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General control line discussion => Open Forum => Topic started by: John Carrodus on October 18, 2024, 11:15:08 PM
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generally
What is the relationship between CG and Bellvcrank location generally.....
And - its effect on flight characteristics in stunt
PS ..Great to be back!! Many thanks to the good wishes!
( I have been that man over the last few months ,,in that little boat . The sun is going down, the sea rising, a storm is coming, and the boat is beginning to leak. I'm on my knees - then the sound of a horn as a container ship comes to my rescue. Try to tell me there ain't something much bigger than me in the cosmos!! No Chance!!)
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On a scratch build I put the bellcrank at the spar. Mainly because it's the strongest point. Suspended bellcrank with anchor points top and bottom.
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It’s great to have you back John!
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I am with Perry on this. I don't think that it matters much where it goes (within reason) relative to the CG. On my electrics it is at least 1" behind the CG just to fit. Go with the strongest point that allows a decent range of leadout positions at the tip without eliminating the shear web too much.
Ken
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generally
What is the relationship between CG and Bellvcrank location generally.....
And - its effect on flight characteristics in stunt
PS ..Great to be back!! Many thanks to the good wishes!
( I have been that man over the last few months ,,in that little boat . The sun is going down, the sea rising, a storm is coming, and the boat is beginning to leak. I'm on my knees - then the sound of a horn as a container ship comes to my rescue. Try to tell me there ain't something much bigger than me in the cosmos!! No Chance!!)
None. CG and LEAD OUT location travel in partnership fore and aft (actually vertically as well). The only way that the bell crank location matters is severe angles from the bell crank through the lead out guide may create excessive wear on the leadouts where they rub the guide.
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As Dave says the angle of the lead outs may cause excessive wear. I remember back in the early years of my envolment the was an article published that showed what happens. The main thing was it showed why controls were sluggish or hard to move. D>K
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The bellcrank position is determined where it is the best and most logical position based on structure and where its position will create less wear and friction on the leadout guides. It has been shown in several sources that the bellcrank can go anywhere - from behind the engine to just forward of the tail. There was an article years ago that demonstrates this. In another article, Bill Netzeband demonstrated that the bellcrank can go anywhere.
What makes a difference is the leadout position relative to the CG. There are some rule-of-thumb methods to determine this. I understand that there are programs available to determine this. The thing is to minimize the angle the leadouts have to make going through the leadouts to the bellcrank.
This question comes up on a regular basis on this forum and for some reason, many unreasonable reactions result.
Keith
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Tom Morris and I were having a conversation about this years ago and I remember him saying the airplane does not care where the bellcrank is. What Keith said does matter.
Mike
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Thanks all for your responses.
Cheers John