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Old Apr 03, 2011, 05:10 PM
Mike Fields
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United States, CO, Arvada
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Zaic Thermic 72

I have always wanted to build a Thermic 72. My first flying plane was a Jetco Nordic A-2 Top Kick glider for FF towline. I pretty much destroyed it on the first tow. Several years later (OK, more than a decade later) I built a Marks Models Bird of Time which I flew competitively for a couple of years. When Dave Thornberg mentioned he had modeled the plane after Zaic's Thermics, I purchased the Zaic Glider Design Yearbook from Sig. Then I bought the whole Zaic Yearbook series and the die was pretty well cast to hook me on Old Timer designs. The year was 1983.
One of the first things you will find out is Jetco never kitted the original Thermic 72 as shown in the Zaic yearbook 3-views. The original had a pod and boom fuselage very similar to a Bowlus sailplane- the pod is below the boom and the wing and stab set on top of the boom. The span on the horizontal stab is given at 29" and the vertical stab is 7" tall and has a chord only slightly wider than the stab chord.
Being completely ignorant at first, I bought a Jetco Thermic 72 kit off of eBay and noticed immediately there were several discrepancies. The Jetco Thermic 72 I purchased had DT cutaway in the vertical stab and a rear-set horizontal stab like more modern Nordic towliners. The horizontal stab only had a 24" span as well. The pod was also faired into the wing- more like the Thermic 100- which isn't nearly as pretty as the 72. So then I ordered plans for the "early" version. The "early" Jetco version had the same stab dimensions but a much lower aspect ratio vertical stab, only 6" tall and much wider than the horizontal stab. The horizontal stab was also mounted midway on the vertical stab instead of flat on the boom as shown in the Yearbook. So after more searching I finally found a original set of prints for the Jasco version which was the same as the Yearbook.
Now the wings in all versions are the same, but the tail feathers are different in all three; although the horizontal stab is essentially the same in both Jetco versions. The boom itself is thicker and taller in the original Jasco version than the subsequent Jetco versions. The pod is different in the Jasco version (Bowlus type), but the same in both Jetco versions.
So I ended up scratch building the tail feathers per the original Thermic 72 plans and used the wing ribs for the wing from the kit. I also incorporated a rudder and elevator for RC use. The stab bolts onto the boom because the 29" span makes it a bit unwieldy for transport. I also widened the pod from 2" to 3" to make room for the servos.
The boom is built up from 3/32" square spruce and 1/32" aircraft ply sides so I would have a hollow boom to run the pushrods in. The boom is capped with balsa to build it out to the original Jasco dimensions.
The pod is framed out in 1/16" aircraft ply with a nominal 1/4" width and then planked with 1/4" x 1/8" balsa strips which are tapered and edge sanded to an angle so they fit properly. There are a couple of basswood blocks on either side of the plywood keel where the towhook will go. The bottom of the pod was glassed with 3/4 oz fiberglass to keep weeds from dinging up the fuselage.
I added three 1/16" square turbulator-type spars to the top of the ribs ala Lanzo style to help strengthen the wing and give it a bit more torsional rigidity. The wing is held on with rubber bands.
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Old Apr 03, 2011, 05:20 PM
Mike Fields
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United States, CO, Arvada
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Thermic 72 Continued

The covering for the Thermic is old-style Micafilm. Transparent yellow on the top of the wings and stab and transparent on the bottom surfaces.
Please forgive me- I haven't figured out all of the nuances of uploading pictures for these threads.
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Old Apr 03, 2011, 05:22 PM
Mike Fields
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More Thermic 72

Here are the last couple of photos showing half of the canopy and the servo layout.
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Old Apr 04, 2011, 09:59 AM
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wow - what a beauty!
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Old Apr 04, 2011, 11:38 AM
"Butchering Balsa since 1971"
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Joined Dec 2003
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That is gonna be one sweet bird, it's looking really nice. I have fond memories of Jetco products back in the early seventies, before I discovered cars and girls. My successful models were usually kits from, and in order
1. Jetco
2. Comet
3. Sig
4. Guillows

I like Jetco..miss 'em.
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Old Apr 04, 2011, 08:30 PM
Chad H Fly`n Farmer
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Nice work of art.

Where did you purchase the early version full size plans from?
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Old Apr 05, 2011, 08:43 PM
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Jetco

A buddy and I built two Jetco Thermic 50X gliders in one night.. stayed up all night and took out to fly next day..
Mine flew great, my buddy's plane for some reason kept nose diving into the dirt.. really strange..
We towed mine up really high on the last flight and released it..
It flew away.. never saw it again.. I hoped one day someone would call me.. I had laminated my name and phone number in it..
I live in OKC OK.. and it went south.. chased it forever jumping fences.. after jumping one fence looked up and it was no longer visible.
If anyone needs plans i have for most jetco and can make a copy at my cost and send you.
Doug
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Old Apr 05, 2011, 08:45 PM
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Thermic 72

Nice Job Mike,
I have two of those kits.. may build one soon.
I will be in Colorado in May would be a fun one to fly with micro servos.. dont want to loose another plane.
BTW. I built a thermic 50x last year and have hanging in my workout room.. will post a pic.
Doug
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Old Apr 05, 2011, 09:06 PM
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Jetco

Pics of the New Thermic 50X I built.. I lost the first one back in the 70's.. had to have another one.. makes me feel younger.
Doug
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Old Apr 05, 2011, 09:33 PM
Mike Fields
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United States, CO, Arvada
Joined Feb 2006
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Thanks for the nice comments!

Thanks for all of the nice comments, guys! I bought the plans from a guy on eBay. Usually I'm working for a firm with a print copier, but such is not the case right now. I'll dig around to see if I can find the guys email.
I bought a Thermic 72 kit from Bob Holman; bhplans.com. Awesome laser cut kit, modern spar structure and it includes the tailboom and pod parts. It is the early Jetco style with the mid-mounted horizontal stab on the vertical stab. This one will be built for free flight- there's just something about turning planes loose to do their thing that blows my skirt up, so to speak.
I included some poor pictures of the bird at a the Wings Over the Rockies show in Denver. The show is to expose the general public to the different modeling groups in the area.
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Old Apr 05, 2011, 09:34 PM
Mike Fields
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Very nice plane there, Doug! If you ever get tired of it...
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Old Apr 05, 2011, 09:54 PM
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50x

I love that plane.. I have 150CC planes I fly and I find myself picking it up on calm days and tossing it for short flights.
I like the old dope and silk we used to use.. this one needs another coat on the wings.
Going to try to get a Nordic done so when I am in CO I can toss it off a mountain with radio equip and fly.. just have to find a good place to do it.
Doug
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Old Apr 06, 2011, 02:35 AM
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Quote:
Originally Posted by CashRC View Post
That is gonna be one sweet bird, it's looking really nice. I have fond memories of Jetco products back in the early seventies, before I discovered cars and girls. My successful models were usually kits from, and in order
1. Jetco
2. Comet
3. Sig
4. Guillows

I like Jetco..miss 'em.
I had a Jetco Talon Nordic glider years ago, it flew away. sniff..sob.
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Old Apr 07, 2011, 07:24 PM
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This is a great thread. I've always liked the Thermic series.
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Old Apr 08, 2011, 05:09 PM
Mike Fields
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United States, CO, Arvada
Joined Feb 2006
24 Posts
Quote:
Originally Posted by Chad H View Post
Nice work of art.

Where did you purchase the early version full size plans from?
A guy on eBay called Hollans- I think he is currently listing them for $19.95
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