Kite foil hum

Gammo · Since 23 Apr 2011 15 Posts

Just tried my phantasm PS360 stabilizer on my kite setup. 92 mast with a ptm684 front wing. It has a crazy harmonic hum. Did not do it with the 400 stabilizer. Any help on how to sand that 360. Or ideas other than sanding trailing edge?

eric · Since 13 Jan 2006 1839 Posts XTreme Poster

Search "The Donaldson trailing edge, no more hum."

https://colas.nahaboo.net/Surf/TheDonaldsonTrailingEdge

Super easy and has eliminated hum over the years for me on a variety of foils, stabs and masts.

Eric

Hein · Since 08 Mar 2005 1314 Posts Possessed

try a shim

Gammo · Since 23 Apr 2011 15 Posts

Thanks. I’ll try the sanding. Finding a shim in Baja could be tough.

Gammo · Since 23 Apr 2011 15 Posts

Thanks. I’ll try the sanding. Finding a shim in Baja could be tough.

Nak · Tue Oct 22, 24 9:17 am

eric is absolutely right, sanding is the answer to foil hum. The "Donaldson TE" has been shown to be about the most effective trailing edge design, but to actually achieve the geometry that Donaldson specifies is pretty difficult in practice. However, it's pretty easy to achieve a very similar edge that is close enough for our purposes.

First, use a rigid sanding block to back the sandpaper. If you just use your fingers you'll get a rounded edge that will most likely hum. I start with 120 grit sandpaper, then 150, 220, 400. Really, in a pinch, you can skip the 400. If you want to really keep the edge pretty, or seconds matter in a race, add in 600 and wet sanding with 1000.

Start by sanding the top and bottom of the edge at a 30 degree angle. this will make for a pretty sharp edge, so once the edge is starting to be sharp sand perpendicular to the edge so that the edge is blunted with a square--flat--trailing edge. You want this square edge to be 1 - 2mm thick. Any more than 2mm and you might get humming again. This eliminates the sharp trailing edge, but gives you two edges--at the top and bottom of the square trailing edge. Take some 400 grit sandpaper and very lightly dull those two edges, just enough so they lose the feel of "sharpness."

Bear in mind, that although this trailing edge is safer--and faster--than just sharpening the trailing edge, it is still more dangerous than a rounded trailing edge. Rounded trailing edges are the least dangerous, but they sing like a mother. Given the litigious nature of our society, it's not hard to figure out why most factory trailing edges are rounded.

Gammo · Since 23 Apr 2011 15 Posts

Thanks guys. After four times sanding just a little each time I’ve eleminated 90% of the hum. Now just a short hum on some transitions that goes away quickly. At first it was crazy humming. You could feel it through the board in your legs.

eric · Since 13 Jan 2006 1839 Posts XTreme Poster

You might try a light Donaldson on the mast too. Since the mast does not have a high pressure side, you only need to do one side or the other.