PROP Question

[srf471]

On my 85Hp L2M I can't get above 75-80 mph IAS. I can climb excellent, but at cruise (2300 rpm) I'm very slow.

I was checking my prop today and found TWO size markings. On the side of the hub it is stamped CF7148. After removing the spinner, I found another stamp CF 70 1/2-44. Also, it is obvious that the 44 was stamped over a 48, so it appears the the prop was repitched at some point.

How can I tell what the pitch really is and more important, what size prop works best for cruise on this plane? BTW, I live in South Florida and operate out of a 4000' grass strip, so climb is not as important as is cruise.

Thanks in advance

Nick Preble
N58075
N471F

[Rick_Utley]

Re: PROP Question

Sounds like maybe the prop was reworked, the first part of the number is length and the last is its pitch. With the first number being CF7148 and the second being CF70 1/2-44. I'm guessing that if you measure the length it will be 70 1/2. If so the pitch is 44, which falls between Climb(43) & Standard (45). But then, everybody knows more about this that I do.

Other thoughts folks?

[flyguy]

Re: PROP Question

You said indicated airspeed. You might want check it with a gps or however. My experience with 3 BC12D's is that Taylorcraft pitot static systems are way out to lunch on the high end. I'm not familiar with the L2 system. The problem seems to be where the 12D picks off the static pressure (in the wing.)
The plane I have now is about 8 statute optimistic (high) on the top end, and dead on on the bottom.
What the tachometer does in level flight with the throttle to the firewall will go a long way towards confirming what pitch your prop is. Climb props go past redline, cruise props will run below redline, and standard props will just do redline. A standard prop will give you the best top speed and a cruise prop should give you the best cruise speed at a given rpm. I suspect the cruise is getting a few more horsepower at that rpm due at least in part to less pumping losses.(operating closer to WOT.) I have a 7146 and it gives me 97 statute GPS two way at 2300 and will not quite pull redline. But it still gives me 850 ft/min. up to 1500 or so even on a warm day.
Darryl

[Yellow Duck]

Re: PROP Question

I have posted some of this before. But, I now have a Mac 74/41 works very well for climb and not to bad on the cruise. However I have a polished 70/45 that had a nick, I dressed it out and repolished the prop. Looks very good. Going to put this prop (70/45) and see how it does, out of my short field and cruise.

Haven't tried the 2600 RPM yet. Don't know if the 70/45 will get there.

[Dano"T"]

Re: PROP Question

I tried mine (BC12D-85) to redline at level flight last night...I hit 2600rpm. I got 2450 static at run-up. I really wish these prop shops would stamp the pitch on the prop somewhere where a guy can see it without removing the prop. I still don't know for sure what prop I have...I guess I'll pull it off and check...I do know its a 71" McCauley IB90....I just don't know the pitch. The prop has a sticker on it from Maxwell propeller shop in Minnepolis, MN, but the stampings cannot be seen without removal of the prop. It sure seems like a lot of guys are in the same boat as me.....wondering what prop they have. I'm going to guess 71-44 and if I'm right I hope I win a prize. Those of you with Sensenich props remember...CK74-2-44 means that you have a 72" long prop per Sensenich Propeller....the -2 means the prop starts out at 74" and then 2 inches is cut off. That's what they told me.

[Yellow Duck]

Re: PROP Question

I would guess that your prop is a little more flat, maybe a 40 or 41 inch pitch. Interesting to find out if you can. In order to get 2450 static (if tach is correct) would require a pretty flat prop. I think ?

[Jim Hartley]

Re: PROP Question

I have a Sensenich 74CK-0-40. Pitch changed from 44 to 40 inches. Show about 2450 Rpm breaking water at take off and about 2550 Rpm full throttle thereafter. I suspect the tach is close to correct calibration,but I do not know for sure. I operate at 460 feet MSL.

Jim

[Dano"T"]

Re: PROP Question

Jim,

You get about the same as me...but your prop is 74" long, so your pitch is probably less than mine. My plane goes on floats next week (Baumann BF-1500's) then we do the FAA flight test, so I'm making sure I have the correct prop etc. before that takes place. ATC sheet for BC12D-85 list propeller limits at not over 72", not under 70" Seaplane....so I'll leave her as is for now until after the test at least. Then I might try a 74-40 to see if I get more thrust.

[Yellow Duck]

Re: PROP Question

Some one asked me if I had tried full throttle (2600 rpm's) I hadn't, but yesterday I tried. Couldn't get much over 2300 at full throttle, but did indicate about 105 MPH. On take off I was turning 2100 RPM's and 50 MPH, let the speed move up to 65 MPH and 2300 RPM's climbing at about 850 FPM to about 500 ft, then 70 MPH and about 450 FPM to 1500 ft to play. Went out over the marsh and Gulf of Mexico (very close to my home). Lots of haze, vis was only a couple of miles. Always need to keep an eve out for the Helicopters. Lots of them working the Oil Industry. Especially yesterday. Many are starting to carry people back from the off shore drilling rigs and production platforms because of "Katrina".

After the storm, I will put my 74/45 prop and see the difference. This one is a 74/41