Boomilever for 2013

[retired1]

The longer a tube is that is unsupported, the more prone it is to a buckle. Tubes are extremely strong for their weight. Unfortunately, I think that a tube will be subject to the same criteria as apiece of wood, IE: 1/4 x1/4"
You can not say that it is a built up member, because if you build a tube from material that is 1/4 or less, it will fail or you are extremely good or lucky.

[iwonder]

Kinda confused about your terminology... What do you mean by a built up member? Also, what is a tube built out of 1/4 or less? And what would make it so failure prone? Finally, what criteria would a tube be subject to that's the same as a rectangular section? Unless you mean a .25" Square piece of balsa and a .25" diameter tube, which would exhibit the same properties(or similar properties).

[retired1]

Built up member- a piece that is made up of several parts as a box beam or an I beam or a laminated beam.
Rule 2b of the trial event is very specific in that your starting wood an not be larger than 1/4 x 1/4".
If you made a tube out of say 1/16 x 1/4 , it would be nearly impossible to have it round and you would have numerous glue joints to fail. It would add a lot of weight, negating some of the advantages of a tube.
I recant on the tube diameter-I was not thinking of the 1/4 starting wood when I said that. There is a possibility that they would allow a 1/4 dia tube, but that would have to be built with 1/32 or thinner balsa and I question the strength of it. Remember that a long tube will need to be supported and a thin wall tube is not going to accept most bracing (based on airplane tubes)
I hope that the 2013 rules clarify that. If not, it will be an early question on the rules.

[iwonder]

It's been brought up before, and thoroughly discussed, as to why the .25" square cross section will, in all likelihood, not apply. Also, a few pages back jander14indoor had a very good link to a method that produces very nice round tubes of ~.25" diameter without much glue. The bracing issue has also been discussed, but because the cross-section limit will most likely not apply, it hasn't been a large problem.

[retired1]

Well, the rules will be out in 6 weeks and then we should know or at least have more discussions on interpretations.

[LKN]

(If there is a 1/4 inch cross section rule)

For boom all members need to meet the 1/4 inch cross section requirement. I understand the base is excluded from the 1/4 inch cross section limit, but what about gussets? Aia's booms have a distal end connection that looks larger than just 1/4 inch, and I don't see how it is feasible for the critical connections if you are limited to a quarter inch.

[Aia]

(If there is a 1/4 inch cross section rule)

For boom all members need to meet the 1/4 inch cross section requirement. I understand the base is excluded from the 1/4 inch cross section limit, but what about gussets? Aia's booms have a distal end connection that looks larger than just 1/4 inch, and I don't see how it is feasible for the critical connections if you are limited to a quarter inch.

Actually, I never used wood that was wider than 1/4". If you go to my guide under "Distal End", you'll see a pretty good picture of my gusset. I used 1/4" by 1/16" balsa (if I recall correctly, it's been awhile), laminated over the top of the connection, and sanded down the excess wood. At that point, the wood was definitely just a hair below 1/4" wide. The angle between the compression and the tension is small enough that the 1/4" by 1/16" balsa covered the connection perfectly well.

Admittedly, the diagram in that section of the guide is not the best-- my paint skills made the lamination look larger and more square than it actually was.

[retired1]

Ala, Did you use any particular height on the bass triangles that you CA glued to the tension member at the base.
Was this your idea or was it borrowed? I have been looking for a method to "pin" the member to the base. This certainly does that.

[Aia]

Ala, Did you use any particular height on the bass triangles that you CA glued to the tension member at the base.
Was this your idea or was it borrowed? I have been looking for a method to "pin" the member to the base. This certainly does that.

I believe those triangles were cut from 3/32" square bass. I determined how long I wanted the triangle, and then used my exactoknife to cut along the would-be hypotenuse. If you do it correctly, you should end up with two near identical triangles. I usually cut out 8 or so triangles, picked the best four, and moved on from there. I did not ever experiment with a different size for those triangles, so there may be a better height choice out there.

This idea is mostly my own. I watched my predecessor in the boomilever event try many different types of bases in 2007. When it was my turn in 2008 to build, I knew which ideas were and weren't working for him. I then redesigned the base, improved it as I went along, and eventually arrived at what you see on my guide.

[_HenryHscioly_]

is there another way to cut wood into sticks from sheets other than using straight edge + razor blade?
My problem is that I often end up cutting in at an angle.

I want to buy sheets instead of sticks this year since it is cheaper, easier to view the grain, and easier examine the wood density across a sheet of wood than examining a bunch of sticks, but I dont think it's worth it if I cant cut properly.
I'm actually okay with cutting thin balsa(1/16" or 1/32"), but any thicker balsa sheets or any bass sheets, I always mess up.