Don't know why

[Ramflames]

Yesterday, I got my Trex 450 off the ground for the second time. I got it up about five feet, hovered and gently landed. I took it up again, Hovered and landed. Third attempt, there is now a nasty vibration, upon inspection, the main shaft is bent and a push rod between the swash plate and one of the blade grips is bent. Totally confused to why this happen. It is an Align main shaft, so it is not some cheap knock off. There was not an impact or crash prior to this happening with this main shaft installed. The bearings seem to be fine. I did get this heli second hand. I have had it up before and I crashed it. This main shaft was replaced after the last crash with one that I had. There is no visual damage to the frame and the main shaft bearing supports.

[bazsound]

450 mainshafts are pretty thick i cant see it noticably bending unless you crash.

[macdad]

Sounds weird to me... I have never had a main shaft bend on its own. Is it possible that the main shaft was bent when you purchased it? Perhaps it was made from a batch of soft steel. Just guessing.

What headspeed are you running?

[Ramflames]

I'm very new to this. It happened at my local flying club field during Heli Flight School, under the supervision of an experienced plot/instructor. I just replaced the main shaft from a previous crash. The shaft I used came with the heli with a bunch of parts. Head speed? no Idea. It started to vibrate on the ground. I suppose it is possible that the shaft I used, was used and weakened from a crash before I became the owner of this heli.

[Thoemse]

You wrote that you just replaced the main shaft from a previous crash.

My guess is that you overlooked additional damage. Did you replace the bearings? Are the bearing blocks tight? If the bearings are shot bad enough that the shaft can move back and forth it is possible that it got into a very bad vibrating state that ended up bending it.
I had a tail shaft bend because of tail vibrations allready.

[Ramflames]

Originally Posted by Thoemse

You wrote that you just replaced the main shaft from a previous crash.

My guess is that you overlooked additional damage. Did you replace the bearings? Are the bearing blocks tight? If the bearings are shot bad enough that the shaft can move back and forth it is possible that it got into a very bad vibrating state that ended up bending it.
I had a tail shaft bend because of tail vibrations allready.

What your saying makes sense. I have not torn it down yet. I will look in to it.

[learnedthehardway]

Also if the spare main shaft that came with the heli wasn't in a sealed package then there's a good chance it was bent already.

[bazsound]

take a close look at shafts that are not in a package you opened you can usually tell if they are used or not, there will be marks where the head and main gear are.

Unsused shafts look, well super smooth and clean.

Also like said about bearings, check them in crashes like this, the bearings usually take a hit even in crashes that dont noticably bend the mainshaft.

[Ramflames]

Well, my new shafts arrived. I torn down the heli. I did find the two shaft bearings were clunky. So, I replaced the bearings and the shaft. Re-leveled the swash plate. Checked main blade pitch and blade tracking. Now I just have to wait on the weather.

[bazsound]

Originally Posted by Ramflames

Well, my new shafts arrived. I torn down the heli. I did find the two shaft bearings were clunky. So, I replaced the bearings and the shaft. Re-leveled the swash plate. Checked main blade pitch and blade tracking. Now I just have to wait on the weather.

that was one of the things that frustrated me in the beginning was replacing bent shafts and then to find bearings notchy so having to order new parts.

Now i check before ordering parts. the mainshafts bearings uslly get notchy in a good crash. they will cause less noticably vibrations but a bent mainshaft will definatly cause the heli to shake badly.

[Ramflames]

Originally Posted by bazsound

that was one of the things that frustrated me in the beginning was replacing bent shafts and then to find bearings notchy so having to order new parts.

Now i check before ordering parts. the mainshafts bearings uslly get notchy in a good crash. they will cause less noticably vibrations but a bent mainshaft will definatly cause the heli to shake badly.

What I want to know is, did the bearings go bad, causing a vibration that lead to the main shaft bending or, did the main shaft bending, causing a vibration, then causing damage to the bearings?

I want to believe that the bearings failed first from a prior crash. This would explain why the main shaft bent with out a crash since the main shaft was replaced after the last crash, but the bearings were not replaced at that time. The bearings did not make any strange noises after the crash and before the main shaft bent.

[bad007]

Originally Posted by Ramflames

I want to believe that the bearings failed first from a prior crash. This would explain why the main shaft bent with out a crash since the main shaft was replaced after the last crash, but the bearings were not replaced at that time. The bearings did not make any strange noises after the crash and before the main shaft bent.

Bearings always need replaced after a crash, you can't have a blade strike, bend shafts and expect the bearings to be any good after that. They will feel notchey if you check each on individually with a shaft. If you go in a 450 motor bearing can get rough and bend the shaft. My 450 got a new motor shaft and bearings every time I put it in.

[Ramflames]

Last night I got my Heli off the ground and flew it 3 times with no issues.

Woke up this morning excited to get out with her again today, only to be let down by heavy winds,

[learnedthehardway]

Originally Posted by bad007

Bearings always need replaced after a crash, you can't have a blade strike, bend shafts and expect the bearings to be any good after that. They will feel notchey if you check each on individually with a shaft. If you go in a 450 motor bearing can get rough and bend the shaft. My 450 got a new motor shaft and bearings every time I put it in.

Depends on the model. My Oxy3 would eat main shaft bearings on a tip over but the main shaft bearings in one of my Mini Protos have 4 hard crashes on them that I know of and are still smooth as silk going on 500 flights since the last rebuild.

Could be more than 4 crashes since I bought it used

[learnedthehardway]

Originally Posted by Ramflames

Last night I got my Heli off the ground and flew it 3 times with no issues.

Woke up this morning excited to get out with her again today, only to be let down by heavy winds,

I feel your pain, ridiculously windy here as well and will be for the next few days until it starts raining this weekend. Mother Nature's a cruel bitch..lol

[bad007]

Originally Posted by learnedthehardway

Depends on the model. My Oxy3 would eat main shaft bearings on a tip over but the main shaft bearings in one of my Mini Protos have 4 hard crashes on them that I know of and are still smooth as silk going on 500 flights since the last rebuild.

Could be more than 4 crashes since I bought it used

LOL, wrong forum for a OXY, . This is a REX 450 forum. My Gobs don't either.