I succeeded in getting my mach 2 to go really fast, and I also I accidentally got it to flutter when going into a full throttle dive to see how much speed I could get out of it. It only does it if I get gravity to help me speed up, but I would like to try and prevent it. I accidentally got it to do it twice before the end of the day. I'm lucky I still have a plane I think. A guy at the field told me to put a strip of covering into the space between the aileron and wing on the bottom side to prevent air from going through. Any suggestions? A real pilot and former FAA crash investigator told me to ensure that the control surfaces are even in adjustment, I'm gonna double check them, but that kinda goes without saying. It didn't yaw or pitch when it happened so I don't think it was the tail surfaces fluttering.

Now that you know what causes flutter, you know how to stay away from it. Flutter will eventually cause your plane to crash

Forcing an airplane beyond its design speed in a full power dive is not a sensible thing to do especially when it has demonstrated the onset of flutter.

Sealing the control surface will do nothing. The only practical way to stop it and it will work everytime for our stuff is to mass balance and its very simple to do. I've posted photos of simple balances many times.

Check all your control surfaces closely - make sure the hinges aren't worn/damaged. Sky Raiders before the pinched nose had pinned hinges that could wear, the pinched nose versions have CA hinges. Also check your aileron torque rod's for any movement. I had to cut into the bottom of the TE and glue mine back in, and the routing the TE block was way too large for them allowing for forward/aft movement of the torque rod. Also make sure your servo's don't have any slop in them. We race Sky Raiders with the .46 AX and routinely dive them full throttle vertically with no flutter issues.

Hogflyer

What engine are you running? These planes are really intended for .40's and bushing .46's like the .46-LA and they perform very well with that kind of power. That doesn't stop people (like me) from bolting a .46-AX or even more in the nose.

I've seen catastrophic wing failures on these planes from excessive speed, often in a dive. If you have a big engine and you're looking for maximum speed, it might be worthwhile to add some fiberglass to the wing center section and maybe even beef up other parts of the wing structure.

As Hogflyer pointed out, look at the aileron torque rods. Any slop there could lead to problems. If max speed is your goal, you might want to try upgrading to dual aileron servos with a tight, short linkage. Even then, the problem might not be cured if you go too fast. Counterbalancing as suggested by JohnBuckner might be another option.

Going insanely fast is a lot of fun, just understand that there are trade-off's and something could fail.

The strength of your rigging and the weight of the surface are what allows flutter to happen. Everything has a flutter speed, even a bowling ball. So if you get any model going fast enough, and your servos aren't strong enough or there is slop in the rigging, you'll see it. Well, you'll actually hear it but if it does what it usually does, and blows a wing or tail apart, THEN you'll see it.

You don't usually see models with mass balanced surfaces for a couple of reasons. But when you have a finished model, that's one thing that'll work. But it's almost the last thing to do.

Look at your rigging. Is the pushrod strong and supported so it won't bow? Does it connect to the servo arm and the surface horn without slop. Try to move the surface with your hand. Do that with the power on. If the surface moves easily, find out if the pushrod is bending or the servo is giving up. Flutter is the air pushing on the surface and winning the pushing match.

Sealing the hingeline sometimes works from stiffening up the surface. But what's already been mentioned is almost always the problem.

BTW, 3D models usually have surface sizes that are designed to work at very slow airspeeds. And the leverages found with their rigging gives the air a huge advantage over their servos. That's why a bunch of those designs have aerodynamic balancing as part of the plan. And you really won't make them flutterproof every time. FWIW........

Brett,

Are you guys racing the Sky Raider Mk II down there, or are you planning on using the plane for racing?

Hogflyer

I might use it for combat, maybe. I made it look so good with warbird markings and its so easy to fly especially at low speeds that I may not want to risk using it as a possible collision plane.

You need to bring it up here when we have a weekend Sky Raider race next year.

Hogflyer

Flutter is caused by too much flexing in the control surface linkage.

I switched all my planes over to PULL _ PULL Dacron fishing line cables. What a huge difference. I snug the lines a little. Put a TINY drop of CA in 1 thread hole at each end of the control arms. Want to change holes ? Snip. It is SOO light compared metal or plastic. PLUS you can paint the exposed lines.

I am tired of tooting the horn.

flutter is not always in the controlled surface such as ailerons or elevators. The main surface itself can go into flutter; i.e. the wing itself or the stabalizer. I agree that mass balance sometimes help prevent flutter but not always, in fact less than half the time. As DaRock says, everything will flutter if given the proper stimulus and means to maintain the energy. In most cases, just eliminating all slop in hinges and using very stiff control rods will help. It is also important to have the moveable surfaces as stiff as possible, no soft balsa or springy structure if it is the moveable surface (the most common area of flutter) that is fluttering. I agree that sealing the hinge line help sometimes only because it does slightly stiffen the structure and eliminating the leakage turbulence that might initiate the onset of the flutter.

Rodney is right about the entire surface......fixed & the moveable part starting to flutter. Harbor Freight & GWS .....Cubs can easily do enough dive speed to vibrate & then fold the wing. At first we thought it was a bad part . Until almost every over powered plane started folding wings. Some vibrated, some just folded one side.

I had flutter today on my 7th full tank at full throttle on my club-40 SRM2 with the TT.40 Pro and break-in APC 10x6 prop. The flutter appeared during a 25 degree run with a strong tail wind. Perhaps @120mph flight speed. It had never appeared on the previous 6 flights but it wasn't nearly as windy before.

I landed it right away and checked for tail tale signs of loose linkages, torn covering, something loose and even the spinner and muffler... found nothing. So I put it back up and it fluttered again doing the same shallow dive at full throttle.

Landed it and took off the stock plactic spinner and back plate.... it still flutters so it wasn't a fluttering spinner lol..

Landed it and taped the elevator and rudder hinge lines...... it still fluttered.

Taped the aileron hinge lines and the fluttering went away.

I'm now at the hobby bench to tighten the control linkages and CA the aileron torque rod tubes.

I'll update in a few days. I'm only getting 16,000 rpm on the APC 10x6 and will be going to the APC 9.5x7.5 prop which will give me more speed.

-WL

Me too! It was on a maiden flight on my Sky Raider Mach 2 back a few years. I understood the issues of flutter but didn't hear it happening at the time, I just wanted to go fast too and how cool I thought to do it on a $99 plane ($69 at the time) with some tweaking.
The top side of my entire wing flew off at full throttle in a downward angle but I wouldn't call it a dive , it was moving good with an AX 46 on it using a GMS muffler. The wing was under too much strain exceeding the speed for which the wing was intended to be flown. It's not even fully symmetrical? I did all the anti-flutter chores, but the wing failed. In my ignorance I mailed the pieces of the plane back to World Models asking for a replacement thinking it was poorly glued.

They replaced the plane no questions asked but a note saying they couldn't determine the cause of failure was included.

I later realized it was more likely I pushed the plane too hard. It really goes to show you how nice World Models was to replace the plane, probably knowing all along I was wrong, but wanted me to be a happy customer. I buy a lot from them ever since, without incident, cutting back on my abuse of overpowering the wrong planes. Unless you're competing with Sky Raiders as a requirement for the event, get yourself a "fast" plane to go fast. I learned by a few crashes, you can't defy physics with just a bigger engine and a higher steep dive.

You want to go fast? Get one of these!

http://www.rcplanet.com/ProductDetai...=22233_daa71c1

There are a lot of reasons it can flutter. The main reason is usually sloppy or limp linkage or servos. Others reasons/combinations like long narrow control surface, stabs too flimsy, sharp trailing edges on control surfaces or the leading edge of the control surface thinner than the trailing edge of the wing or stab.

This over powered, streamlined Raider would flutter in level flight even with upgraded linkage all around and dual push rods on the elevator.
Just too much work to fix so I pulled off the gear and sold it. I put my efforts elsewhere.

I found my aileron torque tubes loose and CA'd them in place. Flutter is gone. There are 15 other SRM2 in our club-40 group, all running the TT .40 Pro and mine was the only one to flutter. Some of these are noticably faster than mine.

-WL

Actually when all else fails what will work every time are these, simple to make and simple to install:

The balancers (counterweights) are what I thought of, too. But if you only get flutter in a full-power dive you have a fine set-up already. Some models will tear themselves up at full throttle in straight & level flight (overpowered 3-D models, for instance). My Ultimates and my Hot Stik could shred control surfaces at full-power in level flight. Avoid full-powered dives. "Real" aircraft do.

Mass Balances do work and I have never found a case where they would not regardless of power or velocitys. Mass balances simply move the onset of flutter beyond any speed the airplane is capable of ever reaching at any power or dive angle.

I was in the habit of making up bunchs of them to take to the old SWRA warbird races Here in the southwest and later in RC Pro warbird races. Flutter issues were/are common at these events and in most cases it tended to be the ailerons, especially with strip ailerons.

When one of the fellows survived an episode of severe flutter (meaning extremely obvious) I just shared a pair and all he needed to do was go poke a hole in his ailerons and he was good to go for his remaining rounds, works every time.

John

My observation was in regards to Club-40 pylon racing and the fact that for some strange reason, lol... I was the only one in the group who "just had to be non-comforming!" We have onboard GPS that show some SRM2s hitting 125mph, while mine had flutter @105mph..

I'm not sure this mod can be used on the pylon racer since rules are pretty simple, few things can be modified.

But I like the idea and will add them to my other SRM2 I don't race.

-WL

Brett: You just learned something about harmonics, resonance, and the frequency at which things oscillate. Everything has a resonant frequency. You just found out what that was on your Skyraider. There isn't much you can do about it. All the suggestions above are good, the basic issue is what causes it and speed is right at the top of the list.

I know that you already know this, but here's a short refresher: The picture is of harmonics. Resonance occurrs when the length of something is coincident with it's fundamental frequency. If you reach that point, and give it a trigger, like perhaps vibration caused just about anything (engine perhaps...) it will make it oscillate at that resonant frequency, well, it will vibrate.... flutter. The harder you push it, the stronger the vibration will be at that fundamental frequency.. and at the harmonics, by the way. The combination can really tear things apart, and in short order.

My brother makes his own fishing rods. When he sets the line loops, he uses a method that I found fascinating. He applies a weight to the end of the line, attaches the loops on the rod at evenly spaced points along the length, then goes outside and casts the weight as he would while fishing. He watches the line as it pays out and adjusts the loops so that they will be at the nulls of the vibrations or oscillations of the line as it passes through the loops. He knows he has reached the most optimum setting for the loops when all the nulls occur at the loops. This where there is the least resistance for the line passing through the loops and his line travels a good deal further than they would if the loops were just placed anywhere along the pole. Believe me, it works. And, unfortunately what helps him with his construction of fishing rods hurts us with something called flutter.

If you want something that goes fast, well, you will probably have to invest in something designed to go fast.


CGr.