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John, If I'm reading the FAA PDF file that you referenced correctly, it appears that my prop, a 1B90CM 7351, is ok on 85 hp with a maximum rpm of not above 2600. I did see that the length is limited to 70 inches max with higher rpms. However, Ed said that the C85 upgrade needs a shorter length prop(71 inches max) to spin the engine up to the higher C85 rpms vs the C75 lower numbers. So again, if I'm reading it right, at the moment my prop's happy but the engine might not be. I did call a prop shop to check trimming. Trimming, painting, and balancing would run about $150. I've included the URL to the FAA site in a "tinyurl" format. The one you provided didn't get me there because of its length. Hope the following one works ok. Roger http://tinyurl.com/yqsfm ----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[email protected]> Sent: Wednesday, February 25, 2004 11:22 AM Subject: Re: [COUPERS-TECH] C75 to C85 > ----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]---- > > > I'm no prop expert, either, but generally length restrictions are related to > vibration characteristics. In fact, if you look at the tcds for the McCauley > 1A/B90 prop, you'll see that there are the same length restrictions for the > various engines on which it can be installed. (look here: > http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/ 0/5a5d18d5be78684c85256712 > 006e7721/$FILE/p-842.pdf ) > > So, if you're flying behind a C85 and you're running at C85 RPMs then you > best have a prop that's certified for a C85. > > There are no legal requirements as to pitch. The pitch is indirectly > regulated by the static RPM requirements. Any suitable prop that meets the length > requirement and the static RPM requirement is "acceptable" wrt pitch. > > John > ========================================================================== == == > To leave this forum go to: http://ercoupers.com/lists.htm > Search the archives on http://escribe.com/aviation/coupers-tech/ > > > ========================================================================== ==== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers-tech/
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