jamesjoneill

A friend of mine has just finished his Onyx and is having problems with excessive vibration. Engine is YS 140L on a modified Dave Brown mount (before anyone replies saying this isn't sufficient for this engine it has been modified and I have been running my dingo on one all season with no problems, the motion is very similar to a Hyde mount). The servos are JR 8401's.

The vibration is such that the ailerons will at times be vibrating by up to 1/2" at the tips - indeed the whole wingtip moves by about this amount. It flys fine but with this much vibration the servos and airframe won't last too long. It has baffled us because the set-up is virtualy identical to my Alliance - same engine mount (although an L rather than a DZ), same servos and the wing on the Onyx seems just as stiff as the one on my Alliance. And yet my Alliance shows virtually no vibration on the wings at all.

Has anyone else had this problem with their Onyx, or indeed any balsa fuz?

Any ideas most gratefully received.

James

flyn4Him

Sounds to me that you have two choices here. First, change out the engine mount and see what results you get. If the setup is identical to yours, then maybe you can switch out engines only and see if you get the same amount of vibration in your airframe. You can also install your engine in the Onyx and see if the vibration has been removed. Eliminate one thing at a time. Hope that helps some.

In Christ,

Joel Chavez

jamesjoneill

Thanks for the suggestions. Part of the problem is that the set-ups really are almost identical, even the engine used to be mine until I replaced it with the dingo six months ago.

The only real difference is that my aircraft has a composite fuz whereas the Onyx is a built up, balsa fuz. Has anyone else had any experience of using the two types of plane, and the differneces in vibration transmission between the two?

James

flyn4Him

James, if my memory serves me right, I believe that a balsa fuse would have less vibration than a composite. You might want to verify that. Hope you resolve you plight.

In Christ,

Joel Chavez

flywilly

My Feedback: (121)

How old are the isolators in the Dave Brown mount? Maybe they need to be replaced?

I assume everything (prop, spinner) has been balanced. Is the vibration problem consistent throughout the RPM range?

I'm flying a wood fuselage pattern ship with a Bully 1.20 on a DB mount with no problem.

-Will B.

Rune

hi!
cant understnad why change from Alliance to Onyx ...
the A. should be a better aircraft...i had some problems with mine ..some off the work thta was done on it was not that wery good!
i change the wings also i destroyed those original and build new one with Alliance airfoils...i like them more than the original!
but all in all ..ok plane !

wolf123

Hi all.
do you use nose ring ?
My Onyx have 1 year and i use Dz140 and 140L on it with a Yamada soft mount and never have this problem, yes i 've a little shake but identical to other airframe i used. I think the problem is your mont.
I've modified the nose of the Onyx in order to accept the Ys mounts.
Try to use a glow driver like the glow4b from microsens electronic,because on low rpm the 140L have some missfiring and this make the vibration on high level.
have a nice day
Mirco

jamesjoneill

I really don't think it is a problem with the mount - it is the same mount with brand new rubbers and the same nose ring that I use in the Alliance with the Dingo, and before that the same 140L that is now in the Onyx. I must be something to do with the airframe?

I still have and fly the Alliance - it is a great plane! The Onyx belongs to a friend of mine, I am reporting here on his behalf! The Onyx appears to be a great plane but I wouldn't swap my Alliance for one.

James

bla bla

I have a Focus 1 (same aeroplane) with an OS 1.40. It shakes real bad, so much so I'm often concerned that the tail may come off!
Guess what? DB Soft mount... With nose ring. Tried harder rubber, didn't help at all, just increased the sound, when back to the softest I could find...definately the best solution.
The mount just plain old fashioned school of design, period. Hydes and similar are the way to go.

By the way, It's been shakin' for over 3 years and nothings fallen off or come loose... yet.

EHFAI

James

I had a very similar problem with a balsa Typhoon D with a DB mount after installing a new, more powerful, YS engine. The ailerons would vibrate as you describe. The airplane would oscillate in roll during flight, battery power consumption was huge, and in short order the aileron servo motors burnt up.

Accelerometers were mounted in place of the servos to measure the vibration and various different duro isolators tried. Interestingly, solid aluminum was best - but then the noise was horrendous.

Static balancing of the ailerons helped a little, but not enough. The dampening characteristics of the mount and resonance nodes of the airframe simply could not accommodate the exciting forces of the engine. Unfortunately, there's no way, besides experience, to determine if these factors will combine to provide satisfactory performance or not.

In desperation, I contacted Merle Hyde and he custom built a mount to fit the existing firewall location, space. Installation of this mount totally eliminated the problem. Haven't used anything but a Hyde Mount since. (Something that works is a good value, regardless of price.)

Earl

wolf123

Hi James
You never compare Alliance with an Onyx or a Focus1, but i 've 3 f3a , a Rhapsody that's full mould, Alize from Pl-Prod carbon-kevlar fuselage an foam wing and an Onyx with balsa fuselage and foam wing.The Onyx ,with a YS soft mount is the airframe that make less vibration! So the problem is r your mount or eccessive wear on engine (check the cranckshaft because they are not hardened and bent easy). try to mount the Dingo on Onyx and observe it,if shake are the same the problem is in airframe but if are less the problem is engine!
Can you please post some pics of yours friend Onyx ?

Ehfai i agree with you on Hyde mount, but on wood fuselage the YS soft mounts works much better( the only problem is make a mount to accept it)
The Hyde is great on composite fuselage because they need a rigid chassis to work better.( and works very very better)

Mirco

jamesjoneill

As soon as I have some pictures I will post them, probably won't get to take any for a few days though.

The thing that still bugs me about all of these suggestions is that I have exactly the same mount set-up in the Alliance (I know this because he copied what I had done, as it works extremely well for 1/4 price of a hyde mount). Given that a balsa fuz should damp out the vibration better than a composite one, why should we get all this vibration? Comparing the motion of my mount to various hyde-mount installations I have seen the motion of the engine from idle through to full throttle is indistiguishable.

The engine is fine - it went straight from my Alliance to his Onyx and when bench run is as smooth as a kitten so we have eliminated this from the equation. I can only think it must be a too flexible wing, for instance, or some other part of the structure that it amplifying the vibrations.

Thanks for all the input so far - keep the ideas coming!

James

byoung466

My Feedback: (16)

Are bothe planes one piece wings?

jamesjoneill

No. The Alliance is one piece but the Onyx is plug in. The mounts have been double and triple checked for integrity and there isn't any play in them (there was a little initially but that was removed - it helped but only slightly). Do you think this could be an issue?

byoung466

My Feedback: (16)

The one piece wing should be stiffer than the two piece wing. Does the plane only shake around at idle? The only things you can easily change is the softness of the mount blocks, or change the engine. Theres not much else to try unless the prop is way out of balance.

jamesjoneill

The vibration reaches a peak at about 25% throttle. We will play aorund with different stiffnesses of mount and see what difference it makes.

James

wolf123

Hi James
if you have max vibration at 25% of throttle i think the engine is a little rich on transition from idle to max rpm,try to lean the regulator 1\4 turn.
Regards Mirco

bla bla

Believe me, the softer the better. I tried different rubber and even tried stiff mounting it to cure the problem. It didn't, just got worse and worse. The best solution was as soft as possible. The problem seems to be cause by the design if the mounting box... others i've seen with straight forward fire wall mounted engines appeared to be far better off. They where using hyde mounts so that ain't such a good comparision. The box though, by shear coincidence could be of such dimensions that it just hits a point of resonace, some type of harmonic frequency at about 25%(ish) throttle that kinda sets of the rest of the model shaking. Mine freaks at exactly the same point and I'm using a different engine... a 2 stroke which in theory, should be smoother. Not!