Excess Aileron sensitivity around neutral

[paul]

Troy,
    Responses are below.
    So far my impressions from the feedback I have received are :  
TE may be too rounded and pointy
I may be expecting too much w/o the higher (45%) expo.
    My basis of comparison is the Prophecy that I normally fly in Intermediate.  Compared to the Meridian it seems to lock in on the roll axis better and not have the twitchiness around neutral (expo is 26%).  
One thing about the Meridian is that it weighs ~ 9.5 lbs due to having a YS 91 AC up fromt rather than a 2 stroke.  This was a double whammy since the YS makes it nose heavy and I had to add tail weight.  Going to a 2 stroke would reduce weigh by 1/2 to 1 pound.  Still, a lead sled doesn't usually have roll twitch problems.

Thanks,
Paul
  ----- Original Message ----- 
  From: Troy A. Newman 
  To: discussion at nsrca.org 
  Sent: Monday, December 05, 2005 2:08 PM
  Subject: Re: Excess Aileron sensitivity around neutral


  Paul,

  Everything looks Ok so far....What deflections are you using with those 100% ATV values....?Both ailerons Up and down please?  15 degrees up and down

  As for the TE being too sharp if it is 1/8" is fine. Getting down to less than 1/16th is getting too thin. Its a little sharper than many of the newer models have but it is OK...The sharp TE will tend to hunt. It will also be more of a problem with servo pot wear.  It can also feel a little touchy at Neutral as Del mentioned because you are over shooting hand eye stuff as the servo hunts center. The result can be that you feel like the wings can never stay level, and you keep over shooting. This can give the feel of touchy right off neutral.  I really think this is not the issue at hand 1/8" is common out there today, not the best but not the worst either.  1/8 " thick with 1/16 " radius at the TE end.  Tapers from 1/2 inch at wing down to 1/8 " at end over a 2" width.

  9252's should be fine and not have the blow back problem. Good torque at 92oz... a little fast than most guys are using at 0.14sec...but this is good as long as you have a good linkage setup. I have never run those servos but I know Futaba digital servos are pretty good. It is very close to the servo I'm using...9411SA at like 82oz of torque and 0.15sec..But I'm also running a little higher voltage than the 4.8V spec so I'm probably up close to what you have. Maybe slightly less torque like 89-90 or something.

  We need to make sure you have good mechanical advantage of stuff. Pushrod at 90 degs to the servo arm and all that is good too....Stiff linkages (CF rods) is also good   MA : 25 mm control horn 15 mm servo arm.

  But the Next Questions:

  Distance from hinge line to the aileron horn clevis pivot point? Just slide a thin metal or plastic ruler down in the hinge line and measure up to the pivot point. Just need a rough idea on the number...within 1/8" to 1/4" is fine for this measurement.  30 mm

  Distance from Servo wheel connection point to the center of the servo wheel? Try to get with a 1/16" of so.  15 mm

  What servo wheels are you using? Futaba so you have the black plastic ones right or aftermarket (dubro, aluminum?)
  If you are using the Futaba plastic horns these are OK but which one are you using the (X, star, or the round wheel-big one or the small one that comes installed on the servo?) Reason I ask is Servo arm flex...Sometimes the servo arms can flex and this can act a little spongy on the ailerons... Again at a higher speed it could be different than a lower speed. I understand that you are not have a speed sensitivity issue but the hotness feel at neutral is seeming to change at low speeds right?  The futaba X arm is being used.  The sensitivity is not related to speed, twichy at all speeds.

  Differential setting in the radio? None

  One more thing. Because the servo wheel is rotational it will impart a little reverse expo around neutral. The linear distance traveled by the linkage is different for the first 1-2 deg off neutral than it is the last 1-2 degs at the ends of the stick travel. This means that on most setups you need to run about 25-35% expo just to get the thing back to linear output. Common Expo values like 45% like you have sound like a bunch but in reality you are only getting a little soft at center. I will also say that the expo function between radios is different not just between JR-Futaba but I have found a different feel between Futaba 8uap and 9Z, and JR 10X and 8103. The 9303 and 10X by JR seem to be very close if not identical if that matters. Moral of this story a blatant statement that you need 45% expo or 60% is tough to confirm in all applications. I have found as the expo creeps up around 70-80% you start to get a knee kick in inflection point in the curve...but again it depends on so many other things. I would say currently you are 45% this is not excessive. This is not light expo either....But maybe increasing up to say 55% would smooth it out a bit better for you. Small little tweaks can sometimes make a huge difference in feel. You wouldn't think 5% would make a huge difference...but the subtle difference is the comfort level you might need. But the amount of expo you need is a function of lots of things...
  So lets look at actual deflections of the ailerons as well as servo horn and control horn lengths.
  Interesting, Initally I ran 25% expo and the plane was twichy.  Since I increased it to 45% it has settled down a lot.  In light of your comments, this may be  a cockpit problem !

  We'll get it figured out. I never owned a Meridian, but I flew a couple helping guys trim them out. It should be fine. Piorun designed some good models...Rick Allison was in on many of those designs too and he knows the ins and outs as well.


  have patience with the process. A little check out here and there will give us some data that we can work with. Since I'm not there to help you fly the thing looking into various aspects can help us eliminate things one at a time.

  Troy Newman
    ----- Original Message ----- 
    From: paul 
    To: discussion at nsrca.org 
    Sent: Monday, December 05, 2005 9:10 AM
    Subject: Re: Excess Aileron sensitivity around neutral


        Oops, when I said the ailerons were OK at full throttle I meant to describe that the aileron authority was not excessive, not that the excessive sensitivity is speed or throttle related - it is not.  Sorry I was not more specific.
        Some more details:
    * Servos are two digital 9252s, should be plenty of torque and have excellent resolution around neutral - no pot problems.
    * Linkage is carbon fiber rod and no slop.
    * Expo is - 45% to reduce the twich.  ATV is 100 % high rate 90% low 75% (normally high would be 100% but is dialed down while working this problem).
    * Airframe - no loose covering, clevis pin is over hinge line at neutral, servo arm and control horn are 90 degrees at neutral (control geometry).  CG is rearward but not tail heavy - pitch is not twichy. 
    * have not measured  wing and stab incidence angles.

    *** one thing that Del mentioned - Aileron trailing edge (and wing) taper to a very sharp radius ~ 3/32 to 1/8 inch.

    Thanks,
    Paul
      ----- Original Message ----- 
      From: paul 
      To: discussion at nsrca.org 
      Sent: Sunday, December 04, 2005 5:26 PM
      Subject: Excess Aileron sensitivity around neutral


          I have a Meridian with a frustrating characteristic, the ailerons are excessively sensitive around neutral.
      I'm the second owner of this plane but the first owner said he had the same problem.  Aileron authority at full throttle is not excessive - in fact it slightly on the mild side.    
      Any ideas ?
      Thanks,
      Paul
      NSRCA 3606
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