We the main deck is on. There is a bit of trimming to do but its about 7kg so I am happy with progress so far. With the minimal wings planned I am sure we will have one of the lightest moths around.
Now I'm sorting out the wand/flap linkages.
Hinged the flap today with a true no gap hinge line, its a real barrel hinge full depth of the foil made from carbon tubes and SS wire. Had one many years ago on a really dodgy foil, the hinge worked then but not the foil. This time its in one of John Ilett's proven moldings. The subtle hinge line with no gap top and bottom certainly looks like it should reduce drag, and it moves so freely.
Nice to see Mach2 has a raked rudder bearing on the gantry. Its a good idea, Andrew tried it early this season and I have since modified mine to match. It seems to help reduce ventilation by raking the rudder like the centreboard. Back when my Tiger was new I tried raking the blade without raking the pivot, but even with all the blade behind the pivot, steering got lighter and lighter the higher the boat flew, and it was very unsteadying. (see the picture on the right of this page). Matching the pivot with the rake does make the feel more consistant but it does apply a bow up component when the rudder is turned. I have not tried it yet but this might make sailing downwind in big waves a bit more difficult than it already is? Anyway the Karma gantry I built last week has 5 degrees of rake built in.
Seems all the new boats now have carbon or SS pushrods instead of the old Bowden cables which seemed to be good when new but were susceptible to damage and increased friction with use. Since we all converted the number of crashes from ride height control has reduced dramatically.
My Tiger never had a cable but the first generation thru deck rod/tube was not great and since replacing it last winter with a better aligned setup, everything just works great. For Karma I have reversed the bellcrank directions so now the " pushrod" will be in tension so I am looking at using a simple low stretch line, lighter, less likely to kink, bend or jam and just simpler, exactly the theme of the whole boat.
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8 comments:
How are you gonna get the flap to move up? springs? bungee cords?
JG
The flap will be pulled up with bungee as normal except it attaches to the bellcrank at the top of the fin, just like I have been doing for three years. Much more direct than driving the flap via May stick, wand, pushrod etc. And heaps less load on most of the components so they can be lighter?
Phil:
Can you detail the push rod set-up? What diameter rod (carbon or ss?) and what diameter tube? Obviously, I think, there is no need to support the tube as it passes through the foredeck and front bulkhead, but how about in the space from the bulkhead to the top of the daggerboard? I assume the rod avoids the kicker by running under it, perhaps on the cockpit floor? What happens if there's a violent stack and your body parts start crashing into that part of the boat. The flexible cable can take some abuse, but how about the carbon tube? Any the particulars about the end fittings?
A picture would be helpful.
Thanks,
Joe
Phil make sure your hinge does not leak from the high pressure side through to the low. Needs to be tight with virtually no gap.
Joe,
Andrew and I are using 8mm carbon pultruded tubes running in a 12mm ID carbon tube through the fore deck. It does not align perfectly because the stump is in the way so we have a reinforced plastic hose universal joint just behind the bulkhead. Its only just above the cockpit floor so it can not bend enough to break even if we tread on it.
Karma will have a smaller tube through the foredeck and a 3mm spetra line instead of pushrods.
Karl, gap is small and will get smaller with painting, If I detect a problem a rubber seal might solve issue.
So, a 8mm OD tube in a 12mm ID tube? That answered my other question about the end fittings - I suppose the metal ball is simply threaded into the smaller tube with sufficient epoxy to keep it in place. Now, to the web to find some sources!
Joe
We have stopped using the metal ball joint, too heavy and not enough rotation without modifying it.
We have been gluing a pair of thin C plates to the pushrod aft end and attaching to the bellcrank with a 3/16 pin, the type with the tiny ball retainer you get with Ronstan chainplate adjusters.
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