jsm77777

My Feedback: (4)

I have finished my SuperExtra 3.1, and am balancing the plane now. I have 4 servo's on the elevators, and have ended up very tail heavy. Looks like 3 pounds needed in the nose, and I can't believe it's that far off. I have a 3W 150QS on cannisters, and my L-ion packs are mounted on the wing spar carrythrough. The only change was adding the extra 2 servo's on the stabs. Has anyone else had this propblem? The wing is in the rear position and am 5 1/4" back from the LE at the wing tip. I have heard that this supposedly rear position for the CG, should be the starting point for the CG. Any help would be appreciated from any other C-Arf owners. Thank's, Scott

Plane Bob

Hi Scott
The proper CG location should be 4 3/4 from the leading edge of the wing at the tip
In order to do this on my plane I used a solid back plate on my spinner , a 3 Blade prop and a special prop washer that weighs 7oz. This was ordered from Tru-turn. I am planning on a few more ounces on the inside of the lower cowl, just below my baffles. Move your batteries onto the inside of the motor dome, to get some more weight foward. every bit helps. this brings the CG into range and gets that locked in feeling that you are looking for.
If you have any other questions or any assistance , please contact me.
Thanks
Bob
Bob Shapiro
Sales Rep.
Composite-arf.com
Composite-arf-world.com
(941) 232-8188

CDignition

My Feedback: (9)

No adding dead weight tho, thats always a bad Idea,lol.. If you are tail heavy, ditch the 2 servo setup for the elevators. This is not the correct fix for the flutter troubles anyhow, stiffening up the hingeline and linkages is the preferable way to fix it...I know this will come with some disagreement, but a single 8611 is plenty for any elevator bar none...

rcdart

My mate out here in aus is flying his with the cg at the rear measure as in the manual (I think 130mm) with the wings in the back position, 4 servos in tail, batts on the spar, ignition pack on th firewall, really stable, I will PM you with his email if you want to talk to him

Mick

jsm77777

My Feedback: (4)

With my batteries on the spar, ignition at the firewall, and a standard set-up, and 4 servo's on the elevators, I am balancing 1 3/4" behind the 5 1/4" at the wing tip. I can't believe adding 2 more servos would move the CG that far aft. I figured I'd have to add some weight, but not that much. I guess this plane is tailheavy to begin with only 2 servo's on the elevatos, and adding 2 more throws it off more. I heard that some say the 5 1/4" back from the LE at the wing tip with the wing in the rear position would be a good starting point, as the 4.4 - 5 1/4" range is very conservitive. I just would like to know where others may be flying thiers. Thank's for the help so far, Scott

jsm77777

My Feedback: (4)

I just weighed the plane, and with 13 servo's, dual Rx's, dual 4800 Li-Ion Rx pack's, 2400 Li-Ion ignition pack, 3W 150 QS on cannisters, 32-10 Biela prop, 5" Tru-Turn spinner, ready to fly weight is 37 3/4 pounds. I am still balancing 1 3/4" behind the rear limit so I will need to add some nose weight, but not as much as I originally figured. I will be re-checking it today, but worst case scenario would be a pound or so on the cowl lip, so full weight would be, say, 39 pounds. Still not bad with that size plane. Scott

mu2driver

My Feedback: (15)

Scott,

I too did the 4 servo setup, mine was 5.5" from the leading edge, it was ok for 3D but wasent locked in for precision flight, I ended up adding weight to get it to feel nice.

The plane is very big and for 40 lbs it flys very well...

Bobs advice is sound,

CD you have not had enough time on your plane to say 2 is good and 4 is not good, flutter is a serious issue with big surfaces and sharp trailing edges such as these have, what I can say is I had my SX setup with the single 8611, and had over 250 flights with out issue, BUT I did wear out 2 sets of servos because of the leverage the 1.5" arms have on the gear train. This is the main reason the the company wants you to use 4 servos, even Scott at SWB will tell you that with a 1.5" arm your servo output is reduced by HALF or 50%, so our 8611's that started out having 260 in.oz. now only has 130 in.oz of available power and "trust me" one servo is Minimum and should NOT be setup using the 1.5" arm, if only one servo is used then DO NOT use over a 1.25" but preferably a 1" arm and no more than 25 to 30 degrees of travel, this is the only way I will recommend someone use a single 8611 on the Super-Xtra..

This advise is from Hours of flying my plane in every situation possible...

jsm77777

My Feedback: (4)

Yours sounds close to what I've found. With 1 1/4 pounds of lead in the cowl lip, mine balances at the 5 1/4" mark right now. I have heard that the 5 1/4" mark is ideal for all around flying, and have a friend who had flown it further back than that, and still said it was solid. So to make a long story short, mine is 37 3/4 pounds, and with the 1 1/4 pounds in the cowl lip I will weigh 39 pounds ready to fly. That still seems pretty light for this size plane, and should be no issue. Scott

CDignition

My Feedback: (9)

I havent flown my SX yet, just finished setting it up today, but 200 flights on my Jtec Radiowave tells me that 1 servo works good...I compared the elevators, and they are almost exactly the same, just a slightly diffrent shape...I also did the Ballbearing mod, and used 4MM CF shafts. this is in my opinion the root of the flutter issues..I guess if this servo isnt enough, you could run a newer Hitec on it, but I dont think it needs it....if it worries ya, run 2 , but it is overkill to be sure...

My setup is as follows:

Set CG @ 4.5" from leading edge, with the wings in the rear position..so I have a bunch of rearward CG wit hthe front wing position...a 4400 Mah batt for Ignition on motordome, DA150 with Crossover pipes and MTW 110 cans, Single Seiko Servo, 2 4400 Mah batteries on CG with Rudder BAtt also on CG (in the little trays they give you next to gas tank) and a single RX ...works out good I thinks.. will fly it this week and report back.. I will also weigh it.

mu2driver

My Feedback: (15)

Sounds like a good setup CD, take it slow man, and may it have many many wonderful mind blowing flights to come...

I sure hope I get to get back in the air soon with another SX, they are like nothing else out there...

Oh yeah and I like the seiko, its a beast...

jsm77777

My Feedback: (4)

I am sure 2 servo's on the stab may be overkill, but a couple extra servo's for the extra power and piece of mind, makes sense to me. I also fly my planes somewhat hard in the unlimited level with freestyle and all, and the extra servo's should hold up better in the long run. Also, with these long servo arms that C-Arf uses, it's probably more needed than overkill. I also think the possible flutter issue comes from flying the plane for a period of time with a single elevator servo, and some servo slop developes, then the flutter happens. With 2 servo's on each stab, that should slow down that possiblity. I know several people using a singe servos on 40% elevators, but they don't fly as much as me, and for now, are, "getting away with it". I am quite certain my next plane, which will be a 42% Edge 540, will also have 4 elevator servo's on it too, even though I have seen a single work fine on that type plane. Scott

Warren H. Fox

My Feedback: (1)

I had my SX break in half in the air with only one 8611 per elevator side. C ARF replaced the plane free of charge! I wouldn't fly it with only one servo per side. 2 servos did put the CG way back so I put all 3 of the batteries up against the firewall. It flies great this way. But I like the cg a bit back.

I've also had trouble with the aileron 8611's on this plane wearing out, i.e., they wouldn't center after snap rolls. Anyone else out there with a similar problem?

Warren

CDignition

My Feedback: (9)

I really dont see this as a "not enough Torque/Power" issue, but one of sloppiness and wear...You have to remember, the Comp-Arf horns may be 1.5" long, but the Horns on the elevator are equally long...this restores lost torque due to longer servo arms...Let me explain:

You have Plane "A". It has 1" servo arms on the 8611 servos, and the length of the lever(arm on elevator) on the elevator is also 1". That means you have full 260" Pounds of torque working for you...

You have Plane "B". It has 1.5" horns on the Servo, and the Length of the lever(Arm on Elevator) is 1.5"..you still have full 260" pounds of torque, as the Arm ratios are the same.

You have Plane "C" with 1.5" Servo arms, and 1" Elevator horns...THIS is where you now will lose power of the servo. The leverage on the Elevator horn is less, as it is closer to the hingeline, and the Servo horn is less, as it is farther from the CL of rotation of the servo. Thankfully, Comp ARF planes have longer Elevator horns, and there is no worry..

Tighten em up guys, thats the real fix, not jamming 2 servos in there... just my "Out of the Box" thinking that gets me into trouble, hee hee..

rjklein

My Feedback: (1)

Shim the motor out 1/2" this will fix your problem.

mu2driver

My Feedback: (15)

CD not all of the SX crashes were due to sloppy linkages, in fact most were within the first flight or soon after, the linkages were infact brand new with no slop... so your thinking is totaly off.

My Advise is to please "Stop Recommending a single servo setup unless you plan on replaceing peoples planes" Composite-Arf has been replacing planes all last year, they have made a Statement and have also changed the recommended setup in the manual....

Matt Merciez

My Feedback: (34)

Warren,

Was elevator flutter the cause for the fuse breaking in half?

CDignition

My Feedback: (9)

I have seen so many sloppy linkages on brand new planes my head is still spinning, so to assume since a plane is fresh and new it is nice and tight is a fallacy.


Unless you have personally seen and tested each plane BEFORE it fluttered to death, you can't know for sure what went wrong, it is all speculation.

I have personally seen piss poor linkage setups on these Composite planes...as a matter of fact, I fixed all the linkages on my SX after I got it. The elevator horns had ball links on them and we all know Ball links on a cheesy Phenolic horn is sure death waiting to happen. I threw out the horns and Plastic hubs, and went with Aluminum arms.

Things like this are the likley root cause of these failures.

Why would my advice make me liable to replace a guys plane??.. I just tell it the way it is on my planes, if you have any doubts, dont do it my way, I dont care. But dont try to say that adding more servos is the real fix, as we all know it really isnt, and Darcy, your plane is a prime example. It was likley setup properly, with a single servo on each elevator, and got over 250 flights with no trouble. Thats most likley cause you did not use a ball link on the side of a Phenolic servo arm., and you did routing maintenance, right??..


If Comp ARF knows of a structural flaw in this plane that they are trying to band aid with more servos, they better get their act together and get it right, as the market wont stand for a pile of planes that self destruct in the air. Seeing them replace complete planes free of charge is an indication that there is a bigger problem here than servos....

Bottom line is, if ya cant afford to lose it, sell it and take up knitting...

jsm77777

My Feedback: (4)

I have alreadt shimmed my engine out as far as I want to go. Any further and the space between the cowl and backplate will look awful. I already have almost a half inch gap on the left side of the engine, as I am running 3 degrees right thrust. I have to add some weight to the cowl lip, and since the plane is already somewhat light, I will still be 39 pounds ready to fly. That is not bad for the size plane.

I really didn't want this to end up in a debate between using 2 or 4 elevator servo's. My opinion is this on that, I will not risk losing an 7K plane over 200 dollars in servo's. I do my own set-up, and linkages, as do most building this size plane, as we all use what works for us. My linkages are tight and slop free, but I still would use 2 servo's per side. No matter what, there will be some play in the servo gear train that we can't control, and it will become worse over time, as the plane is flown. With 2 servo's you slow that process down, as all that load is spread out over 2 servo gear trains instead of one. For me I will use 2 elevator servo's per side, and have the peace of mind. If others feel fine with 1 servo a side, go for it. If you have no problems, great, but I will not worry eitherwith mine. Scott

CDignition

My Feedback: (9)

[sm=thumbup.gif][sm=thumbup.gif][sm=thumbup.gif][sm=thumbup.gif]

mu2driver

My Feedback: (15)

Warren H. Fox

My Feedback: (1)

The cause of the fuse breaking half in 2 was severe elevator flutter of my CA 3.1. Like I mentioned before CA replaced the plane free of charge. I have never used the phenolic servo arms that CA supplies with their kits. I use Airwild servo arms which fit very tight and so slop is minimized. Another 3.1 crashed at my field because of elevator flutter destroying the elevator servos (new 8611's) and CA also replaced this plane free of charge. It was the 1st flight! I had several hours of flite time on mine. Anyone who flies this plane with one servo per elevator is asking for trouble. CA now says use 2. If you don't you are on your own. Appreciate the comments.

Warren

CDignition

My Feedback: (9)

Just for chuckles, I am going to ask a few questions, as I know Comp ARF people are looking at this thread (Hi Bob)...(I am always the devils advocate)

Since the advent of the 8611, mamy, many people have successfully used a single 8611 on all sorts of elevators for many hours of good non eventful flight time...

The 3.0M Extra that Comp ARF makes apparently has not had these flutter issues, just the 3.1M SX. Why is that??.. the planes are almost the same size, fly in the same speed range, and use the same power. It has even been said that the elevators are the exact same parts from the same molds(I do not have a 3.0M set to compare to). If this is the case, then C-ARF has a serious flaw in the fuselage design of this plane, and must, must do something real to correct it, not just add a few servos to the elevator.

Flutter is a big time techical deal that even NASA dosent fully understand, so to assume some guys that make toy airplanes are all knowing about it is foolhardy.

Has there been any reports of 4 servo setups fluttering to death?? The only people that really know this answer is Comp ARF.

Another question I have is this:

Lets say there was a servo available that is the same size as the 8611, but has 550 In pounds of torque(double the standard 8611). Would this single servo still flutter to death?? since it is mainly a "Power" issue, I would think it would be OK then. OR would CompARF stillwant 4 servos in the elevators??..

mu2driver

My Feedback: (15)

Here is a tid bit about flutter, since this is now the topic of discusion..

Takin from the book "Hammer"

Flutter has always been aviation's dirty little secret. Seldom reported and little understood, it occupies one of those dimly lit and unsafe places that decent people prefer not to visit. The idea that an airplane could shatter, disintegrate, for no reason other than its own motion through the air--better to let sleeping horrors lie. Compared with most other concepts in aeronautics, flutter is obscure and difficult to grasp, but there are examples of the phenomenon in everyday non-aeronautical life. An out-of-balance tire is one; it begins to vibrate at a certain speed as the car accelerates; at some higher speed the vibration subsides. What is happening is that when the tire's natural bounce frequency matches its rate of rotation, the wobble due to imbalance--which is always present--is amplified by the bouncing of the tire on the road. Another example is a child on a swing: the amplitude of the pendulum motion increases when the motions of the torso and legs are properly synchronized with it, but not otherwise.

We use different terms for different instances of the same underlying phenomenon. When we talk about riding a swing, we call it "pumping"; when it's a vibrating tire, we say "resonance" or "sympathetic vibration." When the subject is music, we speak of harmony or being in tune.

"Flutter" is the term used for synchronized vibration when it takes place in a flexible structure moving through a fluid medium--for instance, an airplane in flight. It occurs when two regular, rhythmic motions coincide in such a way that one feeds the other, drawing additional energy from the surrounding flow. In airplanes, there are countless combinations of vibrations that can join forces in this way.

Each component of the airplane has, like a guitar string, a natural or fundamental frequency, plus a whole family of harmonics--integral multiples of the fundamental frequency--of diminishing strength. A classic case of wing flutter might combine wing bending--a flapping motion of the entire wing--with either wing twisting (torsion) or the flapping of an aileron, which has the same lift-amplifying effect as twisting the wing does. But there are myriad other possibilities involving all sorts of combinations of bending, twisting, and flapping, each with its own fundamental and harmonic frequencies, in wings, tails, fuselages, control surfaces, and trim tabs. Out-of-balance tires seldom lead to structural failure of the car because automobile suspensions are vastly overbuilt for the loads they normally encounter. But airplanes, which must be kept as light as possible, are not superfluously stout. They are capable of failing with explosive suddenness when flutter sets in.


And Lastly to sum it all up for the time being:

Flutter is all about stiffness, not strength; even the strongest structure may fail if it flutters. In general, structures that are light and stiff vibrate more rapidly; they are said to have higher natural frequencies. Structures more massive or less stiff have lower frequencies. The usual treatment for a flutter problem is to raise the natural frequency of one structure by stiffening it, but sometimes the opposite approach is used: lowering a frequency by the careful placement of damping weights. The essential thing is to eliminate coincident frequencies in structures that can feed energy to one another. A wing that is very stiff in bending should be made "softer" in torsion, and vice versa.

All it takes is One Case Top to break or a little bit of Play in the Gears and...well you know its over...

Warren H. Fox

My Feedback: (1)

I have a couple of comments. If you are wondering abut flutter just look at a flag on a windy day. It flutters. Our planes are subjected to a lot more wind that that flag. Your 100 mph or faster plane has to contend with hurricane force wind going by the airframe and the control surfaces. So, the control surfaces have to be either aerodynamically balanced or held in place by strong servo gear trains. The gear train on one servo is insufficient to stop flutter on the 3.1 Extra elevator. The elevators are larger than the 3.0 and so need 2 servos to provide additional strength in the gear trains. 2 servos equal half the force trying to make the elevators flutter.

By the way, anybody out there had trouble with the servos for the airlerons on the 3.1 Extra?

Now it is time to go fly, if the wind abates a little and it doesn't rain. It's tuff being retired.

Warren

mu2driver

My Feedback: (15)

All good points Warren, as for the Ailerons Other than wearing out the servos I havent heard of flutter issues, not to say it cant happen, I just havent heard of any troubles. There has been a few that have cut in a 3rd servo towards the outboard.