Rap 50 Woof and poof

[WayneBrown]

I flew with LPeragallo this afternoon, his Rap 50 with Mavvrick head went into serious woof 'n poof mode twice during his flight.
Been a long time since I have experienced this issue, and totally drew a blank.
What are the root causes for this phenomenon?
He did a couple hail Mary moves with full pitch, tracking went off 2-3" easy and the sound was wicked.
After he switched to normal mode and the HS dropped, tracking went back to dead on.
TIA

[JimLerch]

Ok, that's freaky. I was at the field today and another pilot has a raptor 50 with a Kasama head and he went into WOOF and POOF. He said he had this problem in the past but got it to stop, but wasn't certain how. (that was a year or two ago)

He said this woof and poof problem came back after his last crash.

After today's event, (which was WOW violent!) he had a heck of a time getting it to stop doing it. Finally it snapped back into normal flight and he put it on the ground.

Post inspection didn't reveal anything odd until we grabbed the blade grips and twisted in collective. We found that the collective servo was damaged to the point that when we tried to unscrew the servo horn the end of the servo just broke off.

The question is "Did the servo fail causing the woof and poof, or did the woof and poof kill the servo" I'm pretty certain he would not have been able to get off the ground with the damage seen to the servo..

I'm not convinced that a collective servo can explain what I saw. It looked like he was in a hover with perfect tracking, flew up, did a back flip, it made a gawd awful noise, and looked like one blade was at +10 degrees while the other was at -10 degrees pitch (kinda looked like an X wing fighter from star wars.)

Once he got out of the woof and poof by translating thru zero pitch a few times, the tracking went back to perfect and landed normally. **SPOOKY**

He's getting a gear set for the collective servo tomorrow, then I'm meeting him at the field with all the camera gear I can bring to bare and see if we can get this thing on film. Maybe it will reveal something about what's going on when it happens..

In any event, if I had not seen this with my own eyes, I'd have sworn this is not possible.. Its just freaking crazy... :confused:

Clearly its some kind of self reinforcing feed back (like a gyro with the gain too high). However I don't see anything wrong with anything on his heli other than the damaged servo. Actually, I'm thinking that because he doesn't have ANY slop in his head the problem is being amplified somehow.

Questions:


In your case, could you tell if one blade was high and the other low, or were both blades rapidly oscillating in pitch?
Could you see what the flybar or paddles were doing?
Could you see the swash plate?
Post event, did you see any slop anywhere?

[WayneBrown]

Questions:

In your case, could you tell if one blade was high and the other low, or were both blades rapidly oscillating in pitch?
Could you see what the flybar or paddles were doing?
Could you see the swash plate?
Post event, did you see any slop anywhere?
1. I saw a vast difference between the plane of both blades, but it was too far out to determine if it was oscillating.
2. Flybar was in track
3. it was the shiney silver thing waaaaaaaaaaaaaaaaaay off in the distance.
4. god yes there's slop, this is a 'well loved' machine. :)

[Funky]

My Titan does this every time I put V blades on it. I heard the grip flip mod can fix this problem, but I never tried myself.

[BarracudaHockey]

Crappy blades (aft cg) mavrikks are great for it.
Slop in the collective system
Blade grip ball link screw bent.
Slop in the collective system somewhere.
Radial bearings loose in the blade grips (metal grips are susceptable to this if you don't use green locktite to seat the bearings) or just worn out plastic ones.
Thrust bearings installed backwards.

Check the spindle, if it went out that far you can bet its bent.

Using a wheel with a hole drilled is stiffer than the star style arms for the collective servo.

[WayneBrown]

Using Radix blades, so that should not be it.
Slop in the collective. There's where I place my money. :)Crappy blades (aft cg) mavrikks are great for it.
Slop in the collective system
Blade grip ball link screw bent.
Slop in the collective system somewhere.
Radial bearings loose in the blade grips (metal grips are susceptable to this if you don't use green locktite to seat the bearings) or just worn out plastic ones.
Thrust bearings installed backwards.

Check the spindle, if it went out that far you can bet its bent.

Using a wheel with a hole drilled is stiffer than the star style arms for the collective servo.

[I3DM]

Using Radix blades, so that should not be it.
Slop in the collective. There's where I place my money. :)

Im with you 100%.