450 Oscillation forward and back

[Sesame]

My 450 has developed a wobble.

ok I know where it comes from I had a bit of a crash in the week ive repaired all the bits I thought were bent broken or generally worn out but since reflying it it has a definate and constant fore and aft rock. A little like what you get with a rail when you have your gain set too high only in the other plain.

simple question really, I thought I had repaired it all obviously not, anyone any ideas of where I may start looking for the cure to the problem.

Parts replaced were

blades
main shaft
feathering spindle
flybar
baseplate
canopy
skids


I was told that I should also replace the tail rotor shaft as this could be out, however, would this cause this type of problem, I would have thought it more a cyclic problem.

it is very constant from takeoff to landing faster at higher revs

think thats all the info I can give

cheers

[Stuart]

They may seem to be okay, I did have an elevator oscillation on my vibe once after I checked everything and found no faults I eventually changed the servo and bingo it was fixed.

[Raptorite]

It could well be the tail output shaft or maybe the tail hub as these are easily bent in a crash and are not always noticable as being bent.

Cheers,
Pete.

[moyesboy]

I heard that the fore/aft oscillation can come from blades either too tight or too loose in the grips. Can't remember which though...

[Sesame]

I have changed blades because I didnt think the align ones that were on it would work too well with tape holding them together

ive put radix blades on it, I dont suppose they could be causing the prob. ive not got any other blades at the mo to try, but in the meantime I think the bearings in the blade holders are on their way out so im going to replace those, plus i'll also replace the tail shaft to see if it makes a difference.

all help appreciated guys

[Sesame]

Problem solved, I put another feather spindle in as I was having problems with the bearings over the origional replacement.

plus I replaced all the bearings in the blade holders which smoothed them up. flew it this morning for a few minutes and it was rock solid again. well until the next crash.

ive also invested in a 2.4gig transmitter etc. so hopefully any interference if that was what it was will be a thing of the past.(we'll see). gonna put that in tonight and see what happens.

[Sesame]

Ok so problem not as solved as I first thought.

Once I had finished changing parts I had a quick hover in the back garden and it all seamed ok. However once in an open field like this weekend its still got the ocillation, which is really annoying.

Ive changed

Main Shaft
Feather Shaft
Tail Rotor Shaft
Flybar
Blade Holder Bearings
blades

Ive made sure the blades are balanced and the measurments are correct for the padles on the flybar.

if anyone has any ideas of other things I could check I would appreciate it, when flying right its a lovely little bird like this its the most annoying little so n so going.

[Nutz]

How tiight are your blades and what head speed have you got?

[Sesame]

its happening at all head speeds, seams to be quite constant just faster as the headspeed increases.

The Blades at the mo they are tight enough that they hold position tipped onto the side but if you tap the head a little they start to move down under their own weight.

[Nutz]

How about the head dampers, have you tried replacing them?

[robgt]

Have you checked the tail rotor hub?
Cheers,
Rob

[Sesame]

Nope, thats one thing ive not done as yet.

One thing that has changed. However because I didnt put it together when I took out the feathering spindle I found out it was about 5mm longer than the standard one I replaced it with, the guy who had it before me had packed it out with spacers.

the spindle through the head is very tight, could this cause this style of problem.

[robgt]

It shouldn't - but it's possible I guess. As long as the blade grips can turn freely on the spindle, then there should not be a problem there. (Detach the blade grip double links and they should move very freely).

Cheers,
Rob

[Sesame]

Sorry thought I had answered that one previously but I havn't have I.

Nope thats one thing ive not replaced as yet, the dampers, but also not entirely sure which parts they are, is it the rubber inside the head?


The blade holders turned very badly after the crash but now ive changed the bearings they are ok.

[Nutz]

You should have 2 rubber orings (dampers) inside the head (on each side), then a alu spacer, then the blade grip.

It there is anything makng one side push out more than the other it will give you an out of balance head and wobbles.