Skymaster F-15 Steering Stability
iAll,
I just finished my Skymaster F-15 ARF Plus and was taxi testing it today with hopes of a maiden this weekend. Everything seems to be working properly except for steering. At anything above about 5MPH, the plane becomes almost impossible to steer and control. While rolling down the runway, any attempt to correct for a slight drift left or right sets up a side to side wobble that continues to amplify until either a wing tip scrapes or the brakes are engaged and it comes to a stop. Any attempt to correct this wobble just causes it to become worse. By not touching the steering on the take off roll I could probably take off but I would be very concerned that any steering correction needed following landing would start this wobble and would continue to compound into a big problem before the model came to a stop.
I have tried taxing with and without the aid of a Gyro. I would say without the Gyro was slightly better.
I have the steering mixed to the rudder channel and I'm using high and low rate settings. Both lead to the wobble problem. Obviously High rates gets you there much faster. Just for reference, on high rates I could turn the model around on a 20' wide auxiliary taxi way. On low rates, it wouldn’t come close to making a u-turn in that same width.
The CG is slightly forward of the recommended 150mm - 160mm range since I have not located the 2S LiPo for the ECU in the aircraft yet to obtain a 155mm CG. Moving this battery aft slightly brought the model to the needed CG but I needed to extend the battery leads by 5"...which I have not done yet. Since I wasn't planning to fly, I just placed the battery in the nose so I could run the turbine.
The main gear is pointed straight...there is no toe in or out.
Main gear tire pressure is 40psi
The main gear springs seemed to allow the suspension to sag quite a bit (almost bottoming) so I disassembled the struts and added a little o-ring grease and stretched (elongated) the spring a little to offer a little preload. After doing this, each main gear strut had a 1/4 inch of travel remaining before bottoming.
I also noticed that my Kevlar Pull-Pull steering set up was a little loose. So I changed this over to a steel cable setup at the field that had much less play.
With all these changes/improvements, the model was better than when I first attempted to taxi but still way too unstable above 5 to 10 MPH for comfort.
Any help would be much appreciated.
Mike