3 Per Rev Vibration in Helicopter Rotor System
3 Per Rev Vibration in Helicopter Rotor System
(OP)
Hello Everyone,
Needing some help/ideas on locating abnormal vibration in Hughes 269 rotor system. Have been dealing with the "experts" in the industry, but absolutely no success in correcting this. I have a lot of vibration data logged with a MicrovibeII analyzer that can be emailed if necessary. If anyone has an interest in assisting me with this, your effort would be greatly appreciated. Thanks in advance.
Jerry
Needing some help/ideas on locating abnormal vibration in Hughes 269 rotor system. Have been dealing with the "experts" in the industry, but absolutely no success in correcting this. I have a lot of vibration data logged with a MicrovibeII analyzer that can be emailed if necessary. If anyone has an interest in assisting me with this, your effort would be greatly appreciated. Thanks in advance.
Jerry





RE: 3 Per Rev Vibration in Helicopter Rotor System
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: 3 Per Rev Vibration in Helicopter Rotor System
Thanks for the reply. This vibration is "new" and not normal. It registers as high as 1.5ips (inches per second)in the cabin at about 1350 cpm. The blades turn at approximately 450rpm. The rotor system itself registers about .07ips vertical and around .14 lateral. Anything under .2 is within spec. This vibration until recently would "come and go", but is now present about 99% of the time. I've taken spectrum analysis readings in many various locations/situations. Pretty much anything and everything that would be "typical" according to 269 mechanics has been checked, tried, or replaced. No luck.
Jerry
RE: 3 Per Rev Vibration in Helicopter Rotor System
The blades turn at approximately 450rpm
The use of the words 'about' and 'approximately' suggests that you cannot be entirely sure the the problem vibration is 3X rotor turning speed - you need to confirm this before going off on tangents. There is a world of difference in trying to figure out a problem vibration that is exactly 3X turning speed and one that is close to, but not exactly 3X running speed.
Is the problem '3X' vibration present at all rotor speeds or just at 450rpm? Whereabouts are you measuring the problem vibration - is it at all measurement locations or just specific points in the cabin - is it possible that you are seeing a structural resonance local to your measurement points (e.g. panel) that is casing this grief?
RE: 3 Per Rev Vibration in Helicopter Rotor System
The operational rpm of the enging during flight is 2700-2900 rpm, which varies the rotor rpm proportionately. Unfortunately the analysis equipment is not 100% accurate at the lower frequencies (rotor), so I've used 'about'. I have several pdf plots with notes (location of sensor, hovering, forward flight, etc.), if you have an interest in looking at them.
Jerry
RE: 3 Per Rev Vibration in Helicopter Rotor System
RE: 3 Per Rev Vibration in Helicopter Rotor System
RE: 3 Per Rev Vibration in Helicopter Rotor System
As a starting point, look at the plot labelled 'Cooling Fan Sensor on Top of Engine' - the peak at 1373cpm is followed by many low amplitude multiples, with the 4th multiple being quite high - I'd be looking for a) a worn bushing or b) a damaged rolling element bearing.
For b) I would want to see acceleration data out to at least 5kHz
RE: 3 Per Rev Vibration in Helicopter Rotor System
Jerry
http://www.airfliteok.com/parts.asp
RE: 3 Per Rev Vibration in Helicopter Rotor System
On thing did strike me - what is the speed ratio between the main rotor and the tail rotor drive?
RE: 3 Per Rev Vibration in Helicopter Rotor System
RE: 3 Per Rev Vibration in Helicopter Rotor System
Jerry
RE: 3 Per Rev Vibration in Helicopter Rotor System
Where are you? Perhaps there is someone on this forum that is closer than you think. It is a very international group.
RE: 3 Per Rev Vibration in Helicopter Rotor System
RE: 3 Per Rev Vibration in Helicopter Rotor System
I'm in Tulsa, OK.
RE: 3 Per Rev Vibration in Helicopter Rotor System
RE: 3 Per Rev Vibration in Helicopter Rotor System
This sounds like a problem that is getting worse with time -if a fatality results, how are you going to defend yourself?
Despite your efforts, I think you would be culpable. You knew there was a problem; the problem got worse with time, you were unable to solve the problem; you allowed the aircraft to continue flying: someone got hurt. You will be in the firing line
RE: 3 Per Rev Vibration in Helicopter Rotor System
RE: 3 Per Rev Vibration in Helicopter Rotor System
RE: 3 Per Rev Vibration in Helicopter Rotor System
There are "true" engineers available to you locally. You could try DRD technology. They are located at approximately 51st and Lewis on the West side of the road. That is just one off the top of my head.
You could also contact some of the engineering professors at Oklahoma State University in Stillwater, which is only 1 hour away. They regularly consult with people in industry. Try contacting the Mechanical and Aerospace Engineering (MAE) school.
Tulsa University (TU) has an engineering school you could contact them. You could also do a search for PEs in Tulsa that work for consulting firms on the Oklahoma State Board of Engineering website http://www.ok.gov/pels/
You could even google for consulting engineers in Tulsa.
Help is closer than you think.
Steve
RE: 3 Per Rev Vibration in Helicopter Rotor System
Thank you for the suggestions. I really didn't know where to start searching as this is an unusual situation. I'll give them a try. I assume your local since you know the area?
Jerry
RE: 3 Per Rev Vibration in Helicopter Rotor System
RE: 3 Per Rev Vibration in Helicopter Rotor System
Just wanted to thank you again. I contacted a Professor at TU that is going to help me out.
Jerry
RE: 3 Per Rev Vibration in Helicopter Rotor System
Let us all know what the ultimate problem and solution ends up being.
Good luck,
Steve