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Old Jun 09, 2014, 05:29 PM
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United States, NY, Buffalo
Joined May 2013
988 Posts
Build Log
Art Hobby Sky 2m V-tail

Just got my Sky 2-meter from Art Hobby today. Kit looks good. Total weight of all components is 404g (14.2 oz). If I'm lucky, I can build it right around 19 oz., which would be terrific. Wing thickness is pretty generous, much thicker than my HN1033-foiled Thermic 2.5m wing. The chord is also just about identical to the larger Thermic wing, too. The Sky looks like it might be a good floater.

My plan is to build this with a V-dihedral and spoilerons. No flaps, no polyhedral.

But I am already planning on making a few mods. They are:

1. Increase wing dihedral from 3 degrees to 5.5 degrees. This will be a thermal-only glider, no sloping. I don't need the flat-wing maneuverability, I'd much rather have the added stability of the slightly larger dihedral. Dr. Drela (and many others) call for around 6 degrees dihedral for a thermal aileron ship, so I'm going to trust their expertise.

2. Change the V-tail arrangement from the stock "elevator-only" configuration to a more traditional ruddervator setup. I don't like the idea of having no yaw control for a thermal glider.

3. I may change the pushrod configuration for the V-tail to a pull-string/spring setup. I'm hoping I can save some weight in the tail and avoid having to add nose weight. My plan is to set up the glider with everything temporarily in place and check the balance first. If it seems tail-heavy, then I'll go for the pull-string setup. The pushrods are 13 grams total, which would add maybe another 20 grams up front for balance, for a total of over 1 oz. of useless weight. I think the pull/spring setup will be better.

I have to admit, I'm pleasantly surprised at how light all of the components are in the Sky kit. In contrast, the Thermic seemed heavier overall and I needed about 2-3 oz. of nose weight. But in the Thermic, the pod was heavier and the tail boom was MUCH heavier than the parts in the Sky. The tail boom in the Sky is very well made and lightweight -- exactly 15 grams. In addition, the Sky boom is much, much stiffer than the one in the Thermic kit. I'm happy with the changes that Art Hobby has made with their construction techniques.

I welcome any opinions about my proposed modifications. Also, has anyone built an Art Hobby plane with a V-tail that is set up as elevator-only? That seems odd to me, leaving only roll and pitch control available for the plane. I can see where it would probably work (DLGs are sometimes built rudderless), with an increase in aileron differential. But I've gotten accustomed to rudder/aileron coordination, so I think I'd prefer to build it more traditional with yaw control.
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Old Jun 09, 2014, 06:26 PM
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United States, NY, Buffalo
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Interesting... found my first problem with the kit. The wing root thickness at the front hold-down bolt is 17mm, but the wing mount blocks are only 13mm thick. I'm going to have to add some basswood to the front block to thicken it up a bit. I don't mind doing this, because it's not a huge problem, but even still you would expect the kit to at least contain properly-sized parts. I mean, didn't the manufacturer build this kit? Didn't they realize the blocks aren't thick enough?

Strange.
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Old Jun 09, 2014, 06:38 PM
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Canada, ON, Toronto
Joined Jan 2014
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Quote:
Originally Posted by DrewV View Post
Interesting... found my first problem with the kit. The wing root thickness at the front hold-down bolt is 17mm, but the wing mount blocks are only 13mm thick. I'm going to have to add some basswood to the front block to thicken it up a bit. I don't mind doing this, because it's not a huge problem, but even still you would expect the kit to at least contain properly-sized parts. I mean, didn't the manufacturer build this kit? Didn't they realize the blocks aren't thick enough?

Strange.
Is it possibly a production error - including the blocks from a wing with a different profile in the Sky 2M kit?
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Old Jun 09, 2014, 09:32 PM
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United States, NY, Buffalo
Joined May 2013
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Other issues:

1) The center dihedral is pre-sanded to approximately HALF of what it should be per the plans. My Thermic was pre-sanded spot-on. I'm going to have to sand a good portion of the roots to get the angle I need.

2) The V-tail control surfaces interfere with each other when the two pieces are put together. They are literally touching each other in the middle and cannot move upward. Again, I'll have to re-contour these to shape. Very strange.

3) The V-tail is just plain bare balsa. My Thermic had balsa tail surfaces that were laminated with glass/epoxy. The lamination made them very stiff and straight. I have the feeling that the bare balsa V-tail will quickly warp over time, even with a spray lacquer (Deft) treatment.

See attached images for details. Note the aforementioned wing hold-down block in the front is way too thin for the airfoil. I added 1/8" spruce to the top and it is just barely tall enough.
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Old Jun 09, 2014, 10:50 PM
altitude adjustment
thumbhead's Avatar
USA, CA, Irvine
Joined Mar 2005
493 Posts
Drew, regarding your bare balsa tails:

I am current putting an ArtHobby Serena together and it came with a bare balsa horizontal stab which seemed a bit floppy. I bagged it with light glass and it's pretty stiff now. In the past, I've used laminating film on bare balsa and ended up with a pretty rigid part without adding much weight. The 1.3mil or 1.7mil stuff works great and is really light. Maybe even lighter than .75 oz glass.

Mark
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Old Jun 09, 2014, 11:08 PM
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United States, UT, Draper
Joined Dec 2012
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Subbed. Am looking at getting an AH 2M ship soon. It was a toss between the Sky and the Boar. Mine will be primarily slope and some thermal or slermal. Contacted AH and Andre recommended the Serena.

Mark did you do a build log on your Serena?

Could the wing blocks be undersized for filling the gaps with splooge top and bottom? I ask because I have built 5 DLGs and they all got splooge(micro balloon/epoxy paste) for the wing mount hardpoints. No wood inserts used. Or are they just plain too small?
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Old Jun 09, 2014, 11:41 PM
altitude adjustment
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USA, CA, Irvine
Joined Mar 2005
493 Posts
I've done mini build threads in the past but only after I complete the model because I'm usually a really slow builder and would hate to leave everyone hanging. I plan on posting pics of the Serena when I finish. I always use epoxy hard points on AH planes mainly because it's easier to get the proper angle of the bolt hole when the wing is in two pieces. I plan on flying the Serena mostly at the slope in DLG conditions. I'm thinking ailerons only for a bit of weight saving. Also tempted to build it with a one piece wing to have full span flapperons. Not sure which way I'll go. Sorry for the highjack Drew. Now back to our regular program....

Mark
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Old Jun 10, 2014, 12:58 AM
Slope-a-Dope
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Thanks, Mark, for the info. Not meaning to hijack either. Here to see what I'm getting into. Seems to me that AH has a dedicated following to their planes.

I kinda like the flaperons route myself as it is what I'm used to on my DLGs.

Only 1.5 years in RC flying and have gravitated to sloping, soaring, DLG, and enjoy planks quite a bit so this will be an expansion for me, moving up from 1.5 M. Very many of my locals fly 3M moldies like Ceres, crossfire, pikes, ascots, among others. They keep telling me bigger flies better and i'm a believer.


On with the build.
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Old Jun 10, 2014, 04:57 AM
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United States, NY, Buffalo
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Quote:
Originally Posted by thumbhead View Post
Drew, regarding your bare balsa tails:

I am current putting an ArtHobby Serena together and it came with a bare balsa horizontal stab which seemed a bit floppy. I bagged it with light glass and it's pretty stiff now. In the past, I've used laminating film on bare balsa and ended up with a pretty rigid part without adding much weight. The 1.3mil or 1.7mil stuff works great and is really light. Maybe even lighter than .75 oz glass.

Mark

As I said, my Thermic came with glassed balsa tails. I had read some reports of bare balsa tails fluttering and tearing apart during flight, so I thought Art Hobby had glassed ALL their tails after that. I guess not.

I think I will try your suggestion and find some laminating film. I have used 0.75 oz. glass on fuselages in the past with Polycrylic and it has worked very well, but thin balsa surfaces tend to warp due to the water-based poly. I've also used "finishing epoxy", but that stuff doesn't seem to harden up -- it just remains flexible even after it's cured.

Any suggestion on where to get good laminating film?
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Old Jun 10, 2014, 07:18 AM
Slope-a-Dope
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United States, UT, Draper
Joined Dec 2012
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Laminating film?

Here's a source.

http://www.alofthobbies.com/building-materials.html
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Old Jun 10, 2014, 07:32 AM
Mark LSF # 3792
United States, TX, Garland
Joined Nov 2008
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Quote:
Originally Posted by DrewV View Post
As I said, my Thermic came with glassed balsa tails. I had read some reports of bare balsa tails fluttering and tearing apart during flight, so I thought Art Hobby had glassed ALL their tails after that. I guess not.

I think I will try your suggestion and find some laminating film. I have used 0.75 oz. glass on fuselages in the past with Polycrylic and it has worked very well, but thin balsa surfaces tend to warp due to the water-based poly. I've also used "finishing epoxy", but that stuff doesn't seem to harden up -- it just remains flexible even after it's cured.

Any suggestion on where to get good laminating film?
DrewV, I have noticed the same about hobby "finishing" resins. What you need to use is a good laminating resin. I have heard good things about Pro Set , but have not used it. West Systems is another good laminating resin and is readily available in many areas. Seeing your in Buffalo there might be a store near you.

Mark
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Old Jun 10, 2014, 07:37 PM
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United States, NY, Buffalo
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Minor progress

Glued up the wing today. Also did some more modification on the V-tail. The CA-hinges from the factory were very tight and did not allow much movement. When I simulated the movement of the control horn, the surfaces just deformed, really. They didn't completely deflect. So I decided to make some tape hinges instead. I used them on a plane from 1990 and the hinges are still in beautiful condition. They are just like Monokote hinges, but a bit easier to apply.

I also made some 0.015" spring wires for the V-tail. Basically just 1-inch long wire with 1/2-inch tag ends that get pushed into the balsa. I was fortunate enough to have access to 17-7PH spring wire, heat treated to spring temper. They seem to have a reasonable amount of restoring force, so I think they'll be okay for such a light plane.

Not much more to share. I'll try to finish up the wing in the next couple of days and finish up the tail/boom. I'm just going to go with the bare balsa V-tail with Deft spray lacquer. If it warps, I'll just make another tail. At this stage, I'm going for the lightest possible build. I can always re-build the tail in a short time if needed.
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Old Jun 10, 2014, 08:32 PM
Theoretical Modeler..
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Joined Oct 2007
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Drew- looks good. Makin me want to get another one from AH.
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Old Jun 11, 2014, 02:18 PM
Less Whinning, More Flying
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SF Bay Area, USA
Joined Feb 2003
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I'll be interested in the final look of the finished plane with the huge dihedral. Like to see how it compares to the Sky 2M I just finished.
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Old Jun 11, 2014, 04:24 PM
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Well, I think "huge" is a relative term. The dihedral is exactly what my DLGs have. And it's much less than my other 2-meter polyhedral TD planes have. Between 5 and 6 degrees is also what Blaine Rawdon and Mark Drela recommend. So, I'm not necessarily sure I'd say it's "huge".

Just as an update, my V-tail taped hinges didn't really hold very well to the bare balsa. So I'm going to have to spray lacquer seal the balsa first, then I might go with some silicone hinges instead. I think they'll be a big stronger and less likely to have problems down the road.
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