chuck l

My Feedback: (17)

I'm in the process of getting my new Sun Dancer shaken down and set up. Today while doing tight loops, the plane was rotating about 90 degrees through the loop. In big loops, a touch of aileron is needed to bring the plane out level. The plane has separate servos on each elevator half, and on the ground they move pretty much in sync, at least to the naked eye. Before digging into it, doesn't any one have suggestions as to what to look for?

Chuck

lsnover

My Feedback: (19)

I've got a similar problem with my GP Eagle. What engine are you running in the Sun Dancer? I've got a DA50 in my Eagle, and I'm thinking it's engine torque. I'm interested to hear what others might have to say.

Regards,
Lee Snover

rmh

most likely you are simply stalling it on the tight loops
Loop tracking tho does sometimes take some sorting out - the slightest effective rudder will corkscrew the model --as will slightly more elevator on one side -in each case it yaws the modl
Roll in a loop is typically stall (tight loop ) or --trim in ailerons or warp in wing or soft ailerons which easily flex when loaded (going up) and relax as load is removed .
In a few cases it is weight of the wing panel -but really, fixing with tip weights is a poor option.

sillyness

My Feedback: (25)

Check the elevators first... make sure they track EXACTLY together throughout their range. I had one plane I needed to use a curved mix on to get the elevators to track together (pre-drilled horn holes were at different angles resulting in less tahn ideal tracking).

Then, try a little rudder trim. Keep in mind that you SHOULD need to fly the rudder a little through the loop... all mine do. It's a fact of aerodynamics... P-Factor increases as angle of attack (a.k.a. G loading) increases.

lsnover

My Feedback: (19)

Dick:

In my case it's not too tight a loop. It's consistent in a large loop or a big one. It could be some wing warp. I have a slight deviation (about 1/2 a degree) on the top wing from one side to the other and the cabanes do not fit particularly well on this Eagle, which may be causing some added deflection. It's difficult to get everything 100% square, as there's no absolute reference point. But it seems to be more pronounced then what would be caused by a small deviation on the top wing.

I have to get some more time in the air with it and experiment some more.

Regards,
Lee

PacificNWSkyPilot

My Feedback: (19)

Here's my thoughts. You may have some rudder dialed in to counter torque thrust in level flight, maybe even aileron as well. During maneuvers it may be manifesting itself as a twist out of a loop and such. Before you can count on clean maneuvers you want to make sure the plane is dialed in correctly on things like engine thrust. Not saying that's exactly what is causing that, but you want to eliminate those items first. Make sure that when the control surfaces are zeroed that the plane flies straight and level and does not wander. Also, it should not twist too much toward one side during takeoff from engine torque..
It could also be be much more simple than that, too much control throw on the elevator can cause a plane to twist during a loop or even snap out of it. But you've said that this is not happening during tight loops, so it's likely not the case here.
Make the plane fly straight and true as you can WITHOUT the benefit of additional elevator or aileron inputs. This could involve checking wing and tailfeather incidences and alignments. One wingtip closer to the rear than the other can cause the same problem that you're describing. Good luck!

Jim

bipeaddict

My sun dancer does the same thing but it has to be a very tight loop. I am about to put a match box on the elevator servos to make sure I have equal travel. I will trim from there.

PacificNWSkyPilot

My Feedback: (19)

Bipeaddict, I have a question for you. Is your Sun Dancer also snapping out of the tight loops or just not tracking straight through the loop?

Jim

bipeaddict

It appears to be snapping out while applying maximum elevator deflection. Otherwise, I track very nice loops. I have to apply a tiny bit of rudder while climbing and a hint of aileron coming over the top to keep the wings level.

The reason for the match box was to help me perfectly match the maxium deflection on the elevators.

PacificNWSkyPilot

My Feedback: (19)

To me, that's a simple diagnosis. You've got a lot of elevator surface area and so it does not require a lot of surface travel to pull a tight loop. GeeBees have big elevators and this happens with them easily. When this happens with me, I just dial down my elevator throw until it no longer snaps, and then a bit more until it stops "skipping", where you can see the tail doing little "skips", squaring off as it goes instead of just running smoothly through a tight loop. That's all the throw that plane could ever use anyway, at least under any conditions I could imagine. I should point out that I don't do 3D flying.

Jim

chuck l

My Feedback: (17)

Well, I almost lost the plane twice today. About a week ago I found that the elevators weren't very close to being the same at the center position, so I readjusted them. The loops got a lot better, so today I thought I would try hovering the plane, brought the plane level at a slow pace, 3-4 clicks of throttle, and pulled up elevator, not full, but a lot. The plane momentarily rose then violently rotated to the ground. Later, with the plane flying level and at low speed, which requires a little elevator on low rates, the plane went to the right and almost went in. This has happened twice before when turning to set up for landing. The plane is suddenly going in the opposite direction. Giving it some power brings it right back under control. My first Sun Dancer did not handle this way.

Checking over the plane and radio, I found the left elevator didn't follow the right elevator when trimming (the right elevator is the master in Futaba 9C language). That was a programming error which has been corrected. The elevators halves were off by 3/16", at the most, at full deflection, they are now set as close as possible which is about 1/16". It will have to be flown to see if this makes a difference, but I'm still not feeling right about it. At moderate to higher speeds, I don't notice at problem at all. Are the settings for split elevators that critical? It seems like a tip stall, but the plane lands slower than the speeds that this is happening at.

Any comments? Anything else I should look at? At tests I can try in the air to explore the problem?

Chuck

Dugster

Elevators, elevators, elevators! [X(] They must move exactly together through the entire range of the control throw, not just center and end points. If they are not exactly the same you will induce roll. Think about that for a minute.

You can match them with the 9C with Trim, Sub-trim and end points. What I do is tape a piece of carbon fiber tube to the back of each elevator and have them come together behind the rudder to act as pointers. Then you can get the match down to less than a 32nd of an inch. Work on the mechanical linkage first (arms and links must be identical), then program the Tx. If all else fails use an Equalizer II from Smart fly or a JR Matchbox.

chuck l

My Feedback: (17)

Dugster,

When I found the elevators out of alignment at week ago, in hindsight it was because of not having the trim command turned on in the program mix. Today I zeroed the trim, set the sub-trim followed by the end points. I will do the carbon tube check tomorrow and program linear movement if necesscary, but I'm still troubled as to why the problem is only noticable at slower speeds and not higher speeds.

Chuck

PacificNWSkyPilot

My Feedback: (19)

Sounds like something is "fighting" the natural flying of the plane. You seem to have done a really good job of sorting out things around the elevators.
At this point, it certainly can't hurt to give it a thorough going-over, check the angle of attack on the lower wing and make sure it zeros with the rear horizontal. Then check the upper wing's angle of attack. When in doubt, I zero-zero-zero everything. Too much of several trims can cause something a lot like what you're describing, causes a snap when there's not enough wind to keep the trim adjustments holding the plane steady because they're fighting each other. If, say, your rudder has some noticeable trim for straight flight, it might be causing a stall at slow speeds. In the past I've actually pulled and reinstalled a vertical fin straight the way it should be. But before you do something like that make sure your motor install isn't causing it to go astray one way or the other. Make real sure your CG is right on, it should fly level without a lot of up or down elevator trim. That can convert into problems like these as well. A plane flies best when it flies straight and level without more than a couple of clicks of trim on any of the surfaces. That about covers what thoughts I have on the info we have right now.

Jim