Tandem Project page 3
Jan, 4 2004
Recently, I have decided to change from JR radios to Futaba radios. I bought a new 9ZHPSWC. I am not sure if it was a wise thing to do, but it seemed like a good idea at the time. The down side is that I have so much JR equipment, receivers servos etc, that it may take a while to re-outfit my fleet with Futaba receivers and such.
So I removed the JR 10channel Rx from the Tandem and installed the 9channel Futaba. But it really only an 8 channel Rx as ch9 is shared with the battery plug and it is not proportional. Now I'm thinking "go back to JR", two more proportional channels and more mixes. But we'll see...
4-5 hours later I re-plugged all the servos, (7 servos plus gyro = 8) to the futaba Rx and reprogrammed all the slaves, mixes directions, curves and assignments. Reset the blade pitches on both heads. This was all done the day before it was to be flown again.
I installed, for the first time, a Hobbico dual servo aircraft gyro on the Yaw function. I had it set to turn on and off with a switch. I had the gyro and another like it for almost a year and a half. I just never got to use them till now. I had the gyro turned off for the first lift off so that I could evaluate my new radio setup and the aircraft handling.
I brought the heli out to the flying field on Jan1st, New Years Day. This heli had not be started in over 2 years. We had a some trouble getting it stated, but it finally fired up and ran steady. I also had changed over to 30% fuel with my other helis, so this was also a change for the Tandems old 15% setup. With a little bit of richening of the needles, the MDS38 really liked the 30% WildCat as it had never run better.
The first lift off was near perfect. only some slight back pressure on the elevator stick to keep it at a comfortable hover. Some trim took care of that. The Yaw, without a gyro wandered pretty bad. It took a lot of anticipation to manage the mushy yaw response. Elevator/fore&aft control was still pretty sensitive. Though manageable, onlookers could still see a good bit of bobbing from the sensitive controls. I think if I disconnect the fore&aft collective differential mix or add a gyro, the Tandem should respond like any other single rotor helicopter. The blade tracking on both heads looked right on the money, the extra time spent with the pitch gage really paid off. Hover position the throttle was pretty close to the center mark too, close enough to not worry about it.
I set the Tandem back down and engaged the gyro with the switch. No jump or any sign that anything had changed. A good sign. I lifted the Tandem back into a comfortable 2-3 foot hover and wow, what a difference in the yaw control. No wandering, no gyro feedback, crisp response from a yaw command input. The motor was running very smooth and strong, things were looking really good.
About a half a tank of fuel had burned and I notice that the trim had changed. Then all of sudden the Tandem pitched forward and flew into the grass from a 2 foot hover. There was nothing I could do. There was no response from the tandem. The blades impacted and broke, the fly bars bent and one of the blade grips broke in two. After the parts stopped moving and I got the motor stopped, I brought it back to the bench. A test of the battery showed less than half the voltage left in the battery. This was a relatively new NMh battery, a few month old.
Parts are all on order, and should arrive in about a week. I have taken this opportunity to seek out some good used upgrade items for the Concept Tandem. Metal swashplate, clutch, fan, ball bearings etc.