Boomilever B/C

[sr243]

I noticed in the various boomilevers in this picture of Aia's guide have no bracing on tension members.
http://scioly.org/wiki/index.php/File:A ... embers.jpg
I was wondering how necessary are bracing to the tension members since I brace mine and can't imagine doing without bracing.

[Balsa Man]

I noticed in the various boomilevers in this picture of Aia's guide have no bracing on tension members.
http://scioly.org/wiki/index.php/File:A ... embers.jpg
I was wondering how necessary are bracing to the tension members since I brace mine and can't imagine doing without bracing.

If you'll go back a few pages, and read, you will see this has been discussed in some depth. No, you don't need them; they do nothing for the tension members, and there are better/more efficient ways of getting the compression members strong enough to carry the load without buckling.

[havenguy]

For my last boomilever, I connected the tension and compression members with 1/8" members, then braced them with 1/16" X's. I know this has been talked about a bit a couple of pages back, but I was wondering if these connection pieces are doing anything for my boom, or if they're just adding extra mass. (I'm sort of looking for a yes/no answer).

[iwonder]

Well I'm sorry to say there isn't one

It really depends on the construction of your compression member, the bracing can prevent vertical buckling, but you may not need them if your compression member is strong enough.

[havenguy]

I think my compression member is strong enough (it doesn't buckle or bend), but my tension member is breaking right above the distal end connection, so I'm considering using more of these connection pieces.

[iwonder]

The bracing can't do anything(or, very little) to help the tension member from breaking. The tension member isn't going to buckle, so there's no need to brace it, and the members perpendicular to the tension member won't hold any significant tension force. You problem is probably either the in creating the distal end connection you stress the wood(squeeze it, bend it too much, etc) or that your tension member just isn't strong enough. It's probably the best thing to try a larger tension member or more dense wood first.

Also, you won't really know if your compression member is strong enough to not need the vertical bracing unless you try it without the vertical braces.

[havenguy]

Thanks. I'm glad I posted here before making the next boom.

[Balsa Man]

I think my compression member is strong enough (it doesn't buckle or bend), but my tension member is breaking right above the distal end connection, so I'm considering using more of these connection pieces.

For my last boomilever, I connected the tension and compression members with 1/8" members, then braced them with 1/16" X's. I know this has been talked about a bit a couple of pages back, but I was wondering if these connection pieces are doing anything for my boom, or if they're just adding extra mass. (I'm sort of looking for a yes/no answer).

Well, if your compression member is strong enough (to not buckle vertically), then yes, they are absolutely just extra dead weight. Think about it- braces to brace something that doesn't need bracing?? Using more would just be adding more dead weight.

Besides not being the weight-efficient way to get compression member(s) stiff enough, it is possible they (the one closest to the distal end), are the source of the problem. As a tension gets more and more load on, it gets more and more vulnerable to....lateral force on it-something pushing up against the bottom- the combination of tension and bending. As things load up, the tension members stretch. That allows the distal end of the compression members to move down. If you look closely at the line of the tension member when this happens, you will see that the brace causes a bend. That bend is concentrated right where the brace hits the tension member- a "stress riser". What also bends is the t-member right as it enters the distal joint.

This is just one of a number of reasons I've said this sort of bracing is problematic.

[havenguy]

Yeah, the boomilevers have been breaking right between the perpendicular connection piece and the distal end, which suddenly makes a lot more sense.

What about laminating the sides of the tension members with thinner pieces of wood? Like robotman's picture: http://scioly.org/phpBB3/gallery/image_ ... age_id=980

[iwonder]

Well, the picture doesn't seem to work, but I don't see how that's help... The glue would just add dead weight...