Bird of Time Balsa Kit Build Thread

TexMechsRobot

Posted a thousand or more times
Absolutely. Maybe we can do a double date dinner and then come here for coffee and desert. I know Amy would be up for that.
 

Craftydan

Hostage Taker of Quads
Staff member
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I've been reading through some Build logs on the BoT and it looks like almost everyone practically recuts the kit using much lighter stock. I don't have a lot of experience with sailplanes besides old school floaters but it makes me beg the question, wonder how big of a difference it would really make to the sport flier? Some builds have some pretty significant weight taken out.

It's common, but IMO, ill advised for soaring -- as you've said, trading weight for penetration is a good thing. Light and floaty excels on the beautiful day where the thermals are the only source of wind and they're big fat and lazy . . . then there's the rest of the year, where the lead-sleds will clean their clock on the narrow wind-blown thermals with sink all around. The lead-sled pilot has the speed and the legs to run from sink, where light and floaty is dragged down the first hole it wanders by. Being able to adjust this wildly with ballast is a more modern approach . . . but that's a concept that was only just being explored back in the BoT's era.


As for surfaces and mods, IMO, she's at her best as an electric RES ship (Rudder/Elevator/Spoilers) -- Kudos Tex, on your taste ;) Although ailerons and flaps aren't impossible by a long shot, It's kinda like putting a modern fuel injected engine into a classic 50's Muscle car. Sure you get more power . . . but at what cost?
 

TexMechsRobot

Posted a thousand or more times
I got the plans scanned today and printed off an extra set. So I now have the original plans they sent, a pdf copy, and a copy that I can cut up and destroy as needed.

Here's a picture of the plans with a 24" ruler for scale. This project is going to be a blast :)

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This is a picture of all of the parts I ordered from RCAirMods.com. Not sure if I'll use them all so we'll see.

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nhk750

Aviation Enthusiast
Those plans are huge! Whats the dims on the plans? Im wondering if my building system is even large enough for this. This might be a fun build after the other three I have in mind.
 

TexMechsRobot

Posted a thousand or more times
nhk750 said:
Those plans are huge! Whats the dims on the plans? Im wondering if my building system is even large enough for this. This might be a fun build after the other three I have in mind.

60" x 36" for the plans. Too big for my system as well. I'm going to have to figure out a plan to make it work...

Studying the plans, whats the rubber band for in the nose section of fuse?

It holds the hatch down. Pretty ingenious solution IMHO.
 

nhk750

Aviation Enthusiast
That will fit my new magnetic system as you only build ond wing at a time anyway, so 60" per wing would just fit. Maybe next year I will think about this after I see yours and how it comes out.

I saw this pic and looked pretty cool, unless you crashed on takeoff!

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TexMechsRobot

Posted a thousand or more times
So it begins.

I started on the left wing today. I'm dong my best to take my time building this and have only made one mistake (that I know of). So far it's all going really well and the instructions and materials have been really nice.

My one mistake was when I was clamping and gluing the dihedral blocks and tube for the connecting rod for the wings. I spent a lot of time measuring and sanding and getting things just right and then I mixed up 5 minute epoxy (instead of the 20 minute it recommended) and ran out of time clamping it all together. I frantically scraped drying epoxy out of crevasses that were perfectly sized and didn't have room for dried epoxy residue. I was able to get most of it out but not all of it. What it leaves me with is the top spar above the webbing is about 1/16" of an inch too high and will mess with the sheeting. I think my best solution to fixing this is to sand the spar down until it is flush like it is supposed to be. My only concern is that this weakens the spar at the point that it is most critical. This may not actually be an issue though since all of the extra space was taken by epoxy which is pretty strong. What do you guys think? I can take other pictures and explain better if needed.

So here are some pictures of the progress so far.

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earthsciteach

Moderator
Moderator
Let me see if I have the situation correct in my brain. The spar, as is, would have an area that sticks up 1/16" higher than the surrounding areas. Is that correct?

If that is the situation, I would opt to sand down the top of the spar so that its level. That spar looks nice and beefy. I don't think 1/16" over a short distance is going to cause any problems. What is the depth of the spar in that area?

I would, however, try to fill in the gap between the spar and the bottom sheeting with epoxy.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
And if I'm understanding correctly, you want to sand off the 5 minute epoxy to get the spar back to it's original size, and then coat it with 30 minute epoxy? I don't see any issues with that, other than sanding epoxy is a pain in the butt.
 

TexMechsRobot

Posted a thousand or more times
Here are some more pictures with the trouble area.

The spar is built in layers because of a 1/4" connecting bar. that runs through the inboard side of both wings. The metal bar slots into a carbon shaft that is at an angle to the bottom surface of the wing which creates and holds the dihedral when assembled. To do this, there is (starting from the bottom) a 1/16" balsa sheet, 1/8" hardwood spar, balsa filler block sanded at an angle with a groove, carbon fiber tube, balsa filler block sanded at an angle, 1/8" hardwood spar. There will be another layer of sheeting on top but that isn't in place yet and so it isn't in the pictures.

The trouble came when I was gluing the filler blocks and carbon tube in place. The epoxy dried too fast for me to work with and it filled up some of the space where the last 1/8" hardwood spar was supposed to go. So when I glued the top spar in place, it would only go down about 1/16" leaving 1/6" above the line of the airfoil. I'm positive all of the "space" in this construction is filled with epoxy. I could probably just sand the tops spar down to the airfoil and not have any problems.

The third image from my last post shows this cross section W-W. The printed image is from the perspective of the front of the plane for the left wing and from the back of the plane for the right wing.

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earthsciteach

Moderator
Moderator
I see what's up now. I think you'll be fine with sanding the cap strip down flush with the ribs. You won't lose any strength by doing so. The top cap strip is going to experience compression loads 95% of the time. 1/16" off that assembly won't hurt a thing.
 

nhk750

Aviation Enthusiast
Thanks for posting this as I am learning techniques. Looks like some sanding will do it. Keep up the build thread, i like to see what tools your using and building styles. Im currently out for a while, but will have time to read this thread and others to learn. Im also bringing an airplane along...
 

TexMechsRobot

Posted a thousand or more times
I got one wing pretty much done. I did choose to sand the spar top cap down and it worked out great as far as fit is concerned. We'll see how it holds up over time.

The only thing missing from the wing at the moment is the leading edge. The plan calls for two 7/16" x 1/2" balsa stock sanded to shape on each panel. When I pulled them out of the box, they were severely warped. So I have them soaking in hot water right now and will try to straighten them overnight. My issue is that I don't really have any clamps so I'm going to have to try to weight them down in order to hold them in place while they dry. If this doesn't work, then I'll need to make a trip to my LHS and try to find some balsa stock that'll work.

Overall, it wasn't that bad. I have to replicate everything for the right wing now but I have a bunch of lessons learned that should carry over.

The connector bar is at the correct angle. I was worried about this since, over a long span like this wing, a small error would make for a large deviation.
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Gluing up the ribs!
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Separating the outboard panel in order to create the polyhedral for the outboard panel. There are 4 pieces of 1/16" webbing for the outboard panel. The instruction manual literally says "If you plan to land on the wing tips very often you may want to add shear webs all the way to the tips instead of just the first four bays." I actually laughed out loud when I read that. I chose to stick with 4 bays as I don't plan to land on the tips and keeping weight out of the tips will let the plane be more responsive in flight.
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Setting the polyhedral.
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Gluing on the top sheeting. I think I need to invest in lead shot bags....
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I decided to hold off on installing the spoiler kit from RCAirMods.com until both wings are complete. It looks like they will fit nicely though even though they are designed for the ARF BoT. A few modifications will be necessary but they'll be perfect additions to the stock BoT.
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nhk750

Aviation Enthusiast
This is so cool, makes me want to cry, a thing of beauty! You are working fast, it would take me a month to get that far. I am thinking about some lead shot stuff too, it seems like a lot of serious builders are using them.
 

TexMechsRobot

Posted a thousand or more times
I have no concept of slowing down. Saturday, I spent the morning and afternoon with the Seattle Area Soaring Society. They had a 2M - RES - Wood Wings competition and so I tagged along to score and time for them while learning about the craft of sailing and the club. I had a ton of fun. I plan to join as soon as my budget allows for it. They have a gorgeous site at and old dairy farm and their club lease only allows for gliders. The only motors allowed are for climb out purposes. I like flying the other style too much to give it up so I'll probably just be a member of two clubs!

One of the guys there had an unpowered Bird of Time that he had built back in 1994. He walked away with first place in Wood Wings and I got to see how this thing could fly if built and piloted with skill.

After that, I was exhausted. I didn't realize how much energy I was putting out until I got home around 4:00 PM and just wanted to sleep the night away. I did rest a little and then started setting up the right wing for my plane.

On Sunday, I took a look at the spoiler kit again and figured out how I wanted to make it fit. The ribs contained in the kit didn't extend to my spar and left about a 1/4" gap. So I cut the BoT ribs long enough to butt up against the frame of the spoiler and used epoxy to glue it in place. Other than that, the fit was really nice. I cut a small strip of 1/16" balsa to bridge the gap and make covering easier. I installed the spoiler kit on the right wing during assembly instead of after the fact. This was a better call and is how I would recommend doing it.

I still have some sanding to do (a LOT of sanding is required on this plane) and I need to install the leading edges. I have them clamped to each other to keep them straight until I put them on the wings. Overall, I'm happy with my work so far. I should be able to finish up the wings in a couple of days. Then it's on to the tail surfaces!

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nhk750

Aviation Enthusiast
Nice work! We spent the weekend at Fort Warden and I guess they have a soaring society out here too. They fly gliders in the parade area and electrics are ok also. It was so windy though that no one was flying, I did get out for a quick flight on the beach area yesterday night though and it was scary windy but I did get some onboard video.
I am inspired by your work and am going to get busy on my T-Craft, I had to wait for a miter saw to show up.
 

TexMechsRobot

Posted a thousand or more times
A miter saw? Are you building it out of 2x4's? ;)

I hear Fort Warden is a nice place. I've never been. I've done Fort Casey and Fort Ebey on the Island though. Interesting history between the three of them. Nice slope soaring at Fort Ebey from what I hear. I'm going to take my Alula Trek up there one day and try it out.
 

nhk750

Aviation Enthusiast
Hobby miter box

A miter saw? Are you building it out of 2x4's? ;)

I hear Fort Warden is a nice place. I've never been. I've done Fort Casey and Fort Ebey on the Island though. Interesting history between the three of them. Nice slope soaring at Fort Ebey from what I hear. I'm going to take my Alula Trek up there one day and try it out.

One of my other problems building has always been trying to make straight cuts, so I invested in a hobby miter box- https://www.amazon.com/Excel-Blades-Small-Mitre-Handle/dp/B003AKSYFU/ref=sr_1_1/132-5266244-2669214?ie=UTF8&qid=1493659103&sr=8-1&keywords=hobby+miter+box

Now I will conquer cutting balsa sticks forever!

Im also seriously considering this when I get my Amazon points this month.
https://www.amazon.com/gp/product/B005UKGL58/ref=ox_sc_sfl_title_1?ie=UTF8&psc=1&smid=ATVPDKIKX0DER
 
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