Best method to bend balsa

[Greg Furtman]

Glad it helps. Feel free to ask if you have questions or run into problems.

@Rktman I do have a question. How thick did you ring end up being? Thin plywood or did you end up using balsa?

 

[Rktman]

@Rktman I do have a question. How thick did you ring end up being? Thin plywood or did you end up using balsa?

I used 1/16" A grade contest balsa. After taking some damage on hard landings on rocky soil, I replaced the rings with 1/64" ply. It's much tougher and more resilient, and far easier to bend without kinking.

 

[BABAR]

Glad it helps. Feel free to ask if you have questions or run into problems.

I am impressed that 1/64 balsa holds up so well!

 

[Rktman]

I am impressed that 1/64 balsa holds up so well!

To clarify: thin 1/64" plywood (probably spruce?) not balsa.

 

[BABAR]

To clarify: thin 1/64" plywood (probably spruce?) not balsa.

I didn’t realize that. Still I impressive. But you kept me from going out and buying some 1/64” balsa, so thanks!

 

[Greg Furtman]

Steve Shannon Thanks Steve, looks like this jig would work great on plywood. 1/64" ply is really flexible so it could probably be scarfed before bending

Steve's link no longer works so I Googled for scarfing jigs. Here's an interesting one. Once made it will give repeated results.

https://forum.woodenboat.com/showthread.php?133907-Scarfing-Jig-Ideas

 

[Greg Furtman]

To clarify: thin 1/64" plywood (probably spruce?) not balsa.

@Rktman I picked up some 1/64" plywood today. Amazingly thin. Made by Midwest Products. It's made of birch. I also picked up a piece of 1/32" x 12' x 24", also birch.

I haven't played with it yet but the 1/64th" seems very flexible. Did you have to soak it to get it to bend around the outside of a 4" PVC pipe? I'm using a 4" toilet flange.

 

[Rktman]

@Rktman I picked up some 1/64" plywood today. Amazingly thin. Made by Midwest Products. It's made of birch. I also picked up a piece of 1/32" x 12' x 24", also birch.

I haven't played with it yet but the 1/64th" seems very flexible. Did you have to soak it to get it to bend around the outside of a 4" PVC pipe? I'm using a 4" toilet flange.

Didn't have to soak the 1/64" ply, it bent very easily around the form.

I kept the excess overlap and glued it together rather than trimming the ring ends to the exact diameter and doing a butt joint, because the butt joint tended to bow outward too much.

Here's something you might want to try: form and glue your ply ring together on the inside of your PVC form as per the build instructions, and leave them in there while you glue the fins to the inside of the ring (glue one fin to the overlap area). Your PVC form should help the ply to conform to a circular shape and the fin glued over the overlap area should help keep that area from bowing outward too much.

 

[neil_w]

I solved the bulging butt joint by laminating two layers, with the joints 180 degrees apart. Unfortunately, that might not be practical when you want to absolutely minimize weight.

 

[Greg Furtman]

Great! Estimated weight on each of the ring fins?
Wondering if for the more craftsman challenged guys like me I can replace it with a cardboard cutout from a cylindrical box.
The aerodynamics of this blow by me (pun intended), but then a lot of aerodynamics do.

Looking forward to a great flight report!

@BABAR I'm building a RingHawk. I used 1/64" birch ply to make the rings. These rings weigh 6.68 grams. A 1/16" balsa ring weighs 4.98 grams. The 1/64" ply bends really nice without needing to wet or steam.

 

[BABAR]

Thanks! I will measure weight of cardboard carton rings. Are you going with the dimensions on the original, or are your rings custom size. If latter could you specify?

 

[BABAR]

I still don't understand the aerodynamics of this glider, since it has no up or down, but it is obviously a proven design. I'd be curious how well those thin rings hold up.

 

[BABAR]

Dreaded double post

 

[Greg Furtman]

Thanks! I will measure weight of cardboard carton rings. Are you going with the dimensions on the original, or are your rings custom size. If latter could you specify?

@BABAR I thought I was following the original plans but instead of using a 4" PVC coupler I used a 4" PVC toilet flange I had on hand. The walls must be a little thicker on a toilet flange because when I went to glue the rings to the fins I came up a little short. I had to add small strips to the rings where the fins would attach to make up the difference. So if you plan on following the original plans use a couple and not a toilet flange.

 

[Greg Furtman]

I wish the forum send out a notification when someone tagged you in a post.

It's pretty tight. Like this.
[video=youtube;8ctUkhwE7cw]

I used a rubberband to provide some cushioning.

View attachment 316947

@Charles_McG I'm at the point in my RingHawk build where it is time to glue the elastic band to the upper ring wing section. I'm using FAI 3/16" wide Tan Rubber. Your video on taughtness helped. I'm trying to figure out what kind of glue to use though. I have Titebond II, 5 minute WEST epoxy, and WEST 105 Resin with 205 hardener. What did you use? Which of my choices would you recommend? I did build the ring out of 1/64" Birch ply and the fins out of 1/32" Birch ply.

 

[BABAR]

This is an oatmeal carton cut out which is just under 4 inch outside diameter 1.5 inches in width. Weighs in at between 7 and 8 grams.

Definitely easier than bending balsa

 

[Charles_McG]

@Charles_McG I'm at the point in my RingHawk build where it is time to glue the elastic band to the upper ring wing section. I'm using FAI 3/16" wide Tan Rubber. Your video on taughtness helped. I'm trying to figure out what kind of glue to use though. I have Titebond II, 5 minute WEST epoxy, and WEST 105 Resin with 205 hardener. What did you use? Which of my choices would you recommend? I did build the ring out of 1/64" Birch ply and the fins out of 1/32" Birch ply.

That was along time ago. Either wood glue, or 5 min epoxy. I wasn't doing anything fancier at the time.

 

[Rktman]

@BABAR I thought I was following the original plans but instead of using a 4" PVC coupler I used a 4" PVC toilet flange I had on hand. The walls must be a little thicker on a toilet flange because when I went to glue the rings to the fins I came up a little short. I had to add small strips to the rings where the fins would attach to make up the difference. So if you plan on following the original plans use a couple and not a toilet flange.

Made a similar mistake, formed the ring around the OUTSIDE of the pvc coupler instead of the inside. Like you did, made up the difference with fin extension strips. Works fine.

 

[Rktman]

@Charles_McG I'm at the point in my RingHawk build where it is time to glue the elastic band to the upper ring wing section. I'm using FAI 3/16" wide Tan Rubber. Your video on taughtness helped. I'm trying to figure out what kind of glue to use though. I have Titebond II, 5 minute WEST epoxy, and WEST 105 Resin with 205 hardener. What did you use? Which of my choices would you recommend? I did build the ring out of 1/64" Birch ply and the fins out of 1/32" Birch ply.

Don't forget to slip the small rubber band "shock absorber" over your body tube before you permanently attach your elastic.

 

[Greg Furtman]

Don't forget to slip the small rubber band "shock absorber" over your body tube before you permanently attach your elastic.

Ya, I figured this out at the right time.

 

[K'Tesh]

Best method to bend?


Finally broke down and tried to sign up for Hulu... Any Guesses on what I only just watched 30 minutes ago?

 

[Greg Furtman]

This is an oatmeal carton cut out which is just under 4 inch outside diameter 1.5 inches in width. Weighs in at between 7 and 8 grams.

Definitely easier than bending balsa

How stiff are the rings? Are you going to need to reinforce them somehow?

 

[BABAR]

How stiff are the rings? Are you going to need to reinforce them somehow?

I think with the two balsa wings/spokes/whatever they will be stiff enough.

There is a trick I am thinking of that would allow me to go down a body tube size, basically a minimum diameter 18 mm pop pod, but it involves extending the motor posterior to the rings. Might make up for the extra mass in the ring fins.

 

[shockie]

A-Grain balsa will bend easier than C-Grain will

Select A-grain balsa wood for more difficult curves and bends. A-grain wood is more flexible than B or C-grain pieces, which are more likely to split when bent. When possible, bend the wood so that the grain of the wood runs with the longest side of the piece.
The grain runs the length of A-Grain balsa.

Curving it across the width of the balsa piece vs curving it along its length seems to be far easier, especially with such a severe bend as I'm attempting (360° ring). I'm discovering that the old 2003 plans I'm working with are full of inaccuracies.


"On a related note, does curving your rotor blades take the place of having to airfoil them? I just scratch built a self-designed Helicopter and spent days airfoiling the rotors. They turned out beautiful and the maiden flight turned out far better than I expected, but if curving the blades will give the same results as carving, I'd rather go that route."

Airfoiled and curving combined is the bestof both worlds . Back 10 years or so ago....I would create twisted airfoil helicopter blades using basically hot water.... i would then put the balsa rotor on a former or mandrel that had a piece of .001" teflon film wrapped around it ,at an angle to get the twist.....these were coated with a light epoxy resin....they were then wrapped with heat shrink tape in a spiral pattern and put in the oven to dry for a few hours ..... some I made with esaki tissue applied for additional strength for 1/32" balsa....

unwind the heat shrink tape and even if you overlapped the spirals by at least 1/8" there won't be any ridges across the rotor where the tape meets.....give them a final sanding and there you go.... high strength, low weight twisted airfoiled rotor blades

 

[neil_w]

A-Grain balsa will bend easier than C-Grain will

Select A-grain balsa wood for more difficult curves and bends. A-grain wood is more flexible than B or C-grain pieces, which are more likely to split when bent. When possible, bend the wood so that the grain of the wood runs with the longest side of the piece.
The grain runs the length of A-Grain balsa.

I'm glad you brought that up; I have three sheets of 1/32" balsa that I'll be bending sometime soon, and it looks like they're one of each grain type. So I'll start with the A.

Which is second-best, B or C?

 

[Rktman]

Best direction to bend balsa

Since descriptions can often be misinterpreted, the easiest way to clarify is with pictures.

Balsa is easiest to bend ACROSS the grain. It's more flexible in this direction.




Balsa is harder to bend along the length of its grain since it's less flexible and stronger in this direction.




That said, if your bent pieces require strength, you're going to have to take your chances and bend along the grain, and maybe join less extremely bent sections that you were able to successfully curve into the shape you want.





Description of balsa wood grades:

 

[Rktman]

I'm glad you brought that up; I have three sheets of 1/32" balsa that I'll be bending sometime soon, and it looks like they're one of each grain type. So I'll start with the A.

Which is second-best, B or C?

If you need a bent part longer than 3" or 4" (the width of most balsa sheets) you may have to join more than one piece.

Second best choice is B-grain.

 

[Greg Furtman]

Here's a good website about Balsa.

https://www.rcscalebuilder.com/tuto...text=Eight to twelve lb.,“grades” of the wood.

 

[neil_w]

Ok, I give up. Which grain is which in this picture?

I’ll be bending along the grain. Obviously the bottom piece is “nicer”, and I’ll likely use that one either way, but I’d really like to be able to identify A vs B grain. C is easy.

 

[Rktman]

Ok, I give up. Which grain is which in this picture?
View attachment 441528
I’ll be bending along the grain. Obviously the bottom piece is “nicer”, and I’ll likely use that one either way, but I’d really like to be able to identify A vs B grain. C is easy.

The bottommost looks like A grain. The top pic could be C or B. If you gently flex the sheets, the C would be the stiffest, while the A would be the least so. I usually pick the sheets up by the end and wobble them back and forth gently. You can really get a feel for stiffness and flexibility then.

At any rate, 1/32" is pretty thin so even the C would be kinda bendy (though you could get away with tighter curves with the softer A grain).