Author Topic: My new Cadet/ prop size request  (Read 63 times)

Culver Dreamer

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My new Cadet/ prop size request
« on: November 26, 2018, 07:33:22 AM »
Hello Guys / Gals

I'm the proud new owner of N20U. I couldn't be happier. It flys very straight! It's gear operates smoothly and the C-85 is the smoothest running Continental engine I have ever operated.
Now it's only issue is it has a Wooden Sensensich W69EK52. The 52 pitch is really for a Continental 75 HP engine. So at the moment I'm climbing at 2000 fpm and redline cruise is 110 mph at 1000 ASL
I'd like more cruise speed and am willing to sacrifice the great climb rate.
What type of prop (wood or metal )and pitch are you guys running on your C-85 engines? And what cruise are you getting?
Regards Mark

Bill Poynter

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Re: My new Cadet/ prop size request
« Reply #1 on: November 26, 2018, 08:38:46 PM »

Hi Mark

My previous Cadet usually indicated 120-125 MPH at around 2300 RPM.  I had overhauled the airspeed indicator, but I'm sure there are a lot of installation variations between different Cadets.  My plane also had a current pitot-static certification.  It was a C85 with a metal McCauley model 1B90 CM7051 prop.  This prop didn't turn up as many RPM's during climb as I thought it would.  I'm sure that a metal prop is going to be more efficient than most conventional wood models.

Culver Dreamer

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Re: My new Cadet/ prop size request
« Reply #2 on: November 26, 2018, 11:20:00 PM »
Thanks for the reply Bill
What kind of climb rate were you getting with that prop?
Also were you at full throttle to get the 2300 rpm/ 125 mph cruise?
Or was 2300 rpm a comfortable number for you? Iím wondering if your prop is
Too course pitched. I see the one recommended on the McCauley
Web site for the C-75 is 1A90/CF7045. Obviously I will need more
Pitch than on that prop Iím just trying to figure out the
Optimal number
Thanks Mark

Bill Poynter

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Re: My new Cadet/ prop size request
« Reply #3 on: November 27, 2018, 12:04:42 PM »
I didn't have a manifold pressure gauge, so I can't say for sure what percentage of power I was using.  It wasn't near full throttle though.  The rate of climb was usually about 700 fpm.

I would check that your static rpm falls within the limits on the Type Certificate:  Propeller limits Static rpm at maximum permissible throttle setting, Not over 2370, not under 2070.  No additional tolerance permitted. Diameter:  Not over 70 in., not under 64 in.

Culver Dreamer

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Re: My new Cadet/ prop size request
« Reply #4 on: November 27, 2018, 01:52:28 PM »
Thanks for the info Bill. I think Iíll be looking for a prop
Like yours. I like your performance numbers.
Mark