Best method to bend balsa

BABAR said:

I would really appreciate that!

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BABAR No prob, be glad to.

Waiting on a fin alignment jig I ordered to finish this build. In the meantime I applied some wood hardener and tissued the rings to add a smidge of durability and color without the weight penalty of paint. Overall it came out pretty good and the tissue kind of disguises the overlap joint.

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A tapered joint like that is actually called a scarf joint. There are jigs that allow you to cut the taper. I always thought a scarfing jig would be a great way to bevel fins also.

Looks nice.

Steve Shannon said:

A tapered joint like that is actually called a scarf joint. There are jigs that allow you to cut the taper. I always thought a scarfing jig would be a great way to bevel fins also.

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Steve Shannon I resorted to hand beveling because the balsa was no longer flat but bent into a tight curve. Are there any jigs that you know of that are specifically made for thin fragile balsa? Did an online search and found only scarfing jigs for much thicker ply and hardwood.

neil_w said:

Looks nice.

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neil_w Thanks man!

Rktman said:

Steve Shannon I resorted to hand beveling because the balsa was no longer flat but bent into a tight curve. Are there any jigs that you know of that are specifically made for thin fragile balsa? Did an online search and found only scarfing jigs for much thicker ply and hardwood.

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I haven't seen any, but there must be for veneer.


Steve Shannon

Steve Shannon said:

I haven't seen any, but there must be for veneer.


Steve Shannon

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Most veneers are hand cut using a veneer saw, and many of the joints are butt joints since veneers are usually decorative and not structural ( unless you want plywood of course).

Rktman said:

Steve Shannon I resorted to hand beveling because the balsa was no longer flat but bent into a tight curve. Are there any jigs that you know of that are specifically made for thin fragile balsa? Did an online search and found only scarfing jigs for much thicker ply and hardwood.

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Here is a plan for a scarfing jig that claims it's able to cut scarf joints on thin stock down to 0.4 mm. That's pretty small.
https://www.pilotshop.com/catalog/t...VKKxp-lXKX9Vlr-WIoCRUpWv5Ncz-uxkoYaAocm8P8HAQ


Steve Shannon

Steve Shannon said:

Here is a plan for a scarfing jig that claims it's able to cut scarf joints on thin stock down to 0.4 mm. That's pretty small.
https://www.pilotshop.com/catalog/t...VKKxp-lXKX9Vlr-WIoCRUpWv5Ncz-uxkoYaAocm8P8HAQ
Steve Shannon

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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

Charles_McG said:

I've also built that glider. I never got the booster to separate cleanly. And modern ejection charges really blow the crap out of a small vented model like that.

The ring glider itself glides great if you get the toss correctly. It really locks onto a zero-angle-of-attack path and just goes.

These things appear to be related to the Dyson bladeless fans. The inner leading airfoil makes a low pressure region that draws more air in and 'amplifies' the flow. The fan uses compressed air. The glider uses its forward motion.

Notes on that glider- it does really need the spin to work. And it really like 0 AoA. If it's thrown with a small AoA, it wobbles a bit, then visibly dampens the wobble and locks onto path. If the wobble is too great, it just kind of flops to the ground.

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Charles_McG Question Re: your Ring Hawk -- How did you gauge how much to stretch the elastic cord? Too much and I'm concerned it'll damage the slider tube and/or balsa stops at the front. Not enough and it won't even pull the slider up to where it should be at ejection and deployment.

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

It's pretty tight. Like this.
[video=youtube;8ctUkhwE7cw]https://www.youtube.com/watch?v=8ctUkhwE7cw[/video]

I used a rubberband to provide some cushioning.

Charles_McG said:

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

It's pretty tight. Like this.
[video=youtube;8ctUkhwE7cw]https://www.youtube.com/watch?v=8ctUkhwE7cw[/video]

I used a rubberband to provide some cushioning.

View attachment 316947

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Charles_McG Thanks Charles appreciate the feedback!

Finally completed the build and spent about an hour trimming it out. Following the plan directions for trimming wasn't the best idea; even moving the front tube "wing" all the way forward to counteract diving like it said, it would still do the lawn dart thing after the first 6 feet. I finally used intuition and some common sense and added a small bit of lead fishing weight (since I didn't have any clay handy) to the rear fin and it glided beautifully. That in itself surprised me since this "glider" isn't using any airfoils.



The forward travel to sink ratio is somewhere between an oversized paper airplane and a true glider with airfoiled wings, again surprising because my model is pushing 2 ounces. Guess the paint didn't help, but if anyone decides to build this model and not paint it, I'd suggest at least using wood hardener (or CA) on the nose cone. My trimming efforts ended up putting some major creases in the front of the body tube from all the initial nose dives, but the nose cone wasn't even affected except for some minor paint scratches. If the weather holds I'll be conducting its maiden flight this coming weekend.
BABAR

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Very nice! I bet it would glide even better if you detached it from the fin jig. :cyclops:

Looks great.

It's about the aerofoil- it's all in the angle of attack

neil_w

But then it wouldn't be able to carry a big ole payload...

Charles_McG said:

Looks great.

It's about the aerofoil- it's all in the angle of attack

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Charles_McG Wish I'd known from the beginning...would've prevented all those divots in the grass.

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 said:

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!

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BABAR It didn't really register on my digital mailing scale (it can measure down to 1/10 oz). I'm wondering if the gram measurement scale may be more sensitive? I might try giving this model another go using a hand-rolled paper ring, I'm pretty sure I can get a comparable weight and way more symmetrical rings that match up better when stacked in the launch position. Fingers crossed it's stable even with the aft weight I had to add to make it glide proper.

Yes ammonia or vinegar added to the water helps.

dwinings said:

Yes ammonia or vinegar added to the water helps.

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dwinings It's the only thing that worked in this case, since the curve is so severe. As I understand it, Ammonia breaks down the lignin (temporarily) in the balsa, allowing the molecules/fibers to "slide" past each other. Once dry, the chemical bonds reset and the balsa is locked into its new shape. I tried heating in just below boiling point water for 2 1/2 hours and that was a disaster (cracked, splintered, kinked). I finally used A grade softer balsa soaked in ammonia for a half hour and it bent like rubber. Haven't tried vinegar but that may be a more economical way to go (and easier to obtain too).

Update
Did the maiden flight thing somewhat underpowered with a B6-2 due to the small field size. Weight including the engine was 2.9 oz (82grams). Wind speed was at about 3mph.

It boosted ridiculously straight despite suffering a broken wing ring support fin (or the break could have happened after the front wing ring slammed up against wing stops instead of during its upward flight).

Per rocket altitude calculators that combo would have reached in the vicinity of 600 feet but, honestly I lost it in the overcast (the drawback of painting your model mostly white). By the time I caught sight of it I’d estimate it was at about 70 feet judging by the nearby 45 foot trees.

After the ejection charge kicked off it kind of meandered for 2 seconds, drifting downward horizontally until it determined which end was the “front”. Fortunately air resistance really slowed its downward drift. By now it was at about 50 feet but once oriented, it picked up enough speed to suddenly begin moving forward.

It settled into a flat glide at about a height of 20 or 30 feet and headed directly for the tree line, clipping some of the lower branches/leaves of those kite-eating trees before a slight breeze (whew!) made it transition into a clockwise circling glide toward the clear mid field area at about the same drop rate as a paper airplane.

Flight time was about 22 seconds. Nothing stellar, but surprisingly respectable for something that doesn’t use any airfoil surfaces much less look like a traditional glider. Besides, it’s a sport model (i.e. strictly for fun and not competition right?)

Unfortunately no photos; I was manning the camera and my wife forgot the countdown and instead just pressed the launch button. Everything happened so quickly after that that I wasn’t able to get a focus lock in the middle of trying to keep eyes on both the streamered engine pod and the glider while also trying to time everything.

I’m hoping to get it patched up and back in flying condition in time for the next club launch. I’ll have a better chance of getting photos/video letting the launch controller dude handle the countdown and flight chores.

Sounds like a pretty good flight. I think I had to repair a ring fin joint, too.

I painted my red, yellow and black - and promptly lost it a pear tree during the fall color season. Found it again, still resting in the branches, during late winter pruning season.

Charles_McG said:

Sounds like a pretty good flight. I think I had to repair a ring fin joint, too.

I painted my red, yellow and black - and promptly lost it a pear tree during the fall color season. Found it again, still resting in the branches, during late winter pruning season.

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Charles_McG Mea culpa about the break -- I painted the body tube before I glued on the ring fin. All the joints will probably cut loose the same way after awhile, so I'm thinking of building another using a DIY paper ring. Call me OCD but I'd rather have perfectly symmetrical rings that look almost seamless where they come together vs a gap-toothed smile.

Congrats on the flight, and thanks for the posts. Would really like to hear about a paper ring version if you build it!

BABAR said:

Congrats on the flight, and thanks for the posts. Would really like to hear about a paper ring version if you build it!

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Will do.

Seems like all the photo links stopped working when they switched over to the new interface awhile ago. While I no longer have all the photos that once appeared here, I'm posting the ones I have left that might prove helpful to clarify some of the sections.

Here's the result of the butt joints. There's a small amount of bowing but once the fin is attached, it pulls this area back in so it's far less prominent:




Rings made with 1/64" ply are far faster and easier to accomplish, and the amount of outward bowing is far less:


And a shot of the finished model:


BTW as of last year she was still flying, and gliding, really well and getting times well over a minute on C6-3's. I've had to repair cracks in the fins and replace the ejectable motor pod, and been meaning to build a new one once this one can't fly anymore...but it just keeps on going. Maybe someday when it gives up the ghost I'll get around to throwing together another. For now though all my time is spent on whittling down my build pile or working on clones or scratch building my own experimental designs.

Rktman said:

Seems like all the photo links stopped working when they switched over to the new interface awhile ago. While I no longer have all the photos that once appeared here, I'm posting the ones I have left that might prove helpful to clarify some of the sections.

Here's the result of the butt joints. There's a small amount of bowing but once the fin is attached, it pulls this area back in so it's far less prominent:
View attachment 435083

View attachment 435084

Rings made with 1/64" ply are far faster and easier to accomplish, and the amount of outward bowing is far less:
View attachment 435085

And a shot of the finished model:
View attachment 435086

BTW as of last year she was still flying, and gliding, really well and getting times well over a minute on C6-3's. I've had to repair cracks in the fins and replace the ejectable motor pod, and been meaning to build a new one once this one can't fly anymore...but it just keeps on going. Maybe someday when it gives up the ghost I'll get around to throwing together another. For now though all my time is spent on whittling down my build pile or working on clones or scratch building my own experimental designs.

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@Rktman Thanks for reposting your photos. I'm in the process of building a RingHawk and found this thread to be very helpful.

Greg Furtman said:

@Rktman Thanks for reposting your photos. I'm in the process of building a RingHawk and found this thread to be very helpful.

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