|
|
You wouldn't have any noticeable vibrations if the prop is balanced correctly but that doesn't necessarily mean that there are no problems. My understanding is that engine/prop combinations are tested on specific airframes and the results may not apply to other setups.
My Chipmunk was the prototype for a TCM IO-360 engine conversion STC in the sixties. Part of that is a custom Hartzell prop. I was able to get a copy of the test results and it turns out there's a limitation that centers on 2500 RPM due to harmonics that could stress the blades over time. The prop itself runs very smooth- when I had it dynamically balanced it required almost nothing for weights.
OTOH my Navion has an STC'd engine conversion that uses a Bonanza FWF IO-550 and McCauley prop. I doubt it was tested in the same manner- probably they just put it on and made sure it didn't tear the airplane apart. There is a recent AD on the prop restricting MP/RPM combinations but that's for all installations not just mine. Go figure.
Hope this helps but now you're probably as confused as I am- Bill Wade
----- Original Message ----- From: <mmcmanus@grandecom.net>
To: <lml@lancaironline.net>
Sent: Saturday, November 15, 2008 7:36 AM
Subject: [LML] Prop Length for 360
I'm in the middle of getting my Hartzell 2 blade prop overhauled for my Lancair
360. I got a new hub at 50% discount from Hartzell to eliminate the recurring
eddy current inspection. The prop shop doing the overhaul has issues with the
blades and they will not issue the formal 8131 (I think) paperwork for the
overhaul. The problem is the blade length.
I bought the airplane 3 years ago and it had an overhauled "0" time prop when
the airplane was built in 2002. The blades are 70" long according to the prop
shop. They also say that the Hartzell recommends a 72" blade. But Hartzell
also allows a 68" blade for the Lyc 360. They do not however, recommend a 70"
blade.
The question is, since I've had no problems or vibration issues with my 70"
blades - should I be concerned? I guess Hartzell's recommendation is based on
some harmonic resonance or some other vibration related things (which are
outside my knowledge). Does my 70" blade length provide cruise or climb
capabilities that are greater or lesser than a 68" prop.
I'm planning to have the 70" blades reinstalled on the new hub, and the log
entry will just say the standard overhaul stuff (except the IAW stuff), and it
will specify "experimental A/C usage only."
Any thoughts?
Thanks,
Matt McManus
lnc2 360
408 hours total time airplane.
--
For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html
|
|