To Replace or Not to Replace the ARF SV-11 Bellcrank

[JHildreth]

I have a question concerning the control system configuration in the Brodak SV-11 ARF.  This post may end up moved to the ARF section under Building Tips, however my question also has elements of control system design/philosophy.  That is why I decided to post here first.

First, I would like to say that I am thoroughly impressed with the SV-11 ARF.  This product is much superior to the AFC Cardinals and ARF Pathfinder I had 10-12 years ago.  I am having trouble figuring out how some of the supplied hardware is to be used, but that is another issue.

The supplied control horns are not to my liking.  I am spoiled by Tom Morris’ hardware. The SV-11 horns are most likely adequate, but they are not as robust as I would prefer.  Replacing the horns is easy, but I am not sure if this means I need to replace the bellcrank as well.  The geometries (bellcrank and horn arm lengths) are different.  The supplied flap horn arm is 1 inch versus 1.25 inches for the Morris horn.  The supplied bellcrank arm length is .75 inches versus .875 to .9375 inches for a Morris bellcrank depending on how close to the end of the bellcrank you drill the hole.  The ratio of the horn arm to the bellcrank arm for the supplied hardware is 0.75.  For the Morris hardware the ratio is 0.7 to 0.75.  If I don’t replace the bellcrank, the ratio will be 0.6.

My specific question is should I replace the bellcrank?  The design/philosophical question is what is the design range for this ratio?  A lower ratio desensitizes the controls.  Some amount of this can be made up with handle adjustment assuming there is sufficient space in the wing center section to not interfere with additional bellcrank rotation.  When does it become too much from a control system geometry perspective?

Joe

[Dan McEntee]

  Easy answer. If you have become accustomed to and really like a certain ratio and geometry of Tom Morris stuff, by all means replace the kit hardware with what you know you like. That will put you that much closer to final bench trim right off the bat. If you have the bell crank and an idea of how to go about it,  as the Nike adds say, JUST DO IT!
  Type at you later,
   Dan McEntee

[Randy Cuberly]

HHmmmmmmm...I know what I would do but I'm more interested in hearing what the designer of the airplane Randy Smith says.  i don't think the ratios you listed in the ARF are the same as the ratios shown on my SV11 plans from Randy S.

My guess is; that's not enough of a difference that it can't easily be made up by simply enlarging the line spread at the handle and that the bellcrank displacement will not be an issue but I too want to hear what Randy says!  I know that he has all those numbers at his fingertips, and I'm too lazy to calculate them.

I have an SV11 ARF and will run into the same issue, as I also will use Tom Morris hardware! If I ever get around to assembling the thing!   

Randy Cuberly

[RandySmith]

Hi Joe

It works as is, however  If I were building one, I would use the  stock bellcrank supplied, and  use  a  new  1.25 inch high flap horn,  the  either use or replace  the  elev  horn, I would use a  1 to 1  ratio  with the  flap vs bellcrank horn, or   use a slider adjustable  elev  horn, set  it  1 to 1  to start,  that would be   either  1 in to 1 inch   or  3/4in  to  3/4  in,  BOTH  are  1 to 1.  After  first flights, you may want to  slide the  elev  adjustment  UP  1/16 to 3/32  inch, this will speed up the elevators,  se  what works best for you.
On the handle, start  with a  1 to 1  ratio with the bellcrank, meaning  4 inch line spacing, then adjust to suit your  "feel"

Regards
Randy

[Randy Cuberly]

Randy,
That's precisely what I meant in my post above when I said I know what I would do but wanted to hear it from you again to be sure I was right.  I know that's basically what came out of our conversation on the phone the other day about your recommended control ratios for the SV11.

Thanks, (again)
Randy Cuberly

[RandySmith]

Randy,
That's precisely what I meant in my post above when I said I know what I would do but wanted to hear it from you again to be sure I was right.  I know that's basically what came out of our conversation on the phone the other day about your recommended control ratios for the SV11.

Thanks, (again)
Randy Cuberly

Hi Randy   
No problem  and  have fun with them

Regards
Randy