Trex 450 Pro 3GX vibrations solution?

[Ranger89]

Hey guys,

I have a 450 3GX that probably has about 15 flights. I've crashed it once and fully repaired it. However, it has a vibration at around 70-75 % throttle that has me very worried. Can anybody help? I dont know where to start looking for the source and eliminate it. What is the best and most thorough method to go through part by part? What are some frequent causes or maybe the first things that I should look at before taking the machine apart??

Thank you very much everybody!


David

[wanderer56]

Main shaft, feathering shaft, tail rotor shaft, bent head block, blades split/cracked, bent tail blade grip hub are the most common damage from crashes.

Exactly what parts were replaced?

Just start by taking off the main blades and disconnecting the tail control rod or remove the tail blades also so it doesn't go sideways on you. Spool it up and see if it still vibrates. If it does, start taking more parts off like the the tail rotor assy. Then disconnect belt/TT, etc until it stops vibrating. Then you will have found the culprit.

[Ranger89]

Thanks!! I replaced all the blades, the boom and torque tube, the main shaft, all the links, the maingear, the auto gear, the skids, thats pretty much it.

I have started taking it apart and i replaced the main shaft again, however i did find that my thrust bearings were gritty, might that add to the vibrations?? I think that might have caused the sloppy flight characteristics so im waiing for new thrust bearings, as well as a new spindle.

Going down to the blades, I checked them out and they were pretty much balanced, their CG was off by 3 millimeters.

Other than that, I also put the head back on and spooled her up. She still vibrates a little bit, but less than before.

I feel a vibration coming from the TT when I touch the tail with no blades. Might the TT be bent? Might the bearing be causing vibration at different frequencies??

Anything further I can do to really eliminate vibrations?


David

[Ranger89]

Hey guys, I am a real noob at this, and this is the thread im going to use to ask you all my Trex 450 related questions, thank you for your help!!!

I am really frustrated with my thrust bearings, they are NEW and they have been gritty out of the box. I have greased them over and over again, and when I tighten up the spindle bolts the main grips are pretty gritty, and I know they should be 100% smooth!! What shouldI do?? Why would both sides be like this out of the box?? Should i get new ones or is there a way that I dont know about to get them silky smooth???

[jclifford]

did you measure them to get the proper installation sequence? I just installed them on a 450, as I remember the inner bearing was 0.20 mm larger than the outer.
as far as the vibrations go. Is your head speed high enough? blades too tight?

[wanderer56]

Check your tail rotor shaft also. It will get bent in a crash also. Try a low speed spool up with the main and tail blades removed. If it still vibrates, remove the tail rotor hub and do the spool up. It's going to basically be the process of elimination.

Closely inspect the front and rear umbrella gears for a missing tooth.

If the spindle got bent, which it often will in a crash, that would cause a gritty feeling in your main blade grips. Roll it on a flat service and look for daylight at the bottom of the shaft. Also doulble check your assembly sequence. As mentioned above, the thrust bearing races have an inner and outer race. If those were assembled incorrectly, you could get some binding or gritty feeling in the main blade grips.

Since you didn't list replacing the spindle, I'd look there first. I've hardley ever heard of a crash and not getting a bent spindle.

[Ranger89]

I will replace the spindlemand check the tail shaft and get back with my results!! Thankyou!