LOW SPEED FLUTTER I THINK

[PURPHAZ]

Hey guys was flying my 35% carden and saw the elevator moving a little at just under half throtle the servos are 20 flights old maybe they are jr 8611`s . when on the ground no problem at higher speed no problem i put them in because my 8411`s did the same thing but all the time had no trouble with the 8611`s the only differance is i was trying my new vess prop that i think is going to be great i am not sure if it is engine vibration or my servos are taking a crap plane flew fine everytime up just dont know whats up with my elevator what do you guys think

[Biff]

Dude, I feel for you! Could you post a picture of your set up? I think it would help. Would probably save you a bunch of writing! Also incluse measurements of the geometry,distance from servo screw to push rod,distance from elevators to push rods, I bet we'll get to the bottom of it or at least offer suggestions. I love this stuff!

[rc4flying]

PURPHAZ,
I had a very similar problem a few weeks ago at Joe Nall. I came across the field on a pass and noticed the tail fluttering. No....I did not see that, I thought. So I made another pass and saw the same thing along with other helpful spectators on the line that noticed it also. Made some additional passes at different speeds to check things over. After landing it was decided that it was gear lash in the servos on the elevators which only has one per EL surface on this 40%er. By the way, this was a Carden Extra. The surface may have looked like flutter, but it was just the gear lash allowing the surface to osscilate some, apearing to be flutter at slow speeds. Changed them out and the flights for the rest of the week showed up nothing. Still nothing to this date. I had about a year of flying on these 2 servos. I don't think it was a major problem at the time, but it sure could have lead to it in the very near future. My suggestion is try new gears.

[Pro1Foam]

8611..... there lies the problem.


Friend had the same thing happen on his 40% Katana but his was "fluttering" on the ground. Either a bad POT or gear slop.


Im die hard JR, but since I received my 5955's there is no turning back.

[Bunky F. Knuckle]

I've got 8611's on my 35% Extra elevator. I see no signs of flutter. The 8611, I feel, is not the problem. I've been wrong before, but I do not think that it is the source of problems. Maybe mechanical advantage is off?????

Also, what size servo horn are you using?? What is the distance from the elevator to the centerline of your elevator control linkage? Stuff like that........ Pics will help as well!!!

Chris~

[PURPHAZ]

i am at work will try to get pics tonight its a extra 330 carden and set up like they say jim short built the plane and did a great job on it i had 8411 in the elevator that had 25 flights and they did the same so put the 8611`s in and gone now they do the same and iam using jr metal arms i think that it might be gear slop it seems that jr servos dont last long for the money and i have alot of them should i pull them and send them in to jr and or change servos

[PURPHAZ]

sorry about the double post must have hit the wrong button

[KrisW]

OKAY Y Y Y

This is NOT to start a Flame War, or Manufacturers "Gotcha". . only to present the facts and possibilities.

when the 8411's came out 4-5 years ago. .they were the "Wunderservo". . Fast, powerful, etc etc etc. I got a set for my DR 109 (10 servos .. expensive) and thought OH YEAH. . this thing flies SOO much better . .which it did. . for about 25 flights. then I started getting ptich trim problems, constantly having to touch the trim a click or two during flights. Then, I came by on a mdeium speed pass and saw exactly the same thing you described. One of the elevators was "flapping" up and down about 2-3 times a second. ab out an inch or so. It was not really "flutter" but the darned thing was wobbling itself to death. I immediately landed and checked things over.

I was using Rocket City 10-32 horns . .they were NOT flexing. neither was the control surface, and the HD Dubro ball link was not the culprit either. What was happening was that the servos were "chasing" center, and overshooting before they could stop. This turned out to be caused by excessive gear wear, because I slammed a new set of gears in both servos and the problem disappeared with the next flight. 25-30 flights later the same thing happened again, and I started getting REALLY sick of it in a big hurry. Bout that time HiTec came out with the 5945's, with programmers, and I jumped on them as quick as I could. 100. . 150. . 200 flights later and the elevators were still tighter than the 8411's after only 25-30 flights.

I've never bought another JR servo after that.8611's are an improvement over the 8411's, but still get excessive gear wear very quickly. I got a set with a Composite-ARF SuperXtra I bought as a package deal, and gave them a try. After 25 flights I had an elevator "wobble". This was NOT acceptable to me, so I sprang for a complete set of 5955 HiTecs to replace the 8611's and sold the JR's. 150 flights later, on the same servos, and they are still tight and better than the 8611's after 25 flights.

Now. . WHAT is happening?? The gears are wearing .. it's as simple as that. It's not the linkages .. but possibly exacerbated by heavy control surfaces. If you have ever seen a JR Digital "jitter" a rudder on the ground. . this is what is happening to the elevators in the air. The momentum of the control surface is causing an overshoot on center, and the servo is responding and trying to re-center the control surface, but because of sloppy gears, the motor cannot slow the surface down fast enough, and you wind up with an overshoot of center, and the surface begins to oscillate. You have to remember that if the surface is loaded 9deflected into the airflow), it binds up all the gears solidly, so the servo has good tight control of things. But the moment you get near center, where aerodynamic forces are minimized, the surface can begin the "overshoot" oscillation due to almost no load on the surface.

heavy contorl surfaces will show this tendency more than light control surfaces, but they can all do it. Best thing to do is check for play in the geartrain of the servo. If the Trailing edge of the elevator can be moved up and down more than 1/4-5/16" before the servo reacts and locks it in place, then that is too much slop in the geartrain, and you will need another set of gears.

Another thing to remember. ANY kind of slop. . in the linkages or hinges, can cause this problem as well, because the servo will still try to center the elevator, and sloppy hinges or ball links will allow thesurface to overshoot slightly, as well as cause an off-center problem at the servo arm that the servo tries to correct for . .which will then result in "wobble"

First thing .. check the geatrain for slop. then check all ball links and hinges. With the servo arm disconnected from the linkages, the arm should be firmly locked in place. As little as 1/32" of back-forth movement 1" from center is borderlne for the servo being able to keep up with things. If you see 1/16" of play, it's time for a new set of gears. Less than 3/32" will cause the surface oscillation you are experiencing with almost no provocation at all, and being a digital servo, should not exist at all.

Hope this helps. Some pics of your setup will help make sure everything is lined up properly, but if the problem is only now becoming evident, then it is probably a gear wear induced issue.

[PURPHAZ]

THANKS i think your right i also had a 8411 that i put in my show time for rudder and it started to fight to find center and i am with you about the servos to much work to keep them right i put all hitec digitil servos in my show time now that i changed the rudder have always had good luck with none digitil hitecs so i might just send these in and change them to hitec but the jrs have been good it seems the more i fly the more work they need