Mini Zephyr (oz12069)

About this Plan

Mini Zephyr. Radio control sport model for electric power. Wingspan 22 in. Wing area 110 sq in. Designed for the Astro Flight Firefly coreless motor with a 2 cell 250 mAh lipo pack.

Quote: "Steve, I have attached plans, photos, and article from Flying Models for a series of models based on the 1936 Abe Bergman Zephyr. I have published most of these in RC Groups. Jim Zare"

See Jim's Zephyr thread on RCGroups for more details at https://www.rcgroups.com/forums/showthread.php?3524...

Direct submission to Outerzone.

Quote: "Although over 70 years old in design, the Zephyr adapts well to today's small e-power. Mini Zephyr, by Jim Zare.

The original Zephyr (oz5583) was a 12-inch wing span rubber powered ROG model designed by Abe Bergman. It appeared in the December 1936 FLYING ACES and was revived in July 1979 Model Builder.

When I saw the plan I was intrigued with the elliptical wing and stabi-lizer planform. This is right out of the 1930's streamlined era and very appropriate for a nostalgic 21st century electric backyard flier.

Mini Zephyr was designed specifically for the Astro Firefly Coreless motor. This motor is a high precision 9-watt gear motor that is virtually silent in flight. The tiny 22-inch wing span Zephyr weighs in at a mere 3.5 ounces ready to fly. Powered by a two-cell 250 mAh Li-Po pack the Zephyr draws less than one amp and will fly for 20 to 25 minutes per charge. The Zephyr has some unique design features including:

• Flat-bottomed elliptical swept back wing
• Lightweight laminated fuselage for strength, easy R/C installation
• Unique method of mounting landing gear
• Laminated rudder and stab, with integral Mylar hinges
• Pull-pull control system
• Nifty simulated pilot and insignias using paper cutouts

The Zephyr is very easy to build in just a couple of evenings. It flies slowly, is rock steady in the air and is responsive to rudder. It has a great climb rate and will do loops and nice rudder rolls. It is fun to build and a joy to fly.

Construction: Wing: The wing uses an unusual swept back elliptical planform. Cut out the wing ribs, leading and trailing edges and other wing components from 3/32-inch balsa. Pin down the leading edges and trailing edges of the wing panels and glue the W-5 wing tips in place. I highly recommend using Great Planes Pro Wood Glue sandable white glue for building the wing. It is strong, light weight and very easy to sand.

Add the lower 3/32-inch square spar and ribs W-2, W-3 and W-4. You should bevel the front of ribs W-3 and W-4 to accept the leading edge reinforcement before you begin the assembly.

Next glue the W-6 shear webs in place. Finally add the W-1 ribs at the centers section making sure they are angled to match the shear web. At this point glue the top spar in place. Note that the top spar stops at rib W-4.

Soak the leading edge reinforcement (3/32-inch square x 20-5/8-inch balsa) in hot water for about five minutes and glue it to the leading edge bottom in front of the wing ribs with the wood glue.

When everything has dried, sand the leading edge and trailing edge to the profile shown on the side view and glue the two wing halves together using CyA or epoxy.

Wing covering: The wings of the original models were all covered with Solite - this is an acronym for Solarfilm Lite. This is a strong synthetic material, which is airtight, waterproof, and heat shrinkable. It is very light with a weight of .6 ounces per square yard. For the 110 square inches of the Zephyr wing this translates to about .101 ounces of total covering weight. I don't think you can cover a wing with tissue and match this weight and strength combination.

I have been able to cover both the top and bottom of the Zephyr wings with one piece of Solite each. Make sure that you are careful when heat shrinking this material because you can actually apply too much heat and shrink the material right off the leading or trailing edge.

The nice thing about iron-on covering is that you can correct warps or add washout after the fact. I have added about 1/8 inch of washout to the trailing edge at each tip on the Zephyr prototypes.

For indoor flying I have made a separate wing with only the top surface covered. This single surface airfoil really slows down the model for flying in small gyms.

Rudder and stabilizer: Many small models have 1/26-inch sheet balsa rudders and stabilizers with Scotch Crystal Clear tape for the hinges. This is quite effective and is very easy to build. However, I found that after a number of flying sessions the tape tends to loosen with a pull-pull system and the balsa often warps. The laminated control surfaces used in the Zephyr have embedded Mylar hinges that are designed to give reliable long term warp free service.

The Mylar is sold in 8-1/2 x 11 inch sheets and can be found in stores that provide materials for drafting and engineering repro-duction.

Begin by stacking two layers of 1/32-inch balsa and pin or tape them together while you cut out the fin, rudder, and stabilizer and elevator sections. Pin down the stabilizer and rudder over the plan and use thick cyanoacrylate to position the Mylar hinges. Make sure you leave a gap between the movable surfaces as shown on the plan. Hold each hinge in place with your fingers over a small piece of wax paper until it sets up..."

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