This is my first nitro. Do I worry about bubbles in the tank?

[Steviepoo]

Should I expect to be able to get to a point where the heli doesn't vibrate so bad I can see bubbles forming in the tank?

I'm running a YS 120 which I recently found out is known to vibrate more than other engines. Admittedly, I haven't gotten the tune completely dialed in but I think it's pretty close.

I'm wondering if I should've went with an OS 105...

[Chris Sexton]

Ideally you don't want the fuel to bubble but 100% vib free is nearly impossible with a nitro.  If the fuel isn't foaming the fuel is probably ok.  Does the heli show any other signs of vibs? Odd FBL behavior, stable hovers?

[Steviepoo]

The tail is obviously not happy, I haven't played with it too much so far but lowering the gain hasn't stopped the slow twitch. I've got plenty of high vibration and a few extreme vibe entries in the VBAR log.

If it makes a difference, the engine was used but had at least the piston and ring replaced by YS before I got it. I've put a little over 4L through it so far.

[Chris Sexton]

Without seeing it for myself, I would say you are fighting motor tuning/vibrations.

[bmclaurin]

The tail is obviously not happy, I haven't played with it too much so far but lowering the gain hasn't stopped the slow twitch.

I agree that you are probably chasing vibes/engine tuning issues. However, one other thing to consider, just in case, is whether you have any binding in your tail pitch slider mechanism. If you detach the rudder pushrod, is the tail pitch slider absolutely free of binding? Can you effortlessly move it across its entire range of motion along the entire length of the tail output shaft? It should almost "flop" back and forth. Even the slightest drag or snag at any point along the shaft can lead to anomolies in flight. If so, make sure you size the ball links on tail pitch slider as well as the bell crank until it slides effortlessly across the entire length of the tail output shaft. Then reconnect your push rod and see it still moves freely. If not, then size the ball link at the end of the push rod. Continue in this fashion until you have worked your way all the way back to the tail servo itself. This method has worked well for me for several builds.

Lastly, you can try Mother's Mag & Aluminum Polish on the tail output shaft.

http://www.mothers.com/02_products/05100-05101.html

This stuff works wonders to put an absolutely smooth surface on the output shaft. I usually just apply a small amount to a microfiber rag and then carefully spin the output shaft in a drill while applying the rag to the shaft. Obviously, it's best to do this with the shaft removed from the heli, but if you're careful (remove blades, etc.), you can even do it while the shaft is installed.

Hope you get it worked out.

[GScott]

If you are using a Silverline Vbar then you should not see any extreme vibration messages except during harder 3D. During hovering and basic FFF you probably shouldn't see many high vibration alerts either. My guess is it's the engine vibrations. I would get it tuned in but that motor is known for some nasty vibrations so it will probably never run as smooth as the OS 105.

[Matt Botos]

Don't quote me on this but..... I believe YS is coming out with a new version of that motor. 
Until then I would stay with the OS91 - 105 or YS91

Matt

[Steviepoo]

Don't quote me on this but..... I believe YS is coming out with a new version of that motor. 
Until then I would stay with the OS91 - 105 or YS91

Matt

They sure are, according to rcjapan.net it's supposed to be released this month. I just might pre-order one since I've already invested in the Hatori pipe.

https://rcjapan.net/ys-engine-engines-c-81_109/120srx-helicopter-2-cylcle-engine-coming-soon-p-16330?zenid=sveoc39u015eqc37djlg1bpng0

[Steviepoo]

The tail is obviously not happy, I haven't played with it too much so far but lowering the gain hasn't stopped the slow twitch.

However, one other thing to consider, just in case, is whether you have any binding in your tail pitch slider mechanism.

Thanks for the tip.

During assembly I was pretty meticulous about getting all the links, especially on the tail, smooth. I've noticed that they tend to tighten up slightly so I'll go through them again to make sure.

[Steviepoo]

Without seeing it for myself, I would say you are fighting motor tuning/vibrations.

I'm convinced that's a big part of it. I was going through some threads on HeliFreak and someone mentioned that the 120 runs well between 16,000 and 16,500 rpm. On the stock N7 gearing that's about 2000rpm on the head so I tested it this morning and it does seem to be better than the 1800 and 1950 I was running yesterday.

[beans07]

Pit an extra headshim in it and run 15-20%. It will help. Also,try and keep the load on it as much as possible. It's smoother under a load than a not loaded up in a hover.

[Steviepoo]

Pit an extra headshim in it and run 15-20%. It will help. Also,try and keep the load on it as much as possible. It's smoother under a load than a not loaded up in a hover.

I should add that I'm already running 15%. Everything I've read so far regarding a second shim says that it's required if you want to run a 30% mix.

Thanks for the tip about the load. I'm going to get a Bluetooth dongle for the vbar soon so I can take a closer look at the source of the vibration.

[beans07]

A flying buddy and myself spent a couple of days worth of flying and a few galons (probably about 6) of fuel on his Heli to get it right. It was an align 700n.

To get it right we used 20% nitro so that we could also use it in our 55 engines. We added a shim, settled on 7.75 gear ratio, and upped the tail ratio as well to about what the synergy is to keep the load on the Heli at all time. We used a header tank as well as a fuel,magnet in both tanks and made sure there were absolutely no leaks at all. 16,000RPM was the engines happiest and stop using a vbar gov and used a rev lock. We use OS8 plugs. The vbar gov can be very problematic on certain motors and setups. Note that this motor was an early one and has not had the update head on it which has more volume and decreases the compression.

It still vibrate quite a lot in a hover but absolutely hammers inflight. Much much more power than my OS105.

[Steviepoo]

Well, after losing 3 of the 4 balls in the canopy mounts, two more screws and finding two more loose screws, I've decided to buy a friends OS 91 SZ until the new YS120srX is released.

[MadBird]

Well, after losing 3 of the 4 balls in the canopy mounts, two more screws and finding two more loose screws, I've decided to buy a friends OS 91 SZ until the new YS120srX is released.

Thats a shame that you're having so much trouble with your 120. I saw one fly last night in an RJX airframe (beans07's mate) and holy sh!t did that thing go!!
I'm only new to helis, so don't but have much experience with big nitros, but the YS 120 pulls like a freight train and with the TJ Pro gov it ran flawlessly on the mid and high needles. The low end still needs a bit of tuning, but man I was inpressed with it's power. He was running a Blue full size vbar and had no issues with vibes causing drift or tail issues at all.