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Old Jan 04, 2009, 07:07 PM
a.k.a. Matt Nelson
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North Tustin, CA
Joined Oct 2008
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Build Log
Peak Hobby Binary-900 Build

During December 2008, Peak Hobby had many of their gliders on sale. Unable to pass it up, I purchased a Binary-III and two (!) Binary-900's. The Binary-900 is a 35" 2-channel dihedral DLG built with their molded inner-core (MIC) fabrication method for smooth, accurate wings. At $118, it seemed like a great deal - there seem to be very few high-quality sub-1m DLGs on the market at any price, the closest probably being the $100 Apogee Sport.

There is already a good discussion around the Binary-III, but there is almost no information "out there" on the Binary-900, so I figured I would start a build log to let people see the kit and how it goes together.

Buying direct from China

The purchase experience was a joy - 10 minutes after submitting my order, Harry Ha replied with the shipping options. I chose one (EMS express), payed via PayPal, and he had my order out the door in Shanghai that same day. I did luck out a bit - I ordered late in the evening while Peak Hobby was still open, and just caught their weekly shipment (every Saturday, I believe). 5 working days later, the package was on my doorstep in So. California. I'm still amazed at how small a world we live in!

First things first: The kit itself.

The kit contains a FG fuse with slip-on hatch cover, MIC wing panels, covered balsa tail, CF-reinforced bulkhead, FG cloth, aluminum wing pylons w/ screws, FRP control horns, CF launch peg and reinforcements, CA hinges, wire for the pull-pull and pull-spring controls, and a balsa stab mount with elevator spring. The only missing hardware are the miscellaneous bits required for the radio/servo install.

The FG fuse appears to be doubled-up at the nose and have some carbon tow layed up around the edge for added strength, and my impression is that it is quite sturdy. The hatch cover slips on very nicely. It is quite small, so I anticipate some 'fun' getting the battery, RX and servos in that little compartment.

Stay tuned for the next installment: joining the wing.

-matt
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Old Jan 04, 2009, 07:42 PM
a.k.a. Matt Nelson
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North Tustin, CA
Joined Oct 2008
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Joining the Binary-900 wing

The two wing panels supplied with the kit need to be joined together in the normal fashion with epoxy and FG cloth reinforcement.

Out of the box, the wing roots have some dihedral bevel already present. The instructions call for 128mm of dihedral when one wing is flat on the bench. I measured a little less than this, so I did a little sanding to get it just right. The instructions suggest setting the wing panel with it's tip raised 64mm and sanding against a vertical support. This worked really nicely. In only took a half dozen light passes to get the angle perfect. Note: don't be tempted to stray too far from the recommended dihedral - the wing mount pylons have this angle built into them.

I then taped the bottom of the wings together, applied some 20 min epoxy with microballoons, set the angle, and let the joint cure (overnight, in this case).
Tangent:

I've been thinking about wing joints, and I think there are a lot of misconceptions out there about the role of the epoxy/microballoon mix. I've seen lots of builders mention the importance of a strong glue joint at the root, but I just don't buy it.

Consider: the wing joint experiences both tensional and compressional forces as it flexes up and down. It seems obvious to me that the FG cloth is responsible for resisting all tensional forces experienced by the wing. The interior of the wing joint, being composed of only weak foam, is completely incapable of resisting any tensional force. Think about it; if you pulled on it, you would end up with a hunk of foam in your hand. Conversely, the FG cloth is essentially incapable of resisting any compression; it will simply buckle and fold if you try to push it together. The interior of the joint, on the other hand, can do this quite well. I therefore propose that the epoxy/microballoon mix functions as a filler only for the purpose of resisting compressional forces. The fact it is glue is unimportant - plaster would work just as well (other than being heavier).
The next step will be to install the wing mounts in the wing and glass it up.

-matt
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Old Jan 04, 2009, 08:04 PM
Physics hate's my ideas
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USA, NY, Dunkirk
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question what are balloons?
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Old Jan 04, 2009, 08:21 PM
a.k.a. Matt Nelson
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North Tustin, CA
Joined Oct 2008
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Quote:
Originally Posted by GreenAce92
question what are balloons?
Microballoons are microscopic air-filled glass spheres. They look like a white powder when you pour them out of their bottle. They are extremely light-weight - a pint of them probably weighs less than an ounce. They are mixed into epoxy as a filler in a 1:3 ratio or so - it makes the epoxy lighter and easier to sand when cured. Usually it is used when you need epoxy for bonding and gap filling, but want to avoid some of the associated weight (epoxy is quite heavy).

-matt
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Old Jan 04, 2009, 08:39 PM
DLG Fan
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Tempe, AZ
Joined Nov 2002
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Quote:
Originally Posted by pivlrs


Consider: the wing joint experiences both tensional and compressional forces as it flexes up and down. It seems obvious to me that the FG cloth is responsible for resisting all tensional forces experienced by the wing. The interior of the wing joint, being composed of only weak foam, is completely incapable of resisting any tensional force. Think about it; if you pulled on it, you would end up with a hunk of foam in your hand. Conversely, the FG cloth is essentially incapable of resisting any compression; it will simply buckle and fold if you try to push it together. The interior of the joint, on the other hand, can do this quite well. I therefore propose that the epoxy/microballoon mix functions as a filler only for the purpose of resisting compressional forces. The fact it is glue is unimportant - plaster would work just as well (other than being heavier).
[/INDENT]The next step will be to install the wing mounts in the wing and glass it up.

-matt
I think there is something to your thinking.

But when the wing is under load and the wings are flexing up, wouldn't the top part of the joint come under compressive forces? Then the epoxy in the joint would be doing its job.

And that's also when the fiberglass over the joint on the bottom of the wing would come into tension - and would be doing its job...

My 2 cents.

I'm interested in your results with the Binary 900. Thanks for posting this.
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Old Jan 04, 2009, 08:46 PM
a.k.a. Matt Nelson
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North Tustin, CA
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Quote:
Originally Posted by AZ_Astro
I think there is something to your thinking.

But when the wing is under load and the wings are flexing up, wouldn't the top part of the joint come under compressive forces? Then the epoxy in the joint would be doing its job.

And that's also when the fiberglass over the joint on the bottom of the wing would come into tension - and would be doing its job...

My 2 cents.

I'm interested in your results with the Binary 900. Thanks for posting this.
You have re-stated exactly what I was trying to express. In the case you describe, the top part of the fill will be compressed, while the bottom part of the fill will just be going along for the ride. Similarly, the bottom glass will be in tension, while the top glass will be doing nothing.

Someone in these forums suggested skipping the epoxy entirely and simply CA-ing the glass cloth to save weight. If you have a perfect root joint (i.e., no gaps anywhere) this would probably work. But in this case, I would still add epoxy, since very little (none?) would be retained in the joint as filler, and would be good insurance.

-matt
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Old Jan 04, 2009, 08:51 PM
DLG Fan
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Tempe, AZ
Joined Nov 2002
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Yes, right.

Maybe it calls for very light glassing on the joint on the top of the wing, and light epoxy in the joint at the bottom...

And then don't fly upside down... Heh heh.

I'd be nervous about not epoxying at all or not glassing at all.
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Old Jan 04, 2009, 10:06 PM
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You beat me on starting a build log on this plane, glad that someone finally started one. Mine should arrive sometime this week.
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Old Jan 04, 2009, 10:25 PM
a.k.a. Matt Nelson
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North Tustin, CA
Joined Oct 2008
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Finishing the Binary-900 Wing

The B900 uses a somewhat unique wing mounting system - it is similar to stab mounts used on some high-end ships. There are two aluminum pylons with sleeves that slide over the tail boom. The pylons have tapped screw holes, so that when completed, the wing bolts onto the pylons with metal screws. On the wing side, we need to drill holes through the wing and install three thick-walled plastic tubes. These act as hardpoints for the mounting screws.

Fit the mounts.

The instructions provide measured plans showing where to drill the holes. I followed the instructions - measured and marked the locations, and drilled the holes.

At this point, you can assemble the pylon-tube-screw assemblies and test fit them into the holes you drilled into the wing. The tubes are quite a bit longer than necessary, and should be trimmed down so that they are flush with the upper surface of the wing. There is one odd thing there about the design of the kit - the mounting holes on the forward pylon are not perpendicular to the wing, but are instead vertical. This means that one end of each tube must be angled to fit snugly against the pylon, and the other end must be square to support the mounting screw (see the attached photo). The down side of this is that you cant really cut the tops of the tubes flush with the upper surface of the wing, since the wing is at a dihedral angle, and the bolts are not. Seems to me that it would be better to have the mounting holes perpendicular to the wing - it would be simpler to install, cleaner when done, and I can't imagine it would be any weaker.

Now you can slip the pylons over the boom, dry fit the pylons into the wing, and check the whole thing for square. Measure from each wing tip to the aft end of the boom - the distances should be the same. If not, you can drift the wing holes to one side or the other to give slop to move the mounts as needed.

Glue it up.

The assembled pylon/tube/screw assemblies will be epoxied into the holes. It's done this way so you can maintain alignment of the boom and wing. The objective is to get the tubes glued into the wings accurately. But you don't want to glue the assemblies together; you need to be able to remove the screws and get the pylons off. To do this, I applied Scotch tape to the flat side of the pylon to prevent bonding to that surface. I then applied more Scotch tape to the surface of the wing around the holes (top and bottom), so that any squeeze-out wouldn't bond to the wing skin. I also applied some lip balm to the screw threads, so even if some epoxy got into the interior of the tube, it wouldn't adhere to the threads. When I screwed down the assembly, I finished it off with some more lip balm to the head of the screw. This would ensure that any epoxy that gets on the head of the screw can be easy popped off.

This whole procedure was a bit of a head scratcher for me: the wing is horizontal when being glued so that alignment can be maintained, but there are three through-holes that need to be filled with epoxy/microballoons. How do we keep the glue from just running out? Well, my solution was to tape over the holes in the wing, leaving a small hole in the tape so that the screw head would have someplace to go (see attached picture). Hopefully that would keep most of the epoxy in place.

I mixed up some epoxy with microballoons and applied it liberally to the interior of the holes (these need to be completely filled in order to provide sufficient strength for the wing mount), and also to the tubes themselves. I dropped the pylons into their places, threaded the boom through the sleeves, and applied a little bit of weight to keep everything in place. Check that the boom is square to the wing, and let it cure.

The attached picture shows that there was indeed some epoxy that ran out the bottoms of the holes. That side is where the heads of the screws are - I'm glad they're covered in lip balm!

After curing, everything came apart easily, and all stray epoxy squeeze-out was easily removed. Even the heads of the screws cleaned up easily, as planned.

Glass the joint.

Things are easy from here out. The instructions call for a piece of FG cloth over the front mounting points, and then a strip of FG cloth around the entire root joint. The order wasn't specified, so I applied the mount point reinforcement first. After it had set up, I applied the rest of the glass. For the glassing, I sprayed the glass lightly with 3M-77 adhesive, positioned it, then wetted it with standard 20min epoxy. Be sure to soak up as much excess epoxy as you can with paper towels. After completely cured, use an xacto knife to cut the glass away from the mounting holes. Voila!


Next step: tail feathers.

-matt
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Old Jan 04, 2009, 10:28 PM
Guz
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Tempe, AZ
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Something I have noticed in most kits, is that they provide extremely heavy glass for the wing root.

I've gotten by with .75oz cloth done with a "dry layup" with 30 min finishing epoxy. Then using wax paper to create a smooth surface. Using some strips of thin balsa, or ply, and some clamps and clothes pins to press it smooth. Let it sit overnight.
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Old Jan 04, 2009, 11:04 PM
a.k.a. Matt Nelson
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North Tustin, CA
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Quote:
Originally Posted by Guz
Something I have noticed in most kits, is that they provide extremely heavy glass for the wing root.

I've gotten by with .75oz cloth done with a "dry layup" with 30 min finishing epoxy. Then using wax paper to create a smooth surface. Using some strips of thin balsa, or ply, and some clamps and clothes pins to press it smooth. Let it sit overnight.
Not a bad idea. It will certainly will create a nicer finish, and maybe save some weight. I doubt the smooth surface would make much aerodynamic difference, however, since the wing root isn't really working like an airfoil since the fuse is disrupting the air flow over the lower surface.

My photo makes the glass look a little thicker than it seems in person. This is a really small wing, so that might be enhancing the effect, too.

-matt
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Old Jan 05, 2009, 09:47 AM
Guz
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Quote:
Originally Posted by pivlrs
Not a bad idea. It will certainly will create a nicer finish, and maybe save some weight. I doubt the smooth surface would make much aerodynamic difference, however, since the wing root isn't really working like an airfoil since the fuse is disrupting the air flow over the lower surface.

My photo makes the glass look a little thicker than it seems in person. This is a really small wing, so that might be enhancing the effect, too.

-matt
For me, it's primarily for looks. These planes are works of art in my eye, and seeing a rough glass patch at the root just 'irks' me

The secondary reason is to reduce drag. Sure the wing root may not produce much lift, but any rough surface will induce some drag.

It's like what others have said about trying to lighten a plane by say 10 grams, you find 10 places where you can shave off 1 gram. The same thing goes for drag, go find every place where you can smooth things out.
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Old Jan 05, 2009, 05:13 PM
Physics hate's my ideas
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The build is looking nice! what you say the wing was made of again? will this bird get above 100ft tosses and glide for more than a minute? id imagine so... looking great again!
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Old Jan 05, 2009, 05:24 PM
a.k.a. Matt Nelson
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North Tustin, CA
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Quote:
Originally Posted by GreenAce92
The build is looking nice! what you say the wing was made of again? will this bird get above 100ft tosses and glide for more than a minute? id imagine so... looking great again!
The wing is built using Peak Hobby's own method they call "molded inner core". I don't know how it's made, but it has a hard, shiny surface like a moldie, but has a full foam core, too. The claim is that it offers the benefits of both bagged (easy to repair) and molded (accurate and efficient) wings.

I have no idea how it will fly - there are a few videos on the web, and one of them shows a pretty good launch. We'll have to see.

-matt
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Old Jan 05, 2009, 07:06 PM
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Just got mine today... Wings are made of foam core covered with very light fiberglass.
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