Covering Props
An article from Larry Coslick & Steve Gardner,
in Indoor News and Views (INAV)
A neat easy way to cover built-up Propellers with plastic or microfilm
The following method is based on the one developed by Larry Coslick and myself for covering props with the new Y2K film It is applicable to any other covering material including microfilm and any sized prop. It has the double advantage of being very easy and working really well.
First build the basic jig base for the size props you are going to cover. Larger jigs may be used for smaller props with a bitof care, but of course smaller Jigs are no good for the larger props, so unless you build a bunch of those little ROGs start with a large jig. See the drawings.
Next, build a pair of covering frames. These are made from 1/8 X 1/4 firm balsa strips of the appropriate length joined by 1/16 dia aluminum tubing at each end. The ends of the aluminum tubes are flattened and
Aluminum tubing is bent about ¼" to form the cylindrical shape so that the covering has the proper slack and curve for following the prop twist.
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Covering is attached to the frame with Prang brand glue pen. This allows minor adjustment of the film position and tension Film is trimmed away from the aluminum tubing at the ends of the frame |
glued into holes drilled into the balsa strips. This aluminum tubing allows the frames to be bent to shape after the covering material is applied
Once the two frames are built and are covered with film the tubes are bent into arcs so as to allow the covering material to take the shape of a section of a cylinder. The covering material is then cut free from the tubing with a hot soldering iron. For microfilm a small length of thread is glued to the tip of the propeller and to the aluminum tube nearest the prop tip. This thread prevents the film from tearing when most of the film has been trimmed around the prop outline.
Before you can spray the prop with the 77 Sprayment glue you must take a Length of masking tape 1/8 wide and cover the prop spar so that the covering material will not adhere to it. Drafting tape or other very low tack tape is good here to prevent trouble getting this tape off of the prop without damaging it. Once the prop has the glue sprayed onto it remove the tape and it is ready to place on the film. Have a 1" bit of the same low tack tape ready before you proceed
Position the prop at the classic 15-degree angle so that the twist of the blade matches the curve of the covering on the frame. The prop is placed by putting the hub at the hook onto the tubing and rocking the prop down onto the film. Carefully position the prop so the leading and trailing edges meet the film at the same time. Once the prop is in contact with the film lake the bit of tape mentioned before and tape the hub to the tubing of the frame. Now the prop and film are held at one end by the tape and the other by the length of thread (for microfilm only). Gently push the prop outline down onto the covering, or reach underneath the frame and lift the covering up to the outline as needed to get the outline attached to the film everywhere.
Once the outline is attached to the film everywhere you can trim the film around the prop. The thread will prevent the prop moving and tearing the microfilm once most of the outline is cut free, and in the case of plastic film, leave the very tip of the prop until last when trimming. Remember to remove the tape at the hub before trying to lift the prop from the frame.
