Help! FT Simple Cub does not fly!

[JanF]

Hi. I am lost now. My son and I build a great looking FT Simple Cub.
The motor is a Pulso swining a 9x5 prop. It has plenty of pulling power. I am using a 1300mAh 3s LiPo battery. The problem is the cub does not want to fly - it constantly tips over to the left (dropping the left wing), nose diving to the ground. I have repaired the nose twice already, and fitted different motors as well. Hand launch and normal takeoffs does the same. My CG is also as per the recommendations of the plans.
Does anyone have any idea what could cause this. I have never had a plane behaving so badly. :-|
Regards

 

[Hai-Lee]

The simple cub!
Firstly one thing to know is that the plane wing may require a slight increase in incidence if the bird is even the slightest bit heavy. This is normally easiest achieved by fitting a paddle pop stick under the wing leading edge.

Second is that the plane is capable of lifting off of the ground before the ailerons are truly effective. Try increasing the speed of the take off run before attempting to rotate and fly. When doing a maiden for someone's build i run it very fast along the ground before lift off.

Finally the thrust angle is zero and so using a little packing behind the motor mount on one side so that the motor points slightly to the right will help reduce the tendency to swing violently to the left.

The above three actions will calm the beast and allow it to fly well and quite slowly. Just remember it is the speed of the plane that allows it to fly and not the motor power setting. My cub will take off calmly at just over half throttle even in the strongest of breezes.

Let us know how you get on!

Have fun!

 

[JanF]

The simple cub!
Firstly one thing to know is that the plane wing may require a slight increase in incidence if the bird is even the slightest bit heavy. This is normally easiest achieved by fitting a paddle pop stick under the wing leading edge.

Second is that the plane is capable of lifting off of the ground before the ailerons are truly effective. Try increasing the speed of the take off run before attempting to rotate and fly. When doing a maiden for someone's build i run it very fast along the ground before lift off.

Finally the thrust angle is zero and so using a little packing behind the motor mount on one side so that the motor points slightly to the right will help reduce the tendency to swing violently to the left.

The above three actions will calm the beast and allow it to fly well and quite slowly. Just remember it is the speed of the plane that allows it to fly and not the motor power setting. My cub will take off calmly at just over half throttle even in the strongest of breezes.

Let us know how you get on!

Have fun!

Thank you for your reply. I am confident that the speed was not too bad, but I will keep that in mind. I will change the thrust angle and increase the incidence a bit and see what it does. Just to be clear, the pop stick is placed under the wing's leading edge where it touches the fuse (on top of the fuse) to increase the wing angle, aka incidence? Will keep you posted.

 

[Hai-Lee]

Thank you for your reply. I am confident that the speed was not too bad, but I will keep that in mind. I will change the thrust angle and increase the incidence a bit and see what it does. Just to be clear, the pop stick is placed under the wing's leading edge where it touches the fuse (on top of the fuse) to increase the wing angle, aka incidence? Will keep you posted.

Yes as far as the use of the paddle pop stick. It is just to raise the front of the wing slightly more than 1 mm. It does not need to be extremely accurate but the increase makes a great deal of difference to the way it flies.

Have fun!

 

[daxian]

never tried the ailerons on the cub ,or the incidence change ! but did find the cub turned to the left on hand launch .
my first thought was rudder mis-alignment and a little trim was induced which helped ,but still a left turn on launch at half throttle ,but once corrected it flew well ..did a check and found an imbalance in the wing (to much glue on one side ).
which may have contributed to the turn ...
this was the maiden ::

might help !!

 

[JanF]

never tried the ailerons on the cub ,or the incidence change ! but did find the cub turned to the left on hand launch .
my first thought was rudder mis-alignment and a little trim was induced which helped ,but still a left turn on launch at half throttle ,but once corrected it flew well ..did a check and found an imbalance in the wing (to much glue on one side ).
which may have contributed to the turn ...
this was the maiden ::

might help !!

I will check the wing balance as well, thank you daxian.

 

[quorneng]

JanF
Does your Simple Cub have ailerons?
If not then it is vital that both wings present an identical aspect to the airflow. In others words there are no twists or if there is that it is absolutely identical in each wing. It only takes a tiny angle difference for a wing to develop significantly more or less lift.
With ailerons you have a degree of control to counter any lift differences but with only a rudder the wings have to be pretty well matched or the plane will at best try to circle all the time or at worst 'spiral in' as you try to keep it straight.

 

[JanF]

Thank you all for your help. I have added about 1mm of right thrust (added spacers on the left hand side of the motor mount) and added the pop stick. It made a huge difference. I was actually able to land the cub for the first time today. I might have to add a little more to the thrust angle since it seems quite sensitive to the motor torque when you approach 3/4 throttle. Or I might just program some right rudder with the throttle....
But it starts to behave in such a way that I can actually fly and control it! I will fine tune further. Now to maiden the Mini Sparrow that we built over the past weekend. :-| That seems like a little beast.
Regards