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Author Topic: Bellcrank and Control Horn ratios  (Read 5374 times)

Offline Douglas Ames

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Bellcrank and Control Horn ratios
« on: January 30, 2015, 02:33:25 PM »
So here I am building a SIG/ Blackhawk Fokker DVII and I cut down a Perfect 3" BC (control horn) tab to the 5/8" position for clearance.

That's a ratio of 4.8:1.

Do I use 5/8" (.625") as a basis for the elavator pushrod position,or is there some formula? (bellcrank width vs. throw)

All these years I've just winged it and adjusted the throw at the horn. Is it that simple?

As you can see we have our choices...
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Offline Howard Rush

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Re: Bellcrank and Control Horn ratios
« Reply #1 on: January 30, 2015, 03:15:29 PM »
There's a formula.  You got Excel?

If you're not doing stunts, adjusting the throw at the control horn should do the trick.
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Online Dave_Trible

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Re: Bellcrank and Control Horn ratios
« Reply #2 on: January 30, 2015, 03:57:14 PM »
Just as a matter of experience I'd start with about 3/4" on the elevator horn.  5/8" bc to 3/4" flap horn is what I use with one to one flap/elevator and it seems a good start.  Your can then adjust either horn or handle line spacing to suit.

Dave
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Offline Target

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Re: Bellcrank and Control Horn ratios
« Reply #3 on: April 28, 2015, 05:37:29 PM »
Quote from: Howard Rush on January 30, 2015, 03:15:29 PM
There's a formula.  You got Excel?

If you're not doing stunts, adjusting the throw at the control horn should do the trick.

I have Excel. Can you post a file here? Zipped maybe?
I'd like to have that.

Regards,
Chris
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Chris
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Offline Howard Rush

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Re: Bellcrank and Control Horn ratios
« Reply #4 on: April 28, 2015, 10:27:00 PM »
Email me and I'll send you the program.
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Offline Target

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Re: Bellcrank and Control Horn ratios
« Reply #5 on: April 29, 2015, 07:29:44 AM »
Quote from: Howard Rush on April 28, 2015, 10:27:00 PM
Email me and I'll send you the program.
Your email is hidden, but I sent you mine in a pm. Thanks so much in advance.
Kind regards,
Chris Behm
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Offline Howard Rush

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Re: Bellcrank and Control Horn ratios
« Reply #6 on: April 29, 2015, 09:25:07 AM »
Sorry.  It's unhidden now.  I have nothing to hide.
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Re: Bellcrank and Control Horn ratios
« Reply #7 on: April 29, 2015, 02:32:19 PM »
No worries, and thanks for the program. Appreciate your time, thanks. ;)
Regards,
Chris
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Online Dennis Toth

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Re: Bellcrank and Control Horn ratios
« Reply #8 on: May 05, 2015, 09:03:36 AM »
Howard,
Is there a simple ratio calculation between the old 3" Veco bellcrank with the flap hole at ~5/8" the Veco flap horn connected to the BC at 5/8" and the flap to elevator at 1/2" if you use a 4" bellcrank? Wouldn't you just multiply all the hole distance dimensions by the 4/3 (1.33) to get the same leverage? Or if going from 4" BC numbers back to a 3" BC, take the 4" BC numbers and multiply them by 3/4 (0.75)?

Best,        DennisT
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Offline Howard Rush

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Re: Bellcrank and Control Horn ratios
« Reply #9 on: May 05, 2015, 05:42:19 PM »
It's a 3-D problem, so other stuff is involved, but doing what you suggest would give pretty much the same relationship between bellcrank deflection and control surface deflection.  However, that's not what counts.  I'd define the leverage as the ratio of differential leadout travel to control surface deflection.  For your example, that would give the 3" bellcrank about 3/4 the leverage of the 4" bellcrank.
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Offline Tim Wescott

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Re: Bellcrank and Control Horn ratios
« Reply #10 on: May 05, 2015, 06:54:10 PM »
Isn't this over-complicating things for a sport model with (I'm pretty sure) no flaps?

I'd just aim for a reasonable amount of elevator deflection when the bellcrank is more or less fully deflected (60 degrees off center in each direction, more or less).

Then I'd finish the model and go have a ball.
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Offline Howard Rush

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Re: Bellcrank and Control Horn ratios
« Reply #11 on: May 05, 2015, 07:03:30 PM »
Quote from: Tim Wescott on May 05, 2015, 06:54:10 PM
Isn't this over-complicating things for a sport model with (I'm pretty sure) no flaps?

That's what reply #1 said.

Reply #9 responds to Reply #$8.
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Offline Phil Krankowski

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Re: Bellcrank and Control Horn ratios
« Reply #12 on: May 07, 2015, 07:30:23 AM »
Here's a similar question, asked in a different manner.  Some good replies on here.
http://stunthanger.com/smf/index.php/topic,38803.0.html

Phil
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