I have a Sig HERR Engineering Little Something Extra that I converted to electric. It flys just great the way I have it set up. But when I do a loop, it does an 'eight' sided loop. Well, not a round one, but one that seems to straighten out then continue to loop when pulling a loop. I pull on the elevator and the plane starts to go up, slightly straightens out, then continues to loop, then slightly straightens out, and so on until I ease the elevator back to straight level flight.

I have Hitec H55 servo's for just about all controls on this plane. The ailerons work fine, or seem to, but the elevator seem to give me these strange loops. I was thinking it's either the servo (weak) or the control wires are bending and straightening out during 'high G' maneuvers.

Anyone have an idea? I bought a higher torque micro servo as a replacement, but am also thinking that I may have to either replace the control wire or add some sort of strengthening to keep it from flexing?

Ideas?

DS.

Based on the description I'd say the control rod is flexing and the pressure on the control surface is enough to bend it slightly. Add some guide supports along the length of the rod or change to a stiffer one.

Try moving the elevator by hand while looking at the rod inside the plane to see if it does flex (don't use more than one or two lbs of force). Keep an eye on the control horn. too. Some are "flexi". Could also be slop in the servo to control to horn linkages. Should be none. Ony takes 1/16" of control movement to make a noticable wobble.

Don't have an easy answer but do have a nice link for you to read
http://www.tmac.asn.au/articles/Little_Extra.pdf
This guy didn't seem to have any problems so I just don't know.

I think that I would have to agree with Charlie P. It sounds like something is giving way in your control setup. The most likely culprit would be that the control line/rod is flexing. This means that when you move the elevator surface the rod will flex and allow the elevator to move back to center briefly. But you should also look at your elevator servo. Move the servo to full extension and push on the servo arm and see if it moves back any.

This would be my opinion on what you problem is.

Ken

I will take a look at the linkage tonite to see if there is anything obvious. My first instinct was linkage but I did buy a more powerful micro-servo from my LHS. It was only $25.00 so no harm done to my pocketbook if I don't use it. I will just put it in my spare servo box for future use.

I am trying to recall how I built it and what linkage I used from the servo to the elevator, but can't for the life of me remember... so I have to wait till I get home to see... but as Charlie P said, it does seem more and more likely that it's linkage.

Bruce, thanks for the link to the .PDF. Interesting reading and what he did was basically what I ended up doing, however, I needed two extra ounces of nose weight just to make it slightly more nose heavy to neutral than it was without the weights. But, it flys great other than the minor issues with loops. I will fix that and it will be a good flyer.

A little history, here, when I first got it built, I used one of those small GWS receivers (foamy type receivers) thinking that was just fine and lighter. Well, during a trim flight, and not watching the wind, which was right on my back, I didn't notice the plane moving further and further away from me until I had no rudder, then no aileron, then no elevator as I tried to turn it and get it headed back to me. I ended up throttling back (it responded to that but no more after that) as I watched it drop into the trees in the woods about 300 yards away. I found it about a half hour later.. on the ground.. only a broken prop. Wphew!!! I changed out the receiver for a standard Airtonics receiver and it's behaved itself ever since.

Thanks again, guys.

DS.

Update.

I checked the linkage. Pretty solid from the servo to the control horn. Rule flexing out... at least for now. Next, I checked to see if there was any slop in the linkage anywhere. Nope, none. Nice and tight. The servo is my next option.. if it is not strong enough for this application. Have not yet swapped them out, but I do have a higher torque Hitec to put in the place of the existing H55 servo.

Dave, at our LHS, suggested that the elevator, by design, may be flexing in high-G maneuvers... meaning that it may warp or twist 'under load' causing what I described. He suggested that the elevators are pretty small by nature and not well reinforced internally (again by design to keep it light) and that I may be asking for more than the plane is capable of giving. If the servo does not fix the problem, then I will have to assume it's a design issue and leave it at that. I can still fly it this way, no big deal, I just have to slow it down a tad and take some of those possibly excessive G forces out of the equation.

DS.

It's also possible that you're stalling the wing a little. While I do agree that the servo or linkage would be the first thing to look at, that kind of plane can have a fairly gentle stall, so it's possible that you're losing a bit of lift, which opens the loop, picking up a bit of airspeed, which allows you to tigten the loop, and repeat. I've actually seen that exact kind of thing with some planes.

Try playing with the throttle through the loop. I don't know what you're doing now, but try looping at higher and lower throttle settings, and using less throttle on the downline side and so on. It won't "fix" anything, but it might help you get a feel for exactly what is going on.

Also, try moving the CG back a little. If you are nose heavy, you need more elevator to rotate the nose up, and your stall will tend to be more gentle and can help cause the kind of thing you're talking about. Moving the CG back might allow you to snaproll out of the loop though, so be careful, do it a little at a time, and test-fly and test the elevator response at altitude after each change.

An hs 55 is not enough servo for a control surface unless we're talkin foam parkflyer,(floater not 3D) they are for throttle use and not much more...Rog

Hi Rog. They seem to be ok on the ailerons, but you could be right.. maybe the cause of my problems on the elevator. I have a new higher torque micro that I will install and see if that corrects the problem. Also, those servo arms that come with those H55 servo's are, in themselves, quite flimsy, adequate for foamies, but not strong enough by any stretch for normal operation. I bought the Dubro micro servo arms that seem to be at least thicker.. maybe thicker = stronger.. dunno.. but that's what I used on my other plane. I also am using stronger Airtronics micro servo's. They have about twice the torque (??).. maybe.. of the H55's.

Thanks for the hint. I will swap that servo out with the one remaining spare I have and see what happens.

DS.

For what it's worth, i flew this plane with a Norvel .074, Hitec reciever and HS-55 servos and had no problems with it. It flew and maneuvered great. All the other suggestions sound reasonable to me.