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Old Mar 09, 2014, 08:57 PM
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Nodd's Avatar
United States, CT, Fairfield
Joined Mar 2012
720 Posts
Build Log
Nodd's Great Planes Spectra



Back in the '80s I used to fly the heck out of my wooden rudder/elevator Gentle Lady. Wonderful little glider, would launch her from a high-start. Most flights were only a couple of minutes but once in a while I'd hook a thermal & it was game on. Since then I've flown all manner of sailplanes & I still enjoy thermal duration. Recently I've had a yearning to return to my roots & fly an old wooden two channel. My buddy Roger had an old beat up Spectra collecting dust so offered me the airframe. Okay so its not a Gentle Lady & it is electric powered (no high-start) but close enough.

So anyway after looking the airframe over & doing some surfing online I've decided I'd like to make a few modifications before slapping some electronics in her. The following is a record of my adventures with this fun little glider.

And before you guys start in with the comments, which I welcome by the way... I should mention that I'm not at all worried about maximizing performance or optimising handeling. This project is purely for the fun of tinkering with an old airframe. While I welcome advice you should know I'm a stubborn SoB & will invariably end up doing things my way anyway. I have a pretty clear idea of what I'd like to do here & I think you'll like what I have planned. And if not, then you can tell me "told you so" when she falls out of the sky. Enjoy...
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Old Mar 09, 2014, 08:58 PM
Build something.
Nodd's Avatar
United States, CT, Fairfield
Joined Mar 2012
720 Posts
The Wing
First thing is to remove the patchwork of old covering. There had to be four or five different brands of covering on there, this wing has been repaired that many times. A heat-gun helps release the covering, comes right off...



Now I've heard lots about how the Spectra is prone to tip-stalling. Folks have had success taming this beast by simply adding sheeting to the outer panels.

Mine are in pretty bad shape. The trailing edge is all sorts of warped-n-chewed up & sheeting her is not going to be as simple as slapping some 1/16" on there. So I've decided to rebuild them. First order of business is to cut off the old outer wing panels...



And seeing as I'm rebuilding these wing panels I figure I may as well take this opportunity to have some fun & do a little modding. Using the stock airfoil shape I drafted a new longer set of wing panels...



The new design will increase the wing-span from six feet to eight. I also decided to try using half-ribs instead of sheeting. Like sheeting these little riblets help maintain the airfoil shape between each main rib but at a fraction of the weight. No they're not as effective as sheeting but good enough for this old gal. So here's how the new wing panels might look...



And here's my template for cutting the ribs...



After printing my rip templates on regular 8" x 11 paper I use contact cement to glue those to my balsa. Then after rough cutting the ribs on a scroll-saw I use a belt sander to finalize the shape. Not as slick as laser-cut but a lot faster than hand cutting with a knife...



I'll cut the notches for the spar tomorrow & then we can start assembling these...

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Old Mar 10, 2014, 12:32 AM
Always room for one more!
chawkins's Avatar
United States, MI, Midland
Joined Jul 2012
252 Posts
Looks great so far, I really like the idea of extending the wing. Have you thought about spoilers? I have them in my Spectra, dont use them every time, but when needed I'm glad I have them.
Just curious, the rib templates, how did you get them on your computer? I am guessing you scanned the orginals?

Chris
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Old Mar 10, 2014, 11:51 AM
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United States, NY, Kingston
Joined Feb 2006
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in for the build
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Old Mar 10, 2014, 12:36 PM
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Nodd's Avatar
United States, CT, Fairfield
Joined Mar 2012
720 Posts
Quote:
Originally Posted by chawkins View Post
...Just curious, the rib templates, how did you get them on your computer?...
I took this photograph & imported that into my 2D CAD software (CorelDRAW). I then digitally traced the shape & used that to create my design...

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Old Mar 10, 2014, 06:14 PM
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United States, CT, Fairfield
Joined Mar 2012
720 Posts
Over on another forum I had a suggestion regarding turbulator strips & also concerns about extending the wingspan. Valid points, both. Here's my thinking on those...

Because I'd like to keep the tip panels light I'll not be using sheeting so we need some way to keep the covering from sagging between the ribs. Saggy covering is no good for the airfoil, no doubt. I've had a couple of people suggest turbulator strips...

Turbulator Strips


Sheeting or turbulator strips are not the only solutions however. There's also the half-ribs option. Much like turbulator strips these also help maintain the airfoil by supporting the covering between the main ribs. For this sailplane I'll be using half-ribs, one between each full-rib...

Half Ribs


Slapping an eight foot wing on an airframe made for six will affect its handling, no doubt. However I've run the numbers through my sailplane calculator & the horizontal stabilizer, while on the low end, does has sufficient area. The vertical stabilizer on the other hand will need to be enlarged a little. So with a slightly bigger rudder she should not wallow too badly.
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Old Mar 10, 2014, 09:44 PM
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Nodd's Avatar
United States, CT, Fairfield
Joined Mar 2012
720 Posts
Wing Assembly
I printed my CAD work on 8" x 11" paper, taped the sheets together & we have plans...



Started gluing the structure together...



This will have to do for the day...

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Old Mar 11, 2014, 10:36 AM
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Central California
Joined Jan 2010
990 Posts
Nodd,

I love watching your builds. I've learned a lot from them. I also like building and experimenting and your builds have inspired me to do a couple scratch builds and some pretty good kit bashing.

Keep up the great work. I'll be following along.

Eddie
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Old Mar 13, 2014, 11:37 PM
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Nodd's Avatar
United States, CT, Fairfield
Joined Mar 2012
720 Posts
Thanks Eddie. Yeah no doubt experimenting with this hobby can be a lot of fun. Even when things don't work out, you're still learning valuable stuff.

Sheer-Webs
I swear I'm not doing this just to make you guys crazy. Yes the grain in my sheer-webs is NOT vertical *shudder*. I've been over this again & again in my other build logs so I'd appreciate not having to wade through this topic again here. In a nutshell, I've discovered grain direction is not as critical as you'd think (please feel free to read up on the subject & form your own opinion, fascinating stuff). I do it this way simply because it's easier. Nuff said.

These outer wing panels are tapered so the sheer-webs are not all the same height. So to simplify production I cut a tapered strip of balsa based on the height of the spars...



I then cut each sheer-web to length...



Glue it in place & ta-da! it's the correct height...



I then took a closer look at the sheer-webbing in the wing center section & was horrified to find the webbing missing from these four bays. Now granted this wing has been repaired a gazillion times but as far as I can tell, there's no sign that sheer-webs were ever installed in these four bays. Very odd, I wonder what the story behind that was? Ran out of wood maybe? Geesh!...



Anyway I added sheer-webs to these missing bays (used vertical grain this time to match the existing webbing).

Half-Ribs
With the sheer-webs installed on both sides of the spar it was time to install my nifty little ribblets. I've always wanted to give these a try, liking the look of this...

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Last edited by Nodd; Mar 13, 2014 at 11:54 PM.
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Old Mar 14, 2014, 01:15 AM
A&P Mechanic
T_arvis's Avatar
United States, NC, Charlotte
Joined Feb 2004
151 Posts
I recently built one of these planes, and the instructions and the plans do not have sheer webbing in those spots you pointed out. I have no idea why, but that is how they designed it.
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Old Mar 14, 2014, 11:30 AM
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United States, CT, Fairfield
Joined Mar 2012
720 Posts
Now when you say there's no sheer-webbing in those spots do you mean just those four rib bays or along the entire wing-span? These four bays are only missing on my left wing panel. The right side has sheer-webs from root to tip. Very odd.
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Old Mar 14, 2014, 01:53 PM
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United States, NC, Charlotte
Joined Feb 2004
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It should be just the 4 bays on both wings.
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Old Mar 14, 2014, 04:54 PM
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Nodd's Avatar
United States, CT, Fairfield
Joined Mar 2012
720 Posts
Yeah that's really weird, wonder why on Earth they'd design it that way? *shrug*

Anyway my wing now has sheer-webbing on both sides of the spare from root to tip.
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Old Mar 20, 2014, 09:30 AM
Tim Lampe; Hobbico R&D
KRProton's Avatar
Champaign, IL
Joined Dec 2009
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Quote:
Originally Posted by Nodd View Post

Sheer-Webs
I swear I'm not doing this just to make you guys crazy. Yes the grain in my sheer-webs is NOT vertical *shudder*. I've been over this again & again in my other build logs so I'd appreciate not having to wade through this topic again here. In a nutshell, I've discovered grain direction is not as critical as you'd think (please feel free to read up on the subject & form your own opinion, fascinating stuff). I do it this way simply because it's easier. Nuff said.
I admire your sentiments Nodd about returning to your roots via the build in your thread. I had lots of good times on a couple of Gentle Lady's too (that doesn't quite sound right, but you know what I mean - the Carl Goldberg Gentle Lady).

I recall years ago we did some shear web grain direction testing here in Hobbico R&D and as best as I can remember, we found the same thing...the grain direction doesn't seem to have much effect either way.

Tim
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Old Mar 30, 2014, 10:27 PM
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Nodd's Avatar
United States, CT, Fairfield
Joined Mar 2012
720 Posts
Its been a couple of weeks, have been busy with other projects but I have made some progress...

Wing Rods
When I got this plane the six foot wing was one piece. Now that I've extended it some, there's no way that's going to fit in the family car. So this will be a three piece wing. The outer wing panels will be connected via wing rods. First thing to do was make some end ribs with matching holes...



I'm using a length of brass tube capped at both ends with some epoxy...



This prevents the glue (epoxy mixed with micro-balloons) from entering the tube...



Then on goes the end rib...



Once that's curred I added the outer wing panel. Note the brass tube protruding into the first rib-bay...



Setting up the dihedral...



Some scrap wood to help fill the space around the brass tube...



In goes the epoxy/micro balloons goop...



Added a plywood spar-cap to seal everything up. Note the hacksaw blades positioned between the end-ribs...



The hacksaw blades were there to create a gap just big enough to fit a... well... a hacksaw blade so I could cut the brass tube...



There we go, two perfectly aligned wing-rod tubes...



A short length of carbon-fiber rod & we're in business...



That's starting to look like a wing...

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