Isthmus Models Zephyr II build thread - RC Groups
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Jan 01, 2005, 02:45 PM
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chlee's Avatar

Isthmus Models Zephyr II build thread

Hi everyone,

Despite the popularity of DLGs, I enjoy flying built-up javelin-style HLGs. A simple hi-start made from a $2 pack of #84 rubber bands, monofilament line and red streamer can take these planes up to 100-150 ft without too much setup time. Because of the lower structural requirement, these balsa gliders can be built relatively light, which in turn allows tighter circling in small, low bubbles.

Mark Miller of Isthmus Models was kind enough to send me a beta kit for this model:
I totally dropped the ball and proceeded to build at a snail's pace. No longer!
I'm now waiting for some the wing sheeting glue to dry, so here's a build thread for everyone's viewing pleasure. Your comments and advice are welcome.

Also see this page for the Liftzone review by Paul Johnson:
I'll see if I can get anywhere close to his 7.5 oz.

- Chung

Here's the kit:
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Jan 01, 2005, 03:16 PM
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chlee's Avatar
(Approximate measurements)

Wing area: 358
Aspect ratio: 10
Airfoil thickness: 9.4% (modified S3014)
Equivalent dihedral angle: 12.5 degrees
Vertical tail volume: 0.017
Horizontal tail volume: 0.49

The fuselage builds in about three hours (less if you use CA throughout; I used aliphatic resin on many parts).

The fit of the lasercut parts is similar to most other lasercut kits.
When I put the fuselage sub-assemblies together, the nose block protruded slightly past the fuse sides (see below). This is of little consequence, because the nose is shaped and sanded anyway.
Last edited by chlee; Jan 02, 2005 at 10:29 PM.
Jan 03, 2005, 10:45 PM
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Mark Miller's Avatar
WooHoo! I love the smell of balsa shavings in the morning.

Last edited by Mark Miller; Jan 04, 2005 at 11:35 AM.
Jan 03, 2005, 11:13 PM
In the (inclined) loop
Originally Posted by Mark Miller
WooHoo! I live the smell of balsa shavings in the morning.

Pillow Stuffing! For sweet dreams!

Jan 06, 2005, 04:45 PM
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chlee's Avatar
Shaping the canopy and nose was quite satisfying. Just remove anything that doesn't look like an airplane...

Tail feathers and wing build!
The tail parts aren't sanded yet in these pictures. Mark seems to have carefully selected some hard B and C-grain balsa sticks for the tail. I tried to make the parts lighter by building them out of contest-grade wood--and found that they were ridiculously flimsy. So I chucked them, used the supplied wood, sanded/tapered the tail feathers razor thin.

Since the stabilizers are built up from sticks, you can easily adjust the tail size to your own preference.
I personally like more yaw damping, so I've built the tail with a vertical tail volume of 0.025 rather than 0.017. Obviously, if I end up with poor lateral handling qualities, I've nobody to blame but myself. I've attached the vertical stab with just a few of drops of thick CA, so that I can pull it out easily and compare it with the stock stabilizer.

Flight pictures coming up, as soon as: 1) I locate a USB cable to upload more pictures, and 2) the blasted sleet/snow/hail in Boston lets up.

Can't wait to get this thing in the air!

- Chung
Last edited by chlee; Jan 06, 2005 at 09:04 PM.
Jan 10, 2005, 06:22 PM
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chlee's Avatar
The build is finished.

Wing and tail feathers covered with 1.5 mil Doculam, fuse painted with a single coat of Minwax Polycrylic and blotted, and a small patch of 0.75 oz glass applied to the 'chin' with Polycrylic for dent-resistance.

GWS R-6P II Rx, 110 mAh NiCd battery, and HES 5.4 g servos yields an AUW of 7.8 oz. However, I still haven't hollowed out the solid balsa canopy, and this should reduce weight.

Still waiting on weather for a test flight. Stay tuned...
- Chung
Jan 11, 2005, 04:10 PM
WAA-08 Survivor
Griffin's Avatar
Very nice looking! This one is on the list to build. thanks for the comments and pics--looking forward to hearing about your first flights. -Steve
Jan 11, 2005, 04:26 PM
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pda4you's Avatar
Great job on the build! Let us know how you like it!
Jan 29, 2005, 05:43 PM
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well i just ordered one of these - how's it go? Mark is certainly a helpful vendor. Great stuff!
Jan 30, 2005, 07:48 PM
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chlee's Avatar

Unfortunately, I've still not had a chance to fly it between work and a huge snowstorm. Will update soon, hopefully.

Last edited by chlee; Jan 30, 2005 at 07:50 PM.
Jan 30, 2005, 10:58 PM
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thermite's Avatar
Beautiful bird! nice build, I like the finish, simple and light.

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