# About the duo tailsitter

**URL:** <https://discuss.px4.io/t/about-the-duo-tailsitter/3452>\
**Category:** PX4 Autopilot\
**Created:** [June 2, 2017, 1:23am UTC](https://discuss.px4.io/t/about-the-duo-tailsitter/3452 "2017-06-02T01:23:59Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![david212](https://discuss.px4.io/letter_avatar_proxy/v4/letter/d/e36b37/32.png) [@david212](https://discuss.px4.io/u/david212)\
**Post date:** [June 2, 2017, 1:23am UTC](https://discuss.px4.io/t/about-the-duo-tailsitter/3452/1 "2017-06-02T01:23:59Z")

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Hi,I have build a duo tailsitter with wing wing z84,and calibrated the sensor with PITCH\_90,leveled the airframe with PITCH\_90 and nose-up,and modified the mixer file to make the response of control surface is correct. when I test it on my hand in multirotor mode with stabilize flight mode,the response of roll/yaw/pitch control is correct,but when I speed up the motors,the airframe tilt down to the ground.I don’t know why.can anybody help me?my controller is pixhawk 2.4.6,firmware is the dev master 1.6.0,thanks very much.

maybe I have to enlarge the control surface area?  
I do calibration with fllowing steps:  
1.calibrate compass with PITCH\_90;  
2.calibrate Gyroscope (keep the airframe on the PITCH\_90(nose up) position);  
3.calibrate Accelerometer with PITCH\_90;  
4.Level Horizon(keep the airframe on the PITCH\_90(nose up) position);

I’m not sure it’s right?

another question,I noted that when I put the airframe on the PITCH -90 degree and keep it still,the roll displayed on the qgc is not correct untill moving it slightly. is it a bug of EKF2?