Elevated Bridge B/C

[andrewwski]

Using gussets will go a long way as well. I wish they allowed stiff paper as a building material, but even getting some 1/32" balsa will work. Just make sure you keep them less than 1/4".

[jander14indoor]

The argument of balsa cement (ambroid, duco, testor's, etc) vs CA (cyano acrylate or superglue) is as old as CA and there's no resolution yet. But I'll say I'm REALLY shocked to here an F1D flyer admitting to CA use!! Anyway, they both have places in our structures, see the following in depth discussion on glue joint design and execution for strength at minimum weight. And yes, I wrote it for one of these discussion groups originally, others found valuable enought to add to the national site, hope you find it useful.

http://www.soinc.org/events/wrightstuff/glueweight.htm

And LISTEN to the suggestion about gussets. Not needed everywhere, but very effective for light weight strength gain when used selectively.

Jeff Anderson
Livonia, MI

[carneyf1d]

CA makes for a really strong joint. I use it all the time in pennyplanes, ezbs, and especially SO. it's quick, fast drying, and easy...get a hypodermic needle or a tube to narrow the glue opening when applying. allows for more precision and less glue.
using ambroid and applying acetone can also do the trick

[Pleiades]

I just tested my first chopstick bridge and it ended up getting an efficiency of 106. The bridge weighed 19g and it held just over 2kg. It's not THAT BAD considering it's made out of chopsticks glued with elmer's school glue but i know that balsa bridges will be getting efficiencies WAY higher. A lot of the joints failed. Of course the major problem was the two sides pushing away from each other. it's going to be tough to avoid that. The chopsticks were also really weak.

Here's a picture of my first bridge i ever built. Yes, its the one made from chopsticks and elmer's school glue. Any suggestions?

[carneyf1d]

what kind of glue did you use?

[Pleiades]

Elmer's school glue. only because at the time that i built it i didn't have any superglue. now that i have superglue i know that it wouldn't have worked anyway because the glue doesn't want to stick to the chopsticks for some reason...

[carneyf1d]

hmm balsa wood is probably a lot more porous than chopstick...
when you use superglue buy some small glue tips: http://www.hobbylinc.com/gr/adc/adc121.jpg
something like those will work, saves a ton of glue weight and allows you to put the glue exactly where you want and only where you want.

[Aia]

now that i have superglue i know that it wouldn't have worked anyway because the glue doesn't want to stick to the chopsticks for some reason...

There's a similar problem with bass. I've found that balsa + balsa + CA glue provides for a pretty strong connection point.

Was this bridge made to the specs of a B or C division bridge?

Btw: By your definition of an A frame bridge, I did not build one. I may have to try building one of those soon... just to see its capabilities.

[Pleiades]

This was my div B bridge. i'll test my div C one later once it stops raining here. it's been raining all week My div C one is just like the B one only it doesnt have the triangle thing on top. basically its like the one they show in the draft rules.

[andrewwski]

Elmer's glue should be just fine for that bridge. I too have found thin CA doesn't work great for bass like it does balsa (but it still will work).

Obviously that design wasn't anything serious...but that form of lateral bracing isn't very effective. Try X's next time.

That type of bridge is interesting...I don't think it'll work out too well for C...but still interesting. I'm also thinking one overlooked design might be just raising a traditional bridge with pillars...supposing you build them like a small tower, I'd think they could stay light enough while still supporting the bridge. From there, it would be traditional bridge design, which I am a lot more comfortable with over anything else.

Also...just a tip...chain works much better than rope for hanging the bucket...I used string/rope for most of last year for Boomilever, once I tried a chain it made the bucket a lot less likely to spin and wobble.