HELP - Stalling elevator

[hoppy]

My ROTO with anything but very small (+/- 17deg) elevator throws does square loops. Does a 90, then goes straight up, another 90, starts back down, and another 90. Of course these are more or less but you get the idea. With a constant over 20 deg elevator deflection, it performs herky jerky loops. The low throw is OK but the loops are very large and don't allow fast reactions in emergency conditions.

What can I do to correct this problem?

Thanks
hoppy

[Sparky Paul]

The elevator isn't "stalling", the wing is.
Move the c.g. forward.

[hoppy]

Ah so, that's easier than rebuilding the elevator.
Thanks
hoppy

[hoppy]

Moved cg forward 3/8" forward from where it was which was at manufacturers recommended location.

Performance was unchanged. Plane makes a 70-90deg to vertical, flies up with a couple of twitchs before it makes another 70-90deg to a somwhat down angle and another couple small turns before making another turn to a level flight mode. Kind of a ratchet like loop. Large loops are smooth.

hoppy

[Sparky Paul]

Now how much elevator do you really have?
The wing can still be stalled if there's too much, with the c.g. correct.
Do you have dual rates or expo?
For planes where lots of travel is occassionally needed, these come in handy.
And these let the c.g. aft to a sweet spot.

[hoppy]

I really have +/- 15 deg on low rate and +/- 23 deg on high rate. That 8 deg difference makes a big difference in the loop shape.

I was wondering but with the large stabilizer area and small elevator area (at least to what I'm used to), upon making a sharp up movement, the stabilizer "blankets" the small elevator with dirty air and it takes a little straight ahead flight to re-establish a clean airflow over the elevator. Any thoughts on that gut feeling?
hoppy

[Gene Bond]

Hoppy: I know what you're talking about, and I've referred to it similarly. On one model I was Beta'ing, there was a point where if too much elevator was used, it just went into a stall, and slowly fell. If there was more speed, it didn't happen. I just called it an 'elevator stall'.

I wound up increasing the elevator to double, and the problem went away. I think it was the Hstab shadowing the elevator, and with a larger surface, the elevator could 'peek around' the shadow of the Hstab.

[Gastronom]

I just built an Eagle 2 for my wife this last summer and got the same results that you did. I determined that , 1.) the hinges aren;t alligned causing the elevator not to respond properly and 2.) the elevator itself was bowed (not like a normal bow but forward and aft bow). The hinge line being off makes the elevator 'snap' when deflected and teh bowed elevator makes it so that when deflected it would pull hinges out of the horizontal stab. I know that I have to rebuild the elevator..
Good luck locating your problem.

[hoppy]

The ROTO got a new horizontal control surface which improved loop performance. The loops are much tighter now and the ratching effect has dissappeared.
hoppy

[Gene Bond]

Looks about right :)