Form Fitting Body Tubes Into Different Shapes...

[lakeroadster]

Has anybody tried making a rectangular, triangular or other such shape as a wooden buck... and then soaking a carboard body tube, placing / forcing it over the buck, and then letting it dry?

If needed, after the tube is dry, it could be soaked in CA for strength? As @Daddyisabar would say, "Poor Man's Phenolic".

Seems like a workable concept for making odd-roc models?

I know fiberglass is an option, a messy sticky nasty option. Let's stay focused here... cardboard tubes.

 

[neil_w]

I don't recall anyone ever showing such a technique here on TRF. If someone has then I am interested to hear about it.

I always feel like cardboard is never quite the same after getting wet, but it could be a reasonable thing to test. I suspect it'd take some work to find the optimal procedure, if one exists.

 

[rharshberger]

Might work better to layup your own tube using the adhesive backed kraft paper tape rather than trying to wet and form a regular round airframe tube into a square or triangular shape.

 

[Azamiryou]

I've thought about (but haven't tried) making oddly shaped tubes using standard paper tube techniques (adhesive backed craft paper) on oddly shaped mandrels (bucks).

Challenges I've considered:

• A fixed width strip of paper won't necessarily cover an odd shape evenly. It's probably possible to plan out and cut wedge shaped strips to make it reasonably even, or just use lots of extra layers and eyeball it. That won't be perfect, but probably good enough.
• A round tube is a pretty strong shape; making an oddly shaped tube will compromise that. Building up extra layers is probably enough to deal with it, at the cost of extra weight.

It makes the rocket heavier, but I think extra layers would mitigate both of those problems.

 

[GlenP]

One problem with wetting the premade tube is that the water might dissolve some of the glue and delaminate the tube itself.

 

[kuririn]

How about heavy cardstock?
Cut, score and glue to your desired shape.
Thin CA or Minwax wood hardener for stiffness.
No mandrel or buck needed.

 

[Daddyisabar]

I have always used round tubes wrapped in cardstock. Custom shaped balsa where lightness in the behind is needed. Custom shaped epoxy clay for the nose.

The Noris Natter uses a thin, weak tube that squishes into the oval fuselage. It's a Euro thing as the Noris tubing is considered an abomination by Yankee kit builder's.

 

[lakeroadster]

I have always used round tubes wrapped in cardstock. Custom shaped balsa where lightness in the behind is needed. Custom shaped epoxy clay for the nose.

The Noris Natter uses a thin, weak tube that squishes into the oval fuselage. It's a Euro thing as the Noris tubing is considered an abomination by Yankee kit builder's.
View attachment 647321

No wonder we won WWII. Look at the size of that cat!​

 

[Daddyisabar]

Birch laminate over frame, like high end model airplanes. John Boren did his Navajo in this style here on the forum. Big time wood working.

 

[lakeroadster]

Birch laminate over frame, like high end model airplanes. John Boren did his Navajo in this style here on the forum. Big time wood working.

That won't work for tube fins, plus it's likely overkill for LPR / MPR.​

 

[Daddyisabar]

Kidz these days would 3D print it in a heartbeat.

How are your paper modeling skills?

 

[Daddyisabar]

Old school vacuform!

 

[lakeroadster]

Kidz these days would 3D print it in a heartbeat.

How are your paper modeling skills?

I'll try the wooden buck idea and report back. I'll start with some C-50 tubing that's 0.88" inside diameter x 4" long.​

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[KenECoyote]

Sounds like paper mache? (Old school 3D printing lol!)

I think it would work, but like paper mache, use thin strips or pieces wet/soaked with glue.

Great brainstorming!

 

[Daddyisabar]

Thin leather boiled in oil!

 

[John Kemker]

Thin leather boiled in oil!

Cuirboilli

 

[lakeroadster]

Thin leather boiled in oil!

I'll check with Buffalo Bill, I know he's home, I heard his little dog barking in the basement.​

 

[lakeroadster]

Cuirboilli

Boiled leather... rabbit hole... engage! cuir bouill

 

[mjennings]

Steam might be better than water to soften the cardboard.
Alternately you could go the bulkhead stringer skin rout like a Gillows aircraft model but I would use cardstock instead of tissue paper. If done right it can be quiet strong. I've seen people sit on rc plane wings suspended between 2 tables.

 

[lakeroadster]

Steam might be better than water to soften the cardboard.

Thanks.​

.... Alternately you could go the bulkhead stringer skin rout like a Gillows aircraft model but I would use cardstock instead of tissue paper. If done right it can be quiet strong....

Again... that won't work for tube fins or other hollow structures that are needed for air flow.​

 

[Alex (Boyce Aerospace)]

You can also use 3D printing to make two part pressure molds for paper or cardboard. Every wonder how cardboard egg cartons are made?
You can make almost any shape and easily repeat the process. Here's a YouTube link:



Alex

 

[GlenP]

Thanks.​

Again... that won't work for tube fins or other hollow structures that are needed for air flow.​

Well, maybe consider the structure of an airplane nacelle around an engine inlet, but thinner for your purpose of a tube fin. The construction technique of a tissue covered balsa stick model airplane body could be used as inspriation, but with some modification. Think of an very thin airfoil shaped support stringer in between an inner cardstock skin and an outer cardstock skin, like a wing, but wrapped around a mandrel of the desired shape. More of a ring-wing than a fuselage, you know? Just an idea...

 

[lakeroadster]

Well, maybe consider the structure of an airplane nacelle around an engine inlet, but thinner for your purpose of a tube fin. The construction technique of a tissue covered balsa stick model airplane body could be used as inspriation, but with some modification. Think of an very thin airfoil shaped support stringer in between an inner cardstock skin and an outer cardstock skin, like a wing, but wrapped around a mandrel of the desired shape. More of a ring-wing than a fuselage, you know? Just an idea...

View attachment 647378

Got it...

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All joking aside, I get your point. But for BT-50H tube fins... nope.

 

[les]

Using matt board I built up some triangular tubes for my Tri-Trident. The process I used is here
I did go a bit overboard but they worked great.

Tri-Trident

 

[lakeroadster]

Wooden Buck Meets C-50

I made the wooden buck, 1.00" x 0.50".​

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I soaked the BT-50H / C-50 tube for 5 minutes.​

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I quickly realized once I tried to fit the C-50 over the buck that I needed a bit more clearance, so I sanded the buck down to 0.90" x 0.50".​

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Using a hammer I drove the buck into the tube. The BT-50H separated from the C-50. I removed the BT-50H.​

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I then placed the wooden buck / formed C-50 back into water for 5 minutes.​

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I'll report back once it dries and the wooden buck is removed.​

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[lakeroadster]

Viola!

Well, that worked pretty sweet! We'll let her dry and see how it looks in the morning.​

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[Daddyisabar]

Viola!

Well, that worked pretty sweet! We'll let her dry and see how it looks in the morning.​

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View attachment 647592 View attachment 647593​

A good CA soak will fix any delamination. Be very careful to keep any surface needed to be glued nice and raw.

 

[lakeroadster]

Saw Cut Tube

I let the tube dry for 24 hours, then used my chop saw to trim the edges... looks as good as the original tube, but now it's rectangular. I'll chalk this up as a success.
Now, I need to make some of these for my IHSF Strike Fighter.

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[lakeroadster]

4 Rectangular Tubes

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