jgrischow1 wrote:So we just got back from Regionals and have had an odd pattern lately. Many of our flights do decent, ~1:20 range. Many flights have kind of an upward trajectory and then start dropping into a slow, shallow, nosedive after a while, like a tilted ring/donut shape, and then hit or skim on the ground. Can't figure out why as we don't see any difference between the OK flights and the bad ones except for after launch. ~7.02 g, .080 rubber, winds/torque close to breaking. Any help appreciated.
We see that exact same behavior sometimes too. You need to check if your wing is warped. Assuming that your are flying in a left-turn circle (counter clockwise as seen from above), you want the left wing to have slightly more angle of attack than the right wing. By left, I mean the side pointing in to the circle. You can break your wing slightly on the front left side and then re-glue it to have a little bit of an upward direction so that you get slightly more lift on the left side than the right side. This should help balance your plane when flying in a left-turn circle.
Also, pay close attention to your stabilizer. Your stabilizer should be flat or slightly positive angle of attack. If your stabilizer is aimed downward a little (negative angle of attack), it won't always have the effect you want and the effect will change with different plane speeds. Often that is the reason a plane turns nicely when climbing (high speed), but straightens out when descending (low speed). If your stabilizer has a negative angle of attack, change it to a positive angle of attack. That will, in-turn, cause you to nose dive at first, so you need to move the wing more forward on the motor stick and also maybe increase the angle of attack of your wing, but I would try just moving the wing forward 3-4 cm first. Better to stall first and work back than to nose dive first and break your propeller.
So check your wing for warping, check your stabilizer for warping, and check your stabilizer for a positive angle of attack.