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-   -   Nodd's Great Planes Spectra (http://www.Wattflyer.com/forums/showthread.php?t=73323)

Nodd 03-10-2014 03:01 AM

Nodd's Great Planes Spectra
 
http://www.scipie.com/rc/spectra/gre...tra_splash.jpg

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 handling. 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...

Nodd 03-10-2014 03:01 AM

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...

http://www.scipie.com/rc/spectra/IMG_0280.jpg

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...

http://www.scipie.com/rc/spectra/IMG_0282.jpg

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...

http://www.scipie.com/rc/spectra/IMG_0284.jpg

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...

http://www.scipie.com/rc/spectra/spectra_cad_003.jpg

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

http://www.scipie.com/rc/spectra/spectra_cad_004.jpg

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...

http://www.scipie.com/rc/spectra/IMG_0329.jpg

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

http://www.scipie.com/rc/spectra/IMG_0330.jpg

kyleservicetech 03-10-2014 03:32 AM

Quote:

Originally Posted by Nodd (Post 942111)
The Wing


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.

For my sailplanes in the mid 1980's the plans called for a bit of washout in the wing tips to reduce tipstalling. My feeble memory suggests it was a degree or two of wash-out.

Nodd 03-10-2014 03:45 AM

Yes washout is a given on these planes.

Apparently even with washout this plane is somewhat of a tip-stalling bugger. But I'm totally redesigning the outer wing panel, different shape, less sagging of the covering etc. I don't expect any weirdness like the stock version suffered. We'll see though.

CHELLIE 03-10-2014 06:00 AM

Quote:

Originally Posted by Nodd (Post 942110)
http://www.scipie.com/rc/spectra/gre...tra_splash.jpg

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 handling. 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...

Dont Feel Like The Lone Ranger Nodd :D You have Lots of Company Here :D So Am I :Q :Q :Q LOL

Neet Project :$ Subcribed ;-)

Yakfishingfool 03-10-2014 12:20 PM

cant wait to see the results!

thepiper92 03-10-2014 03:14 PM

I enjoy your builds Nodd, you have such an attention to detail, especially for reinforcing weaker areas of the planes.

tobydogs 03-10-2014 05:12 PM

[popcorn]subscribed.

Nodd 03-11-2014 12:20 AM

Nice to see some interest in this project. I think we're going to have some fun with this.

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
http://www.scipie.com/rc/spectra/turbulators.jpg

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
http://www.scipie.com/rc/spectra/half_ribs.jpg

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.

Nodd 03-11-2014 03:43 AM

Wing Assembly
I printed my CAD work on 8" x 11" paper, taped the sheets together & we have plans...

http://www.scipie.com/rc/spectra/IMG_0333.jpg

Started gluing the structure together...

http://www.scipie.com/rc/spectra/IMG_0335.jpg

This will have to do for the day...

http://www.scipie.com/rc/spectra/IMG_0338.jpg

Nodd 03-14-2014 05:38 AM

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...

http://www.scipie.com/rc/spectra/IMG_0345.jpg

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

http://www.scipie.com/rc/spectra/IMG_0346.jpg

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

http://www.scipie.com/rc/spectra/IMG_0350.jpg

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!...

http://www.scipie.com/rc/spectra/IMG_0352.jpg

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...

http://www.scipie.com/rc/spectra/IMG_0357.jpg

thepiper92 03-14-2014 06:38 AM

Wow, I hope my building can look this nice at some point. What blade do you use, I find mine are not easy to cut against the grain.

Yakfishingfool 03-14-2014 12:00 PM

Nodd, won't lateral grained sheer webbing induce a severe irreparable twist in the wing resulting in a permant tendency for left wing tip stalls at speeds below average temp plus barometric pressure minus windchill? ;) Looking great so far! Very jealous of your mad building skillz!!!

BroncoSquid 03-14-2014 03:49 PM

Quote:

Originally Posted by Nodd (Post 942492)
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!...

http://www.scipie.com/rc/spectra/IMG_0352.jpg

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

NODD, I had a Great Planes Spirit that had optional spoilers you could install in the top of the wing that were about that long, and about that location. (been 15 years or so:()

Oh, wait. After a closer look, never mind. You are right, it makes no sence. I thought the missing webbing was on the trailing edge at first. Disregard.

riverrat 03-14-2014 03:54 PM

Subscribed!

Nodd 03-14-2014 05:56 PM

Quote:

Originally Posted by thepiper92 (Post 942496)
...What blade do you use, I find mine are not easy to cut against the grain...

I use a standard #11 x-acto blade. I find that fresh blades don't stay sharp very long. The tip tends to break off almost immediately. However I don't keep swapping them out for new ones like most folks suggest. Instead I have a $10 kitchen knife sharpener doohickey that helps keeps them sharp for months. Even with a good edge on the blade it takes several passes to cut cross-grain & you need to take care when exiting the wood's edge so as not to split the wood.

Quote:

Originally Posted by Yakfishingfool (Post 942504)
Nodd, won't lateral grained sheer webbing induce a severe irreparable twist in the wing resulting in a permant tendency for left wing tip stalls at speeds below average temp plus barometric pressure minus windchill?...

You forgot the moon's tidal influence on the webbing :roll:

Quote:

Originally Posted by BroncoSquid (Post 942523)
...I had a Great Planes Spirit that had optional spoilers you could install in the top of the wing that were about that long, and about that location...

I'd accept some logical explanation like that if these sheer-webs were missing from both sides of the wing but there's a full set on the right half. A guy over on another forum who'd just completed a Spectra said the plans don't call for sheer-webs in that area. Hard to say if he meant just that side of the spar or just those four rib bays. Regardless, my wing now has full webbing, both sides of the spar from root to tip.

thepiper92 03-14-2014 06:18 PM

I usually make the cut wider and sand down to where I need it, so that way if its not quite perfect the sanding will make it so.

Dave180 03-15-2014 03:23 AM

I have a Spectra. It's very relaxing to fly it. The buzzards and hawks like it too. Best flight so far is 45 minutes.

fhhuber 03-15-2014 06:04 AM

Sheer webs do not ever induce a twist in a wing... Twisting the wing while the glue for the sheer web sets up can hold the twist in the wing though.

The purpose of the sheer web is to stabilize the spar spacing under load. You can add considerable strength to the wing for a modest weight gain by adding the webs.

There's not much point of adding the webs to the tip panels. It doesn't really hurt much but its unnecessary weight.

The probable reason one wing had the webs and the other didn't is seen in the repairs done to the wing. The one that was repaired the most got the webs to help make up for strength lost due to splicing the sheeting.

thepiper92 03-15-2014 06:32 AM

So webbing connects the bottom spar to the top spar, in between each former, at the mid wing. This would be more useful the larger the wingspan correct? I cannot see wood grain direction making a difference when most of the surface of the webbing is glued down. I wouls think that it just forces the spars to become one, in a sense, to avoid twisting.

fhhuber 03-15-2014 06:56 AM

You can use thinner webbing when the grain is vertical, thus saving weight. The purpose of the web is to maintain spacing between the spars, preventing them from bending. If they don't bend they resist breaking better.

For "one side" webbing its most effective if centered as in an I beam. That's a bit harder to put in correctly than affixing to the sides of the spars. The I beam style has to be sanded to an exact fit.

Even 1/16 balsa is overkill for webbing on the Spectra when its vertical, but if its horizontal you need 1/8 to 3/16 to do the same job.

If you box in the spars with web both sides you get a very rigid structure and can use even thinner webbing... but 1/64 balsa is hard to find.

Since you boxed in your spar... don't worry about having gone with the web's grain the wrong way. But in the future do it vertically.

thepiper92 03-15-2014 07:24 AM

Strength would also depend on distance between each former too then? I'm just curious how necessary webbing is; I would think a lot of force would be needed to snap the spars.

Nodd 03-15-2014 07:34 AM

As I mentioned, I've been over this webbing subject several times already in my other build threads. I'd appreciate it if we not do that again here. There's lots of threads out there already on the subject of sheer-webs, their purpose, grain orientation etc. The following is a good thread to start if you'd like to learn more or discuss webbing further...

http://www.rcgroups.com/forums/showt...00#post6164407

Dave180 03-15-2014 08:15 AM

You might want to look at beefing up the tail/stab also. Mines warped. Not enough bracing and weak wood. It still flys though.

Nodd 03-15-2014 05:28 PM

That's good to know Dave. I'm planning to recover the entire airframe so I'll take a look at the tail structure once it's back to bare-bones. Thanks.


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