----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----
At 10:36 AM 9/28/2004 -0500, McClure, Rich wrote: >I have a CM7150 prop which is approved for both. Actually, just to be a nit picker: What is approved is a prop type, length and static RPM. In this case, both engines can use the same type (1A90CF or 1B90CM) and length. It gets a little dicey with length as the C75 requires no less than 71" ( and no more than 73")while the C85 requires no more than 71" (and no less than 69.5"). These length requirements are for vibration considerations. The only way your prop could be approved for both is if it is exactly 71". (This is actual length, not manufactured length. It's perfectly OK to take a 1A90CF74XX and cut it down to 71 inches and mount it on a C85. First time you land in the tall grass it's no longer suitable for the C75, though... Lastly we have the static RPM requirement. this is where pitch comes in, and noter that pitch is not specified anywhere. The C85 has a static RPM requirement of not over 2225 and not under 2025. The C75 requires not over 2100 and not under 1900. Your prop must have a pitch and length combination that meets the length restrictions and results in a static RPM reading that falls in this range. A prop at the bottom of the length range will require more pitch to make the same RPM, and vice-versa. That said, a prop that is exactly 71 inches long with a pitch of 50 may or may not meet all the requirements. If it does, it's going to be a climb prop if you have aC75 and a cruise prop if you have a C85. And stay out of the tall grass... ;~) John Cooper Skyport Services PO Box 249 4996 Delaware Tnpk Rensselaerville, NY 12147 518 797-3064 ========================================================================== ==== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers-tech/
<<attachment: winmail.dat>>
