I zoomed in on two hi res pics taken with same camera as part of a Legacy formation photo shoot – check out the spinners - VH–XTZ (slight port wing tip vibration), and VH-ZYA (no vibration). You'll see that the XTZ's spinner tip appears to be moving laterally; whereas that of ZYA indicates nil lateral movement. In both cases, you can see the front of the cowling adjacent the spinners – theses do not appear to be moving.
This does not of course indicate what's causing the vibration… but nevertheless, it may trigger some ideas or thoughts? Any views?
As it happens, I have a spare spinner / backplate assy. I guess an easy thing to do is to change just the spinner, and then go flying with iPhone vibration app, and see if I can detect any visual changes (wing tip movement) or whether the vibration amplitude/frequency signature changes from prior. If no change, may be I'll change the back plate over….
Colyn – the data base you are collecting… Would it be worth asking everyone to advise what engine mount isolators they are using? For what its worth I am using the stock standard Lancair supply isolators.
BTW – the pics I tried to post of my vibration amplitude / frequency plots captured on an iPhone didn't come up on my post. Trying to find out why…
Regards,
John
John N G Smith
Tel / fax: +61-8-9385-8891
Mobile: +61-409-372-975
Email: john@jjts.net.au
Good info Paul. I am a little chagrined to find that, after loading "Vibration" on my iPhone and going out to collect data, things were a bunch smoother than I recalled. The only thing I changed was new spark plugs. But I think it's clear that the vibration in my Legacy/IO550 is much less than what I hear Bob and Steve describe.
Kyrilian, would you care to examine vibration data from a test ride? I have about 8 files of 15sec X 100Hz data taken with the iPhone secured to the instrument panel and I don't know what to make of it.
Charley
On Jul 29, 2013, at 10:23 AM, Paul Miller wrote:
One thing to keep in mind is that the prop balancing on the ground is not as accurate as when the scimitar is loaded in flight. This comes directly from one of the SX300 guys testing one of the Scimitars for Hartzell on his Lyc 580. What he did was run the cables through the heat duct and perform the balance in flight conditions. He reported that balancing the scimitars was not easy. I had a hard time finding a good balance on the ground on the Legacy but it was passable. I may try the in-flight balance next time at the 2300 rpm mark. Our Legacy scimitars are simply cut shorter than the longer bladed scimitars for ground clearance.
Second, the engine and cowl moves a lot and the clearances are very tight in the Legacy. At 2700 RPM and low airspeed the cowl is different shape than at cruise and the engine is in a different position relative to the mounts that at 2300. The torque on the engine mounts is much different at 2300 versus 2700. I found a lot of interference showed up as the RPM came down from 2700 to 2300 and then the engine and cowling were slightly separated so that the banging was transmitted. I believe at other settings the engine was up against parts of the cowl and the actual vibration was transmitted. I had the nose gear interference as well plus the baffling hit the prop governor cable in cruise. Lots of areas where interference fits are really tight. My point is that there are many factors that can affect vibration with changing throttle and RPM and it isn't just the prop/crankshaft combo that can be at issue. I was seeing almost two inches of cowl movement between rest and flight at certain locations. Thats a lot.
Not to take anything away from the issue under discussion except to say that, in my Legacy, vibration amplitude did change with varying RPM as a result of mechanical interference.
Paul
Legacy