It slips when it flips

My Futura SE and Concept SRX both do this to some degree. Not much, probably not enough to be noticed by more observers, but enough to be noticed by me, and it bugs me. A lot.

I notice it most during async loops and simple forward half-flips inverted. Just before the helicopter gets level again, it 'slips' just a little bit on the yaw axis. If I do a forward half-flip from an upright hover, I need to give it a touch of left rudder right after I get into the inverted hover. This is so predictable it's almost automatic now. Still, tt really aggravates me during asyncs, because to me this maneuver is all about smoothness, and the slip+correction just interrupts the flow of the maneuver. Drives me nuts!

I had some vibration issues with my Futura SE last summer and this was one of the symptoms. When it had the vibration problem, the gyro slip during a flip was more pronounced. When it was running smooth as glass, it would still slip, but only just barely.

Unable to solve the problem, I started looking at other peoples' helis. I've observed the same thing while flipping friends' helicopters so I know it isn't just me. In fact, I've made a point of watching for this at fun-flys, and as far as I can tell this happens to everyone, whether they realize it or not.

What follows is something that's been on my mind for a while but I haven't posted about it yet. These are my observations and conclusions so far, and if anyone has anything to add, please do. This has been bugging me for a couple of seasons. I don't fully understand what's going on here, and I'd like to!

I think it's a side effect of the ring vortex that happens when the helicopter descends through the turbulent air below the rotor.

For a textbook example of a ring vortex, try hovering upright at 12 feet, then descend to 5 or 6 feet, then stop the descent. Depending on the rate of descent, you may have trouble stopping the helicopter because the blades are flying through turbulent air (the vortex ring). I understand that in full-scale this can become a serious problem ("settling under power"). With RC helis you can just slam the collective and power out of it, but you will notice a lag between slamming the collective and seeing the helicopter rise up.

If you watch the exhaust smoke during the "settling" phase, you can see the smoke hanging around in the rotor disc during the descent. Then you add collective, there's a slight lag while all the smoke is ejected out the bottom the rotor disc (you hear a soft "whump" sort of noise), and suddenly you're in control again.

I think the same thing happens during a flip. I'm definitely hearing the same noise just before the helicopter gets level, and this is the moment when the gyro slips. I'd like to videotape this in the right conditions and see if the smoke shows the same "vortex ring" behavior.

I wasn't deliberately trying to capture evidence of this stuff, when I shot my last round of videos, but I think this footage indicates that I'm onto something.

About 17 seconds into Nate_03, you can't see the vortex ring well at all, but you can see the ejection of the smoke just as the blades bite into clean air and the descent stops.

About 7 seconds into Nate_05, a vortex just begins to form on the left edge of the disc before being blown out. Wind and sideways movement stop it from getting significant (in full scale helis, translation (forward speed) is recommended to escape the vortex, since they don't necessarily have the power to just blow it out).

All in all, the video I have so far is not real useful when it comes to illustrating this phenomenom. I'll have to deliberately try to capture this on tape some time...

During the transition from the vortex ring to regular airflow, the gyro slips. I don't know if this is due to the sudden torque change when the main rotor blades finally bite into some clean air, or if the tail rotor loses traction because it's in the vortex, or what... You might see this a little bit in the descending hover exercise I described above, but when you're doing a flip or an async loop, the slip is much more pronounced - possibly because the cyclic input adds vibration and make things worse for the gyro.

When I get a chance to fly a heli with a 5000T gyro, this is **THE** test I have in mind. If that gyro can solve this problem, I might buy one. Even when I had my Arcamax PI Pro working at its best (may it rest in peace), this problem was still there - just barely, but still there. Short of the PI Pro, the best gyro I know of is a CSM ICG-360 that doesn't drift. I have one and I won't sell it at any price. But when I find a gyro that solves this problem, I'll buy one in a heartbeat.