F1d 

How one gets built !

By Jim Longstreth and edited by Andrew Tagliafico/Portland, Oregon

Several years ago former F1d World Champion Bud Romak came to Portland, Oregon, at the request of a group of Northwest modelers and demonstrated his construction techniques for this most challenging category of competitive indoor models.  The seminar was hosted by Oregonian Dave Hagen at his home over a weekend.  During that time Bud Romak built a complete, flyable, F1d model.  I took the following series of photographs during that symposium.

For those not familiar with this type of indoor endurance model let me give a brief description here.  The term "F1d" refers to the FAI rule category.  I don't have the rule book in front of me, but basically the models weigh in at minimum of 1 gram and a maximum of 2 grams.  The wingspans are 65cm, or 25-1/2",  long and a chord of 8" to 10".  The propellors are 20" to 24" inches in diameter.  The flying surfaces and the propellor are covered with "microfilm", which will be described later.  The motor stick is a hollow tube of rolled balsa, and the model is braced with a superfine tungsten wire or kevlar fiber.  Some competitors have developed spring mechanisms operated by the torque of the rubber band motors to effect variable pitch propellors!

World Championships are held every 2 years.  Flights approaching 50 minutes are required to be competitive.  The Kibbie Dome at the University of Idaho, in Moscow, Idaho, is one of the favored US flying sites and is pictured below.  The balloons dotting the photo are used to steer the models at altitude in the event they are drifting into hazard.  There are several models aloft in this picture, but due to their transparent covering and almost non-existent structure they are nearly invisible.



An album of photographs from the 1996 F1d World Championships in Moscow, Idaho at the University of Idaho in the Kibbie Dome.


1996 F1d World Championships/Kibbie Dome-University of Idaho, Moscow Idaho (Photo Collage: Jim Longstreth)



F1d competitors and Models at the 1996 World Championships

     
2nd Place World Champion Cezar Banks                   F1d in holding stand

           
 F1d in Flight at Kibbie Dome                       Jake Palmer of Salem, Oregon/Sr. World Champ
 

 



Building an F1d 
as demonstrated by Bud Romak



 

Making Microfilm
 1.  Pouring Microfilm       
              Building and F1d starts with the making of the covering material called Microfilm.  A shallow tank of water is allowed to "cure"- for 12 or more hours allowing volatile chemicals to escape.  The ideal water temperature is between 68 to 74 degrees F.  The microfilm based on nitrate aircraft dope with plasticizers added.  There are commercial solutions available, and most of the competitors rely on their favorite of the two best film manufacturers.
 
          A small amount of the solution is poured out onto the surface of the water in one smooth, extended linear motion..  The solution spreads out on the surface of the water to a nearly mono molecular thickness.  It is allowed to "set" on the water's surface for several minutes.

2.  Microfilm Onto Holding Frames 
        In the photo above, the excess film around the frame is being gathered around the outside of the holding frame prior to the attempt to lift the holding frame off the surface of the tank.

 

        This is the point at which most would-be F1d flyers bail!  One needs at least 4 good frames of Microfilm to build a model.  And one needs at least 4 to 6 models to compete, not to mention 1 or 2 dozen props of various diameters and pitches.

          The proper thickness of the Microfilm is judged by the colors it refracts.  "Good" film is in the blue to gold range.  The tricky part of transferring the film to the holding frame is the breaking of the surface tension of the water.  Breaking that surface tension without tearing the film is a challenge.  But once you have successfully lifted some frames, you then set it aside to "cure".
          There is much debate in this field as to just how long to "cure" the microfilm.  In this demonstration the film was allowed only a few hours before it was put on the model.  It seemed to work fine at the time but did warp badly later on.  It is always best to have an aged supply of film on hand.  A year of "curing" is not too long.


Construction of the F1d Model

3.    Forming Curved Pieces
  

          Construction of these delicate models requires thin cardboard or sheetwood patterns and templates of the flying surface outlines.  The wood for wing spars is about .030" thick so it is quite flexible, particularly when wetted and formed around a template, as in the first photo.  After the wood has dried and the curve has set, the second photo above shows the placement of the curved elevator outline around the building template.  The slots in the template are for the placement of the 3 ribs in the horizontal stabilizer.
 

   The stabilizer outline is formed in 2 pieces.  Bud is adding second outline piece.  They are spliced in the middle, and then the ribs are added.  Just like any indoor endurance model, the ribs are sliced in slender curves using a template and glued in place on the structure.

Note: Bud built each flying surface and then covered it.  My photos show that progression, though one could build and cover in any sort of sequence your personal building habits dictate.

4.   Applying Microfilm 
      
 
        In the first of the 2 photos above, Bud is applying water to the stabilizer structure.  Water is a fine adhesive for Microfilm.  As the water dries it pulls the film into the pores of the wood.  In the second picture, he has simply placed a holding frame with Microfilm over the stabilizer structure right on the building board.

 
T
he covered stabilizer is removed from under the film on the holding frame by running a hot wire, just to the outside of the covered structure.  The finished stabilizer is then VERY CAREFULLY set aside in a safe place.  I noticed that Bud used a thin knife blade to lift the piece off the board and carried the finished stabilizer in the flat of his hand.

        Once touched the Microfilm will have a hole.  Indeed it seemed impossible that one could build such a model without making holes, and that was the case.  The model had several patches in it by the time it was finished.

5.  Rolling Motor Tubes and Tail Booms
   
         The motor tube and tail booms are rolled not unlike a cigarette.  The motor boom is cylindrical whereas the tail boom is a slender cone.  Sheets of balsa about .013" thick are used to fabricate the motor stick.  After a 10 minute soak in water the sheet of wood is rolled onto a 1/4" round x 18" long form or mandrel.

        In the first photo, Bud has laid the mandrel, a piece of aluminum tubing of appropriate length on a length of silkspan.  He has rolled a little of the silkspan around the mandrel and is wetting the silkspan, a model tissue covering material.

        In the second photo, the sheet of wood for the motor boom has been tightly rolled over the mandrel, between it and the wet silkspan.  There is sufficient wet silkspan to hold all in place while drying.

        The next 2 photos show the same process, but for the tail boom.  As this structure is a tapered shape it pivots, when rolled, around the thinner tip portion.  Hence the different position of Bud's hands in these last 2 pictures from the first.

6.  Assembling the Tube and Booms 

       The motor tubes and tail booms need to have the seam edges glued together.  The silkspan has been removed, and the balsa placed back around the mandrel.  The seams often dry off center.
        Before gluing the seam must be straightened.  Bud has done this and is gluing the seam.

                   
Here, in these 2 pictures, the 1990 US F1d Team Manager, Andrew Tagliafico, demonstrates the use of jigs for aligning and gluing the seams to the rolled balsa forms used on F1d models.

7.  Building and Covering the Main Wing
  
The Main Wing is built in much the same way as the stabilizer, but with a series of short pieces of 1/16th balsa instead of a  template to provide a backstop for pinning the wood forming the wing structure in place.   The building board Bud is using has the drawn outline of the Main Wing on it.  The wing is basically rectilinear in outline, save for a slight rounding of the forward edge of the wing tip.  This was done by wetting the wood and then bending it directly over a hot light bulb.  The heat of the lamp evaporated the moisture and set the curve in one motion.

 
W
hen the wing is finished, it is weighed.  All the parts of the model have been weighed as construction progressed.  It is critical that the sum of the parts weigh as close to 1 gram as is humanly possible.

      

          Once more the finished wing frame is wetted and the Microfilm laid over the structure.  Note that the wing is still flat.  The dihedral is added to the wing and tips after the covering, and before the rigging.
        The finished wing is set in a holding jig prior to rigging. 

Note:  The sequence of rigging was not photographed due to the fact that the wire or fibers are virtually invisible.  There are drawings of the rigging of F1d models in the books listed in the bibliography.

8.  Building and covering the Propellor
        The propellor is both the source of thrust and a flying surface.  It is built in just the same manner as the wing or stabilizer, but with the added complication of the pitch.  To ensure proper pitch and alignments, the prop form is a series of protractors made of balsa.  After doing the pitch calculations for a particular diameter/pitch configurations, the protractors are adjusted and secured.  The prop spar is laid on the protractor centerlines.  The outline of the prop blade has been formed on a jig like the stabilizer.  This outline is pinned in place on the protractor prop form.  The ribs are then attached at each protractor station.

                
        In the first photo, you can see the curve of the helical pitch the protractors form.  In the second photo you can see how each blade is covered with Microfilm.  Unlike the other flying surfaces the prop is applied to the film in an angular, rotational, motion.  This is necessary due to the changing surface curvature of the prop blades.  The Microfilm on the holding frame is divided into sections with masking tape.  This allows for the preservation of the rest of the film on the frame, and thus the covering of several blades.


Test Flights!

9. 
 

N
ote the extra holding frames of Microfilm resting on the fireplace.  You can see something of their refractive colors.  Also, I didn't photograph the construction of the rudder.  It has no airfoil, and is no different in construction from the other pieces.  The prop is held in place at the front of the motor stick by a hand formed wire thrust bearing.  The rudder and elevator are glued in place and braced with the ultra-thin tungsten wire mentioned earlier.  The main wing is removable, and fits into paper tube sockets glued into the motor stick.

10. Handling an F1d  

Andrew Tagliafico's F1d in a holding stand

   
Lew Gitlow walks VERY SLOWLY with his F1d!                 His F1d in flight

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