Too much negative pitch in normal mode

[malcolmm]

I hope I'm posting this is the right forum - I'm definitely a newbie.

I have a T-Rex 450 SA, which I recently crashed quite hard. I've finally got it mostly fixed, except for one thing. I mostly just hover so far, so I fly only in Normal mode. I am trying to get a pitch range of around -2 at low collective/throttle, to around 10. For some reason I can't get much closer than -5 to around 7 pitch.

As I said, I'm a real newbie, but it seems like this would indicate the swashplate is too low. However my linkages are very close to what is specified in the manual, and the rods for the pitch and aileron servos don't have any extra threads left. The servo arms are horizontal at middle throttle/collective.

Or is their something I messed up in installing the main shaft - is it possible to install this incorrectly?

I had everything setup up fine before the crash, but can't seem to get it right now. Thanks for any info, I'm really lost.

Malcolm

[chris52]

hi you need to set your pitch up mechanically at -11 deg to + 11deg
then you need to alter your pitch curve in order to only have -2 deg at 0% throttle. if you watch bobs video on pitch and throttle curves it explains all.
link here (http://www.helifreak.com/showthread.php?t=11373)

chris

[malcolmm]

hi you need to set your pitch up mechanically at -11 deg to + 11deg
then you need to alter your pitch curve in order to only have -2 deg at 0% throttle. if you watch bobs video on pitch and throttle curves it explains all.
link here (http://www.helifreak.com/showthread.php?t=11373)

chris

Thanks, but I forgot to mention that I already did set my pitch curve. My pitch curve goes from 40% at low throttle, to 100% at full. So I can't get more positive pitch from the pitch curve. I can increase the pitch at low throttle to get less negative pitch, but I can't get more positive pitch at full throttle.

Malcolm

[TheBum]

chris52 was referring to mechanical setup, not radio setup. With your radio set up for zero pitch at center stick, you need to make sure the swashplate, washout arms (both on the washout block and the flybar hub), flybar cage, and blade grips are all level at center stick (with the flybar level), and that the swashplate/washout block combination is centered vertically on the shaft at center stick. You do this by adjusting the length of the linkages. Watch Finless's T-Rex CCPM videos for more information.

[malcolmm]

chris52 was referring to mechanical setup, not radio setup. With your radio set up for zero pitch at center stick, you need to make sure the swashplate, washout arms (both on the washout block and the flybar hub), flybar cage, and blade grips are all level at center stick (with the flybar level), and that the swashplate/washout block combination is centered vertically on the shaft at center stick. You do this by adjusting the length of the linkages. Watch Finless's T-Rex CCPM videos for more information.

Thanks, but I did follow the video and leveled everything at center stick.

I think my confusion comes from something the hobbyshop owner did to my heli when it was first setup. I had it setup for around -2 to 10 pitch, with 0 pitch at middle throttle, like the manual said.

The shop owner said that the swashplate movement was not smooth, i.e. it moved a little at low throttle, and then a lot. He adjusted the pitch curve to make the swashplate travel linear, and I didn't measure the pitch after he did this.

I can get the pitch adjust correctly if I don't have linear travel on the swashplate. And it makes sense to me that this would have to be how it works (in Normal mode), since you are going from -2 to 0 over the first half of the throttle travel, then from 0 to 10 from half to full throttle.

I hope this isn't all sounding like nonsense, I'm a long time airplane guy trying to make the big jump into heli's and it's all pretty confusing. I've watched the video's many times, they do help a lot.

Thanks
Malcolm

[TheBum]

I'd say he messed up your setup. Your Normal mode setup was just fine and the swashplate would move in the way you describe (slowly to half stick and then faster the rest of the way).

After double-checking the levelness of the various head elements mechanically, I'd suggest resetting the radio settings and starting over with the radio setup. Leave the radio set up with a linear pitch curve until you've verified that you get symmetrical pitch + and - and then dial it down to +/- 10 in the swash menu. Then, and only then, adjust your pitch curve back to -2 to +10. Finally, don't let that person at the LHS mess it up again.

[malcolmm]

I'd say he messed up your setup. Your Normal mode setup was just fine and the swashplate would move in the way you describe (slowly to half stick and then faster the rest of the way).

After double-checking the levelness of the various head elements mechanically, I'd suggest resetting the radio settings and starting over with the radio setup. Leave the radio set up with a linear pitch curve until you've verified that you get symmetrical pitch + and - and then dial it down to +/- 10 in the swash menu. Then, and only then, adjust your pitch curve back to -2 to +10. Finally, don't let that person at the LHS mess it up again.

It's beginning to make sense to me now. I reviewed the videos yet again, and I understand what you are saying.

I was beginnning to suspect the LHS guy did mess things up a bit. Strange, because he is pretty good with helis.

Thanks for the help

Malcolm

[TheBum]

You're welcome. I just got it figured out myself, so it's pretty fresh in my mind.