I've been building this
 

I know it's not very conventional and not straight exactly, but is more a proof of concept/mock-up then a real piece of bicycle perfection, I cannibalized an old cheap frame and slapped it together with tubes laying around. It does not have brakes as of yet, but it rides quite smoothly.
Oh, and I,m new here!
Greetings from the Netherlands!

http://bikeforums.net/attachment.php...hmentid=373941http://bikeforums.net/attachment.php...hmentid=373942http://bikeforums.net/attachment.php...hmentid=373943

that's pretty neat, thanks for sharing

Stealth bike!

Very cool, thanks for sharing.

An update:
my bike ? coaster brake added

Interesting, flat black it and call it the Blackbird or B1. Stealth bomber bike fkr sure.

From an engineering perspective, it looks like an accident waiting to happen with the first significant bump, nothing stealth about the impending road rash. Sorry.

Why no down tube or seat stays?

My thought too.

Triangulation has its merits.

In frame design more than tubing.

well after a few ( careful) testrides it still holds, most old fashioned folding and recumben tbikes have one tube by the way. so, gonna try (and maybe fail, but there is no shame in failure) it anyway.

Maybe no shame, but significant pain. I would wish you luck but its all about physics and material properites and no luck.

sjofels; Noting your example of bikes with single main tube are bikes that have that tube used in a completely opposite part of the frame design. If you were to remove the top tube from your design and replace it with a down tube, then your revised design would be closer to the examples you cite and would be at least marginally viable. Of course putting in both tubes will dramatically improve the strength...

/K

triangulation is only important if you are going for light weight. Given the OP's location, weight probably isn't as much of an issue for him. And it looks to be plenty sturdy enough

Agreed. That looks like ~50 mm tubing, with likely heavy walls.