How much vibe is normal?

[Mega Stumbler]

I have about 10 flights on my 450X. It is completely stock and the heli and TX are setup accouding to the manual. I have had no crashes or hard landings. It seems very stable and flies very well. However, the tail has a high speed vibration. The tail fin moves from side to side about 2 inches total. It does this so fast that the fin becomes a blur. It does it at all head speeds including normal and IU. Blades are same weight and blade COG is near perfect.

I know how much vibration is acceptable for the mCPx but I am not sure on these larger helis. Is this tail fin vibe normal? If not, what are the usual suspects.

Thank you in advance

[azezeil]

Sounds like your gyro gain is to high. Try lowering it 0.5% at a time and giving it a quick test fly until it stops.

[nbisme]

just for s&g's, try playing with the tightness (looseness) of the boom/belt.

I've found that my heli likes the belt on the tight side, which gets rid of that sort of high speed vibe.

Of course, there is also the tail shaft pulley that needs to be flawlessly straight, and the tail rotor hub which should be totally concentric. If either of those are slightly off, then vibes will occur. Not to mention well matched tail blades that need to be properly tightened down and tail grips that like to work themselves loose without loktite.

let us know what affect the belt tightness had.

[Flying_Amp]

Originally Posted by azezeil

Sounds like your gyro gain is to high. Try lowering it 0.5% at a time and giving it a quick test fly until it stops.

+1

[Mega Stumbler]

I will look at both the belt tension and the gyro gain. I did not think to check the gain because the vibration is so fast. Can the gyro and servos make corrections so fast that the fin becomes a blur? It looks like a hummingbird's wing. It flies great. The tail holds well and it piros well but it looks like that fin can shake its self to peices the way it's going.

I know the blade micros inside and out but I am just learning all the settings and adjustments on these larger helis. I just adjust the gain from the TX correct? Also, is it possible to do this in flight or should I land before each gyro gain adjustment?

Thank you for the help everyone.

[Talesin]

Heya MS, welcome to the bigger world.

Is the vibration you're getting just the bottom tip of the vertical stabilizer? Is the tailcase also blurring, or just the fin tips? My bottom tailfin tip does the blur thing too, but only really in idle-up, and even then only about 1-2cm, not a full inch.

I'm pretty sure what the others are talking about is the tail shake problem (whole heli rotates back and forth about 2 inches violently) which it doesn't sound like is your issue. Tail belt tightness and gyro gain would help to reduce that... not so much the tail holding position and just the stabilizer vibrating. The amount you described is definitely not normal, especially so if you mean it's occurring in normal (non-IU) flight at around 60% max throttle. Mine has less than 1mm visible vibration in standard flight mode.

Have you disassembled/reassembled it (to re-loctite)? If so, over-tightening a few screws (the jesus bolt at the bottom of the main shaft most notably!) can lead to excessive vibration. Same with if your horizontal stabilizer is loose. Do check your belt tightness, and your motor for lateral (not so much vertical) play.

[Mega Stumbler]

Talesin, it is just the tip of the vertical stab. The rest of the tail seems stable. From a flying distance of about 10-15 feet I can not see any shaking of the tail case. I did a quick check of all the screws before my maiden but I am still unsure how tight everything needs to be. I know that some things need to be just snug while others need to be tight. I am still learning what each screw needs.

I checked the belt tension by following the instructions in the manual but those seemed vague. I guess belt tension is something you just have to get the feel for like blade tightness. I have not looked at my motor yet. I did a quick check on the mesh but that is as far as I went. I will look further into the motor play, jesus bolt, and general hardware.

The way it is now, the heli is OK. I am just concerned that the vibs will upset the BX and cause uncommanded maneuvers if I don't track it down and get it to a more acceptible limit.

Once again, thank you.

[Talesin]

Screws into plastic = snug (no loctite)
Screws into metal = snug (loctite)

And yes, the tail belt is a very subjective thing. As I understand it, with this heli the belt can be run quite loose (just so long as it can't touch the other side of the belt when pressed over) and not risk slipping.
Motor, just grab the can and lift/rock it back and forth. There'll likely be about 1mm vertical play, but there should be no lateral play. Pinion/main mesh can be set properly by loosening the four motor mount bolts, sliding away, strip of standard copy paper between, push together, tighten and then rotate the head to feed the paper out. Should have nice crisp crimps.

You can also take off the main and tail blades and spool it up on a bench to safely get a closer look at your main/tail gear tracking, and watch for main shaft transitional harmonic wobble.
Definitely check your feathering shaft tightness at the same time, a few people have reported that the heli came with one or both of the shaft screws fairly loose (should be snug, with loctite inside the feathering shaft hole rather than on the screw, to prevent it getting into the thrust bearings). Check the blade grip f.shaft play (should be next to zero in/out, and only a little up/down/left/right) as well.

So you're getting the severe tailfin vibration in normal mode, or just idle-up?

[missle]

I noticed the same thing when I would go into IU but it turned out that when I went to the CF tail blades (everything else completely stock), that i may have had them a little to tight. Now the blades are close to "loose" where if I shake, they fall but they are tight enough to rotate the main blades without moving. I was shocked at the difference but I can't deny it when it worked for me.

[TheHeliDude]

I had this really fast tail vibe in certain maneuvers. Backward flight in particular. Lowering gain 1% fixed this for me. I don't think you have to have the heli on or do it repeatedly or anything like that. I'm using a dx6i.

[lovespicyfood]

I noticed this shake on my heli this past weekend. Not real bad, but a noticeable blur on the bottom of the vertical fin. I will mess with my gyro gain...I think it is set at 54% "Stock" on the gear channel?

Pete

[Talesin]

Oddly, it's only 54 on the DX7s/8. On the DX6i and DX7/se it's 77% (which is where I have mine set).