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FMS 1300 Sbach & Yak54 - Behavior issue i do not understand. Very annoying! :(

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FMS 1300 Sbach & Yak54 - Behavior issue i do not understand. Very annoying! :(

Old 03-03-2014, 02:18 AM
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aleksanderdev
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Default FMS 1300 Sbach & Yak54 - Behavior issue i do not understand. Very annoying! :(

Hi.
Half a year ago i bought and FMS 1300 Yak epo.
I was a total new comer to 3d planes at the time so some small crashes where inevitable.
The result is a new motor in my yak with a 2 bladed prop, instead of the 3 bladed prop and the original motor. Should be about the same weight.
After a few crashes etc, I'm now having a very weird and annoying issue in the air with the yak.

When i do a loop, not a long one but not a snap either. Half way trough the plane it starts to roll to the right.
If i fly strait forward and yank the elevator fully down, the plane starts a little loop but very fast does a twist instead and ends up changing the flight direction almost 90 degrees to the right.
This makes it very hard for me to do any kind of acrobatics at all.

Now just a week ago, i saw my self tired of the yaks behavior and bought a similar Sbach 1300FMS.
Thinking that it might be that iv damaged the yak somehow, or that the new motor with a 2 bladed prop caused the issue.
But no, they Sbach does the same thing, making it impossible to hover.

Im using the same 3200 4S batteri in theme, and thinking it might not be as heavy as it should be, putting off the CG.
Can a CG cause this kind of problem?

If not I'm starting to think its my remote controller, that is damaged.
Though Im flying an F4U with the same remote and I never had the issue as far as i could tell, though i haven't done such tight pullbacks on the elevator on it either.


Anyway i just really want to enjoy a good acro plane and get into the 3d flying.
I dont have a lot of money so i was very sad to see that the new sbach i just bought doing the same damn'd thing.

Thanks a lot for your help.
Old 03-03-2014, 09:48 AM
  #2  
BMatthews
 
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None of this stuff works perfectly out of the box. You need to do some fine tuning and trimming.

Tuning the models starts with setting up and checking alignment of all surfaces and fuselage center line. Do not assume ANYTHING is correct, straight or square.

First off is to find the center line of the motor mount and extend a line from that point back to the middle of the fin's tail post. That will be your reference center line. Don't trust anything in the middle as the fuselage may be slightly banana shaped. With a center line established you can then check the wing for being centered and square to this line. Then check the tail to make sure all surfaces are centered and square to the line. Depending on the model doing all this might require some imaginative tricks to work around the shapes. For example a large rectangle with a big "C" shaped cutout that works as a square will allow you to reference a line drawn on the table and extend the line up and around the fuselage so you can mark and establish a center line on the upper side of the model. And there are articles written on how to make measurements both span wise and diagonally to check the wing for accurate centering and for square.

Once you do all that and get things corrected then check for warps in the wing and tail surfaces. Correct these as needed so all surfaces are flat. And for ailerons be sure that both are set accurately for neutral to the wing. With the elevators check that both are in line so you don't have some roll from the two sides.

Check for lateral balance too. One wing heavier than the other can produce this sort of behaviour.

For wings that use separate servos on the ailerons check that both sides deflect by the same angle for both small and large control throws.


If the model is still doing tricks like this then you can begin playing with adjusting the motor's side thrust. That will reduce the propeller's "P" effect that will show up when operating at higher angles of attack such as during looping maneuvers.

And finally try some looping where you just push the stick with one finger so you KNOW you are not accidentally inputting any aileron input. With the soft spring centering on modern transmitters this is easier to do by mistake than you think.
Old 03-03-2014, 01:05 PM
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opjose
 
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Your elevator throws are too much for the maneuver you are attempting causing one wing to stall out before the other.

This is NOT due to your transmitter, but is in part due to both the weight of your plane ( lightly wing loaded planes have less of a tendency to do this... ) and the amount of elevator your are commanding coupled with C.G., P-Factor, right thrust & gyro precession.

Try lowering the amount of elevator for your high rates and repeat the maneuver.

Continue doing the same until you get to the point that your plane will loop without stalling a wing. That should be your new high rate.

If you want to be able to command a higher elevator movement, you'll need to lighten the plane and/or move the C.G. forward a bit.

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