Why will this time be different? (feel like I'm getting back together with an old girlfriend)
1: I will mask the epoxy goop fill line to insure no excess goop bead width. If you open the picture below you can see all the extra goop I was getting all over).
I waited about 25 minutes before pulling the tape off. hopefully this helps.
2: After goop bead is cured, I will apply thickened goop bead to outside leading edge (to prevent delamination of the plywood). I'm getting better at manipulating loose goop
3: Will defer bonding in AYC spar until rudder is compressed. Locating strategy-TBD.
4: Updated wedges (also considering putting tape on jig faces to reduce friction).
Parting thought. R3 was very nearly closed when it cracked. So the hope is that some marginal improvements will be enough.
Hi Esteban
ReplyDeletesorry, but the angle of the jig is flat out wrong. There is no other way to put it. I just included a new photo on my Aug 2014 page showing the correct angle. Do a test piece using your modified jig that matches, and you will have no more problems. You can see from your photos compared to mine how much wider the angle of your jig is.
regards
Bryan
Bryan,
ReplyDeleteDon't get frustrated. I took a good bit of time determining the angle from the scaled drawings (some of the first posts under the Rudders tab). The important thing to remember is that Bernd specified a NACA shape for the rudders. Bernd being Bernd selected the best spec for the particulars of the application. I just printed out the rudder section drawing and compared it to R1. Its not perfect but its close. If I get things sorted out in a satisfactory way I may go back and re-build R1 (unfortunately I'm getting good at making rudder faces). Back to the NACA shape, there are about a zillion of these set up for differing dynamics (mostly comes down to speed, lift and angle of attack) they are REALLY fiddly. Aerodynamics guys argue endlessly over which is best and when you look at the sections they are arguing over, you can't tell difference. This is important because you are trying to get the most lift for the least drag. You are right that cutting down the angle will make my construction problems go away. But then I will end up with a sub-optimal rudder. The hard thing about this is knowing how big a deal it is (how significant is the potential performance boost) . At the end of the day, you are sailing, and I'm breaking rudders. I've been humbled by aerodynamics enough in my career to put in a little more pain before giving up on getting the right shape. An interesting aside, if you have the inclination would be to make a new set of rudders with a better shape and see if you can tell the difference. Your angle is off enough that I bet you could.
-Esteban .
Hi Esteban
DeleteNo worries, I’m not getting frustrated. My boat is long finished and performing well up to my expectations, as is Rodney’s , whose advice I immediately accepted after my first failure. His rudders have the identical cross section to mine (mine is just a single, centrally located rudder, btw). Don’t think I didn’t advise Bernd of what we did. When I told him about it he said: “if the ply is breaking, close the angle up a bit , or else the ply will break”. I told him mine matched Rodney’s.
I have to say, this was the only area of contention I had with the entire boat. Sure there were lots of details that I had to figure out, and a lot of questions, but as Bernd since said, he would have to make up a 500 page instruction book to cover every detail, and then his plan prices would be a lot more. You will be the same. There will be a lot of details that will require thought and planning, without getting bogged down at this stage.
Judging by the performance Rodney has been getting out of his KD650, (14 knots with a 30 year old Hobie 16 mainsail, and a jib that looks even older) I think the rudder cross section is a non event, in terms of what we are discussing. His boat would be roughly comparable to yours, as far as potential performance goes, I think.
Of far greater importance is getting the leading and trailing edges perfectly straight and true, both on the bare ply, as well as after glassing.
I know you managed to get one rudder to stay together. It worries me, with the amount of pressure on it, as to what will happen when it is subjected to stress, both physical and thermal. Not to mention that one side of the stringer is not making complete contact with the ply.
Finally , again, I urge you to do at least the following: make up some internal wedge shaped pieces to match what you currently have. Split the difference with the angle between what you have , and what I and Rodney used, and make up a test panel with that, by putting packing strips in the top of your jig. If that works , then it may partially satisfy your concerns about incorrect cross sections.
I truly hope, and I am being completely genuine here, that as I check in on your blog, that in 6 months time you have got (at least) one hull built, and not just 10 or 20 broken rudder sections. I really am interested in your project, I offer you nothing but the best wishes with getting it done, but for now, it’s the old water and horses story.
Regards
Bryan
Hi Bryan,
ReplyDeleteI hear you, I was actually commenting to my friend, the venerable Bob Burt, that my project is turning into a rudder construction study. And I know you harbor only the best wishes for my project. I'm just the kind of person that isnt happy until I've really hurt myself. So far these rudder set-backs haven't hurt too bad. When I'm out of ideas and patience, I'll reduce the angle.
-Esteban