About this Plan
Pentafly. Simple Jetex model. All-sheet design.
Note plan shows model sizes: 'Pentafly at 13 in span and 'Baby Pentafly' at 9in span for Jetex 50.
Quote: "Unusual and exciting free flight design for Jetex power. Distinguished for its easy building, unusual lines and to quote the author, snappy performance. A fun machine for expert/beginner. Pentafly, by Thomas Alden.
This unusual and modern looking aircraft is distinguished by easy structure and snappy flight performance. Featuring a spectacular climb and a good glide, durations from 20 seconds to 1 minute are possible. The all sheet structure goes together very quickly and is easily repaired in event of damage. The 'Baby Pentafly', powered by the Jetex 50, is a truly miniature power model, all the flying surfaces being constructed from 1 sheet of 1/32 x 3 x 36 in.
Although distinctive in appearance, the design was worked out in standard fashion. The stabilizer has adequate area and is set at -2° relative to the wing to assure longitudinal stability. Experimentation with dihedral angle and rudder area was done to obtain spiral stability (see book on model aerodynamics by DK Foote). The high engine mount position aids accessibility and gives a 'down-thrust' effect which helps prevent stalling under power.
The plan shows full size patterns for all parts. Use thinner stock for the small model. The balsa sheet employed for the wing and tail surfaces should be light and must be flat. Save the warped sheet for another plane. SIG 'contest balsa' is particularly recommended.
Begin by glueing short lengths of sheet edge to edge to make up the necessary widths. Use a metal straight edge to assist in cutting the parts. Note direction of wood grain. Be sure that the wing halves and rudders are identical. Sand the completed parts lightly with a fine sanding block. Pin the wing panels to the board, then glue the rudders to the wing halves at a 20° angle to the vertical, so that when the wing halves are raised to the 20° dihedral angle, the rudders will be vertical. Glue the wing halves together, then add the stabilizer. Taper the fuselage bottom where it contacts the wing so that the parts fit flush, then glue together. Finally, add the longitudinal braces under the wing. Make sure to use straight wood! The engine mount is a piece of plywood secured with glue and reinforced with thin plywood braces. I did not use any dope, but one well-plasticized coat may be used.
A small paper or celluloid tab is added to one rudder for turn adjustment. Test glide the model on a calm day when the grass is dry. Try to achieve a fast, straight glide, with a not too nose-high attitude. Use modeling clay for balance. Turn adjustments with a Jetex model are delicate, so don't try to obtain very much glide turn. Use one pellet for test flights. The ideal flight pattern is a moderate turn in the climb, as this will suppress stalling or looping tendencies. Too much turn will cause a spiral dive. Bring your glue tube for those easy repairs.
A couple of points on handling the Jetex motor. If the weather is cold, the fuse will often go out at the nozzle, because it is quenched by the cold metal. Use SIG dethermalizer fuse, a cigarette, or small torch to heat the nozzle before lighting the fuse. With a match you cannot do this because the heat cannot be directed. Another troublesome feature is the wait for the motor to cool after a flight. The solution is easy when you think of it; buy two motors. They are not expensive.
These models are very appealing to youngsters. Try one out on yours or the neighbors. They can build them too!"
Direct submission to Outerzone.
Update 02/07/2021: Added vectorPDF and CAD (dxf and dwg) versions of this plan, thanks to Valeria367.
Quote: "Hi, Steve and May. Good morning. Today, I want to share with all the Outerzone community my latest CAD redraw: the plan of Pentafly model (oz13131). As usual, I add the redraw in PDF format, and both vector CAD formats: DWG and DXF. Greetings, from your friend. Valeria367"
Supplementary file notes
VectorPDF plan tracing.
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