700n Vibrations

[chadvandonkey]

I get mega engine vibrations from my 700n, so much so that I get tail creep from the 3gx, which is mounted on 2 sticky pads. The heli itself runs sweet and true but the sound of vibration is quite loud. Having a 2 piece pipe doesn't help (GP exhaust with short manifold piece) so I'll swap to Align pipe when I see one.

Are there any obvious things to look for or maybe someting known that can be done to help?

It is vibration from the engine on tickover that is worst. I'm sure when up to speed it is much better but I feel I need to look at what I can do to help reduce vibes.

Cheers.

[coolice]

I get mega engine vibrations from my 700n, so much so that I get tail creep from the 3gx, which is mounted on 2 sticky pads. The heli itself runs sweet and true but the sound of vibration is quite loud. Having a 2 piece pipe doesn't help (GP exhaust with short manifold piece) so I'll swap to Align pipe when I see one.

Are there any obvious things to look for or maybe someting known that can be done to help?

It is vibration from the engine on tickover that is worst. I'm sure when up to speed it is much better but I feel I need to look at what I can do to help reduce vibes.

Cheers.

Hey.

First thing to check is if the cooling fan is out fo balance, if it is then this will be a source of high frequency vibration and an electroncis killer. It's a tedious task balancing cooling fans, but it pays off in the end with a smoother model.
If you can you are best to balance the whole fan hub/fan/clutch assembly as one and assemble in the same way back on the model once done.

Using a dial indicator you can check for any runout of the clutch/fan once fitted to the engine also, sometimes rotating the whoel assembly on the engines crank shaft can help reduce the amount the fan etc moves off from the centre line while rotating. The more the runout, the worse teh vibration will be generated as this is similar to running out of balance blades but at much higher rpms.

With the 3GX, instead of two mounting pads, perhaps a pad~metal plate~thin pad will be better. The metal plate helping to dampen any vibrations transmitted from the airfame to the gyros.
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[chadvandonkey]

Hi mate,

How do you balance out the clutch & fan assembly? I presume it's a tool I can buy? The vibrations do seem much worse since I have just rebuilt the engine and had the clutch and fan off. I've already promised myself a Lynx metal fan the next time the engine comes out so maybe now I need to get it swapped over. I did think the plastic fan did flex a little when you tighten the 4 fasteners which must put it out of true.

As soon as I know what I need I'll get it stripped and rebuilt. This will obviously help with my 3GX and the tail creep too. As you said with the metal sandwiched by a sticky pad - the only one I've seen in the one for the normal square gyro - presumably you use the gyro mount kit and just stick the 3gx on the top?

Cheers for the help Ian.

[coolice]

Hi mate,

How do you balance out the clutch & fan assembly? I presume it's a tool I can buy? The vibrations do seem much worse since I have just rebuilt the engine and had the clutch and fan off. I've already promised myself a Lynx metal fan the next time the engine comes out so maybe now I need to get it swapped over. I did think the plastic fan did flex a little when you tighten the 4 fasteners which must put it out of true.

As soon as I know what I need I'll get it stripped and rebuilt. This will obviously help with my 3GX and the tail creep too. As you said with the metal sandwiched by a sticky pad - the only one I've seen in the one for the normal square gyro - presumably you use the gyro mount kit and just stick the 3gx on the top?

Cheers for the help Ian.

Hey.

Ideally you need a HiPoint Balancer, like this;



A Dubro Tru-Spin Prop Balancer.

UK shops will have it, but I just did a quick Google for the visual.
With this unit you can have the whole fan/hub/clutch assembly on the supplied shaft, which you then rotate and wait until it stops. At the low (or high, up to you) mark the fan using a fien line marker for instance and spin the assembly again. If it repeatedly stops with the mark in the same place you know the bottom point of the fan is the heaviest and needs to be lightened, either by drilling a shallow dimple or using a dremmel to shave some plastic/metal off the fan. Then spin the assembly again, wait for it to stop and adjust as necassary.
It's a tedious process and can be frustrating, I've done it on previous models back for the F3C which dictated the fan and start shaft had to be balanced and dial indicated to less then 3 thou runout. Needless to say I spent ages doing it in the workshop on many occasions, both swearing and singing to the radio along the way!

I'm not sure if your metal fan will come balanced or not, some do. However unlike the plastic fan it may be better balanced out of the packet, due to it being machined rather than moulded and also less flexible as a result. Another problem area, although from memory the 700N fan is actually quite small and efficient.

Yeah a metal plate for the 3GX is a difficult one, ideally it needs to be slightly larger in dimension size compared to the 3GX's foot print, but there is no metal plate on the market currently. You could use two, or one & a half to make one suitable for the 3GX.
On my old 700N with the 3G, straight away I used a metal plate method to isolate as many vibes as possible from the sensors.

Keep me posted and as always glad to offer any advice I can, which you are very welcome for.
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