Guru
Joined: 15/07/2006
Location: AustraliaPosts: 676
| Posted: 10:00am 10 Jul 2011 |
No steel tube, I see no benefit of steel tube. The alloy extrusion is like an 'I Beam' by itself. Adding weight in steel tube only makes it heavier and centrifical forces then are greater.
A 19mm solid bar inside the 25mm x 3 wall thickness tube is much weaker than 25mm solid. The weak point is at the hub. This is where the 25mm solid bar bent.
I don't believe that the 300mm length of bar is a problem. My problem was that I should have put in at least 2 bolts through the extrusion/solid bar to stop the extrusion outer skins seperating and allowing it to pivot on one bolt. I assumed the extrusion internal shape would hold it. I had to hit the bar in with a hammer. It was tight.
Yes Glenn, I have seen that method of balancing. I just assumed the extrusion to be of similar weight. I do agree that the blade set does need to be balanced properly.
The angle is no problem, they are set exactly the same.
Phil, with big heavy blades, I would want my mill furling at 10 m/s, thats 36km/hr. That happens about once a year here.
Karl, 15kg is heavy. I never weighed this extrusion set, but the weight does concern me some. My fibreglass 2.9 blades are only 1.5kg each.
Karl, with the hole for the bolt in the hub, I drilled a 1/2 inch hole in the steel bar that allows for twisting.
All good advice, thanks guys, I have made note.
For now I have the shortened extrusion fitted with 3 bolts through the extrusion/steel bar and only one bolt through the hub/steel bar. The bar is the same pieces, straightened as much as possible. They are 25mm diameter and 300mm long, about 60mm in the hub and the rest in the extrusion.
With bar slightly bent and 2 of the extrusions bent, they are not true at the tip and are not equal spacing at the tip. But they are static balanced. They run fine. Quiet too.
I do have concerns about the alloy fatigue issues as well. Only time will tell how that goes.
Trev @ drivebynature.com