Donna’s Dragonfly

In Uncategorized on April 25, 2013 by nicholasandrewray

Donna’s Dragonfly

By Yuan Kang Lee

Donnas Dragonfly Plan 2013 copy

Bottom Page DD copyClick here to download a copy of Kang’s plan.

I have tried to push the limits of flying very light EZB’s.  My two-time nationals winning EZB, “BS 6”, weighs 340 mg.  I tell people that that’s less than the weight of a Monarch Butterfly.   Larry Coslick, Jim Richmond, and Max Zaluska have all successfully flown lightweight EZB’s.  But this quest to further test the limits of the EZB was not finished — it had been on my mind for some time to take the weight down to yet another level.

The key to reducing significant weight is to take a lot of weight from a couple of key areas and a little bit of weight from a lot of different areas.  For this ultra light EZB, a lot of weight was reduced from the motor stick and the wing, and a little bit of weight was taken from everywhere else, including the boom, stab, prop, and wing posts.    The finished motor stick (with bearing, hook, and posts), at 61 mg, is extremely light.  So is the wing, at 67 mg.  I also made sure to use a minimum amount of glue throughout.

Building this light model required about 20 hours in total, with a lot of the time spent under magnification.  By comparison, a typical lightweight EZB takes me about 5 hours.  Much time was spent carefully cutting wood, all done free hand using a scalpel and straight edge.   All wing and stab spars, including the tips, were tapered to save weight.  Further adding to the build time was that many of the components took two or three iterations.  I was really tired when I finally finished the model after three days.  I felt the strain of working under magnification and handling very small components.

The finished model weighed 238 mg and was outfitted with a relatively beefy motor stick.   In my living room, I repeatedly launched the model under high torque, and it launched well every time.  I did not doubt that this model could reach the highest ceilings.

Fast forward to the 2012 Labor Day weekend at Lakehurst, New Jersey.  It was around 7:15 pm and getting dark inside Hangar 1.   The model launched without fuss and climbed steadily, reaching its peak in about 10 minutes.  My lucky charm, Rob Romash, was on the clock.  Brett Sanborn and John Kagan were also on hand to give moral support.  We took turns with the flashlight to keep the model in sight.   It was too dark to determine the peak height of the model, but I think it was 170’, 5’ below the ceiling.  It stayed at its peak for a very long time.   With a very slow descent, it broke the previous record of 35:01 at around 30 feet.  It finally landed at 37:48, after an uneventful, yet thrilling, no-touch, no-steer flight.

The motor was 7/99 (not 5/99) Tan II, 10.6” long, and weighed 0.275g.  The rubber width was approximately .022”.  It was gently wound to .085 in-oz and 2700 turns.  (Breaking torque and turns are estimated to be .115 in-oz and 3000 turns.)  I backed off 100 turns and launched the model at .045 in-oz.  140 turns remained at the end of the flight.  Average flight RPM was 65.1.

All the balsa on this model came from A2Z, with the exception of the prop wood from Jeff Hood.  The Y2K2 film used to keep the flying surfaces light was generously given by Mark Bennett.  Finally, the 7/99 Tan II rubber, although not super like 5/99, was good enough.  It was purchased from the estate of the late Fred Behrenberg, an indoor flier from the Philadelphia area.  Fred — thanks for keeping the rubber in good shape all those years.

I named this ultra light EZB “Donna’s Dragonfly”, or “DDF”, after my late sister-in-law, Donna.  She often admired how my EZB would fly in our living room and remarked that it looked like a big, floating dragonfly.

“Donna’s Dragonfly” EZB by Yuan Kang Lee

DD Table
















Editor’s Note: This plan was drawn by Nick Aikman who generously donated his time to the project. He worked closely with Kang to insure the accuracy of the plan.

Donna's Dragonfly at Lakehurst, NJ

Donna’s Dragonfly at Lakehurst, NJ

DDF Lakehurst 2

Donna’s Dragonfly at Lakehurst, NJ

DDF Lakehurst 3

Donna’s Dragonfly at Lakehurst, NJ

One Response to “Donna’s Dragonfly”

  1. How much lighter can you expect to go with EZBs?

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