Shuddering Vibration In A 407?

[Jet B]

I just want to pick the brain of some of you guys with alot of 407 experience.

 

Myself and the other guys at this company are fairly new to the 407 and we are moving drills with it.

 

Two very odd things it does intermittently are:

 

1. A fairly strong vertical hop comes in the hover sometimes. The machine was tracked in very cold weather and the hop is only noticeable when the weather warms up. Is it typical for this rotor system to get so rough with a 30 degree outside temperature change?

 

2. Every once in a while the machine will set into a quite noisy shuddering vibration in the hover. It's hard to describe it, but you don't feel it in any of the controls, just through the fuselage. This vibration goes away if you reduce power a bunch or if you get airspeed.

 

We are doing everything we can to try and track down the cause of these two problems and thinking maybe it's being caused by the tranny mounting system? Our engineer is crawling all over the thing and can't find anything wrong and he is calling Bell tomorrow to talk to them about it. I just know alot of you guys have been working 407's a long time and figured it was worth a shot to see if anyone recognizes the symptoms.

 

Any insight would be greatly appreciatd, thanks.

[Wiggins]

QUOTE (Jet B @ Mar 15 2008, 09:50 PM) <{POST_SNAPBACK}>

I just want to pick the brain of some of you guys with alot of 407 experience.

 

Myself and the other guys at this company are fairly new to the 407 and we are moving drills with it.

 

Two very odd things it does intermittently are:

 

1. A fairly strong vertical hop comes in the hover sometimes. The machine was tracked in very cold weather and the hop is only noticeable when the weather warms up. Is it typical for this rotor system to get so rough with a 30 degree outside temperature change?

 

2. Every once in a while the machine will set into a quite noisy shuddering vibration in the hover. It's hard to describe it, but you don't feel it in any of the controls, just through the fuselage. This vibration goes away if you reduce power a bunch or if you get airspeed.

 

We are doing everything we can to try and track down the cause of these two problems and thinking maybe it's being caused by the tranny mounting system? Our engineer is crawling all over the thing and can't find anything wrong and he is calling Bell tomorrow to talk to them about it. I just know alot of you guys have been working 407's a long time and figured it was worth a shot to see if anyone recognizes the symptoms.

 

Any insight would be greatly appreciatd, thanks.

 

Cut and paste what you have written and send it to pselight@bellhelicopter.textron.com

 

They will give you an answer.

[3BX2]

The elastomerics are temperature sensitive.

 

The shuddering may be finlet vibration, I have seen that. check to make sure that the correct weights are installed on the finlets. There is a small balance weight on each.

[Jet B]

Thanks for the advice, I will pass that on to the engineer.

[Jet B]

I also sent the whole message to that Bell address you gave me. Thanks.

[Trigger]

Do you have the FRAHM installed or not? If not that could be part of the problem as well.

[Skidbiter]

QUOTE (Jet B @ Mar 15 2008, 09:50 PM) <{POST_SNAPBACK}>

I just want to pick the brain of some of you guys with alot of 407 experience.

 

Myself and the other guys at this company are fairly new to the 407 and we are moving drills with it.

 

Two very odd things it does intermittently are:

 

1. A fairly strong vertical hop comes in the hover sometimes. The machine was tracked in very cold weather and the hop is only noticeable when the weather warms up. Is it typical for this rotor system to get so rough with a 30 degree outside temperature change?

 

2. Every once in a while the machine will set into a quite noisy shuddering vibration in the hover. It's hard to describe it, but you don't feel it in any of the controls, just through the fuselage. This vibration goes away if you reduce power a bunch or if you get airspeed.

 

We are doing everything we can to try and track down the cause of these two problems and thinking maybe it's being caused by the tranny mounting system? Our engineer is crawling all over the thing and can't find anything wrong and he is calling Bell tomorrow to talk to them about it. I just know alot of you guys have been working 407's a long time and figured it was worth a shot to see if anyone recognizes the symptoms.

 

Any insight would be greatly appreciatd, thanks.

 

 

 

#1 One that I flew did the same thing, they found the (not sure of the proper name for them) 4 elastomer mounts on the tranny to be stuffed, or at least a couple were bad, they had to suspend the thing by its head and found they were had it.....could be worth checking.

 

 

#2 Had a bad high freq vibe and noise associated with it in another one about a month ago, sounds similar to what you have, felt like the speed of the T/R drive shaft, it would also only happen in a hover and not all the time, I got the engineer to check the T/R drive shaft bearings, as to me thats all i could think of, one bearing you could shake a little, and get it to make a little noise, like it was dry or something, anyway, it went back to the hanger and they changed that bearing.

Unfortunately I haven't flown that one again, but by the sounds of it, talking to the other pilots, it hasn't come back since....so once again, may be worth a look at them?

 

Hope this helps?

[DGP]

you could be having cone shift up inside the mast...had this happen once..gets really rough and then if you pull in some pitch it will usually smooth out for a while...only way ot tell is to pull the head off and check the cones...vibration is VERY bad if this is happening...not just a...hey what is that...its more like...WHAT THE H%#L IS THAT...kind of shake.When it first happened to me I landed the machine...looked all over the head...could see nothing loose or broken...went flying...ship was perfectly smooth....in about 5 minutes it came back...said sorry to my passengers...took them home...flew home very slowly and got that thing on the ground...they scraped the cone set..they being the bell service rep...new set of cones...proper torque on mast nut and the NEW tool for installing the head...hasn't happened again... :shock:

[DGP]

I should also add that there are 3 cone sets on the 407 head...the one that was loose was the middle set...the one you lockwire to the mast before you lower the head onto the mast...I also have seen the lower set loose their torque...this will also cause a vibration to occur at various stages of flight...you can do a quick check on the lower set but they are usually covered with proseal which will have to be removed first and if you are outside in the cold this will be a real pain in the butt....joy...pottsy

[Jet B]

Some more great advice guys, thanks.

 

I will pass some of these ideas to our engineer.

 

We were wondering if the vertical hopping was maybe tranny mounts, since it feels alot like a jetbox with a worn out isolation mount when it starts to hump you.

 

The other higher speed vibration does feel like tailrotor drive shaft speed, and I know he is checking out the hanger bearings. Also I will pass on to check the finlets. I know he was going to go over the head carefully as well, to make sure there wasn't any mast cracking.

 

I havn't been with this company long, and they are fairly new to the 407 as well. It's a learning process for everyone. LOL

 

Thanks again!