i think an upside down V would probably be the best.
like this:
like this:
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Latiff?Originally posted by j.m. View Post
That Is good thinking. I bet It would turn good but, what about the drag from a outward/upside down v like this?
DComment
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shouldn't be any more than a turn fin.Comment
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Twin fins In a outward v imho, would cause quite a bit of drag. What do I know...Originally posted by j.m. View Post
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seriously.
The shape has nothing to do with it.
If they were each half the width of "normal" turn fins, then they would suffice, and have just as much drag.Comment
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Dude, Two fins?... And I believe shape has some to do with It also. Have you run two fins like this? What Is your background In boating? Where do these Ideas come from?
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It's not quite that easy.Originally posted by j.m. View Post
you say half the width but what about the frontal area of each ?? What about the combined total wet area of the fins ??
Think airplane wings.There's a reason bi planes are no longer built (much) . Besides building costs they were large, draggy, slow and inefficient.
GhostComment
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Buddy, i've taken 3 aerospace engineering courses, and nothing you said about bipes is really true.
The older bipes were actually MORE efficient than the mono's because they actually flew.
Nowadays, most bipes are aerobatic planes, and slow they are not. You've basically got twice the wingspan, so you only need half the lift for a given section of wing.
Thinner wing, less drag, you (hopefully) know the rest...
Like i said, the combined total wet area would be that of a turn fin like those seen on most boats these days. The frontal area? I was going to use thin guage hardened stainless. Thinner than most turn fins.Comment
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Originally posted by j.m. View Post
LOL...that's why I always see bipes racing the unlimited class in Reno every year
GhostComment
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Back to the topic now of sponson bottom profile and turn fins on a rigger.
This discussion has been thrashed about before here and on at least one other forum that I use a lot.
These are a few little gems that I now know based on research and time at the pond.
A rigger runs very well without a turn fin, in a straight line.
A centre mounted turn fin can work. There are a whole load of other effects that then come into play including water spray lift etc.
Two turn fins = drag, you can dress this one up as much as you like and use 1 micron thick teflon coated super steel if you like. Fins and other appendages in the water = drag. End.
Riggers turn better one way than the other and that is due to the rear being suspended on the prop. one, two or three fins will not change this.
One fin on each sponson even verticaly mounted will cause a bunch of handling issues. I think squirrely is the term here.
Cant those two fins inwards and you are heading towards a hydrofoil.
Shaping the bottom of the riggers sponsons like a tunnel's so that it will behave like a tunnel is not going to happen. One is an outrigger and the other is a tunnel hull. There is a reason for that ! I have one of each so can speak a little on this.
Take a little time to read as much as you can about turn fins, and rigger design.
You may find some interesting stuff. I did !See it....find the photos.....sketch it it....build it........with woodComment
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JM,
Did you end up getting a motor for your rigger? I had a BBY rigger (22") with an 8S motor. I started out on 6 cells and a 632 prop, and it went well, but not too exciting. Then I went to 2S lipo and it was a rocket!
So I think on 6 cells, I would try a 7S as it will give you more speed than an 8S and a bit more prop selection than a 6S, and allow you to switch over to lipo more easily in the future.
Regarding your turn fin ideas, why not build 2 sets of sponsons? One with the standard deadrise angles and a single turn fin, and another with increased deadrise and no turn fins (like your tunnel hull idea)? Could make for an interesting experiment, and won't cost much to do.
Cheers,
ScottComment
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haven't gotten anything yet, (other than plans) still sorting out what i want to do.
I think that i'm going to go with these:
http://www.hobbycity.com/hobbycity/s...tor_(5mm_Shaft)
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Here's our Reno Bipe, you may have seen it.Originally posted by ghostofpf1 View PostLOL...that's why I always see bipes racing the unlimited class in Reno every year
GhostA nation of sheep breeds a government of wolvesComment
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I love that plane.
Isn't that a sportsman class plane.??To be honest I haven't been for a couple years and always camped out at turn 6 where the sportsman races were too far away to appreciate.always spent time in the pits checking them out though
GhostComment
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Been thinking about the two fin thing, and i've come up with what seems to me like a really good idea.
If i used two turn fins, about the same size as most peoples, with the straight edge foreward, mounted on the sides of the tub where the sponson tubes go into it with the tips canted in.
When teh boat is up on plane, the fins would be about 1/4"-3/8" higher up out of the water than on most boats, so there won't be as much drag as in my previous idea, and the effects of each would be less noticeable because they are closer to the center of the boat. I believe this would be necessary because i would be using two fins. In a turn, the outside fin would lift that side of the boat up slightly, while the inside fin would suck that sponson down into the water more, giving the boat more bit in the turn. The inside turn fin would have the same effect as a regular one, but wouldn't cause the boat to flip when turning the opposite way.
Also, with this mounting position, the fins are out of the prop's water flow.
I'm thinking that they should be at the front of the tub, if not slightly forward, to decrease the touchiness that might result from the
bow tracking so straight. (increasing the arm between the pivot point(turn fin(s)) and the rudder)Comment
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