate Airplane Contest.
Snowflake got 2 minutes on its first outing. Like its namesake, it comes down slowly. Here is a 2 minute flight video:
There was frost on the ground. At first my fingers were burning from the cold, but they soon went numb. It was difficult to get the O-ring at the end of the tightly wound, lubricated rubber motor onto the wire hook without being able to feel anything. I lost it once, had to make up lost turns with finger turns. Two minutes is about the best I could get on this field. I might get a few more turns into the motor. It had few left when I picked it up. I put in 2,400 out of an estimated 2,690 maximum turns, 89%. I used a 22 1/4 loop of 0.045 x 0.086. If you dont want to strip rubber, stock 3/32 is the closest. That will get a good climb without having to wind to 90% of capacity. A longer motor might get more time.
The seagulls were on the ground. When they saw the plane going up, they made a run for the expected thermal. A bunch of them came right toward the plane when it turned into the group. They scattered to both sides. They continued searching for lift, flying around the plane, but eventually settled back to the ground. Ive had the same thing happen with hawks in another location.
There is no plan. It isnt necessary to have a plan, as everything is rectangular or trapezoidal. All the necessary dimensions are given above. Anyone who is in a hurry can build one from that information. The build is essentially similar to the Sierra Nevada Special.
Just got back from some photo flying. Got a good one of it flying overhead.
I made a second one. Couldnt get it to fly right in the descent. More right rudder, twist wings, nothing. Got it to go straight, but not turn. Not something you want when flying from a small park. Finally I tried twisting the stick to tilt the tailplane. Made it worse. So I tilted it the other way. Now it flys OK. The tail must have negative lift on it. A tilted tailplane produces a side force that turns the plane.
This complete, illustrated tutorial will guide you step by step through the process of building your own Snowflake. This may be used by individuals or groups like scouts, school classes, senior centers or recreation programs. There are a lot of steps, but none of them are especially difficult. Be patient and take your time.
This picture shows the parts you will make. There are only 18 parts in this airplane and 6 of them are preformed. The plastic prop, prop bearing/hanger and steel prop shaft will be bought. The rubber motor is cut from a length of strip and tied into a loop. The motor is looped around a hook on the back of the prop shaft and a wire hook attached to the back end of the fuselage stick. The wing mounts to a saddle made of balsa parts and held to the stick by two dental rubber bands. The flight surfaces are cut from foam plates. The wing is creased to form a cambered airfoil shape. This curve improves both the aerodynamics and the strength of the wing compared with a flat plate.
Here is what you will need to build your own Snowflake.
A 7 Peck Polymers plastic propeller.
You can use the bearing and shaft from a6 propeller assembly, as I did, or you can order theProp HangerandShaftseparately. You can make your own shaft from 0.039 steel wire, which matches the diameter of the wire on the 6 propeller assembly.
The stock rubber motor is 52 1/2 of3/32 rubber strip. This will make a 26 loop, with an estimated maximum turn count of around 3,000 turns.
You can put more turns into a motor with less chance of breaking if you usemotor lube. You can make your own lube by mixing together equal volumes of green soap and glycerin. The green soap is slippery and the glycerin is a moisturizer.
It is easier to get the tightly wound motor onto the hook if it has anO-Ringat the back end.
Heavy3/16 dental bandsare used to hold the wing on.
You will need several sizes of balsa wood, which you can find at local hobby, hardware, art and craft stores, or you can order fromSigorMidwest. Experienced builders can use lighter wood. Inexperienced builders may be safer with harder wood, especially for the fuselage.
The fuselage stick is a 16 length of 1/8 x 1/4. (If you make it 15, you can get two fuselages and two rib pieces from the standard 36 stick. This would work well for a group build.)
The nose block is 1/2 of 1/8 square. This should be medium to hard wood.
The rib block is a 3 length of 1/8 x 1/4. It can be light wood, or it can come from the same stock as the fuselage stick.
The hold down stick is 3 5/8 of 1/16 x 1/8. It should be medium to hard wood.
The wing saddle face plates are made from 1/16 x 3 sheet balsa. Each plane will need about a 1 1/4 length. The grain goes vertical.
Each plane needs arear motor hook. These are easy to make from a straight sewing pin, 0.020 steel wire or you can buy them.
Each plane will require four foam plates. We have been calling these 9 plates, although the package says they are 8 7/8 diameter. Make sure there is at least a 6 diameter flat circle in the center. Some 8 7/8 plates have only 5 1/2 of flat area. You can use 1 mm Depron foam if you prefer, but planes made for the Foam Plate Airplane Contest must be made from plates.
I find it is helpful to have a box in which to keep all the small parts and subassemblies, to keep things from wandering off and getting lost or broken.
You will need a well lighted, flat surface to work on. You may want to protect the surface with a work board or several layers of newspaper. Cutting is done on a piece of corrugated box cardboard, to prevent cutting into the surface of the table.
I keep my tools in a box, but I get tired of pawing through a jumble of tools looking for just the one I want. For a given project, I will need only certain ones. It is convenient to lay them out in plain sight across the back of my work table in roughly the order in which they will be needed.
The foam parts are made by cutting around cardboard patterns or templates. We must make the templates first.
The templates are made from thin cardboard. In this case, I used the cover of a graph paper notebook. Cereal, cake or cracker boxes make good template material.
Make the wing pattern. Start by making two marks 5 3/16 apart along one of the straight edges of the cardboard.
Draw perpendiculars to the edge at both marks.
Put marks at 1 1/4 and 3 1/16 from the edge on each perpendicular. (Note that I made a mistake on the one along the ruler, I marked at 1 3/4. That had to be corrected. Both mark locations must be measured from the same edge.)
One edge must be cut on a curve so the cambered wings will fit together with a dihedral angle between them. (This will become clear later when you see how the wing panels fit together.) At the 1 1/4 mark along one edge, put a mark 1/32the edge. This will be the high point of the curve.
Draw a smooth curve through the three points; the leading edge, the high point and the trailing edge. The tangent to the curve atshould be parallel with the base line. You may need to move the curve and do it in two arcs.
Cut out the wing panel along the straight edges with a steel straight edge and razor.
Use the curve to guide the pointed knife in cutting the curved edge. Make several shallow cuts, rather than trying to cut through in one pass. It is easier to make precise cuts with gentle pressure. The blade is kept tangent to the curve, so it will not cut into the curve. You will need to move the curve and make the cut in two arcs.
Make an arrow to point toward the leading edge of the wing. This is the edge that is 1 1/4 away from the high point of camber.
Along the straight edge, make 6 marks at 1/4 intervals, starting from the leading edge. These mark the positions of the camber creases. (I now suggest making a seventh crease, 1/2 beyond the sixth.)
Mark a point halfway along the leading and trailing edges, 2 19/32 from the ends. These mark the center line of the center wing panel. This template will be used to make all three wing panels. Note that I have written a label on the template so it can be identified later.
Punch holes on the centerline about 3/32 in from both edges. These holes will be transferred to the foam center wing panel to locate it on the center rib.
Now we will make the template for the wing saddle side plates. Cut a 3 wide rectangle from your cardboard. Mark both perpendicular edges 5/16 out from the 3 side.
Draw a line connecting those two points.
Make a mark 1 1/4 from one end of the 3 pencil line.
Mark a little cross 1/4 out from the previous mark.
Use the curve to draw the airfoil shape. The curve must pass through the leading edge, the high point and the trailing edge, and the tangent at the high point must be parallel with the baseline.
Use the knife and the curve to cut along the airfoil. Make several shallow cuts, rather than trying to cut through in one pass. It is easier to make precise cuts with gentle pressure. The blade is kept tangent to the curve, so it will not cut into the curve. You will need to move the curve and make the cut in two arcs.
These are the four templates you will need to cut out the sheet parts. Make the fin and tailplane according to the dimensions given. Mark the centerline on the tailplane and punch pin holes 3/32 in from each end on the centerline. Mark a rudder hinge line 1/4 forward of the fin trailing edge. It starts 3/8 up from the base. Poke pin holes 3/32 down from the top of the hinge line and at the bottom corner of the rudder.
It is a good idea to store the templates in a labeled envelope, so they dont get misplaced.
Place a plate over the cutting board, locate the tailplane template in the flat area of the plate and cut around the template. The foam is soft, little pressure is required to cut through it. Keep the face of the blade flat on the edge of the template and draw the knife slowly, just like drawing a line with a pencil.
Push a pin through the holes which mark the ends of the centerline to make holes through the tailplane. These holes will help align the tailplane with the center of the stick.
Place the fin template on the remaining flat area of the plate with its trailing edge aligned along the cut of the tailplane trailing edge. Cut around the fin template. You get two parts from one plate.
When the fin is free from the surrounding foam, punch the two holes that mark the rudder hinge line.
Place the fin on a block with the holes marking the rudder hinge line aligned over the edge. Press the rudder down, forming a crease on the rudder hinge line. The rudder should be bent toward the right side of the fin.
Like this. We will adjust the exact amount of rudder deflection in the field during flight tests.
Now place the wing panel template in the flat part of another plate and cut around it, as before. This will be a wing tip, with one straight edge and one curved edge. The straight edge will be the outer tip, the curved edge will be where this tip panel joins the center wing panel. This curve must be cut very precisely. We must be careful to keep track of the orientation of these panels; leading edge/trailing edge, upper surface/lower surface. They must be properly oriented when they go together to form the wing.
Align the leading edges of the template and the wing panel, with the template offset a bit to the inside of the wing tip, and transfer the marks for the positions of the creases onto the wing panel.
The crease marks are on the under surface of the wing. That and the position of the curved edge tells us that this is going to be the right wing tip. Put an R in the corner near the leading edge and the curved end.
Flip the template over, place it in the flat part of another plate and repeat the process of cutting out a wing panel. Pay attention to which edge is the leading edge. I marked it on the plate before cutting it out.
Repeat the process of marking crease locations on both edges and put an L in the corner near the leading edge and the curved end.
The center panel is next. This requires curved edges onends. Place the template in the center of another plate and mark the centerline position on the plate.
Punch holes through the foam to mark the centerline on the foam wing.
Cut along the leading edge, the curved end and the trailing edge, but
Flip the pattern over, aligning the leading and trailing edges of the template with the leading and trailing edges of the wing panel, and aligning the centerline holes in the template with the centerline marks on the plate, and cut along the curved end. Be sure the curves are oriented in the same way, so the leading edges of both ends correspond.
Mark the crease locations on both ends of the center panel.
That completes the cutting out of the foam parts.
Place a block of wood (or a stiff ruler) on the wing panel, with an edge aligned with corresponding crease marks.
Press the edge of the block against the table, creasing the foam. Be careful to not crease the foam along the
Make creases between all six pairs of marks.
Shape the curve with your fingers until it fits the rib pattern. (This is where that seventh crease helps the aft portion conform to the rib curve.)
Another way to do this is to place the wing panel on a piece of paper, align the edge of a block or ruler with the corresponding crease marks, and pull the paper up. You must press down firmly on the block to keep the paper from slipping out.
With the wing panels aligned side to side, we see that there is a tapered gap between them.
This curved gore allows the tip panels to be raised up, forming the dihedral angles in the wing. Raising the tips closes the gaps so the panels may be glued together.
If you are a hero, you can spread glue on the edge of one panel, bring the leading and trailing edges of adjacent panels together, bring the high points together and hold the panels in place as the glue dries. Watching glue dry is not one of the more exciting things to do in life.
Cut out six, plus a couple extra, pieces of tape, 1/4 x 1/2. The roll of tape is divided by placing a razor blade on top of a 1/2 high spacer and rotating the roll against the point of the blade.
Place bits of tape extending off a curved end at the leading and trailing edges. Press the tape down firmly.
Spread a bead of glue along the curved edge of the adjoining wing panel.
Bring the two edges together and slide them back and forth to spread glue uniformly over both pieces.
Carefully align the trailing edges, butt the ends firmly against each other and back up the second panel with a block of wood.
Push the tape across the join and press it firmly onto the other panel, against the block of wood.
Press a piece of tape firmly to one panel between the 50% and 60% marks.
Carefully align all the intermediate panels so their edges are firmly butted against each other. Put a block behind the other panel, push the tape across the joint and press it firmly in place on the other panel.
A bead of glue is run along the top of the joint and smoothed out with a wet finger tip. Gaps in the underside of the joint can be filled by wiping glue across the joint.
Do the same with the other wing panel. Set the wing on blocks in an out of the way place and let the glue dry.
I had already cut all the sticks to length. Measure, mark and cut in the miter box with the razor saw. If you are planing to do a group build, you might want tocut parts in bulk.
Weight and balance are critical considerations with airplanes. We want the weight forward. Mark the midpoint 8 along the 16 length of the stick. (7 1/2 if you use a 15 stick.)
Balance the stick at its midpoint on the edge of the ruler. The heavy end will go down.
Mark the heavy end. This will be the front end where the propeller goes. The tail goes on the back end. The stick has a front end and a back end. It has a top and a bottom. The wing and fin go on top, the propeller bearing, tailplane and rear motor hook go on the bottom.
Mark 3/16 up from the bottom surface at the tail end of the 1/4 wide stick.
Mark 2 1/4 from the tail end along the under side of the stick.
Draw a line between these two marks.
Cut the 3/16 x 2 1/4 triangle off. This is waste. Cut into the waste, rather than into the stick. This cut will be finished with sandpaper, so leaving a little waste is better than cutting into the final part.
Place the stick on top of a block with the surface to be sanded extended a little over the edge. Back it up with a piece of hard 1/8 x 1/2 or similar. Place the edge of the sanding block flat on the table and gently sand down to the line. The sides of the stick are parallel with the table top, the sandpaper is perpendicular to the table top, so the sanded surface will be perpendicular to the side surfaces of the stick.
You can press the sanded surface to the table top to check that it is perpendicular.
Spread glue on the top of the nose bock. Just enough glue so the surface is shiny, but you can still see wood through it is right. I use wood glue for the wood joints.
Press the nose block to the under surface of the stick at the nose end. Align it carefully with the end and sides of the stick.
Check that the nose block and the tailplane taper are both on the same side of the stick.
Run a bead of glue along the tailplane taper.
Spread the glue uniformly across the entire surface.
Align the pinholes in the tailplane with the centerline of the stick and press it into place.
Press it in place. Set it aside in a safe place with a weight holding it down while the glue dries.
With a block of wood, align the flat edge of the rib template with the end of the 3 wide 1/16 balsa sheet. Cut along the curved top edge of the rib. Make several shallow cuts, rather than trying to cut through in one pass. It is easier to make precise cuts with gentle pressure. The blade is kept tangent to the template curve, so it will not cut into the template.
Cut inward at the edges. If you cut out across an edge, the wood will splinter. Make two of these.