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Tiny Trainer Twin Motor Pulls Left

#1
I have a twin motor tiny trainer (2 x 2204 2300 kv) running 6x4 APC props. Props are counter rotating with CCW on the starboard side and the CW on the left side. Every time I attempt to fly, the plane pulls violently to the left and noses in. I've had twins in the past that flew well but this one has me stumped.
Any ideas gladly accepted.

Thanks.
trainer.jpg
 

JasonK

Well-known member
#2
hopefully this is just an issue with the camera angle, but what is the measurement from the fuslage to the nacelles? are they the same or is there a difference? (there looks liek a difference to me. The one on the right of the photo (so the left) appears to be farther out.
 

Homey

Well-known member
#4
On top of what the others said, one other thing it might be is that the esc's aren't in sync. I forgot about that with my last twin and they revved differently so had to do the throttle up initiation thing and then all was good.

Peter
 
#5
The photo is of the prototype, which flew well but all the wires were outside of the wing so I rebuilt the wing. The ESCs are calibrated and both props turn in the appropriate direction. I was thinking about the thrust angle on the twins and wondering if I shipped the CW motor if that would make any difference?
 

JasonK

Well-known member
#6
you have a thrust angle on both motors? My understanding for a dual like that you don't need any angle (at least horizontally).
 
#7
Can't spell either. Meant to shim not shp the motor. Since I am being pulled to the left, would it make sense to shim the motors to the right? I know on the original single engine tiny trainer the thrust angle was very important.
 

Hai-Lee

Old and Bold RC PILOT
#8
Your initial photo brings up the issue of weight distribution that was so VERY important in the days of Balsa 2 channel RC models and earlier.

The lift distribution on each wing is not linearly distributed across the entire wing span. The portion closest to the fuselage generates most lift and the wing tip generates none. Mind you generally the lift differences between wings is minimal.

The weight that each wing supports must be equal for level and stable flight. If one wing has a heavier loading then the plane will turn and roll in the direction of the heaviest wing.

Not only must the weight be equally distributed between the wings but ALSO the weight must be equally distributed. This means that when fitting a load to the wing externally, (bombs, motor nacelles, parasitic flighter etc), their weight multiplied by the distance from the fuselage centre line must be equal. If one wing has its load further from the fuselage centre line than the other wing the plane will turn and roll towards the side that has its load furtherest from the fuselage.

It is simply that the overall centre of mass is no longer on the fuselage centre line and one wing becomes more hevily loaded than the other.

Do a little investigation into assymetrical flight and you will soon discover it is always just a matter of weight and lift balance.

Just what works for me!

Have fun!
 
#9
Your initial photo brings up the issue of weight distribution that was so VERY important in the days of Balsa 2 channel RC models and earlier.

The lift distribution on each wing is not linearly distributed across the entire wing span. The portion closest to the fuselage generates most lift and the wing tip generates none. Mind you generally the lift differences between wings is minimal.

The weight that each wing supports must be equal for level and stable flight. If one wing has a heavier loading then the plane will turn and roll in the direction of the heaviest wing.

Not only must the weight be equally distributed between the wings but ALSO the weight must be equally distributed. This means that when fitting a load to the wing externally, (bombs, motor nacelles, parasitic flighter etc), their weight multiplied by the distance from the fuselage centre line must be equal. If one wing has its load further from the fuselage centre line than the other wing the plane will turn and roll towards the side that has its load furtherest from the fuselage.

It is simply that the overall centre of mass is no longer on the fuselage centre line and one wing becomes more hevily loaded than the other.

Do a little investigation into assymetrical flight and you will soon discover it is always just a matter of weight and lift balance.

Just what works for me!

Have fun!
Thanks for your assessment. The picture is of the prototype. Even with the misalignment of the engines it did fly. I redid the wing on the current plane to have the power wires within the wing, not externally. My current setup has the center of the prop shaft exactly 4 inches from the side of the fuselage. Not wanting to risk a prop getting too close, I use 8 rubber bands to hold the wing in place. After shimming the motors it feels like the pull to the left has somewhat been reduced if not resolved. I have also noticed with this Tiny Trainer as well as my single engine version, they are very sensitive to the amount of power used. I may have been using too much power trying to take off and that affected the result. I know with the single engine version, it takes a very small amount of power to successfully launch it. Will try again when the weather breaks later this week.
 

Hai-Lee

Old and Bold RC PILOT
#12
Thanks for your assessment. The picture is of the prototype. Even with the misalignment of the engines it did fly. I redid the wing on the current plane to have the power wires within the wing, not externally. My current setup has the center of the prop shaft exactly 4 inches from the side of the fuselage. Not wanting to risk a prop getting too close, I use 8 rubber bands to hold the wing in place. After shimming the motors it feels like the pull to the left has somewhat been reduced if not resolved. I have also noticed with this Tiny Trainer as well as my single engine version, they are very sensitive to the amount of power used. I may have been using too much power trying to take off and that affected the result. I know with the single engine version, it takes a very small amount of power to successfully launch it. Will try again when the weather breaks later this week.
With a overpowered installation I would definately institute differential thrust mixing so that I could trim out any possible thrust differences due to slight variations in the motor installation performances!

Have fun!
 
#13
I agree with @Homey.
Try calibrating the ESC’s.
Are you using a Y connectors or are you going for differential thrust? If you are going for differential thrust, check your mixes for something out of place.
ESCs have been calibrated. I don't have a means to check the RPM, but both motors spin up instantly and shut down at the same time. Audibly it seems like they are at the same speed.
 
#16
I can see the prop label on the one prop, but can't on the other. They LOOK like they aren't on backwards, but double check.. that's issue has bitten a lot of us. You could also swap props between motors and reverse both motors to see if the issue stays with the prop or the motor. Then swap motors to see if the issue stays with the motor or the ESC. Eliminate one thing at a time.