Mike,

I have 2 problems with the H9260...

1. The wings are fluttering, JR DS8401s on the Ailerons. The wing flutter occurs at half throttle and above....its not violant to break the wing, but enuff to scare me...I have had about 10 flights with it so far, with the last 4 showing the flutter. I am using 8 pitch prop on the Saito 220.

a. The linkages are pretty tight, no slop.
b. The hinge gap is sealed.
c. The control surface horns are setup per manual.
d. The servo arms are Dubro HD horns.

2. The landing gear is delaminating, on the right side, I can see the cracks and I assure you that I have NOT landed it hard.


Please advise what do I need to do to solve this problem and FLY the plane.

Thanks.

regards
Marcus

I'm about 99% sure its not wing flutter its aileron flutter. Once ailerons start to flutter, it can excite the wing and I'm sure that is what is happening.

I'm not familiar with the JR 8401 servo, do you mean the 8411 by chance?

The linkage hardware isnt the issue, its the geometry of the linkages that is probably the cause. In general that is normally the issue with flutter. Take a look a the recent threads on that in this forum. It should help explain what I think is probably going on.
FWIW, I'd probably also use metal servo arms rather than the nylon ones, but I also doubt its the root cause here.

Here is my post from that thread:

The geometry looks normal to me. What is important in setting up geometry is to gat as much mechanical advantage to the servo as possible. Start by doing two things.

1. Determine the maximum amount of control surface throw you want. For 3D stuff, thats usually 40 deg to 55 deg. If not doing any 3D it might br more like 15 deg for elev or 20 to 25 deg for ailerons.

2. Set your Travel Adjust (ATV on Funtaba tx) to about 15% under the max. (On JR thats 135%).

After that, adjust the mechanics to achieve the throw you decided you want (step 1). Use Travel Adjust (ATV) by increasing a few points to fine tune to match up left and right sides and up and down throws so all is symmetrical.

That way your mechanical advantage as as good as it can be. If setting up a model for 3D, they mechanical advantage will be less because of the large throws, and thus the servo will work harder, and wear faster. If you have an insufficient servo for the particular job, or are trying to get too much throw then something will give, probably the servo.

What I'm getting at is that there isnt any one best way to set-up the geometry. It depends on how much throw you want. But it should always be maximized s the servo isnt working any harder than it has to.

I hope this helps.

Happy New Year!

Mike,

Thanks for your prompt reply....you are correct, it starts with the ailerons and then goes to the wings. The DS8401 is the asian version of the 8411, but its nylon gears, 11kg servo.

I will try it as per your advise and report back.

Thanks again.

regards
Marcus

Hello,
I have posted this before about a similar problem I had with my Showtime. Ball Links and DuBro arms dont seem to mix. The ball link causes the arm to flex. DuBro arms are best used with regular clevises. Definately use aluminum arms....what a differeance they will make, and switch your servos to "Metal-Gear " . I have come to the conclusion that using nylon geared servos in planes of this size is just asking for trouble. At the least, they will were out quicker........When the flutter started on my Showtime, it was at a pretty low speed, and the nylon-geared servos ( 92oz torque ) stripped ( on both ailerons ), before I could blink!
I replaced my servos with metal geared ones, and changed the DuBro arms to H9 aluminum 3D arms, and problem solved.
Hope this helps........
Blair

I wish we could isolate EXACTLY what produces flutter. Yes, we know that sloppy linkages, open hinge lines, etc., are the common villains.

But WHY does one installation with nylon gear servos in a 14 pound plane (my Extra) show no symptoms, yet Blair's smaller, lighter model was destroyed???

Here's ANOTHER puzzle. I set the throws on my ShowTime last night; 9252s on pitch and roll, 9151 on rudder. Servo horn length is 3/4", control surface horn distance is one inch. On LOW rates (10 degrees deflection) sometime the aileron servo will "flutter" at full stick. There is no pattern, and both do it indiscriminately. Sometimes they do, sometimes they don't. The surface can be up or down; there is no pattern to it. No such problem on the elevators. BTW, this is on the bench. The model hasn't flown yet, and now I'm afraid to.

What's up with THAT? Are my servos going out? Do I have some sort of harmonic in this particular linkage causing it? What?

Mike, your opinion would be appreciated.

.

A few answers here. On the Dubo arms, I cant agree with the blanket statement that ball links and dubro arms dont mix. It depends entirely on the application. If it is a 3D set up and a lot is being asked of the servo and linkages, then the little bit of arm flex that can happen isnt good. But, for example, my 1994 TOC model (Godfrey Extra 330S) used Dubro nylon arms and ball links on all surfaces. It worked great, but we werent doing 3D yet (except for Quique) and only had maybe 20 degrees max throw.

On the subject of flutter, there are different things that cause it, not one cause. Depending on the cuase of flutter in a particular model, a measure taken to fix it could work, or it could agrivate it if the guess was wrong. I'll give a great example later in this post.
Some common causes are:
- Mass - (control surface is too heavy and an oscillation builts into a volent flutter that the servo/linkage cant overcome. This is a common cause in many cases. It is greatly aggrivated by using 3D throws, because the servo looses mechanical advantage over the surface in order to get that much throw and it becomes a lot harder for the servo/linkages system to overcome the load of a surface if it wants to flutter.
- Twist - The surface is structurally weak and even though the servo holds it at the attachment point, it buzzes or flutters outward because of low torsional strength.
- Similar to twist, linkage strength is also an issue. If the linkage system is flexable or week the surface can flutter.

Flutter is in general a condition where the control surfaces oscillate at a natural frequency, so it can be excited by engine RPM if it hits the natrual freq, or by aerodynamic factors if airflow hits a natural frequency. Thats why in some cases the flutter we get doesnt happen at full speed, but at a lower throttle setting and in level flight not a dive. Many factory contribute. I believe that any control surface can flutter if the natural frequency is reched, but in some cases the natural frequency that will excite the flutter is well outside of the flight envelope of the aiplane so it can never happen.


Of course if a surface is not aerodynamically prone to flutter (within the airplanes flight envelope), then it wont even if things arent ideal. Some surfaces can sit still even if completely disconnected from the servo. Getting to that point aerodynamically is very difficult is is very elusive. Most models, especialy 3D or aerobatic models with larger surfaces arent there.
The best rules of thumb are to make the control surfaces as light weight and as stiff as possible. Mass is the biggest enemy in a control surface flutter with models. Mass balances are also an option to help is mass is the cause of the flutter.

Good example of looking for the wrong cause and how the fix actually hurts the situation is a mistake I made several years ago when I worked for Midwest. We were developing the Super Stinker. It originally used 2 x aileron servos with slave rods connecting the top and bottom ailerons. It flew well, but I kept hearing a buzz that I was pretty sure was from the ailerons, I was right there. (buzz is generally a slight, very high frequency but low amplitude oscillation of a control surface around neutral that does not grow into a high amplitude or destructive flutter). I used 4-40 rods connected at the trailing edge of the ailerons as slave pushrods and I thought it might be buzzing and causing the ailerons to buzz with it. So, I added airfoiled aluminum over the rods to stiffen them and to make then less aerodynamically prone to buzz than a round rod. I also knew that I was adding mass to the trailing edge of the ailerons by doing this and if I was wrong and the buzz was a mass realted issue I just made it worse.
I took off, made a turn and went to full throttle in level flight, since that was a condition where I was hearing the buzz before. Did it buzz...no. Instead there was a violent explosion and a bilpane came out one side and 4 ailerons the other. Fortunately it was a Pitts, so the rudder generated a ton of roll and I landed the model. Lesson learned, and I went to 4 x servos on ailerons and the issue was solved.

On the Showtime set-up, what you are seeing on the bench isnt flutter, its servo jitter. They are two completely unrelated issues. Flutter is aerodynamically induced. Jitter is a electronic or mechanical issue. It can also be a case of the mass of the surface sets up a natural frequency that starts,the servo oscillating. But in the air the load of the surface will be very different. It is probably an issue of servo wear causing it. I see it all the time, and it usually isnt a problem. When it becomes a problem, it doesnt cause flutter, the model normally just doesnt fly as well becuase the servo has lost precision. Typically if the jitter stops if the damp the surface (touch it wth your fingers) then its fine and the ail loads in flight will damp it out. If it wont stop, there is a servo problem and soemthing needs to be changed (servo pot, or the entire servo)

Many thanks for that concise explanation, Mike.

You nailed it; when I touch the aileron, the jitter stops.

I'm not going to chance this new airplane. I'll have to replace both aileron servos. This particular set is several years old and has been on three different airplanes. They've never been crashed, or even flown particulary hard; but it would seem they're about worn out, have bad pots, whatever.

Between that hair-pulling VP 30 pump on the Extra, and now this, I'm about ready to go back to four-channel 40 size planes; or take up golf.[&o]

Mike

i have a futaba 7ch rec in my showtime
and all the surfaces slightly chatter any ideas??

Please help!
Thanks

38

Thats a radio issue. Cant say for sure. Oftr times servos with tight deadband (like good digitals) will oscillate when the model is at rear. Hard to say exactly whats up were w/o more info.

Mike,

i have Hitec HS-5955TGs in everything but the trottle
i'm using a a futaba 3001 for the trottle

38

What rx and how many volts?

Mike

the receiver is a futaba 7ch FP-R127DF FM
i'm using a 2cell thunder power 7.4v lipo
i'm also using a MPI miracle switch 6V

38

I'm not familiar with the switch. Does it have a 6v regulator built into it? If not, running the system on 7.4V could be the cause of the issue.

mike

i put in a pcm rec and the servos stoped chatering

thanks for your help
38

Hi Mike
How strong is the 27% Extra 260? Will it hold together in full throttle level fligh with an Evolution 45GX (using good servos, in my case 5945)? Or should that be avoided?

I'd avoid it. There is just no reason to fly it, or any model short of a racer like that.

Some guy in the huuuge thread in the 3D forum messured his to 160 mph with a laser gun. I have no intentions of racing mine at all though. My Funtana 90 has never been above ½ throttle in level fligh, and thats even with an OS 91FX - but I have been extra carefull with it because of many reports that its prone to flutter. I more trying to get a clue on how delicate the Extra is. Do I have to be as carefull with the throttle as with my Funtana 90 or will the Extra take more abuse in terms of speed?

The Funtana 90 will handle full throttle power combined with pylonesque turns provided you do not use the std pathetic aileron control horns. Put on some decent metal ones like Dubro and Sullivan and with HS635's and a Moki 135 the thing outruns a piped 46 delta! Flutter can be cured, just make sure you use the correct hardware [8D]

An H9 Extra at 160mph????

What engine?

Sorry, I meant 100 mph. I live in Europe and converted it in my head to 160 kmh. [&:]