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Design => Engineering board => Topic started by: TomLaw on July 10, 2012, 02:55:00 PM

Title: The Big Picture
Post by: TomLaw on July 10, 2012, 02:55:00 PM

Semispan-28”
Bellcrank width-4”
Bellcrank arm-.75”
L/O offset- 1”
Horn radii-1.25”/1”/1”
Horiz. Stab offset - .75”
Flap horn raised-.75”
Del-Change in L/O length
Alpha-Flap angle
Beta-Elevator angle


Note that alpha has a 3 degree asymmetry and beta has a 5 degree asymmetry.
This can’t be corrected at the handle without introducing initial flap and elevator deflection.

Title: Re: The Big Picture
Post by: Brett Buck on July 10, 2012, 08:36:28 PM

Quote from: TomLaw on July 10, 2012, 02:55:00 PM

Semispan-28”
Bellcrank width-4”
Bellcrank arm-.75”
L/O offset- 1”
Horn radii-1.25”/1”/1”
Horiz. Stab offset - .75”
Flap horn raised-.75”
Del-Change in L/O length
Alpha-Flap angle
Beta-Elevator angle


Note that alpha has a 3 degree asymmetry and beta has a 5 degree asymmetry.
This can’t be corrected at the handle without introducing initial flap and elevator deflection.

    Tom - I appreciate the work you are doing here. I am able to figure it out for the most part. But I think these posts would be far more effective if you explained what you were doing and why you were doing it. It's my real-life job to create/review/approve similar work directed towards vastly experienced aerospace engineers in life-critical applications.  A problem statement, a description of terms, and some drawings to aid in visualizing the problem you are solving would help tremendously.

    Brett

Title: Re: The Big Picture
Post by: TomLaw on July 10, 2012, 09:07:20 PM

I am downloading a drawing program as I write this. Reading about canted bellcranks got me interested in research into model control systems. I currently have a mathematical model that simulates the motion of the entire control system from L/O to bellcrank to flaps to elevator. Every object is allowed to be repositioned in 3d space. The bellcrank plane may be tilted, as well as both horns.  The whole thing comprises 46,299 characters and numerous spreadsheets.  I keep tweaking it daily.I am 90% of the way through a similar analysis of the Rabe rudder. Only another 90% to go! The ultimate goal would be to find an 'optimum' relationship among the various pieces.

Title: Re: The Big Picture
Post by: Douglas Ames on July 12, 2012, 11:50:48 PM

Why not split the bellcrank arms so the resulting angle at the vertical flap horn is 90 deg.?

Wouldn't that achieve the same thing as a canted BC ?

Title: Re: The Big Picture
Post by: TomLaw on July 13, 2012, 10:55:55 AM

It might even be better. It is different though, since when canted, both horn holes move through the same angle. It is also not necessarily so that 90 degrees is the 'best' angle.

Title: Re: The Big Picture
Post by: Howard Rush on July 13, 2012, 10:06:22 PM

This has all been done, including diagrams, and was offered free to everyone.  What's the point of repeating it half (um) way?

Title: Re: The Big Picture
Post by: TomLaw on July 14, 2012, 02:56:50 PM

Unfortunately, I have only been reading this forum for a month.

Title: Re: The Big Picture
Post by: Howard Rush on July 15, 2012, 11:04:56 PM

Quote from: Douglas Ames on July 12, 2012, 11:50:48 PM

Why not split the bellcrank arms so the resulting angle at the vertical flap horn is 90 deg.?

Wouldn't that achieve the same thing as a canted BC ?

I think you can do that with my program and see what happens.  I'm not home now and don't have it with me, but if you'd like a copy, I can send you one later.