The International Cessna^® 170 Association

I’m a newer 170 owner (A model), and ordered a new 8043 prop. I do not have the prop yet, but wanted to check static rpm on my current prop (Sensenich MD74, w/54” climb prop). In the run up area, break on and full throttle, it will go to redline 2700 rpm before I pull the throttle back. This doesn’t sound right to me. Any ideas? I have the C 145-2h with 240 hours SMOH

Something is not right.

Your saying your engine can turn this prop 400 rpm higher than is should be able.

Is the prop between 72" and 74". if it is shorter than 74" some of the rpm is because of this. if it is shorter than 72", it is not legal and it is even more reason for higher rpm.

I don't know where you found this prop in a 54" pitch is a climb prop. Best info I found quickly is 53" would be climb and 56" cruise. So if it is 54" and until we found 170 specific info, 54"would be between climb and standard. This actually makes your result even more out of normal. The most you should be able to achieve if the prop is in the 72-74" diameter range at 54" pitch would be under 2320 if climb prop is 53".

Are you having difficulty keeping the engine with this prop from exceeding red line in the air. You should be if the info you gave us is correct and no errors are found.

Somethings out of wack here. I'd suggest your tach has error, but I'd think you would have noticed something not right if your tack had a 400 rpm error in it. Did you check your tack against a digital tack?

Yes, I agree with Bruce, the FIRST thing to do is verify your tachometer is accurate. Borrow your mechanic’s tach-check (or if unable, contact me and I’ll loan you mine for postage.)

This was the prop that was on it when I bought the plane. The log books show it was installed in 1959 and has been overhauled at least twice, with several repitches.

While airborne I can easily go over redline if I don’t watch my gauge. I’ll get my mechanic to check my tach gauge. At 2450 rpm in cruise I’m only going 80-85 mph IAS

I would be checking what’s stamped on the prop hub for the correct pitch. But after saying that I would have the pitch checked by a prop overhaul shop. The number of incorrect entries in log books and what’s stamped on the prop and incorrect stamping on props is a common issue .

Well since you can easily overspeed in flight, it all sort of makes sense except that you likely have a much flatter pitch prop than 54" And this is why you can red line static which exceeds the rpm limits of the TCDS for that prop at what ever pitch it is on a 170.

Deputydog wrote:I’m a newer 170 owner (A model), and ordered a new 8043 prop. I do not have the prop yet, but wanted to check static rpm on my current prop (Sensenich MD74, w/54” climb prop). In the run up area, break on and full throttle, it will go to redline 2700 rpm before I pull the throttle back. This doesn’t sound right to me. Any ideas? I have the C 145-2h with 240 hours SMOH

This is very interesting to me. I agree with what the others have said. I had an 8043 on my 170A with a O300A my RPMs were at redline on the take off roll and and I had to throttle back in cruise flight. At around 2500 RPM I would cruise around 100 MPH. It sounds to me that someone has re-pitched your prop extremely flat. But I am curious what the diameter of your prop is. Measure it with a tape measure. In that you are only getting 80 to 85 MPH if all your instruments are reading correctly my guess it that you have a very short prop or an very flat pitched 76 inch prop. With my 8043 my climb rate a sea level was nearly 1,000 ft/minute. I'll bet your not getting that. I would hate to see you buy an 8043 if you already had one. But I doubt it.
Jim

Thanks for the reply Jim,

I ordered an 8043 prop, just haven't received it yet. The prop I have is a Sensenich MD74, It was a climb prop originally, the previous owner of my 170 had it repitched to a cruise prop. I took it to AC Propeller in Seattle and had them pitch it back to a climb prop. They didn't measure it or do anything else other than repitch it.

Before I had the prop repitched back, I didn't redline like I do now so its possible its too flat or something. It may just be wore out.

I will measure it next time I'm at my hangar. I'm thinking its just wore out, but I want to make sure I don't have a problem with a gauge as well so I will have those checked.

I have a buddy with a 170 who has a McCauley climb prop, and he can pull away from me as we are cruising somewhere.

gahorn wrote:Yes, I agree with Bruce, the FIRST thing to do is verify your tachometer is accurate. Borrow your mechanic’s tach-check (or if unable, contact me and I’ll loan you mine for postage.)

What George said! I have been using an 8040 for 30 years I fly with a Tach check on the glare shield all the times don't look at the Mech tach they are usually wrong. I overhauled mine twice replaced and lubed the cable they just are not worth a crap.

mit wrote:

gahorn wrote:Yes, I agree with Bruce, the FIRST thing to do is verify your tachometer is accurate. Borrow your mechanic’s tach-check (or if unable, contact me and I’ll loan you mine for postage.)

What George said! I have been using an 8040 for 30 years I fly with a Tach check on the glare shield all the times don't look at the Mech tach they are usually wrong. I overhauled mine twice replaced and lubed the cable they just are not worth a crap.

This one?

https://www.aircraftspruce.com/catalog/ ... rutach.php

Deputydog wrote:

mit wrote:

gahorn wrote:Yes, I agree with Bruce, the FIRST thing to do is verify your tachometer is accurate. Borrow your mechanic’s tach-check (or if unable, contact me and I’ll loan you mine for postage.)

What George said! I have been using an 8040 for 30 years I fly with a Tach check on the glare shield all the times don't look at the Mech tach they are usually wrong. I overhauled mine twice replaced and lubed the cable they just are not worth a crap.

This one?

https://www.aircraftspruce.com/catalog/ ... rutach.php

NO! NOT that one.

This one?

https://www.aircraftspruce.com/catalog/ ... rutach.php[/quote]

NO! NOT that one.[/quote]



This one?

https://slate.secure-host.com/synergyso ... index.html

Thats ( true tach ) the one I use to check my tach, it’s easy to use and I have no complaints with it.

I also use a Tru-Tach. I know they are expensive and overpriced. But they are easy to use and reliable. Plus you can check the calibration with a common fluorescent light. Mine always checks out within 1 rpm of the fluorescent value. For a less expensive option, you might try finding a digital tach for model airplanes. I've never tried one of those, but it might work as long as you can check it's calibration.

Btw, I only use the tach in my panel for flying and pre-flight run-up. I use the digital tach for all maintenance and static checks on my and other aircraft. It's so much easier to use and see than a panel tach for those checks.

Try this one for less than $30. Although not specified for certified aircraft, it looks to be almost identical to one I got from Sporty’s Pilot Shop 15 years ago, which works simply and accurately.

https://www.horizonhobby.com/HAN156?KPI ... gKpg_D_BwE