The International Cessna^® 170 Association

You guys running 80" props how much speed do you lose?
How much shorter takeoff do you get?
I tested my stock 170 B on a 80 degree day at 315 MSL with one notch of flaps ,200lbd pilotand full of fuel . took 550 ft did three takeoffs and were the same. My prop is 1a170 dm 7651.
Next I have to see what it will do at gross weigth.

Can someone tell me if the RPM ranges are right for this prop?
takeoff run 2250 climb 2350 level full throttle 2525

Seems low for RPM. I'm running a DM7654 and at nearly sea level that your an can get 2650 or nearly so (backed by electronic tack) at level flight. You should be able to get 2700 I'd think. Your 2250 seems a bit low as well. I'd suspect your tach is not accurate.

I've got an 8041 prop on mine, and 8.50/6's. It only cruises about 105 mph indicated on these cold days.(45-55F and 2450 rpm). But it sure gets off the ground here at sea level. I'm flying off of gravel so I cant do a static takeoff but at about 1900lbs, it takes less than 500 ft. to get airborne with 20 degrees of flaps. Static RPM is 2400 (unverified). Bottom line, you will like the takeoff and climb performance. The cruise leaves a little to be desired.

I thought that my rpm was low on that prop, my tach is verified with a prop tach. Know to find where my rpm are going any ideas?

varr wrote:I thought that my rpm was low on that prop, my tach is verified with a prop tach. Know to find where my rpm are going any ideas?

I have a 7651 prop, static I get - ahem - exactly 2350 rpm Actually I might get just a wee bit more than that, but not much

Got 20 more horses than you so takeoff distance won't be comparable.

Have you verified that your prop is in fact pitched to 51? Shops are supposed to stamp it each time they tweak it..."but."

I've got a 8043 prop, at 700' AGL, I get off at about 350'. Thats when I grab 20 notches. I have to be airbourne by 650' because after that I've run outa' strip....

Joe[ toes curling over rudder pedals]

varr,

Your RPM is definitely low at full throttle in level flight. Have you closely checked your ignition timing and mixture? They will both have an effect on max power.

With my 8043 I turn 2700 while climbing at 89 mph. At 2450, I cruise about 105-108 mph. I think I could bury the tach in cruise if I wanted to!

Joe
4518C

You are far below the 2750 RPM that most any O-300 will show in level flight (almost full throttle at 1000'msl) with a 76" prop no mater what the pitch. I'd suspect the tach not being properly matched or calibrated. Have you done the electronic tach thing? Most of them are fairly accurate.

Like Joe reports, many of the lower pitched props can in fact let the engine go beyond red-line at lower altitudes. Here is another question though - - Say you have a 76-51 and can turn 2350 static. You probably shouldn't expect the same RPM if you have an 80 - 51 on the crank. But is there such an animal as an 80-51?