Author Topic: Control Trim question - snap turn (Read 3249 times)

Dennis Toth · « **on:** April 19, 2015, 07:06:58 PM »

Guys,
While starting to get ready for our upcoming AirStomers contest (May 17, Indiantown, FL) I have been flying my YAK-YAK for the Super 52 event (any plane, OTS pattern) I have noticed that at the top of the climb the ship can snap the corner. Now I didn't bang the corner the ship just kinda snapped around it. It wasn't uncontrollable just rather quick not the smooth control I was intending. Then the other day I was flying a friends ship for the first time, as I started into a nice smooth big loop to get the feel for it as it got over the top of the loop it snapped tight around on the second half really quick. I thought maybe I got a little lose up top so I tried a second loop a little tighter, same thing, smooth first have half then snap tight around the back half.

So the question is has anyone else experience this and what is the cure?

Best, DennisT

Steve Helmick · « **Reply #1 on:** April 19, 2015, 07:30:39 PM »

I had something similar happen when I changed the old blue Fancherized Twister to 1:1 flap/elevator ratio. It would climb into the loop and do a lovely "Figure 9"...but starting at the bottom of the "9" and climbing out at the middle. I changed to a narrow handle spacing and gradually widened the spacing until I could control it. Adding nose weight might be the correct thing to do, but I didn't do that. Naturally!

Steve

Brett Buck · « **Reply #2 on:** April 19, 2015, 09:04:39 PM »

Quote from: Dennis Toth on April 19, 2015, 07:06:58 PM

Guys,
While starting to get ready for our upcoming AirStomers contest (May 17, Indiantown, FL) I have been flying my YAK-YAK for the Super 52 event (any plane, OTS pattern) I have noticed that at the top of the climb the ship can snap the corner. Now I didn't bang the corner the ship just kinda snapped around it. It wasn't uncontrollable just rather quick not the smooth control I was intending. Then the other day I was flying a friends ship for the first time, as I started into a nice smooth big loop to get the feel for it as it got over the top of the loop it snapped tight around on the second half really quick. I thought maybe I got a little lose up top so I tried a second loop a little tighter, same thing, smooth first have half then snap tight around the back half.

So the question is has anyone else experience this and what is the cure?

Best, DennisT

Probably stalled, then rotated abruptly when the pitching moment suddenly went away.

Brett

Dennis Toth · « **Reply #3 on:** April 20, 2015, 08:00:50 PM »

Not sure about the stall the ship saw flying at a pretty good speed, lots of line tension and was very flyable with no tendency to hunt or roll in at all. Just went through the first part of the loop very smooth and controllable then seemed like it did a combat tight back half. I am at a loss for what trim change should be made?

Best, DennisT

Dave Harmon · « **Reply #4 on:** April 20, 2015, 10:16:34 PM »

Quote from: Dennis Toth on April 20, 2015, 08:00:50 PM

Not sure about the stall the ship saw flying at a pretty good speed, lots of line tension and was very flyable with no tendency to hunt or roll in at all. Just went through the first part of the loop very smooth and controllable then seemed like it did a combat tight back half. I am at a loss for what trim change should be made?

Best, DennisT

Were you flying downwind when you started the loop?

Dick Pacini · « **Reply #5 on:** April 20, 2015, 11:18:36 PM »

I can remember that happening if I hit the wind the wrong way.

Joe Yau · « **Reply #6 on:** April 21, 2015, 10:15:21 AM »

I had a plane that had that issue.. after bunch of trim changes that made no difference or very little. turns out it was the handle's adjustment lacking the necessary down control needed for the second half of the loop, and also hand position as well. some planes are very sensitive.. and you really needs to fly it through.

Flying off the wind is tricky sometimes.. especially 90 degrees to the left of down wind. the plane could floats like a kite on the second half of the loop.. and could ends up with 12' bottom etc.

Will Davis · « **Reply #7 on:** April 21, 2015, 02:12:04 PM »

I have a e powered Skyray that has a lot of the same issues, I hope someone finds a magic cure for it. really has me puzzled,

Leaning towards it being a power issue

Brett Buck · « **Reply #8 on:** April 21, 2015, 05:39:05 PM »

Quote from: Will Davis on April 21, 2015, 02:12:04 PM

I have a e powered Skyray that has a lot of the same issues, I hope someone finds a magic cure for it. really has me puzzled,

Leaning towards it being a power issue

Very unlikely. I would check the CG, mine is extremely predictable with the CG about an inch from the LE.

Brett

john e. holliday · « **Reply #9 on:** April 21, 2015, 06:32:41 PM »

Is every thing on a zero -zero set up in relation to each other??? Also the main are you unwittingly giving more control un consciously? Remember you give and follow the plane with the arm. I have caught my self doing that at times when I haven't flown in a while. An after thought, I had an ARF Oriental that I thought was the greatest and it started doing jumpy maneuvers on me. Figured out the wing had come unglued in the fuse.

Dennis Toth · « **Reply #10 on:** April 22, 2015, 08:03:20 AM »

I flew a flight at the same circle with my own ship, put the maneuver in the same place with no problms, wind had not changed and several other flyers also put their maneuvers in the same location. this was a nice smooth entry, with no arm movement. The ship is stable in level flight, not touchy, has LA46 power, normal lap time (around 5.0), wings are level.

One thing I didn't check was the pushrod stiffness. Could be that the rod between the flap and elevator was bowing and at the top it unloaded that might cause the snap. Since it was windy and with the reaction I got on a simple inside loop I just flew it out level and did not try an outside (which would pull the rod). I can't say if there is a difference on the outside maneuvers. Anything else that could do this?

Best, DennisT

phil c · « **Reply #11 on:** April 22, 2015, 08:21:38 AM »

Quote from: john e. holliday on April 21, 2015, 06:32:41 PM

Is every thing on a zero -zero set up in relation to each other??? Also the main are you unwittingly giving more control un consciously? Remember you give and follow the plane with the arm. I have caught my self doing that at times when I haven't flown in a while. An after thought, I had an ARF Oriental that I thought was the greatest and it started doing jumpy maneuvers on me. Figured out the wing had come unglued in the fuse.

This is the most likely cause. If you stop following the plane with your arm, assuming you have the handle upright, after the top of the loop the plane goes down below your hand automatically giving more up. Second most likely is if the pushrod has to push for up it could be bending from control loads on the up side of the loop and straightening, applying more up, when the loads slack off as it starts down.

Major structural issues with wing/stab alignment, flaps(if it has them) etc. probably would have shown up consistently long ago.

Dennis Toth · « **Reply #12 on:** April 23, 2015, 09:01:03 AM »

In this case I can rule out the arm position as I always follow the plan through the maneuver.

The pushrod flexing could be the problem as it was a bit breezy. One other item that might also result in a similar control input is if the joiner wire was flexing. The ship used a bolt on nylon horn with a joiner wirer connecting the two elevator halves. This was something that I didn't check. Again, with the breeze we were flying in it could flex and snap back as the load lessened a the top causing the tight back half.

One last thing could be if the tail horn twisted and snapped back but I think that is the least likely. I think those two areas (pushrod and joiner) are the place to start.

Best, DennisT

Ted Fancher · « **Reply #13 on:** April 23, 2015, 12:56:22 PM »

The symptoms do sound more mechanical than aerodynamic. You might want to try deflecting the controls with a ten pound bag on each leadout to simulate line tension and see if there isn't some restriction to movement under load that goes away as line tension decreases.

I'm assuming this only happens on inside loops...right?

Ted

Ted Fancher · « **Reply #14 on:** April 23, 2015, 01:20:03 PM »

Dennis,

I haven't seen any information on the configuration of the ship. Is it a more or less conventional stunter. If not, in what way is it "odd?" Is it a flapped wing? Are the hingelines sealed?

Along those lines here's another thing to check if the hingelines aren't sealed. See if the elevator hingeline seals itself up as you increase the elevator deflection. If so, and if the seal at greater deflection is noticably tighter than at lesser deflections you could be experiencing a rapid increase in lift at the point the gap seals itself. This could be the cause of a rapid increase in pitch rotation.

Many stunt ships will require more up control on the back side of the loop as the airplane is accelerating downhill and the additional "1G" of gravity is trying to open up the radius of the loop. This, combined with an "iffy" hingeline situation as above, might be something worth looking at. This condition would be exacerbated by a more forward CG than optimum as well.

Ted Fancher

Ted Fancher · « **Reply #15 on:** April 23, 2015, 01:24:11 PM »

Deleted...double post.

Ted

Dennis Toth · « **Reply #16 on:** April 23, 2015, 02:37:50 PM »

Ship is a Pathfinder, LA46, in level flight was very tame. I have flown other PF's and they smooth and predictable flying. I never got to do any outside maneuvers cause I didn't have confidence in the controllability of the ship and it wasn't mine (not good to put a friends ship in when you think there is a control issue).

One other far out though - the fuse on the PF is a little flimsy in the back, could it have been flexed out at the top of the loop by the wind thus forcing in more up control? Several things to check.

Best, DennisT

Bob Reeves · « **Reply #17 on:** April 24, 2015, 05:14:38 AM »

Don't have an answer but it isn't limited to profiles. Several years ago I flew a buddies stunt ship that had this issue. Somehow he could fly a half way respectable pattern with it but no matter how careful I was on the handle I could not fly a round loop. just as described best I could do was a mirrored figure 9. Also didn't try an outside as after several attempts at insides I gave up and just flew the tank out level. I'm just thankful I have never had an airplane with this issue, wouldn't have a clue as to how to fix it.

Dave_Trible · « **Reply #18 on:** April 24, 2015, 05:59:44 AM »

I wonder how the control throws are set up. If the horns are too short it could be there isn't much authority over the control deflection at different airspeeds. At a good speed entering a loop there is a fair amount of air pressure pushing against the elevator. As it goes over the top the airplane slows a bunch and the pressure fades allowing a sudden release of the elevator to over-travel. Bad enough and it might even cam over. Maybe longer control horns with more leverage would help.

Dave

Dennis Toth · « **Reply #19 on:** April 24, 2015, 11:23:27 AM »

Dave,
Good point, your description adds to the flexing pushrod or joiner hypotheses. I think the horns were within the normal range but in the wind. The idea that the ship slowed at the top reducing the force on the elevator gives an explanation for how the flexed rod could suddenly pop back.

Best, DennisT

Steve Helmick · « **Reply #20 on:** April 24, 2015, 09:42:31 PM »

Quote from: Dennis Toth on April 23, 2015, 02:37:50 PM

Ship is a Pathfinder, LA46, in level flight was very tame. I have flown other PF's and they smooth and predictable flying. I never got to do any outside maneuvers cause I didn't have confidence in the controllability of the ship and it wasn't mine (not good to put a friends ship in when you think there is a control issue).

One other far out though - the fuse on the PF is a little flimsy in the back, could it have been flexed out at the top of the loop by the wind thus forcing in more up control? Several things to check.

Best, DennisT

In your first post, you said it was your "YAK-YAK".

??

Steve

John Cralley · « **Reply #21 on:** April 25, 2015, 06:21:32 AM »

Quote from: Steve Helmick on April 24, 2015, 09:42:31 PM

In your first post, you said it was your "YAK-YAK". ?? Steve

Steve, He talks about both planes in the first post. His Yak-Yak and a friend's plane which he did not name.

Motorman · « **Reply #22 on:** April 25, 2015, 08:19:06 AM »

I had that problem on my Tanager. Good insides but the outsides would snap over on the top of the loop. Thought I was over controlling due to inverted panic syndrome lol but after a while I knew it wasn't me. Finally put some up thrust in it and smoothed it right out. I guess when the plane slows down the thrust line has a bigger influence?

MM

Dennis Toth · « **Reply #23 on:** April 25, 2015, 11:29:59 AM »

Steve,
Yes I did mention my Biplane Yak-Yak, it had a little quicker outside at the top of the climb (ship is used in Super 52 event - any plane flying the OTS pattern). After some of the discussion here I checked it and found I had set it up with more down control then up. I was concerned that I needed to be able to do tighter outsides for the vertical eight. This turned out to be not the case and I have re-adjusted the throws to equal up and down, should fix the problem and help tighten up the insides also.

On the PF some of it might be the handle position as I find that I naturally hold slightly up at neutral but I have flow many other ships with other peoples settings and can fly ok (not great but could do the pattern). You should not have to fight the plane through a maneuver. It should track if all is in trim and there are no outside forces on the plane. Small corrections from wind guests are normal but the mirror figure 9 is not. I need to have my friend check the pushrod for flex and the elevator joiner wire for flex as a first step to solving this. I think he is giving up a lot of points having to work very hard to keep this ship on path through maneuvers.

Best, DennisT