300X Intermittent Vibe ONLY under pitch load???

[adambowersva]

My 300x has had seemingly almost everything replaced. On the table with main blades off it is smooth as silk all the way up aside from maybe a small vibe around 30% throttle that quickly goes away as spool up continues.

I had rebuilt it following a crash. Upon lift off from the ground it starts vibrating badly...as in the skids get very blurry and you can see/hear the whole head seemingly shaking back and forth. This seemed to be intermittent. Without changing anything I went through 4 packs with little issue. It would vibe a little on take off and then fly fine. Then it started vibing badly again at take off so I set it down for fear of it getting confused.

I pulled everything (head/blade grips, shaft, swash, main gear, hub) off a donor parts heli that was never flown. Still vibrated on take off. Took it to "my guy" at local hobby shop. My swash was a bit out of level and front elevator arm wasn't at 90 in reference position. We took it outside and it flew fine for the short hover we did.

Get home, go to fly, first pack....vibing again.

I swapped out the LYNX Plastic Blades I had on it (they were perfectly balanced and had same COG straight out of package) for a set of Woodies (and lowered throttle max to 75%) and have flown 8 packs now with no issues, but I'm not totally convinced that the LYNX Blades are the issue since so many have no problems with them at all.

Anyone have any ideas? Could it be the BeastX?

Gear mesh is good, belt isn't too tight, screws in tail box are all only just over snug....I'm at a bit of a loss

[James Recard]

I had same issues... this is what fixed mine... a small cable tie around the tail box. pulled nice and tight. my theory is the tail box (fin) screws strip and its hard to tell because we don't ever tighten them enough... might be worth a try.

[adambowersva]

K-rash I will give that a try. Thanks.

For further developments I also got a hold of a pair of stock carbon fiber blades and was able to turn my throttle speed back up to 100% and there are still 0 problems. In fact she runs like a dream and probably better than when she was new out of the box. So clearly there is not a mechanical vibration that is being caused at throttle higher than 75%. I am pretty timid to put the plastic blades back on to see if the problem happens again. I've gotten at least 15 great flights on the carbones now with no vibe.

Quite bizarre when the only thing that has changed is the main rotor blades.

[adambowersva]

Ok I take it back. I tried swapping out for a 10 tooth pinion and the vibes returned. Again, only shortly after lifting off the ground. I tried an 11 - tooth pinion from a buddies cfx also and same thing.

K-rash, I also tried the mentioned cable tie to no avail .

This is the strangest intermittent vibe I've ever seen.

Any hep please?

[helidude71]

Dynamic balance your blades.

Put a small piece of tape on one blade.
Go fly, worse?, remove the tape and put on the other blade.
If you have less vibs on one blade, try a bigger or smaller piece on that same blade as well.
Do this for main and tail blades.

Works great here.

[Uriah]

Originally Posted by helidude71

Dynamic balance your blades.

Put a small piece of tape on one blade.
Go fly, worse?, remove the tape and put on the other blade.
If you have less vibs on one blade, try a bigger or smaller piece on that same blade as well.
Do this for main and tail blades.

Works great here.

+10



I *always* dynamically balance my tails at full loads. In regards to the mains, the only birds where I dynamically balance my main blades at full load is on my two 300Xs that are still running the stock plastic frames. I only recently started doing this when I had a vibration issue after one of my crashes on my mostly stocker 300X that my usual remedies couldn't track down. Even with the Lynx frame braces, the stock plastic frames will still flex a little if the head is not perfectly balanced, and thus a slight imperfection can get amplified, especially at higher RPMs. On all of my other birds, including my two Lynx framed 300Xs, I statically balance my main blades and call it good (I still dynamically balance the tails, though). But like you, the only way I've found to safely dynamically balance the main blades is to just fly it and see if it gets better or worse. With the tails, I can obviously do full power run ups without the main blades on.

For everyone with aftermarket carbon fiber skids - I would recommend you install the stock plastic skids until you get your vibration problems solved and know everything is running smoothly. The stock plastic skids are an excellent indicator for head vibes. Obviously, if your skids are vibrating (i.e. fuzzing), you can rule out tail vibes, assuming you've already taken the time to dynamically balance your tail at full load. All that could cause vibrations at this point (practically speaking) would be your head or main shaft, since you would have noticed any potential motor vibes while you were balancing your tail on the workbench.

[adambowersva]

Yesterday I flew a pack and was great (back on 9 tooth). Then 3nd pack vibes on lift off. Set it down and then ramped up throttle real slow in normal mode then it flew rest of pack fine. Third pack rifht back to vibe.

Is it possible to be heat related with the motor? Motor pretty hot to touch even after one flight.

[adambowersva]

Oh and as for dynamic balancing, my main blades i had found cog spot on same on both blades. Static balance only needed 2" piece of scotch tape. Since cog was spot on isn't the dynamic balance of the mains already done then?

[Uriah]

Originally Posted by adambowersva

Oh and as for dynamic balancing, my main blades i had found cog spot on same on both blades. Static balance only needed 2" piece of scotch tape. Since cog was spot on isn't the dynamic balance of the mains already done then?

Yes and no. You have to remember that under full load, the head and grips may flex a little, and the bearings will seat themselves and may move a little bit due to the centrifugal force of the blades. That's why we dynamically balance the tails under full load (the tails are much more sensitive since they spin 4x faster than the heads), but the same concept applies to your head as well. The 300X with the stock plastic frame is the only bird where I've ever needed to balance the main blades under load (i.e. fly and see if it's better). Most birds (especially larger birds) can handle a slight imperfection in the head with no ill effects, so usually static balancing is more than sufficient. But even with a frame brace, the stock 300X frame will flex a little and so your balance must be spot on to never have vibes. All of this is, of course, assuming you've addressed vibes elsewhere (i.e. motor, tail, etc.) and have properly assembled your head.

Generally speaking, most people can get away with the stock frame (with a frame brace) and never dynamically balance the head under full load, because it's assumed that the bearings and dampers will usually seat themselves evenly. But I've found that's not always the case. Perhaps it's a deformed head, or maybe the grips are deformed a little; or maybe it's a combination of the two. But I have had a few head assemblies on the stock frames that vibrated even with new feathering shafts, and continued to vibrate until I dynamically balanced them under load. On aftermarket frames, the head assemblies would obviously still be out of balance, but it would not cause any noticeable ill effects and the imbalance could safely be ignored.

[Epoweredrc]

since talking about balancing tail blades, how tight or loose do most run 300x tail blades? mine came pretty darn snug and i loosen up a lil. my blade 450 i have them where they stay wherever i put them but on spool up with sling out but there not loose ( falling around like i see some folks running)

[adambowersva]

The way u do it with your 450 is the way should be done with 300.

Some helis do however need blades to run loose to help mitigate vibes. The 130x is a prime example.

[adambowersva]

And back on my issue for some more info...After replacing the tail rotor hub the problem has remained mostly nonexistent. Strangely though, it has happened about 4 times in the last 10-12 flights. But these times, not right at lift off. All of these times it happened inverted nose in close by. I would fly out in front of me a good 100ft, flip backwards to nose in inverted, bring in towards me, and then go into a piro climb out. Each time it happened just before climb out. I simply flipped back over, knocked iu back down to 75% and would go away quickly. Then I would get back into normal flight and kick headspeed back up.

Very strange. But I haven't tried the dynamic balance under load on main blades yet as its now not consistent enough I don't thk to do it lol.

But maybe this gives more info on what could be. Maybe it is all just frame flex related. I don't have a frame stiffener at the moment either, but shall soon.