Hatz Biplane Association

Howdy builders.

Having recently learned that round tubing is 9X more draggy than streamlined, I started thinking maybe those aileron slave struts should be streamlined. Doe anybody have any thoughts on this, or experience? Has anyone done it? Any reason why not?

Thanks for your advice.

Nick

As per discussions in the Nuzletters from many years ago, the steamlined struts have to be fitted with a special bracket to prevent flutter. If memory serves, it was Lorin Wilkinson's Snooty Hatz. His bracket effectively eliminated the flutter.
The strut flutters because the end fittings are rod bearings and allow the strut to pivot freely in it's vertical axis. The streamlined shape creates a rapid back and forth flutter in flight. The special bracket captures the strut and prevents the flutter. A round rod doesn't have a flutter problem to deal with. I, too, want to eliminate as much drag as possible, but decided that the small amount of drag created by round struts is more desirable than the dangerous flutter situation or having to fabricate the braces.

Ah, well that makes total sense. Thanks for that Mike.
I suppose one could drill and cotter pin the rod end bearing.

Nick

A friend has an Acrosport II and one day I noticed a lengthwise piece of tape with a string under it on each streamlined aileron salve strut. The purpose he said was to stop flutter. The struts on the ASII don't have rod-end bearings and can't turn but apparently, and for reasons I don't fully understand, flutter still occurs. I think it happens at speeds much higher then a Hatz can reach. The Acrosport II isn't the only design to experience flutter with streamlined struts. It's been reported by Christen Eagle and Pitts owners too. See: http://www.biplaneforum.com/forum_posts ... ut+flutter

-Scott

The slave struts streamlined or round: We decided to go with the round, as we felt we should save some weight there. At the speed range of a Hatz we think drag should not be a serious problem, but vibration and flutter definitively is.
We went a radical way and made ours from dia 18 x 1mm carbon tube with special glued in aluminum ends. The weight nothing compared to a 3/4" steel tubing!
However, this is experimental and we might change it when it is not successful.

Hans & Sam, H.C.#78, Switzerland