Elevator slop - how mech or aero?

[Dennis Toth]

Guys,

I have a flapped ship that is very happy both upright and inverted but it wants to fly at 12'. Now I've moved the CG forward and it helps but this requires harder control input and doesn't grove as well. The linkage is all tight. I was wondering about adding in some elevator slop. How much? Instead of drilling out the elevator horn is there a way to get the same effect by changing the stab geometry?

Best,             DennisT

[Andrew Tinsley]

Hi Dennis,
  After telling everyone here that slop in the elevator linkage of a non-flapped stunter does work, to cure hunting, please don't go down that road! If the plane hunts, then there is something wrong! Do your best to find what is causing the problem, don't use a palliative "cure" to mask something else that is incorrect! I don't even know if hunting in a flapped stunter can be masked by slop in the elevator linkage. For elevator only models it does "work", but two wrongs don't make a right!

Regards,

Andrew.

[Brett Buck]

I have a flapped ship that is very happy both upright and inverted but it wants to fly at 12'. Now I've moved the CG forward and it helps but this requires harder control input and doesn't grove as well. The linkage is all tight. I was wondering about adding in some elevator slop. How much? Instead of drilling out the elevator horn is there a way to get the same effect by changing the stab geometry?

   I don't see why you needed to move the CG forward to get it to fly lower. Is this just upright or inverted, or both? If it's one or the other, it's probably a handle, incidence, or flap/elevator neutral problem, if it's both, it's probably a combination of these issues.

     The answer to the question is that you can sort of get the same effect by making the stab smaller than the elevator, but that will soften your response around neutral and not really entirely get the effect. Slop doesn't really do what traditional wisdom says, anyway - back in the good old days, with bent wire pushrods and bushings, you had either slop, or binding. If it binds up it is very likely to hunt or not groove well. If you get it loose enough to not bind up, it has some slop. Now, we have had plenty of models with ball links everywhere that have no slop, but don't bind. AND, you can adjust the flap/elevator neutral. Suddenly, despite air being roughly the same as it was in 1960, you no longer need slop!

   

      Brett

[Dennis Toth]

Thanks for the input. The ship flys the same upright and inverted, turns consistant inside and outside. It has a flat stab and elevator 1/4" thick. Other ships I have sit nicely at 6' ish. This one just likes the higher groove. If I push it lower it will go but it is not happy, that's why I was thinking about the slop.

Did you mean that the stab should be thicker then the elevator to soften the neutral?

Best,               DennisT

[Mark Scarborough]

on a corallary to Bretts comments, for ME, ( and I am not Brett, nor anywhere near as good at trimming) I found that the handle neutral seems the most relevant issue with getting the level flight down. Assuming CG is correct, and alignment is good. I found while working trim on the Avenger, it was wanting to fly to high level, and then the other thing I noted was that my NORMAL control inputs in the squares found the plane wanting to drift down while flying across the top. shortening the DOWN line slightly lowered both the level flight Norm position, and made the plane stay up across the inverted part of the square. Again, Just my findings

[Brett Buck]

Thanks for the input. The ship flys the same upright and inverted, turns consistant inside and outside. It has a flat stab and elevator 1/4" thick. Other ships I have sit nicely at 6' ish. This one just likes the higher groove. If I push it lower it will go but it is not happy, that's why I was thinking about the slop.

Did you mean that the stab should be thicker then the elevator to soften the neutral?

   Yes, although I think that is a very bad idea.

      Brett

[Larry Fulwider]

. . . 
 . . .  Slop doesn't really do what traditional wisdom says, anyway - back in the good old days, with bent wire pushrods and bushings, you had either slop, or binding.  . . .
 . . .
      Brett

Can we better define "slop" ?? I was fitting a UHP clevis with the machined .094 pin into a an ARF horn with a "Junior Achievement" quality level bushing. The bushing had a .104 -- .105 ID.    I had reluctantly decided to let it go with the .010 "slop", but was not happy. (The supplied pushrod was about .097, so it was a loose fit also)
       Fortune intervened when I tried to narrow the bushing for the UHP clevis -- the bushing loosened (the chewing gum holding the bushing warmed up, I guess), so I soldered in a new "right size" bushing. 

Would you guys would have replaced the oversize bushing (or horn) if it hadn't loosened on its own? Or would you have lived with the .010 -- .011 slop???

       Larry Fulwider