Looking for insight into carbon tubes for tail booms (and other model uses)

[Mostly Harmless]

Hi all;

Trying my hand at scratch building a plane of my own design of the sort seen here:

http://www.flitetest.com/articles/300-g-plane-design-80-mins-with-1600-mah-battery

Along with learning how to minimize weight by construction techniques, I need to learn to use new materials -- specifically the carbon fiber tubes and rods.

I'm trying to gauge what size tube would be needed for a ~30" tail boom for a 60" wingspan aircraft -- minimizing weight, while keeping it strong enough to survive flight (and not flex mid-flight). Looking at all the various sources on line, I can't get a good feel for what size and wall thickness will meet my needs.

Can anyone offer any suggestions or guidance on selecting the right size for a tail boom? And the sizes adequate for wing spar reinforcement?


Ultimately, I'd like to get down to below the 250 gram limit so as to have at least one aircraft that I can legally fly without permission from the FAA (and will give me some nice soaring capabilities), but this is a serious challenge. I'm pretty sure a 2 meter wingspan is probably out of the question, so I'm aiming for a 60" wingspan. My current design is a combination of the Armin wing and FT techniques. It is tapered towards the ends, so provides some additional challenges with the main spar. My first prototype wing weighs in at just over 180 grams, so is already a substantial portion of the limit before even adding the fuselage, tail, and electronics.

To get that weight down, it looks like I'll have to remove paper from both sides of the foamboard before construction (which seems to be almost half of the weight of DTFB), then use packing tape for covering the outside. A carbon rod might be needed for reinforcing the spar, but I'll have to see how it does without, first.

I'll post pictures as it comes together....

Thanks!

 

[TEAJR66]

Check out the materials available here.

http://www.modelplanefoam.com/

The 4mm tubes, both square and round are a good starting point for tail booms.

For soaring a 60" wing will work fine with just a foam spar. At that length the strength comes from the shape. The spar helps the wing hold its shape.

This wing is 100" and only uses a wooden paint stirrers at the wing joints.


These booms were 4mm square tubes. The wings were only foam spars. The fat wing is MPF at 48" span and the longer thin wings were 60" DTFB.

 

[The-One-Who-Never-Crashes]

I had the same thought: foam plane, foam boom. I would suggest not peeling the paper off the outside of the foam; tape is heavier and won't stick well. Another option is low-temperature iron-on covering. Since keeping the weight down is so important, maybe you'll want to use depron foam or similar?

Back to the boom: a foam boom with a triangular shape will both be strong and dimensionally stable. Side width should be at least ~1.5". Run a couple of BBQ skewers along its length and you'll be good to go.

Good luck!

 

[RAM]

Don't exclude using balsa designs.

What wieght are you at now with just the motor, esc, battery and wires?

I found this one online. It's all up weight is 354 grams. Getting under 250g would be great if you can do it.

 

[BobK]

One way of possibly getting more of a hands on 'feel' is to stop at an archery store and check out cf arrows, they come in many different sizes and weights and you can physically bend them and get a real world feel. Remember also that even if they feel heavy most of the weight is in the fletching and point..once you strip those off the actual shaft is very light.

This is just a way to get an idea and like I said a real world feel that you can't get off a computer screen, I am not saying a cf boom is the answer. Another option is cf fishing rod blanks for tapered spars.

 

[Mostly Harmless]

TEAJR66: Nice builds! Thanks for the source info -- looks like some good building material.

RAM: Nope, I haven't ruled out balsa. But foam is a great material for rapid prototyping. And I'm curious to see just how light I can make a foamboard plane with a reasonable wingspan (my target is a 60" wing with a decent wing chord that I can make from 2 sheets of DTFB). If I get something that flies reasonably well made out of foam, I just might have to make a balsa version to see if it will be lighter.

BobK: Arrow shafts were my first thought. I just need to find a place that has a good selection to sort through. Strangely enough, the local rural WV WalMart (that normally has a decent selection of hunting stuff) had almost no archery equipment, but 2 full aisles of fishing stuff on display (not a lot of fishing going on this time of year).

I'm beginning to question the ability of getting down below 250 grams for an aircraft of this size, but will see what I can find out. At least I'll learn some new construction techniques.

BTW, what adhesives work well for carbon/foam joints?

Cheers!

 

[Pancho]

Another place to find tapered carbon fiber tubes is at goodwill/second hand stores. Go look for the used golf clubs and you'll typically find some no name clubs (or brand name) with carbon fiber shafts for $5 or less. You can find them at some golf shops too, but tend to be more pricey. Some people say to only buy the "stiff" rated shafts, but they all work fine. They also have nicer finish coatings on them, if you are into that.

 

[Craftydan]

These are very much on the high end of things, but worth it:

https://goodwinds.com/carbon.html

particularly their wrapped carbon booms. I purchased the allegro boom from them for my "FrankEncore" DLG, and I couldn't be more pleased with how it came out:



For regular carbon tubes, they've got a fair selection at high-but-not-unreasonably-so prices up to 60" in length and 3/4" in diameter.

Otherwise, if you can live under 32" with a 3/8" diameter, you can do a LOT with cheap CF arrow shafts . . . but you gotta shop in bow season to get cheap.