Foam Dinner Plate Free Flight Model FDP-15

FDP-15 Free Flight Plans  <---Click to Open 

Summer is back in much of the country.  Long summer evenings usher in more chances to go fly, and more opportunities to introduce kids to the joy of building and flying things!  Free Flight is a great and easy way to introduce the fundamentals of flight.  This simple flier can be built in under an hour, and will easily do over a minute in still air.  With thermal help, newcomers can watch it disappear into a cloud which can be a life changing experience! I still remember losing my first model in a thermal over thirty years ago, and I have been hooked on building ever since!

Quick Introduction: My name is Jim Buxton, and this is my first article for Flite Test, but I have been building and flying since I was four years old.  I started flying Control Line when I was four, and have flown everything from Control Line speed to F1D (Indoor Free Flight Duration).  I have flown outdoor Rubber in Poland for the USA Junior Free Flight team in 1988, and set a few National and International Indoor Hand Launched Glider records along the way as well.  Currently R/C (and raising my children) gets most of my attention, but I recently revisited the joys of flying small Free Flight models under the lights of a parking lot after dark.  It was like reliving my childhood!  This model is perfect for such activities and can be built very easily.  There is something very rewardng about watching someting you built with your own hands beat the odds off gravity in silent lazy circles.

Construction Materials:

• The foam dinner plates are 8-7/8", and make up the flying surfaces of the model.
• Fuselage is sliced from a hard sheet of 1/8" balsa.
• A piece of 1/32" music wire, a pin, or even a paperclip can be used for the rear motor hook.
• Some scrap foamboard with paper removed for the outer ribs
• A 5-1/2" North Pacific style prop with nose piece is needed.  These can be purchased for a dollar with some other specialty supplies from many vendors.  I got mine here:
  http://volareproducts.com/BUY/index.php?main_page=product_info&cPath=56_42_49&products_id=216
• Print the plans located at the top of the article.  If you do not have access to an 11"X17" printer, the templates can be printed full sise on an 8.5" X 11" (letter) paper on page two.

Create Templates:

• It is best to mount the paper outlines to some thin cardboard to make them easier to trace.  I like to use old cereal boxes.  Ths one happens to be Raisin Bran:)
• Use spray glue or even glue stick to attach the sheet to the box, then cut out with scissors or a razor blade and a straight edge.
• Use an awl or a small drill bit (1/16"-ish) to make holes to mark centerlines and crease lines on the parts.
• Sanding is good therapy.  I sand my templates straight if I cut with scissors.  Straight templates make straight models.

Prepare Foam Plates:

• Much like balsa, foam has a grain.  By grain I mean it has a strong axis and a weak axis that are perpendicualr to each other. 
• The photo above shows two identical trimmed plates with the strong axis spanning the supports on the left.
• The grain direction can be easily determined by simply flexing the plate once the raised rim of the plate is removed.
• Cut out the plate to leave only the flat center area and flex it in various rotations until you feel the most resistance, this is the strong axis.. 
• Note the strong axis and lay out the surfaces so the strong axis is length-wise, to act as a spar.

Trace Templates on Foam:

• Trace each template onto the foam plate centers.  Four plates will be needed.
• Mark center lines and bend lines with dots as shown above.
• Parts can be cut out with scissors, or a razor blade/exacto knife and a straight edge.  
• Blades makes cleaner cuts, but for kids scissors work just fine.  Added bonus: Teach them the joys of sanding!

Decorations:

• The joy of building models is in making them unique.  I like to design or decorate so I know that no other model exists just the same as mine.
• Sharpie markers, and acrylic paints work great on foam.  For this simple model some free advertising seemed perfect.

Bend Lines:

• Simple scored bend lines create a basic airfoil that really strengthens the wing (by adding depth) and improving performance.
• Use a staight edge to lighty score the bottom of each wing and bend up *almost* 90 degrees.  The outside radius of the bend may crack a slight bit, this is OK.

• After folding you can see the airfoil is preshaped to match the ribs of the model.
• Shown above is the center rib, which is balsa as it creates a strong joint between the wooden fuselage and the wing.
• Tip ribs can be made from foam board, without paper attached.

Wing Assembly:

• The wing and all foam parts can be assembled wiht FOAM SAFE CA or hot glue.
• When using hot glue, go sparingly with the glue, glue is heavy!
• Glue the wooden center rib to the wing center section first.
• Next glue the dihedral ribs to the center section, as seen above.
• Allow half of the thickness of the dihedral rib to extend beyond the center section.  This makes installing the tips easier.

• Glue the tips to the center section after ribs are installed.
• The wing tips should have 2" of dihedral, use a scrap of foam or block 2" tall under tip when assembling.

Fuselage Construction:

• The fuselage is cut from a medium hard piece (10-15 Lb/Cu') of 1/8" X 3X 36" balsa.
• To calculate the density of a sheet, weigh the sheet and look here: http://www.nclra.org/Programs/BalsaDensity.php
• The Master Airscrew balsa stripper shown above is great for this (and cutting strips of foam board!).
• A sharp single edged razor blade or X-Acto knife and a straight edge will also work.
• Be sure to cut or sand the bevel on the bottom rear of the fuselage.  This provides the wing/tail angle of incidence critical for stable flight.
• Cut a scap of the same 1/8" balsa sheet for the rear hook gusset and spacer to make the nose bearing fit snug.
• Bend the rear hook from wire.
• Once parts are complete they can be assembled with CA as show below.

Final Assembly:

• First glue the wing to the fuselage, with the leading edge 3.25" back from the nose.  If you used a wooden center rib, any CA can be used.
• Next use FOAM SAFE CA or hot glue glue to attach the stabilizer to the beveled lower portion of the fuselage.
• When viewed front the rear the stabilizer should be higher on the left side by about 1/4".  This will help the model circle left during glide.
• Install the rudder on the left side of the fuselage, also touching the top op the stabilzer.  This makes for a strong and straight rudder joint.

Congratulations!
You are the proud builder of a free flight rubber powered airplane!  The next step is to get some power for it.  The best rubber strip for this is FAI Super Sport rubber.  It is available along with rubber winders and lubricant to allow more turns from Volare Products as well.  1/8" Super Sport is the strip you want to get: http://volareproducts.com/BUY/index.php?main_page=product_info&cPath=77_37&products_id=117

Winding can be done by hand, but a 5:1 or 15:1 winder is a good inverstment and will certainly make the flying more enjoyable.  A little rubber lube helps the rubber motor take more turns.  There are several choices in winder and lube on the Volare Products website.

Flying:
After assembly give the model a good look from the front.  Make sure there are no warps and that all surfaces are nice and straight without any twists. Make 13" loop rubber motor from the rubber strip.  This is done as shown in the following photographs.

1. Holding loose ends together, tie an overhand knot.
2. Tighten the overhand knot, leaving about 1" of loose ends, then tie a half knot behind it.
3. Tighten the half knot up to the overhand knot, and trim the ends to about 1/8" long.

• Once the rubber motor is made and lubed, install it on the model.
• Check the Center of Gravity against the plans.  You should need a little dab of clay on the nose to get it forward enough.
• Test glide the model with no turns in the motor.  Look for a smooth left hand glide circle.  If it stalls add a little clay.  Bend the rudder a tad to the left to tighten the turn if needed.
• Begin powered test flights with about 200 turns in the motor.
• Increase turns and look for a right hand circle under power.  If the turn is not tight enough and the model stalls under power, bend the nylon nose bearing to the right to add more right thrust.
• Work your way up to 1000 turns in a 13" motor for 90 second flights on calm evenings.
• Shown below is everything needed for a fun filled evening of flying:  15:1 winder, Some FAI Super Sport 1/8" rubber strip, FAI SIL-SLICK lube, and the FDP-15.

Have fun with your new model!  Go ahead and experiment with different wing shapes, longer wing spans, biplanes and triplanes!  I would love to hear from those that build this model and will be glad to answer any questions.  Look for the FDP-15 thread in the Forum.