Need help on my twin elevator setup. I do have individual servos (on each side of the fuse-rear). I have tried my best to level the throws and while I had them wise on the scale, proved otherwise during flying as I experienced severe differential during sharp elevator movements like squares. So my flying is limited to level, large loops and rolls, but then it’s a Kyosho Giles with a 90 4S and I would love to wring her.
I am planning to move the rudder servo to the rear and use a single high torque for the elevators with pull-pull setup. Not keen on the push rod setup because I need to keep the tail as light as possible (no way can pay for CF rods besides can’t get those in INDIA). I have used pull-pull setup for rudders and found them good, but this is going to be my first for elev. My worry is that, if I have the cables from both elev-halves joined together at each servo arm end (for each direction of throw), would I still land up with some differential? Let’s say I take care of equaling the lengths of the horns so that no errors can take place there.
Also, is it all right to bind cables (crimp) together and join them with threaded links at servo-arm ends?
Appreciate any inputs on this, pictures and links.
Thanks.

If you have the dual servos set up equally and the throws match on the ground, then chances are that it's merely snapping out on you in flight when too much elevator input is applied. That's common for many SA planes. Unless you're doing some 3D, keep the elevator travel low. You may go through a lot of work changing the setup to a pull-pull and end up with the same results.

Then, do I need to upgrade my servos to higher torque and maybe even thicker rods?

Gyri,

I did a pull-pull set up for my Cap-232 elevator without problem. The slight difference in the line lengths do not cause a differential (none that i can see, no problems in flight) as long as your servo is centered.

However, Stickjammer has a very valid point, better to check on your throws than to rebuild unnecessarily.

Any pics of the installation. What size CAP BTW and what is the servo torque? I went with twin standard servos which amount to 45 oz-in each and its a 90 FS Giles 202. It does have large elev surfaces. My concern is that I am getting these difference even for manuvers like squares and tight loops (far from 3D). On ground they are bang on through out the travel range. Would stiffer rods help?

Still sounds to me as though your problem is too much elevator travel. When you are doing a square corner or a tight loop you are pulling more elevator than a normal maneuver requires and the plane is snapping out. This type of plane needs very little elevator travel to fly pattern maneuvers. Try setting the low rate elevator for less throw and see if it helps. Stiffer rods won't help this condition. Your linkages are probably fine or you would most likely be experiencing flutter, which is a totally different problem.

Gyri,

Mine was a 40 size CAP the kyosho one. It was basically a test be to try and do a pull-pull set up.

If your getting the throws equal on the ground there is no reason for it to differ in the air. Have you checked your lateral balance?? Does it always pull out to one side only? And are your throws within the recommended range? your aircraft is a larger one than mine, so it wont do maneuvers as tightly

Hi Malaysianflyer,
Re Kyosho Cap 232, what engine and where put your battery? I'm doing one now.
Thanks.
Bob

I HAVE A KYOSHO CAP 232 WHICH IS A 40 SIZE AEROBATIC AIRPLANE, AND I PUT A THUNDER TIGER .61 IN IT. I USED THIS ENGINE FOR BALANCE MORE THAN FOR POWER. BY DOING THIS I DID NOT HAVE TO ADD NOSE WEIGHT TO BALANCE. SO THE ENGINE WAS A TRADE OFF FOR DEAD WEIGHT. NOW I USE LOTS OF THROTTLE MANAGMENT AND FLYING IS MORE FUN. I FOUND THAT THESE AEROBATIC PLANES ARE SENSATIVE TO BALANCE WEIGHT AND CONTROL THROWS. IF YOUR PLANE IS SNAPPING OUT OF A LOOP AT THE BOTTOM, CHECK BALANCE OR REDUCE THE CONTROL THROWS. ONCE I GOT MY CAP SET UP AND TRIMMED OUT PROPERLY, THE PLANE FLEW AS IF IT WAS ON RAILS. I REALLY LIKE THE PLANE NOW.

GOOD LUCK

FLASHINGRED

Thanks for all your suggestions. I did fly the plane today with much less throws and still experienced the same differential effect, just flips to her right on squares and tight loops. The wings aren't stalling as there was enough entry speed. I found that one of the elev servos on it's max travel fluttered a bit (much like a backlash), could be the extreme end of the linkage. Replaced the servo and the new one did the same. But then, so far never flown the aircraft anywhere close to that range. I wonder if it still could be playing a part at low throws?
I am not very apprehensive about putting in time for doing the pull pull setup for the elevator (with a single servo only), only I would like to know if that would take care of the problem.
ALso, the model is balanced both ways and the throws have been re-checked for trueness through their travel.

Hi Gyri,
I had a similar problem on my 30% Lanier Edge with Hitec 5945 servos driving the elevators.
the plane would sbap inverted every time I pulled into a wall or did a parachute or would spiral out in a elevator.

I tried re-programming the servos several times using pointers taped to the elevators to make sure that the travels matched exactly. Not just at the end points, but I had them moving as close to identical thru out the entire movement range.
Still, the problem in the air was not getting any better, still snapped like it was a heavy loaded Cap.

I was about to give up trying on that day but I decided to try one more thing just out of frustration.

Since my plane kept snapping to the right, I programed my end points of the left elevator to actually move more than the right elevator.
Went up into the air and, what do you know, no more snapping! Now it drops into elevators, and harriers, walls no longer flip inverted.
I know this is probably not the right way of solving the problem, but I ran out of other ideas.
Had already balanced the plane laterally too. So far it seems to be working. I'll try to get some more trim flights in to see if anything weird shows up.

Its worth a try and cost nothing and just a few quick blips on the transmitter. If it doesn't work, just blip back to your old setting.

Hmmmm... I like to try this although I am worried about inducing a trim of such sorts, but I got my elev on a Y connector to a single channel. Would I get the same effect if I am able to reduce the throws (on right side to which the model flips) by manually adjusting the horn screws? MY radio doesn't have a dual elev support (6XAS), just some programing loop holes which doesn't really offer any place for fine tuning, even Futaba doesn't really recommend it. Thats why I am inclined to consider a single high torque servo (got one) on a pull-pull arrangment. SInce I haven't tried this on the elev (only on rudder), concered whether it would solve the problem and also looking for some pics, notes on it's installation.

Gyri,
I think that you can either reduce the throw on the right elev or increase the throw on the left elev by screwing in or out the control horns.
I'm pretty sure that there is some sort of cause to induce an aerodynamic inbalance that is causing the snapping. Perhaps slightly different hinge locations, pushrod stiffness, servo mounting flex, etc......
Remember to keep your neutral point the same. I didn't notice any other difference in flight due to the purposely mismatched elevators. But I need more time.
If your adjustments don't work, just undo it back to where you were.
Good luck.

Bob

I put my battery pack under the fuel tank to get it to balance (I have my cg back about 1/4"from the recommended point). Engine is an MVVS 0.49, with APC 13x4W prop. FLies very nice with this combo.

Hi,
Thanks for the info on battery and engine. I'm going to use a Rossi .45 and will try the battery under the tank. Without a pitts muff, I had to mount he engine rotated 135 degrees clockwise with muffler on pilots left. This puts the carb niple very low; also, the fuse slot likits tank placement. Right now, engine floods easily, so may change everything. Bob

Hi again,
Incidentally, how good is the MVVS? I have a NIB MVVS .45 w/muff I was thinking of selling. Sold for about $130 new. Should be worth $95 plus shipping. Bob

Bob,

I am in love with the MVVS engines. I currently own the 0.49, two 0.91s, one 1.60, and am waiting for the 58cc petrol to arrive. The Mvvs has plenty of power and very high torque, which allows it to swing big props with ease. It runs perfectly with 0% nitro, it doesn not like nitro, and still gives great power without nitro, so my fuel cost are cheap. The only drawbacks are as follows: 1. Tuning the engine is a little difficult till you get the hang of it. 2. Idle needle screw thends to come loose, so use loctite on it once you get the correct setting. 3. Muffler tends to come off in air, partly due to the bolt length, and to the gasket. The gasket is a good one, its like a cars gasket where it compresses and sticks on, but it takes time to settle, which means after tightening the bolts on the muffler, you have to re-tighten them again to avoid it coming loose ( like the double lock system on a car engine).

But for the price, and the fuel cost it is a brilliant engine to run.

Of course the Rossi is better, but the I cant stand the cost