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Building Tips and technical articles. => Building techniques => Topic started by: Chancey Chorney on December 12, 2016, 08:42:36 PM
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Hi all. So I am in the process of building a .15 sized coroplast 'Platter' and have come to the bellcrank situation. Do I make a 2" bellcrank or a 3" bellcrank. The disc is 16" radius with 2" nose added. I am also going to power it with an Enya 09 as well, so would like to keep it as light as possible. I noticed that the Sig Akromaster comes with a 2" bellcrank. So, I would gladly value all of your opinions in this matter, as I will be able to make either one. Thank you.
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Plans do not indicate the size. I have all the room I need. There are no ribs in the way as it is a flat sheet coroplast wing. Thank you for your time and advice.
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Bigger is better.
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A low performance sport plane like you describe would be just fine with a 2" bellcrank. People were very happy with 2" bellcranks for many decades. Now "experts" say only 4" works. I will take there advice if I ever build a big F2B stunter.
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As space is not an issue, bigger might be a little easier to work with.
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If you're making the bellcrank, make a light weight 3" one. If I ever build my Akromaster it's getting a 3" crank.
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In time I'm going to fins out about a 2 inch bell crank versus a 3 inch on a combat wing I'm working on. The plans says do not use any thing larger than 2 inch. Was told by the person that gave me the kit years ago, follow the plans. I'm also duplicating the plane and will have a 3 inch in it. By the way using the kit as parts patterns.
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In time I'm going to fins out about a 2 inch bell crank versus a 3 inch on a combat wing I'm working on. The plans says do not use any thing larger than 2 inch. Was told by the person that gave me the kit years ago, follow the plans. I'm also duplicating the plane and will have a 3 inch in it. By the way using the kit as parts patterns.
I've been doing design engineering for almost three decades now, and there's basically three things that can happen when you're confronted by some unexplained directive like that:
- Whoever came up with it did it wrong, and you're an idiot to do it their way. The chances of this being true goes down the more people have tried different ways and failed.
- Whoever came up with it did it right, by chance or by genius, and you're an idiot to do it differently -- but you still need to figure out why other folks who tried to tweak the method failed.
- Whoever came up with it did it right, by chance or by genius, but technology has changed -- this doesn't apply here, but it sure could if there was an engine or a motor involved in the decision!
I always find it harder to justify doing things "because that's the only way that works" when there isn't a good, obviously testable (and tested) explanation of why. But that's in an engineering context that doesn't involve such a wacky field as fluid dynamics. I think I'd build two, with two different bellcranks...
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Thank you all. 3" bellcrank it will be. Off to the dungeon shortly to do some more work on this little thing. Pictures to come.
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I would think that a design with limited performance potential would be better off with a control system that makes it easier to make control inputs as precise and appropriate as possible. Therefore, bigger is better when referring to the bellcrank and control horn(s).
Slower controls is better. You can always speed up the control response by making a wider spacing at the handle, with zero loss of precision. You can slow the control response by narrowing the spacing at the handle, but at a significant loss of precision. D>K Steve
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Thank you all. 3" bellcrank it will be. Off to the dungeon shortly to do some more work on this little thing. Pictures to come.
Yes, give us a build thread, please!
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Sounds like it may end up nose heavy. That's only 200 sq.in. An 049 or so will fly it, but the 15 will give it plenty of power to actually stunt to some degree with the short span.
The pushrod forces depend on the mechanical ratios between the handle, the bellcrank, the control horn, the chord of the elevator, and the location of the hinge line on the elevator A longer bellcrank reduces the amount of tension you feel at the handle. Since it's a coroplast fun fly plane the original may have given more control feel with the shorter bellcrank.
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Chancey,
I agree, bigger is better. I put 3" bell cranks in my akromasters. Awesome
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Thanks Dane. I did make and install a 3" bellcrank and appears to function fine, BUT, only time will tell...