How to control speed in Auto mode turning?

Hi there!
I am trying constant speed mission flight in Auto mode.
My aircraft does not have airspeed sensor so the speed is set by TRIM_THROTTLE parameter. Same altitudes are set for square waypoints.

The aircraft flies at a reasonable constant speed during straight courses but when it turns the throttle goes up significantly and speed also increases. Altitude holds its specified value.

I want constant speed turn. Could anyone help me how I can make a constant speed mission flight?

Would recommend that you attach some logs.

You are probably getting a throttle up to prevent a stall - are you able to fly turns of that radius manually at the same airspeed?

Thank you Anthony,
Unfortunately I have no log but I set that turn at around 20m/sec which is well above the stall speed of 8 m/sec. SO I did not touch the throttle during the turn. I can easily turn the aircraft manually at the same airspeed.

are you using airspeed?

No as I have stated in my first message.