Boomilever B/C

[noobforce]

Many thanks, I understand it mostly now.

But how do you balance the loading block to prevent it from tipping? Or will it not matter?

[Balsa Man]

I read through past and present Boomilever forums, and I am still not quote grasping the tube concept.
1. How do you get the loading block to fit and stay on the tube?
2. Is the tube hollow or solid?
3. How do you connect tension member(s) to the tube? Wouldn't there be minimal contact because the tube detracts connection points?

Quite a silly question, but I'll ask it anyway since I also don't understand it.
4. How would you go about testing what is a good balsa sheet size and tube thickness to use?

Sorry for asking silly questions. I'll keep reading in the meantime.

Not silly questions- some very good ones.

1- The eyebolt goes through the tube and the load block. The hole the eye bolt goes through is a tight slip fit- eye bolt shaft doesn’t have room to move around. The hole is centered; the load block sits in contact with the tube along the top centerline; the eyebolt keeps it from moving. The centerline of the tension member runs from the back(wall side) of the eyebolt hole on the bottom side of the tube up to the wall mount. That means that it comes through the tube a bit more that 2.5cm inboard og the center of the hole. That means the block does not hit/interfere with the tension member.
2- It is hollow; if it were solid, it would be a rod, not a tube
3- The trick here is inside the tube. The tubes we used were 5/8th inch inside diameter. There are 2 pieces of 5/8ths balsa dowel in the portion from about ¼ inch inboard of where the tension member enters the tube out to the distal end. These two pieces have faces cut at an angle- the exact same angle the tension member runs at, The inner one has a trough filed in it- ¼ inch wide (the width of the tension member), and 1/32nd inch deep (the thickness of the tension member). It is positioned inside the tube so that the tension member fits in that trough. The outer dowel piece (once the inner one’s glued in place) is then pushed in from the distal end, so it’s angled face fits right up against the face of the inner one that holds the tension member. So, when it’s all glued together, you have one piece- glued to the inside walls, glued to the tension member. That gives you massive glue area for the tension member, and the section with the dowel inside is crazy stiff. By using low density dowel, the two pieces together are less than 1/5 grams.
4- Not sure what you’re asking about testing – to test the boom, like any other one, hang it on a test wall and load. Sheet size and thickness ; What we ran was at a wall thickness of 1/32nd inch. It was “machined” rather than rolled (from a sheet). Using a router. Using ½ inch by 1 inch, and a 5/8th inch “round nose” bit, you put a 5/8ths semi-circular grove in the middle of each. You glue them together, you have a 1x1 with a 5/8ths hole down the middle. Then use an “overcut” bit to “take the corners off, a quarter round at a time, and end up with a tube. With an 11/32nds radius (that’s 1/32nd more than the radius of the 5/8ths grove), you get a tube with a 1/32nds wall thickness. You make the 1x1 a couple inches longer than the tube length you want, you leave the last inch on each end unmilled- so you have square/flat ends to run against the router fence, and you cut the ends off at the end. Sheets. After State, I worked with out local B—Div team going to nationals. We went from 1/32nd inch wall machined to 1/64th inch wall rolled tubes. There are instructions out there from the rubber powered flying world. Sheet size, length a bit larger than you need at the finish, an inch or two longer, width, the circumference plus maybe a ¼ inch overlap. You end up trimming the overlap, so you have a single glued seam.
With either, it then becomes a matter of dealing with the inherent variability of wood. With the machined approach, you can, say, make 4 tubes out of ½ x 1 pieces that weigh exactly the same, and the tubes will… often come out with considerably different weights, also, the grain structure will vary, depending on the angle of the grain plane in each piece, With 1/64th sheet, you have the same problem of building two that aree close to the same (in actual strength). In that B- boom that went to nationals, sorted through about 200 36x3” sheets to get 20. Tested one at almost 1900, the nationals one was built from what we thought was slightly stronger, yet is went about 1300. Tubes are inherently more efficient, but the problem of consistency is major.

[noobforce]

Wow, that's a lot of information . I think I get it now.

But one last question, also pertaining to the base. When you drill a hole, the hole is circular. How do you make it square to accommodate tension members?

EDIT: Another question, is it just very careful alignments and measuring that will make everything fit? So even slight non-alignments will be very detrimental?

[chinesesushi]

Wow, that's a lot of information . I think I get it now.

But one last question, also pertaining to the base. When you drill a hole, the hole is circular. How do you make it square to accommodate tension members?

EDIT: Another question, is it just very careful alignments and measuring that will make everything fit? So even slight non-alignments will be very detrimental?

you can file it with like a flat file thing https://carpediemstore.com/viewItem.asp?idProduct=4520 something like this maybe?

[GeorgeInNePa]

Wow, that's a lot of information . I think I get it now.

But one last question, also pertaining to the base. When you drill a hole, the hole is circular. How do you make it square to accommodate tension members?

EDIT: Another question, is it just very careful alignments and measuring that will make everything fit? So even slight non-alignments will be very detrimental?

Needle files. This 12pc set that we use has a square file that works perfectly on thin balsa.



http://www.harborfreight.com/12-piece-p ... -4614.html

You can save 20% by printing their coupon...

http://images.harborfreight.com/hftweb/ ... mobile.pdf

[Balsa Man]

Wow, that's a lot of information . I think I get it now.

But one last question, also pertaining to the base. When you drill a hole, the hole is circular. How do you make it square to accommodate tension members?

EDIT: Another question, is it just very careful alignments and measuring that will make everything fit? So even slight non-alignments will be very detrimental?

Yup, needle/small files work great. The trick is getting a starting hole punched in the right place- pin, needle, etc
Square if you're using square tension member, flat if using strip.
YES, very careful alignment is VERY very important- ts of previous discussion about this, and ways to do it. Its all about making tools, to then make a structure, or to make a piece that then goes into a structure

[iwonder]

Here's another question, I was thinking about trying a tube boom this year, and I fully understand how they could've been made last year, but I could never figure out how to handle a base this year. The only thing I could think of is a dowel and you would have to have two tension members the went into the distal end as one member, but split and attached to either side of the base. Is there some other method I'm not thinking of?

[chinesesushi]

Here's another question, I was thinking about trying a tube boom this year, and I fully understand how they could've been made last year, but I could never figure out how to handle a base this year. The only thing I could think of is a dowel and you would have to have two tension members the went into the distal end as one member, but split and attached to either side of the base. Is there some other method I'm not thinking of?

Well, I experimented slightly with tube booms and put the tension members on the sides. I got an efficiency of 900+ before the balsa wood at the distal end of the compression tube ripped off. So, it wasn't the tension members problem. You could glue the tension members to the sides.

[GeorgeInNePa]

Here's another question, I was thinking about trying a tube boom this year, and I fully understand how they could've been made last year, but I could never figure out how to handle a base this year. The only thing I could think of is a dowel and you would have to have two tension members the went into the distal end as one member, but split and attached to either side of the base. Is there some other method I'm not thinking of?

I'll post a pic, of what we are trying, later today.

[GeorgeInNePa]

Our tube boom weighed 13.54g (too heavy) and held the full 15kg for a 1107.8 efficiency.

Now we need to lighten it up.