The International Cessna^® 170 Association

I was wondering what type of prop I have. It has 76/53 stamped on the prop. I have learned a few things about airplanes. More power is better, planes are like drugs, they are addicting and they are expensive. And the worst one of all is the wife gets jealous when you give the plane more attention than the wife. Anyways back to the topic. I have no idea what the ‘76/53’ means. I know the ‘76’ is the length and ‘53’ is the pitch but is it a climb prop or a cruise prop?

I also know the sole purpose of a prop. It is to keep the pilot cool. If the prop stops turning, the pilot will start sweating!!!!!!

Someone with a lot more expertise will no doubt answer you soon, but in case you are eagerly waiting by the computer...

Basically a 7653 is the standard prop that came with the landplane version of all the 170's, and the one that is listed as the primary prop on the type certificate data sheet for the 170 (the McCauley 1A70.) 76 is the diameter, and 53 is the pitch.

So technically, your prop is not what others would term either a climb prop, or a cruise prop. It is the standard prop specified by Cessna to give the best of both worlds. (I know George discussed this in a previous post but I'm too lazy to search for it.)

Most cruise props for the 170 I've seen discussed are 76/55. Most "climb" props have been tweaked to a 51 pitch. Or a 8042 (80 inch diameter) installed under STC or field approval.

What you gain in climb, you lose in cruise, or vice versa. No such thing as a free lunch and all that.

Anyway, read this thread: http://www.cessna170.org/phpBB2/viewtop ... ight=props

And this is the most gawd-awful example of a "everything you ever wanted to know about airplane propellers but still won't understand" page I've seen: http://www.epi-eng.com/Prop-Selection.htm

Apparently the pitch number ("53" as an example on your prop) is: "The pitch angle of a blade (ß) is typically the angle measured at 75% of the radial distance from the center of rotation to the prop tip."

If you are further interested in the details about propellers on the 170, use the search function at the top of the page and type in "prop" or "propeller." I gather they have been discussed here once or twice

BTW I was looking through the 337's for my plane and noticed that my 76 inch prop was re pitched to 56 as part of the Franklin engine conversion in the 60's. I'll be interested in playing with the static and takeoff operating RPM's to see exactly what it does at that pitch, with my horsepower, once I get down there this weekend. I suspect it will be nearly identical RPMs to a 53 pitch on a O-300.

On fixed pitch propelleres, the pitch is given in inches the prop would move forward in one revolution were it in a "solid medium". It is the same as is used on boat propellers.

blueldr wrote:On fixed pitch propelleres, the pitch is given in inches the prop would move forward in one revolution were it in a "solid medium". It is the same as is used on boat propellers.

And it's closer than you might think in air. If multiply 53 inches by 2450 rpm and convert inches per minute to miles per hour you come up with 123 mph.

Miles

Sure wish I could go 123 mph @ 2450 or any other rpm under 2700

blueldr wrote:On fixed pitch propelleres, the pitch is given in inches the prop would move forward in one revolution were it in a "solid medium". It is the same as is used on boat propellers.

I knew that was true with boat propellers, but I wasn't sure about aircraft. See, why the experts should answer